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Further input to the algorithm is the viewing geometry at each pixel which is defined by the viewing zenith angle (VZA), the Sun zenith angle (SZA) and the azimuth difference angle (ADA). All the data are given in the Level 1b files of MERIS (see MERIS Product Handbook).
2.2 Auxiliary Data
The algorithm needs additional information in order to reliably estimate the water vapour. The current state of the atmosphere (temperature, pressure) is approximated by using reanalysis fields.
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