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C-band Scatterometers

C-band Scatterometers. From ERS to ASCAT and Beyond Ad.Stoffelen@KNMI.nl. ’90. ’00. ’10. ’20. ERS-1. ERS-2. ?. NSCAT. SeaWinds-1. SeaWinds-2. ASCAT-1. ASCAT-2. ASCAT-3. RFSCAT ??. Continuity of C-band scatterometers?. Outline. ERS scatterometer (SCAT) Advanced SCAT (ASCAT)

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C-band Scatterometers

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  1. C-band Scatterometers From ERS to ASCAT and Beyond Ad.Stoffelen@KNMI.nl

  2. ’90 ’00 ’10 ’20 ERS-1 ERS-2 ? NSCAT SeaWinds-1 SeaWinds-2 ASCAT-1 ASCAT-2 ASCAT-3 RFSCAT ?? Continuity of C-band scatterometers?

  3. Outline • ERS scatterometer (SCAT) • Advanced SCAT (ASCAT) • Satellite Application Facilities (SAF) / Products • Rotating Fan-beam SCATterometer (RFSCAT) • Summary and references

  4. Scatterometers • Improved forecasts of cyclones and storms (no rain gaps) Isaksen & Stoffelen, 2000

  5. Local revived real-time ERS scatterometer service ERS Monday 6 Sep 04

  6. http://www.knmi.nl/scatterometer ERS Monday 6 Sep 04 Mouse click

  7. http://www.knmi.nl/scatterometer ERS Monday 6 Sep 04 • Remnence of Frances Mouse click

  8. Fast developing low over the ocean missed by HiRLAMESA press release “Nowcasting”

  9. GRAS GOME-2 AVHRR-3 HIRS-4 IASI ASCAT AMSU-A1 AMSU-A2 MHS The METOP Instrument Payload

  10. The ASCAT Mission • Primary objective: To provide global ocean wind vector measurements operationally. Main application: assimilation in Numerical Weather Prediction models • Additional objectives supported: • Retrieval of sea ice boundaries, concentration and type • Retrieval of land surface parameters: snow cover and soil moisture • Nowcasting • Probably stress product

  11. Beam geometry 45o C-Band VV polarisation 90o Spatial averaging in overlapping cells (one o ‘triplet’ per WVC) 135o 50 km resolution; one WVC every 25 km (19 across swath) Heritage from ERS scatterometers and new ASCAT features

  12. Increased time and swath coverage Beam geometry 45o 45o C-Band VV polarisation Higher incidence angle range 90o 90o Spatial averaging in overlapping cells (one o ‘triplet’ per node) Additional product at ~25 km resolution, every 12.5 km (41 nodes per swath) 135o 135o i.a.: 25o - 65o 50 km resolution; one WVC every 25 km (19 across swath) Improved instrument design and on-board processing concept 550 km Heritage from ERS scatterometers and new ASCAT features

  13. The spatial averaging: one and consecutive 50 km resolution WVCs

  14. ASCAT Products • Level 1B (EUMETSAT) • 50 km resolution o triplets with a 25 km WVC spacing • ~25 km resolution o triplets with a 12.5 km WVC spacing • Full-resolution o values for the three beams on each swath (research product) • Level 2 (Ocean and Sea Ice SAF) • 50 km resolution wind vectors with a 25 km WVC spacing • ~25 km resolution wind vectors with a 12.5 km WVC spacing

  15. ASCAT products disseminated to users Product Contents Format Dissemination Timeliness Source Level 0ASCAT EPS HRPT NRT MetOp source packets format L-band real time platform Level 1Bo triplets EPS NRT terminals 2h 15 min EUMETSAT 50 and ~25km BUFR EuMetCast >15 min resolution Level 2winds + o BUFR RMDCN, 2 h 30 min OSI SAF triplets internet and >20 min information EuMetCast over ocean ADP data processor s/w - - OSI SAF NRT terminals are being substituted by increased EuMetCast capability Note that o data is available in both L1B and Level 2 products Archive data is available from EUMETSAT from 2007 including full resolution

  16. The SAF concept

  17. Satellite Application Facilities Scatterometer sea surface wind R&D • Quality control, rain and ice screening • Spatial averaging (100 km  25 km) • Inversion: Computation of wind solutions and associated probabilities frommeasurementinformation • Determination of information content; Observation operatorAmbiguity removal (spatial filter to determine unique field) • Active monitoring and control (of instrument and processing) • Web site (visualisation) and product distribution • ERS and QuikScat product enhancement • Preparation for ASCAT wind production (METOP; 2006)

  18. Flow around rain cells Mesoscale flow Rain Contamination ? 12 July 2004 1:30Z

  19. C- and Ku-band synergy ERS-2 21:30 GMT September 2004 QuikScat 5 GMT

  20. Ice Line & Wind Cone • CMOD5 provides cone • Ice model (ice age a) • WVC dependence through incidence angle

  21. Overlap Cone and Line Mixed points

  22. Along-the-ice parameter indicates ice type • Red/yellow: multi-year ice • Green/blue: first-year ice <-10 0 >10 a

  23. Blended Operational Ocean/Ice Products See: OSI-SAF web page • DNMI:OSI SAF at high-lat. • Under Météo France contract to with DNMI (N), DMI (DK) and SMHI (SWE). • 3 Std. OSI SAF Products • Ice concentration (%) • Ice edge: probability of ice coverage • Ice type: probability of multi-year/ first-year • Sensors • SSM/I + ERS Scatt + AVHRR - blended ice concentration • QSCAT vector wind (dealiased) • Blended Products (see right) • Ice Coverage/Type (as above) + Wind (HIRLAM + QSCAT) • Used in “met. workstation” by met. Institutes in Eumetsat Courtesy Lars-Anders Breivik - DNMI

  24. climexp.knmi.nl • ERS and NCEP re-analysis stresses deviate substantially • Few gaps in dynamic areas (unbiased)

  25. Rotating Fan Beam Scatterometer (RFSCAT) • Coverage • Resolution • Quality

  26. RFSCAT options

  27. Comparison • Figure of Merit (FoM) • Complementary quality in a WVC • User requirement • Errors • Wind ambiguity • Coverage not yet included • H-pol useful

  28. RFSCAT • Preliminary conclusions • A C-band VV-pol RFSCAT does not gain much performance on ASCAT • An added HH-pol channel provides more information around the satellite ground track. • With a polarimetric RFSCAT at moderate cost for RF power a significant gain in wind retrieval may be achieved, but capitalizing this in spatial resolution remains to be seen • Wind variability within a WVC limits performance at high SNR

  29. C-band scatterometers • Continuity may be possible ERS-1 -> ERS-2 -> ASCAT-1,2,3 -> ? • Proven useful for dynamic weather forecasts • Few gaps in dynamic areas (no climatological bias) • Combination of H-pol and V-pol would improve performance • Wind, land, ice, nowcasting • Ongoing improvement of GMF, its inversion, QC, data assimilation, monitoring • Near coastal application remains to be investigated (see SAR)

  30. For more info... …on the web • EUMETSAT web page, www.eumetsat.de • ESA MetOp web page, www.esa.int/export/esaME/ • KNMI OSI SAF, page www.knmi.nl/scatterometer or mail scat@knmi.nl …publications • ESA bulletin, Special Issue on MetOp (nr. 102, May 2000) • J. Figa-Saldaña, J.J.W.Wilson, E.Attema, R.Gelsthorpe, M.R.Drinkwater and A.Stoffelen, The Advanced scatterometer (ASCAT) on the meteorological operational (MetOp) platform: A follow on for European wind scatterometers, Can. J. Remote Sensing, Vol.28, No.3, pp. 404 - 412, 2002

  31. Scatterometer • Verbeterde voorspelling van cyclonen Isaksen & Stoffelen, 2000 Geen ERS Scatterometer Wel ERS Isabel

  32. NWP impact@100-km Gain At DNMI and DMI: • About 10% gain in forecast length for Autumn 2001 • More neutral in January2002 © Frank Tveter, DNMI

  33. noise cone shape  space constant Calibration method: Look for the transf. constant

  34. Problem: CMOD5 cone too wide

  35. Ifremer ice map Distance to ice line ERS-2, Jan.3-Jan.9, 2000 0 1 2 3 4 >5 dice

  36. 3. Wind Retrieval • Bayesian approach: • MLE inversion: • constant • Is MLE inversion still valid?

  37. ERS Scatterometer SeaWinds • In general, wind retrieval of reasonable quality • However, wind direction distributions present unrealistic peaks & gaps

  38. WVC x 1  x 2 x 4 x 7 3 x FOV 5 x 6 8 x x uFOV = uFOV + u vFOV = vFOV + v u, v  N(0,0.75) Generally, <GMF(uFOV, vFOV)>  <GMF(uWVC, vWVC)>

  39. EUMETSAT Polar System: an Integrated European Effort Areas of involvement • ESA: Space Segment (MetOp platforms and ASCAT, GRAS, GOME instruments) • EUMETSAT:Space Segment, Ground Segment, Launcher services, EPS Operations • EUMETSAT Member States: Satellite Applications Facilities (SAFs)

  40. EPS operational mission schedule Operational mission planned for 14 years of operations • Three MetOp platforms launched in: • October 2005 • 2010 • 2014 • Commissioning planned to last 6 months for each of the three satellites • Overlaps between missions foreseen during the Commissioning periods

  41. ASCAT Instrument Design/ on-board processing Long pulse with LFM (‘chirp’) • After de-chirping, the resulting signal is spectrally analysed and detected. In the power spectrum, frequency maps into slant range. • The above processing is in effect a pulse compression, which provides range resolution. • Radiometric and geometric performance specification in line with ERS scatterometers

  42. ASCAT calibration • Internal calibration • compensates for transmitter power and receiver gain variations. Automatic mechanism applied during the ground processing. • External calibration • Objective is that o from a target is accurately measured (absolute calibration) over all incidence angles and between beams (relative calibration), during the whole mission (calibration stability). • Baseline is absolute and relative calibration with 3 transponders and calibration stability monitoring over natural targets (rainforest, ice and ocean). • Additionally, cross-calibration with the ERS scatterometers will be assessed.

  43. The spatial averaging: objectives and method • Objective: to achieve radiometric resolution or Kp (standard noise of the measurement) • Hamming window of two different sizes at two different spatial grids: • 50 km resolution at 25 km node spacing • ~25 km resolution at 12.5 m node spacing

  44. Archived ASCAT products available to users Product Contents Format Source “Timeliness” Level 1Bo triplets EPS and UMARF 8-9 h at 50 and 25-30 km HDF formats resolution Level 1Bo values EPS and UMARF 8-9 h Full resolutionbefore spatial HDF formats averaging Level 2winds + BUFR and UMARF 8-9 h essential o HDF formats information over ocean UMARF is the EUMETSAT Unified Meteorological Archive and Retrieval Facility

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