Abstract
The paper introduces a three-dimensional model to derive the spatial patterns of photosynthetically active radiation (PAR) reflected and absorbed by a non-uniform forest canopy with a multi-species structure, as well as a model algorithm application to retrieve forest canopy composition from reflected PAR measured along some trajectory above the forest stand. This radiative transfer model is based on steady-state transport equations, initially suggested by Ross, and 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. Numerical experiments showed that reflected solar radiation of a typical mixed forest stand consisting of coniferous and deciduous tree species was strongly governed by canopy structure, soil properties and sun elevation. The suggested algorithm based on the developed model allows for retrieving the proportion of different tree species in a mixed forest stand from measured canopy reflection coefficients. The method accuracy strictly depends on the number of points for canopy reflection measurements.
Highlights
Solar radiation is both a direct and indirect driver for most biophysical and biochemical processes occurring in plant ecosystems
In this study we developed and applied a 3D model of radiative transfer in a non-uniform plant canopy to derive the possible influence of multi-specific forest structure on reflected photosynthetically active radiation (PAR)
Numerous experimental and modeling studies during recent decades showed that PAR albedo measured by different remote sensing equipment or by devices installed at meteorological towers can be broadly used to estimate canopy structure and architecture, surface net radiation, gross and net primary production, etc. [25,37,38,39,40]
Summary
Solar radiation is both a direct and indirect driver for most biophysical and biochemical processes occurring in plant ecosystems. It influences canopy microclimate as well as CO2 and H2O exchange processes between plants and the atmosphere [1,2], thereby affecting the function and growth of the plant community, and the concentration of greenhouse gases in the atmosphere and Earth’s climate system [3,4]. Plant canopy reflection and absorption of solar radiation are determined by factors including the structure of vegetation cover, the optical properties of photosynthesizing and non-photosynthesizing parts of plants, surface topography, and soil [1,5]. A limited number of input parameters allow these models to be used for a broad spectrum of scientific tasks, including solving direct and inverse problems related to remote sensing [10,15,20]
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