International Journal of Advanced Engineering Research and Science (IJAERS) [Vol-1, Issue-6, Nov.- 2014] ISSN: 2349-6495 Page | 78 Absolute Radiometric Calibration of FRS-1 and MRS mode of RISAT-1 Synthetic Aperture Radar (SAR) data using Corner Reflectors Mayank D Mishra 1 , Parul Patel 2 , H S Srivastava 3 , P R Patel 1 , A Shukla 4 , A K Shukla 2 1 Institute of Technology, Nirma University, Ahmedabad, GUJARAT Email: mayank.mishra@nirmauni.ac.in 2 Space Applications Centre, Ahmedabad, GUJARAT Email: parul@sac.isro.gov.in 3 Indian Institute of Remote Sensing, Dehradun,UTTARAKHAND Email: hari.isro@gmail.com 4 M G Science Institute, Ahmedabad, GUJARAT Abstract— It’s been more than two years since the launch of RISAT-1, India’s first indigenous satellite SAR mission. Prior to radiometric calibration of any SAR data, no comparison can be made with any other data. Calibration procedure provides a reference mechanism to SAR DN values. With radiometric calibration digital numbers of SAR data are converted to backscattering coefficients which can be compared with backscattering coefficients of other SAR sensors. An experiment for absolute radiometric calibration of 13 (thirteen) beams of RISAT-1 FRS-1 mode data and 1 (one) beam of RISAT-1 MRS mode data has been carried out using standard point targets. In this experiment, triangular trihedral corner reflectors were used as standard point targets and deployed prior to satellite overpass with precise azimuth and elevation angles in various selected research sites in India. For FRS-1 mode total 42 (forty two) triangular trihedral corner reflectors were deployed during 2012 – 2014 for 19 (nineteen) dates. 11 (eleven) beams for RH-RV, 4 (four) beams for HH and 1 (one) beam for VV polarisation RISAT -1 data was acquired. For MRS mode during 2013 – 2014 for (six) dates, a total of 14 (fourteen) reflectors were deployed for 1 (one) beam 87-97. These deployed corner reflectors were then located on SAR image and impulse response function for reflectors were derived using box integral method. The derived IRF were used to calculate calibration constant for each of the reflector. Keywords— Calibration constant, Corner reflector, FRS-1, Impulse Response Function, MRS, RISAT-1. I. INTRODUCTION During eighties of twentieth century with launch of SeaSAT spaceborne synthetic aperture radar (SAR) lots of analysis was performed on qualitative basis. However with later spaceborne SAR satellite missions e.g ERS-1/2, Envisat, RADARSAT-1/2, ALOS-PALSAR-1, RISAT-1 data availability has also increased to research community. This increased amount of data has helped building up number of hypothesis and lots of them converted to established theories [1-3]. Thus it is very important to be assured that any SAR data being used for a research study should provide accurate backscatter value. This assurance is derived by a procedure called calibration and data undergone the procedure is referred as calibrated data. Calibration provides a reference mechanism to SAR DN (Digital Number) value so that they represent correct properties of the area illuminated by the sensor. After calibration of SAR data results from obtained from it, can be compared to data from other sensors [4-6]. This assurance also leads to development of parameter retrieval models for various applications [7-15]. For a given SAR image, its DN value is proportional to the received voltage [16]. Therefore, the image intensity I, is proportional to the received power Pr. The process to retrieve SAR backscattering coefficient from the observed SAR image intensity is known as radiometric calibration. [17]. Calibration establishes a relationship between the SAR sensor output and Radar Cross Section (RCS) of a known standard target or distributed target of known RCS [18-20]. Calibration procedure on SAR data can be applied by analysing standard targets response as well as reference distributed targets analysis [21 - 23]. In this study an experiment has been attempted for absolute calibration of