Vegetation reflectance is a function of tissue optical properties, canopy biophysical attributes, viewing geometry, illumination conditions and background effects (Asner, 1998; Barret and Curtis, 1992; Goel, 1998; Jacquemoud et al., 1992; Myneni et al., 1989; Ross, 1981). The biophysical attributes of a vegetation crop shows canopy reflectance characteristics due to three dimensional orientations that provides better structure and opportunities for photons to interact with multiple surfaces of different plant parts, this favouring radiometric reception. Various biochemical factors also affect vegetation reflectance. Weeds and pest infestation strongly affect vegetation reflectance depending on the magnitude of interference. Application of multispectral remote sensing to crop condition monitoring has been adopted for various purposes (Cloutis et al., 1996; Franandez et. al., 1994; Wallace et al., 1993). In many case spectral responses of crop conditions have been somewhat mixed due to lack of high spectral resolution and to various symptom causing agents occurring at the same time (Carter, 1993; Tingle; Malthus and Madeira, 1993 and Stoll, 1990). Such information is helpful in assessing the growth status of crop vegetation, in discriminating between species and genotypes and in estimating productivity from remotely sensed datasets (Blackburn, 1998; Yoder and Pettigrew-Crosby, 1995).  Figure 8: Spectral information in the image (Janssen, 2001) 1.2.4.1. Generation of Spectral Profiles from LANDSAT, LISS III and ASTER Images: Using the LANDSAT, LISS III and ASTER images, the spectral reflectance profiles were generated. The classes were identified from the images and then the profiles were generated using the standard deviation values. The variations in the bands show the reflectance of different classes present in the images. It was observed from the images that river bed gave the highest reflectance for all the images. In the LANDSAT image, the NIR band showed the high reflectance value for healthy, moderately healthy and diseased tea patches. The LISS III showed high reflectance value in the Band1 (Green) for healthy, moderately healthy and diseased tea patches while Band1 (Green) in ASTER showed high reflectance value for healthy, moderately healthy and diseased tea patches. The profiles have been shown in the results and discussion chapter.  Figure 9: Spectral Reflectance of Healthy Vegetation Source: Janssen and Huuenemen (2001) |