Scatterometer winds.

Transcription

1 Scatterometer winds Manager NWP SAF at KNMI Manager OSI SAF at KNMI PI European OSCAT Cal/Val project Leader KNMI Satellite Winds Group

2 Overview Introduction σ 0 or Normalised Radar Cross Section Geophysics, GMF Swath geometry, orbit (ASCAT example) Accuracy, resolution Some limitations Applications 2

3 :03 utc OSI SAF ASCAT Coastal product viewer ASCAT12+, status: pre-operational Ascending passes Click in the map to zoom in Descending passes Click in the map to zoom in Select view Monitoring information Buoy validations Data from previous day Background information Modifications/anomalies Description of plots Access to products Acknowledgements ASCAT Product User Manual ASCAT Coastal Validation report Home OSI SAF Wind Centre OSI SAF Wind Products ASCAT A 25-km winds Operational status ASCAT A 12.5-km winds Operational status ASCAT A coastal winds Operational status ASCAT B 25-km winds Operational status ASCAT B 12.5-km winds Operational status ASCAT B coastal winds Operational status Oceansat-2 winds Operational status QuikSCAT winds Discontinued status Wind Products Processing Status Other Wind Services at KNMI ASCAT 25-km winds (EARS) Operational status ASCAT 12.5-km winds (EARS) Operational status ERS-2 winds (EARS) Discontinued status Scatterometer work at KNMI Software BUFR reader Related links EUMETSAT Ocean and Sea Ice SAF EUMETSAT EARS system Numerical Weather Prediction SAF Description of ASCAT instrument a ASCAT archived data at the EUMET ASCAT archived NetCDF data at PO

4 2011/10/26 21:11 UTC 21:00 UTC 21:00 UTC 2011/10/27 13:09 UTC 12:00 UTC 14:00 UTC

5 2011/10/27 7:47 UTC 6:00 UTC 7:30 UTC

6 Overview Introduction σ 0 or Normalised Radar Cross Section Geophysics, GMF Swath geometry, orbit (ASCAT example) Accuracy, resolution Some limitations Applications 6

7 toon/the-beaufort-scale/

8 Backscatter modulation by surface roughness Z.Jelenak

9 Backscatter modulation by surface roughness Z.Jelenak

10 Backscatter modulation by surface roughness Z.Jelenak

11 Backscatter modulation by surface roughness Z.Jelenak

12 Backscatter as a Function of Wind Speed and Incidence Angle Most sensitivity to wind at moderate incidence angles Z.Jelenak

13 Backscatter as a Function of Wind Speed and Incidence Angle Most sensitivity to wind at moderate incidence angles Z.Jelenak

14 Backscatter as a Function of Wind Speed and Incidence Angle Most sensitivity to wind at moderate incidence angles Z.Jelenak

15 Backscatter as a Function of Wind Speed and Incidence Angle Most sensitivity to wind at moderate incidence angles Z.Jelenak

16 Backscatter Sensitivity to Wind Direction 5m/s Z.Jelenak

17 Backscatter Sensitivity to Wind Direction 20m/s 15m/s 10m/s 5m/s Z.Jelenak

18 Backscatter Sensitivity to Wind Direction 30m/s 25m/s 20m/s 15m/s 10m/s 5m/s Z.Jelenak

19 Overview Introduction σ 0 or Normalised Radar Cross Section Geophysics, GMF Swath geometry, orbit (ASCAT example) Accuracy, resolution Some limitations Applications 19

20 Back Scattering Theory Bragg scattering Incoming microwave radiation in resonance with short waves (dominant for 30 < θ < 70 ) λ B = λ/(2sin(θ) Specular reflection Ocean facets normal to incident radiation (nonnegligible for θ < 30 ) Accuracy of theoretical models ~1 db and not adequate λ ~ 2cm (Ku-band) ; λ ~ 5cm (C-band)

21 Geophysical Model Function An empirical geophysical model function (GMF) relates ocean surface wind speed and direction to the backscatter cross section measurements. model o σ = GMF U, φ, θ, p, ( 10 N λ U 10N : equivalent neutral wind speed φ : wind direction w.r.t. beam pointing θ : incidence angle p : radar beam polarization λ : microwave wavelength )

22 Roughness caused by momentum Exchange The atmospheric momentum transfer to the ocean, stress : This relation depends on: L Stability (Portabella&Stoffelen, 2010; Hersbach, Jtech 2010) u oc Ocean current (Kelly 2001) ρ a Air density α ch Charnock parameter, depends on sea state (Portabella&Stoffelen, 2010; Janssen Ocean roughness is generated by momentum, so water density plays a role Ocean refractive index Scattering on roughness elements depends on microwave refractive index, Slide 22 which is assumed globally constant, e.g.,

23 Sea surface water mass density The atmospheric stress forces wave motion by momentum transfer Wave momentum depends on water mass density Varies by 1% (< 0.1 m/s) Slide 23

24 Air mass density effect on scatterometer wind In the Tropics, scatterometer data seem to have a negative bias compared to bu May be induced by consistent differences in air density and sea state Scatterometer relates to stress. Lower air density (Tropics) relates to higher winds. 10% Pole vs Tropics, gives 5%, or ~0.4 m/s ECMWF, Hans Hersbach Slide 24

25 u Equivalent neutral wind U 10N [ ( 10/ z ) ψ (10/ L) ] u* ln 0 U 10 = + k ( z ) ln 10 / k * 0 U10N = U S U 10 depends on air stability ψ while σ 0 is a sea property Surface roughness z 0 relates to σ 0 and depends on friction velocity u * U 10N is computed from u * by setting ψ = 0 and is available from NWP models and buoys Portabella & Stoffelen, 2009 GMF fits σ 0 and collocated U 10N So, σ 0 = GMF ( U 10N, φ, θ, p, λ ) NWP models usually ignore current (U s = 0), but a scatterometer does measure relative to ocean motion IKOM, May

26 Overview Introduction σ 0 or Normalised Radar Cross Section Geophysics, GMF Swath geometry, orbit (ASCAT example) Accuracy, resolution Some limitations Applications 26

27 Polar Orbiters Polar-orbiting satellites orbit at approximately 800 km above the earth and image most areas on the globe twice daily. Polar regions have the most frequent coverage. Meteorological polar-orbiters are placed in sun-synchronous orbits which means that the satellite orbit remains fixed with respect to the sun with the earth rotating under the satellite. This provides a 24-h cycle 27

28 Current scatterometer instruments Fixed fan beam C-band (5 cm) VV-pol Sampling km Static geometry ASCAT, double swath ERS2, single swath Rotating pencil beam Ku-band (2 cm) Dual polarization Sampling 25 km, 50 km Rotating antenna OSCAT, QuikScat, HY2A RAIN IKOM, May

29 ASCAT scatterometer Three ASCAT arms Fan beams 29

30 ASCAT observation geometry Left swath 550 km Right swath km Real aperture radar, GHz (C-band), VV polarisation All weather measuring capability Measuring geometry: 3 fan-beam antennas, double swath, incidence angles between 25 and 65 deg Measurement: normalised radar cross-section (NRCS, backscatter, σ0) Swath gridded into nodes (25 km and 12.5 km spacing), one triplet of averaged backscatter measurements per node 30

31 ASCAT observation geometry Left swath Right swath Each swath is divided into 21 Wind Vector Cells (WVCs) for the 25 km product For the 12.5-km product 43 WVCs exist on each side 550 km 550 km 31

32 Spatial representation Wind scales 40 Wind speed (m/s) Buoy ASCAT ECMWF Distance (km) We estimate area-mean (WVC) winds using the empirical GMFs 25-km areal winds are less extreme than 10-minute sustained in situ winds (e.g., from buoys) So, extreme buoy winds should be higher than extreme scatterometer winds (allow for gustiness factor) Extreme NWP winds are again somewhat lower due to lacking resolution 32

33 Generic Processing ESCAT, SeaWinds, ASCAT, OSCAT Input (σ 0 values) Pre-processing Inversion multiple < 4 solutions 2D Var AR Quality Control NWP model Ambiguity Removal Quality Monitoring Output wind field

34 Overview Introduction σ 0 or Normalised Radar Cross Section Geophysics, GMF Swath geometry, orbit (ASCAT example) Accuracy, resolution Some limitations Applications 34

35 Buoy Verification 35

36 Buoy verification January

37 160 W 140 W 120 W 100 W 80 W 60 W 40 W 20 W 0 20 E 40 E 60 E 80 E 100 E 120 E 140 E 160 E 70 N 70 N Buoy verification 60 N 60 N 50 N 50 N 40 N 40 N 30 N 30 N 20 N 20 N 10 N 10 N S 10 S 20 S 20 S 30 S 30 S 40 S 40 S 50 S 50 S October S 60 S ASCAT 12.5 ASCAT 25 SeaWinds 25 SeaWinds S 70 S KNMI 160 W 140 W 120 W 100 W 80 W 60 W 40 W 20 W 0 20 E 40 E 60 E 80 E 100 E 120 E 140 E 160 E USA σ u [m/s] σ v [m/s] σ u [m/s] σ v [m/s] σ u [m/s] σ v [m/s] σ u [m/s] σ v [m/s] compares best to buoys is slightly noisier than 37

38 Triple collocation result Bias ASCAT (m/s) Bias ECMWF (m/s) Trend ASCAT Trend ECMWF σ ASCAT (m/s) σ ECMWF (m/s) u v On scatterometer scale (25 km) OSI SAF NRT req. 2 m/s, WMO in speed/dir. See also Vogelzang et al., JGR, 2011

39 Operational 12.5-km product Convective systems SST Currents 39

40 ASCAT 12.5 km 25 km 40

41 Quality Control (QC) Scatterometers provide good quality sea surface winds except for: Sea ice or land contamination Large spatial wind variability (e.g., vicinity of fronts and low-pressure centres,, downbursts) Rain (especially in Ku-band systems, e.g.,oceansat-2)

42 Rain Effects The radar signal is attenuated by the rain as it travels to and from the Earth s surface σ 0 Retrieved wind speed The radar signal is scattered by the raindrops. Some of this scattered energy returns to the instrument σ 0 Retrieved wind speed ( to ~ 15 m/s) Directional information can be lost 42

43 Rain Effects The radar signal is attenuated by the rain as it travels to and from the Earth s surface σ 0 Retrieved wind speed The radar signal is scattered by the raindrops. Some of this scattered energy returns to the instrument σ 0 Retrieved wind speed ( to ~ 15 m/s) Directional information can be lost The roughness of the sea surface is increased because of the splashing due to raindrops σ 0 Retrieved wind speed (at low winds) Directional information can be lost Variable roughness due to wind downbursts Confused sea state, speed/direction unclear 43

44 Typical Rain Patterns Rain effects: Cross swath vectors Higher wind speeds Some intense rain not flagged by RSS RSS slide

45 Quality Control Inversion residual value (MLE) low = good quality wind high = low quality wind A uniform metric is derived (Rn( Rn) A Rn threshold is derived to optimize rejection of low quality accept good quality SeaWinds ECMWF Portabella and Stoffelen, 2001

46 Quality Control Areas with significant Rain (large squares) effectively detected Frontal and low-pressure centre areas effectively removed Vast majority of spatially consitent winds are accepted (green arrows)

47 Overview Introduction σ 0 or Normalised Radar Cross Section Geophysics, GMF Swath geometry, orbit (ASCAT example) Accuracy, resolution Some limitations Applications 47

48 NOAA/NASA KNMI QuikScat Improved cold front Better Around rain

49 Discrimination of land, water and ice Detached sea ice field of 400kmx400km at South Pole 49

50 Monitoring of each product 1 st rank MLE Speed bias RMS u&v scat - EC Timeliness ASCAT NWP SAF integrated monitoring at /research/interproj /nwpsaf/scatter_report

51 Overview Introduction σ 0 or Normalised Radar Cross Section Geophysics, GMF Swath geometry, orbit (ASCAT example) Accuracy, resolution Some limitations Applications 51

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53 Storm and surge Delfzijl 31/10/ 6 18Z 1/11/ 06 4Z

54 NWP 100 km Storm near HIRLAM misses wave; SeaWinds should be beneficial!

55 ERS-2 scatterometer wave train; missed by HiRLAM

56 Missed wave train in QuikScat

57 Challenges in forecasting Polar Lows: Lack of real time observations in the area Lack of satellite visual or IR imagery NWP models relatively good, but still: Some positional error Some error in center pressure and 10m Wind Rapid developments Sharp gradients, both in wind and precipitation Shift in forecasting perspective Short lived, affecting a small area down the forecast funnel Norwegian Meteorological Institute met.no

58 Case I: Polar Low NOAA-17 AVHRR , 18 utc ASCAT 10m wind ASCAT 10m wind OK Norwegian Meteorological Institute met.no

59 Case I: Polar Low NOAA-17 AVHRR , 18 utc Hirlam8 10m wind Wind prognosis overestimated at center? Norwegian Meteorological Institute met.no

60 OSCAT 50-km product 14:30 Polar satellites cover high latitudes well Satellite constellations cover all times of day Norwegian Meteorological Institute met.no

61 25/3/ 13 26/3/ 13 26/3/ 13 16:10 ASCAT coastal A single scatterometer does not capture the dynamics near land-water interfaces A constellation of scatterometers may do so Norwegian Meteorological Institute met.no

62 ASCAT coastal 24/3/ 13 Dynamics near the eastern coast and in the south Correspondence in wind and cloud structures Norwegian Meteorological Institute met.no

63 March 2013 October

64 Soil Water Index 64 EPS Talkshow, 15 June 2005 ERS Science Workshop

65 GLOBAL SCATTEROMETER MISSIONS (CEOS VC) Launch Date 10/06 6/ C-band Ku-band QuikSCAT USA EPS SG Europe Combined C- and Ku-band HY-2A China No NRT global availability Availability? FY-3E with 2FS China Operating Approved Extended Operational Series with 2FS India sw 24feb11

66 Overview of current altimeter and scatterometer NRT products, points of access Julia Figa, with contributions from: Vinca Rosmorduc (AVISO) Pierre Femenias (ESA) Saleh Abdalla (ECMWF) Paul Chang (NOAA) Ad Stoffelen (OSI-SAF/KNMI) Use of scatterometer and altimeter wind and wave data in marine forecasting Oostende, December 2009

67 Altimeter NRT products overview Prod Name Param. Spacing of observ. Product duration Delay Source Access point Format OGDR OGDR- BUFR Global SWH, wind speed, range 6 km along track Ground station dump (2-4 h) 2.5 (5 h) EUM+ NOAA EUMETCast/ NOAA DDS EUMETCast/ NOAA DDS/ GTS netcdf BUFR OGDR- SSHA EUMETCast/ NOAA DDS netcdf OSDR RA_ WWV Global SWH, wind speed, range Global SWH, wind speed 6 km along track 7 km along track Ground station dump (2-4 h) Ground station dump (<100 min) 2.5 (5 h) CNES Meteo- France (encoding ) EUMETCast/ AVISO ftp / NASA JPL ftp EUMETCast/ GTS 3 h ESA ESRIN ftp/ GTS (expected soon) Use of scatterometer and altimeter wind and wave data in marine forecasting Oostende, December 2009 netcdf BUFR ENVISAT format/ BUFR

68 Scatterometer NRT products overview Prod. Name Param. Spacing of observ. Product duration Delay Source Access point Format OSI SAF ASCAT winds NOAA ASCAT winds Global 10 m neutral wind vectors Two swaths of 500 km with gap in between of 600 km, winds every 12.5 and 25 km along nd across track 3 min 2 h OSI SAF OSI SAF EUMETCas t GTS KNMI ftp 3 min 2 h NOAA NOAA DDS BUFR BUFR/ netcdf BUFR/ Binary/ lite EARS ASCAT winds Regional 10 m neutral wind vectors Same as above 30 min 45 min KNMI EUMETCas t GTS BUFR NRT service discontinued for QuikSCAT, data and information are available for familiarisation with Ku-band rotating pencil beam scatterometer winds at and in preparation for when Oceansat-2 winds become available Use of scatterometer and altimeter wind and wave data in marine forecasting Oostende, December 2009

69 Altimeter and scatterometer NRT products access points EUMETCast registration (need specific equipment) NOAA DDS registration for Jason2 data and ASCAT data and KNMI ftp registration AVISO Jason 1 ftp registration aviso@cls.fr NASA/JPL Jason1 ftp ftp://podaac.jpl.nasa.gov/pub/sea_surface_height/jason/osdr/data/ ESA/ESRIN ftp registration for RA2 data eohelp@esa.int GTS Use of scatterometer and altimeter wind and wave data in marine forecasting Oostende, December 2009

70 Data bulletins on the GTS J2 OGDR-BUFR ISZX01, originating centres KNES and EUMS J1 OSDR: ISZ[A-D, I-L]01,originating centre LFPW RA2 BUFR (expected soon): ISXXii (ii from 41 to 60), originating centre EUSR ASCAT OSI SAF global: ISXXii (ii from 01 to 10 for 25 km and 11 to 99 for 12.5 km) originating centre EHDB ASCAT EARS regional: ISXNii (ii from 01 to 10 for 25 km and 11 to 99 for 12.5 km) originating centre EHDB Use of scatterometer and altimeter wind and wave data in marine forecasting Oostende, December 2009

71 Scatterometer winds Represent the mean WVC wind Are provided as equivalent neutral winds Verify very well with NWP model Verify very well with buoys Show spectra close to that expected for 3D turbulence for scales < 500 km Spatial plots show small-scale features in line with these three features Can be contaminated by land, sea ice and rain Winds > 30 m/s are difficult to measure/calibrate Are ambiguous 71

72 Further references Registration for data, software, service messages Help desk EUMETCAST, RMDCN, KNMI FTP Viewer Status, monitoring, validation User Manual EUMETrain, forecasters forum NWP SAF monitoring /interproj/nwpsaf/monitoring.html

73 Training/interaction Training Course Applications of Satellite Wind and Wave Products for Marine Forecasting (video) Forecasters forum Xynthia storm case EUMETrain ocean and sea week (video) NWP SAF scatterometer training workshop ometer/data_assimilation_workshop/ Use of Satellite Wind & Wave Products for Marine Forecasting Satellite and ECMWF data vizualisation

74 Ocean references MyOcean, PODAAC, podaac.jpl.nasa.gov/ esurge, MyWave 2011 scatterometer conference, p/index.htm?l=en IOVWST, coaps.fsu.edu/scatterometry/meeting/ June 2012, Utrecht, the Netherlands

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