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Modeling the Spectral Reflectance of Wet Soils

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Technical Report,01 Feb 2015,31 Jul 2018

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Cornell University Ithaca United States

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The goal of this project was to develop a physically-based model describing reflectance of radiation from 350-2500 nm from dry, moist, and saturated soil. The intent was to account for the optical and structural soil characteristics including moisture content that contribute to the observed reflectance in order to functionally describe the effect of wetting on the spectral and directional reflectance of soil. The underlying scientific interest was to understand how wetting and drying alters the observable optical character of the soil as exhibited in the reflectance spectra. The initial intent was to build on existing models however, existing models proved to be a poor match to the task of characterizing reflectance from moist, but not saturated soils. In particular, existing models fail to account for the distinction between pore water and adsorbed water, and ignore the effect of water on the directional reflectance. Another difficulty was that current models do not explicitly account for scattering within soil particles, a process which would tend to increase the strength of absorption by the particles. Given the poor fit of the existing models for dealing with wet soils, the effort shifted to exploring the details of how water altered the directional reflectance of soils, with the goal of defining the requirements for an effective radiative transfer model. The experimental effort was already a part of the research plan, given the limited number of observations of sufficient detail to support and verify model predictions. That was particularly true for moist soils the preponderance of the existing spectral observations are for dry soils. Even then, there were very few directional observations that considered directional illumination and viewing. Thus, the revised goal was to make a series of spectral-directional reflectance observations of soils at all drying stages from air-dry to saturated.

Subject Categories:

  • Soil Mechanics
  • Electricity and Magnetism

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