Bidirectional transmittance and reflectance models for soil signature analysis

Area of Science:

• Radiative transfer in terrestrial environments.
• Soil optics and remote sensing.
• Computational physics and numerical methods.

Background:

• Understanding radiation propagation in soil is crucial for applications like remote sensing and agricultural monitoring.
• Soil properties, including refractive index, significantly influence radiative transfer.
• Accurate modeling of reflectance and transmittance is essential for interpreting soil surface characteristics.

Purpose of the Study:

• To investigate radiation propagation in absorbing-scattering soil with constant and spatially varying refractive indices.
• To develop and validate a numerical method for predicting radiative transfer in soil.
• To examine the impact of refractive index variations on soil reflectance and transmittance.

Main Methods:

• Application of the discrete spherical harmonics method (DSHM).
• Implementation of Marshak boundary conditions for accurate flux approximation.
• Modeling of plane-parallel soil layers with Fresnel reflection at boundaries.
• Analysis of diffuse and collimated incident radiation.

Main Results:

• The DSHM with Marshak boundary conditions accurately predicts directional hemispherical reflectance and transmittance.
• The method achieves high accuracy for optically thin and thick soils, with a maximum relative error below 1%.
• Spatially varying refractive indices and anisotropic soil interfaces significantly decrease reflected and transmitted energy and bidirectional reflectance.

Conclusions:

• The developed DSHM provides a reliable tool for simulating radiative transfer in soils with complex refractive index profiles.
• Anisotropic soil interfaces have a substantial impact on the overall energy balance and directional radiance.
• The findings contribute to more accurate remote sensing retrievals and understanding of soil-surface interactions.