Evapotranspiração e produtividade primária bruta em áreas agrícolas utilizando técnicas de sensoriamento remoto surface temperature.

Abstract

The use of water in agriculture is a topic that has been discussed by the scientific community, mainly because it is one of the human activities that consume much more water on our planet. Evapotranspiration is a statement of fundamental climatic significance and plays an important role in the redistribution of energy and mass in our planet. The role of irrigated areas in requesting atmospheric C02 by vegetation is very important, especially in studies of climate change. Thus, this study aims to determine the actual evapotranspiration - ETr and water consumption in irrigated areas of the Perímetro Irrigado São Gonçalo – PISG, as well as the gross primary productivity - GPP, using remote sensing techniques. In this sense, we determined the radiation and energy balance through TM - Landsat 5 and OLI/TIRS - Landsat 8 imagery using the SEBAL / METRIC algorithm, and MODIS - Terra data for validation of the results of GPP. We evaluated the impact of topography on radiative balance and three targets were selected for validation of the results. Five images of TM and five of OLI/IRTS collected on the years 2008 and 2013, respectively, were selected. The surface albedo was obtained through the SEBAL and METRIC and the results showed that the METRIC promotes excessive atmospheric correction, leading to underestimation of the albedo. The areas of very steep topography exhibit great variability in instantaneous global solar radiation, directly impacting the net radiation data. It was evident that the net radiation obtained from Landsat 8 was substantially lower than that obtained with Landsat 5, most probably caused by calibration problems in OLI and TIRS sensors, especially in the thermal bands. The average Absolute and Relative Errors, and the Root Mean Square Error associated to the ETr values obtained with the SEBAL compared with ETr according to FAO-56, with Landsat 5 images were well below those obtained with Landsat 8, which may be a consequence of calibration problems and possibly the drought of 2013 year, which affected the irrigation system of the PISG. The ETr obtained by MOD16 was substantially higher than the values obtained by SEBAL, and far above the ETo from the days under investigation.