Effect of Shadows on the Reflectance Spectra of Vegetation and their Digital Classification.
Abstract
Change in solar altitude alters the reflectance spectra of the plant canopy by affecting the highlight/shadow ratio of the canopy. The reflectance spectra of canopies with high contrast between sunlit and shaded leaves had a strong, direct relation with solar altitude, e.g., the visible and NIR regions of gray colored plants and the NIR region for green colored plants. Canopies with low reflectance contrast did not have a strong relation with solar altitude, e.g., the visible region for green plants. The anisotrophic effect of solar altitude on the visible and NIR reflectance varied the NIR/Red and Normalized Difference Vegetation Index ratios, commonly associated with plant productivity parameters. These ratios varied inversely with solar altitude. These results are directly applicable to Army tasks involving the detection of change in terrain conditions by means of multi-date, multi-spectral imagery. The use of band ratio techniques or imagery adjustments for shadow must consider the effect of solar altitude on the reflectance spectra of different colored vegetation in the vegetation-soil mosaic. The multi-temporal spectral imagery should by normalized for the vegetation spectral difference associated with solar altitude differences that occur daily, seasonally, or latitudinally.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 30, 1985
- Accession Number
- ADA188143
Entities
People
- Jack N. Rinker
- Melvin B. Satterwhite
Organizations
- Geospatial Research Laboratory