A Novel In-Orbit Method for Spaceborne SAR Absolute Radiometric Calibration Using Small Calibration Satellite

This paper presents a novel space-based approach for the absolute radiometric calibration of spaceborne Synthetic Aperture Radar (SAR) systems using a small calibration satellite equipped with calibration instruments such as transponders or passive reflectors to provide precise reference measurements. With the known orbital parameters of the SAR satellite, the calibration satellite parameters are appropriately designed based on Relative Orbital Element Method(ROEM), allowing the small calibration satellite to operate in a coordinated formation with the SAR satellite. In this formation, the SAR satellite can frequently observe and image the calibration satellite under the side-looking acquisition geometry, and calculate the calibration factor(CF). The proposed method reduces reliance on groundbased calibration sites, enables calibration intervals to align with the orbital period, and extends the capability for inorbit radiometric performance evaluation. More importantly, the entire calibration process is performed in the space environment, free from distortions caused by atmosphere, ionosphere, ground clutter, multipath effects and ambiguities, ensuring a truly 'end-to-end' measurement process.