Beam scan mode analysis and design for geosynchronous SAR

The beam velocity of geosynchronous synthetic aperture radar (GEO SAR) varies seriously with the orbital position and the scene position, which leads to a significant variation of the scene length and the azimuth resolution in the stripmap (SM) mode. To obtain uniform scene length and azimuth resolution, beam scan modes can be utilized in GEO SAR, such as the sliding spotlight (SLL) mode and the terrain observation by progressive scans (TOPS) mode. However, the conventional design method of the beam scan mode is based on the straight line model (SLM), which does not consider the effects of the curved satellite track and the spherical earth surface. To solve this problem, a curvature circle model (CCM) is proposed considering the actual satellite-earth relationship. By using the CCM, the beam velocity after the beam scan is derived. The scene length and the azimuth resolution are analyzed. The SLL mode and the TOPS mode are recommended for GEO SAR. After that, a design method of the beam scan mode is proposed based on the CMM. The performance of the proposed method is verified by computer simulations.