© 2000 Heron Publishing—Victoria, Canada
Light spectral composition in a tropical forest: measurements and model
Francisco de Castro (1, 2)
1. Department of Biology, University of Puerto Rico, P. O. Box 23360, UPR. Río Piedras, Puerto Rico 00931-3360, USA / 2. Department of Fisheries and Wildlife, University of Minnesota, 200 Hodson Hall, 1980 Folwell Avenue, St. Paul, MN 55108, USA (fdecastr@rabbit.gis.umn.edu) / Received February 18, 1999
Summary
I present a simple model that simulates vertical variations in the light spectrum within a forest canopy. The model considers
only the vertical, downward transmission of light. The light in each canopy level was assumed to consist of non-intercepted
radiation and radiation intercepted within the level and transmitted. The spectrum of non-intercepted light in each canopy
level is the same as that of incident light above the canopy (input parameter), whereas the spectrum of transmitted light
depends on leaf area index (LAI) and the mean transmission spectrum of leaves. The model was tested in a forest and provided
adequate predictions of measured values. Stronger deviations were produced in the near infrared (NIR) waveband in lower canopy
levels. Multiple regression between LAI, as the dependent variable, and spectral characteristics (Blue, Green, Red and NIR
intensities) had an r2 of 0.926. As a complement to other methods, I suggest light spectrum analysis as a non-destructive technique for estimating
LAI in forest canopies.
Keywords:
canopy, irradiance, radiation, leaf area index, Puerto Rico, transmission.
