Appraisal of multispectral scanner systems from analysis of high-resolution plant spectra

Abstract

The use of high-resolution spectra (⩾ I nm resolution) obtained from plants with a ground-based spectroradiometer for selecting multiband scanners and determining bandwidth suitability is presented (350-1850 nm) The highly structured features of crop radiance requires careful analyses to minimize the number of bands, the irrelevent radiance data and subsequent digital analyses. Several structural features were clearly defined at early stages of plant development and became progressively indiscernible as maturity approached. These occurred at wavelengths known to be affected by chlorophyll concentration and leaf structure (e.g. 640-680 nm, and near infrared from 730-690 nm) by H and Mg compounds (480-520 nm bands) and water (720 nm) Several others varied without known association. Others varied little with crop development but coincided with the molecular absorption bands of different chemical elements (e.g. Ca and Fe, 430 nm and 0₂ The bandwidths of the various structural features were compared to the bandwidths of the channels for several space- and airborne multispectral systems. The comparisons of the radiance values showed that only a few of the channels in each system had bandwidths corresponding to structural features associated with specific plant characteristics and chemical compounds. Thus, much of the spectral data obtained would have little specificity for identifying or measuring biophysical properties of crops. Similar care in the selection of filters for photographic systems would also be applicable. A numerical system for identifying bands of uniform radiance is presented to facilitate referencing of the various bands