RISAT-1 SAR External Calibration – A Summary

This paper summarizes the radiometric and geometric calibration results achieved during commissioning and operational phase of RISAT-1. To ascertain long term stability, all the imaging modes pertaining to Stripmap, ScanSAR and High resolution Spotlight light modes were calibrated and validated using data collected over ISRO Cal sites and homogenous distributed targets. The characterization of RISAT-1 SAR has been performed by deriving the Elevation Antenna Patterns using gamma naught analysis, distributed target analysis, image quality metrics of the data products, estimation of calibration factor along with RCS characterization of Corner reflectors. The performance evaluation of nominal Medium Resolution ScanSAR mode having 25days repetivity of India’s carpet coverage was carried out periodically. Nonetheless scattering mechanisms pertaining to Hybrid polarimetry were also studied against the response of corner reflectors. The experience gained in carrying out SAR calibration activity to perform absolute and relative calibration of RISAT-1 and their results are described in this paper.