A MODELING STUDY OF BACKSCATTERING FROM SOIL SURFACES

An examination of soil particles from very fine to medium sand surface s has indicated that they are generally on the order of 50 to 500 mu m . Thus, at an incident wavelength around 0.6 mu m, the incident light should ''see'' microscopic roughness features on the particle rather t han its macroscopic features. It is anticipated that the macroscopic f eatures of a soil particle are responsible for the shadowing and tilti ng. Note that these smaller scales of roughness may still be larger th an the incident wavelength. In view of this physical structure, a soil particle is modeled as a layer with two arbitrarily oriented surface boundaries to simulate the overall roughness effect, A scattering phas e function is then developed for this layer by considering wave scatte ring from and propagating through it. A probability distribution funct ion for the orientation of the layer boundaries is assumed for the cal culation of this phase function, After the phase function is developed , it is incorporated into a matrix doubling algorithm to calculate the backscattering coefficients for a half space of soil particles. Preli minary results indicate that backscattering is dominated by the small scales of roughness riding on the particle, and those large scales of roughness are responsible for tilting and shadowing.