Although there are several parameters of interest in the quantitative aspects of vegetative remote sensing, leaf area index (LAI) has been one of the most useful and important parameters to characterize the vegetation activities from local to global scales. LAI, defined as the sum of the leaf area per unit ground area, can be used to measure the activities (photosynthesis, transpiration, and evapotranspiration) and the production of plant ecosystems (Pierce and Running, 1988; Bonan, 1993). The measurement of LAI on the ground is very difficult and requires a great amount of labor and cost (Gower et al., 1999). Since the plant canopy is composed of leaves, which is a direct source of the energy-matter interactions in most earth-observing remote sensing systems, LAI has been an attractive variable of interest in vegetative remote sensing.