Intercomparison and Validation of Winds from Scatsat-1 and in situ Buoys

Abstract

ISRO’s Scatsat-1 scatterometer, launched on 26th September 2016, supports the OSCAT-2 scatterometer as a continuation and enhancement of the OSCAT onboard the OceanSat-2. This paper carries out a detailed inter-comparison between the swath-wise level 2B (L2B) data from Scatsat-1 with in situ wind velocity data derived from three different moored buoy arrays: the Global Tropical Moored Buoy Array (GTMBA,) National Data Buoy Center (NDBC), and the Ocean Moored buoy Network for northern Indian Ocean (OMNI.) While the three arrays collectively span most of the ocean basins, they are primarily concentrated in the tropical regions and the coast of North America; therefore, to facilitate an assessment of the agreement between the satellite and in situ data in different regions, the comparison is split between tropical, extra-tropical and coastal regions for each ocean basin. The statistics thus derived are however biased towards buoys with a greater number of collocated observations and therefore the agreement between the two wind vector datasets are also estimated at each buoy location. As wind direction is a circular variable, circular/directional statistics has been used to compute the relevant parameters for wind direction. A temporal analysis of the agreement between WS and WD has also been carried out and it indicates that months with high WD bias contain a relatively greater number of observations with errors close to 180°.