Estimativa do balanço de radiação à superfície terrestre utilizando imagens TM - Landsat 5 e modelo de elevação digital.

Abstract

The objective of this research was the determination of the surface radiation balance, by using images of TM - Landsat 5 and Digital Elevation Model. Two images, generated on December 04, 2000 and October 04, 2001, in the orbit 217 and point 67, were used in the study. The calculations were accomplished with and without the use of the Digital Elevation Model. The atmospheric transmissivity and the surface emissivity did not present significant variations, showing uniformity in both methods. The Normalized Difference Vegetation Index presented small variation among the methods. The albedo values with DEM were larger than the albedo without DEM in both years. They presented values between 6.9% to 46.4% for 2000; 4.1% to 42.0%, for 2001, with DEM and without DEM, 6.5% to 37.8%, for 2000 and 4.9% to 40%, for 2001. The surface temperature with DEM, for the 04/12/2000 varied from 22.74ºC to 35.80ºC and presenting values a little larger than the one without DEM, which presented variation from 22.18ºC to 37.35ºC. For 2001 the surface temperature was practically the same with and without DEM. The incident long wave radiation (RL) values presented difference of 32 Wm-2 in 2000 and 33 Wm-2 in 2001, with the correction of the surface thermal radiance. The instantaneous values of the surface net radiation for selected areas using MED for 04/12/2000 were: at P1, Rn = 431.45 Wm-2 with an inclination of 7o for northeast; at P2, Rn = 543.33 Wm-2, with inclination of 3o for northeast; at P3, Rn = 489.24 Wm-2 with inclination of 14o for southeast and at P4, Rn = 621.72 Wm-2 with inclination of 9o for southeast. The values of the same areas to the same year, without the application of DEM, were: at P1, Rn = 424.81 Wm-2; at P2, Rn = 583.22 Wm-2; at P3, Rn = 546.0 Wm-2; and at P4, Rn = 719.25 Wm-2. For 2001 year, at P1 Rn = 312.63 Wm-2 with inclination of 7o for northeast; at P2, Rn = 575.21 Wm-2 with inclination of 1o fro southeast; at P3, Rn = 493.16 Wm-2 with inclination of 2o for northeast; and at P4, Rn = 701.31 Wm-2 with inclination of 1o for the southeast.Without the application of DEM they were: at P1, Rn = 399.50 Wm-2; at P2, Rn = 618.0 Wm-2; at P3, Rn = 547.61 Wm-2; and at P4, Rn = 744.53 Wm-2. The results of the net radiation corrected with the DEM were smaller than the Rn without such correction, showing the importance of taking in consideration the topographical effects over the incident solar radiation.