Balanço de radiação fotossinteticamente ativa por sensoriamento remoto em floresta tropical sazonalmente seca no Nordeste brasileiro

Abstract

Photosynthetically active radiation (PAR) is essential for plant development. Upon reaching the surface, this radiation can undergo processes of reflection, absorption and transmission and the quantification of these fractionations is of significant importance, in view of the understanding of radiative processes on the Earth's surface. Thus, the main objective of this work was to characterize the fractionation of Photosynthetically Active Radiation (PAR) and its interaction with the vegetation cover of a portion of Seasonally Dry Tropical Forest at the end of the rainy season in Northeast Brazil. Vegetation use and coverage were classified according to the Woody Vegetation Biomass Index (IBVL) and MapBiomas (collection 5) to assess the contribution of the PAR balance sheet components. The leaf area index was also correlated with each component of the PAR radiation balance to find the best fit models. Second order Polynomial models were used to identify the relationship between the PAR components and the IAF. The studied region covered the municipalities of Petrolina, Juazeiro, Lagoa Grande and Curaçá, located in the states of Bahia and Pernambuco. The images came from the Landsat-5 and Landsat-8 satellites, between the years 2009 to 2019, being one image per year, obtained at the end of the region's rainy season, considering the cloud cover below 10%. Digital processing was performed using the QGIS 3.6.2 Software to obtain the vegetation indices (NDVI, SAVI and IAF) and the PAR radiation balance. The surface data were obtained from the meteorological stations of the Institute for Space Research and the National Institute of Meteorology located in the city of Petrolina, Pernambuco. It was observed that the fractionation of the reflected PAR radiation, absorbed, transmitted and reflected PAR by the soil and absorbed by the canopy varied according to the class of use and vegetation cover. In addition, as the density of vegetation increased, there was a decrease in transmitted PAR and reflected PAR and an increase in absorbed PAR and reflected PAR by the soil and absorbed by the canopy, on all the dates analyzed. It was also found that vegetated areas showed greater use of PAR radiation (greater absorption) compared to other areas such as urban infrastructure. The vegetation of the São Francisco Valley has great heterogeneity and, consequently, there is a complex relationship with the distribution of photosynthetically active radiation on the surface.