The GHRSST-PP Level-2 Pre-processed (L2P) data format specification is a netCDF file
following the Climate Forecast (CF)
convention. A full product specificification can be found in the GHRSST-PP Data processing Specification
(GDS).The common format of L2P products allows data users to code with the security that as new
satellite derived SST data sets are brought on-line, very mminimal code changes are required to make full use of the data. Time
previously spent on coding different i/o routines for each satellite data set can be spent working with the data to produce results.
GHRSST-PP L2P format data products are
netCDF files containing SST data,
error estimates (bias error and standard deviation) for each pixel and a series of
ancillary fields to help interpret and use the SST data themselves.
The power of L2P lies in the fact that all satellite SST data are presented in a common easy to use data format
so that only a single i/o utility is required to start using data rather than having to re-code and maintain code
for ingestion of different satellite data. The ancillary fields provide users with a suite of dynamic flags that
can be used to filter data based on criteria tuned to a particular application. For example,
if data contaminated by diurnal warming are unwanted then surface wind speed and solar radiation
auxiliary fields can be used to flag data at low wind speeds with high solar radiation.
For IR SST data, aerosol optical depth can be used to filter data suspect due to contamination.
L2P files are the basic building blocks from which all other GHRSST-PP
SST data products can be derived. They include SST data as delivered by a data provider in their native format (swath, grid, vector),
together with a number of ancillary fields (some shown to the left) that simplify interpretation an application
of the SST data. For example, the time of SST observation, geo-location data, land and ice flags are just a few fields included
with every GHRSST-PP L2P file. Ancillary data is also included to help interpret the quality and character
of the SST data. Ancillary data are referred to as dynamic flags. L2P dynamic flags
include estimates of the surface wind field (that can be used to flag low wind speed areas prone to
surface solar irradiance (SSI, that can also be used to flag areas of diurnal variability), aerosol optical depth
(used to flag areas contamintaed with atmospheric dust, important for infrared SST retrievals from space)
and sea ice concentration.