Spectral analysis of radiation transmitted and reflected by different vegetations

Abstract

Summary The spectral composition of the short wave radiation (400–1,050 nanometres) transmitted and reflected by 16 contrasting vegetation types is given. The transmission and reflection spectra were similar for a particular vegetation. All green vegetation had low reflection and transmission of visible radiation and high of infra-red radiation. By contrast, dry and dead vegetation showed a continuons increase through the visible and infra-red. The infra-red transmission and reflection spectra of green vegetation tended towards three types: (1) Approximately uniform levels at all wavelengths. (2) Increasing transmission or reflection at the longer wavelengths. (3) In one case (sweet corn) decreasing reflection at the longer wavelengths. Reported single leaf studies show the first pattern only. In the visible radiation there were considerable differences in the proportion of green radiation transmitted or reflected by the different vegetations, some having a sharp peak and others having none. Transmission spectra showed a higher proportion of blue as compared with reflection spectra. The relative transmission coefficient between wavelengths changed for the upper and lower parts of the canopy. There was a difference in the amount of radiation reflected in various directions. Over all vegetations 43% more radiation was reflected back in the direction of the sun as compared with that reflected vertically upwards.