RESOLUTION ENHANCEMENT OF SPACEBORNE SCATTEROMETER DATA

Spaceborne wind scatterometers are designed principally to measure rad ar backscatter from the ocean's surface for the determination of the n ear-surface wind direction and speed. Although measurements of the rad ar backscatter are made over land, application of these measurements h as been limited primarily to the calibration of the instrument. This h as been due in part to the low resolution of the scatterometer measure ments (nominally 50 km for the Seasat-A Scatterometer [SASS]). In this paper we present a method for generating enhanced resolution radar im ages of the earth's surface using spaceborne scatterometry. The techni que is based on a new image reconstruction technique which takes advan tage of the spatial overlap in scatterometer measurements made at diff erent times to provide enhanced imaging resolution. We describe the re construction algorithm and demonstrate the technique using both simula ted and actual SASS measurements. The technique can also be used with ERS-1 scatterometer data. The SASS-derived images, which have approxim ately 4 km resolution, dramatically illustrate the resolution enhancem ent capability of the new technique. The technique permits utilization of both historic and contemporary scatterometer data for medium-scale monitoring of vegetation and polar ice. We discuss the tradeoff betwe en imaging noise and resolution inherent in the technique. The instrum ent processing method employed by SASS limits the ultimate resolution which can be obtained with our method. However, with minor modificatio ns to future Doppler scatterometer systems (such as the NASA scatterom eter [NSCAT] and its follow-on EoS-era scatterometer) imaging resoluti ons down to 1-2 km for land/ice and 5-10 km for wind measurement can b e achieved with a moderate increase in downlink bandwidth (from 5 kbps to 700 kpbs). We describe these modifications and briefly describe so me of the applications of this medium-scale Ku-band imagery for vegeta tion studies, hydrology, sea ice mapping, and the study of mesoscale w inds.