Radar Backscatter Measurement Accuracy for Spaceborne Scanning Pencil-beam Scatterometers

A radar scatterometer transmits a series of RF pulses and measures the total-power (energy) of the backscattered signal. Measurements of the backscattered energy from the ocean's surface can be used to infer the near-surface wind vector [7]. Accurate backscatter energy measurements are required to insure accurate wind estimates. Unfortunately, the signal measurement is noisy so a separate measurement of the noise-only total-power is subtracted from the signal measurement to estimate the echo signal energy. A common metric for evaluating the accuracy of the scatterometer energy measurement is the normalized signal variance, termed K . In designing a p scatterometer tradeoffs in design parameters are made to minimize K . p Spaceborne scatterometers have traditionally been based on fan-beam antennas and CW modulation for which expressions for K exist. Advanced pencil-beam p scatterometers, such as SeaWinds currently being developed by NASA use modulated Signals so that new K expressions are required. This paper outlines the derivation of p the generalized K expression. While very complicated in its exact form, with a p simplified geometry the K expression can be related to the radar ambiguity function. p The resulting analysis yields insights into the tradeoffs inherent in a scatterometer design and permits analytic tradeoffs in system performance.