Validation of wind speed retrieval from RISAT-1 SAR images of the North Indian Ocean

ABSTRACT

An algorithm has been developed to retrieve ocean surface wind speed from Synthetic Aperture Radar (SAR) on-board Radar Imaging Satellite-1 (RISAT-1). The retrieved wind speed is subsequently validated using observations from Advanced Scatterometers (on-board Metop-A, Metop-B) for the period from July 2012 to September 2016. The quality of the retrieved wind speed was assessed using observations from offshore moored buoys in the Bay of Bengal and Arabian Sea. It has been observed that the RISAT-1 derived wind speed, retrieved using three Geophysical Model Functions (GMFs) viz., CMOD5.N, CMOD5 and CMOD_IFR2 are negatively biased relative to ASCAT as well as Buoy. The biases with ASCAT are 0.38 (0.98) ms⁻¹, 0.96 (1.24) ms⁻¹ and 1.31 (1.55) ms⁻¹ respectively for the coastal (offshore) region. The Root Mean Square Difference (RMSD) between RISAT-1 and ASCAT are 1.58 (1.78), 1.8 (1.85) and 1.96 (1.99) in m s⁻¹ respectively for coastal (offshore) waters, which is well within the acceptable limits. Thus it is found that the quality of the wind speed retrieved using CMOD5.N GMF is better than other GMFs. The high resolution wind data available from RISAT-1 SAR opens new pathways for assessing wind energy potential along the Indian coast.

Acknowledgments

The authors are thankful to Shri Tapan Misra, Director, Space Applications Centre. The RISAT-1 data were obtained from the National Remote Sensing Centre (NRSC). Authors are thankful to JPL NASA for providing ASCAT wind data. Thanks are also extended to Indian National Centre for Ocean Information Services (INCOIS) for providing buoy data.