A Comparison of Two Photographic Techniques for Estimating Foliage Angle Distribution

Abstract

There is an increasing interest in theoretical models which describe the interaction of solar radiation with vegetation canopies. Common to these models is a need to describe mathematically the geometric structure of the plant canopy. The amount of radiation reflected or absorbed by the canopy is primarily determined by the distribution of gaps in the foliage with respect to the radiation source. A measure of canopy geometry related to gap frequency at various view angles is the distribution of leaf angles. Two methods for measuring the distribution of leaf angles are discussed. The first method is to project orthogonally and photograph individual plants and relate the measured leaf angles in the projections to the canopy distribution of angles. The second method is a rapid in situ method based on ground level multiple view angle photography. A Fredholm integral equation relating foliage angles to the proportion of gap in the canopy as a function of view angle is then solved. Comparisons of the results using the two methods are made for a canopy of Western wheat grass (Agropyron smithii).