HR: 09:00h
AN: OS31A-05    [Abstracts]
TI: A Validated 20-year SSM/I Satellite Wind Dataset for Climate Monitoring
AU: Wentz, F J
EM: frank.wentz@remss.com
AF: Remote Sensing Systems, 438 First St Suite 200, Santa Rosa, CA 95401, United States
AU: * Smith, D K
EM: smith@remss.com
AF: Remote Sensing Systems, 438 First St Suite 200, Santa Rosa, CA 95401, United States
AU: Hilburn, K
EM: hilburn@remss.com
AF: Remote Sensing Systems, 438 First St Suite 200, Santa Rosa, CA 95401, United States
AU: Ricciardulli, L
EM: ricciardulli@remss.com
AF: Remote Sensing Systems, 438 First St Suite 200, Santa Rosa, CA 95401, United States
AB: A 20-year time series of satellite winds has been constructed for climate applications. To accomplish this, the Special Sensor Microwave Imager (SSM/I) brightness temperature dataset was recalibrated to remove small intersatellite offsets and instrumental drifts. Improvements to the SSM/I ocean retrieval algorithm were also implemented to bring this algorithm up to date with those currently being used for AMSR-E and the TRMM microwave imager (TMI). The entire 20-year SSM/I dataset was then reprocessed. The new wind retrievals represent the Remote Sensing Systems 6th generation of SSM/I ocean products. Most climate applications are very demanding when it comes to radiometer calibration and intersatellite debaising. Long-term stability accuracies (after applying on-orbit corrections) need to be at the 0.1 m/s/decade level or better, and it is essential that this required performance be validated by independent means. Accordingly, the SSM/I winds are compared to in situ measurements coming from three moored buoy arrays and to scatterometer wind retrievals. The scatterometer retrievals are particularly useful in that one expects scatterometers to be less prone to calibration drifts than radiometers. The scatterometer wind retrieval is based on the ratio of received power to transmitted power, and this ratio should be insensitive to instrument drift. Care must be taken when doing the buoy validation. Due to their particular location with respect to ocean currents, upwelling area, atmospheric stability, and wind fetch, each buoy has a unique wind speed bias relative to the satellite retrieval of wind stress. This wind bias must be removed before doing the long-term stability validation or else buoys at new locations coming on-line and buoys at old locations going off-line will corrupt the analysis. The SSM/I versus buoy analysis shows good agreement between the satellite and buoy winds. There is no significant bias (because the SSM/I were specifically calibrated to remove the overall bias) and the standard deviation is 1.21 m/s and 0.85 m/s for the NDBC and TAO/Pirata arrays, respectively. The NDBC results are less accurate because the NDBC buoys are not calibrated as well as the TAO/Pirata buoys and they are located in areas of higher wind gradients, both temporally and spatially. The long-term stability analysis shows a +0.08 (- 0.13) m/s/decade relative trend of SSM/I versus the TAO/Pirata (NDBC) buoys. Giving equal weight to each buoy array results in an overall trend difference of -0.02 m/s/decade. Although the overall trend difference is very small, the time series of SSM/I minus buoy winds shows features similar to those that are found with SSM/I as compared to the NASA scatterometer QuikScat. Thus we apply a small post-hoc adjustment to the SSM/I winds to bring them into agreement with the buoy winds. This adjustment is a simple table of 20 numbers that correspond to the SSM/I minus buoy wind speed difference for each year. The magnitude of these annual adjustments is about 0.1 m/s or less. When the adjusted winds are compared to the European scatterometer ERS-1 during the 1992-1996 period and to QuikScat during the 1999- 2006 period, the SSM/I minus scatterometer trend difference is +0.03 m/s/decade for both.
DE: 4215 Climate and interannual variability (1616, 1635, 3305, 3309, 4513)
DE: 4275 Remote sensing and electromagnetic processes (0689, 2487, 3285, 4455, 6934)
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly