Mapeamento das estimativas do saldo de radiação e índices de vegetação em área do estado de Alagoas com base em sensores remotos.

Abstract

The balance of radiation at the surface is of great importance in studies related to the flow of heat in the atmosphere, particularly in agricultural crops in areas and basins. This work mapped the components of the radiation balance of the land surface and vegetation indices of the area with the river basin Pratagy in Alagoas, by means of remote sensing data in days of clear sky. In the estimation of the components of the balance of radiation were used data from TM-Landsat 5 and algorithm SEBAL - Surface Energy Balance Algorithm for Land is proposed by Bastiaanssen Land (1995). We analyzed the images of the day 06/11/1990, 09/21/1998 and 09/03/2003. The average value of the Normalized Difference Vegetation Index (NDVI) in 0.633 was 06/11/1990, 0.607 and 0.502 on 09/21/1998 to 09/03/2003, evidencing reduction of vegetation in the area in 1990 to study 1998 and also from 1998 to 2003. The gradual reduction of NDVI that occurred between the years studied, where the low values of 0 - 0.20 are found in more urbanized area, may have resulted from the urbanization process which intensified in these years. The classified image of the subtraction of NDVI between 1990 and 1998, however, demonstrated that in 59.5% of the area in study was little variation in the index. Once in the image of the subtraction of NDVI between 1998 the 2003 evidenced more that in almost 50% of the area in study was loss of vegetation and more spatially distributed in the central part of it. The instantaneous average value of the balance of radiation to the surface (Rn) increased from 1990 to 1998 and decreased between 1998 and 2003, with ranges of 129.6 W/m2 and 77.3 W/m2 respectively. In the classified image subtraction of Rn between 1990 and 1998 found that the increase was well distributed in 93.4% of the area. And the image of the subtraction of Rn between 1998 and 2003 showed that the decrease of Rn was also well distributed spatially in 82.5% of the area. The estimated average snapshot of the surface temperature (Ts) between 1990 and 1998 was an increase in the range of 3.3ºC, while from 1998 to 2003 occurred decrease of 2.7ºC. The gradual increase Ts between 1990 and 1998, where values above 26ºC are found in more urbanized regions of the area under study may have been due to the intensification of the process of urbanization. The analysis of critical areas in relation to the occurrence of loss of vegetation cover has proved that the NDVI is related with the indireta the surface albedo and the Ts, while the Rn with a direct relationship. The analysis of the critical areas of loss or gain of Rn showed that the albedo and Ts almost always act inversely with the Rn and the rates of vegetation directly. It was evident to appropriate employment potential of SEBAL in studies of changes in vegetation and land use in watersheds of scale, since the identification of changes in species can occur by studying the maps of net radiation and rates of vegetation.