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  Definitions: buoy matchups

Each week, AATSR SSTs are collocated with observations over the previous 7 days from the global network of drifting and moored buoys on the GTS. Each buoy reporting during the week undergoes a quality check. All SST observations from each buoy during the week are compared to the Met Office NWP model analysis SST matched to the observation time and location. If the mean or standard deviation of the differences between observed and analysis SST are above threshold values, that buoy is discounted as unreliable.

Observations from those buoys that pass the quality check are collocated to the nearest AATSR cell (a 10 x 10 arc minute spatial average). The buoy observation must be coincident to within 3 hours of the AATSR data time. The AATSR SSTs are those derived using the dual-view, 2-channel algorithm during the day, and the dual-view, 3-channel algorithm at night. A final gross check on the quality of the matchup compares the buoy SST against the NWP analysis SST: if the difference is too large, the matchup is discarded.

Results for three different satellite-derived SSTs are considered: the operational skin SST reported in ESA's Meteo product, the skin SST retrieved by the Met Office from the Meteo product brightness temperature data, and the bulk SST derived in the Met Office by applying a skin effect correction to the Met Office skin SST.

The temperature from buoys is a bulk SST measured at a nominal depth of 1 metre. The AATSR skin SSTs represent the temperature of the top few microns of the ocean surface, and so these may be cooler than the buoy bulk SST. The AATSR derived "bulk SST" has been corrected for the skin effect and can be considered a "subskin" SST, but during the day it may still contain the effect of stronger diurnal heating in the ocean layer above the depth of buoy measurement: occasionally this SST may be warmer than the buoy bulk SST.

Comparisons against AATSR

The distribution of successful matchups during the week is shown in the global location plot. This displays the location of matchups where at least one of the three AATSR-derived SSTs is available.

Time series show daily comparisons between AATSR-derived SSTs and SSTs reported by buoys. The difference of AATSR SST minus buoy SST is calculated and the plots show global means, standard deviations and number of matchups.

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