5.4. PCA. The most common understanding of the PCA
is that it is a data compression technique used to reduce
the dimensionality of the multidimensional datasets [7]. It
is also helpful for image encoding, enhancement, change
detection, and multitemporal dimensionality [21]. PCA is a
statistical technique that transforms amultivariate data set of
intercorrelated variables into a set of new uncorrelated linear
combinations of the original variables, thus generating a new
set of orthogonal axes.
5.5. Ehlers Fusion. This is a fusion technique used for the
spectral characteristics preservation of multitemporal and
multisensor data sets. The fusion is based on an IHS transformation
combined with filtering in the Fourier domain,
and the IHS transform is used for optimal colour separation.
As the spectral characteristics of the multispectral bands are
preserved during the fusion process, there is no dependency
on the selection or order of bands for the IHS transform
[14, 30].