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

the situation where mixing freedom within the pixel is halfway between the background-
plus-noise freedom of a 0% filled pixel and the noise-only-freedom of the pixel filled to
50% (Boardman and Kruse, 2011). It is this concept that allows the MTMF process to
identify false positives by placing pixels well outside their plausible mixing freedom into
an infeasible mixtures category. Finally, MTMF creates a distribution range for feasible
mixtures (Boardman and Kruse, 2011). Further details on the mathematics behind this
process are given in the paper by Boardman and Kruse (2011).
The MNF process revealed that the eigenvalues for the AVIRIS
f110512t01p00r07 flight log drop to 1 at approximately eigenvalue band 49, which
means that the bands after eigenvalue band 49 contain mainly noise. Based on this, the
data were then reduced from the initial 207 bands used to using only the first 50 bands in
steps after the MNF process in order to eliminate noise from the data and providing a new
dimensionality of 50 (Figure 22).
Figure 22. The plot (A) shows that the eigenvalues calculated for the image drop
toward 1 at approximately eigenvalue band 50, meaning that most of the
data in this band is noise. The bottom figure (B) is a visualization of
eigenvalue band 50, confirming that though there is some signal present,
band 50 is dominated by noise.
As an example of the Pixel Purity Index (PPI) calculation using the f110512t01p00r07
data set, the number of PPI iterations was set at the default setting of 5,000 iterations, and
a PPI threshold value of 2.5. The resulting plot can be seen in Figure 23. When looking
at the plot, the curve flattens off at around 2000 iterations, so the index was run a second
time with 3000 iterations because 5000 seemed unnecessary. The lower iteration plot can
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