Comparison of Results From Transit Satellite Tracking

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Abstract
Large-scale motions and strain-rates over great distances on polar ice sheets are often obtained from the tracking of Transit (or doppler) satellites. The results of different processing techniques for these tracking data are compared, using some of the data collected on and near Ice Stream C. Reduction is made by using the software packages CALIPER, GEODOP V, MAGNET, and the micro-processor on the Magnavox MX 1502 satellite receiver. The orbital data broadcast by the satellites are used, as well as more precise orbits obtained afterward. In addition, calculations are made for single sites individually (point positioning) and for many sites with simultaneous tracking data (network adjustment). The results agree within the range of known errors associated with the orbits. Earth-based positions (latitude, longitude, ellipsoidal height), based on the broadcast orbits, agree to within 41.1 m. Positions with more precise orbits are within 0.7 m of one another. Relative positions are best obtained by using network techniques, and these agree with terrestrial survey results within 0.2 m in horizontal separation for sites 19 km apart, and are within 4.8 m in elevation difference. The calculated azimuth differs by 1.5 m/19 km or 10−4 rad.