# High-Resolution and Wide-Swath 3D Imaging for Urban Areas Based on Distributed Spaceborne SAR
This paper combines distributed SAR HRMS imaging with tomographic 3D reconstruction technology through the distribution of tangent lines of multiple satellites. On the one hand, it achieves HRMS imaging by overcoming the size limitation of traditional single-satellite antennas through the distribution of multiple satellites in a multi-channel. On the other hand, it uses the high directional resolution of the distributed SAR system to reconstruct 3D terrain such as overlapping areas. Compared with traditional 3D imaging systems, distributed HRMS SAR has a long baseline and high resolution, and can achieve wide-swath imaging with a single pass, enhancing the temporal correlation while reducing information redundancy, and greatly improving mapping efficiency. However, the contradiction between a high azimuth resolution and a wide mapping swath cannot be reconciled effectively, especially in spaceborne SAR, which causes range ambiguity in the imaging process of large mapping scenes, seriously affecting the imaging quality and image registration. The HRWS spaceborne SAR system usually uses the SCORE (scan-on-receive) method to process echo signals in the elevation direction of the receiver to achieve range ambiguity resolution [26; 27]. The processing method divides the receiving antenna into several pitch sub-apertures, with each pitch sub-aperture receiving its echo independently for low-noise amplification, down-conversion, and digitization. Then, time-varying weighting synthesis is carried out by a digital beamforming (DBF) processor to form an equivalent high-gain digital beam scan to receive echoes in the entire wide mapping band scene. The SCORE method determines the relationship between the target return time and the DOA (direction of arrival) based on the globe smooth sphere model, and it obtains the DBF weighting vector corresponding to the sampling time at each distance, thereby enabling the receiving beam center to track the point-to-return signal at all times. However, in areas with large topographic relief, the DBF receiving beam formed by the SCORE method will deviate in direction due to a large difference between the earth's smooth sphere model and the real terrain. This results in a decline in echo gain and a deterioration in the signal-to-noise ratio, thus affecting the imaging quality of the SAR system. To solve this problem, in 2009, [PERSON] [28] presented a processing method called adaptive digital beamforming (ADBF). The spatial spectrum estimation algorithm was adopted to estimate the DOA of the echo signal, and then the DOA estimator DBF weighting vector was exploited to adjust the receiving beam direction. However, the above technologies are mainly used in single-station multi-channel SAR and are mostly applied to HRWS 2D imaging, without consideration of the overlapping targets. Meanwhile, the existing range ambiguity resolution technology cannot be directly applied to the research of distributed SAR. Therefore, it is urgent to investigate the range ambiguity resolution technology of distributed SAR 3D imaging. In this paper, the technical scheme of distributed SAR HRWS 3D imaging through the multi-channel arrangement of multiple satellite SAR ranges is innovatively put forward. It is combined with tomography processing technology to realize the 3D imaging of difficult areas while overcoming the size limitation of the traditional single-satellite antenna. The main contributions of this paper are summarized as follows:  
1. A scheme of a distributed SAR HRWS 3D imaging system with a multi-channel arrangement is innovatively proposed, which addresses the issues of long imaging time, low efficiency, and data redundancy in traditional 3D imaging. 2. A range ambiguity resolution method based on multi-beam forming is proposed. This method effectively achieves range ambiguity resolution for overlapping targets with non-unique wave direction. 3.