Discovery

For complementing its Central Facilities capability in Darmstadt and taking more benefit from specialized expertise in Member States, EUMETSAT created Satellite Application Facilities (SAFs), based on co-operation between several institutes and hosted by a National Meteorological Service. The Ocean and Sea Ice Satellite Application Facility (OSI SAF) is an answer to the common requirements of meteorology and oceanography for a comprehensive information on the ocean-atmosphere interface. One of the objectives of the OSI SAF is to produce, control and distribute operationally in near real-time OSI SAF products using available satellite data with the necessary Users Support activities.

Earth observing sensors handled in CERSAT database are onboard polar orbiting satellites, performing several revolutions per day. The main characteristics of the related data products are :

• observation pattern corresponding to a band, or swath, relative to the satellite track (the virtual line on the Earth's surface followed by the satellite nadir),
• swath forming a nearly regular grid with axes parallel and perpendicular to the satellite track.
• swath grid resolution depending on sensor resolution,
• data files generally storing the observations collected during a complete (or half) revolution,
• high volume of data
• duration necessary to cover the whole Earth's surface related to the orbital characteristics of the satellite and the swath width of the sensor.

These products are intended for users requiring direct, geolocated and dated observations. The constraint is that the data availability over a given region within a given time range depends on whether the sensor spotted this region at the requested moment or not.

They consist in synoptic fields of various geophysical quantities at regular space/time resolutions, depending on each sensor's sampling pattern. Estimating these gridded value-added products requires :

• mapping the swath data over a regular grid
• estimating new geophysical quantities by merging data from different sensors
• using accurate spatio-temporal re-sampling methods (averaging, objective analysis, data merging,...) to average where overlap occurs and interpolate (over the gaps)

The gridded product are much more easier and practical to handle than swath products :

• global long-term homogeneous and consistent temporal series of geophysical parameters
• not depending on the sequential acquisition along the sensor swath
• lower volume of data

Available gridded products at CERSAT include global mean wind fields, sea-ice maps, radar backscatter over land.

The colocation consist in relating together data from various sources (in-situ or satellite sensors, numerical models), according to space and time criteria, which means :

• retrieving n-uplets of the closer (in space and time) single observations from two (or more) sources ( minimal level)
• or collecting all almost simultaneous observations from several sources over a given geographical area ( total level)

These products are specially intended for the following studies :

• calibration/validation or inter-comparison of sensors
• monitoring the quality and possibly drift of sensors
• estimating the relations between various geophysical parameters (each retrieved from a different source)

• monitoring geophysical features or events over specific areas and time periods (from various sensors)

  Many colocation products, coupling satellite, in-situ (TAO, TOGA, ...buoy networks) and models (ECMWF) observations are now generated and distributed at CERSAT.

The temperature at the surface of the ocean (SST) is an important physical property that can be measured quite easily from Earth Observation satellites. SST has a strong influence on the exchange of heat, momentum, water and gases beteen the ocean and the atmosphere. Knowledge of the geographical distribution of SST and its variation with time is therefore essential for predicting the dynamical behaviour of the atmosphere and the ocean. SST is also an important indicator of climate and climate change, giving us a finger on the pulse of the planet itself. Climate quality sea surface temperatures are needed on an operational basis to develop better predication of climate change.

The CERSAT is a major center for the delivery of sea surface temperature in teh frame of several international projects (such as Medspiration, Mersea or GODAE/GHRSST-PP), and in partnership with other european agencies such as Météo-France/CMS, ESA or the EUMETSAT Ocean and Sea-ice SAF (SAF O&SI).