KEYWORDS: Photons, 3D modeling, Scattering, Monte Carlo methods, Multiple scattering, Computer simulations, Sun, Performance modeling, Data modeling, Reflectivity
In mountainous regions, the radiometric signal recorded at the sensor depends on a number of factors such as sun angle,
atmospheric conditions, surface cover type, and topography. In this paper, a computer simulation model of radiation
transfer is designed and evaluated. This model implements the Monte Carlo ray-tracing techniques and is specifically
dedicated to the study of light propagation in mountainous regions. The radiative processes between sun light and the
objects within the mountainous region are realized by using forward Monte Carlo ray-tracing methods. The performance
of the model is evaluated through detailed comparisons with the well-established 3D computer simulation model: RGM
(Radiosity-Graphics combined Model) based on the same scenes and identical spectral parameters, which shows good
agreements between these two models' results. By using the newly developed computer model, series of typical
mountainous scenes are generated to analyze the physical mechanism of mountainous radiation transfer. The results
show that the effects of the adjacent slopes are important for deep valleys and they particularly affect shadowed pixels,
and the topographic effect needs to be considered in mountainous terrain before accurate inferences from remotely
sensed data can be made.
KEYWORDS: 3D modeling, Monte Carlo methods, Soil science, Reflectivity, Scattering, Sun, Remote sensing, Solar radiation, Particles, Statistical analysis
A good understanding of interactions of electromagnetic radiation with soil surface is important for a further
improvement of remote sensing methods. In this paper, a radiosity-based analytical model for soil Directional
Reflectance Factor's (DRF) distributions was developed and evaluated.
The model was specifically dedicated to the study of radiation transfer for the soil surface under tillage practices. The
soil was abstracted as two dimensional U-shaped or V-shaped geometric structures with periodic macroscopic variations.
The roughness of the simulated surfaces was expressed as a ratio of the height to the width for the U and V-shaped
structures. The assumption was made that the shadowing of soil surface, simulated by U or V-shaped grooves, has a
greater influence on the soil reflectance distribution than the scattering properties of basic soil particles of silt and clay.
Another assumption was that the soil is a perfectly diffuse reflector at a microscopic level, which is a prerequisite for the
application of the radiosity method.
This radiosity-based analytical model was evaluated by a forward Monte Carlo ray-tracing model under the same
structural scenes and identical spectral parameters. The statistics of these two models' BRF fitting results for several soil
structures under the same conditions showed the good agreements. By using the model, the physical mechanism of the
soil bidirectional reflectance pattern was revealed.
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