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The GHRSST Match-Up Database Facility

The Match-up Database Facility (MDB-F) is a service implemented and hosted at Ifremer/Cersat in the context of GHRSST project. It offers to sea surface temperature (SST) providers a portal where they can provide and deliver their co-located satellite and in situ SST datasets (or match-up databases) and to users a way of selecting and accessing these match-ups either interactively or through ftp. It is required by GHRSST as a critical tool to assess the quality of satellite SST datasets, in particular for deriving or verifying sensor's specific errors using in situ SST observations from ships, buoys and profiling floats. Such observations provide indeed a reliable independent reference data set that must be matched in space and time to satellite observations.

buoy colocationSeveral independent MDB systems have previously been created by agencies responsible for particular SST products, their format and content are diverse, as well as the way to access them (when there is any access available). The MDB-F tries to remedy this by collecting the various available MDBs at these agencies (Meteo-France, RSMAS, ABoM,...) and making them accessible through a single portal in the most homogeneous way as possible, trying to reduce the heterogeneity existing between them (naming of parameters, quality control,...). Alternatively, when no MDB is existing for a GHRSST dataset (or could not be obtained), the MDB-F is able to produce a local MDB for this particular dataset.

The implementation of the MDB-F has been supported by Ifremer, ESA (through Medspiration project) and the European Commission (MyOcean project).

 

Available match-up databases

One single MDB contains only the match-ups for only one single satellite source (sensor or GHRSST dataset). The various MDBs available at the MDB-F may come from two different sources, directly from a producer of a given satellite SST dataset or from the MDB-F itself where match-ups are created periodically.

Match-up databases by satellite SST providers

These MDBs are the most heterogeneous, they differ strongly for each provider :

  • the in situ sources (mostly from GTS) used for comparison with the satellite may be different, or the filtering and quality control applied to the in situ measurements. Some may use only drifting buoys whereas others will mix ship and buoy measurements. Whenever the source of in situ data is known (type of measurement and identifier of the buoy or ship), it is reported in the MDB-F.
  • the procedure to compute the satellite to in situ match-ups, as well as the temporal (from 30 min to 6 hours) and spatial constraints (1km to 25km distance) may also be very different for each provider. We try to add the time difference and spatial distance between satellite and in situ measurements when it is possible (so that users can apply tighter criteria).
  • on the good side, they can also be far richer because they provide sometimes additional information compared to what is delivered in the GHRSST dataset, such as ancillary parameters (atmosphere, ocean) or the brightness temperatures used to compute the sea surface temperature.

In order to homogenize these match-up databases, some parameters are standardized (like time and location) and an additional quality control is applied (whose result is reported in two additional flags).

Satellite source

Provider

In situ source

Colocation criteria

Time frame

METOP-A/AVHRR (L2)

O&SI SAF

GTS

6 hours/1 km

Jul 2007 - ongoing

MSG/SEVIRI (L2)

O&SI SAF

GTS

6 hours/1 km

Mar 2011 - ongoing

GOES-13/Imager (L2)

O&SI SAF

GTS

6 hours/1 km

Jan 2011 - ongoing

AQUA/MODIS (L2)

RSMAS

TERRA/MODIS (L2)

RSMAS

Match-up databases by Ifremer

For some GHRSST datasets for which an MDB is not available, ifremer produces locally this MDB itself. The processing scheme, described here, and the source of in situ data (data held within the Coriolis system, responsible for the collection and archiving of global in situ oceanographic data) is the same for all the MDBs provided at Ifremer. An additional quality control is applied to the match-ups as for the external MDBs.

Satellite source

Provider

In situ source

Colocation criteria

Time frame

ENVISAT/AATSR (L2P)

ESA

Coriolis

6 hours/25 km

Sep 2010 - ongoing

GOES11/Imager (L2P)

NOAA/OSDPD

Coriolis

6 hours/25 km

Dec 2010 - ongoing

TRMM/TMI (L2P)

REMSS

Coriolis

6 hours/25 km

Dec 2010 - ongoing

AQUA/AMSR-E (L2P)

REMSS

Coriolis

6 hours/25 km

Dec 2010 - ongoing

NOAA19 / AVHRR LAC (L2P)

NAVOCEANO

Coriolis

6 hours/25 km

Sep 2010 - ongoing

NOAA18 / AVHRR GAC (L2P)

NAVOCEANO

Coriolis

6 hours/25 km

Sep 2010 - ongoing

NOAA19 / AVHRR GAC (L2P)

NAVOCEANO

Coriolis

6 hours/25 km

Sep 2010 - ongoing

Access

The match-ups stored at the MDB-F in Ifremer can be accessed in different ways :

  • FTP : daily data files are extracted for each satellite dataset (GHRSST-PP product) and each type of in situ (drifters, ships, moored buoys, argo floats,..). They contain the whole data available in the database so that users have to perform their own filtering if they are only interested for instance in a specific geographical area or in mach-up records with a specific quality level. The data file are in netCDF-4 format only. They contain all the variables available in the database, plus additional fields added afterwards to each match-up file such as the MDB-F quality flags, climatology values, solar zenital angle. They are available in two forms : with the neighbouring values for each match-up (files with extension "_full") or without (lighter file size).
  • Advance Web user interface : this online application allows users to select match-ups with respect to different criteria and to extract the data or to produce dynamic plots and statistics in order to interactively assess the quality of the satellite SST dataset, investigate the quality of the in situ measurement used in these comparisons, etc.... more details on this application are provided here.