Multiplatform calibration and validation of CFOSAT ocean surface waves

Abstract The nadir and off-nadir ocean wind and wave products of the Surface Waves Investigation and Monitoring (SWIM) instrument onboard the China France Oceanography Satellite (CFOSAT) are validated against multiple wave buoy datasets. These include a moored buoy in the Southern Ocean, the Northern Hemisphere focused wave buoys of the National Data Buoy Centre (NDBC), and a globally distributed Sofar drifting spotter buoy archive. SWIM nadir comparisons of significant wave height and wind speed data against NDBC buoy measurements showed that SWIM can capture these parameters with high accuracy and temporal stability. The off-nadir comparisons of SWIM bulk statistics of significant wave height and peak wave direction indicate high correlation and low errors against all buoy datasets. The performance of wave period (both mean and peak) is relatively poorer and varies by buoy dataset considered, with best results obtained against the Sofar archive. The accuracy of SWIM mean wave period against all buoy datasets is significantly improved by using a recently published neural networks-based inversion approach. Finally, quantitative evaluation of SWIM omni-directional spectra indicated an overall best performance for SWIM 10° beam product amongst the four SWIM products and against all exploited wave buoy datasets. This calibration and validation work is comprehensive and valuable because it describes the performance of CFOSAT wind/wave products in global oceanic conditions and against both moored and drifting wave buoy networks, with satellite-buoy collocations varying from 1605 to 7233 respectively for nadir wave and wind comparisons and over 3000 for off-nadir comparisons across all platforms. It is the intention that this work will enable the uptake of SWIM data with better-informed quantification of errors and accuracies.