An Imaging Method for Spaceborne Cooperative Multistatic SAR Formations With Nonzero Cross-Track Baselines

Abstract

Spaceborne multistatic synthetic aperture radar (M-SAR) formations can deploy multiple spatially separated receiving phase centers along the along-track (AT) direction to achieve high-resolution wide-swath. However, the cross-track (XT) separation between the spacecraft is inevitable due to the formation design like orbital safety and application potential like the XT interferometry. In addition, the different motion vectors of two or more satellites caused by the Helix formation will lead to the difference of the Doppler parameters at the same range gate. Therefore, nonzero XT baselines and space-variant characteristics pose new challenges to the focusing and phase-preserving of the M-SAR imaging. To this end, an imaging method for spaceborne cooperative M-SAR formations with nonzero XT baselines is proposed in this paper. Firstly, an spaceborne cooperative M-SAR formation is demonstrated. Afterwards, the imaging method is described in detail. The motion compensation technology and the idea of partitioned equivalent velocity are adopted to solve the problems of nonzero XT baselines and spacevariant characteristics, respectively. Finally, the simulations of point targets and distributed targets are carried out to verify the proposed method, and the results show that the precise focusing of spaceborne cooperative M-SAR with nonzero XT baselines can be achieved by the proposed imaging method.Index Terms-Multistatic synthetic aperture radar (M-SAR), M-SAR formations, M-SAR imaging processing, nonzero crosstrack(XT) baselines. I. INTRODUCTIONS PACEBORNE multistatic synthetic aperture radar (SAR) is an extension of the concept of bistatic SAR (BiSAR), which is characterized by deploying multiple physically separate transceiver to obtain three or more simultaneous echo data sets [1], [2]. Multistatic SAR (M-SAR) has many unique characteristics that meet the application requirements of the nextgeneration spaceborne SAR system, such as high-resolution wide-swath (HRWS) imaging, along-track (AT) interferometry, cross-track (XT) interferometry and so on, so it has received extensive attention [3]-[5]. Another trend is adopting cheaper systems with the intention to shift the complexity from the space segment to software. Thus, small satellites which received echoes only can be deployed in the formation of M-

Translational-Invariant Ultrahigh-Resolution Spaceborne Bistatic SAR Focusing and Image Coordinate Analysis Using Bistatic Polynomial Model

“…Using this advantage, spaceborne BSAR with a TI configuration has been operated for interferometry and tomography, e.g., TanDEM-X [7] and RADARSAT-2/3 [8]. Moreover in the future, more advanced TI BSAR systems will be developed, as multiple TI BSARs can be used to establish a multistatic SAR configuration, which is one of the future development directions of the SAR system for providing wide-swath and high-resolution images [41], [42], [43]. In particular, with the increasing demand for centimeterscale SAR images, ultrahigh-resolution (UHR) imaging is becoming imperative in TI spaceborne BSAR applications, for which dedicated SAR processing should be devised.…”