L4 Data File Description

GHRSST-PP L4 products are designed to provide the best available estimate of the SST from a combined analysis of all available SST data. In situ data form an important component of the L4 process as these data are used to correct for biases between the satellite data sets. GHRSST-PP bias and standard deviation errors are provided as Single Sensor Error Statistics (SSES). L4 products capoitalisae on the synergy benefits of using in situ, microwave satellite SST and infra-red satellite SST.

The GHRSST-PP L4 data format specification is a netCDF file following the Climate Forecast (CF) convention. A full product specification can be found in the GHRSST-PP Data processing Specification (GDS).

Several methods are available for the generation of complete SST fields from incomplete L2P input data (e.g., Reynolds and Smith, 1994; Reynolds et al, 2002; Guan and Kawamura, 2003; Murray et al. 2002; Murray et al. 1994; Fieguth et al., 1998;2000, Menemenelis et al. 1997; Lorenc, 1981 although none of these methods has been fully developed for use of an operational high resolution processor such as the GDS demands. Bias correction of all input data to the analysis procedure is critical to obtaining a valid output (see for example Reynolds et al, 2002). The GDS will use the L2P SSES derived bias as a measure of the overall uncertainty associated with each input data stream. In addition, bias due to diurnal stratification and cool skin effects must also be accounted for using additional data. Some satellite sensors provide a direct estimate of the SSTskin (AATSR) that must be adjusted to the SSTfnd. These data can then be used in an optimal analysis procedure to derive complete global fields. As the GHRSST-PP Science Team and RDAC project teams gain experience, it is expected that the bias correction strategy will evolve.

There are a variety of operational L4 SST analysis products available from different agencies. Some systems use only a limited number of satellite inputs (e.g.,1º global Reynolds OIv2 uses only AVHRR data) whereas others try to blend data from complementary sources (e.g., JMA MGDSST operational 25km global SST based on AVHHRR and AMSR-E). Not all products make use of GHRSST-PP data at this time (e.g., NOAA 0.5º global RTG_SST) whereas others use GHRSST-PP data almost exclusively (e.g., 1/20 º NCOF-OSTIA).

Ultra-high Resolution SST_fnd products

In addition to global L4 products (typically 10 -50km spatial resolution), several Ultra-high resolution (UHR, <5km resolution) regional SST analysis products are available for example, the Mediterranean UHR SST shown here is a 2km analysis. UHR products are dificult to generate as the analysis system must capture the local dynamics of the region in a way that preserves structure and minimuses noise.