Wednesday, 12 February 2003
Results of QuikScat high wind data validation
Traditional validation of satellite derived ocean surface winds involves comparison with insitu data collected by instruments located on buoy platforms or ship masts. These comparisons, though not perfect due to the spatial/temporal mismatch between the observations, are useful for most of the typical wind conditions found over the oceans. Validation of satellite high wind speeds are more difficult as buoy and ship data are frequently not available or are not always accurate under intense weather conditions. The Ku2001 geophysical model function used to derive 10m surface wind speeds and directions from the SeaWinds (on QuikScat) scatterometer observations delivers wind speeds between 0 and 70 m/s. Validation studies of winds below 15 m/s have been performed by many and are well documented showing rms accuracies of less than 1.5 m/s and 18 degrees. We present at this meeting a summary of case studies used to determine the accuracy of the QuikScat Ku2001 winds greater than 25 m/s and describe in greater detail two of these cases. The presence of rain within any individual wind vector measurement cell affects the accuracy of the winds retrieved. Rain effects at lower wind speeds produce overexaggerated winds. Under high wind conditions greater than 45 m/s the radar signal is attenuated by heavy rain and underexaggerated winds result. When rain is not present, QuikScat winds above 25 m/s are found to be within +/- 5 m/s of available wind estimates.