With the development of satellite constellations and fierce competition for limited spectrum resources, Mutual Terrain Scattered Interference (MTSI) has become an emerging issue for spaceborne SAR systems. Existing mitigation methods mainly focus on strong wideband MTSI that satisfies the low-rank property. However, in most scenarios, MTSI presents as weak wideband or ultra-wideband interference occupying most of the spectrum, violating the low-rank assumption. This paper introduces two mitigation schemes employing the multi-view subspace representation to tackle these challenges. The first scheme divides the spectrum to construct a clean dictionary composed of subspaces with high correlation, which makes it possible to mitigate wideband MTSI by sparse constraint. Further, based on the differences in amplitude statistical characteristics between polluted and clean pulses, the second scheme utilizes histogram normalization to construct a clean dictionary from the polluted spectrum. Therefore, the wideband and ultrawideband MTSI could be mitigated by solving the subspace clustering problem. Experimental results in the simulated and real measured Sentinel-1 and GaoFen-3 data demonstrate superior image quality improvement by the proposed mitigation schemes.

Spaceborne spotlight SAR mode has advantages of relative wide coverage and high resolution. Moving target imaging using spaceborne SAR system is important in both civil and military applications. Current researches focus on ground and maritime target like vehicle and large ship, the topic about aeroplane is rear. Therefore, based on Chinese GF-3 spotlight SAR SLC data, a new moving aeroplane imaging method is proposed. the moving target signal model in spotlight SAR SLC is deduced, the residual range migration and azimuth quadratic phase are then analyzed. it turns out that the residual range cell migration and quadratic phase relate to the relative speed. then, the moving aeroplane can be focused iteratively via tuning the relative speed parameter. The GF-3 spotlight SAR data of a non-cooperative aeroplane is used to validate proposed method.

Compared with the broadside imaging mode in multichannel SAR system, high-squint imaging mode in azimuth would be much more flexible to achieve high-resolution and wide-swath (HRWS) imaging and greatly improve the efficiency of application for Earth dynamic monitoring. However, the high-squint angle would result in more complex problem of spectrum folding after down-sampled, which would pose new challenge to the unambiguous signal reconstruction for multichannel SAR system. In this paper, the processing procedure of the unambiguous signal reconstruction for high-squint multichannel SAR is proposed. Then, an onboard experiment based on Chinese GF-3 dual receiving channel (DRC) spaceborne SAR system were successfully carried out to validate the practicality of high-squint imaging mode for multichannel SAR system in azimuth in January 2022. Experimental data validates the effectiveness of the proposed processing procedure.

In azimuth multichannel high-resolution and wide-swath (AMC-HRWS) synthetic aperture radar (SAR) system, undersampling of azimuth signal results in the failure of the single-channel echo imaging, so the echoes of all the channels should be reconstructed to obtain the unambiguous SAR image. Many methods have been proposed to reconstruct the stationary scene echoes. However, moving targets (MTs) will cause false targets in the reconstructed SAR image, which has a great influence on SAR image interpretation and moving target detection, especially in maritime scenes. Hence, we propose an unambiguous imaging method of the moving target for maritime scenes with AMC-HRWS SAR. First, azimuth deramp processing is introduced to obtain coarse-focused moving targets, and then their echoes can be extracted from the sea clutter. Based on the extracted data, a radial velocity estimation method is proposed, which is high efficiency and does not require redundant channels. In addition, based on the estimated radial velocity and the characteristics of the coarse-focused signal, a novel signal reconstruction method of moving target is presented. The reconstruction performance of this method is not affected by channel imbalance, and false targets can be removed even if there is radial velocity error. Besides, the effectiveness of this scheme is verified by the simulation data and GaoFen-3 SAR real data. The estimated radial velocities of ships are verified by automatic identification system (AIS) information. The imaging results show that false targets are effectively suppressed, and moving targets are located in correct positions.

This paper unrolls some preliminary results of a spaceborne-airborne bistatic SAR experiment, conducted in October, 2020 in Zhejiang, China, using GF-3 SAR satellite as the transmitter. Some important aspects of the experiment are firstly introduced, including bistatic acquisition geometry, receiving system, signal synchronization and theoretical spatial resolution. Then, the imaging processing flow is given, with emphasis on the data synchronization. A modified BP imaging method is proposed, which is suitable for direct signal synchronization scheme commonly used in spaceborne-airborne experiments. Finally, the imaging result is given with evaluation of the spatial resolution.

Image coregistration is a key step in tomographic SAR (TomoSAR) signal processing, and the quality of coregistration directly determines the tomographic results. Traditional coregistration is performed based on the far-field assumption, where the scattering characteristics remain constant with different look angles and distances. However, for near-field TomoSAR observation, the traditional coregistration method will fail because of the mismatch caused by the change of scattering characteristics. In this study, we propose a new structure-based coregistration method for near-field ground-based MIMO TomoSAR. Corse coregistration based on the structure and fine coregistration combining correlation function and singular modification are conducted to achieve coregistration accurately and robustly. The validity of the presented approach is validated by real data.