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

spectrometer, reflectance values were used to identify regions of change in absorption
feature overall spectral reflectance for the zunyite mixtures. These endmembers were
also analyzed using the continuum removed method to calculate the absorption depths at
500 nm, 1125 nm, and 2200 nm for endmembers. Absorption feature depths for
endmembers 6, 9, 14, 28, 34, 43, and 42 are 0.056, 0.133, 0.0340; 0.225, 0.1281, 0.0350;
0.034, 0.0693, 0.0376; 0.028, 0.0688, 0.0535; 0.047, 0.076, 0.0293; 0.026, 0.128, 0.050,
and 0.109, 0.301, 0.117, respectively (Table 3). The similarity between the band depth
calculation results of both the user-supplied endmembers and the imagery-derived
endmembers suggest that differences in the features can potentially be related to different
levels of disturbance affecting the surface material (Table 3). The spectra in Figure 28
also show slight shifts in location and prominence of the features. Widths of features in
this case varied as well.
For the clay collect, the hill clay sample appeared to be the least impacted by
disturbance and was therefore used as a control to determine the disturbance-related
differences. Since the least impacted clay sample had similar reflectance characteristics
to the imagery derived zunyite endmember 28, that endmember was used for the zunyite
control. The average differences in absorption depth at 500 nm, 1125 nm, and 2200 nm
for the ASD collected clay spectra and imagery derived zunyite endmembers are 0.0342,
0.0190, .0738; 0.0476, 0.0553, and 0.0207, respectively (Table 2). These values shown
represent the difference in depth of absorption features (including the averages) at each
respective wavelength for two different materials with similar, not identical properties.
Since these materials are similar, not identical, some minor differences are expected.
For example, impact-related disturbances in the clay showed a decrease in the
feature at 2200 nm; endmembers derived from the imagery also showed patterns of
absorption features decreasing in the SWIR region of the electromagnetic spectrum with
respect to what is thought to be an undisturbed zunyite spectrum; but unlike the clay, they
show an increase at 1125 nm. While the patterns of feature depth do not match those of
the clay at 1125 nm, the correlation is still possible because the clay and zunyite materials
are not an exact match. Certain features may express themselves differently at 1125 nm
because those features are related to vibrational processes while wavelengths less than
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