Preliminary studies on corner reflectors responses as seen in Sentinel-1A images over Kanakapura region
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Spaceborne synthetic aperture radar (SAR) performance may get degraded due to component degradation, aging, thermal variations of the environment and so on. Performance degradation should be corrected when the spaceborne SAR is in orbit. Calibration is implemented on the radar imagery by radiometric calibration which gives the relationship between digital number and backscattering coefficient. Radiometric calibration gives calibration constant, which is the key parameter to convert the SAR digital numbers into backscattering coefficient. With radiometrically calibrated image, the performance of one sensor can be compared with other sensors through multiple acquisitions to improve quantitative analysis of SAR performance. Radiometric calibration is done by ground deployed corner reflectors (CR). CRs have well-known radar cross sections, and hence, the derived radar cross sections from the SAR image are compared with the theoretical RCS to characterize the SAR sensor. An attempt is made to study the effectiveness of calibration, using different combination of CRs (various sizes and shapes) by deploying CR’s in the Jain Global institutions—JGI global Campus, Jakkasandra, Bangalore, and average sigma-naught (σ0) is estimated through multiple acquisitions of Sentinel-1A. Sentinel-1A was launched by European Space agency in 2014, having SAR as a payload. Sentinel-1A is an open source system which operates in four different modes with different resolution schemes. In this paper, Interferometric Wide swath mode of Sentinel-1A is used as that particular mode of acquisition is available over Jain Global campus. This paper presents the general criteria for selection of CRs and the measures taken during deployment. Integral method is used to estimate the calibration coefficient of Sentinel SAR data with different interpolation factors.
KeywordsRadiometric calibration Synthetic aperture radar Corner reflectors Integral method
Authors gratefully thank the support extended by ISRO-SAC senior scientists, Dr. A. K. Mathur, Shri. V. Ramanujam, Smt. Shweta, Shri. Raghav Mehra for very useful discussions and also acknowledge the encouragement received from Dr. Hari prasad, Director SET, Prof. V. Parameshwaran, Director IIAEM Shri. Shine Gopal, Facility manager SET during deployments. Also authors acknowledge the technical support and co-operation received from Mr. Vaisakh, Mr. Abrar Khan, Mr. Akshay Raj, the final year students of IIAEM with gratitude. Authors appreciate the response received from SENTINEL forum toward learning the SNAP toolbox. This work is being carried out at Jain University under the RESPOND project on “On-Orbit Characterization of Space-Borne Synthetic Aperture Radar using Ground Deployed Corner reflectors.”
- Feng, Z., Huang, L., Tang, Z., Liu, J., & Zhao, L. (2014). Airborne SAR radiometric calibration using point targets. In 35th International symposium on remote sensing of environment (ISRSE35) IOP publishing IOP conference series: Earth and environmental science 17, 012186. https://doi.org/10.1088/1755-1315/17/1/012186.
- Internal technical report (XXXX) Selection of field for deploying corner reflectors. JU/ISRO-RESPOND/Aero/TR-001Google Scholar
- Mishra, M. D., Patel, P., Srivastava, H. S., Patel1, P. R., Shukla, A., & Shukla, A. K. (2014). Absolute radiometric calibration of FRS-1 and MRS mode of RISAT-1 synthetic aperture radar (SAR) data using corner reflectors. International Journal of Advanced Engineering Research and Science (IJAERS),1(6), ISSN: 2349–6495Google Scholar
- Mishra, Mayank, Patel, Parul, Srivastava, Hari, Shukla, A., Patel, Pratik, & Shukla, A. K. (2015). Approach for absolute radiometric calibration of RISAT-1 SAR data using standard target. International Journal of Remote Sensing & Geoscience (IJRSG), 4, 28–32.Google Scholar
- Norris, J., Vachon, P. W, Schlingmeier, D., English, R., & Gallop, L. (2004). Expendable trihedral corner reflectors for target enhancement and position control in RADARSAT-1 fine beam mode SAR imagery: Results from an exercise Narwhal Pre-Trial Deployment, 2004, Defence Research and Development Canada Ottawa, Active & Passive Radar Detection & Equipment Optics, Technical memo, accession number: ADA633794.Google Scholar
- RISAT-Handbook (2012) ISRO document 2012 Issue 1. https://nrsc.gov.in/sites/all/pdf/RISAT-1BROCHUREV4.pdf
- Sentinel-1 User Handbook (2013) ESA standard document date 1/09/2013 Issue 1 Rev 0. https://sentinel.esa.int/web/sentinel/userguides/sentinel-1-sar
- Stastny, J., Cheung, S., Wiafe, G., Agyekum, K., & Greidanus, H. (2015). Application of RADAR corner reflectors for the detection of small vessels in synthetic aperture radar. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 8(3), 1099–1107.Google Scholar
- Ulaby, F. T., Moore, R. K., & Fung. A. K. (1981) Microwave remote sensing: Microwave remote sensing fundamentals and radiometry (Vols. 1, 2). Artech House, Technology & EngineeringGoogle Scholar