PRODUCT USER MANUAL For Sea Level TAC product

Transcription

1 PRODUCT USER MANUAL For Sea Level TAC product SEALEVEL_MED_SLA_TREND_TIMESERIES_TARGETED_004 SEALEVEL_BS_SLA_TREND_TIMESERIES_TARGETED_005 SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_006 WP leader: SL TAC, Gilles Larnicol Issue: 1.0 Contributors: F. Mertz MyOcean version scope : Version 4.3 Approval Date : 7/11/2014 Project N : FP7-SPACE Work programme topic: SPA Prototype operational continuity of GMES services in the Marine Area. Duration: 30 months

2 CHANGE RECORD Issue Date Description of Change Author Checked By /10/14 Initial version F. Mertz L. Crosnier Page 2/ 20

3 TABLE OF CONTENTS I INTRODUCTION... 6 II HOW TO DOWNLOAD A PRODUCT... 7 II.1 Download a product through the MyOcean Web Portal Ftp Service... 7 III DESCRIPTION OF THE PRODUCT SPECIFICATION... 8 III.1 General Information... 8 III.2 Details of datasets IV NOmenclature of files IV IV.1.2 SEALEVEL_MED_SLA_TREND_TIMESERIES_TARGETED_ IV.1.3 SEALEVEL_BS_SLA_TREND_TIMESERIES_TARGETED_ IV.1.4 SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_ IV.2 Domain coverage IV IV.2.1 SEALEVEL_MED_SLA_TREND_TIMESERIES_TARGETED_ IV.2.2 SEALEVEL_BS_SLA_TREND_TIMESERIES_TARGETED_ IV.2.3 SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_ IV.3 Processing IV.3.1 Input data IV.3.2 Method IV Mapping process IV Computation of Mean Sea Level V file format V.1 netcdf V.2 Structure and semantic of netcdf file V V V.3 Reading software Page 3/ 20

4 GLOSSARY AND ABBREVIATIONS CF DT FTP MFC MSS NetCDF NOAA NRT SLA SSH Subsetter Directgetfile Climate Forecast (convention for NetCDF) Delayed Time File Transfer Protocol Monitoring and Forecasting Centre Mean Sea Surface Network Common Data Form National Oceanic and Atmospheric Administration Near Real Time Sea Level Anomaly Sea surface height MyOcean service tool to download a NetCDF file of a selected geographical box using values of longitude an latitude, and time range MyOcean service tool (FTP like) to download a NetCDF file Page 4/ 20

5 REFERENCE DOCUMENTS [1] AVISO gridded products: [2] Duacs webpage on the AVISO website: [3] Ssalto/Duacs User Handbook: (M)SLA and (M)ADT Near-Real Time and Delayed Time Products (pdf version, 700 KB): [4] Dibarboure Gerald, 2011: Jason-2 in Duacs, First tandem results and impact on processing and products. Marine Geodesy, Special issue on OSTM/Jason-2 Calibration/Validation Part 2, Vol.34, Issue 3-4, pp , doi: / [5] Jason-1, Jason-2, Envisat, T/P, ERS-2 quality assessment report: [6] Annual validation report of altimetric data by comparison with tide gauge and T/S measurements: [7] Ablain, M., A. Cazenave, G. Valladeau, and S. Guinehut (2009). A new assessment of the error budget of global mean sea level rate estimated by satellite altimetry over Ocean Science, 5, [8] Validation and estimation of MSL altimetry errors: [9] Dorandeu, J, Introduction/Overview: from a global system error budget to application-specific error budgets, presentation at the 2009 OSTST meeting: [10] Ablain, M., S. Philipps, L. Carrere, G. Valladeau, J.-F. Legeais, E. Bronner, and N. Picot, Analysis of day signal observed on the MSL derived from Jason-1&2 and TOPEX data, presentation at the 2010 OSTST meeting: n.pdf [11] Vignudelli, S., A.G. Kostianoy, P. Cipollini, and J. Benveniste (Ed.), in Coastal Altimetry, Springer- Verlag, Berlin, doi: / , 578 pp, [12] Altimetry principle: [13] Altimetry principle: [14] Ducet, N., P.-Y. Le Traon, and G. Reverdin, 2000: Global high resolution mapping of ocean circulation from TOPEX/Poseidon and ERS-1 and -2. J. Geophys. Res., 105, [15] Le Traon, P.-Y., F. Nadal, and N. Ducet, 1998: An improved mapping method of multisatellite altimeter data. J. Atmos. Oceanic Technol., 15, [16] Le Traon, P.-Y. and G. Dibarboure, 1999: Mesoscale mapping capabilities of multi-satellite altimeter missions. J. Atmos. Oceanic Technol., 16, [17] Le Traon, P.-Y., G. Dibarboure, and N. Ducet, 2001: Use of a High-Resolution Model to Analyze the Mapping Capabilities of Multiple-Altimeter Missions. J. Atmos. Oceanic Technol., 18, [18] Pascual, A., Y. Faugère, G. Larnicol, P-Y Le Traon, 2006: Improved description of the ocean mesoscale variability by combining four satellite altimeters. Geophys. Res. Lett., 33 Page 5/ 20

6 I INTRODUCTION This guide describes the TARGETED data product files from the MyOcean SL-CLS-TOULOUSE-FR PU, what data services are available to access it, and how to use the file and services. The products described here are. It contains one dataset: dataset-duacs-europe-merged-sla-trend-l4-v4 SEALEVEL_MED_SLA_TREND_TIMESERIES_TARGETED_004 It contains one dataset: dataset-duacs-medsea-merged-sla-trend-timeseries-v4-3 SEALEVEL_BS_SLA_TREND_TIMESERIES_TARGETED_005 It contains one dataset: dataset-duacs-blacksea-merged-sla-trend-timeseries-v4-3 SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_006 It contains one dataset: dataset-duacs-europe-merged-sla-trend-timeseries-v4-3 The mean level of the oceans is one of the most important indicators of climate change. It incorporates the reactions from several components of the climate system. Precise monitoring of changes in the mean level of the oceans, particularly through the use of altimetry satellites, is vitally important, for understanding not just the climate but also the socioeconomic consequences of any rise in sea level. Product shows a map of the trends of the Mean Sea Level over the European region. Then products SEALEVEL_MED_SLA_TREND_TIMESERIES_TARGETED_004 SEALEVEL_BS_SLA_TREND_TIMESERIES_TARGETED_005 SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_006 give the time series of the trends of Mean Sea Level on the Mediterranean Sea, the Black Sea and the Europe region respectively. Those products have been computed with Sea Level Anomalies Maps from altimetry and are derived from the main altimeter missions: ERS-1, ERS-2, Envisat, TOPEX/Poseidon, Jason-1, Jason-2, Geosat-Follow-On. The period covered for the product is from October to December The period covered for the products is from January 1 st 1993 to December 31st Page 6/ 20

7 II HOW TO DOWNLOAD A PRODUCT II.1 Download a product through the MyOcean Web Portal Ftp Service You first need to register. Please find below the registration steps: products-and-services-faq.php#1 Once registered, the MyOcean FAQ will guide you on How to download a product through the MyOcean Web Portal Ftp Service. Page 7/ 20

8 III DESCRIPTION OF THE PRODUCT SPECIFICATION III.1 General Information Product Specification Customer Name Geographical coverage Variables Available time series Europe (30 N-60 N 15 W-42 E) Trend of sea level anomalies between October 14, 1992 and December 26, 2012 One shot Temporal resolution - Target delivery time - Delivery mechanism Horizontal resolution Number of vertical levels Format MyOcean Information Service (MFTP) 1/4 on a Rectangular grid Surface Netcdf CF1.6 Table 1: product Page 8/ 20

9 Product Specification Customer Name Geographical coverage Variables Available time series SEALEVEL_MED_SLA_TREND_TIMESERIES_TARGETED_004 Mediterranean Sea Time series of Mean Sea Level between January 1 st, 1993 and December 31 st, 2013 One shot Temporal resolution January 1 st, 1993 and December 31 st, 2013 Target delivery time - Delivery mechanism MyOcean Information Service (MFTP) Horizontal resolution - Number of vertical levels Format Surface Netcdf CF1.6 Table 2: SEALEVEL_MED_SLA_TREND_TIMESERIES_TARGETED_004 product Page 9/ 20

10 Product Specification Customer Name Geographical coverage Variables Available time series SEALEVEL_BS_SLA_TREND_TIMESERIES_TARGETED_005 Black Sea Time series of Mean Sea Level between January 1 st, 1993 and December 31 st, 2013 One shot Temporal resolution January 1 st, 1993 and December 31 st, 2013 Target delivery time - Delivery mechanism MyOcean Information Service (MFTP) Horizontal resolution - Number of vertical levels Format Surface Netcdf CF1.6 Table 3: SEALEVEL_BS_SLA_TREND_TIMESERIES_TARGETED_005 product Page 10/ 20

11 Product Specification Customer Name Geographical coverage Variables Available time series SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_006 North East Atlantic ocean and the North Sea (>25 W; 21 N-66 N). The Mediterranean Sea, the Baltic Sea and Black Sea are not included Time series of Mean Sea Level between January 1 st, 1993 and December 31 st, 2013 One shot Temporal resolution January 1 st, 1993 and December 31 st, 2013 Target delivery time - Delivery mechanism MyOcean Information Service (MFTP) Horizontal resolution - Number of vertical levels Format Surface Netcdf CF1.6 Table 4: SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_006 product Detailed information on the systems and products are on MyOcean web site: Page 11/ 20

12 III.2 Details of datasets DATASETS VARIABLES AND UNIT NAME OF VARIABLES IN THE NETCDF FILE dataset-duacs-europe-merged-sla-trend-l4-v4 Latitude of the grid point [degrees_north] Longitude of the grid point [degrees_east] Interval in latitude of the grid pixel [degrees_north] Interval in longitude of the grid pixel [degrees_east] Parameters of the grid Local MSL trend [mm/year] Lat lon lat_bnds lon_bnds crs msl_trend Table 5: List of the datasets (column 1), of the variable for each dataset (column 2) and their names in the NetCDF files (column 3) for SEALEVEL_MED_SLA_TREND_TIMESERIES_TARGETED_004 DATASETS VARIABLES AND UNIT NAME OF VARIABLES IN THE NETCDF FILE dataset-duacs-medsea-merged-sla-trendtimeseries-v4-3 Time of the mean sea level [days since ] Mean Sea Level [m] Number of pass not used, only for compliance format Number of cycle not used, only for compliance format time msl pass cycle Table 6: List of the datasets (column 1), of the variable for each dataset (column 2) and their names in the NetCDF files (column 3) for SEALEVEL_MED_SLA_TREND_TIMESERIES_TARGETED_004 Page 12/ 20

13 SEALEVEL_BS_SLA_TREND_TIMESERIES_TARGETED_005 DATASETS VARIABLES AND UNIT NAME OF VARIABLES IN THE NETCDF FILE Time of the mean sea level [days since ] Mean Sea Level [m] Number of pass not used, only for compliance format Number of cycle not used, only for compliance format time msl pass cycle Table 7: List of the datasets (column 1), of the variable for each dataset (column 2) and their names in the NetCDF files (column 3) for SEALEVEL_BS_SLA_TREND_TIMESERIES_TARGETED_005 SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_006 DATASETS VARIABLES AND UNIT NAME OF VARIABLES IN THE NETCDF FILE dataset-duacs-blacksea-merged-sla-trendtimeseries-v4-3 dataset-duacs-europe-merged-sla-trendtimeseries-v4-3 Time of the mean sea level [days since ] Mean Sea Level [m] Number of pass not used, only for compliance format Number of cycle not used, only for compliance format time msl pass cycle Table 8: List of the datasets (column 1), of the variable for each dataset (column 2) and their names in the NetCDF files (column 3) for SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_006 Page 13/ 20

14 IV NOMENCLATURE OF FILES The nomenclature of the files delivered on download mechanism MyOcean FTP service are: IV.1.1 dt_europe_merged_sla_trend.nc IV.1.2 SEALEVEL_MED_SLA_TREND_TIMESERIES_TARGETED_004 dt_medsea_merged_sla_trend_timeseries.nc IV.1.3 SEALEVEL_BS_SLA_TREND_TIMESERIES_TARGETED_005 dt_blacksea_merged_sla_trend_timeseries.nc IV.1.4 SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_006 dt_europe_merged_sla_trend_timeseries.nc IV.2 Domain coverage IV.2.1 The coverage of the data is 30 N-60 N, 15 W-42 E and the data are projected on a 1/4 Rectangular grid. IV.2.1 SEALEVEL_MED_SLA_TREND_TIMESERIES_TARGETED_004 The Mean Sea Level has been computed with the data of the Mediterranean Sea IV.2.2 SEALEVEL_BS_SLA_TREND_TIMESERIES_TARGETED_005 The Mean Sea Level has been computed with the data of the Black Sea Page 14/ 20

15 IV.2.3 SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_006 The Mean Sea Level has been computed with the data of the North-East Atlantic ocean and the North Sea (>25 W ; 21 N-66 N) excluding the Mediterranean, Baltic and Black Seas: Figure 1: Map of the area covered by the mean sea level targeted product: SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_006. Page 15/ 20

16 IV.3 Processing IV.3.1 Input data The data taken into account to compute the Mean Sea Level trends are the weekly maps of merged Sea Level Anomalies. Those maps are computed with SEA LEVEL TAC products: SEALEVEL_GLO_SLA_L3_REP_OBSERVATIONS_008_018 from the following missions: ERS-1, ERS-2, Envisat, TOPEX/Poseidon, Jason-1, Jason-2, GFO. All the information about those products is detailed in the Product User Manual : MYO2-SL-PUM v1.5.pdf. The altimetric standards applied to calculate the SSH are summarized in tables 6, 7, and 8 of this PUM. IV.3.2 Method IV Mapping process A mapping procedure using optimal interpolation with realistic correlation functions is applied to produce SLA maps at a given date. The procedure generates a combined map merging measurements from all available altimeter missions (Ducet et al., 2000 [14]). The mapping process takes into account an updated suboptimal Optimal Interpolation parameterization to minimize transition artefacts. Combining data from different missions significantly improves the estimation of mesoscale signals (Le Traon and Dibarboure, 1999[16]), (Le Traon et al., 2001[17]), (Pascual et al., 2006[18]). Several improvements were made compared to the version used by (Le Traon et al., 1998[15]). An improved statistical description of sea level variability, noise and long wavelength errors is used. Covariance functions including propagation velocities that depend on geographical position were thus used. In addition to instrumental noise, a noise of 10% of the signal variance was used to take into account the small scale variability which cannot be mapped and should be filtered in the analysis. Long wavelengths errors (LWE) due to residual orbit errors but also tidal or inverse barometer errors and high frequency ocean signals were also derived from an analysis of TP and ERS data. IV Computation of Mean Sea Level The Mean Sea Level is then computed by doing a mean per box weighted as a function of the latitude. For the SEALEVEL_EUR_SLA_TREND_TIMESERIES_TARGETED_005 product, the map gives the above calculated values. For the time series products, an average of the above calculated values is made for each day of the period and adjusted from annual and semi-annual signals and 2-month filtered. The method of computation is described in the AVISO website ( ). Page 16/ 20

17 V FILE FORMAT V.1 netcdf The product is stored using the NetCDF CF format. NetCDF (network Common Data Form) is an interface for array-oriented data access and a library that provides an implementation of the interface. The netcdf library also defines a machine-independent format for representing scientific data. Together, the interface, library, and format support the creation, access, and sharing of scientific data. The netcdf software was developed at the Unidata Program Center in Boulder, Colorado. Please see Unidata netcdf pages for more information, and to retrieve netcdf software package. NetCDF data is: * Self-Describing. A netcdf file includes information about the data it contains. * Architecture-independent. A netcdf file is represented in a form that can be accessed by computers with different ways of storing integers, characters, and floating-point numbers. * Direct-access. A small subset of a large dataset may be accessed efficiently, without first reading through all the preceding data. * Appendable. Data can be appended to a netcdf dataset along one dimension without copying the dataset or redefining its structure. The structure of a netcdf dataset can be changed, though this sometimes causes the dataset to be copied. * Sharable. One writer and multiple readers may simultaneously access the same netcdf file. V.2 Structure and semantic of netcdf file V dimensions are defined: lat: Latitude of measurements. lon: Longitude of measurements. nv: definition of bounds. 7 variables are defined: float lon : contains the longitude for each measurement, float lat : contains the latitude for each measurement, float lon_bounds : contains the bounds in longitude, float lat_bounds : contains the bounds in latitude, int crs : useful for mapping, int msl_trend: trend at the measurement. global attributes: the global attributes gives information about the creation of the file. Dump of the NetCDF file: Page 17/ 20

18 netcdf dt_europe_merged_sla_trend { dimensions: lat = 121 ; lon = 229 ; nv = 2 ; variables: float lat(lat) ; lat:long_name = "Latitude" ; lat:standard_name = "latitude" ; lat:units = "degrees_north" ; lat:bounds = "lat_bnds" ; lat:axis = "Y" ; lat:valid_min = "30.0" ; lat:valid_max = "60.0" ; float lat_bnds(lat, nv) ; float lon(lon) ; lon:long_name = "Longitude" ; lon:standard_name = "longitude" ; lon:units = "degrees_east" ; lon:bounds = "lon_bnds" ; lon:axis = "X" ; lon:valid_min = "-15.0" ; lon:valid_max = "42.0" ; float lon_bnds(lon, nv) ; int crs ; crs:grid_mapping_name = "latitude_longitude" ; crs:semi_major_axis = ; crs:inverse_flattening = 0 ; int msl_trend(lat, lon) ; msl_trend:_fillvalue = ; msl_trend:long_name = "Sea Level Trends for the European area" ; msl_trend:standard_name = "sea_level_trend" ; msl_trend:units = "mm/year" ; // global attributes: :cdm_data_type = "Grid" ; :title = "DT merged Ocean Gridded Sea Level Trends of anomalies above ellipsoid from SSALTO/Duacs L4 product for the European area" ; :summary = "This dataset contains Delayed Time Level-4 sea level trends of anomalies above ellipsoid products from multi-satellite observations over the European area." ; :comment = "Surface product; Sea Level Trends of Anomalies referenced to the [1993, 2012] period" ; :time_coverage_start = " " ; :time_coverage_end = " " ; :product_version = "5.0" ; :institution = "CNES, CLS, LEGOS" ; :project = "SSALTO/DUACS" ; :references = " ; :contact = "aviso@altimetry.fr" ; :geospatial_lat_resolution = 0.25 ; :geospatial_lon_resolution = 0.25 ; :geospatial_lat_min = ; :geospatial_lat_max = ; :geospatial_lon_min = ; :geospatial_lon_max = ; :date_created = " :07:07" ; :history = " :07:07:creation" ; :Conventions = "CF-1.6" ; :standard_name_vocabulary = " ; :geospatial_vertical_min = "0.0" ; :geospatial_vertical_max = "0.0" ; :geospatial_lat_units = "degrees_north" ; :geospatial_lon_units = "degrees_east" ; } Page 18/ 20

19 V dimension is defined: time: date of measurements. 4 variables are defined: short pass : Number of pass not used, only for compliance format double time : contains the time for each measurement, double msl : mean sea level short cycle: Number of cycle not used, only for compliance format global attributes: the global attributes gives information about the creation of the file. Example of a NetCDF file: netcdf dt_medsea_merged_sla_trend_timeseries { dimensions: time = 7670 ; variables: short pass(time) ; pass:_fillvalue = 32767s ; pass:long_name = "pass number" ; double time(time) ; time:_fillvalue = e+19 ; time:axis = "T" ; time:standard_name = "time" ; time:units = "days since " ; double msl(time) ; msl:coordinates = "time" ; msl:_fillvalue = e+19 ; msl:long_name = "mean sea level (satellite=multi Missions, zone=med. Sea)" ; msl:standard_name = "sea_surface_height_above_sea_level" ; msl:units = "m" ; short cycle(time) ; cycle:_fillvalue = 32767s ; cycle:long_name = "cycle number" ; // global attributes: :history = " :00:00:creation" ; :cls_default_ordinate = "msl" ; :references = " ; :title = "Mean Sea Level temporal variations in the Mediterranean Sea" ; :Conventions = "CF-1.6" ; :institution = "CNES/CLS/LEGOS" ; :cdm_data_type = "Station" ; :summary = "This dataset contains delayed time mean Sea Level variations in the Mediterranean Sea from SSALTO/Duacs L4 product" ; :comment = "Surface product; Sea Level Trends of Anomalies referenced to the [1993, 2012] period" ; :time_coverage_start = " " ; :time_coverage_end = " " ; :product_version = "5" ; :contact = "aviso@altimetry.fr" ; :date_created = " :00:00" ; :standard_name_vocabulary = " ; Page 19/ 20

20 V.3 Reading software The products are stored using the NetCDF-CF format. Note that these data can be browsed and used through several softwares, like: Basic Radar Altimetry Toolbox: ncbrowse: NetCDF Operator (NCO): Page 20/ 20