Use of WindSat to Extend a Microwave-Based Daily Optimum Interpolation Sea Surface Temperature Time Series

The NOAA ¼° daily optimum interpolation sea surface temperature analysis (DOISST) is available either as a 31-yr (from 1981 onward) time series based on Advanced Very High Resolution Radiometer (AVHRR) observations or as a 9-yr (2002–11) time series that incorporates additional data from the Advanced Microwave Scanning Radiometer (AMSR) on the Earth Observing System (EOS) platform. In October 2011, AVHRR + AMSR DOISST production was discontinued when the AMSR instrument lost its capability to collect daily, global-coverage data. Sea surface temperatures from the follow-up AMSR2 instrument will not be available until mid-2013. To ensure an uninterrupted consistent long-term microwave-based DOISST time series, this study tested the feasibility of bridging the gap between AMSR and AMSR2 using WindSat Polarimetric Radiometer (WSAT) data. Comparison of WSAT and AMSR SST data during their period of overlap from 2004 to 2011 showed temporal gaps were common for WSAT, especially before 2009. The WSAT daily spatial coverage was slightly inferior to AMSR but still far superior to AVHRR. When satellite SSTs were bias adjusted with respect to in situ data, the resulting AMSR- and WSAT-only analyses were very similar. Monthly zonal averages agreed to within 0.1 K, except when WSAT data were continuously missing for over three weeks. However, if satellite SSTs were not bias adjusted prior to analysis, seasonally varying zonal average differences were observed, with maxima of ∼0.3 K occurring at midlatitudes. Thus, WSAT can be used to continue the microwave-based DOISST time series because the methodology compensates for the different equatorial crossing times of the two satellites.