Improved resolution backscatter measurements with the SeaWinds pencil-beamscatterometer

The SeaWinds scatterometer was launched on the NASA QuikSCAT spacecraft in June 1999 and is planned for the Japanese ADEOS-II mission in 2000. In addi tion to generating a global Ku-band backscatter data set useful for a varie ty of climate studies, these flights will provide ocean-surface wind estima tes for use in operational weather forecasting. SeaWinds employs a compact " pencil-beam " design rather than the "fan-beam" approach previously used with SASS on Seasat, NSCAT on ADEOS-I, and the AMI scatterometer on ERS-1, 2, As originally envisioned and reported, the resolution of the SeaWinds ba ckscatter measurements were to be antenna-beamwidth limited. In order to sa tisfy an emerging demand for higher resolution backscatter data, however, t he SeaWinds signal-processing design has been significantly modified. Here, the various options considered for improving the resolution of the SeaWind s measurements are discussed, and the selected:hardware modification (the a ddition of deramp processing for range discrimination) is described. The ra dar equation specific to a rotating pencil-beam scatterometer with digital range filtering is developed, and the new challenges associated with calibr ating the resulting improved resolution measurements are discussed. A formu lation for assessing the variance of the measurements due to fading and the rmal noise is presented. Finally, the utility of improved resolution SeaWin ds measurements for land and ice studies is demonstrated by simulated enhan ced-resolution imaging of a synthetic Earth backscatter scene.