B. St-onge, Topographic effects on the texture of high-resolution forest-stand images measured by the semivariogram, PHOTOGR E R, 65(8), 1999, pp. 923-935
By studying the statistical relationship between terrain gradient and the r
ange of the semivariogram of simulated high resolution images of forest sta
nds, we assessed the effects of topography on estimates of tree size and de
nsity obtained through texture measures. Three-dimensional computer models
of hardwood and softwood forest stands were overlaid on slopes of varying g
radient. Using a geometrical-optical approach, one-meter-resolution images
were generated in 120 series representing different combinations of forest
types and sun-terrain geometry. The range of the semivariogram of these ima
ges was measured in four directions and its relation with gradient was eval
uated through regression. Results show that topography affects texture most
ly in sparse stands, and that the gradient-induced absolute error in the es
timates of tree size and density is low.