Densidade de biomassa na Amazônia Legal : estimativa com modelos espaciais
Marina Paez
In this work our aim is to estimate the biomass density over Amazônia Legal, extrapolating the punctual data from the project Radam-Brasil. Under the hypothesis that the density, or one of it's components, varies smoothly in space, we worked with two different model specifications: Armae [Anselin (1988)] and PVE [Besag (1975) and Gamerman, Moreira and Rue (2001)]. To specify the models we considered two preliminary tasks: establish a criterion to define neighborhood and choose explanatory variables. After some analysis, we established an 80 km limit of neighborhood. We chose the best solo and vegetal classification available, and obtained the best model. To analyze the effect of rainfall data in this model it was necessary to extrapolate the original data (observed in other locations then Radam), but this extrapolation didn't help to increase the model explanatory power. We suggested three specifications to the neighborhood matrix W, one considering 0-1 weights, and two with weighs depending on the distance between the points and a decay parameter. We verified that these last two models were superior by the model comparison criterion of Gelfand and Ghosh (1998). Graphically, however, it's not possible to observe such superiority. The PVE model was better then the Armae ones by the Gelfand and Ghosh criterion and graphically it showed to fit the data better.