Comparison of Oceansat-2 scatterometer winds with buoy observations over the Indian Ocean and the Pacific Ocean

Abstract

Oceansat-2 scatterometer (OSCAT)-derived winds were compared with in situ observations made by Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA) and Triangle Trans-Ocean Buoy Network (TRITON) buoys in the Indian Ocean and the Pacific Ocean, respectively. Root mean square deviation (RMSD) for wind speed is 1.71 m s⁻¹ for the Indian Ocean and 1.92 m s⁻¹ for the Pacific Ocean. The wind speed accuracies are within the mission requirement (<2 m s⁻¹), but the wind direction errors are higher than the mission requirement (>20°). The RMSD values of wind direction are 51.38° and 44.61° for the Indian Ocean and the Pacific Ocean, respectively. OSCAT winds tend to underestimate the buoy value when the wind speeds were low (<4 m s⁻¹) and overestimate the buoy value when the wind speeds were high (>4 m s⁻¹). The wind speed residuals show an increasing trend with the increase of wind speeds. Interestingly, the wind direction residuals decrease with increasing wind speed and deviations of wind directions are conspicuously large for lower wind speeds than for higher wind speeds. OSCAT wind speeds were relatively more accurate for the Indian Ocean than those for the Pacific Ocean.

Acknowledgements

This study was carried out as part of the project work under Oceansat-2 Utilisation Programme (UP) funded by Space Applications Centre (SAC), Ahmedabad. The authors are very thankful to Dr. Raj Kumar, the Project Director, Oceansat-2 UP for his valuable help and suggestions during the course of these investigations. The authors also thank the National Remote Sensing Centre (NRSC), India, and the National Oceanic and Atmospheric Administration (NOAA), USA, for the data sets used in this study from their respective websites. The authors place on record their sincere thanks to the Director, Naval Physical and Oceanographic Laboratory (NPOL), Kochi, and the Director, SAC, for making the resources available and encouragement for this study.