http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Soil spectral effects on reflectance factor data transformations
Bidirectional reflectance factor data were acquired over three cotton canopy - soil background combinations with a truck mounted Barnes Modular Multichannel Radiometer simulating Thematic Mapper wavebands. Strong soil background spectral effects were identified in single band responses. These effects were not removed by the ratio vegetation index, the normalized difference vegetation index nor a six band principal component analysis data transformation. Measurements of irradiance at the soil surface beneath the canopy revealed a canopy spectra-soil spectra interaction. The soil irradiance in sunlit areas beneath the canopy was altered from that which entered the top of the canopy. This alteration occurred in the diffuse radiation category which showed a depletion in visible wavelengths and an enrichment in near infrared wavelengths. Soil irradiance in shaded areas beneath the canopy took on some of the spectral characteristics of the overlying canopy. Thus the soil contribution to composite reflectance depended in some measure on the transmittance and scattering properties of the overlying canopy. Canopy reflectance model calculations indicated that although this interaction existed it was not strong enough to account for basic differences in index response due to soil background. It may however explain why differences in vegetation index values due to soil properties actually increased as soil cover decreased. A modified principal component analysis described by Miller et al. (1985) was found to be sucessful in controlling soil background spectral effects in vegetation assessment. This procedure however, required that bare soil data be isolated from canopy data prior to the analysis. The procedure was shown to be adversely effected when low percent cover measurements were misclassified as bare soil data.
Includes bibliographical references (leaves 93-96).