AIRWAVE: an algorithm for the retrieval of the total column of water from the measurements of the ATSR series and Sentinel 3/SLSTR

The Advanced Infra-Red WAter Vapour Estimator (AIRWAVE) algorithm has been developed by Casadio et al. (2016) and applied to the measurements of the Along Track Scanning Radiometer (ATSR) missions for the retrieval of the Total Column of Water Vapour (TCWV). It produced a 20-year day-night TCWV dataset over sea in clear sky conditions. The quality of the obtained dataset has been evaluated against independent products derived from space borne sensors (SSM/I, MWR), from ground based remote sensing (GPS, sun-photometers), from WMO sondes (ARSA and IGRA databases) and from NWP (ECMWF ERA-Interim). The comparisons showed a general good agreement. The algorithm, that is independent from external constrains, makes use of a set of tabulated parameters calculated off-line using a Radiative Transfer Model (RTM) specifically developed to simulate the ATSR radiances. The approach exploits the clear sky Brightness Temperature measured over the sea in forward and nadir directions in the TIR channels. The AIRWAVE algorithm has been recently extended to the Sea and Land Surface Temperature Radiometer (SLSTR) instrument, on board the European Copernicus Sentinel 3. SLSTR has the same dual view capability and TIR spectral channels of the ATSR instruments and therefore it is possible to use a similar approach for the TCWV retrieval. With respect to its precursors, SLSTR has different nadir and oblique viewing angles, a larger swath (more across track measurements) and different spectral response functions in the two TIR channels. We will show some examples of the application of the AIRWAVE algorithm to the ATSR series and to the SLSTR measurements, evaluating the performances with comparisons against other sensors (e.g. SSM/I or MWR).