In situ measurements are used as truth values to assess and monitor the quality of satellites products. Various sources of in situ sea surface temperature data (ships, drifting buoys, Argo floats,...) are available in near real-time or delayed mode and can be used for that purpose. They are collected by CERSAT from Coriolis data center, quality controlled and formatted to a more easy to use for direct comparison with satellite SST products or to produce satellite to in situ match-up databases.
The in situ made available by Coriolis are collected daily. Currently we only collect drifting buoys (obtained by Coriolis from GTS) but other sources will be processed to in future. Gross check is performed to estimate a quality level for each measurement, filter out invalid data and select only the surface measurements :
- control of the geolocation and various quality flags available in the original Coriolis files
- control against climatology (measurements with a deviation greater than 5 degrees are flagged)
- control against UKMet and Meteo-France blacklist made available through MyOcean project and updated every 10 days
The climatalogy value as well as the sun zenital angle (to discreminate night and day data) are added for each measurements. Daily files containing all the data for a single day are produced in netCDF3 format and made available in open access through ftp :
- files are named as <date>_<type>_<area>.nc where:
- date = YYYYMMDD (ex: 20101001_DB_global.nc contains the data of 1st October 2010)
- type = 'DB' for drfting buoys
- area is the covered area. Only files with area='global' should be used (other areas use a former delivery of Coriolis data and will not be maintained in future)
We also process from these data gridded files at various resolution and over various areas, for direct comparison with satellite gridded products :
- Global, 10km resolution
- Global, 25km resolution
- Mediterranean sea, 2km resolution
- Europe north-western shelves, 2km resolution
- South-Africa, 2km resolution
- Brazil and Tropical Atlantic, 2km resolution
- Great Barrier Reef, Australia, 2km resolution
To produce these datasets, only nighttime and highest quality in situ data are selected. Data of a single buoy over a grid cell are averaged. Data from two (or more) different buoys are not averaged together and will result in two separate values (one for each buoy), thus there may be more than one value in the same grid cell.
These data are available on request to firstname.lastname@example.org.
Monitoring of data availability
The following graphs monitor the number of in situ measurements retrieved and selected from Coriolis, on a hourly basis, and the number of measurements - per day - available in each gridded in situ products.