Outgoing longwave radiation at the top of the atmosphere: preliminary assessment using GOES-8 imager data
GOES-8 Imager radiances in water vapor and infrared channels 3, 4 and 5 were used for assessing outgoing longwave radiation (OLR) at the top of the atmosphere. Estimation by ITPP5 software applied to HIRS/NOAA 14 passes over Brazil was considered as "true reference". Imagery from both satellites is currently acquired and processed at CPTEC/INPE. GOES full-resolution imagery allows assessment of mean irradiance for sets of GOES pixels contained within the area of a single HIRS pixel. Additional GOES variables were estimated, such as: an "equivalent channel" at 8 mm and a "longwave tail" for l>15 mm (this one is not detected neither by HIRS nor GOES sensors). Isotropic outgoing radiance was assumed. Multivariate regression of GOES irradiances on OLR ITPP estimates provided a GOES estimator with accuracy comparable with others already published and based on AVHRR/NOAA information. It was found that a regression based only on channel 4 and the longwave tail yielded estimates with the same accuracy: mean deviation of 3 W.m-2 and standard deviation of 11 W.m-2. The application for another period in the year, averaged over 1º´1º grid cells, yielded similar mean deviation and standard deviation of 7 W.m-2. These results suggest that the algorithm applied in this work has physical rather than purely statistical meaning and could be used for OLR monitoring in daily and seasonal scales.
Sociedade Brasileira de Geofísica
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