Abstract: 【Objective】 To seek a fast and accurate method for determining the light transmission rate and extinction coefficient.【Method】The LAI, foliar obliquity, canopy openness and light transmission rate in different plant colonies were measured using canopy analyzer LAI-2000 and the solar radiation instruments including the data logger LI-1400, solar radiation sensor LI-190 and LI-191.【Result】 (1) the canopy openness measured by using LAI-2000 had a very close relationship with the sunlight transmission rate of the colonies. The correlation coefficient was 0.9308, the intercept of the regression line was 0.015, which was almost equal to 0, and the slope was 1.0668, which was almost equal to 1. So the canopy openness could be used to estimate the light transmission rate, and the cloudy weather was more suitable. (2) Using the measured LAI and colony light transmission rate, the extinction coefficient of different canopies were calculated accurately. Under the corn canopy, the extinction coefficient changed clearly during the daytime. It had two maximum values and one minimum value. The minimum value happened in the noon.【Conclusion】LAI-2000 canopy analyzer can provide the sky openness of different zenith angles, so it can describe the colony structure in detail; The canopy openness under the canopy is almost equal to the light transmission rate, therefore the measurement of light transmission rate no longer needs the light measurements of over and under the canopy. The LAI of agricultural and forestry canopy measured by LAI-2000 without damaging the colony can be used to calculate the extinction coefficient, and the extinction coefficient calculated in this paper is close to those reported in the references.

Key words: canopy analyze, light penetrating rate, extinction coefficient, LAI-2000 canopy analyzer