Initial Results on the Cross-Calibration of QuikSCAT and Oceansat-2 Scatterometers

1. Initial Results on the Cross-Calibration of QuikSCAT and Oceansat-2 Scatterometers David G. Long Department of Electrical and Computer Engineering Brigham Young University May 2011

2. QuikSCAT vs OSCAT

3. OSCAT & QuikSCAT Hi Res QuikSCAT GRD QuikSCAT SIR • QuikSCAT and OceanSat-2 Scatterometer (OSCAT) have comparable spatial sampling and resolution • Similar image enhancement possible • Can use QuikSCAT algorithms for OSCAT OSCAT GRD OSCAT SIR

4. Enhanced Resolution* OSCAT Image Conventional resolution 25 km/pixel JD 309, 2009 * Preliminary 2.225 km/pixel

5. QuikSCAT/OSCAT Image Comparison Comparison of one day BYU backscatter images OSCAT and QuikSCAT have nearly identical characteristics Differences due to azimuth and local time of day Similar variances and means Similar spatial enhancement possible OSCAT can contribute to the multi-decade scatterometer climate record of land and ice observations OSCAT H QuikSCAT H OSCAT V QuikSCAT V

6. OSCAT/QuikSCAT Differences for the Land/Ice Scatterometer Climate Record Nominal incidence angle differs H: QuikSCAT=46°, OSCAT=48° V: QuikSCAT=54°, OSCAT=56° Orbit geometry differs OSCAT has better coverage near poles (smaller holes) Time of orbit ascending node differ QuikSCAT=6:30 am OSCAT=noon Local time of measurements vary (location dependent) Orbit revisit time (Q=4 day repeat, O=2 day repeat) Azimuth angle distributions differ and vary Need to apply azimuth angle corrections Improved sigma-0 cross-calibration needed

7. Linear model for sigma-0 vs incidence angle • Simplified model • Can also use for egg/slice incidence angle correction ASCAT Amazon Rain Forest Example (dB) (dB) ASCAT ASCAT

8. Backscatter Anisotropy • Due to sastrugi and topography, some polar regions exhibit anisotropic backscatter response - Differences in azimuth geometry can be confused with climate changes if not accounted for •Do not expect azimuth variations over the Amazon ASCAT Wilkes Land Example ASCAT (C-Band) V-pol 40 inc (dB) ASCAT (C-Band)

9. QuikSCAT Anisotropy 54 inc • QuikSCAT has fixed incidence angles but high diversity in azimuth angle observations • Similar anisotropy observed QuikSCAT V-pol (Ku-Band) 46 inc QuikSCAT (Ku-Band) QuikSCAT H-pol (Ku-Band)

10. QuikSCAT / ASCAT Comparison • Different frequencies (5.4 GHz vs 13.5 GHz) and incidence angles (40 V vs 46 H & 54 V) • Consistent with dominant sastrugi scattering

11. OSCAT Azimuth Modulation Analysis 25 km 25 km OSCAT 310-311, 2009 Locations of OSCAT sigma-0 measurements within study region JD 309-327, 2009 OSCAT slice measurements: 13,099 QuikSCAT slice measurements: 14,118

12. Slice Sigma-0 vs Azimuth Angle

13. Azimuth Corrected Slice Sigma-0 vs Azimuth Angle

14. Comparison of OSCAT and QuikSCAT modulation for the study region • OSCAT azimuth modulation does not match QuikSCAT azimuth modulation • Improved processing is expected to resolve this H-pol V-pol OSCAT QuikSCAT

15. OSCAT Slice Sigma-0 vs Incidence Angle (narrow incidence angle range)

16. Azimuth Corrected Slice Sigma-0 vs Incidence Angle

17. Comparison of Sigma-0 Distributions in the Antarctic Study Region H-pol bias 0.7 dB V-pol bias 0.0 dB

18. Comparison of Azimuth Corrected Sigma-0 Distributions in the Antarctic Test Region H-pol bias 0.6 dB V-pol bias 0.2 dB

19. Amazon Study Region • Rain forest is a good calibration target (anisotropic), but exhibits spatial inhomogeneity • Select homogenous region • Time-of-day variation • Sigma-0 varies with time of day as moisture moves up/down in canopy • Several tenths of a dB effect • OSCAT and QuikSCAT observe at different local times • No azimuth variation expected • Different incidence angles • Small mean differences Select region that both QuikSCAT and OSCAT sigma-0 fall within narrow range

20. Egg Sigma-0 vs Incidence Angle

21. Incidence-Corrected Egg Sigma-0 vs Incidence Angle

22. Egg Sigma-0 vs Azimuth Angle

23. Azimuth-Corrected Egg Sigma-0 vs Azimuth Angle

24. Comparison of Egg Sigma-0 distribution in Amazon Study Region H-pol bias 0.05 dB V-pol bias 0.25 dB

25. Comparison of Corrected Sigma-0 Distribution in Amazon Study Region H-pol bias 0 dB V-pol bias 0.25 dB

26. OSCAT Local Time of Day Analysis Time in minutes from start

27. OSCAT Local Time of Day Analysis Arctic Antarctic Equi-latitude strips used for measurement extraction in LTD analysis superimposed upon OSCAT gridded sigma-0 images of the polar regions

28. Comparison of Northern Hemisphere Local Time of Day Observations OSCAT SeaWinds QuikSCAT Scatterplot of LTD vs UTC in the Northern Hemisphere for different longitude bins (a) OSCAT, (b) Seawinds, (c) QuikSCAT LTD (hours) = UTC + Local_Longitude / 15

29. Comparison of Southern Hemisphere Local Time of Day Observations OSCAT SeaWinds QuikSCAT Scatterplot of LTD vs UTC in the Southern Hemisphere for different longitude bins (a) OSCAT, (b) Seawinds, (c) QuikSCAT LTD (hours) = UTC + Local_Longitude / 15

30. Diagram of LTD Divisions for Four Scatterometers LTD (hrs) = UTC + Local_Longitude / 15 24 hours 24 hours

31. Conclusion QuikSCAT and OSCAT sensors very similar Calibrated OSCAT products will be similar to QuikSCAT products Validated QuikSCAT land/ice SCP products Daily Antarctic iceberg products (operational) Daily sea ice extent and mapping (operational, widely distributed) Daily FY/MY ice classification (relatively new) Can be averaged to longer time scales Post wind mission (PWM) QuikSCAT data supports OSCAT calibration PWM QuikSCAT Coverage is too limited for less than monthly maps, aliasing an issue for ice movement for monthly maps