Estimativa de componentes do fluxo radiativo na superfície mediante satélite.

Abstract

In the present work, the surface components of the radiation balance obtained from the satellite data are compared with the ground data. The are data collected during the Integrated Experiment in the Semi-Arid of the Radiation Through Satellite (Experimento Integrado no Semi-Árido, do projeto Radiação por Satélite - EIS-RADSAT). The experiment was realized in the area covered with the native vegetation ("caatinga"), in the region of São Gonçalo, PB (-6,83° S; -38,25° W) at the end of the rainy season (end of March, 1995). The computational methods of solar radiation, albedo and temperature of the surface were applied to the satellite imagery of Meteosat-5 and NOAA-14 for the pixels close to the experimental site. The global solar radiation at the surface is estimated using a radiative transference model,which utilizes the data obtained from the images of Meteosat-5 (visible channel) and AVHRR/NOAA- 14 (channels 1 and 2). The surface albedo (wide band) is evaluated by a weighted mean between the surface albedo in the narrow band estimated by the satellite and the surface albedo in the solar infrared. The component of the longwave descendent radiation from the atmosphere is determined from the equations of Brunt and Swinbank, which uses air temperature and vapor pressure data. The component of the longwave radiation emitted by the surface is determined from the Law of Stefan-Boltzman, which is a function of the temperature and emissivity of the surface. The surface temperature is estimated by two methods: the mono-window method which utilizes the satellite imagery obtained in the IR channel of the Meteosat-5; and the split-window method which utilizes the brightness temperature of channels 4 e 5 of AVHRR/NOAA-14. From the analysis of the results it can be observed that the estimating methods are reasonable for clear and cloudy days. To determine the surface temperature though satellite it can be observed that the split-window method presents better results than the mono-window method, when they are compared with the ground truth. The surface global solar radiation estimates in both the cases of Meteosat-5 and NOAA-14 presented good results when compared with the ground truth values.