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

After data have been converted to reflectance, they must then be
atmospherically corrected to account for interactions with the atmosphere such as
scattering and absorption by atmospheric gas and particulate material (Kruse et al., 2000).
Atmospheric correction is a necessary step that allows for determining physical aspects of
imaged materials and making inferences with the data during analysis (Kruse et al.,
2000).
c. Analysis Using Continuum Removal
A continuum can be thought of as a mathematical means by which you
can isolate a particular absorption feature of a spectrum and is related to the electronic
and vibrational processes that occur within surface materials discussed earlier (Clark and
Roush, 1984). The purpose of continuum removal is to rid the spectrum being analyzed
of affects from other processes within the material or other materials in a mixture so
characteristics of an individual feature can be better examined (Clark and Roush, 1984;
Clark, 1999; Clark et al., 2003; Kruse, 2008). The continuum removal is done by
estimating the other absorption processes using functions such as, but not limited to
Gaussians and straight-line segments (Clark and Roush, 1984). The mathematical
function for continuum removal, according to Clark and Roush (1984) is expressed as:
r( )
e e e
where:
( k1l1) ( k2
l2)
( kl
3 3 )
(3)
r is reflectance,
k1, l 1 are functions of the wavelength and represent absorption of some process of
interest in the material,
k2, l 2 are absorption related to other processes in the mineral,
k3, l 3 are absorption related to other processes from other materials.
Continuum removal during spectral analysis is useful in both biological and
mineralogical analysis. This method has been found to be successful in correlation of
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