Spaceborne bistatic synthetic aperture radar (SAR) system with an inclined geosynchronous (GEO) illuminator and a low-earth-orbit (LEO) receiver is capable of providing a vast area of surveillance and fine spatial resolution, which presents huge potentials for future earth observation. In this letter, inclined GEO–LEO azimuth multichannel SAR (MC-SAR) system for high-resolution wide-swath imaging is investigated. Starting from modeling geometry of inclined GEO–LEO bistatic MC-SAR, the signal model is analyzed in detail for the first time, and the equivalent positions of the received channels are obtained. Then, we found the spatial-variant residual phase error cannot be compensated accurately by conventional effective phase center (EPC) processing. Moreover, because of the complex bistatic configuration, the frequency-domain imaging algorithms become extremely difficult to achieve a well-focused and phase-preserved image. Meanwhile, the time-domain back-projection algorithm (BPA) faces with a technical challenge due to the nonuniform sampling in azimuth. To address these issues, a bistatic weighted BPA (BWBPA) for GEO–LEO MC-SAR is derived and presented. Without the procedure of EPC, the BWBPA can suppress azimuth ambiguities effectively and yield phase-preserved SAR images. Simulated data results show the validity of the presented method.

Spaceborne azimuth multichannel bistatic synthetic aperture radar (AMC-BiSAR) system employed inclined geosynchronous (GEO) transmitter and low-Earth-orbit (LEO) receiver is capable of providing a vast area of surveillance and fine spatial resolution, which presents great potentials for Earth observation. Nevertheless, owing to complex geometry and big differences of orbital characteristics, high-resolution wide-swath (HRWS) imaging for GEO-LEO AMC-BiSARs remains three major issues: 1) “Stop-and-Go” approximation is invalid because of long round-trip delay and high receiver velocity; 2) Due to the special bistatic configuration, the conventional effective phase center (EPC) operation for unambiguous signal reconstruction cannot be directly used; 3) Two-dimension spatial-variant characteristics of the echo signal caused by nonlinear and nonparallel trajectories of transmitter and receiver raise challenges for BiSAR focusing. To address these problems, starting from modeling geometry of inclined GEO-LEO AMC-BiSAR, an accurate slant range model without “Stop-and-Go” approximation is derived in the paper. Then the new effective positions of the receiving channels in GEO-LEO AMC-BiSARs are obtained based on the geometry, and the unambiguous Doppler spectrum can be recovered effectively. Finally, a nonlinear chirp scaling imaging algorithm based on the time-domain perturbation (TP-NLCS) is derived and presented, which can correct the variation of range cell migration and azimuth frequency modulation rate. Simulation results show the validity of the proposed method, which can implement GEO-LEO AMC-BiSAR HRWS focusing and has fine phase-preserved capability.

To obtain digital elevation model (DEM) data through spaceborne interferometric synthetic aperture radar (InSAR) technology, the solution of nonlinear InSAR geolocation equations is one of the most important steps. On one hand, Newton iterative method is time-consuming to solve the equations. On the other hand, the conventional closed-form solution for low earth orbit (LEO) bistatic InSAR system is not suitable for the novel InSAR configuration of geostationary (GEO) transmitter with LEO receivers because of the significant geometry difference. To address these issues, this letter analyzes the bistatic GEO-LEO geometry in detail and exploits the bistatic InSAR equations to propose a GEO-LEO fast location method (GFLM), which obtains the effective closed-form solution for the novel system. Compared with the general Newton iterative method, the GFLM significantly improves the efficiency of geolocation for the bistatic GEO-LEO InSAR system with high precision. Moreover, the geolocation accuracy of the novel system under realistic parameters uncertainties is introduced. Finally, we carry out simulation experiments to verify the effectiveness and superiority of GFLM.

Spaceborne bistatic multichannel synthetic aperture radar (MC‐SAR) system employed inclined geosynchronous Earth orbit (GEO) transmitter and low‐Earth‐orbit (LEO) receiver can provide fine spatial resolution and a vast area of surveillance, which presents great potentials for future Earth observation. Nevertheless, owing to special geometry and big differences of orbital characteristics, the conventional effective phase centre (EPC) operation for unambiguous SAR signal reconstruction cannot be directly used. To address the issue, starting from geometry model of GEO‐LEO bistatic MC‐SAR, the new effective positions of the receiving channels are obtained. Then, the time‐variant characteristics of residual phase error after the presented EPC processing is analysed. Finally, the method of reconstructing unambiguous SAR signal is presented. Simulation results show the validity of the proposed method, which can efficiently reconstruct the unambiguous signal for GEO‐LEO bistatic SAR.

Azimuth multichannel (AMC) synthetic aperture radar (SAR) system, utilizing digital beam forming (DBF) processing, is capable of achieving high-resolution and wide-swath (HRWS) focusing, presenting significant potential for Earth observation. Nevertheless, owing to inevitable channel phase biases, the performance of the Doppler ambiguity suppression will suffer great losses. To address the issue, a robust minimum-entropy-based weighted back-projection algorithm (ME-WBPA), a time-domain algorithm, is developed to obtain high-quality images for AMC HRWS SAR in this paper. Considering phase mismatches among receiving channels in AMC SAR system, the signal model in SAR complex-imagery domain is first established. Then, channel phase biases can be estimated and calibrated according to minimum entropy criterion. Validation of the proposed approach is demonstrated with the simulated and real measured airborne AMC SAR data.