Obtenção de parâmetros biofísicos e evapotranspiração da cana-de-açúcar mediante imagens orbitais na região do sub médio São Francisco.

Abstract

The new technologies application such as remote sensing and geographic information systems have been of great importance in environmental studies, specially to monitoring of large cropped irrigated areas, with trading products, meanly. The sustainable use of water resources in view to increase of the competitive water utilization which contributes to the expansion of much more productive areas, and thus making sure the food availability around world. In recent years several algorithms were developed to determine the crops actual evapotranspiration through remote sensing data obtained as a residual of the energy balance at the earth's surface, which have been applied and validated in many countries in world, including Brazil. The objective of this work was to evaluate the efficiency of water use in Agrovale as of actual daily evapotranspiration data estimated by TM-Landsat 5 images and SEBAL/METRIC algorithms for the whole sugarcane area. The studied area is located in Northeast of Brazil, in semi-arid region close to Sao Francisco River, (8° 59'and 9° 50' S; 39° 29' and 42° 30' W; 389 m). It was used five satellite images of TM-Landsat 5 sensor of 12TH October 2004,13T H November 2004,15T H October 2005, 30TH July 2006 and 22N D January 2005 of Sao Francisco region and the sugarcane irrigated area was delimited. For the days of images besides of the evapotranspiration, it was also evaluated by the model, the soil water content, fresh biomass, bioproductivity and water productivity parameters. The soil water content was estimated using evaporative fraction data and the values obtained presented uniformity and it was not observed distortion of them amongst the studied days, showing, however, higher spatial variability in the surface irrigated areas irrigated, furrow irrigation. The instantaneous values of the energy balance components and actual evapotranspiration estimated by the model were validated with data measured at surface by Bowen ratio method so that the net radiation (Rn) and latent heat flux (ALE) showed satisfactory results for the days 211 of 2006 and 22 of 2007, presenting relative error around 9.20% between the values of Rn in 2006 and 5.62% for the values of ALE referring to the day 22 of2007. The sensible heat flux (H) results showed significant differences between the values estimated by the model and that ones measured at surface with high relative error in the two dates. The soil heat flux was the component that showed a greater discrepancy between the values estimated and measured at surface. The actual evapotranspiration values estimated and measured presented good agreement and values of 5.85 mm day-1 and 7.96 mm day-1 estimated by the model and 4.70 mm day-1 and 6.43 mm day-1 measured at surface. It observes which the averaged values of the water productivity estimated by the SEBAL/METRIC model in the day 2 1 1 of 2006 varied from 5,52 kg m-3 to 7,40 kg m-3. In all images the highest values of |he estimated parameters were identified in the center pivot irrigated areas, which may be related to permanent using of irrigation and efficient practice management.