Validation of sea surface temperature, wind speed and integrated water vapour from MSMR measurements. Project report

Abstract

IRS-P4 (OCEANSAT-1) is the first operational oceanographic satellite that India has launched. An extensive validation campaign was unleashed immediately after its launch in May 1999. Various platforms (viz., ship, moored buoy, drifting buoy and autonomous weather station) were utilized for measuring sea truth parameters such as sea surface temperature (SST), Sea Surface Wind Speed (WS) and Columnar Water Vapor (WV). Total match-ups for SST and WS measured from various platforms exceeded 1400 (2 hrs and 2 degree temporal and spatial windows) whereas the match-ups for WV was just close to 60. An indirect method was therefore attempted for validating WV by computing a third term, surface specific humidity (Qa), from both satellite and sea truth derived parameters. Grid 1 data product appeared to be closer to sea truth-values for all the three parameters and was used for further comparisons. Strangely the drifting buoy SST's were better correlated with the satellite SST (R=0.84). It is interesting to note that the SST's were closer to the satellite values during night hours when the WS varied from 0 to 10 m/s while the day time correlation was better at higher wind speeds (greater than 10 m/s). Stationary platforms (MB and AWS) did exhibit better correlation when the time window slides from 120 hrs to 15 minutes. The correlation, however, deteriorated for moving platforms such as ships. Day time winds exhibited better correlation for ocean platforms (MB and Ship) but the night time winds were better correlated for land based platform (AWS). The surface level specific humidity (Qa) also showed this day-night discrepancy. Night time Qa values exhibited consistently higher correlation than their day time counterpart.