EFFECTS OF EMERGENT GRASS ON MIDINFRARED LASER REFLECTANCE OF SOIL

Mid-infrared laser reflectances of soils containing specific minerals show diagnostic features in the 9- to 11-mu m wavelength range, and ar e thus useful for remote sensing of terrestrial lithology. However, th e presence of actively growing vegetation can obscure these diagnostic features to such an extent as to make mineral identification virtuall y 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 wavelengths, incidence ang les, and polarization combinations from a large movable soil container . Initial measurements were made on bare Soil under various wetness an d surface roughness conditions. Grass was then grown on the soil, and three different grass densities were used in different sub-plots of th e container. Reflectance data were gathered from each sub-plot as the grass-blade height increased. Reflectance ratios (indicative of diagno stic features) were plotted as a function of grass-blade height for di fferent grass densities. There appeared a grass-blade height value at which the diagnostic ratios level off to a value of 1.0, thereby maski ng the underlying soil reflectance features. These results should be u seful for identifying optimal conditions under which soil mineralogy c an be identified under overlying vegetation using mid-infrared laser s pectroscopy.