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

The full pattern for a large antenna is usually not well known because of the difficulty in measuring it on a range. For spaceborne synthetic aperture radar (SAR), the antenna may also be subjected to different gravitational stresses and temperature gradients that might deform its structure, so it is very likely that its pattern will be different from that on the ground. Moreover loss of elements on a distributed array can distort its pattern. In these cases, one can extract the relative vertical antenna pattern from the SAR images of target areas that are uniform on average. In this report, images taken from the Amazon rain-forest region are analyzed to yield an estimate of the inflight relative-gain vertical antenna pattern for the SIR-C. The method is the same as that used with SIR-B (Moore and Hemmat, 1988), with X-SAR (Fang and Moore, 1995), and for scatterometer antennas on Seasat. Here we give the SIR-C vertical (elevation) antenna patterns for different incident angles and beam spoiling modes over a range of 6 dB for SIR-C. Because only a few of the antenna modes were used over the Amazon, these patterns are only representative.