Atmospheric attenuation correction and ice flag algorithms for NSCAT

The paper investigates atmospheric attenuation correction and ice flag algorithms for the NASA Scatterometer (NSCAT). The data from the Special Sensor Microwave/Imager (SSM/I) and SeaSat scatterometer (SASS) are analyzed to define and evaluate the applicability of potential algorithms. The results show that the monthly-averaged attenuation maps derived from the SSM/I data can be used to correct NSCAT data with a residual error of about 0.1 dB rms under rain-free conditions. However, when there is rain, the climatological attenuation map is not applicable because of the temporal and spatial variability of rain, and algorithms for rain flagging or correction remain to be investigated. NSCAT is designed to perform wind measurements over ice-free oceans. To reduce the temporal uncertainty of ice growth and motion, a sea-ice classification algorithm using the NSCAT data and the distinct physical scattering signatures of ocean surfaces and sea ice is proposed. This ice-flagging algorithm extends the performance of NSCAT into the polar oceans.