The satellite to in situ match-up database
Objective
The GHRSST Match-up Database (MDB) of co-located satellite and in situ SST is a service of Medspiration project funded by ESA. It is required by GHRSST for quality control of satellite SST datasets, in particular for deriving or verifying SSES using in situ SST observations from ships, buoys and profiling floats. Such observations provide a reliable independent reference data set that must be matched in space and time to satellite observations.Although several independent MDB systems have previously been created by agencies responsible for particular SST products, their formats are diverse, their in situ data sources may be different, and they do not share uniform quality control and spatial/temporal match-up criteria. These important differences make it difficult to compare MDB analyses of different SST products with each other. The GHRSST-MDB is intended to remedy this. It is a new multi-sensor SST MDB being developed at the IFREMER centre in Brest, France by integrating in situ data held within the Coriolis system (responsible for the collection and archiving of global in situ oceanographic data, http://www.coriolis.eu.org) and an archive of GHRSST data products, both hosted by IFREMER.
Processing
In situ and satellite data are co-located on a daily basis within 25km and 6 hours of the satellite overpass as a worst case scenario and the match-up criteria can be constrained further in space and time as required. By adopting a single source of independent quality-controlled in situ data and automating the match up procedure for all satellite data sets, the GHRSST-PP MDB ensures that all match-ups are computed with the same in situ data and with the same level of quality. The SSES derived in this way can then be reliably compared between satellite sensors The in situ temperature data sources available within Coriolis that are used for the match-ups currently include all surface measurements (thermosalinographs on ships and drifting buoy) and data from profiling sensors (Argo floats, XBT/CTD/XCTD from ships, moored buoys). The satellite sources are so far restricted to products from the European Medspiration project and they will be progressively extended to other GHRSST datasets. Between 100000 and 150000 match-ups are registered each month within the MDB. All the ancillary data attached to L2P and L4 products are available for each satellite match-up in the MDB.Data
The data are made available to users through two access means- pre-extracted files (just click and save), in NetCDF format, providing all the available match-ups for each dataset, within periodic time periods. These data files can contain more information than what is contained in the MDB, added afterwards such as the matching climatology value or the solar zenital angle at satellite pixel measurement time and location. These data files also indicate the covered time period for each dataset.
- a user interface allowing customized requests, using selection filters (such as as time/spatial criteria, colocation criteria, data quality, range pf parameters, etc...). The data can be extracted in both NetCDF or Ascii format.
Additional information on the satellite and in situ data used to populate the MDB can also be found in, respectively :