Two Decades of Water Vapour Total Column from ATSRs using the Advanced Infra-Red Water Vapour Estimator (AIRWAVE) tool

new algorithm has been developed enabling an accurate and precise estimate of Total Column Water Vapour (TCWV) using the Thermal Infra-Red (TIR) channels of the Along Track Scanning Radiometer (ATSR) instruments. The retrieval scheme, called Advanced Infra-Red Water Vapour Estimator (AIRWAVE), has been developed in the frame of the ESA contract 'ATSR Long Term Stability (ALTS)' in the optic of a better exploitation of the (A)ATSR instruments and can be easily adapted to the Sea and Land Surface Temperature Radiometer (SLSTR) instrument on board the Copernicus Sentinel 3 satellites. The current version of the algorithm works on ocean/cloud-free scenes by combining advanced radiative transfer models and a sea surface spectral emissivity database. The simultaneous use of forward and nadir measurements minimise the impact of the knowledge of the sea surface temperature and of the atmospheric radiation on the quality of the retrieved TCWV. Exploiting only the TIR channels of the instrument, the algorithm enables the estimation of TCWV both in the day and night part of the orbits and the full exploitation of the ATSR instrument series, spanning from 1991 to 2012. The AIRWAVE Prototype Processor (AIRWAVE-PP) has been integrated in the ESA GRID environment (GPOD) for testing purposes, and for the bulk processing of the three ATSR missions. The AIRWAVE TCWV data record has been analysed in terms of cross-instrument consistency and retrieval stability. Outcomes will be discussed in details, along with the preliminary results of the cross comparison with the latest version of the Special Sensor Microwave Imager (SSM/I) water vapour products. Finally, the possible mechanisms for the accessibility of AIRWAVE TCWV products to the user community will be discussed.