Simulation of Multitemporal and Hyperspectral Vegetation Canopy Bidirectional Reflectance Using Detailed Virtual 3-D Canopy Models

Abstract

The influence of plant and canopy architecture on canopy bidirectional reflectance and the BRDF is subject of this study. To understand BRDF-influenced reflectance signals, this influence must be identified and quantified, which requires detailed knowledge concerning the structure and BRDF of the observed canopies. BRDF measurements of in-situ canopies are time-consuming and depend on the availability of a field goniometer. In contrast to field measurements, computer based simulations of the canopy BRDF offer an alternative approach that considers parameter-driven setups of virtual canopies under constant illumination conditions. This paper presents the HySimCaR system, which has been developed in the context of the EnMAP mission. This spectral, spatial and temporal simulation system consists of detailed virtual 3D cereal canopies of different phenological stages, whose geometries are linked to corresponding spectral information. The system enables the simulation of realistic bidirectional reflectance spectra on the basis of virtual 3D scenarios by incorporating any possible viewing position with ray tracing techniques. The parameterization of a number of canopy structure parameters, such as phenological stage, row distance and row orientation, enables the modeling of the bidirectional reflectance and based on them the approximation of the BRDF for many structurally different cereal canopies. HySimCaR has been validated with respect to structural and spectral accuracy using three cereal types, including wheat, rye and barley, and 13 different phenological stages. The results show that the virtual cereal canopies are recreated in a realistic way, and it is possible to model their detailed canopy bidirectional reflectance and their BRDF using HySimCaR.

Influence of the Viewing Geometry Within Hyperspectral Images Retrieved From Uav Snapshot Cameras

“…Thus, they are closer to the hotspot feature apparent for anisotropic surfaces and show a higher reflectance. These results aligns with other studies, which also found that the relative influence of the view angle on the apparent reflection of vegetation in the VIS is considerable higher than in the NIR, were light is scattered within the canopy Küster et al, 2014;Sandmeier et al, 1999;Schläpfer et al, 2015).…”

“…Additionally, they show a hotspot feature directed towards the direct incidence irradiance, which is more pronounced in the visible region (VIS) than in the near infrared region (NIR). Additionally, at nadir they show a local maximum in the VIS and an local minimum at the NIR (Gerstl and Simmer, 1986;Küster et al, 2014).…”

The EnMAP Spaceborne Imaging Spectroscopy Mission for Earth Observation

“…The approach uses a tightly-coupled system of crop growth and crop radiative transfer models to derive spatio-temporal fields of crop parameters through iterative ensemble analysis [57]. A model for the realistic simulation of the hyperspectral and multiangular reflectance response of virtual 3D cereal canopies has also been implemented in the framework of EnMAP [58].…”

Generation and application of hyperspectral 3D plant models: methods and challenges

“…In an inverse conception, illuminated leaves can be seen as light sources emitting a distorted light spectrum. High-performance simulation techniques and hyperspectral ray-tracing methods are requirements to exploit the full potential of the sensor signal [21] and at the same time for the generation of more realistic 3D plant models for virtual reality applications. Therefore, computer vision may contribute an important share to trends in plant science.…”