The Cross-Calibrated Multi-Platform (CCMP) Ocean Surface Wind Vector Analyses (Atlas et al., 2011) provide a consistent, gap-free long-term time-series of ocean surface wind vector analysis fields from July 1987 through June 2011. The CCMP datasets combine cross-calibrated satellite winds using a Variational Analysis Method (VAM) to produce a high-resolution (0.25 degree) gridded analysis. The CCMP dataset uses satellite winds derived by Remote Sensing Systems (RSS) from a number of microwave satellite instruments. RSS intercalibrates radiometers on the brightness temperature level to within 0.5 deg C and applies a highly refined sea-surface emissivity model and radiative transfer function to derive surface winds. This results in high consistency between wind speed retrievals from microwave radiometers (i.e., SSM/I, SSMIS, AMSR, TMI, and WindSat). RSS also has developed a geophysical model function for deriving wind speeds and directions from microwave scatterometers (including QuikScat and SeaWinds). Both radiometer and scatterometer data are validated against ocean moored buoys, which prove the measurements are in excellent agreement (within 0.8 m/s) despite the different instrument measurement dynamics wind retrieval methodologies. The VAM (Hoffman et al., 2003) combines the RSS data with in situ measurements and a starting estimate (first guess) of the wind field. The European Center for Medium-Range Weather Forecasts (ECMWF) ERA-40 Reanalysis is used as the first-guess from 1987 to 1998. The ECMWF Operational analysis is used from January 1999 onward. All wind observations and analysis fields are referenced to a height of 10 meters. Three globally gridded datasets are distributed to complete the CCMP dataset series: 1) gridded swaths of ascending and descending platform-specific passive radiometer wind speeds with CCMP-derived wind directions (L2.5); 2) fully-assimilated gap-free 6-hourly surface wind fields (L3.0); and 3) monthly and 5-day averaged surface wind fields (L3.5).
RMS speed difference (top) and mean speed difference (bottom) for each analysis versus the cross-calibrated satellite surface wind datasets that were assimilated. A negative mean speed difference indicates that the analysis wind speed is less than the satellite wind speed. Statistics were calculated in 1-month bins starting in July 1987. Image from Atlas et al., 2011.