Engineering considerations pertaining to the use of GPS for single pass satellite SAR interferometer attitude measurement

Deficiencies in the terrain elevation measurement capabilities of repeat pass synthetic aperture radar (SAR) interferometer and a co-orbit twin satellite SAR interferometer can be eliminated by using a single pass SAR interferometer. A single pass SAR interferometer at 450 km altitude with SAR receiver antennas mounted on the ends of a 60 meter boom can produce terrain elevation data meeting Defense Mapping Agency (DMA) digital terrain elevation data (DTED) level 3 specification (i.e., ten meter posting and one to three meter LE-90 elevation precision) over 50 kilometer swaths. The system could provide global coverage within one year after IOC and high precision large area change detection and measurement with short revisit periods. Achievement of this performance requires that the error in knowledge of the SAR interferometer baseline tilt in the zero Doppler plane not exceed 6.6 micro-radians. This may be realized by using a GPS interferometer with GPS antennas rigidly mounted on the SAR antennas. The interferometer and other parts of the satellite must be placed so that the number of GPS signal reflections off surfaces and edges is minimized. Un-preventable reflected path signals can be suppressed by using GPS antenna arrays with adaptive null steering. A GPS signal simulator can be used to generate expected GPS signals and then processing may be used to extract interference form the signal