The provided codes allow to compute leaf area index (LAI) from the simultaneous measurements of the photosynthetically active radiation (PAR) above and below canopy under all sky conditions (clear sky-cloudy).
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Daughtry CST. 1990. Direct measurements of canopy structure. Remote Sensing Reviews 5:45-60.
Norman JM, Jarvis PG. 1974. Photosynthesis in Sitka Spruce (Picea sitchensis (Bong.) Carr.). V. Radiation penetration theory and a test case. Journal of Applied Ecology 12:839-878.
Norman JM, Welles JM. 1983. Radiative transfer in an array of canopies. Agronomy Journal 75:481-488.
Wang YP, Jarvis PG. 1988. Mean leaf angles for the ellipsoidal inclination angle distribution. Agricultural and Forest Meteorology 43:319-321.