Accupar LP-80 by Decagon Devices estimates LAI based on light (photosynthetically active radiation – PAR) measurements done above and below canopy.
The instrument comprises of a probe with 80 PAR sensors. It calculates LAI based on Beer’s law and utilising ratio of PAR measurements done above and below canopy. The model calculates radiation extinction coefficient based on canopy specific values of leaf angle distribution. The device is readily used in short and regular canopies.
The LAI measurements by LP-80 have been found to be reasonably accurate even with the default parameters, however, the instrument is prone to limitations such as measuring woody components in forested areas, inaccuracies in highly heterogeneous canopies and also limited due to requirement of steady radiation conditions while taking above and below canopy measurements. The accuracy is also dependent on measurement protocol followed.
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Wilhelm, W. W., Ruwe, K. & Schlemmer, M. R. Comparison of three leaf area index meters in a corn canopy. Crop Sci. 40, 1179–1183 (2000).