Estudo comparativo de parâmetros da vegetação sobre diferentes alvos utilizando dados do AVHRR e TM.

Abstract

In this study we try to find functional relationships between vegetation parameters estimated by the sensors AVHRR/NOAA and TM/LANDSAT-5 over different targets at Frutacor Farm and in the vicinity of Quixere, both located in the state of Ceara, in the years of 2005 and 2006. The TM/LANDSAT images were turned to a 1-km spatial resolution in order to yield a comparable spatial grid as AVHRR/NOAA images. The image reprojections were carried out by the Model Maker of the software ERDAS Image 8.7, using the SEBAL (Surface Energy Balance Algorithm for Land) parameterisation. The Least-square linear regression model was used to find functional relationships between various parameters estimated by the satellite, namely, NDVI, SAVI, L A I and albedo. The results showed striking differences in the spatial variability of the parameters over the two years studied. This is partly because 2005 was predominantly dry whilst 2006 was characterized as a rainy year. The functional relationship between AVHRR and TM data presented satisfactory correlation coefficients (r): rO.87 for NDVI, r=0.81 for SAVI, r=0.84 for L A I . The correlation coefficient for the albedo was, however, somewhat lower with a value o f r=0.62. Values of albedo estimated by the AVHRR and TM, and compared against values measured by the net radiometers CNR1, presented average errors of 1.25% and 3.57%, respectively. The vegetation fraction increased over almost the entire region during 2006, except in the irrigated area of Frutacor Farm which did not present any significant difference.