ConGaLSAR: A Constellation of Geostationary and Low Earth Orbit Synthetic Aperture Radar

Synthetic aperture radar (SAR), with its all-weather and day/night capabilities, plays an important role in Earth observation. Traditionally, SAR satellites fly in low Earth orbits, which can result in fast Doppler accumulation but long revisiting intervals. Although increasing the number of satellites extends the observation coverage significantly, a complex constellation leads to unacceptable cost. The geosynchronous SAR system realizes sustained observations for a specific area; however, the long integral time results in the obvious defocusing of objects, even in micro-motion. To achieve a fast response and a short revisiting time with high accuracy and low costs, a constellation of imaging radar satellites called Constellation of Geostationary and Low Earth Orbit SAR (ConGaLSAR) is proposed in this letter; ConGaLSAR employs a novel transponding mode (MirrorSAR) to economically achieve efficient revisiting and phase/time synchronizations. In this system, the ground echoes are amplified by the low-orbit satellites and then retransmitted back to the illuminating system for sampling and downlinking. In view of the specific geometry of the system, the sensitivity, resolutions, and effective observing area are discussed and precisely defined. Based on the theoretical analyses, a typical case of ConGaLSAR, consisting of one geostationary orbit illuminator and 24 low-orbit transponders, can achieve a 92.4-min revisiting interval and 3-m resolution for the Pacific Ocean.