Establishing the relationship between the CERES window and total channel measured radiances for conditions involving deep convective clouds at night

radiometers, the CERES instrument measures radiances in the shortwave (>2000 cm � 1 ), infrared window (835–1250 cm � 1 ), and total regions of the spectrum. Such a choice of radiometers does not allow for a straightforward three channel intercomparison of the CERES measurements. We observed, however, the outgoing infrared spectra of high, cold, optically thick clouds were fairly representative of blackbody emission. This observation suggested a potential relationship between the infrared window radiometer and longwave portion of the total radiometer. Using nighttime measurements made by the CERES instrument aboard the Tropical Rainfall Measuring Mission (TRMM) spacecraft during the first eight months of 1998, we were able to determine a highly correlated relationship between the infrared window and total channel radiances for conditions corresponding to high, cold, optically thick clouds. Comparisons were then made between the measurements and reference line-by-line calculations. From these comparisons, a quantified relationship was derived between the total and window channel radiances which could accurately reproduce one set of results from the other. Such a relationship has allowed for the establishment of a three channel intercomparison for the CERES instrument with an accuracy of � 1% for the case of high, cold, optically thick clouds. An independent relationship based upon the tropical mean is shown to produce results which support the three channel analysis for the deep convective cloud systems. INDEX TERMS: 0394 Atmospheric Composition and Structure: Instruments and techniques; 1694 Global Change: Instruments and techniques; 0325 Atmospheric Composition and Structure: Evolution of the atmosphere; 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 1640 Global Change: Remote sensing; KEYWORDS: CERES, TRMM, radiometer, three-channel-intercomparison, deep-convectiveclouds, infrared-window

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