Specification of L2P core (L2Pc), L2P ancillary (L2Pa) and full L2P data content
At the 6th GHRSST-PP Science Team Meeting (Met Office, Exeter, United Kingdom, 2005) the following amendments to the specification of GHRSST-PP L2P core data products within the GDSv1.6 were agreed by the GHRSST-PP Science Team.
1.1. The GHRSST-PP Science Team agreed the principle that there will be 6 mandatory fields that form the core data content of a GHRSST-PP L2P data file. These fields will be known as L2P ‘core' fields. In addition to global attributes and geolocation information, RDACs must produce the following within a L2P file:
- SST
- sst_dtime
- SSES bias and std.
- rejection_flags
- confidence_flag
- proximity_confidence
Whenever possible RDACs should add the remaining ancillary fields, called L2P ‘auxiliary' (L2Pa) fields. When a L2P file contains all L2P core and L2P auxiliary fields together with full L2P metadata, it will be known as a full-L2P file. Only full L2P data files should be registered and ingested at the GHRSST-PP GDAC system. These distinctions will assist in the data management of the GHRSST-PP GDS-v1.7.
1.2. Missing L2Pa fields not provided by an RDAC may be filled up by the GDAC with prior arrangement. In this case data required the L2Pa files will be procured, checked for quality and interpolated/processed according to the GDS-v1.7 specification. L2Pc data will be complemented with L2Pa data and appropriate metadata to provide a full L2P file which is made available by GDAC to users. The following paragraphs describe specific issues relating to L2Pa definitions.
- DT_analysis: In the first instance the reference analysis will be that produced by FNMOC (FNMOC GHRSST HI-RES SST_ICE) and available from the US-GODAE (http://www.usgodae.org) server. If this is not available, the previous NRL analysis available within 3 days should be used. If this is not available, the Reynolds weekly OIv2 SST analysis (http://www.emc.ncep.noaa.gov/research/cmb/sst_analysis/) should be used. It was noted that, although some members of the ST had expressed doubts about the need for this field, it is definitely required by the European MERSEA programme. The field was retained following a formal request by the Medspiration team.
- wind_speed: Where there are wind fields contemporaneous with SST (e.g.. the microwave sensors or, in future METOP) they should be used. In their absence ECMWF (or other NWP) fields can be used. For other sensors a specified NWP wind speed analysis, which at present is the ECMW or NCEP. If the analysis is not available forecast products valid for the L2P time may be used. In most cases the source of wind speed will be the same for the whole of each data product, in which case this source is specified in the attributes field and the array containing sources_of_wind_field can be removed from the L2P product. However, if more than one source is used, the attribute will report mixed wind sources, and the sources_of_wind_field array must be included.
- sea_ice_concentration: OSI-SAF will be used as the primary source. If not available a secondary source (defined in the GDS-v1.7) may be used. The same source will be used consistently for the whole file (but may vary between north and south poles). There is thus no need for a sources_of_sea_ice field, but for each file there will be attributes to define which source is used in which polar region.
- Aerosol optical depth. There are only two operational sources of AOD data presently available - NESDIS or NAAPS. The same source will be used for all the fields in a given product file, and this will be specified in the attributes. There will be no need for a sources_of_AOD field. Note that in future, AOD products from the MODIS and other sensors may be available in an operational real time manner.
- Surface solar irradiance (SSI). SSI is available from MSG, from GOES or from NWP. If this field has not been filled by RDAC, the GDAC will add appropriate NWP values following the rules laid out in the GDS-v1.7.
1.3. When RDACs do not attempt to enter any values for a particular ancillary field, that field should be absent from the L2Pc submission (that is there is no need to enter placeholders). This field will then be added by GDAC. RDAC can and are encouraged to provide L2Pc and as many of the L2Pa fields as possible (rather than just a L2Pc file). The RDAC team is often the best placed to decide on the best data content for all L2P fields given regional/local knowledge of the ocean and atmosphere.
(Last Updated: 15-02-2007)