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Volume 83, Issue 5 p. 818-825
Crops

Instrument for Indirect Measurement of Canopy Architecture

J. M. Welles

Corresponding Author

J. M. Welles

LI-COR, Inc., 4421 Superior St., Lincoln, NE, 68504

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J. M. Norman

J. M. Norman

Dep. of Soil Science, University of Wisconsin, Madison, WI, 53706

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First published: 01 September 1991
Citations: 600

Abstract

Leaf area index (LAI) and leaf angle distribution are widely used indices of vegetative canopy structure that are difficult to measure directly. This study was conducted to test a commercially available instrument for rapidly determining LAI and foliage inclination information from “fisheye” measurements of light interception. The instrument's estimates of LAI are compared with direct measurements in soybean [Glycine max (L.) Merr.], winter wheat (Triticum aestivum L.), and prairie grass. The dominant grass species in the plots were indian grass [Sorghastrum nutans (L.) Nash], switchgrass (Panicum virgatum L.), and big bluestem (Andropogon gerardii Vitman). The instrument's LAI resolution was better than 3%, and its LAI error was generally less than 15%. Variations in sky brightness patterns caused variations in LAI estimates in winter wheat of less than 10%, and the presence of direct solar radiation increased LAI errors to more than 30% in canopies of differing species and LAI. In the presence of gaps in the canopy, the sensor's azimuthal view should be reduced. A simple test indicates if a canopy's gaps are significant.