Available product types

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.