Spectral Unmixing Applied to Desert Soils for the - Naval ...

Looking at Figure 25 it is apparent that the top four spectra are the same material
based on the similarity of the visible features. The only exception to the similarities of
the spectra is the hard packed picnic area clay. However, the picnic clay spectrum (with
the continuum line) has heavily subdued features that are much shallower in depth and
shifted slightly. When considering this, there are some similarities between it and the
other spectra. The burnt clay expresses higher overall reflectance values than the gopher
till, but has more similarity to the hard packed clay than the other soil spectra. Like the
hard packed clay, the burnt clay absorption features are subdued and the absorption
feature at 2200 nm seems to have disappeared altogether. The home hill clay is the least
disturbed of the samples, the gopher till was a recent dig site and had not been exposed to
any rains or sitting long. Gate clay was a less recent dig site conducted a few months
prior to collection that was then packed back down, and the field road clay has been
exposed to impact disturbance on a level between the home hill and picnic clay spectra.
Based on the fact that each spectrum is comprised of the same soil material and were
collected under the same weather conditions, the only known differentiating factor
between them is the level and type of disturbance the soil has been exposed to and is
likely the cause of the differences illustrated by the spectra.
Table 1 has spectra ordered by least to greatest disturbance with hill clay being
the least and hard picnic clay considered the greatest; however the type of disturbance
seems more relevant at this point. Using hill clay as the undisturbed reference as
previously discussed, impact-related disturbances show decreases in absorption features
at 500 nm and 2200 nm but increases in depth of absorption features at 1125 nm.
Digging-related disturbances show decreases in absorption features at all three
wavelengths. Burning disturbances show a decrease in feature depth at 500 nm and 2200
nm, and increase in feature depth at 1125 nm similar to impacts. Since the patterns of
depth change at each wavelength are the same for the same type of disturbance, it can be
inferred that depth changes increasing at 500 nm and 2200 nm can be correlated with
impact disturbances and those that decrease at all wavelengths can be correlated with
digging disturbances. Also, a burn disturbance seems to register a pattern similar to that
of impact disturbances but the depths do not appear to change as much.
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