Validation and Evaluation of the Three-Dimensional Analytical Radiative Transfer Model ESRT in Heterogeneous Forest Canopy

The complicated spatial heterogeneity in forest scenes is an important challenge in radiative transfer modeling. To overcome the excessive simplification of forest scenes by classical analytical models and the efficiency limitations of computer simulation models, we developed a three-dimensional (3D) analytical radiative transfer model called ESRT (Stochastic Radical Transfer model for forests with hEterogeneous canopy structure) by extending the stochastic radiative transfer theory. At present, the application of ESRT in different complex forest scenes still needs to be explored, and more field data is essential for model verification. In this study, we validated the performance of ESRT in simulating different kinds of heterogeneous forest canopy reflectance based on survey data from 21 mixed forest plots and 50 pest-stress forest plots, and evaluated the effect of mixing and pest levels on forest canopy reflectance. The results showed that compared to the original SRT model, the extended ESRT model can more accurately simulate the canopy reflectance of mixed forests and pest-damaged forests, showing better consistency with the measured spectra from the sample plots. The conifer-broadleaf ratio and the vertical distribution of damaged foliage can both affect the canopy spectral signals. This study provides a theoretical basis for applications of ESRT in complex forest simulation.