Balanço de Radiação e Energia no Perímetro Irrigado Califórnia-SE Mediante Imagens Orbitais (Radiation and Energy Balance in the Calitornia-SE Irrigated Area Using Orbital Image)

O principal objetivo do presente trabalho foi determinacao dos componentes do balanco de energia e a evapotranspiracao em regiao semiarida usando o algoritmo SEBAL e imagens do satelite Landsat 5. A area de estudo foi o Perimetro Irrigado California localizado no municipio de Caninde do Sao Francisco – SE, Brasil. Para consecucao dos objetivos foram utilizadas imagens obtidas nos dias 8 de abril de 2005 e 7 de dezembro de 2006, que cobrem as areas irrigadas do perimetro, parte do rio Sao Francisco e areas com vegetacao nativa. Foram determinados o albedo da superficie (α), indices de vegetacao (NDVI, SAVI e IAF) e a temperatura da superficie (T s ) para cada pixel. A radiacao incidente de onda curta foi estimada para condicoes de ceu claro segundo Allen et al. (2000). A radiacao de onda longa proveniente da atmosfera teve como base a temperatura do ar medida em estacao meteorologica de superficie e a radiacao de onda longa emitida por cada pixel, a temperatura da superficie e sua emissividade. A partir dessas variaveis determinou-se o saldo de radiacao (R n ), cujo valor medio para o dia 08/04/2005 foi 565,0 W m -2 e para a imagem do dia 07/12/2006, 585,3 W m -2 . O fluxo de calor no solo (G), estimado em funcao do R n , T s , α e do NDVI, apresentou para o dia 08/04/2005 valor medio de 78,9 W m -2 e para a data de 07/12/2006 79,1 W m -2 . O fluxo de calor sensivel (H), estimado com a aplicacao de processo iterativo, em funcao da velocidade do vento em dois pixels de referencia (quente e frio) para se determinar a diferenca de temperatura entre a superficie e o ar proximo a mesma, apresentou para o dia 08/04/2005 valor medio de 115 W m -2 . Em 07/12/2006 o valor medio de H estimado pela tecnica foi de 140,7 W m -2 . O fluxo de calor latente (λE), calculado como parte residual do balanco de energia a superficie, apresentou valores medios de 402,0 W m -2 para a data de 08/04/2005 e de 365,5 W m -2 para o dia 07/12/2006. A B S T R A C T The main objective of the present work went evaluate the components of the swinging of energy and the evapotranspiration in semi-arid area using the algorithm SEBAL and images of the satellite Landsat-5 TM. The study area was the Irrigated Perimeter California located in the municipal district of Caninde of Sao Francisco - SE, Brazil. For attainment of the objectives images obtained in April 8, 2005 and December 7, 2006 were used, that they collect the irrigated areas of the perimeter, it leaves of the river San Francisco and areas with native vegetation. Was the albedo of the surface ( α ), vegetation indexes (NDVI, SAVI and IAF) and the temperature of the surface (Ts) for each pixel. The incident radiation of wave tans it was esteemed in function of the solar constant, of the atmospheric transmissividade, of the solar zenith angle and of the square of the distance relative Earth-sun. The incident radiation of long wave had as base for its estimate the temperature of the air measure in the meteorological station of surface and the emitted radiation of long wave esteemed with base in the surface temperature. Starting from those variables the radiation balance was determined (Rn) whose medium values esteemed by Landsat 5-TM for the 08/04/2005 were 565,0 W m -2 and for the image of the 07/12/2006, 585,3 W m -2 . The flow of heat in the soil (G), esteemed in function of Rn, Ts and of NDVI, it presented for the 08/04/2005 the medium value of 78.9 W m -2 , however, for the date of 07/12/2006 the medium value of that same variable was 79.1 W m -2 . The flow of sensitive heat (H), esteemed with the application of the process, in function of the speed of the wind and of the medium height of the obtained of the meteorological station of surface vegetation and also with base in two reference pixels (hot and cold) to determine the temperature difference between the surface and the close air the same, did it present for the 08/04/2005 the medium value of 115 W m -2 . In 07/12/2006 the medium value of H esteemed by the referred satellite was 140.7 W m -2 . The flow of latent heat ( λ E), calculated as residual part of the of energy to the surface, it presented medium values of 402.0 W m -2 for the date of 08/04/2005 and of 365.5 W m -2 for the 07/12/2006. Keywords: Evapotranspiration; SEBAL; Irrigated Perimeter California.