Inflight vertical antenna patterns for SIR-C from Amazon rain-forest observations

The authors measured the vertical pattern of the Shuttle Imaging Radar C (SIR-C) antenna using images of the Amazon rain forest, the largest flat and homogeneous forest in the world. Its scattering coefficient is nearly independent of the incidence angle. The images produced by JPL use the standard SIR-C CEOS format. The authors must use images without radiometric correction to get the antenna pattern, as the radiometric correction depends on preflight patterns. They can only give a small sample of the patterns for the SIR-C antenna in this paper, as the number of Amazon passes was limited, and only a few of the many modes were available. For both L-band and C-band all possible linear polarizations could be used. In addition, electronic beam steering up to ±20° from the boresight direction could modify the patterns. Also nine “beam spoiling” modes could change the patterns. The authors previously reported on the SIR-B and X-SAR patterns obtained by the same method. If all modes had been tested over the Amazon or some other suitable homogenous area, we would have been able to give details of all patterns. Unfortunately the number of passes over suitable areas was very limited, so the authors can only report on those passes