Canopy transmittance was measured at 1200 and 1400 local solar time using an integrating radiometer on seven coniferous forest stands in western Montana, ranging in projected leaf area index (LAI) from 1.7—5.3 m2/m2. Transmittance of each 1—ha stand was measured at 96,000 points, yet measurement required <1 h because the instrument instantaneously integrates 80 radiometer measurements at once. The Beer—Lambert Law was inverted to estimate LAI using measured transmittance and an extinction coefficient of 0.52. LAI estimated by transmittance was highly correlated with LAI measured by sapwood—based allometric equations at both the 1200 (R2 = 0.97) and 1400 (R2 = 0.94) measurement times. The results suggest that the technique has a wide applicability given the range of LAIs, stand densities (450—4140 trees/ha) and illumination angles (32°—57°) under which it was tested.
© 1988 Ecological Society of America
Pierce, L. L. and Running, S. W. (1988), Rapid Estimation of Coniferous Forest Leaf Area Index Using a Portable Integrating Radiometer. Ecology, 69: 1762–1767. doi:10.2307/1941154