Effects of emergent grass on mid-infrared laser reflectance of soil

Mid-infrared laser reflectances of soils containing specific minerals show diagnostic features in the 9- to 11-μm wave-length range, and are thus useful for remote sensing of terrestrial lithology. However, the presence of actively growing vegetation can obscure these diagnostic features to such an extent as to make mineral identification virtually impossible. The effects of emergent grass on the mid-infrared laser reflectance of bare soil were studied experimentally. Speckle-averaged reflectance data were collected at various wave-lengths, incidence angles, and polarization combinations from a large movable soil container. Initial measurements were made on bare soil under various wetness and surface roughness conditions. Grass was then grown on the soil, and three different grass densities were used in different sub-plots of the container. Reflectance data were gathered from each sub-plot as the grass-blade height increased. Reflectance ratios (indicative of diagnostic features) were plotted as a function of grass-blade eight for different grass densities. There appeared a grass-blade height value at which the diagnostic ratios level off to a value of 1.0, thereby masking the underlying soil reflectance features. These results should be useful for identifying optimal conditions under which soil mineralogy can be identified under overlying vegetation using mid-infrared laser spectroscopy.