Results for calibration of Sentinel-1A using the Australian corner reflector array

Geoscience Australia has permanently deployed 40 trihedral corner reflectors in Queensland, Australia, covering an area of approximately 20,000 km2. The array of corner reflectors was constructed as part of the AuScope Australian Geophysical Observing System (AGOS) initiative to monitor crustal deformation using Interferometric Synthetic Aperture Radar (InSAR) techniques. The array includes 34 corner reflectors of 1.5m, 3 reflectors of 2.0m and 3 reflectors of 2.5m inner leg dimensions. Through the design process and the precision manufacturing techniques employed, the corner reflectors are also highly suitable for calibration and validation of satellite-borne Synthetic Aperture Radar (SAR) instruments. Nine of the 1.5m corner reflectors in the AGOS array had their Radar Cross Section (RCS) individually characterised at the Defence Science and Technology Organisation¿s outdoor ground reflection range, prior to permanent deployment in Queensland. The RCS measurements for the corner reflectors were carried out at X and C-band frequencies for both horizontal and vertical transmit-receive polarisations, and at a range of elevation and azimuth alignments. The field performance of the AGOS corner reflectors has been studied using SAR data from a range of satellites including Sentinel-1A. This study focuses on the calibration of the Sentinel-1A satellite presenting results from exercises undertaken both at Geoscience Australia and the European Space Agency¿s Mission Performance Centre as part of the satellite commissioning and routine phases. Radiometric calibration results in conjunction with geometric calibration and validation results for Sentinel-1A products from Stripmap and Terrain Observation with Progressive Scans (TOPS) modes are presented in this paper. The current configuration for most corner reflectors in the AGOS array is set to serve calibration requirements for a broad range of SAR missions on ascending orbital passes. However, the design allows for mission-specific corner reflector alignment if needed, as in the case of the 2.5m and 2.0m reflectors which have specifically been aligned to support calibration of the L-band SAR instrument on ALOS-2. Results reported in this paper could inform the need for re-configuring one or more corner reflectors in the array to specifically support ongoing calibration of the Sentinel-1A and B satellites. The permanently deployed AGOS corner reflector infrastructure presents an opportunity for independent calibration and comparison of SAR instruments on current and future satellite missions, and is considered an important Australian contribution to the global satellite calibration and validation effort. Presented at the 2016 Living Planet Symposium (LPS16) Prague, Czech Republic