Abstract
In this study, we analyzed the imaging maneuver time, retargeting maneuver time, and attitude maneuvering characteristics in the imaging section (Phase 1) and retargeting maneuver section (Phase 2) when taking multiple-target images in squint spotlight mode in a single pass of a passive SAR satellite. In particular, the synthetic aperture time and attitude maneuvering characteristics in the staring and sliding spotlight modes that can image the wider swath width while maintaining high resolution were compared and analyzed. In the sliding spotlight mode, the rotation center was located below the ground surface when the satellite was maneuvering towards the target. Steering and sliding maneuvers were performed when targeting, and the synthetic aperture time of the sliding spotlight was longer than that of the staring spotlight because overlapping imaging was performed on the point target. The satellite maneuvering during imaging can be considered as a time-fixed problem, because it was performed within synthetic aperture time according to resolution, incidence angle, swath width, etc., by minimizing the Doppler centroid variation. In order to optimize the retargeting maneuver time, an optimal analysis of the attitude maneuvering was carried out and the validity of the optimal analysis algorithm was confirmed. Finally, the scenario was analyzed by assuming a problem of imaging four targets with 5 × 5 km swath width in a 20 km × 20 km densely populated area. It was confirmed that if a squint angle of ±12 degrees is provided in a single pass, four high resolution images of 5 km × 5 km can be imaged in the sliding spotlight mode.
Highlights
Due to the recent miniaturization/light weight of satellites, the passive SAR satellite that requires mechanical beam steering is in the limelight, implementing a foldable reflector antenna with high storage efficiency instead of an active SAR satellite that performs electronic beam steering using a phased array antenna
The analysis is performed by assuming that the MoI of the satellite is Ix = 1000 kgm2 Iy = 700 kgm2, Iz = 500 kgm2 and the PoI is set to be 0 for that simplified simulation based on reflector antenna-based passive SAR satellite configuration
While active SAR satellites perform imaging through electronic beam steering, passive
Summary
Due to the recent miniaturization/light weight of satellites, the passive SAR satellite that requires mechanical beam steering is in the limelight, implementing a foldable reflector antenna with high storage efficiency instead of an active SAR satellite that performs electronic beam steering using a phased array antenna. In the case of active SAR satellites, since beam steering is required for spotlight mode imaging, high agility is not necessary for the satellite. In the case of passive SAR satellites, a highly agile satellite is required to enhance the imaging capability because the satellite itself must maneuver. In the case of passive SAR satellites, since beam steering is performed by satellite attitude control, the ability to take broadside mode images is limited, so squint mode operation is performed to enhance the imaging capability in spotlight mode. There have been few published studies on squint attitude maneuvering in the spotlight mode of passive SAR satellite requiring mechanical beam steering. To analyze the imaging capability of continuous targets in a single pass of the satellite, analysis of the imaging maneuver time, retargeting maneuver time, and attitude maneuvering for both phases is required. We analyze the synthetic aperture time, retargeting maneuver time, and maneuver characteristics in the imaging, as well as the retargeting maneuver stages in the staring and sliding spotlight imaging modes of passive SAR satellites
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