Abstract

A plant canopy gap-size analyzer, the Tracing Radiation and Architecture of Canopies (TRAC), developed by Chen and Cihlar [Appl. Opt. 34, 6211 (1995)] and commercialized by 3rd Wave Engineering (Nepean, Canada), has been used around the world to quantify the fraction of photosynthetically active radiation absorbed by plant canopies, the leaf area index (LAI), and canopy architectural parameters. The TRAC is walked under a canopy along transects to measure sunflecks that are converted into a gap-size distribution. A numerical gap-removal technique is performed to remove gaps that are not theoretically possible in a random canopy. The resulting reduced gap-size distribution is used to quantify the heterogeneity of the canopy and to improve LAI measurements. It is explicitly shown here that the original derivation of the clumping index was missing a normalization factor. For a very clumped canopy with a large gap fraction, the resulting LAI can be more than 100% smaller than previously estimated. A test case is used to demonstrate that the new clumping index derivation allows a more accurate change of LAI to be measured.

© 2002 Optical Society of America

Plant canopy gap-size analysis theory for improving optical measurements of leaf-area index

Jing M. Chen and Josef Cihlar
Appl. Opt. 34(27) 6211-6222 (1995)

Plant canopy light absorption model with application to wheat

J. E. Chance and E. W. LeMaster
Appl. Opt. 17(16) 2629-2636 (1978)

Coupled atmosphere/canopy model for remote sensing of plant reflectance features

Siegfried A. W. Gerstl and Andrew Zardecki
Appl. Opt. 24(1) 94-103 (1985)

Optical characteristics of individual plant elements and plant canopies grown under radiation regimes of different spectral composition and intensity

A. A. Tikhomirov and F. Ya. Sidko
Appl. Opt. 22(18) 2874-2881 (1983)

Canopy architecture measured with a laser

Vern C. Vanderbilt, L. F. Silva, and M. E. Bauer
Appl. Opt. 29(1) 99-106 (1990)