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This article in AJ

  1. Vol. 63 No. 5, p. 739-743

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A Sunfleck Theory for Plant Canopies II. Penumbra Effect: Intensity Distributions along Sunfleck Segments1

  1. E. E. Miller and
  2. J. M. Norman2



The finite (1/2°) angular diameter of the sun causes the fuzziness of the shadow cast onto the ground by a leaf edge to increase in proportion to increase in height of the leaf. When a straight-line sunfleck segment is terminated by a leaf edge that cuts across it at a slant, the apparent width of the penumbral fringe displayed upon the segment-is stretched by the slant.

In this paper the intensity distribution along a slanting traverse of a penumbral shadow edge is computed, the statistical distributions of leaf-edge angles at the ends of segments are analyzed, and these two distributions are combined into a statistically-averaged intensity distribution along the segment, the distribution being dependent upon the segment length. When this intensity distribution is incorporated into the segment length distribution from the preceding paper of this series, a useful prediction is obtained for the complete distribution of intensity within a plant canopy.

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