Comparisons of Two PreliminaryWindsat Vector Wind Data Sets with

QuikSCAT and Buoys

M.H. FreilichB.A. Vanhoff

8 February 2005COAS/OSU

OVERALL OUTLINEOVERALL OUTLINE

• NDBC Buoy comparisons (best-qualityWindsat data)

• Rain Flag – accuracy of flagged data– Windsat Rain Flags– Comparisons with NDBC, SSM/I

• QuikSCAT-NESDIS_0 global comparisons– Directional comparisons

Windsat Data Initial EditingWindsat 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)

QuikSCAT Data & Initial EditingQuikSCAT 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

Windsat:Windsat: Selected NDBC Validation Locations (22) Selected NDBC Validation Locations (22)

Windsat, QSCAT & Buoy:Windsat, QSCAT & Buoy: Collocated winds, non-raining Collocated winds, non-raining

• 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

(Dashed line: NDBC collocated with NESDIS_0)

Windsat & QSCAT (dir. edit) vs. NDBC -- Rain-FreeWindsat & QSCAT (dir. edit) vs. NDBC -- Rain-Free50 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

Direction Comparisons w/ NDBC (Non-Raining)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)

Betten_1 & QSCATBetten_1 & QSCAT: : Vector Wind Accuracies vs. NDBCVector Wind Accuracies vs. NDBC

Overall Betten_1/ QuikSCAT Accuracy Summary Non-Raining, Directional Edited

NESDIS_0 Bett_1: edr only QSCAT Npts (WS/QS)

Speed rms, bias (m/s) 1.43 0.23 1.28 0.28 1.22 0.05 105079 / 62627

Dir. sd (deg), [3/5-20] 25.2 / 21.5 23.2/ 20.6 18.7 / 16.7 105079 / 62627 Crosswind Random Component Error (m/s)

2.8 2.6 2.0

Along-wind Random Component Error (m/s)

1.0 0.75 0.75

• QSCAT statistics and random component errors smaller than Windsat

Windsat, SSM/I F13:Windsat, SSM/I F13: Rain-Flagged Rain-Flagged

• 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

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

Total Flagged

14.4%

17.4%

9.5%

7.9%

Windsat/Buoy:Windsat/Buoy: Raining vs. Non-raining accuracies Raining vs. Non-raining accuracies50 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

2.8 m/s rce

NESDIS_0/QuikSCAT:NESDIS_0/QuikSCAT: Non-raining coverage Non-raining coverage1 hour, 50 km distance threshold

QuikSCAT collocated w/ Windsat

NESDIS_0/QSCAT ComparisonsNESDIS_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

NESDIS_0 & QuikSCAT Directional DistributionsNESDIS_0 & QuikSCAT Directional Distributions

• Collocated global data set; no QS or WS rain (by flags)

Selected direction (rel to N.)

NESDIS_0/QuikSCAT:NESDIS_0/QuikSCAT: Directional Histograms Directional Histograms

ConclusionsConclusions

• 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)