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Results from an experimental polarimetric investigation of 7 different types of land mines and 3 types of plants
with the aim to explore the possibility in discriminating surface land mines from natural backgrounds are presented.
The samples Mueller matrices at both specular and non-specular angles during 405 nm 1570 nm laser
illumination were collected. Also included in this study is reflection spectra from the mines taken from 400 to
2500 nm as well as actual images of surface land mines hidden in a natural environment during different weather
conditions. The mines had a reflection coefficient between 5-15 % with peak values around 510 nm due to the
embedded green pigment. The mines were found to be less reflective in wet compared to dry conditions. The
polarimetric study revealed that the samples had similar retardance and diattenuation values for small incident
angles, but that discrimination between the samples could be made by monitoring the depolarization of the incident
light for several incident angles, as a function of the angular distribution of scattered light. The land mines
generally experience less depolarization than the investigated plants, specifically for specular angles around 1570
nm where the mines act as a non-depolarizing sample with depolarization index close to 1.0. The depolarization
index is significantly smaller for specular angles from the plants, becoming 0.4 or below. Both plants and mines
experience more depolarization for non-specular angles. A non-specular angular scan with a constant bi-static
angle resulted in a Lorentzian shaped depolarization index curve, with characteristic differences in the fitted
line-shape parameters. Remote laser based polarimetry might thus be a promising supplementary technique
in recognizing surface mines or other related man-made objects from a natural background. Conclusively, the
depolarization index as a function of angular distribution of scattered light along with its wavelength dependence
is a metric that produce significant differences in the polarimetric signatures.
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