研究目的
To derive the spatial patterns of photosynthetically active radiation (PAR) reflected and absorbed by a non-uniform forest canopy with a multi-species structure, and to retrieve forest canopy composition from reflected PAR measured along some trajectory above the forest stand.
研究成果
The results of numerical experiments using the 3D radiative transfer model showed that albedo of a mixed forest stand consisting of deciduous (birch) and coniferous (pine) was highly sensitivity to LAI, optical soil properties, and sun elevation. The proposed algorithm provided a feasible approach to determine species composition of a mixed forest stand from PAR reflectance properties. The accuracy of assessing vegetation species using this method depended on the number of points for canopy reflection measurements.
研究不足
The method accuracy strictly depends on the number of points for canopy reflection measurements. Tree species with similar optical properties (reflection, transmission and absorption coefficients) cannot be readily differentiated.
1：Experimental Design and Method Selection:
The study uses a three-dimensional radiative transfer model based on steady-state transport equations to simulate the radiative transfer in a non-uniform plant canopy. The model considers the radiative transfer as a function of the structure of individual trees and forest canopy, optical properties of photosynthesizing and non-photosynthesizing parts of the different tree species, soil reflection, and the ratio of incoming direct and diffuse solar radiation.
2：Sample Selection and Data Sources:
The study considers a mixed forest stand consisting of deciduous (Silver birch; Betula pendula Roth.) and coniferous (Scots pine; Pinus sylvestris L.) tree species. The spatial distributions of the trees of different species were simulated using a random number generator.
3：List of Experimental Equipment and Materials:
The study uses a 3D radiative transfer model and numerical experiments to simulate the radiative transfer in the forest canopy.
4：Experimental Procedures and Operational Workflow:
The study involves numerical experiments to simulate the radiative transfer in the forest canopy under different conditions of sun elevation, soil reflection properties, and forest canopy density.
5：Data Analysis Methods:
The study uses the least square method and Tikhonov regularizing algorithm to retrieve the forest species composition from the intensity of reflected radiation measured by remote sensing at several points above the forest canopy.
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