# Spaceborne Sparse SAR Imaging Mode Design: From Theory to Implementation
###### Abstract  
To satisfy the requirement of the modern spaceborne synthetic aperture radar (SAR) system, SAR imaging mode design makes a trade-off between resolution and swath coverage by controlling radar antenna sweeping. Existing spaceborne SAR systems can perform earth observation missions well in various modes, but they still face challenges in data acquisition, storage, and transmission, especially for high-resolution wide-swath imaging. In the past few years, sparse signal processing technology has been introduced into SAR to try to solve these problems. In addition, sparse SAR imaging shows huge potential to improve system performance, such as offering wider swath coverage and higher recovered image quality. In this paper, the design scheme of spaceborne sparse SAR imaging modes is systematically introduced. In the mode design, we first design the beam positions of the sparse mode based on the corresponding traditional mode. Then, the essential parameters are calculated for system performance analysis based on radar equations. Finally, a sparse SAR imaging method based on mixed-norm regularization is introduced to obtain a high-quality image of the considered scene from the data collected by the designed sparse modes. Compared with the traditional mode, the designed sparse mode only requires us to obtain a wider swath coverage by reducing the pulse repetition rate (PRF), without changing the existing on-board system hardware. At the same time, the reduction in PRF can significantly reduce the system data rate. The problem of the azimuth ambiguity signal ratio (AASR) increasing from antenna beam scanning can be effectively solved by using the mixed-norm regularization-based sparse SAR imaging method. synthetic aperture radar (SAR); mode design; sparse SAR imaging; beam position 2025253888  
22 May 2025222 May 2025  
12 June 202520 June 20  
which can be categorized into two groups: multichannel technology and imaging mode design [5]. Multichannel technology focuses on minimizing the sampling requirements in the time domain such as multidimensional waveform encoding (MWE) [6] and displaced phase center antenna (DPCA) [7]. These methods are efficient but have high requirements for data transmission and power consumption. On the other hand, SAR imaging mode design addresses the compromise between resolution and swath width by controlling antenna beam pointing. By using different imaging modes, SAR systems can satisfy the requirements of different mapping tasks. This approach enables the optimization of imaging parameters to strike a balance between high-resolution and wide-swath coverage. The most common SAR imaging modes are Stripmap [1,2], Spotlight [8,9], and Scan [10,11]. Spotlight mode achieves long-term observation of a specific area by sacrificing azimuth swath coverage, resulting in high-resolution imaging. In contrast, Scan utilizes burst mode to achieve wide-swath observation by switching the antenna beam among subswaths. Building on these fundamental ones, several other imaging modes have been developed, including Terrain Observation by Progressive Scans (TOPS) [12, 13, 14], Mosaic [15, 16, 17], and Sliding Spotlight [18, 19, 20]. As a novel burst imaging mode, TOPS tackles the challenge of wide-swath imaging [12]. Unlike Scan, it achieves the same swath coverage while reducing scalloping by illuminating all targets with the antenna azimuth pattern (AAP) [13,14]. Sliding Spotlight, developed from Spotlight, is a high-resolution imaging mode that provides longer target irradiation time for capturing higher-resolution images [18, 19, 20]. Additionally, it offers wider azimuth swath coverage than Spotlight. Mosaic mode is a novel imaging mode designed to achieve both high-resolution and wide-swath observation [15]. It combines the concept of Scan by controlling the switching of radar antenna beams among subswaths to achieve wider coverage. Moreover, similar to Spotlight/Sliding Spotlight, Mosaic uses azimuth beam sweeping to prolong the target irradiation time and increase the resolution [16].