L4 Gridded SST products
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.
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).
There are a variety of operational L4 SST analysis products available from different agencies on a daily basis within the GHRSST-PP framework. Some systems use only a limited number of satellite inputs (e.g.,1° global Reynolds OIv2 uses only AVHRR data) whereas others try to blend data from complementary sources (e.g., JMA Merged Global Development SST (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 0.5° and 1/12° global RTG_SST) whereas others use GHRSST-PP data almost exclusively (e.g., 1/20° Met Office Operational SST and Sea Ice Analysis (OSTIA)). In the figure above (top left) FNMOC 10 km High Resolution SST/Sea Ice Analysis for GHRSST updated every 6 hours (top right) JMA MGDSST, (bottom left) MWOI global 9km SST analysis system developed by Remote Sensing Systems using TMI, AMSR-E, and AQUA MODIS SST data, (bottom right) OSTIA 1/20° global grid (~6.5 km) L4 SST analysis produced by the Met Office.
Ultra-high Resolution SSTfnd 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 developed by the ESA Medspiration project. 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.
Since 2000, the New Generation Sea Surface Temperature (NGSST) Development Group (see http://www.ocean.caos.tohoku.ac.jp/) has been generating a regional L4 analysis product based on in situ and satellite SST. Satellite observations are objectively merged to generate a daily quality-controlled SST product without gaps due to cloud cover, at high-spatial resolution (0.05º) over the south-west Pacific area 13-63ºN, 116-166ºE. Each SST product is generated at around 16:00 LST (7:00 UT) at day T+1, using observations acquired on day T.
As part of the BLUElink> Ocean Forecasting Australia project (http://www.bom.gov.au/bluelink/), the Australian Bureau of Meteorology has modified its existing operational sea surface temperature (SST) analysis system to produce 1/12° resolution, daily foundation SST analyses over the Australian region (20°N - 70°S, 60°E - 170°W) by blending SST measurements from infrared and microwave sensors on polar-orbiting satellites. The new operational Regional Australian Multi-Sensor Sea Surface Temperature Analysis (RAMSSA) system became part of the Bureau's operational suite in June 2007. The output of the RAMSSA system is available in real-time as GHRSST-PP format L4 data files from http://godae.bom.gov.au and from the GHRSST GDAC and images are available from http://www.bom.gov.au/marine/sst.shtml. The method used to produce the new regional SST analyses and verification and inter-comparison with other SST products is documented in Beggs (2007) (http://www.bom.gov.au/bmrc/pubs/researchreports/RR130.pdf). The format and content of the Bureau's GHRSST-PP format L4 files is documented in http://www.bom.gov.au/bmrc/ocean/BLUElink/SST/BLUElink_L4_file_format_v6.pdf.
Scientific questions on the new analysis should be directed to Dr Helen Beggs, BMRC Ocean and Marine Forecasting Group (h.beggs@bom.gov.au). Feedback on the new RAMSSA product is very welcome.
(Last Updated: 30-05-2008)