Model free analysis from hyperspectral aerial images
Application in field experiments
The first part of aerial image analysis deals with the potential to detect
some common structures in a sugar beet crop and in case those more abstract information can be some associated with population density recorded
from soil sample before planting sugar beets.
Hyperspectral image
Explanation
RGB transformed hyperspectral image
of a sugar beet plot with an extremely high population density of about
4000 eggs and larvae / 100 ml soil determined by soil samples.
The plot is framed by pathways, the plot boundaries are marked by
white standard markers. Picture is taken with a Cubert2
camera, the usable wavelength ranges from 400 to 900 nm.
Octocopter based Cubert2- camera with a resolution of 50 x 50 pixel.
The cluster analysis with
predetermined 8 clusters resulted in a distribution shown in the figure left.
Cluster color is set to a spectral standard from blue to red. The first
5 clusters describe the general background, they determine the white
standards (blue) up to the bare soil
of the paths (green to yellow). The missing plant at the position 20;18
is clearly detectable. Much more interesting are the clusters 6 to
8, as they present the factor nematode population. The resulting
pattern apparently shows different nematode densities, at least the
spatial distribution is exactly how nematode population behave.
Therefore the single cluster are worked out in more detail.
Cluster 7 plus the 95% confidence bands: the variance is high as usual, but no outlier in the
visible domains from 580 to 700 nm. Based on the structure of the signature of cluster 7
it is assumed the cluster represent nematode free areas (or below
threshold densities) of the plot.
The signals of cluster 8 (with confidence bands) describe the high density areas of up to 4000
E&L/100 ml soil. The conclusion is drawn from both, the relative
position compared to cluster 7 and the increased variance in the
domains of 580 to 700 nm. The higher reflectance in the visible
wavelengths and lower reflectance in the infrared range indicate the
nematode effect.
Cluster 6, again compared
to the position of cluster 7. We find high outliers in the domains of
580 to 700 nm. Part of Cluster 6 are spectra which are more typical for
response to leaf pathogens. But it is not entirely clear, parts of the
variance could be related to the bare soil of the paths. Nevertheless,
nematode densities in the range of 600 - 1500 E&L/100 ml soil causes the
pattern of cluster 6.
To provide some kind of proof of the conclusions above, we compare the hyperspectral
signatures of the image (plot) with the ASD FieldSpec signatures. The
signature pattern of that sensor show a larger variance in the domains of
580 to 700 nm, which are related to higher nematode densities (blue and
green areas).
Conclusion: The combination of aerial information and the shapes of the confidence areas of
the spectra allow some kind of conclusion about the underlying nematode
population, or, more theoretically, it links the more abstract clusters more or
less with the scientific hypothesis of the experiment.
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More information (in German only)