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United Technologies' Norden Systems is now fielding a threeaperture interferometric Synthetic Aperture Radar (SAR), flying on a Gulfstream I1 (GII) corporate aircraft. Realtime functions include SAR ground map and enhanced moving target indication (MTI), among others. The MTI function uses interferometric data to compute the Doppler displacement of radially moving targets. Based on that information it overlays symbology at the true target locations on the SAR ground map. Recorded flight data are processed offline to produce interferometric ground maps, displaying intensity and phase information in false color. This paper presents a sampling of results obtained near the Hebrides and Sleat Sound, Scotland, during joint US-UK ocean mapping experiments in July 1991. Examples to be shown will include interferometrically enhanced swells, wind waves and similar features, ship wakes, axd surf breaking along the coastline. Data were collected at ranges of 10 to 50 nm.

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The validation of a radar system for making topographic measurements is described. The system is an interferometric SAR radar flown by Norden Systems in late 1992 and early 1993 under an ARPA-sponsored program. Both absolute and relative height measurements were made, with aircraft position referenced to an INS/GPS and a separate differential GPS. An initial accuracy prediction was obtained from a complete system error analysis.Confirmation of this prediction was a non-trivial task, which consisted of making comparisons with truth models obtained using photogrammetric surveys, using over-water measurements, and using radar data collected from orthogonal flight directions. A photogrammetric survey was performed over a 5 km square area, with residual photogrammetric height errors estimated at less than 1 foot. The size of the survey area was considered large enough that radar system stability could be assessed. The inclusion of four-way comer reflectors in the surveyed scene permitted radar measurements to be tied to the photo-surveyed points so that the image scale factor could be determined. Radar system stability was also assessed by mapping the ocean surface. Both phenomenological and system limitations in accuracy are addressed.

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