USING COINCIDENT MULTISPECTRAL SATELLITE DATA TO ASSESS THE ACCURACY OF SPECIAL SENSOR MICROWAVE IMAGER LIQUID WATER PATH MEASUREMENTS

We present techniques to identify and reduce the sources of error in t he liquid water path (LWP) of marine stratocumulus clouds retrieved fr om the special sensor microwave imager (SSMI), using coincident high-r esolution visible and infrared data provided by the operational linesc an system (OLS). The OLS data are used to identify cloud-free areas in order to determine the degree of error in the estimated dear sky pola rization difference, an important parameter in the SSMI retrieval algo rithm. The retrieval algorithm is refined by including the cloud top t emperature derived from the OLS infrared data. Errors in the LWP measu rements owing to broken or inhomogeneous clouds are difficult to quant ify, but a subpixel analysis of cloud type and spatial variability rev eals which measurements are more likely to be biased. The application of these techniques on a set of sample images confirms that the relati onships between the liquid water path and other cloud parameters are m ost robust in overcast conditions.