DTEMS interferometric SAR design and method of baseline tilt determination

The Digital Terrain Elevation Mapping System (DTEMS) is a Lockheed Martin Missiles and Space (LMMS) commercial system for collection processing and archive of digital terrain matrix (DTM) and geometrically corrected ortho-rectified digital polarimetric radar imagery. DTEMS uses an ER-2 aircraft with an interferometric synthetic aperture radar (IFSAR) and differential GPS to develop a DTM in WGS84 rectangular coordinates with three meter post intervals. This paper describes the DTEMS X-band IFSAR design and presents the results of a system simulation which predicts that, for 45 degree or less terrain slope, DTEMS will achieve an average one σ relative elevation precision of 0.3 meter and absolute one σ elevation precision of 0.6 meter. The ER-2/IFSAR combination can provide up to 190,000 km² of single flight area coverage. With this coverage DTEMS will be able to map the state of California in two flights and the entire United States, including Alaska, in 49 flights. SAR interferometer geometric baseline (IGB) tilt error is the major contributor to terrain elevation error. GPS interferometry (GPSI) and recursive IGB tilt estimation is used to reduce the IGB tilt knowledge error to less than 0.001 degree. The DTEMS implementation of GPSI uses GPS antennas installed on the top of each wing pod at positions just above the radar receiver antennas. In these positions the antennas have rigid coupling to the radar antennas and the 8.5 meter GPS IGB is close and parallel to the 8.5 m SAR IGB between the radar antenna phase centers. Consequently measurement of the GPS IGB attitude constitutes indirect measurement of the SAR IGB attitude