1 / 18

The first ASCAT Scatterometer Winds

The first ASCAT Scatterometer Winds. Ad Stoffelen, Marcos Portabella, Anton Verhoef, Jeroen Verspeek, Jur Vogelzang, Gerrit Burgers. Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands. MetOp-A Launch 19 October 2006. ASCAT scatterometer.

nika
Download Presentation

The first ASCAT Scatterometer Winds

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The first ASCAT Scatterometer Winds Ad Stoffelen, Marcos Portabella, Anton Verhoef, Jeroen Verspeek, Jur Vogelzang, Gerrit Burgers Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands First Ascat Winds

  2. MetOp-A Launch 19 October 2006 ASCAT scatterometer 3 antennas: aft, fore and mid First Ascat Winds

  3. 90 00 10 20 ERS-1 ERS-2 ? NSCAT SeaWinds1 SeaWinds2 ASCAT-1 ASCAT-2 ASCAT-3 NASA/JAXA/India/China Continuity of scatterometers First Ascat Winds

  4. ECMWF FG ASCAT ASCAT QC First Winds on 27 October 2006 • Works fine • Congratulations from ESA, NOAA and NASA HQ • Room for improvement ASCAT demonstration wind service since March 28, 2007 First Ascat Winds

  5. Coverage • Three times as much as ERS • Comparable to Seawinds: smaller nominal area but fewer gaps • because ASCAT C-band sees through rain Seawinds ASCAT 20070406 descending 20070406 descending First Ascat Winds

  6. 100 km 25 km Resolution Effect of Seawinds resolution • ASCAT product has 25 km resolution • 12.5 km product planned • (needs advanced retrieval techniques) First Ascat Winds

  7. OSI SAF ASCAT product release schedule *Integration of regional EARS products into global OSI SAF products in 2008 First Ascat Winds

  8. Quality Accuracy scatterometer: ≈ 2 m/s (vector wind) Available L1b commissioning sets • SS: 19/10/’06 – 29/01/’07 • ZZ: 30/01/’07 – 12/01/’07 • ZZZ: 13/02/’07 – today • New set expected in June, after full transponder calibration • Ocean calibration improves quality First Ascat Winds

  9. Relating backscatter to winds • CMOD5.5 F: (u,v) → (σf, σa, σm ) • F maps (u,v) on cone in σ-space • F depends on elevation and azimuth First Ascat Winds

  10. Ocean Calibration, OCfor improving L2 wind product • Purpose: • To correct for lack in absolute calibration • To make ASCAT compatible with ERS product • To disseminate a “demonstration” wind product • Based on ERS heritage • CMOD5.5, ice model knowledge in ERS  range • Continuity of geophysical data set • Method: 4 mappings that scale σ ’s • Scale such that no bias remains between ASCAT and ECMWF winds • Use of ice model to further verify OC • Scale such that ASCAT data lie on CMOD5.5 cone First Ascat Winds

  11. More on OC corrections • Assume all corrections are backscatter (z) scaling factors (dB additions); all L1b calibration changes so far prove to be so • Use ECMWF wind speed bias at every WVC as absolute wind reference to achieve uniform quality • Use CMOD5.5 wind speed sensitivity to compute beam scaling factors at every WVC • Assume that the CMOD5.5 wind speed sensitivity at 8 m/s is representative of the full wind domain sensitivity (quasi-linear; 8 m/s is mean global speed) • This backscatter data scaling would ideally provide the same wind PDF for all WVCs after CMOD5.5 inversion First Ascat Winds

  12. Vertical cut for WVC #42 (rightmost) Mid-axis scaling σmid σmid . Upwind . Downwind . Upwind . Downwind σf,a σf,a Current Level 1b release KNMI visual correction • CMOD5.5 is better fitted due to the down scaling of mid beam measurements First Ascat Winds

  13. Horizontal projection for WVC #42 Aft-fore axis symmetry correction σa σa . Upwind . Downwind . Upwind . Downwind σf σf Level 1b 1st release KNMI visual correction • CMOD5.5 is better fitted due to the symmetrical scaling of fore and aft measurements First Ascat Winds

  14. Vertical cut for WVC #42 Wind speed bias correction σmid σmid . Upwind . Downwind . Upwind . Downwind σf,a σf,a KNMI visual+wind correction KNMI visual correction • CMOD5.5 is better fitted due to the upward scaling of measurements First Ascat Winds

  15. Wind speed bias correction Horizontal projection for WVC #42 σa σa . Upwind . Downwind . Upwind . Downwind σf σf KNMI visual correction KNMI visual+wind correction • CMOD5.5 is better fitted due to the upward scaling of measurements First Ascat Winds

  16. Level 1b current version KNMI corrected Validation against ECMWF • ASCAT inverted winds do not only have lower and more uniform bias w.r.t. ECMWF, but also much lower wind direction SDE (ECMWF + ASCAT error) First Ascat Winds

  17. Future SAF ASCAT scatterometer R&D - Validation against observations - Higher resolution - Closer to the coast - Better wind quality First Ascat Winds

  18. Concluding remarks • ASCAT winds close to perfect • ASCAT demonstration wind service since 28 March 2007 • Calibration and ERS scatterometer compatibility can be achieved by scaling CMOD5.5 backscatter • After ASCAT L1b transponder calibration, KNMI will reprocess data and incorporate remaining biases in CMODx.x Continuity of current ASCAT L2 wind quality is guaranteed over this L1b calibration More info at http://www.knmi.nl/scatterometer/ First Ascat Winds

More Related