Evaluation of rain effects on NSCAT wind retrievals

This paper describes research to evaluate the effects of rain on Ku-band satellite scatterometer ocean surface wind vector measurements. On a global average basis, rain occurs simultaneously with NASA Scatterometer (NSCAT) measurements about 4% of the time. While this number is not large, unfortunately, the temporal and spatial distribution of rain is not random. Thus, the potential exists for systematic biases in scatterometer inferred wind fields, especially in the tropics and in the vicinity of storms. Therefore, the evaluation of the effects of rain on the scatterometer wind retrievals is a significant issue that warrants further investigation. Because Ku-band data are not presently available (NSCAT launch scheduled August 1996), this paper presents preliminary analyses and review plans for a Calibration/Validation (Cal/Val) Experiment. The authors present simulated NSCAT observations to gain insight into rain effects at satellite scatterometer spatial scales. Also, a post-launch NSCAT Cal/Val experiment is briefly described. In this experiment, rain measurements from ground based meteorological radars will be compared to simultaneous NSCAT normalized radar cross section measurements. The resulting wind retrievals will be compared to independently estimated surface winds.