A scalable plant-resolving radiative transfer model based on optimized GPU ray tracing

Abstract

A new model for radiative transfer in participating media and its application to complex plant canopies is presented. The goal was to be able to efficiently solve complex canopy-scale radiative transfer problems while also representing sub-plant heterogeneity. In the model, individual leaf surfaces are not resolved, but rather vegetation is aggregated into isothermal volumes. Using the leaf angle distribution and leaf area density functions, the volumes realistically augment the radiation field through absorption and anisotropic scattering and reemission. The volumes are grouped to form individual plants, and individual plants are grouped to form entire canopies. The model increases efficiency by performing ray tracing calculations on graphics processing units (GPUs) using the NVIDIA R ⃝ OptiX TM and CUDA TM frameworks, and through efficient algorithms for radiation reflection, scattering, and emission. This efficiency allows for realistic representation of heterogeneity, while also allowing for the solution of problems with very large domains (∼ 10 5 trees) quickly on an inexpensive desktop workstation. Problem execution time scaled nearly linearly with the number of discrete elements in the domain. Model results are compared with experimental data collected from an array of radiation sensors within and above a grapevine canopy and an isolated tree. Agreement between simulated and measured values of shortwave and longwave radiation were very good, with model predictions generally within the expected measurement accuracy.

Evaluating the use of Beer's law for estimating light interception in canopy architectures with varying heterogeneity and anisotropy

“…Grape leaf inclination was skewed toward vertical, and leaf azimuth tended to be oriented parallel with the row (Fig. 2), which is supported by previous manual and LiDAR measurements (Bailey et al, 2014;Bailey and Mahaffee, 2017b).…”

“…The total incoming solar flux was partitioned as 47% in the PAR band and 53% in the NIR band. In the PAR band, ρ was set to 0.056 and τ to 0.042, while in the NIR band, ρ was set to 0.425 and τ to 0.334 (Bailey et al, 2014).…”

“…While this is a simple and practical means of reducing the amount of radiation attenuation predicted by Beer's law, the challenge in applying the clumping coefficient approach is that Ω is a complex function of nearly every applicable variable (Chen et al, 2008), and thus is it is difficult to mechanistically specify. Another approach is to use a model that explicitly resolves plant-level heterogeneity (e.g., Norman and Welles, 1983;North, 1996;Bailey et al, 2014), as it may not be necessary to explicitly resolve every leaf if within-plant heterogeneity is small.…”

Influence of 3D Spruce Tree Representation on Accuracy of Airborne and Satellite Forest Reflectance Simulated in DART

“…Steadily increasing computational capabilities allow for radiative transfer simulations of highly complex 3D canopies wherein the level of detail reaches to the individual leaf or needle. Such examples include the Raytran model of Govaerts and Verstraete [25], radiosity-graphics model of Qin and Gerstl [26], scalable plant RT model of Bailey et al [27] and Discrete Anisotropic Radiative Transfer (DART) model of Gastellu-Etechgorry et al [28,29].…”

The Air-temperature Response to Green/blue-infrastructure Evaluation Tool (TARGET v1.0): an efficient and user-friendly model of city cooling

“…The most complex models are primarily based on computational fluid dynamics (CFD) techniques. These include ENVI-met, hand-coded CFD models (such as OpenFOAM; OpenFOAM, 2011;or STAR-CD;CD-adapco, 2011) and other CFD-based approaches (Bailey et al, 2014(Bailey et al, , 2016Kunz et al, 2000;Schlünzen et al, 2011;Yamada and Koike, 2011;Bruse, 1999). ENVI-met is the most commonly used urban microclimate model.…”