关键词: 计算虚拟测量, 虚拟样地, 光照条件, 冠层遮荫, 三维建模

Abstract:

Objective: In this study, thecomputational virtual measurement (CVM) method was employed to simulate and measure virtual trees within virtual forest sample plots, aiming to acquire biological parameters that are difficult to measure in reality. The technical workflow integrated the construction of virtual sample plots (VSP), tree modeling, and light simulation to quantitatively analyze the impact of adjacent tree canopy shading on the lighting of target trees, explore the role of leaves in light simulation to optimize VSP technology, and improve the accuracy of lighting analysis. Method: An integrated multi-scale modeling technical framework was constructed. Context Capture Center (CCC) for point cloud reconstruction technique, quantitative structure models (QSM), and Voxel modeling methods were comprehensively applied to achieve cross-scale three-dimensional reconstruction from individual tree organs to community canopies. A physics-based dynamic light transport model was introduced, combined with a digital terrain model (DTM) and a solar trajectory simulation algorithm, to construct a realistic virtual light environment. The dual comparative scenarios of “full day illumination” and “neighborhood shading” were designed to systematically analyze the spatiotemporal change patterns of light energy interception by target trees under the dynamic shading influence of neighboring canopies, and effectively isolate the pure energy loss attributable to shading. Result: The results demonstrated that the shading from neighboring trees caused a solar radiation loss of 35.80% to 45.72% for the target trees, indicating high reliability of this method. The model structure significantly influenced the simulation outcomes: the models incorporating leaves exhibited stronger light attenuation effects. The energy loss rate for sample tree T26 followed the order: CCC model (45.72%) > Voxel model (39.26%) > QSM model (35.80%), confirming that geometric completeness is crucial for assessing shading effects. Canopy structural characteristics also predominantly governed the differences in energy loss. The loss for mature Betula pendula T27 with a sparse canopy (35.80%) was significantly lower than that for young Picea asperata T26 with a dense canopy (45.72%), revealing that young trees are more susceptible to suppression from shading. After data correction, the response characteristics of the different models across various light gradients were clarified, reflecting the influence of light environment heterogeneity on the simulation results. Conclusion: This study successfully achieves precise quantification of the shading effects from neighboring trees in forests by integrating the VSP-CVM methodology. The VSP technology proves capable of accurately reconstructing three-dimensional stand structures and supporting light energy distribution simulations with millimeter-level precision, generating more detailed light environment data compared to traditional measurement methods. This method not only overcomes the limitations of traditional measurement methods, but also provides a new technological means for the study of forest light competition. In the future, it can be expanded to multiple climate zones and forest types to verify its universality, and the photosynthesis process model can be integrated into the meteorological model framework to improve the simulation of light energy utilization processes, providing scientific basis for precise forest management and structural optimization.

Key words: computational virtual measurement (CVM), virtual sample plot (VSP), light conditions, canopy shading, three-dimensional modeling