ASCAT Product Guide. Doc.No. : EUM/OPS-EPS/MAN/04/0028 EUMETSAT Eumetsat-Allee 1, D Darmstadt, Germany Date : 16 July 2015 Tel:

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1 Doc.No. : EUM/OPS-EPS/MAN/04/0028 EUMETSAT Eumetsat-Allee, D Darmstadt, Issue : v5 Germany Date : 6 July 205 Tel: Fax: WBS : EUMETSAT The copyright of this document is the property of EUMETSAT.

2 v5, 6 July 205 Document Change Record Issue/Revision Date DCN No. Changed Pages / Paragraphs v 08/09/2004 First issue of the document. v2 3/08/2007 Update to reflect start of Metop/ASCAT v2a 6//2007 Section 3: Configuration history tables updated and enhanced. v2b 8/2/2007 Section 3: Configuration history table 3.2 updated for new PPF version. v2c 8/04/2008 Section 3 Section Configuration history tables updated. v2d 07//2008 Section 3: General Configuration history tables updated and Level 2 tables added. Also several minor text and hyperlink amendments. v3a 0/2/2008 Sec 3: Configuration history tables updated. Sec,2,4,6 and Appendix 2: Introduction of EARS ASCAT and ASCAT L2 soil moisture products. (NB: Document restructured - App. F & G renamed as Sec. 0 &, and common appendices removed v3b /2/2008 Section 6.5: Updates to details of WMO BUFR formats. v4 29/05/2009 Section 3: Configuration history tables updated with new entries for Tables 3-2 & 3-5. Section 5: EPSView description replaced by text on available generic tools. (Also minor associated updates to Sec. 2 & 6.) v4a 30//2009 Full document: Sec. 3: Configuration history tables updated. Sec. 4: Description of dynamic NTBs processing concept. Fig 4-3 (Functional overview) split into two before and after figures. Update of validation section. Sec., 2, 3, 4, 6: Introduction of the ASCAT reprocessed data set Phase. Sec. 8: Introduction of validation results. Sec. 2: New tables for new or updated SOMO records. Other minor text, reference and hyperlink corrections. Page 2 of 64

3 v5, 6 July 205 Issue/Revision Date DCN No. Changed Pages / Paragraphs v4a 30//2009 Sec. 3: Configuration history tables updated. Sec. 4: Description of dynamic NTBs processing concept. Fig 4-3 (Functional overview) split into two before and after figures. Update of validation section. Sec., 2, 3, 4, 6: Introduction of the ASCAT reprocessed data set Phase. Sec. 8: Introduction of validation results. Sec. 2: New tables for new or updated SOMO records. Other minor text, reference and hyperlink corrections. v4b //20 Section 3, Section 4, Section 6 Main update: addition of the ASCAT multiparameter product. Configuration history tables updated. Various text edits (including Table 4-) to bring up to date. Table 6-: Additions for multi-parameter product, OSI SAF FTP service, NetCDF format. Sec. 6.5: Updates to descriptions of products available in WMO BUFR format. New Sec. 6.6 The NetCDF format. Other minor textual and hyperlink updates. v4c /08/20 Section 2: Configuration history tables updated (Tables 3-2, 3-3, 3-5, 3-6). v5 6/07/205 ECP 659 Level V8., V9.3 processors (format change) Level 2 V3., V5.0 processors (format change) Addition of ASCAT-B Signature list reflecting new EUMETSAT organisation Revision of figures, reference documents Removal of references to HDF5 format not supported anymore Page 3 of 64

4 v5, 6 July 205 Table of Contents Introduction Reference Documents EUMETSAT technical documents SAF documents Papers, reports and other technical documentation ASCAT Products Configuration History Near real-time Products ASCAT Lb ASCAT L2 Soil Moisture Index ASCAT L2 Ocean Surface Wind Products Reprocessed data sets ASCLR ASCL2SMR ASCAT Level CF ASCAT Products Overview Inheritance from ERS scatterometers and key features of the ASCAT mission The ASCAT instrument Technical description Instrument modes Instrument calibration Measurement principle, geometry and coverage Overview of the ground processing and calibration The Level ground processing The Level b main processing chain Re-sampling, spatial resolution and spatial correlation Surface type Level b nominal and degraded operation modes The external calibration processing chain The Level 2 ground processing Ocean winds processing Soil moisture processing ASCAT product characteristics and use The ASCAT Level b re-sampled products General characteristics Accuracy Quality information in the products The ASCAT Level b full resolution product General characteristics Accuracy Quality information in the products The ASCAT Level 2 ocean surface wind product General characteristics Accuracy Quality information in the products The ASCAT Level 2 Soil Moisture product General characteristics Quality information in the products Summary of ASCAT product current and potential applications Scatterometer ocean wind applications Ocean winds assimilation in weather forecasting Nowcasting and forecasting of extreme events Winds forcing ocean and wave models Other scatterometer applications Scatterometry over land surfaces...4 Page 4 of 64

5 v5, 6 July Sea Ice monitoring: mapping and analysis Snow accumulation over great ice sheets Data Viewing and Reading ASCAT Product Formats and Dissemination EPS products available dissemination means Satellite Direct Broadcast Service EUMETCast GTS/RMDCN EUMETSAT Data Centre ASCAT products dissemination Near-real-time dissemination Archive retrieval ASCAT EPS native product formats The EPS native formats General overview of the EPS generic product format Granularity of the EPS products Product format version control Product naming convention The ASCAT Level b product formats Level b re-sampled products format Level b full-resolution product format ASCAT Level 2 Soil Moisture product formats The WMO formats The NetCDF format ASCAT Product Processing Algorithms ASCAT Products Validation ASCAT Products Routine Monitoring Record Description of the ASCAT Level b re-sampled Products ASCA_SZO_B product Summary of Product Format Version record contents Contents: MPHR ( name 'mphr', class, subclass 0, version 2 ) SPHR ( name 'sphr', class 2, subclass 0, version 2 ) VIADR ( name 'viadr-oa', class 7, subclass 4, version 2 ) VIADR ( name 'viadr-ver', class 7, subclass 6, version 2 ) MDR ( name 'mdr-b-250', class 8, subclass 2, version 3 ) ASCA_SZR_B product Summary of Product Format Version record contents Contents: MPHR ( name 'mphr', class, subclass 0, version 2 ) SPHR ( name 'sphr', class 2, subclass 0, version 2 ) VIADR ( name 'viadr-oa', class 7, subclass 4, version 2 ) VIADR ( name 'viadr-ver', class 7, subclass 6, version 2 ) MDR ( name 'mdr-b-25km', class 8, subclass, version 3 )...99 Record Description of the ASCAT Level b Full Resolution Product ASCA_SZF_B product Summary of Product Format Version record contents Contents: MPHR ( name 'mphr', class, subclass 0, version 2 ) SPHR ( name 'sphr', class 2, subclass 0, version ) VIADR ( name 'viadr-oa', class 7, subclass 4, version 2 ) VIADR ( name 'viadr-grid', class 7, subclass 8, version ) VIADR ( name 'viadr-ver', class 7, subclass 6, version 2 ) MDR ( name 'mdr-b-full', class 8, subclass 3, version 4 ) Record Description of the ASCAT Level 2 Soil Moisture Products ASCA_SMO_02 product Summary of Product Format Version record contents Contents:...34 Page 5 of 64

6 v5, 6 July MPHR ( name 'mphr', class, subclass 0, version 2 ) MDR ( name 'mdr-2-sm-250', class 8, subclass 5, version ) VIADR ( name 'viadr-ver', class 7, subclass 7, version 2 ) ASCA_SMR_02 product Summary of Product Format Version record contents Contents: MPHR ( name 'mphr', class, subclass 0, version 2 ) MDR ( name 'mdr-2-sm-25km', class 8, subclass 4, version ) VIADR ( name 'viadr-ver', class 7, subclass 6, version 0 )...58 Table of Figures Figure 4-: ASCAT swath geometry for a Metop minimum orbit height (822 km)...24 Figure 4-2: Example of ASCAT swath coverage for day, from top to bottom: Global coverage of ASCAT-A; global coverage of ASCAT-A and ASCAT-B. The values mapped are an RGB composition of the NRCS data from the FORE (Red), MID (Green) and AFT (Blue) beams Figure 4-3: Example of ASCAT swath coverage for day, from top to bottom: Coverage over high latitudes of ASCAT-A; Coverage over high latitudes of ASCAT-A and ASCAT B. The values mapped are an RGB composition of the NRCS data from the FORE (Red), MID (Green) and AFT (Blue) beams Figure 4-4: Functional overview of the ASCAT Level ground processing chain before 9 September 2009 (a) and thereafter (b). This change is explained in Section Figure 4-5: Ground geometry of the across-track component of the spatial smoothing for σ0 values corresponding to two across-track adjacent nodes...29 Figure 4-6: Ground geometry of the across-track component of the spatial smoothing for σ 0 values corresponding to two across-track adjacent nodes...30 Figure 8-: Residual differences between the ASCAT-A antenna gain values estimated from the transponder 202 data and the fitted model gain patterns, for the principal elevation cut and for all beams [RD 9] Figure 8-2: Residual differences between the ASCAT-B antenna gain values estimated from the transponder 203 data and the fitted model gain patterns, for the principal elevation cut and for all beams [RD 0] Figure 8-3: Mean annual ASCAT-A 0 in each beam as a function of incidence angle for the years Each line in these plots corresponds to data from one year [RD9] Figure 8-4: Average rainforest calibration differences with respect to incidence angle between ASCAT-A and ASCAT-B for June Figure 8-5: Time series of monthly averages of ocean Kp (radiometric resolution) for the ASCAT-A 25 km re-sampled product [RD 9] Figure 8-6: Global daily averages ( ) of Kp values for ASCAT-B, for the 25 km re-sampled product (top 6 panels) and 2.5 km re-sampled product (bottom 6 panels) for all six beams Page 6 of 64

7 v5, 6 July 205 Table of Tables Table 3-: ASCAT Lb product format version history....3 Table 3-2: ASCAT Lb PPF software version history...4 Table 3-3: Generic ASCAT Lb PPF auxiliary parameter file version history...4 Table 3-4: ASCAT-A Lb PPF auxiliary parameter file version history for M Table 3-5: ASCAT-B Lb PPF auxiliary parameter file version history for M0...7 Table 3-6: ASCAT L2 Soil Moisture Index product format version history...8 Table 3-7: ASCAT L2 Soil Moisture Index software version history...8 Table 3-8: ASCAT-A L2 Soil Moisture Index auxiliary parameter file version history for M Table 3-9: ASCAT-A L2 Soil Moisture Index auxiliary parameter file version history for M Table 3-0: ASCAT Lb reprocessed data sets configuration history...20 Table 3-: ASCAT L2 Soil Moisture Index reprocessed data sets configuration history...2 Table 4-: Summary of the main characteristics of ASCAT products Table 6-: Summary of dissemination means and formats for ASCAT products...46 Table 6-2: Generalised schematic of the generic product format...49 Table 6-3: Generic ASCAT product names Table 6-4: Record types in ASCAT Level b product for product format version Table 6-5: Occurrence of records in ASCAT Level b spatially averaged product for product format version Table 6-6: Occurrence of records in ASCAT Level b full resolution product for product format version Table 6-7: Record types in ASCAT Level 2 Soil Moisture product...54 Table 6-8: Occurrence of records in ASCAT Level 2 Soil Moisture product...55 Table 6-9: ASCAT products available in WMO (BUFR) format...55 Page 7 of 64

8 v5, 6 July 205 INTRODUCTION This user guide is intended for users of EPS (EUMETSAT Polar System) ASCAT data products. It provides information about the products available, how to access them, how to extract and interpret the data, and it also aims to help the user in choosing a product for a particular application. A full list of EPS products generated at EUMETSAT is given.in Appendix A. These products will be addressed in this guide: ASCAT Level 0 (instrument packets) ASCAT Level b (normalised radar backscatter) ASCAT Level 2 global wind (near surface ocean winds) ASCAT Level 2 regional short-timeliness wind (near surface ocean winds) ASCAT Level 2 soil moisture (surface soil moisture) Note that the ASCAT Level 2 global wind products are generated and distributed by the EUMETSAT Ocean and Sea Ice Satellite Application Facility (OSI SAF), as part of the EPS distributed Applications Ground Segment [RD 22]. References to the OSI SAF user help information will be made when appropriate and the product format and contents will not be discussed here in full detail. Additionally, the ASCAT Level 2 wind product operational quality control is performed by the EUMETSAT Numerical Weather Prediction Satellite Application Facility (NWP SAF). The NWP SAF also makes available to users an ASCAT wind processing software package. The ASCAT Level 2 regional short-timeliness wind product is generated and disseminated within the EUMETSAT Advanced Retransmission Service (EARS), with processing software equivalent to that used for the global chain, but within a system implementation optimised to provide fast products on a regional scale. Refer to our website for more details on the EARS service. The ASCAT Level 2 Soil Moisture products are generated in the EPS Core Ground Segment. The products have been developed by the Department of Geodesy and Geoinformation of the Vienna University of Technology and the data service is provided in partnership with the SAF on support to Operational Hydrology and Water Management (H-SAF). Apart from the near-real-time products listed above, reprocessed Level b and Level 2 soil moisture data for ASCAT on Metop-A has been released and it is referred to in the product configuration section. For further questions not addressed in this guide, on these or other EPS products, see the EUMETSAT Polar System pages on our website or to contact directly the EUMETSAT User Services Helpdesk. These pages should be the main interface for information on access to all EPS products. The help desks of the OSI, NWP and H- SAFs can be accessed directly on, respectively: and A supplement of appendices applicable to all the Product Guides is also available. This contains a product summary and details of generic data, as well as information on the Metop operational orbit, and a list of acronyms and abbreviations. The supplement is available as Document Reference: EUM/OPS-EPS/MAN/08/003. Page 8 of 64

9 v5, 6 July REFERENCE DOCUMENTS The following documents have been used to compile the information in this guide. Some of them are referenced within the text, others are provided here for further reading. 2. EUMETSAT technical documents Ref Title Document ID RD EPS Generic Product Format Specification EPS.GGS.SPE.9667 RD 2 ASCAT Level Product Format Specification EUM/RSP/SPE/3/ RD 3 Estimation of ASCAT Normalised Radar Cross Section: EUM.TSS.SPE ATBD RD 4 ASCAT Calibration and Validation Plan EUM.EPS.SYS.PLN.0.0 RD 5 ASCAT Calibration and Validation Plan EUM.EPS.SYS.PLN.0.0 RD 6 ASCAT Verification, Validation and Validation Plan EUM.MET.TEN..087 RD 7 ASCAT Calibration 200 EUM.MET.TEN..098 RD 8 ASCAT Measurement Data Interface Specification MO.TN.DOR.SC.005 RD 9 ASCAT Calibration 202 EUM.MET.TEN RD 0 ASCAT-B Level Calibration and Validation report EUM.OPS.DOC RD EPS Product file naming for EUMETCast EUM/OPS-EPS-TEN/07/002 RD 2 ASCAT L2 Soil Moisture Product Format Specification EUM/OPS-EPS/SPE/07/0343 RD 3 Metop-A ASCAT Commissioning Quality Report EUM.MET.REP RD 4 ASCAT Level Reprocessing Phase - dataset EUM.OPS.DOC description RD 5 ASCAT Level 2 Soil Moisture reprocessing Phase - EUM.OPS.DOC dataset description RD 6 ASCAT Reprocessing Phase - validation report EUM.OPS.REP RD 7 Metop Space to Ground Interface Specification MO-IF-MMT-SY000 RD 8 Metop-A ASCAT L Data Record Release 2 (CF-003): EUM/OPS-EPS/USR/4/73970 User Guide RD 9 Metop-A ASCAT L Data Record Release 2 (CF-003): EUM.TSS.REP Validation Report RD 20 ASCAT-B Calibration report EUM.RSP.TEN RD 2 ASCAT-B Level 2 soil moisture validation report EUM.OPS.DOC See for more information on the project. Page 9 of 64

10 v5, 6 July SAF documents Ref Title Document ID RD 22 OSI SAF ASCAT Product User Manual RD 23 CMOD5.n - the CMOD5 GMF for neutral winds RD 24 Algorithm Theoretical Basis Document for the OSI SAF wind products RD 25 Calibration and Validation of ASCAT Winds RD 26 ASCAT-B NWP Ocean Calibration and Validation RD 27 Product User Manual for H25/SM-OBS-4, METOP ASCAT Soil Moisture Time Series RD 28 Effects on Level 2 Soil Moisture using Level b sigma- re-sampled with a circular top-hat window and exploration of the Lebel b full-resolution sigma0 product SAF/OSI/KNMI/TEC/MA/34 SAF/OSI/CDOP/KNMI/TEC/TN/65 SAF/OSI/CDOP2/KNMI/SCI/MA/97 SAF/OSI/CDOP/KNMI/TEC/TN/63 SAF/OSI/CDOP2/KNMI/TEC/RP/99 SAF/HSAF/CDOP2/PUM-25/0.7 EUM/RSP/REP/4/ See for more information on the NWP SAF project. See for more information on the OSI SAF project and for more information on the SAF wind products See for more information on the H-SAF project and rs.geo.tuwien.ac.at/products/all/ascat for more information ASCAT soil moisture products. 2.3 Papers, reports and other technical documentation Ref Title Authors RD 29 The Advanced Scatterometer (ASCAT) on J. Figa-Saldaña, J.J.W. Wilson, E. Attema, R. the meteorological operational (MetOp) Gelsthorpe, M.R. Drinkwater and A. Stoffelen platform: A follow on for European wind Can.J.Remote Sensing, Vol.28, No.3, pp , scatterometers 2002 RD 30 ASCAT-MetOp s Advanced Scatterometer Gelsthorpe, R.V., Schied, E., Wilson, J.J.W. ESA Bulletin No. 02, 2000 ( bullet02/gelsthorpe02.pdf) RD 3 Scatterometry A. Stoffelen, PhD Thesis, 998 RD 32 CMOD5 - An improved geophysical model H. Hersbach, 2003 function for ERS C-Band scatterometry RD 33 Manual on the Global Telecommunication WMO - No. 386 System RD 34 World Meteorological Organization Manual WMO - No. 306 on Codes RD 35 ASCAT Soil Moisture Product Handbook ASCAT Soil Moisture Report Series No. 5, Institute of Photogrammetry and Remote Sensing, Vienna University of Technology, Austria, Page 0 of 64

11 v5, 6 July 205 Ref Title Authors RD 36 RD 37 RD 38 RD 39 RD 40 The ASCAT Soil Moisture Product: A Review of its Specifications, Validation Results, and Emerging Applications ERS-ASCAT backscatter and soil moisture inter-comparison First results Analysis of ASCAT Ocean Backscatter Measurement Noise Radiometric Calibration of the Advanced Wind Scatterometer Radar ASCAT carried on board the Metop-A satellite Validation of backscatter measurements from advanced Scatterometer on Metop-A Wagner, W, et al. METEOROL Z. 203; 22(): 5-33 ASCAT Soil Moisture Report Series No. 6, Institute of Photogrammetry and Remote Sensing, Vienna University of Technology, Austria, Anderson, C. et al., IEEE T. Geoscience and Remote Sensing, 50(7): (202) Wilson, J.J.W. et al., IEEE T. Geoscience and Remote Sensing, 48(8): (200) Anderson et al., J. Atm. Oceanic Technology, 29, 77 88, (202) RD 4 Adapting the SIR algorithm to ASCAT. Lindsey, R.D., Long, D.G., Geoscience and Remote Sensing Symposium (IGARSS), 200 IEEE International, pp (200) RD 42 RD 43 On the quality of high-resolution scatterometer winds Land-Contamination Compensation for QuikSCAT Near-Coastal Wind Retrieval Vogelzang, J., A. Stoffelen, A. Verhoef and J. Figa- Saldana, J. Geophys. Res., 6, C0033. (20). Owen M.P., Long, D.G., IEEE T. on Geoscience and Remote Sensing, vol. 47, issue 3, pp (2009) Page of 64

12 v5, 6 July ASCAT PRODUCTS CONFIGURATION HISTORY In all tables in this section, the current versions on the operational Ground Segment are shown on a white background. 3. Near real-time Products 3.. ASCAT Lb On 9 September 2009, an important change in the operational L processing chain was implemented. This consisted of the activation of an orbit-based generation (and utilisation) of the file ASCA_NTB_, previously a static file. After this change, the file ASCA_NTB_xx_M02_ became dynamic and its configuration control will thus not be covered any more in the tables below. Instead, the static input for its generation has been introduced, i.e., the ASCA_XCL file, which contains the latest transponder-based instrument calibration and was used to generate the latest static ASCA_NTB and ASCA_INS files above Page 2 of 64

13 v5, 6 July 205 Date introduced on Product format version PFS version PGS version Comments operational G/S Major number Minor number 9/0/ /04/ / v8b 6.6 Addition of an SPHR, removal of several VIADRs and addition of several VEADRs. No change in any MDR records. 29/05/ v9 7.0/v7B Change to all L formats and several algorithm revisions Table 3-: ASCAT Lb product format version history. PPF software version Date introduced on operational G/S Comments /04/ /0/2007 Improved geolocation /2/2007 Correct implementation of DEFAULT values for missing fields. Correction of Kp range and setting of F_KP flag /04/2008 Implementation of three-transponders absolute sigma0 calibration, as well as a product format change /0/2008 Implementation of several corrections to La and Lb flags /2/2008 Implementation of final results of external calibration campaign with 3 transponders (solving the mid left antenna gain pattern oscillation) /2/2008 Introduction of protection against out of range values for all fields /04/2009 Modification of data gap handling and migration to AIX 6 OS /07/2009 Modification for allowing dynamic Normalisation Table Baseline (NTB) generation /09/2009 Tuning related to dynamic NTB configuration and activation of dynamic NTB generation /09/2009 Processing with dynamic NTB files /08/20 Implementation of the 200 transponder calibration and a revised Kp algorithm /03/202 Revised implementation of the SFE corrections and activation of the HKTM telemetry handling /05/3 Product format change (v2.0), specifically significant for LB SZF products; quality flag revision and new strategy for the along-track generation of lines of nodes. Page 3 of 64

14 v5, 6 July 205 PPF software version Date introduced on operational G/S Comments Update of Level processor to reflect the configuration of the ASCAT-A CDR generation Minor fix related to line of nodes generation and auxiliary file format handling Table 3-2: ASCAT Lb PPF software version history Auxiliary files version Auxiliary files filename Date introduced on operatl. G/S. ASCA_XTC_xx_xxx_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_xxxxxxxxxx 30/0/ ASCA_XTC_xx_xxx_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_TURxxxxMTC 0/0/ ASCA_XTC_xx_xxx_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_TURxxxxMTC 03/04/2008 Comments.8 ASCA_XTC_xx_xxx_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_TURxxxxMTC 8/08/20 Corrected transponder internal delays after transponder maintenance.0 xxxx_lsm_xx_xxx_ z_xxxxxxxxxxxxxxz_ z_xxxx_xxxxxxxxxx 3/0/2007 Table 3-3: Generic ASCAT Lb PPF auxiliary parameter file version history Page 4 of 64

15 v5, 6 July 205 Auxiliary files version Auxiliary files filename Date introduced on operatl. G/S.6 ASCA_PRC_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxxx 26/04/ ASCA_PRC_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxMTC 0/0/ ASCA_PRC_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxTCE 03/04/2008 Comments 3.3 ASCA_PRC_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxTCE 23/0/2008 F_ORBIT threshold for radial distance w.r.t. reference orbit set to 500 m. 3.4 ASCA_PRC_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxTCE 02/2/2008 NTB State vector updated to better reference orbit. 4.0 ASCA_PRC_xx_M02_ Z_ xxxxxxxxxxxxxxz_ z_xxxx_fm2xxxxtce 09/07/2009 Preparation for dynamic NTB generation. 5.0 ASCA_PRC_xx_M02_ Z_ xxxxxxxxxxxxxxz_ z_xxxx_fm2xxxxtce 07/09/2009 Configuration tuning for NTB generation, including an increase of time samples for NTB generation from 20 to 22, necessary for the EARS operational Metop Level0 service activation. 5.2 ASCA_PRC_xx_M02_ Z_ xxxxxxxxxxxxxxz_ z_xxxx_fm2xxxxtce 8/08/20 Correction of Hamming window width function for the SZR product. 7.2 ASCA_PRC_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxTCE 20/03/202 Correction of the configuration of the Solar Array Flagging algorithm, HKTM trending thresholds and new Level 0 data gap handling 8.0 ASCA_PRC_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxTCE Removal of NTG triggering parameters Page 5 of 64

16 v5, 6 July 205 Auxiliary files version Auxiliary files filename Date introduced on operatl. G/S.5 ASCA_NTB_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxMPC 2/02/2007 Comments.9 ASCA_NTB_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxMTC 0/0/2007 July 2007 one-transponder calibration..0 ASCA_NTB_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxMTC 03/04/2008 March 2008 three-transponder calibration.. ASCA_NTB_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxTCE 02/2/2008 Refined March 2008 three transponder calibration (solving the mid left antenna gain pattern oscillation) and better reference orbit used. 2.0 ASCA_NTB_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxTCE 09/07/2009 New format and fast algorithm. n/a ASCA_NTB_xx_M02_<*>_ xxxxxxxxxxxxxxz_<*>_cgs_xxxxxxxxxx 0/09/2009 Dynamic NTBs with 22 entries..3 ASCA_INS_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxMPC 30/0/ ASCA_INS_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxMTC 0/0/2007 Antenna pointing as per July 2007 one-transponder calibration. 2.2 ASCA_INS_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxMTC 03/04/2008 Antenna pointing as per March 2008 one-transponder calibration. 2.4 ASCA_INS_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxTCE 02/2/2008 Refined antenna pointing and correction of typo in receiver characterisation. 2.6 ASCA_INS_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxTCE 8/08/20 Antenna pointing as per 200 transponder calibration, and corrected calibration timeline. 2.7 ASCA_INS_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FMxxxxTCE Antenna pointing as used in ASCAT-A CDR generation Page 6 of 64

17 v5, 6 July 205 Auxiliary files version Auxiliary files filename Date introduced on operatl. G/S Comments 2. ASCA_XCL_xx_M02_ Z xxxxxxxxxxxxxxz_ z_xxxx_ FM2xxxxTCE 09/09/2009 Input to dynamic NTB generation compatible with ASCA_INS_ v2.4 and all ASCA_NTB_ files from v. inclusive. 2.2 ASCA_XCL_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxTCE 7/08/20 Antenna patterns as per 200 transponder calibration. 2.3 ASCA_XCL_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FMxxxxTCE Antenna patterns as used in ASCAT-A CDR generation Auxiliary files version Table 3-4: ASCAT-A Lb PPF auxiliary parameter file version history for M02 Auxiliary files filename Date introduced on operatl. G/S Comments.2 ASCA_PRC_xx_M0_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FMxxxxTCE 22/0/202 Internal calibration locked.3 ASCA_PRC_xx_M0_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FMxxxxTCE 25/06/203 Correction of the configuration of the Solar Array Flagging algorithm 8.0 ASCA_PRC_xx_M0_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxTCE Removal of NTG triggering parameters.0 ASCA_INS_xx_M0_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FMxxxxTCE 22/0/202 Preliminary external calibration. ASCA_INS_xx_M0_ Z_xxxxxxxxxxxxxxxZ_ Z_xxxx_FMxxxxTCE 25/06/203 Transponder-based external calibration ASCA_XCL_xx_M0_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FMxxxxTCE 22/0/202 Preliminary external calibration.3 ASCA_XCL_xx_M0_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FMxxxxTCE 25/06/203 Transponder-based external calibration 203 Table 3-5: ASCAT-B Lb PPF auxiliary parameter file version history for M0 Page 7 of 64

18 v5, 6 July ASCAT L2 Soil Moisture Index Date introduced on operational G/S Major number Product format version PFS version PGS version Comments Minor number 5/05/ v2 n/a Start of trial dissemination. 0/2/ v3a n/a Inclusion of L values 20/07/ v4a n/a Update of L section Table 3-6: ASCAT L2 Soil Moisture Index product format version history PPF software version Date introduced on operational G/S Comments.0.2 5/05/2008 Start of trial dissemination /07/ /0/2008 Soil moisture parameter database update..2. 0/2/2008 Allow more values of Soil Moisture to be generated /05/2009 Correction of left swath biases /2/2009 Format change /08/20 ASCAT-based soil moisture parameter database /07/205 Update of parameter database, format change Table 3-7: ASCAT L2 Soil Moisture Index software version history Page 8 of 64

19 v5, 6 July 205 Auxiliary files version Auxiliary files filename Date introduced on operatl. G/S Comments.0 ASCA_SMC_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_xxxxxxxxx 5/05/2008 Start of trial dissemination..2 ASCA_SMC_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxTCE 02/2/2008 Synchronisation with new ASCAT Lb calibration. 3.2 ASCA_SMC_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxTCE 8/08/20 New (ASCAT-A based) parameter database and synchronisation with new ASCAT Lb calibration. 3.4 ASCA_SMC_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxxTC Synchronisation with new ASCAT Lb calibration. 3. ASCA_SMC_xx_M02_ Z_xxxxxxxxxxxxxxZ_ Z _xxxx_fm2xxxxtc New (ASCAT-A based) parameter database Table 3-8: ASCAT-A L2 Soil Moisture Index auxiliary parameter file version history for M02 Auxiliary files version Auxiliary files filename Date introduced on operatl. G/S Comments.0 ASCA_SMC_xx_M0_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_ FMxxxTCE 4/08/202 Start of trial dissemination..2 ASCA_SMC_xx_M0_ Z_xxxxxxxxxxxxxxZ_ Z_xxxx_FM2xxxTCE 25/06/203 Synchronisation with new ASCAT Lb calibration..4 ASCA_SMC_xx_M0_ Z _xxxxxxxxxxxxxxz_ z _xxxx_fm2xxxtc New (ASCAT-A based) parameter database 3..3 ASCAT L2 Ocean Surface Wind Products Table 3-9: ASCAT-A L2 Soil Moisture Index auxiliary parameter file version history for M0. For details on both the global and regional wind products, please refer to the OSI SAF Scatterometer webpage. Page 9 of 64

20 v5, 6 July Reprocessed data sets In the following tables the configuration of the available reprocessed data sets is described. There have been two re-processing campaigns for ASCAT data on M02: In 2009, including both Level (ASCLR) and Level 2 soil moisture (ASCL2SMR) products In 204, including only Level products (CF-003) The next reprocessing of ASCAT on M0 and M02 is planned for ASCLR Release name Release date Reprocessing period Reprocessing version L processor Static auxiliary file configuration version ASCLR 0//2009 0/0/2007 3/2/ ASCA_INS 2.4 ASCA_PRC 3.4 ASCA_NTB ASCA_INS 2.4 ASCA_PRC 5.0 ASCA_NTB 2.0 Table 3-0: ASCAT Lb reprocessed data sets configuration history See [RD 5] for further details. The document is available on the EUMETSAT Technical Documents web page. See Satellites/Technical Documents. Page 20 of 64

21 v5, 6 July ASCL2SMR Release name ASCL2SMR Release date 0//2009 Reprocessing period 0/0/2007 3/2/2008 Reprocessing version.0 L2 soil moisture processor version.3. Static auxiliary file configuration ASCA_SMC.2 Parameter database.0 Table 3-: ASCAT L2 Soil Moisture Index reprocessed data sets configuration history See [RD 6] for further details. The document is available on the EUMETSAT Technical Documents web page. See Satellites/Technical Documents ASCAT Level CF-003 Release name Release date Reprocessing period Reprocessing version L processor version CF /0/204 0/0/2007 3/03/ , ASCA_INS 27 ASCA_PRC 7.2 Static auxiliary file configuration ASCA_XCL (*) 2.4 before : after :00 (*) This change was introduced to account for an instrument calibration change. See [RD28] for further details. Page 2 of 64

22 v5, 6 July ASCAT PRODUCTS OVERVIEW 4. Inheritance from ERS scatterometers and key features of the ASCAT mission The design of ASCAT is based on the robust and well-understood concept of the ERS scatterometers. Among the common features are: fan-beam geometry with antennas oriented at 45, 90 and 35 with respect to the satellite track VV polarisation Radar frequency: C-band Swath gridded into nodes, one triplet of averaged backscatter measurements per node Generation of an operational product at 50 km resolution on a nodal grid of 25 km The experience acquired with nearly one decade of operations of ERS scatterometers and the use of their data have also identified areas where improvement was possible, in order to allow operational use of the data, as well as for emerging scatterometer applications to develop. This experience has been taken into consideration by introducing a number of new key features, which are listed below and further discussed in detail in the following paragraphs: Continuous data acquisition and product generation without sharing operation time in orbit with other instruments, which has increased the data coverage Increased spatial coverage via the use of a double swath Higher incidence angle range towards an area which offers a higher wind direction sensitivity in the geophysical model and therefore better performance of the wind retrieval algorithm Additional generation of a research product at a higher resolution of approximately 30 km on a 2.5 km nodal grid Improved instrument design, resulting in higher stability and reliability Improved on-board processing concept, allowing for a lower raw data rate 4.2 The ASCAT instrument 4.2. Technical description ASCAT is a real-aperture radar operating at GHz (C-band) and using vertically polarised antennas for transmission and reception. It transmits a long pulse with Linear Frequency Modulation ( chirp ). Ground echoes are received by the instrument and, after de-chirping, the backscattered signal is spectrally analysed and detected. In the power spectrum, frequency can be mapped into slant range provided the chirp rate and the Doppler frequency are known. The above processing is in effect a pulse compression, which provides range resolution. The contribution of the thermal noise to the radar measurement is observed within each pulserepetition interval by monitoring the output of the receiver during a period of time when all the pulse echoes have decayed. Noise measurements are sent to the ground with echo measurements, to enable measurement noise subtraction to be performed during ground processing. Considerable data rate reduction is achieved by pre-processing the noise and echo measurements on board. The on-board processing consists of a power spectrum estimation Page 22 of 64

23 v5, 6 July 205 followed by a spatial low-pass filtering. Different averaging takes place for echo and noise measurements, reducing the raw data rate by a factor of approximately 25. On-board processing carries as a result a degree of spatial correlation between different and within received echoes, which is taken into account later on by the Level b processing Instrument modes The ASCAT instrument may operate in three different modes: Measurement, Calibration and Test. Additionally, in Measurement mode the instrument occasionally generates special source packets for Gain Compression Monitoring. The nominal instrument mode, and the only one that generates science data for the users, is Measurement mode. During external calibration campaigns, the instrument is operated in Calibration mode when it passes over the ground transponders. Additionally, the instrument is operated in Calibration mode over the ground transponders for one ascending pass and one descending pass every orbit cycle (29 days). Operating the instrument in Calibration mode implies an interruption of the Measurement mode for that pass of approximately 6 minutes. Taking into account the measurement geometry (fore and aft viewing), the completeness of the data for a location in the swath may be affected by this 6 minute measurement interruption during up to 5000 km for far swath locations. In addition, the instrument Gain Compression needs to be monitored periodically. This is a special variant of measurement mode, called Gain Compression Monitoring mode, and monitors the relationship between the transmitted power and the RFU drive level setting. These measurements are not used to retrieve science data. The acquisition of Gain Compression Monitoring data interrupts the nominal Measurement mode for approximately 5 minutes. The instrument needs to monitor the Gain Compression once per orbit cycle over land Instrument calibration The Internal Calibration loop is part of the nominal operation. Within every pulse repetition interval, a calibration phase and a noise estimation phase are included. The calibration signal and the noise data are used to correct for the instrument internal effects during the ground processing. This mechanism allows the combined variation of the transmitter power and the receiver gain to be monitored and accounts for internal instrument drifts during the mission lifetime. At the beginning of the mission, the internal calibration level is established, and its monitoring later on is done with respect to this reference value. The objective of the External Calibration is to ensure that the normalised radar backscatter value measured from a target is correct (absolute calibration) for all incidence angles (relative calibration). In order to achieve this, the absolute gain of each antenna and the pointing need to be established in flight, and this is done with the help of ground transponders. Transponders are active devices that, after receiving a pulse from ASCAT, send a delayed pulse back. Each transponder has a known and stable radar cross section as well as a known and stable response delay, and its position on the Earth s surface is accurately known too. ASCAT receives and detects the transponder pulses from within its swath. By comparing the measured transponder echo level and its associated localisation data with the expected data for each transponder, three antenna depointing angles and antenna gain correction values are estimated. This allows a reference calibrated system to be established, against which the system performance can be evaluated and monitored. Page 23 of 64

24 v5, 6 July 205 The three transponders used for the ASCAT absolute calibration are situated in Turkey. Their relative positions have been carefully chosen to allow a continuous and sufficiently dense sampling of the antenna gains for all elevation angles. For the Metop orbit, over a period of one month, this allows transponder measurements to be obtained for each antenna beam over the full range of incidence angles with cuts at approximately 0-20 km intervals in ground range. The external calibration with three transponders has been carried out several times. For each ASCAT, the first external calibration campaign takes place during the Commissioning Phase. 4.3 Measurement principle, geometry and coverage Like the ERS scatterometers, the ASCAT system geometry is based on the use of fan-beam antennas. It covers two 550-km swaths which are separated from the satellite ground track by about 336 km for the minimum orbit height. The ASCAT incidence angle ranges from 25 to 65 (Figure 4-). For each swath, three antennas illuminate the sea surface at three different azimuth angles, measuring the backscattered signal. At such incidence angles and over ocean, the main backscattering mechanism is considered to be Bragg resonance, which describes the interaction of the radar signal with short sea surface waves having a wavelength of a few centimetres. The wind speed and direction near the ocean surface with respect to the antenna viewing angles are determined by using an empirical Geophysical Model Function (GMF), which relates these parameters to the observed normalised radar cross section (NRCS, also known as σ 0 ) [RD 3]. Figure 4-: ASCAT swath geometry for a Metop minimum orbit height (822 km) For the Metop operational orbit (see Appendix B), a coverage maps can be seen in Figure 4-3 for a full day of Metop-A and B ASCAT data. Page 24 of 64

25 EUM/OPS-EPS/MAN/04/0028 v5, 6 July 205 Figure 4-2: Example of ASCAT swath coverage for day, from top to bottom: Global coverage of ASCAT-A; global coverage of ASCAT-A and ASCAT-B. The values mapped are an RGB composition of the NRCS data from the FORE (Red), MID (Green) and AFT (Blue) beams. Page 25 of 64

26 EUM/OPS-EPS/MAN/04/0028 v5, 6 July 205 Figure 4-3: Example of ASCAT swath coverage for day, from top to bottom: Coverage over high latitudes of ASCAT-A; Coverage over high latitudes of ASCAT-A and ASCAT B. The values mapped are an RGB composition of the NRCS data from the FORE (Red), MID (Green) and AFT (Blue) beams. Page 26 of 64

27 v5, 6 July Overview of the ground processing and calibration 4.4. The Level ground processing The Level ground processing chain is illustrated in Figure 4-4. The goal of Level ground processing for ASCAT is the generation of the radiometrically-calibrated Level b NRCS (namely σ 0) values. The functionality of the ASCAT main processing chain is highlighted in blue in Figure 4-4. This chain is data driven and is applied to every science source packet to generate Level b products. The operational processor also includes an external calibration processing chain, highlighted in red, which is driven by the acquisition of calibration source packets and the need for generating in-flight instrument characterisation functions after an external calibration measurement acquisition campaign. In-flight instrument characterisation parameters are generated and validated off-line and highlighted in green. After they are satisfactorily assessed, the instrument in-flight characterisation parameters are uploaded to the main processing chain The Level b main processing chain The ASCAT power echoes corresponding to both Measurement mode and Calibration mode are subject to front-end processing, namely internal calibration (Power-Gain product correction) and noise corrections (receive filter shape correction and noise power subtraction). Corrected measurement power echoes are then normalised into 256 σ 0 values along every antenna beam projection on the ground and localised on the surface of the Earth. The power-to-σ 0 normalisation factors are the coefficients needed within Level b processing to convert instrument raw data into σ 0. Their calculation is based on estimating the power scattered from a distributed target with constant σ 0 = for different discrimination frequencies (e.g. along beam range positions). In order to do this, the System Response Function (SRF) of individual power samples along the beam needs to be estimated from knowledge of the measurement geometry and the range compression process. The normalisation factors and SRFs are estimated by applying the corresponding two-way radar equation while accounting for on-board echo processing corresponding to the ASCAT Measurement mode. In order to account for viewing geometry, the normalisation factors and SRF are currently generated in advance for every actual Metop orbit, using an orbit state vector prediction a few hours before actual sensing time. Spatial averaging (smoothing) in the along- and across-track directions is further applied per beam over all available σ 0 values, with the objective of obtaining a set of three σ 0 values (one from each beam) for each grid node of each swath at the desired radiometric resolution (also called Kp). This implies a re-sampling of the NRCS values from their original geolocation to a swath grid generated during the processing. Page 27 of 64

28 v5, 6 July 205 Figure 4-4: Functional overview of the ASCAT Level ground processing chain before 9 September 2009 (a) and thereafter (b). This change is explained in Section Re-sampling, spatial resolution and spatial correlation The need to deliver re-sampled sigma0s is two-fold. On one hand, most applications need NRCS values from three beams collocated into one location on the Earth surface. On the other hand, resampling through spatial averaging allows reducing the signal standard noise (Kp), also necessary for most applications. The weighting function used to carry out the spatial filtering is currently a two-dimensional Hamming window centred at every swath grid node position, which is based on a cosine function and designed to peak in the centre of the samples and taper to zero at the ends (see figure 4-5 for its geometry). Its width determines in effect the spatial resolution of the σ 0 averaged values, which is defined in the principal cut in each of the along- and across-track directions, as the distance around the centre of the spatial filter when it reaches 50% of the peak value. The averaged σ 0 values at two different horizontal scales and spatial grids are generated this way, leading to two smoothed σ 0 products: with approximately 50 km and 30 km horizontal resolution on grids of 25 km and 2.5 km, respectively. Associated with the spatial filtering, the Kp of the averaged measurement is estimated as the standard noise within the averaging area defined by the Hamming window. In that step, the measurement correlation due to the previous on-board along-track and across-track average is additionally taken into account. Note that for the higher resolution product, a trade-off was necessary between spatial resolution and radiometric accuracy, by applying a Hamming window with variable width across the swath for the different beams. The resulting spatial resolution ranges from 25 km in the near swath to 34 km in the far swath. The choice of Hamming window and grid spacing for the re-sampling was done according to Nyquist theory, in order to generate a NRCS product with reduced Kp that could moreover be further resampled without aliasing into other grids for further processing. This is relevant for the current soil Page 28 of 64

29 v5, 6 July 205 moisture and sea ice retrieval techniques, where the reference algorithms are based on geographic pixels and not on individual NRCS triplet observations. However, the necessarily big of the Hamming window used (about twice the achieved resolution) poses limitations at surface type boundaries (ocean/land/sea ice), and also hampers the efficiency of enhancing resolution techniques, because it effectively acts as a low pass filter of the measured surface sigma0 spatial variability [RD54]. A different NRCS re-sampling technique has been explored in the past years as a pre-processing step in the Level 2 winds generation, in order to obtain winds closer to the coast. This is based on carrying out the re-sampling step with a circular top-hat filter, instead of the two-dimensional Hamming window (see figure 4-5 for its geometry). Several reports and publications generated in the context of both the OSI and NWP SAF work have come to demonstrate through spectral analysis and comparisons with buoy winds that the winds generated from NRCS values re-sampled with a circular top-hat filter window of 5 km diameter are equivalent in open ocean with the Hamming-window based values, when both are generated on a 2.5 km product grid [RD55]. The advantage of the smaller of the circular top-hat window product is that allows estimation of re-sampled land-free NRCS values closer to the coast. Figure 4-5: Ground geometry of the across-track component of the spatial smoothing for σ0 values corresponding to two across-track adjacent nodes Since 29 May 203 EUMETSAT has provided a new ASCAT full resolution Level product, which includes the original NRCS values prior to re-sampling (i.e. different beams not-collocated but with individual geolocation for each value). This product is now available in NRT and includes a reference swath spacing grid of km for customized re-sampling by the user. The OSI SAF is already exploiting this product in the operational generation of the ASCAT Level 2 coastal winds, as well as exploring its potential in the generation of higher resolution wind products (at 6.25 spacing). The H- Page 29 of 64

30 v5, 6 July 205 SAF has also started to assess the use of this product for potential resolution enhancement over land particularly in areas with small lakes and wetlands, as well as from other land cover types such as stony soil rock outcrops and urban areas [RD37]. The resolution of the different ASCAT products prior to res-sampling is defined by the of the target area scattering power back to the instrument, or SRF. The shape and of the SRF of the individual samples of NRCS along the antenna footprint is a consequence of range compression in the along beam direction and limited by the diffraction effect due to the finite of the antenna in the across beam direction (See Figure 4-6). Figure 4-6: Ground geometry of the across-track component of the spatial smoothing for σ 0 values corresponding to two across-track adjacent nodes For the re-sampled product, the Cumulative SRF (CSRF) is composed of the fundamental instrument SRFs of the measurements used in the re-sampling. During the re-sampling, all original NRCS with an associated latitude/longitude location within the specified window are considered for each swath location. Consequently, the CSRF of the re-sampled products will be different after the use of different re-sampling windows (two-dimensional Hamming or circular top-hat) Surface type It is important for the Level 2 product generation to be able to identify the surface type, since different surface scattering mechanisms apply e.g. over ocean, land, snow and sea ice. It is however difficult to do this without relying on ancillary data in addition to NRCS measurements and hence surface type is generally assessed as part of the Level 2 processing. However, a land/ocean flag is indeed included in all Level b products, based on an available coastline database. For the NRCS on original instrument geometry, two different values are available: A binary flag (land/ocean) based on the latitude/longitude location assigned to the measurement A fractional land flag based on the percentage of land within each measurement SRF. For the re-sampled NRCS product, the land flag expresses the percentage of original NRCS values over land (according to the binary flag) used in the re-sampling and is calculated using the same weighting as in the spatial averaging Level b nominal and degraded operation modes The different instrument modes generate data intended for different types of processing. These are all considered nominal and can be of three types; Page 30 of 64

31 v5, 6 July 205 The main nominal processing mode is driven by continuous availability to the processor of measurement data and corresponds to the generation of ASCAT Level b products within the main processor chain. These are the products intended for users; Another nominal processing mode is driven by the availability to the processor of a sequence of Gain Compression Monitoring data, to the end of generating instrument performance assessment data, which are not intended for users but are used internally in the EPS CGS; Finally, the third processing mode considered nominal is the generation of calibration products within the external calibration processing chain, driven by the availability to the processor of a sequence or a number of sequences of calibration data. Calibration products are not intended for users either. Non-nominal operation modes are not defined as such for the ASCAT processor, but both the main Level b and the external calibration processing chains can generate products of non-nominal quality, referred to as degraded products. The ASCAT processor has the capability of flagging any degradation of the products in near real-time, by introducing the necessary flags and qualifiers within the products themselves. Those flags and qualifiers are addressed in detail in the sections of this document describing the ASCAT Level b product contents, but here the main product degradation scenarios are outlined: non-nominal antenna pointing, due to spacecraft orbit manoeuvres or orbit/attitude anomalies; instrument performance anomalies, assessed by examining instrument telemetry data and the estimated noise and internal calibration corrections; measurements of the left fore antenna affected by reflections from the solar array panel; start or end of a measurement mode sequence, due to non-availability of enough echo or noise data to compute the necessary internal calibration and noise correction functions; unavailability of good quality calibration data. As part of the product validation activities, an assessment of the impact on the product accuracy of the above scenarios is carried out during the commissioning phase and thereafter monitored during operations. Guidelines on the usage of degraded products are provided in the product validation section in this document The external calibration processing chain Before launch, the instrument is delivered with a set of characterisation parameters in the form of several LUTs, estimated on-ground and characterising the expected instrument performance. Among them are the antenna absolute gain patterns and their electrical boresight pointing, which determine the values of the normalisation factors used later for the generation of σ 0 values during the Level b processing. Antenna absolute gain patterns and their electrical boresight pointing are expected to depend on in-flight conditions, and they have to be estimated subsequently in flight. Once these parameters have been characterised in flight, a corresponding in-flight set of normalisation factors can be generated (i.e., key data). The normalisation factors are the conversion coefficients needed within Level b processing to convert instrument raw data (in Power units) into σ 0 and are estimated based on the in-flight knowledge of the instrument and the measurement geometry. As illustrated in Figure 4-4, antenna gain measurements in the antenna coordinate system are obtained from every transponder calibration measurement and a set of antenna gain patterns and pointings are Page 3 of 64

32 v5, 6 July 205 derived, which need to be examined off-line and their quality evaluated, before they can be uploaded to the operational processor. A two-dimensional reconstruction of the antenna gain patterns and the estimation of three depointing angles is the method applied in the external calibration processing, based on fitting absolute gain values estimated at different angular positions (antenna azimuth and elevation) by using ground transponders The Level 2 ground processing Ocean winds processing Level 2 ocean winds processing takes the radiometrically-calibrated NRCS product to derive winds near the ocean surface (at a nominal height of 0 m). ASCAT Level 2 ocean wind global and regional products are respectively produced and distributed by the EUMETSAT Ocean and Sea Ice Satellite Application Facility (OSI SAF) and the EARS Project. In both cases the core activities are carried out by KNMI (Royal Netherlands Meteorological Institute). Near-surface ocean wind vectors are derived from ASCAT Level b data, by using a Geophysical Model Function (GMF), which relates σ 0 values to wind speed and direction. The wind retrieval is an inversion problem at each node where, given a set of three σ 0 values and the GMF, the wind vector is computed that has the highest probability of representing the true wind. An inversion problem presented in these probabilistic terms is usually equivalent to the minimisation of a cost function. Usually, two wind vectors are obtained as the most likely solutions, with directions separated by 80. The measurement noise and the harmonic nature of the GMF result in this wind direction ambiguity as two equal-probability minima occurring in the cost function. The GMF currently used to retrieve ASCAT winds is CMOD5. See also [RD 23]. A wind direction ambiguity removal step is further applied, based on variational meteorological analysis and relying on prior numerical weather prediction (NWP) model information. In 2D-VAR a cost function is minimised. The cost function is formulated in terms of wind increments and penalises deviations from both a background wind field and the ambiguous scatterometer wind solutions obtained from scatterometer wind retrieval. Finally, sea ice screening is applied, based on the scatterometer data itself and on sea ice history information. More information on the ASCAT wind retrieval can be found on the OSI SAF scatterometer webpage Soil moisture processing Level 2 soil moisture processing takes the radiometrically calibrated backscatter product to derive soil moisture over land surfaces. ASCAT Level 2 Soil Moisture Index products are produced and distributed by EUMETSAT using a processor developed and prototyped for EUMETSAT by the Department of Geodesy and Geoinformation of the Vienna University of Technology and later on integrated in the operational ground segment. The products are part of the portfolio maintained by the SAF on support of Hydrology and water managements (H-SAF), who also offers user support on their utilisation. The method for retrieving soil moisture from scatterometer data is a change detection method. Instantaneous backscatter measurements are extrapolated to a reference incidence angle (taken at 40 ) and compared to dry and wet backscatter references. By knowing the typical yearly vegetation cycle Page 32 of 64

33 v5, 6 July 205 and how it influences the backscatter-incidence angle relationship for each location on the Earth, the vegetation effects can be removed, revealing the soil moisture variations. Soil moisture is considered to have a linear relationship to backscatter. The historically lowest and highest values of observed soil moisture are then assigned to the 0% (dry) and 00% (wet) references respectively and a value for the relative (surface) soil moisture for each particular ASCAT measurement can be estimated in near real time. The backscatter references are derived a-priori from analysis of multi-annual ASCAT NRCS time series. More information on the ASCAT soil moisture retrieval can be found on rs.geo.tuwien.ac.at/publications/all/e20//ascat. 4.5 ASCAT product characteristics and use This summarises the main characteristics of the operational near real time ASCAT products available to users. All products contain quality control and other information about the retrieval and their use, which are important to know when you choose the product needed for your application. The ASCAT Level 0 product is not considered in this section, but available to expert users and data and s/w services providers, interested in the instrument raw measurements and their further processing. Its contents and format is discussed in Section 6 (the section dedicated to ASCAT product formats and dissemination). Page 33 of 64

34 v5, 6 July 205 Parameter content s0 full-resolution s0 triplets EO portal collection reference Sampling characteristics and resolution EUMETCast GTS FTP (SAF) Spatial representation (sampling) Approx. spatial Spatial averaging 3-min along track product length for resolution window Global products, other for EARS data Original sampling ASCSZFB 92 samples along each of 6 beams (no beam collocation) ASCSZOB swath grid 25 km, 42 nodes 50 km ASCSZRB swath grid 2.5 km, 82 nodes km 0km x 25 km - Native - - Hamming Native/ BUFR BUFR - EUM Other Archive archive Dump or orbits Native Native/ netcdf - - s0 triplets +soil moist s0 triplets +wind s0 triplets +soil moist +wind SOMO25 swath grid 25 km, 42 nodes 50 km SOMO2 swath grid 2.5 km, 82 nodes km Hamming BUFR - Native/ netcdf OSI-04 swath grid 2.5 km, 82 nodes km Top-hat BUFR BUFR KNMI EARS-ASCAT25 swath grid 25 km, 42 nodes 50 km EARS-ASCAT swath grid 2.5 km, 82 nodes km Hamming BUFR (EARS Regional coverage) - - OAS025 swath grid 25 km, 42 nodes 50 km BUFR BUFR KNMI Hamming OAS02 (*) swath grid 2.5 km, 82 nodes km BUFR BUFR KNMI - OSI-04 swath grid 2.5 km, 82 nodes km Top-hat wind OASW025 swath grid 25 km, 42 nodes 50 km - netcdf netcdf Hamming OASW02 (*) swath grid 2.5 km, 82 nodes km soil moist time series - Lat/lon grid 2.5 km km Hamming - - Table 4-: Summary of the main characteristics of ASCAT products. KNMI, PODAAC TU-Wien (netcdf) (*) refers to collections only available for ASCAT-A Page 34 of 64

35 v5, 6 July 205 At the time of writing of this version of the ASCAT Product Guise, a simplification of the ASCAT product portfolio is taking place and the product collections highlighted in red in Table 4. will be discontinued, due to the availability of their content in other more complete products (e.g., ASCSZOB and ASCSZRB) or to the integration of the regional chain into the global chain (e.g. EARS-ASCAT EARS-ASCAT25), or to lack of user demand (OAS02) The ASCAT Level b re-sampled products General characteristics The main geophysical parameter contained is the re-sampled normalised backscatter radar cross section values, known as σ 0 triplets. Each triplet contains three σ 0 values corresponding to each instrument beam for the corresponding swaths, and localised on the surface of the Earth to a set of nodes on a horizontal surface grid. This grid is generated with a node distance of 25 km for the 50-km resolution product and 2.5 km for the higher resolution product. The σ 0 values are calculated through spatially averaging the original ones. Other important information provided for each triplet is incidence angle, azimuth angle, Kp value (associated with each re-sampled σ 0 ) and geographical position of the node. Important to understand is that, due to the processing on-board and to the characteristics of the spatial averaging, the data from adjacent nodes are correlated. As explained in Section 4.4, the of the spatial resolution window is about twice the re-sampling distance, and thus the σ 0 value corresponding to a node contains information from individual σ 0 values corresponding to several adjacent nodes along and across track. Note: Due to the antenna geometry, σ 0 triplets may be partially filled at the start or end of a Measurement mode sequence. Those empty σ 0 values are replaced by a default value Accuracy The accuracy of the σ 0 triplets is summarised by the following parameters. radiometric accuracy and inter-beam radiometric stability, also called calibration accuracy, around 0. db.. radiometric resolution over ocean, also called Kp, around 2 % - 3 % for the product re-sampled at 25 km and around 4 % - 5 % for that at 2.5 km. localisation accuracy, within 4 km Quality information in the products Level b data contain a number of flags that indicate the quality of the σ 0 and Kp values. The summary flags that take an integer value are as follows: Name Description Codes F_USABLE summary flag for σ 0 0 = good = usable 2 = bad F_KP Kp quality flag 0 = good = bad The remaining flags take a value from 0 to (where 0 indicates the highest quality): Page 35 of 64

36 v5, 6 July 205 Name F_F F_V F_OA F_SA F_TEL F_REF F_LAND Description if a non-nominal amount of raw data have been used in the calculation of the echo correction functions if not enough raw data are available to calculate the echo correction functions representing the quality of satellite orbit and attitude (including manoeuvres) data may be corrupted by solar array reflections (affecting the FORE MID beam on descending passes only) if instrument and satellite housekeeping telemetry data are out of limits non-nominal (out of expected range) echo correction functions indicates the fraction of land contributing to a σ 0 node value. The implementation of F_SA is based solely on geometry considerations (relative angle between solar array panel and the ASCAT antennas) and no assessment has been done on the actual impact (if any) of the solar array reflections on the product quality (σ 0 and Kp). This flag has a warning level only ( by triggering a value of F_USABLE = and not usagle = 2), hence not actively affecting the current Level 2 processing. The intention of the F_OA flag is to detect orbit or attitude anomalies that make the normalisation from echo power to σ 0 inaccurate or inappropriate if the actual orbit or attitude deviates from the assumed ones in the generation of the normalisation factors. F_OA also takes into account the effect of manoeuvres. During Out Of Plane (OOP) and In Plane (IP) manoeuvres, the ASCAT instrument is left on and the processor running. In that situation, a manoeuvre flag is triggered, which contributes to F_OA. F_USABLE is an advisory flag on the overall quality of the product. Its value is nominally set to 0 (= GOOD) if: the value of all the specific flags described above is 0 and the instrument calibration is considered good (set via configuration). F_USABLE can also have a value of (= USABLE), triggered by: non-zero values of F_F, F_TEL, F_KP, or cases of inaccurate instrument calibration (set by us via configuration), while F_OA and F_SA still hold a value of 0 and F_V is less than a certain threshold F_USABLE is set to a value of 2 (= BAD) if it is neither GOOD nor USABLE. Typically, this is: if F_V is greater than a certain threshold, and F_REF is different than 0 if either F_OA or F_SA are non-zero (i.e., the normalisation of echo power to σ 0 is not correct or the σ 0 value is potentially affected by solar array reflections), Due to the antenna geometry, the triplets generated at the beginning and end of a measurement mode sequence are incomplete, when the corresponding node locations are only viewed by one or two antennas. There is no flag for incomplete triplets; the missing values are set to the default field value. For the flags listed above referring to a fraction of data affected by some anomaly, the flag is calculated by applying the same Hamming window used for the spatial averaging to the corresponding individual flags associated with the individual σ 0 values averaged for that Page 36 of 64

37 v5, 6 July 205 node. The flags are therefore not a fraction in the strict sense, but rather a weighted average of flags associated with individual σ 0 values The ASCAT Level b full resolution product General characteristics The main geophysical parameter contained in the product is the NRCS - 92 values along each antenna beam - localised on the surface of the Earth. The measurements from the three different beams in each swath are not collocated, but have each their own independent geolocation. This corresponds to an intermediate product generated just before the swath node generation and resampling in the main processing chain, hence called a full resolution product. The data are thus organised per position along each beam, and not per node in a swath. Other important information provided for each σ 0 value is incidence angle, azimuth angle and geographical position of the sample. The 92 samples are a selection of the original 256 retrieved by the Level processing for each beam and correspond to the nominal ASCAT performance swath, i.e., the area of coverage where the instrument performance is expected by design to be nominal. The resolution of these σ 0 values is defined across-beam by the diffraction effect due to the finite of the antenna. The antenna pattern averages about 20 km across-beam on ground, and the sampling rate corresponds to.2 antenna measurements per second pear each antenna, i.e., about 6 km on ground. Along-beam the resolution of the individual σ 0 values is determined by the range discrimination provided by the azimuth pulse compression. This resolution is variable along the beam but is of the order of 0 km. The sampling of individual σ 0 values along-beam is of approximately 2 km for mid beams and 3 km for side beams. As a result, the full resolution σ 0 values along every antenna beam represent footprints of about 0 x 20 km of various shapes and orientations, depending on the Doppler pattern over the surface. Due to the on-board processing, the individual σ 0 values carry a certain amount of measurement correlation. For a deeper understanding of this correlation, see more details about the on-board processing in [RD3] Accuracy The accuracy of the σ 0 individual values is summarised by the following parameters. radiometric accuracy and inter-beam radiometric stability, also called calibration accuracy, around 0. db.. localisation accuracy, within 4 km Quality information in the products A number of quality flags are generated during the Level b processing, associated with every individual σ 0 sample along each antenna beam, and included in the Level b full resolution products. These contain equivalent information to those found in the averaged Level b product, but assigned to individual values of σ 0.. The flags are contained in bit fields (with value = when the flag is set), distributed in five-byte fields: Page 37 of 64

38 v5, 6 July 205 Bit Flag name Category Description FLAGFIELD_RF, related to the quality of the raw echo correction functions 0 F_NOISE amber Noise measurement missing, interpolated value used F_PG amber Degraded power gain product 2 V_PG red Very degraded power gain product 3 F_FILTER amber Degraded filter shape 4 V_FILTER red Very degraded filter shape FLAGFIELD_RF2, further related to the quality of the raw echo correction functions 0 F_PGP red Estimated power gain product outside limits F_NP red Measured noise outside limits 2 F_PGP_DROP amber Small drop in power gain product detected FLAGFIELD_PL, related to the quality of the platform orbit/attitude 0 F_ORBIT red Orbit height used for the NRCS normalisation is outside limits F_ATITUDE red No yaw steering 2 F_OMEGA red Unexpected instrument configuration 3 F_MAN red Satellite manoeuvre 4 F_OSV information Input orbit prediction file missing, OSV taken from L0 header FLAGFIELD_GEN, including other qualifiers associated with the echo lines 0 F_E_TEL_PRES amber Instrument or platform HKTM missing F_E_TEL_IR red Instrument or platform HKTM out of limits FLAGFIELD_GEN2, including other qualifiers associated with the echo samples within a line 0 F_S_A amber Potential interference from solar array F_LAND information Lat/lon position over land 2 F_GEO red Geolocation algorithm failed 3 F_SIGN information The NRCS value is negative Each flag has belongs to a particular category which indicates the impact on data quality. Flags in the "amber" category indicate that the data is slightly degraded but still usable. Flags in the "red" category indicate that the data is severely degraded and should be discarded or used with caution. The ASCAT full resolution product does not contain a utilisation summary flag. A recommendation for the users is provided below instead, equivalent to the criteria followed to set up the F_USABLE (0=GOOD, =USABLE, 2=BAD) for the re-sampled products: If any of the red flags are set, the data should not be used If any of the amber (but none of the red) flags are set, data should be used with caution If none of the amber, nor red flags are set, data is of good quality Note: The full resolution product also provides, as of format version 2.0, a field denominated LAND_FRAC, expected to provide an estimation of the percentage of signal from land within the Spatial Response Function associated to a given full resolution measurement. The algorithm for the estimation of LAND_FRAC is, at the time of writing this version of the product guide (i.e., for processor format version 9.3) not yet implemented. The development of the algorithm is ongoing, based on the approach presented in [RD56]. Page 38 of 64

39 v5, 6 July The ASCAT Level 2 ocean surface wind product Here, only general information is given. For more details, please refer to the OSI SAF scatterometer webpage General characteristics The ASCAT Level 2 ocean surface wind product is generated and distributed in near real-time. The main geophysical parameter is near surface (0 m height) ocean (neutral-equivalent) wind vectors. The operational Level 2 product is nominally generated by the OSI SAF based on the swath-based 50 km resolution Level b product received from EUMETSAT on a 25 km spacing grid. An additional ocean surface wind product with dedicated processing at the coast and based on averaging the NRCS full resolution data with a top-hat window is also available on a 2.5 km swath grid. The products contain the two ambiguous wind vectors located at each node, as well as a flag indicating which one has been selected as corresponding to the correct wind direction by the ambiguity removal step. As an integral part of the product, the necessary geophysical parameters used for the retrieval from the Level b product are also included in the Level 2. Additionally, the Level 2 product contains other auxiliary information used in the retrieval, such as collocated NWP ocean wind values used in the ambiguity removal step Accuracy The expected accuracy of the ASCAT 50-km resolution ocean winds is 2 m/s RMS difference in wind vector components and 0.5 m/s wind speed bias with respect to a reference true wind Quality information in the products With each ASCAT Level 2 wind vector, a value reflecting the likelihood of that retrieved wind solution is also given in the product, which accounts for the residual of the wind retrieval and a probability associated with that wind direction, as given by the wind direction ambiguity removal step The ASCAT Level 2 Soil Moisture product Here, only general information is given. For more details, please refer to [RD 35], available at the TU-Wien ASCAT publications page General characteristics The ASCAT Level 2 Soil Moisture product is generated and distributed in near real-time. The main geophysical parameter is relative land surface soil moisture, based on the swath-based grid. As an integral part of the product, the necessary geophysical parameters used for the retrieval from the Level b product are also included in the Level 2. Accuracy The expected average RMS error of the ASCAT soil moisture index is about 25%, which corresponds to about m 3 water per m 3 soil, depending on soil type Quality information in the products To help users in judge the quality of the soil moisture product, several quality and processing flags are delivered with the data. The quality flags comprise information about the intrinsic product quality, internal quality checks and specific processing details. The flags are derived directly from the incoming scatterometer data. Page 39 of 64

40 v5, 6 July 205 Additionally to these quality flags, advisory flags are defined. The advisory flags will support the user in judging the reliability of the soil moisture product for a particular location on a particular day of the year and will allow the user to consider rejecting unreliable measurements. These indicators are based on average land cover characteristics, soil type and topography, which cannot be derived from the scatterometer data set, but need to rely on external data sets. 4.6 Summary of ASCAT product current and potential applications A number of operational applications of scatterometer data have been developed in meteorology and climate monitoring, after the success of the recent scatterometer missions [RD4]. The main operational product from scatterometers remains the wind over the ocean surface, and the main operational application is the use of scatterometer winds in weather analysis and forecasting. Scatterometer winds are used routinely to track tropical and extra-tropical cyclones. The ASCAT soil moisture products have been the first operational satellite soil moisture data set and also routinely exploited in the context of numerical land surface forecast models. Another group of operational applications, based on the use of scatterometer σ 0 estimates, have been also developed, such as sea ice edge detection and monitoring, where maps of sea ice coverage based on scatterometer data are routinely produced. Besides the operational use of scatterometer data, there are a number of scatterometer applications at various levels of maturity, in the fields of oceanography as well as for monitoring sea ice, snow cover and hydrological modelling and forecasting Scatterometer ocean wind applications Ocean winds assimilation in weather forecasting The main application of scatterometer ocean winds is the assimilation in NWP models. Since the main limitation for this application is the problem of the wind direction ambiguity, the impact and the benefits of the assimilation of scatterometer winds in NWP models were clearly improved when variational data assimilation was developed. These schemes can ingest the two wind direction ambiguities and perform the ambiguity removal within the assimilation process, by weighting one wind direction or another according to the information provided by the background field and the other observations used in the assimilation. ERS and SeaWinds winds have been and are operationally assimilated in global models at ECMWF and the Met Office (UK). Also regional NWP models use scatterometer data following similar principles Nowcasting and forecasting of extreme events Scatterometer ocean winds can be used also in Nowcasting and forecasting of extreme events. The added value of the scatterometer data in this particular application is two-fold. First, the scatterometer measurements are available in data-sparse oceanic regions where extreme weather events such as tropical cyclones are generated, and they are available in cloudy and rainy conditions. Secondly, scatterometer winds contain much sub-synoptic scale information that, though difficult to assimilate into NWP, is vital for Nowcasting applications. Moreover, the increased coverage and timeliness of ASCAT with respect to ERS winds facilitates the routine use of scatterometer winds by operational weather forecasters Winds forcing ocean and wave models An important limitation in the interpretation of the results obtained by ocean models is considered to be the uncertainties in the surface wind fields, especially in tropical areas, Page 40 of 64

41 v5, 6 July 205 where the ocean reacts strongly and quickly to the atmosphere s variability. Again in this case, conventional instrumentation data is generally sparse in these areas. The main parameter of interest in this case is ocean surface wind stress, related to the near-surface ocean winds. The scatterometer winds play also an indirect role in operational ocean wave forecast models, as most of these models are coupled to or forced by an atmospheric model wind analysis that has assimilated scatterometer winds (e.g. ECMWF model) Other scatterometer applications Scatterometry over land surfaces Radar backscatter from land corresponds to a mixture of surface and volume scattering associated with the radar penetration depth. The surface roughness, vegetation cover and terrain dielectric properties play an important role in determining what the dominant backscatter regime is. The response of the land surface to the radar with respect to incidence angle (slope) is different for both regimes. Hence examining not only the backscatter intensity but also the backscatter slope allows assessing surface type, vegetation cover and soil moisture content [RD49] Sea Ice monitoring: mapping and analysis Sea ice detection based on scatterometer data is mainly based on two properties of the backscatter response from sea ice. First, sea ice surfaces have isotropic backscatter response, in contrast to the strong anisotropic response from the open water. Secondly, the dependency of the backscatter response with respect to incidence angle is generally smaller for sea ice than for the ocean. Based on these properties, and on available in situ validation sea ice data, models describing the scatterometer sea ice backscatter signatures have been developed, which point at one key sea ice characteristic driving the backscatter response: sea ice age. Following these results, multi-sensor sea ice detection and classification algorithms relying on multivariate analysis with microwave (active and passive), infrared and visible data as input, have been developed, in which the sea ice information contained in the scatterometer measurements plays a key role Snow accumulation over great ice sheets In order to understand the relationship between global warming and changes in the ice sheets, it is necessary to quantify mass balance and the time and space scales of variability in snow accumulation and ablation. Microwave backscattering depends on both the roughness and physical characteristics of the snow and ice. This provides an efficient means of monitoring backscatter changes, which accompany diagenetic changes in the ice sheets forced by seasonal accumulation, densification, temperature cycling, ablation and/or metamorphic processes. Page 4 of 64

42 v5, 6 July DATA VIEWING AND READING IDL readers for the native EPS format ASCAT Level b products are available online at the EUMETSAT website under the Support Software and Tools section. The products in netcdf formats can be read using standard libraries. For more information on netcdf, a good resource is the Unidata netcdf webpage. Software capable of reading the WMO formats is available from a variety of sources, including ECMWF. Additionally, the KNMI makes available specific ASCAT BUFR reader code, which can be adapted to read NRCS, wind and soil moisture information. Page 42 of 64

43 v5, 6 July ASCAT PRODUCT FORMATS AND DISSEMINATION ASCAT products are available through EUMETSAT and the Satellite Application Facilities through different mechanisms, depending on the latency of the data and the application timeliness requirements. All the mechanisms are described on the EUMETSAT data Delivery pages. The first step to gain access to any EUMETSAT product is a registration at the Earth Observation Portal. I the following paragraphs, a brief description of the difference dissemination mechanisms is provided, focusing down on ASCAT products and their formats. 6. EPS products available dissemination means 6.. Satellite Direct Broadcast Service Instrument and ancillary data acquired by the Metop satellites are broadcast and received by authorised users in real-time via: High Resolution Picture Transmission (HRPT) - transmission of data from all Metop instruments in full resolution The data are received by local reception stations. It is the responsibility of the user to procure and install a local reception station. Specification documentation for a EUMETSAT-based HRPT Reference User Station is available for information on the EUMETSAT webpage Metop - AHRPT. The output format of the EUMETSAT HRPT Reference User Station is Level 0 products in the EPS Native format. See [RD 8] and [RD 7]. The broadcast data are encrypted. To get authorisation to access the data, users need to register with the EUMETSAT User Services and will receive the data decryption information EUMETCast Global EPS products at different levels are distributed in near real-time via EUMETSAT s Data Distribution System (EUMETCast). EUMETCast utilises the services of a satellite operator and telecommunications provider to distribute data files using Digital Video Broadcast (DVB) to a wide audience located within the geographical coverage zone which includes Europe, Africa and the American continent. EUMETCast is part of a wider network known as GEONETCast, with coverage also over Asia and Australia. Within the current EUMETCast configuration, the multicast system is based upon a client/server system with the server side implemented at the EUMETCast uplink site (Usingen, Germany) and the client side installed on the individual EUMETCast reception stations. The telecommunications suppliers provide the DVB multicast distribution mechanism. Data/product files are transferred via a dedicated communications line from EUMETSAT to the uplink facility. These files are encoded and transmitted to a geostationary communications satellite for broadcast to user receiving stations. Each receiving station decodes the signal and recreates the data/products according to a defined directory and file name structure. A single reception station can receive any combination of the provided services. A typical EUMETCast reception station comprises a standard PC with DVB card inserted and a satellite off-set antenna fitted with a digital universal V/H LNB. In addition, users require the multicast client software, which can be obtained via the EUMETSAT User Services. Page 43 of 64

44 v5, 6 July 205 More detailed information on this service can be found in the EUMETSAT webpage EUMETCast Dissemination Scheme. ASCAT Level and Level 2 products distributed on EUMETCast are formatted in EPS native format and the BUFR GTS/RMDCN A subset of EPS products will be disseminated additionally in near real-time via the Global Telecommunication System (GTS). GTS is the World Meteorological Organization integrated network of point-to-point circuits, and multi-point circuits which interconnect meteorological telecommunication centres. Its purpose is to enable an efficient exchange of meteorological data and products in a timely and reliable way to meet the needs of World, Regional and National Meteorological Centres. The circuits of the GTS are composed of a combination of terrestrial and satellite telecommunication links. Meteorological Telecommunication Centres are responsible for receiving data and relaying them selectively on GTS circuits. The GTS is organised on a three-level basis, namely: The Main Telecommunication Network, linking together 3 World meteorological centres and 5 regional telecommunication hubs. The Regional Meteorological Telecommunication Networks, consisting of an integrated network of circuits interconnecting meteorological centres in a region, which are complemented by radio broadcasts where necessary. In Europe, the GTS network is supported by the Regional Meteorological Data Communication Network (RMDCN). The National Meteorological Telecommunication Networks, which extend the GTS network down to national level. More detailed information on this service can be found on the WMO website Products distributed on the GTS are in official WMO formats, namely BUFR for the ASCAT Level and Level 2 products EUMETSAT Data Centre All EPS products and auxiliary data are normally archived and made available to users from the EUMETSAT Data Centre (formerly known as the UMARF or Archive Services) upon request. Information of the Data Centre can be found on the Data Centre webpage. Access is through a Web interface, the Online Ordering Application, through which the users are able to browse and order products, manage their user profile, retrieve products, documentation and software libraries, get help, etc. The Data Centre features include limited geographical and time sub-setting and image preview (only for AVHRR products). ASCAT products archived in the Data Centre can be accessed in a variety of formats, including EPS native format, netcdf BUFR. Page 44 of 64

45 v5, 6 July ASCAT products dissemination This section summarises the different dissemination means and formats for all ASCAT products available to users. For the description of product contents, refer in addition to Table 4-. Real-time broadcast of ASCAT raw data is not covered in this guide. It is noted though for information that the raw data streams mentioned in the table above indicate what is broadcast by the platform. Depending on the reception system used (i.e., the HRPT local reception system), different formats of this raw data stream are produced. This depends on the local reception station provider. For Metop HRPT stations, the Reference User Station has been developed to produce EPS Native Level 0 format products. Although available through the EUMETSAT Data Centre, ASCAT Level 0 products are not considered an end-user product, hence they are not addressed in this guide. Currently, there is no user software package that can accept ASCAT L0 data and process it into Level NRCS information. Page 45 of 64

46 v5, 6 July 205 Format Real-Time Direct Broadcast Near-Real-Time dissemination on EUMETCast (timeliness) Metop raw data format EPS native format HRPT raw data stream and Metop Admin message - ASCSZ(F/O/R)B (60-00 min) - Near-Real-Time dissemination on GTS (timeliness) EUMETSAT Data Centre retrieval (timeliness) - Level 0, ASCSZ(F/O/R)B, SOMO25/2 (8-9 h) NetCDF ASCSZ(O/R)B, SOMO25/2, - OAS025/02, OASW025/02, OSI-04 (8-9 h) WMO (BUFR) - ASCSZ(O/R)B (60-00 min) SOMO25/2, OAS025/02, OSI-04 (70-0 min) EARS-ASCAT/25 (6-8 min) ASCSZ(O/R)B (60-00 min) SOMO25/2, OAS025/02, OSI-04 (70-0 min) EARS-ASCAT/25 (6-8 min) OSI SAF FTP service (timeliness) ASCSZ(O/R)B, SOMO25/2, OAS025/02, OSI-04 (8-9 h) Note: Timeliness refers to the elapsed time between sensing and dissemination. Table 6-: Summary of dissemination means and formats for ASCAT products - -- OAS025/02, OASW025/02, OSI-04 (70-0 min) EARS-ASCAT/25 (6-8 min) OAS025/02, OSI-04 (70-0 min) EARS-ASCAT/25 (6-8 min) H- SAF FTP service (timeliness) Level 2 soil moisture time series (not an NRT product)) - Page 46 of 64

47 v5, 6 July Near-real-time dissemination The ASCAT products disseminated to users in near real-time are: ASCAT Level b products at both resolutions, with a timeliness of 60 to 00 min from sensing ASCAT Level 2 products, with a timeliness of 70 to 0 min from sensing for global products and 6-8 min for regional products. The dissemination granularity of the data is 3 minutes for both Level b and Level 2 global products, and between 3 minutes to 5 minutes for Level 2 regional products. For the ASCAT-A regional Level 2 regional service, the last 30 minutes of every global dump are also processed with a file granularity of 30 minutes Archive retrieval The ASCAT products available from the EUMETSAT Data Centre are as follows: ASCAT Level b spatially averaged products at both resolutions ASCAT Level b full resolution product ASCAT Level 2 ocean winds and soil moisture global products Reprocessed data corresponding to the above products are also available via the Data Centre. All products are archived as full-dump products, but limited sub-setting capabilities are provided to the user in the retrieval step. The products are available for the users in the EUMETSAT Data Centre 8 to 9 hours after sensing. The static auxiliary data used in the generation of all products can also be found there. 6.3 ASCAT EPS native product formats 6.3. The EPS native formats General overview of the EPS generic product format All products in EPS native format are structured and defined according to an EPS Generic Product Format. This format is not ASCAT specific. The general product section breakdown is given, and the following sections will focus on how this generic format is further applied to ASCAT products. This description is not aimed at supporting the writing of reader software for the ASCAT or other EPS products, because readers and product extraction tools are already available (see Section 5). The intention of this and the following sections is to provide enough information to be able to use such available tools and to interpret the retrieved information. For users interested in writing their own product readers for one or several ASCAT products in EPS native format, we refer them to the detailed format specifications provided in [RD ] and [RD 2]. The general structure of the products is broken down in sections, which contain one or more records of different classes. Every single record is accompanied by a Generic Record Header (GRH), which contains the metadata necessary to uniquely identify the record type and occurrence within the product. The following general structure is followed by all EPS products, where all the sections occur always in the given order. Page 47 of 64

48 v5, 6 July 205 Header Section, containing metadata applicable to the entire product. The header section may contain two records, the Main Product Header Record (MPHR) and the Secondary Product Header Record (SPHR). This is the only section that contains ASCII records, the rest of the product is in binary. Pointer Section, containing pointer information to navigate within the product. It consists of a series of Internal Pointer Records (IPR), which include pointers to records within the Global Auxiliary Data, Variable Auxiliary Data and Body Sections that follow. Global Auxiliary Data Section, containing information on the auxiliary data that have been used or produced during the process of the product and applies to the whole length of the product. There can be zero or more records in this section, and they can be of two classes: Global External Auxiliary Data Record (GEADR), containing an ASCII pointer to the source of the auxiliary data used, and Global Internal Auxiliary Data Record (GIADR), containing the auxiliary data used itself. Variable Auxiliary Data Section, containing information on the auxiliary data that have been used or produced during the process of the product and may vary within a product, but with a frequency in any case less than the measurement data itself. There can be zero or more records in this section, and they can be of two classes: Variable External Auxiliary Data Record (VEADR), containing an ASCII pointer to the source of the auxiliary data used, and Variable Internal Auxiliary Data Record (VIADR), containing the auxiliary data used itself. Body Section, which is usually the bulk of the product and contains the raw or processed instrument data and associated information. This section contains time-ordered Measurement Data Records (MDR). A particular type of MDR can occur to indicate the location of an unexpected data gap within any product, the Dummy Measurement Data Record (DMDR). The format of the MPHR, IPRs, GEADR, VEADR and DMDRs is common to all products, while the other records can be of different formats and contents, and identified as of different sub-classes for different products. Every record consists of a series of fields, which can have different data types. See Appendix C for all possible data types. It is important to note that GEADR and VEADR records are included in the products to support processing configuration control for EUMETSAT at product level. They point to the name of auxiliary data files used in the processing, but they are not of any interest or use to the end-user for the utilisation of the products. Two types of records deserve special description, because they are key to navigating within the products, namely the GRH and the IPR. Their format and the meaning of their fields are detailed in Appendix D. Table 6-2 gives an example of the general structure of the Generic Product Format. Page 48 of 64

49 v5, 6 July 205 Section Record Class Record Subclass Start Time HEADER SECTION MAIN PRODUCT HEADER RECORD SECONDARY PRODUCT HEADER RECORD T T Stop Time T6 T6 INTERNAL POINTER SECTION INTERNAL POINTER RECORD (GEADR Subclass A) INTERNAL POINTER RECORD (GEADR Subclass B) INTERNAL POINTER RECORD (GIADR Subclass A) INTERNAL POINTER RECORD (GIADR Subclass B) INTERNAL POINTER RECORD (GIADR Subclass C) INTERNAL POINTER RECORD (VEADR Subclass A) INTERNAL POINTER RECORD (VEADR Subclass B) INTERNAL POINTER RECORD (VEADR Subclass C) INTERNAL POINTER RECORD (VIADR Subclass A) INTERNAL POINTER RECORD (VIADR Subclass B) INTERNAL POINTER RECORD (VIADR Subclass C) INTERNAL POINTER RECORD (MDR Subclass A) INTERNAL POINTER RECORD (MDR Subclass B) INTERNAL POINTER RECORD (MDR DUMMY) INTERNAL POINTER RECORD (MDR Subclass A) INTERNAL POINTER RECORD (MDR Subclass B) T T T T T T T T T T T T T T T T T6 T6 T6 T6 T6 T6 T6 T6 T6 T6 T6 T6 T6 T6 T6 T6 GLOBAL AUXILIARY DATA SECTION GLOBAL INTERNAL AUXILIARY DATA RECORD GLOBAL INTERNAL AUXILIARY DATA RECORD GLOBAL INTERNAL AUXILIARY DATA RECORD GLOBAL INTERNAL AUXILIARY DATA RECORD GLOBAL INTERNAL AUXILIARY DATA RECORD SUBCLASS A SUBCLASS B SUBCLASS A SUBCLASS B SUBCLASS C T T T T T T6 T6 T6 T6 T6 VARIABLE AUXILIARY DATA SECTION VARIABLE INTERNAL AUXILIARY DATA RECORD VARIABLE INTERNAL AUXILIARY DATA RECORD VARIABLE INTERNAL AUXILIARY DATA RECORD VARIABLE INTERNAL AUXILIARY DATA RECORD VARIABLE INTERNAL AUXILIARY DATA RECORD VARIABLE INTERNAL AUXILIARY DATA RECORD VARIABLE INTERNAL AUXILIARY DATA RECORD VARIABLE INTERNAL AUXILIARY DATA RECORD VARIABLE INTERNAL AUXILIARY DATA RECORD VARIABLE INTERNAL AUXILIARY DATA RECORD SUBCLASS A SUBCLASS B SUBCLASS B SUBCLASS C SUBCLASS C SUBCLASS A SUBCLASS A SUBCLASS A SUBCLASS B SUBCLASS C T T T3 T T5 T T2 T4 T T T6 T3 T6 T5 T6 T2 T4 T6 T6 T6 BODY SECTION MEASUREMENT DATA RECORD MEASUREMENT DATA RECORD MEASUREMENT DATA RECORD MEASUREMENT DATA RECORD MEASUREMENT DATA RECORD SUBCLASS A SUBCLASS B DUMMY SUBCLASS A SUBCLASS B T T2 T3 T4 T5 T2 T3 T4 T5 T6 Table 6-2: Generalised schematic of the generic product format Page 49 of 64

50 v5, 6 July Granularity of the EPS products The Full EPS product is produced by processing a dump of data. This is the product used to archive in the EUMETSAT Data Centre. In addition, the Regional EPS product is a full product that has been passed through a geographical filter. This may happen, for example, during the retrieval of the product from the Data Centre. Finally, a Product Dissemination Unit (PDU) is the near-real-time dissemination of the full product, and it is typically of 3 minutes. A PDU is often referred to as a product granule. The EPS Generic Product Format has been defined to apply to any length of sensing. That means that the same generic format described above applies to a 3-minute duration granule, half an orbit or a full dump of data. The length in time of the product is contained in the MPHR Product format version control Every record class and sub-class has an associated record version number contained in its corresponding GRH. In addition, each product has a format version number, which is stored in the MPHR Product naming convention The file naming convention for EPS products in EPS native format provides a product name that uniquely identifies any product and provides a summary of its contents. It follows the convention described in [RD2]. For the ASCAT products, the resulting product file names are as follows: Product Product Name ASCAT Level b 25-km grid spacing ASCA_SZO_B_Mnn_<...> ASCAT Level b 2.5-km grid spacing ASCA_SZR_B_Mnn_<...> ASCAT Level b full resolution ASCA_SZF_B_Mnn_<...> ASCAT Level 2 Soil Moisture 25-km grid spacing ASCA_SMO_02_Mnn_<...> ASCAT Level 2 Soil Moisture 2.5-km grid spacing ASCA_SMR_02_Mnn_<...> Table 6-3: Generic ASCAT product names The products retrieved from the EUMETSAT Data Centre have the same names as the original EPS formatted ones, with the extension appended.nat for products in the native EPS format The ASCAT Level b product formats Records to be found in the ASCAT Level b products are in the following tables, corresponding to the current product format version 2.0: Page 50 of 64

51 v5, 6 July 205 Record name Description Usage Subclass ID MPHR Main Product Header Record Main product identification details SPHR Secondary Product Header Record Summary of product quality flags Necessary IPRs Internal Product Record Pointers Necessary to access directly different records in the product VEADR_OSV GEADR_LSM VEADR-PRC VEADR-INS VEADR-NTB VEADR-XCL Name of input auxiliary file containing orbit parameters Name of input auxiliary file containing land /ocean mask Name of input auxiliary file containing processing parameters Name of input auxiliary file containing instrument parameters Name of input auxiliary file containing normalisation factors Name of input auxiliary file containing deblooming kernels Not relevant for end-user VIADR-OA Orbit/attitude parameters 4 VIADR-VER VIADR-GRID MDR-B-25 MDR-B-250 Summary of processor and auxiliary file configuration 6.25 km spacing swath grid provided for re-sampling Only used in Level b 2.5-km grid spacing products Only used in Level b 25-km grid spacing products Level b main product contents - They contain all the user needs for interpretation and further processing of the data, including relevant product quality information (see next sections for more details) MDR-B-FULL Only used in Level b Full products 3 Table 6-4: Record types in ASCAT Level b product for product format version Level b re-sampled products format These products are organised as successive lines of nodes along track, referenced to by the orbit time that corresponds to that line of node as described in [RD 3]. The START/STOP times indicated in the MPHR and the corresponding VIADR's, are also referenced with respect to that time. The Level b averaged products are organised as follows: by line of nodes across the swath by node within a line by σ 0 within a node Page 5 of 64

52 v5, 6 July 205 Each MDR contains data of the three types, defining fields of three different dimensions. Associated data of the same dimensions, related for example to geometry or quality flags, are also included in the MDR. The number of nodes in an ASCAT Level b product line depends on the resolution of the spatial averaging and the grid spacing between nodes. Every line of the 25-km grid spacing product will have 42 nodes (2 per swath). Every line of the 2.5-km grid spacing product will have 82 nodes (4 per swath). Every line contains data from both swaths, ordered from left swath to right swath and from left to right within the swaths, if one moves in the direction of the instrument. The number of σ 0 values in an ASCAT Level b product node is three as the name of triplet indicates. The occurrence of the different records in the Level b spatially averaged products is as follows: Record MPHR SPHR IPRs GEADR-LSM VEADR-PRC, -INS, -NTB, -XCL, -OSV VIADR-OA, -VER MDR-B-25, -250 Once per product Once per product Once each per product Once per product Occurrence Occurs at least once if the auxiliary file referred to has been used in the processing. Re-occurs each time the applicability of the information changes within the product. Occurs at least once. Re-occurs each time the applicability of the information changes within the product. Once per every line of nodes Table 6-5: Occurrence of records in ASCAT Level b spatially averaged product for product format version 2.0 See Section 0 for more details on the contents and format of the ASCAT Level b spatially averaged products Level b full-resolution product format ASCAT Level b full resolution corresponds to σ 0 values generated from individual echo samples within an echo line in a source packet, together with associated data, referenced by the echo source packet localisation time (T 0 ). The START/STOP times indicated in the MPHR and the corresponding VIADR's, are also referenced by the echo source packet localisation time T 0. The Level b full resolution product is organised per antenna beam firing. Each MDR will therefore contain 92 geographically-localised σ 0 values, plus associated data. Additionally, a swath grid is also provided to allow re-sampling of the products by the user. Each line of grid nodes is contained in one VIADR-GRID record. The occurrence of the different records in the Level b full resolution product is shown in Table 6-6. Page 52 of 64

53 v5, 6 July 205 Record Occurrence MPHR SPHR IPRs GEADR-LSM VEADR-PRC, -INS, -NTB, -XCL, -OSV VIADR-OA, -VER, -GRID MDR-B-FULL Once per product Once per product Once each per product Once per product Occurs at least once if the auxiliary file referred to has been used in the processing. Re-occurs each time the applicability of the information changes within the product. Occurs at least once. Re-occurs each time the applicability of the information changes within the product. Once per every antenna beam firing sequence Table 6-6: Occurrence of records in ASCAT Level b full resolution product for product format version 2.0 See Section for more details on the contents and format of the ASCAT Level b full resolution product. Page 53 of 64

54 v5, 6 July ASCAT Level 2 Soil Moisture product formats Records to be found in the ASCAT Level 2 Soil Moisture products are shown in Table 6-7: Record name Description Usage Subclass ID MPHR Main Product Header Record Main product identification details Necessary IPRs Internal Product Record Pointers Necessary to access directly different records in the product 0-3 MDR-2-SM-25KM MDR-2-SM-50KM VIADR-VER VEADR-SMC Only used in Level km grid spacing products Only used in Level 2 25-km grid spacing products Processor and auxiliary file versions used Name of input auxiliary file containing backscatter correction factors Level 2 main product contents - They contain all the user needs for interpretation and further processing of the data, including relevant product quality information (see next sections for more details) Not relevant for end-user 6 Not relevant for end-user 7 VEADR-CURV Soil Moisture parameter database Not relevant for end-user 8 VEADR-CURV-NOISE Soil Moisture parameter database Not relevant for end-user 9 VEADR-DRY Soil Moisture parameter database Not relevant for end-user 0 VEADR-DRY-NOISE Soil Moisture parameter database Not relevant for end-user VEADR-MS-MEAN Soil Moisture parameter database Not relevant for end-user 2 VEADR-NONSCAT Soil Moisture parameter database Not relevant for end-user 3 VEADR-SLOP Soil Moisture parameter database Not relevant for end-user 4 VEADR-SLOP-NOISE Soil Moisture parameter database Not relevant for end-user 5 VEADR-WET Soil Moisture parameter database Not relevant for end-user 6 VEADR-WET-NOISE Soil Moisture parameter database Not relevant for end-user 7 Table 6-7: Record types in ASCAT Level 2 Soil Moisture product Occurrence information is summarised in Table 6-8: 4 5 Page 54 of 64

55 v5, 6 July 205 Record Occurrence MPHR IPRs MDR-2-SM-50KM, -25KM VIADR-VER VEADR-SMC VEADR-CURV VEADR-CURV-NOISE VEADR-DRY VEADR-DRY-NOISE VEADR-MS-MEAN VEADR-NONSCAT VEADR-SLOP VEADR-SLOP-NOISE VEADR-WET VEADR-WET-NOISE Once per product Once each per product Once per every line of nodes Occurs at least once. Re-occurs each time the applicability of the information changes within the product. Occurs at least once. Re-occurs each time the applicability of the information changes within the product. As for VEADR-SMC As for VEADR-SMC As for VEADR-SMC As for VEADR-SMC As for VEADR-SMC As for VEADR-SMC As for VEADR-SMC As for VEADR-SMC As for VEADR-SMC As for VEADR-SMC Table 6-8: Occurrence of records in ASCAT Level 2 Soil Moisture product See Section 2 for details on the contents and format of the ASCAT Level 2 Soil Moisture product. 6.4 The WMO formats The ASCAT products available in WMO (BUFR) format are summarised in Table 6-9. Product Bulletin header Originating station ASCSZOB IESXii (ii from 0 to 0) ASCSZRB IESXii (ii from to 99) SOMO25 IEOXii (ii from 0 to 0) SOMO2 IEOXii (ii from to 99) ASCAT Level 2 multi-parameter products global: 25 km spacing grid ASCAT Level 2 wind products regional : 25 km spacing grid ASCAT Level 2 wind products regional: 2.5 km spacing grid ISXXii (ii from 0 to 06) ISXNii (ii from 0 to 06) ISXNii (ii from to 6) EUMP EHDB Descriptor sequence Table 6-9: ASCAT products available in WMO (BUFR) format Page 55 of 64

56 v5, 6 July 205 Note: There is a single BUFR format to incorporate the ASCAT Lb spatially averaged products and the L2 Soil Moisture and Near Surface Winds. If any of the product levels are not present, the corresponding fields are set to missing values. The full format description of these products is available in the WMO Manual on Codes [RD 34]. Further information on the ASCAT Level 2 products is available in [RD 32]. In order to distinguish between BUFR products from the global or the EARS processing chain, the descriptor Originating Sub-centre (00034) is set to for the latter. The names of the ASCAT Level b and Level 2 soil moisture BUFR products distributed on EUMETCast follow the WMO convention and are specified in [RD ]. Here are some example filenames: For: ASCSZR on METOP-B W_XX-EUMETSAT Darmstadt,SOUNDING+SATELLITE,METOPB+ASCAT_C_EUMP_ _00808_eps_o_25_l.bin For: ASCSZO on METOP-A W_XX-EUMETSAT Darmstadt,SOUNDING+SATELLITE,METOPA+ASCAT_C_EUMC_ _000_eps_o_250_l.bin ASCSMR on METOP-A W_XX-EUMETSAT Darmstadt,SOUNDING+SATELLITE,METOPA+ASCAT_C_EUMC_ _000_eps_o_25_ssm_l2.bin In case of the ASCAT Level 2 wind and multi parameter (soil moisture + wind) products, the following convention is followed: for the global products ascat_yyyymmdd_hhmmss_satellite_nnnnn_eps_o_iii_xxx.l2_bufr for the regional products ascat_yyyymmdd_hhmmss_satellite_nnnnn_ear_o_iii.l2_bufr Page 56 of 64

57 v5, 6 July 205 where: yyyymmdd hhmmss satellite nnnnn iii_xxx station stands for the UTC year, month, day of the data start sensing time stands for the UTC hour, minute, second of the data start sensing time metopa, metopb is the orbit number can take the value: coa_ovw for OSI for OAS for OAS025 25_{station}_ovw for EARS-ASCAT 250_{station}_ovw for EARS-ASCAT25 can take the value of different HRPT stations, e.g. sva (Svalbard), mas (Maspalomas), lan (Lannoin), etc or if missing, it refers to EARS data processed from the global dump (only for METOP-A). 6.5 The NetCDF format Most of the Level b and Level 2 products are provided additionally in NetCDF format, the structure and contents of the files having been defined following the Climate and Forecast (CF) metadata conventions for the description of Earth sciences data. In the case of the Level b and Level 2 soil moisture products, the filename formats are as per the BUFR products, but adding a.nc at the end, instead of.bin. In the case of the Level 2 wind products, the convention of the BUFR files is also followed, replacing the final _bufr string by _nc and the iii_xxx field by thees values: 25_ovw for for OASW02 250_ovw for for OASW025 A description of the contents of the ASCAT Level b and Level 2 soil moisture netcdf products is provided in Appendix XYZ. In the case of the Level 2 winds, a description of the NetCDF data is provided in [RD32], available via the OSI SAF scatterometer webpage. Page 57 of 64

58 v5, 6 July ASCAT PRODUCT PROCESSING ALGORITHMS See the ASCAT NRCS Algorithm Technical Basis Description for a detailed description of the ASCAT Level processing algorithms. For Level 2 soil moisture, see the ASCAT Soil Moisture Product Handbook [RD 27] that provides the most detailed algorithm description. Finally, for Level 2 winds, see the Algorithm Technical Basis for the OSI SAF Wind Products [RD 24]. Page 58 of 64

59 v5, 6 July ASCAT PRODUCTS VALIDATION The objective of the calibration and validation of Level products is to ensure the following: the NRCS values and their localisation are calibrated and within the accuracy requirements the accompanying information (flags and qualifiers) faithfully address non-nominal quality scenarios the completeness of the data set is as expected, i.e., data gaps being addressed and explained The accuracy requirements related to the: absolute and inter-beam radiometric accuracy relative (with respect to incidence angle) radiometric accuracy radiometric resolution localisation The NRCS is calibrated against ground targets of known radiometric cross-section three ground transponders. The geographic location of these is also precisely known, hence there is an opportunity of assessing the accuracy of the localisation of the NRCS against that reference. The calibrated radiometric accuracy is then validated over targets with well-modelled NRCS responses, such as the rainforest, the ocean and stable sea ice areas. In all cases, the general approach followed and adapted to the context of specific data sets can be summarised in two documents: The ASCAT Calibration and Validation Plan [RD 5] which described the pre-launch plans for calibration and validation of the products, reviewing methods in the context of end-to-end (up to Level 2) validation. The ASCAT Verification, Calibration and Validation Plan [RD 6] which was issued as a more specific step-by-step plan for the commissioning of ASCAT-B Level products Several calibration exercises, associated with extended transponder measurement campaigns have taken place and their assessment documented: For ASCAT-A: in 2007, 200 and 202 ([RD 6], [RD 0]) For ASCAT-B: in 203 [RD30] The release of several ASCAT Level product standards since launch has led to several major validation exercises, which have all been documented: Validation of ASCAT-A products after the commissioning of METOP-A [RD 6] Validation of ASCAT-A re-processed products [RD 5] Validation of ASCAT-B products after the commissioning of METOP-B [RD20] Validation of ASCAT-A re-processed products [RD 9] Some selected key plots from the latest validation reports of ASCAT-A and ASCAT-B are provided in this chapter, illustrating the main accuracy figures: Page 59 of 64

60 v5, 6 July 205 radiometric accuracy and inter-beam radiometric stability, also called calibration accuracy, around 0. db.. radiometric resolution over ocean, also called Kp, around 2-3% for the product re-sampled at 25 km and around 4-5% for that at 2.5 km.. localisation accuracy, within 4 km. Figures 8- and 8-2 show the residual gain differences between the gain values estimated from the transponder data during the ASCAT-A (202) and ASCAT-B (203) transponder calibration campaigns and the fitted antenna gain model, for the main elevation cut. Further error analysis of the calibration error, taking into account the correlations along elevation introduced by the fitting method, reported a calibration accuracy of 0.07 db [RD30]. Figure 8-3 shows yearly averages of the rainforest backscatter model 0 = 0 /cos, with respect to the incidence angle, for ASCAT-A. An incidence angle dependency of around 0. db per 0 o is observed, which is not evident in backscatter plots from transponder data or over ocean. Correcting for the slope of this model, the relative calibration of the NRCS values is shown to be 0.09 db [RD29]. Figure 8-3 shows additionally the excelled radiometric stability of ASCAT-A, estimated to be better than 0.00 db per year [RD29]. Figure 8-4 shows the excelled cross-calibration between the ASCAT-A and B products, currently within 0. db. Finally, Figure 8-5 shows time series of monthly global averages of radiometric resolution over ocean for the 25 km re-sampled product, shown to be very stable around 2.2% [RD29]. In order to examine the incidence angle dependency, Figure 8-6 shows global daily averages over all targets for ASCAT B 2.5 km and 25 km re-sampled products. The apparent gradient change between 0 o and 5 is due to the change in number of looks used in the range compression on board. With respect to the Level 2 products, the OSI SAF is responsible for the validation of the wind products. Prior to the wind estimation, a NWP Ocean Calibration further adjusts the NRCS calibrated values to resolve remaining inter-beam and relative calibration differences, as well as to account for the different NRCS calibrations between the ASCAT data and the ERS scatterometer data used to derived the current C-band GMF function CMOD5.n [RD35][RD36]. The estimated accuracy of the ASCAT-A and B wind products, using ECMWF winds as a reference, can be summarised [RD32] as: Bias wind speed is 0.02 m/s for ASCAT-A and 0.05 m/s for ASCAT-B. Standard deviations of u and v wind components are.72 m/s and.76 m/s for ASCAT-A and.78 m/s and.80 m/s for ASCAT-B, respectively. Validation of the Level 2 soil moisture products is also available in relation to specific data set releases: Validation of ASCAT-A re-processed products [RD 26] Validation of ASCAT-B products after the commissioning of METOP-B [RD 3] These validation exercises have covered data completeness, overall statistics and consistency of the data set, flags and qualifiers. Scientific validation is under the responsibility of the H-SAF and covered in several scientific papers and reports [RD 36][RD 37]. Page 60 of 64

61 v5, 6 July 205 Figure 8-: Residual differences between the ASCAT-A antenna gain values estimated from the transponder 202 data and the fitted model gain patterns, for the principal elevation cut and for all beams [RD 9]. Page 6 of 64

62 v5, 6 July 205 Figure 8-2: Residual differences between the ASCAT-B antenna gain values estimated from the transponder 203 data and the fitted model gain patterns, for the principal elevation cut and for all beams [RD 0]. Page 62 of 64

63 v5, 6 July 205 Figure 8-3: Mean annual ASCAT-A 0 in each beam as a function of incidence angle for the years Each line in these plots corresponds to data from one year [RD9]. Page 63 of 64

64 v5, 6 July 205 Figure 8-4: Average rainforest calibration differences with respect to incidence angle between ASCAT-A and ASCAT-B for June 205. Page 64 of 64

65 v5, 6 July 205 Figure 8-5: Time series of monthly averages of ocean Kp (radiometric resolution) for the ASCAT-A 25 km resampled product [RD 9]. Page 65 of 64

66 v5, 6 July 205 Figure 8-6: Global daily averages ( ) of Kp values for ASCAT-B, for the 25 km re-sampled product (top 6 panels) and 2.5 km re-sampled product (bottom 6 panels) for all six beams. Page 66 of 64