Intercalibration of wave and wind data from TOPEX/POSEIDON and moored buoys off the west coast of Canada

Abstract

Significant wave height (SWH) and wind speed data from the merged geophysical data record (MGDR) of the TOPEX/POSEIDON satellite altimeters, for the first 47 cycles of satellite coverage (September 1992 to December 1993), are compared with measurements from an array of instrumented buoys moored along and off the west coast of Canada. SWH values from the satellite and buoys cover a range of 0.1 to 8 m, in one case exceeding 12 m. The comparison shows TOPEX waves, on average, low by 5% relative to the buoys, with rms scatter about the mean relation of 30 cm. For buoys lying within 10 km of the satellite tracks, this scatter is reduced to about 15 cm. TOPEX tracks pass sufficiently close to each of the buoys for the satellite altimeter to be used as a “transfer standard,” showing a small difference between the two types of buoys in the array and occasional problems with the buoy measurements. A significant difference was found between the satellite and buoy wind speeds, with NASA altimeter winds being high by about 10% relative to the buoys. This can be explained by known factors affecting the buoy data. The small amount of POSEIDON data shows the winds in the MGDR to be 12% low compared with the buoys. The difference between POSEIDON and NASA altimeter winds is confirmed by computing large‐area spatial averages over the Pacific Ocean. The rms scatter for wind speed about the best fit regression was near 2 m/s, reducing to 1.4 m/s when data were restricted to distances less than 10 km from deep water buoys. Atmospheric pressure values, inserted in the satellite data from a global weather model, were found to agree with buoy measurements to within about 1 mbar. Apart from the discrepancy in wind speeds, the results are consistent with both buoy and satellite data meeting or exceeding their design specifications. The effects of spatial variations of wave climate and changes in atmospheric stability are assessed. The comparison demonstrates how satellite and buoy observations can be used for mutual calibration and performance monitoring.