Data Processing Issues

Satellite data processing includes different steps: level 0 and level 1 (from telemetry to calibrated sensor measurements), level 2 (from sensor measurements to geophysical variables), level 3 (space/time composites of level 2 data) and level 4 (merging of different sensors, data assimilation). Processing from level 0 to level 2 is generally carried out as part of the satellite ground segments.

Assembly of level 2 data from different sensors, intercalibration of level 2 products, and higher level data processing is usually done by specific data processing centers or thematic assembly centers. The role of these data processing centers is to provide modelling and data assimilation centers with the real time and delayed mode data sets required for validation and data assimilation. This also includes uncertainty estimates that are critical to an effective use of data in modelling and data assimilation systems. Links with data assimilation centers are needed, in particular, to organize feedback on the quality control performed at the level of data assimilation centers (e.g. comparing an observation with a model forecast), on the impact of data sets and data products in the assimilation systems and on new or future requirements.

High level data products (level 3 and 4) are also needed for applications (e.g. a merged altimeter surface current product for marine safety or offshore applications) and can be used to validate data assimilation systems (e.g. statistical versus dynamical interpolation) and complement products derived through modelling and data as similation systems. It is important, however, to be fully aware of limitations of high level satellite products (e.g. gridded SST or sea level data sets) when using them.

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