The Optimal Across-Track Baseline of Distributed Small Satellites Synthetic Aperture Radar for Terrain Elevation Measurement

In distributed small satellites-synthetic aperture radar (DSS-SAR), the correlation of echoes is determined by both across-track and along-track baselines which are coupling, and the multi-baseline interferometry is obtained with multi small satellites SAR images. The optimal across-track baseline of DSS-SAR for terrain elevation measurement is more complicatedly determined than that of conventional SAR interferometry. A novel approach is presented in this paper to determine the optimal across-track baseline of DSS-SAR multi-baseline interferometry. On the basis of the statistical characteristics of phase difference of complex SAR image pair, the DSS-SAR interferometric phase estimation Crammer-Rao bound is deduced. The relationship between terrain height accuracy and across-track baseline is presented from the bound. And then the optimal across-track baseline is derived via derivative calculation. Finally, the optimal across-track baseline in different DSS-SAR configuration with three small satellites is calculated and analyzed. It is showed that the optimal baseline of single across-track baseline interferometry according to this paper is in agreement with that from known single satellite SAR interferometry. The result validates the novel approach proposed by this paper.