Abstract
Vegetation radiative transfer models (RTMs) are important tools to understand biosphere-atmosphere interactions. The four-stream theory has been successfully applied to solve the radiative transfer problems in homogeneous canopies for both incident solar radiation, thermal and fluorescence emission since 1984. In this note, we describe the development of a unified radiative transfer theory for optical scattering, thermal and fluorescence emission in multi-layer vegetation canopy, and provide a detailed mathematical derivation for the fluxes inside and leaving the canopy. This theory can be used to develop vegetation models for remote sensing applications and plant physiological processes, such as photosynthesis and transpiration. It can also be used to solve the radiative transfer problems in soil-water, soil-water-atmosphere, or soil-vegetation-atmosphere ensembles, besides the soil-vegetation system presented in the note.
Highlights
Vegetation radiative transfer models (RTMs) describe the interaction between light and vegetation canopies, and they simulate radiative fluxes within and above vegetation canopies
This note presents a theory for the simulation of all the four streams, including fluxes in the viewing direction, which supports remote sensing applications
The fluxes inside the canopy can be used to predict net radiation and photosynthesis. This theory can be applied as a component in vegetation energy balance, photosynthesis, or physiological models
Summary
Vegetation radiative transfer models (RTMs) describe the interaction between light and vegetation canopies, and they simulate radiative fluxes within and above vegetation canopies. A unified four-stream theory has been established to solve radiative transfer problems of optical radiation, thermal and fluorescence emission for homogeneous canopies. To investigate the effects of vertical heterogeneity of leaf properties on reflectance, photosynthesis and fluorescence, Yang et al [9] adapted the four-stream theory to multi-layer vegetation canopies for the radiative transfer of optical radiation and fluorescence emission and and developed the mSCOPE model (i.e., multi-layer SCOPE). We focus on the explicit derivation of the four-stream radiative transfer theory in multi-layer vegetation canopies when thermal and fluorescence emission of radiation by leaves and the soil is incorporated. We expect this note could help the readers to better understand the use of the four-stream theory in vegetation radiative transfer modeling and the radiative transfer theory in SAIL, SCOPE, and mSCOPE
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