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

Specimens were sampled during the time periods of 0930–1130 and 1300–1500,
falling within the +/- 2 hours of solar noon described by (Roberts and Herold, 2004).
Collected spectra were then converted to reflectance using spectral math. The spectral
math equation used was s1/s2 where s2 was the average white reference spectrum and s1
was one of the field collected spectra. This process was conducted on each individual
spectrum from each collection site, and utilized the site specific white reference spectrum
for a given calculation. One of the results of this process can be seen in Figure 19. Once
the spectra were in units of reflectance, they were examined for proof of concept with
respect to detecting soil disturbance using reflectance spectroscopy and the continuum
removal method. To verify if differences were significant enough to be considered
spectrally extreme, band depths were analyzed between both the ASD collected spectra
and the imagery derived endmembers using the following equations (5) and (6) described
by Kokaly and Clark, (1999) and Kokaly (2001). Equation (5) calculates the continuum
removed reflectance required to then calculate the band depth using equation (6) (Kokaly
and Clark, 1999; Kokaly (2001).
where:
is the continuum removed reflectance at the absorption feature,
feature.
where:
is the the reflectance at the base of the absorption feature, and
is the reflectance of the fitted continuum line that corresponds to the absorption
is the calculated band depth of the continuum removed absorption feature and
is the previously calculated continuum removed reflectance from equation (5).
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(5)
(6)