Validation of Upper-Tropospheric Humidity from SAPHIR on board Megha-Tropiques Using Tropical Soundings

International audienceThis paper describes the Upper Tropospheric Humidity (UTH) product derived from brightness temperature (BT) measurements of the SAPHIR radiometer onboard the Megha-Tropiques satellite. Under non-scattering conditions, the observations from three channels of SAPHIR, located at ±0.2, ±1.1 and ±2.8GHz respectively around the 183.31GHz strong water vapor absorption band, are interpreted into three different UTHs following a well-established method, thus describing the humidity content of the upper to mid troposphere. The evaluation of the UTHs is performed using reference UTHs defined from relative humidity profiles from radiosoundings of two field campaigns: the CINDY/DYNAMO/AMIE field experiment and a Megha-Tropiques dedicated campaign in Ouagadougou (Burkina Faso) during the summer 2012. A budget of the various uncertainties associated to each component of the methodology of evaluation (such as the radiometric sensitivity and the radiative transfer computations) was performed to achieve a more robust comparison between the two UTH estimates. The comparison between the reference UTHs and the SAPHIR UTHs reveals small global biases lower than 2%RH on average, with correlation coefficients between 0.86 and 0.89. Taking into account the individual uncertainties gives root-mean-square errors of regressions ranging between 0.92% and 4.71%. These three UTHs provide a vertical distribution of the relative humidity, which is suitable to study various temporal and spatial scales of the tropical variability. The signature of a mesoscale convective system on its environment is briefly presented to illustrate the capability of this new dataset