# High-Resolution and Wide-Swath 3D Imaging for Urban Areas Based on Distributed Spaceborne SAR
## 5 Conclusions  
With the development of SAR applications and the increasing complexity of observation tasks, the demand for 3D information on targets in production and military activities is increasing. Meanwhile, the SAR imaging technology of HRWS has attracted more and more attention from SAR researchers, and it has become a research hotspot in the field of remote sensing. High-resolution imagery is the guaranteed when correct information is obtained, and large surveying and mapping zones are important for shortening the revisiting period and obtaining information quickly. Therefore, accurate acquisition of 3D HRWS information including height on the earth's surface is of great value in military reconnaissance, land resources monitoring, map mapping, environmental monitoring, disaster monitoring, and other satellite applications. However, there are many problems with traditional 3D SAR imaging systems, such as long imaging time, large amounts of channel data, and data redundancy, which seriously reduce the efficiency and image quality of 3D reconstructions.  
Aiming to solve the above problems, a distributed SAR HRWS 3D imaging scheme is put forward innovatively in this paper. The proposed distributed SAR multi-channel system combines distributed SAR HRWS imaging with tomographic 3D reconstruction technology by arranging multiple satellite SAR in the tangent direction, which can achieve both HRWS imaging and 3D imaging simultaneously. Compared with traditional 3D imaging systems, distributed HRWS SAR has a longer baseline, a higher resolution, and a larger mapping bandwidth by a single flight, thereby enhancing time correlation, reducing redundancy of information, and greatly improving surveying and mapping efficiency.  
However, due to the long baseline and large detection scene of distributed HRWS SAR, there is range ambiguity in the 3D imaging process. To solve this problem, this paper introduces the geometric model of 3D imaging and the theoretical basis of range ambiguity. Based on this, a range ambiguity resolution method is presented based on multi-beamforming.  
The proposed HRWS 3D imaging methodology is verified on the data set obtained through experiments conducted with airborne array SAR in Rizhao, Shandong province. The coherence coefficient is increased from 0.5845 to 0.9864, i.e., the image quality is greatlyimproved. The proposed method can eliminate range ambiguity successfully, which is significant for realizing HRWS 3D imaging of distributed SAR.  
Conceptualization, Y.Y. and F.Z.; methodology, Y.Y.; validation, Y.Y., F.Z. and Y.T.; formal analysis, L.C.; resources, R.W. and Y.W.; data curation, F.Z.; writing--original draft preparation, Y.Y.; visualization, L.C. and Y.T.; project administration, Y.W.; funding acquisition, F.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key R&D Program of China, 2021 YFA0715404.  
The authors thank all colleagues who participated in this work. The authors would like to express their gratitude to the anonymous reviewers and the editor for their constructive comments on the paper.  
The authors declare no conflict of interest.