A Microstructure Based Ray Tracing Model of Radiative Transfer in Snow
Abstract
An understanding of light reflection and transmission by snow is important for snow thermodynamics, hydrology, ecology, chemistry, and remote sensing. Snow is a highly scattering porous medium consisting of an ice matrix formed of sintered ice grains and air filled pore space. Snow metamorphism induces microstructural evolution with time. Numerical models for studying the physical properties of snow at the micro-scale are emerging. Among those are Discrete Element Models for mechanical properties or Finite Element Models for metamorphic processes. New observational techniques as computed micro-tomography allow for observations at this same length scale. We developed a geometrical optics ray tracing algorithm who takes as input an arbitrary snow microstructure either taken from a discrete element representation or from a 3D tomographic image. Using only fundamental optical laws for refraction, Fresnel reflection, and absorption, the model allows for a detailed examination of the spectral radiance and irradiance above, below, and within the snowpack. In comparison to other optical models for snow, no additional input parameters such as phase functions and scattering coefficients are needed. The model rather follows individual photons through the microstructure, applying the fundamental laws at ice-air boundaries and within the ice matrix. The model was tested using observations and results from discrete ordinates models. Results on tomographic input data were compared to reflectivity measurements performed on the same snowpack. The model was then applied to investigate changes in reflected, absorbed, and transmitted light as a function of wavelength, snow depth, specific surface area, and density. The microstructure based ray tracing model is a powerful tool for examining radiative transfer in snow. It needs only the complex index of refraction of ice as an optical input parameter. Its strength are in treating complex geometries and examining scattering in detail. The model capabilities will implicitly extend through the straightforward coupling to modern observational techniques and to emerging numerical models designed to predict the microstructural evolution during snow metamorphism.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.C21C1161K
- Keywords:
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- 0700 CRYOSPHERE (4540);
- 0736 Snow (1827;
- 1863);
- 0798 Modeling