An Explanation for the Observed Spectral Contrast Reduction Between Field and Laboratory Infrared Measurements of Soils,
HAWAII UNIV AT MANOA HONOLULU
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Comparison of emission spectra 7-14 micron of pristine soils in the field with bidirectional reflectance spectra of soils obtained in the laboratory shows that laboratory spectra tend to have less contrast than field spectra. We investigated this phenomenon by measuring emission spectra of both pristine in situ and sampled soils prepared as if for transport to the laboratory. The sampled soils had much less spectral contrast than the pristine soils in the reststrahlen region near 9 micron. We hypothesize that this effect is due to a difference in grain size distribution of the optically active layer i.e., fine particle coatings. This concept was proposed by Salisbury et al. to explain their observations that soils washed free of small particles adhering to larger grains exhibited greater spectral contrast than unwashed soils. Unrecognized, this phenomenon could influence interpretations of remote sensing data since it is a common practice to use spectra of materials obtained in the laboratory to interpret spectra obtained remotely.
- Soil Mechanics
- Infrared Detection and Detectors