A SIMPLE METHOD FOR TESTING BRIGHTNESS TEMPERATURES FROM SATELLITE MICROWAVE RADIOMETERS

A method is proposed for testing microwave measurements from spaceborn e by computing collocated simulated brightness temperatures from the E CMWF numerical weather meterological meodel using an atmospheric radia tive transfer model and the Stogryn model for the surface emissivity. In this paper this method is tested on Scanning Multichannel Microwave RAdiometer (SMMR) and Special Sensor Microwave/Imager (SSM/I) data. T he comparison with observed brightness temperature underlines a rather good agreement for SSM/I but a significant discrepancy for SSMR in th e vertical polarization, confirming that the SSMR was biased (up to 10 K). Correcting fiunctions are proposed for SSMR 18- and 21-GHz channe ls, which are validated by comparing Wilheit and Chang's water vapor a lgorithm results and radiosonde measurements. Small biases in the SSM/ I 19- and 22-GHz brightness temperatures comparison can be similarly e liminated. This calibration is validated in the same way by applying w ater vapor and surface retrieval algorithms and comparing the results with corresponding local measurements. The SSM/I algorithms were devel oped using the same radiative transfer and surface emissivity model, a pplied toa dataset based on five months of ECMWF analyses. This study established the validity of the model, and the reliability of ECMWF an alyses, both for validating microwave brightness temperatures and for developing retrieval algorithms in view of future sensors.