Radiometric calibration stability assessment for the RISAT-1 SAR sensor using a deployed point target array at the Desalpar site, Rann of Kutch, India

ABSTRACT

Synthetic aperture radar (SAR) data used for quantitative temporal and/or spatial analysis requires calibration to ensure that observed pixel values of amplitude and phase can be related to the geophysical parameters of interest. The process of radiometric calibration of SAR images involves comparison of the backscattered radar reflectivity signal from a ground resolution element containing a calibration target of known signal response, such as a corner reflector. In this study, absolute radiometric calibration of RISAT-1 intensity data of fine resolution stripmap-1 (FRS-1) and medium resolution ScanSAR (MRS) mode was carried out by utilizing array of standard point targets of various types (triangular trihedral, square trihedral, and dihedral) with known radar cross-section deployed prior to satellite overpass with precise azimuth and elevation angles in Desalpar, Rann of Kutch in western India. The derived calibration constants using the integral method were then compared with the values provided in the header file. Deviations in the results are reported in this article. The results obtained show that the difference between the estimated average calibration constants for FRS-1 and MRS mode data with the provided value was found to be within the absolute radiometric accuracy specification of Radar Imaging SATellite (RISAT-1). Near-range to far-range difference of 0.1–0.2 dB for HH (Horizontal transmit, Horizontal receive) polarization and 0.1–0.3 dB for HV (Horizontal transmit, Vertical receive) polarization was estimated for the same scene using distributed target analysis indicating the stability of calibration for the same scene. This study also concluded that Desalpar site in Rann of Kutch has the potential of being an operational SAR calibration site.

Acknowledgements

Authors express their sincere gratitude to Shri Tapan Misra, Director, Space Applications Centre, Ahmedabad, and Dr. Rajkumar, Deputy Director, EPSA, for their guidance and support to carry out this activity. Authors are grateful to Director, Institute of Technology, Nirma University, HOD, Civil Engineering Department, Nirma University, and Principal, M.G. Science Institute, Ahmedabad, for their institutional support for carrying out this activity. Authors also thankfully acknowledge the cooperation and technical help received from Shri D. B. Dave, Dr. Kartikeyan, Shri Ramanujam, Shri Amit Shukla, and Shri Raghav Mehra for this activity. The help and support rendered by Shri Ganuba, Shri Digvijay, and Shri Parvat during the deployment of CRs at Desalpar and their navigational guidance of the local area were of utmost importance for the successful calibration campaigns.

Disclosure statement

No potential conflict of interest was reported by the authors.