Topographic mapping from interferometric synthetic aperture radar observations

Interferometric synthetic aperture radar observations provide a means for obtaining high-resolution topographic terrain maps from data acquired simultaneously at two slightly displaced antennas. Calculation of the three-dimensional coordinates of all the points in a radar image can be made from the combination of along-track, slant range, and interferometer fringe measurements. Thus the result compensates for the layover exhibited by conventional radar maps and removes the false targets generated by multiple signal paths to a given object in the scene. We have derived a topographic map of a portion of the San Francisco Bay Area utilizing data that were recorded by a radar system mounted on a NASA CV990 aircraft and processed by a general purpose digital computer. This map displays the height above sea level of a region approximately 11 km by 10 km in size, sampled on an 11-m pixel grid. Uncertainties in the estimated height result from imprecise knowledge of the observational geometry, radar bandwidth limitations, and finite signal-to-noise ratios. For our system, each factor contributed approximately 3-4 m to a relative rms error of about 6 m. Additional global errors of the order of 10 m can result from inaccurate monitoring of aircraft attitude. The statistical variation of the height measurements from the ocean portion of the map, which we can presume to be quite flat, is 2-10 m rms, which is consistent with the theoretical estimate. Comparison of our results with U.S. Geological Survey contour maps indicates a high degree of correlation between the two sets of altitude data.