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Comparative Analysis of Windsat and QuikSCAT Wind Data with Buoy Data

This study compares the accuracy and reliability of two preliminary Windsat vector wind data sets with QuikSCAT satellite data and buoy measurements. The analysis includes comparisons based on directional data, speed biases, rain flags, and more. The study evaluates the performance of the different data sets in capturing wind speed and direction, highlighting strengths and weaknesses in each. The findings provide insights into the quality of the Windsat and QuikSCAT data sets in relation to buoy data, shedding light on potential discrepancies and areas for improvement in wind data analysis.

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Comparative Analysis of Windsat and QuikSCAT Wind Data with Buoy Data

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  1. Comparisons of Two Preliminary Windsat Vector Wind Data Sets with QuikSCAT and Buoys M.H. Freilich B.A. Vanhoff 8 February 2005 COAS/OSU

  2. OVERALL OUTLINE • NDBC Buoy comparisons (best-quality • Windsat data) • Rain Flag – accuracy of flagged data • Windsat Rain Flags • Comparisons with NDBC, SSM/I • QuikSCAT-NESDIS_0 global comparisons • Directional comparisons

  3. Windsat Data Initial Editing • For Betten_1 data sets, DELETED all data having: • Geographic Flags set (ice[6],land[7],lakes[9],salinity[10]) • No Wind Retrieval Flag set ([0]) • 10 GHz RFI Flag set ([12]) • Sun Glint Flag set ([13]) • For NESDIS_0 data sets, DELETED all data having: • Land Contamination Flag set ([29]) • Any EDR Quality Flag [4-27] set • For all data sets, IGNORED Windsat Speed Range Flag • (analyzed all speeds)

  4. QuikSCAT Data & Initial Editing • Speed, Direction measurements on ~25 km centers from standard • L2B processing • Vector wind estimates have 25 km resolution, 30 km land mask • Used “selected” ambiguity • DELETED all data having: • Autonomous (MUDH Rain Flag set (eliminates ~6% of global data) • Far Swath (outer 100 km on each side, v-pol only retrievals with little azimuthal diversity); WE DID KEEP NADIR SWATH! • This results in “research quality” QuikSCAT data

  5. Windsat: Selected NDBC Validation Locations (22)

  6. Windsat, QSCAT & Buoy: Collocated winds, non-raining (Dashed line: NDBC collocated with NESDIS_0) • All NDBC winds adjusted to 10 m equivalent neutral stability • Betten_1 speed histograms have unrealistic concentration ~9-11 m/s • NESDIS_0 speed histogram narrower than QSCAT or NDBC (or Betten_1) • Betten_1 directional histos have unrealistic small peaks near 0, 120 deg • All Windsat directional histos have sharp drop-offs below 240-250 deg

  7. Windsat & QSCAT (dir. edit) vs. NDBC -- Rain-Free 50 km distance threshold, Non-Raining • Speed bias statistics nearly identical (0.75 m/s along-wind random component error • for QuikSCAT and Betten_1, 1.0 m/s along-wind rce for NESDIS_0) • All Windsat products overpredict wind speed for buoy speeds > 15 m/s • Windsat dir. std. dev. larger than QSCAT for wind speeds < 10 m/s (all 3 WS data sets) • NESDIS_0 dir. std. dev. less than QSCAT for wind speeds > ~15 m/s • Betten_1 dir. std. dev. smallest of all data sets for speeds 12-17 m/s

  8. Direction Comparisons w/ NDBC (Non-Raining) • Thin lines indicate random component error model simulation (1.6, 2.0, 2.4, 2.8 m/s) • Betten_1 (blue) = 2.6 m/s NESDIS_0 = 2.8 m/s QSCAT (red) = 2.0 m/s • Windsat directional std. devs. consistent with random comp. error model for spds < 20 m/s • Windsat may have better ambig removal skill at high wind speed (QSCAT departs from • model because of residual (< 90 deg) ambiguity removal errors)

  9. Betten_1 & QSCAT: Vector Wind Accuracies vs. NDBC • QSCAT statistics and random component errors smaller than Windsat

  10. Windsat, SSM/I F13: Rain-Flagged Total Flagged 14.4% 17.4% 9.5% 7.9% Windsat collocated w/ NDBC SSM/I F13 similarly collocated with NDBC F13 has 6 AM crossing time (similar to Windsat) F13 considered “rain flagged” if rain rate > 0 mm/hr • SDR-based rain flags overflag significantly, systematically with increasing wind speed • (both NESDIS_0 and Betten_1 data sets) • Betten_1 EDR-only flag rate is similar to SSM/I

  11. 2.8 m/s rce Windsat/Buoy: Raining vs. Non-raining accuracies 50 km distance threshold • Rain-flagged data have much larger speed bias for buoy speeds < 11 m/s • (ie., Windsat overpredicts speed in rain) • Generally larger directional noise at all speeds for the rain-flagged data

  12. NESDIS_0/QuikSCAT: Non-raining coverage 1 hour, 50 km distance threshold QuikSCAT collocated w/ Windsat

  13. NESDIS_0/QSCAT Comparisons 50 km, 1 hour collocation thresholds • Random component error sims in blue/red solid lines • 0.75/1.0 m/s alongwind rce, 2.0/2.8 m/s cross-wind rce (QS/WS) • High wind speed saturation for Windsat? • Increase in directional s.d. probably due to QS errors

  14. Selected direction (rel to N.) NESDIS_0 & QuikSCAT Directional Distributions • Collocated global data set; no QS or WS rain (by flags)

  15. NESDIS_0/QuikSCAT: Directional Histograms

  16. Conclusions • Non-raining Windsat retrievals are somewhat less accurate than QSCAT • Betten_1 more accurate overall than NESDIS_0 • Non-raining Windsat directional accuracy better than QSCAT at high • speeds (> 15 m/s) • Windsat SDR-based rain flags are too conservative • EDR-based flag is better • Rain causes speed bias and directional accuracy degradation • Global comparisons suggest Windsat underpredicts high wind speeds • (> 20 m/s) • NESDIS_0 direction retrieval issues (discontinuities in histogram)

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