Multiple Channel Satellite Analysis of Cirrus
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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The Split-window technique is based on the varying radiative properties of clouds and the atmosphere in different wavelengths of the primary infrared IF window. Channels 4 11 micron and 5 12 micron on the NOAA AVHRR are used to apply the technique to determine the differences between thick and thin cirrus and multiple layered clouds. The brightness temperature from channel 5 was subtracted from the brightness temperature from channel 4, resulting in a brightness temperature difference BTD image. The technique was applied to ten subscenes over mid-latitude land areas for both summer and winter cases. The BTD values were compared to surface observations of the same time period as the images. The cases were grouped into five and then three cloud groups based on the surface observations. The analysis of variance showed that the average showed that the average BTD values for the three cloud groups were statistically different for the summer cases but not for the winter cases. The BTD thresholds estimated from these cases are 1 Multiple layered clouds--0.00 to 0.80 2 Thick cirrus--0.81 to 1.50 and 3 Thin cirrus--1.51 and greater . The split- window technique is successful in distinguishing the varying cirrus thicknesses when the surface temperature is warmer than 285 K.