The ATSR Advanced InfraRed WAter Vapour Estimator (AIRWAVE): consistency, homogeneity and validation

We report the results of the validation, long term stability and homogeneity analysis of the AIRWAVE dataset. It consists in atmospheric water vapour total column (TCWV) retrieved using the measurements from the two Thermal InfraRed (TIR) channels of the Along Track Scanning Radiometer (ATSR) instrument series, on board the European Space Agency's ERS-1, ERS-2 and ENVISAT satellites. The retrieval scheme, named Advanced InfraRed WAter Vapour Estimator (AIRWAVE - Casadio et al., 2015), uses the instrument physical characteristics,in combination with advanced radiative transfer models and a sea surface spectral emissivity database. The retrievals therefore do not require algorithm tuning or adjustments to independent water vapour datasets. The use of the dual view capability of the ATSR-type instruments, allows for the accurate and precise day-time and night-time retrievals of cloud free TCWV over oceans. This new physical algorithm can be readily extended to dual view radiometers similar to ATSR, such as the upcoming Sea and Land Surface Temperature Radiometer (SLSTR) instrument on the European Copernicus Sentinel-3 satellite series. The global validation of AIRWAVE TCWV, spanning from 1991 to 2012, is carried out using the WMO soundings located on islands or close to coasts. Validation results will be critically analysed and discussed. Inter-comparisons with the Remote Sensing Systems Special Sensor Microwave Imager (RSS SSM/I) and ECMWF ERA-Interim total water vapour column products have been carried out and results are discussed in detail Finally, the consistency and homogeneity of the AIRWAVE TCWV data across the three ATSRs are analysed and discussed.