Improving Synthetic Aperture Radar Wind Observations by Correcting NOGAPS Wind Direction Fields Using Subjective Analysis

Synthetic aperture radar has proven to be a useful tool for extracting the surface wind speed field over the earth's oceans. The Johns Hopkins University Applied Physics Laboratory, in conjunction with NOAA/NESDIS has developed a technique for extracting wind speed from RADARSAT-1 Scan-SAR imagery of the Gulf of Alaska and the Bering Sea. The accuracy of this method has been demonstrated through buoy comparisons. However, the relationship between radar backscatter cross-section and wind speed depends on an independent estimate of the wind direction. Currently, the JHU/APL technique uses wind directions from the NOGAPS global forecast model. These wind direction estimates are reasonable except when the model has misplaced the significant wind shifts associated with fronts and storms. Here, we examine the effect that this has on the wind field by examining 4 cases where the NOGAPS model had significant errors in its placement of the surface frontal features associated with storms in the Bering Sea. We compare the SAR-derived wind speeds using model wind direction input with those derived from a corrected wind direction obtained via subjective analysis. These winds are compared with winds at the single buoy located in the Bering Sea.