Surveillance operations and search and rescue missions regularly exploit electro-optic imaging systems to detect targets
of interest in both the civilian and military communities. By incorporating the polarization of light as supplementary
information to such electro-optic imaging systems, it is possible to increase their target discrimination capabilities,
considering that man-made objects are known to depolarized light in different manner than natural backgrounds. As it is
known that electro-magnetic radiation emitted and reflected from a smooth surface observed near a grazing angle
becomes partially polarized in the visible and infrared wavelength bands, additional information about the shape,
roughness, shading, and surface temperatures of difficult targets can be extracted by processing effectively such
reflected/emitted polarized signatures. This paper presents a set of polarimetric image processing algorithms devised to
extract meaningful information from a broad range of man-made objects. Passive polarimetric signatures are acquired in
the visible, shortwave infrared, midwave infrared, and longwave infrared bands using a fully automated imaging system
developed at DRDC Valcartier. A fusion algorithm is used to enable the discrimination of some objects lying in
shadowed areas. Performance metrics, derived from the computed Stokes parameters, characterize the degree of
polarization of man-made objects. Field experiments conducted during winter and summer time demonstrate: 1) the
utility of the imaging system to collect polarized signatures of different objects in the visible and infrared spectral bands,
and 2) the enhanced performance of target discrimination and fusion algorithms to exploit the polarized signatures of
man-made objects against cluttered backgrounds.
Spectral sensors are commonly used to measure the intensity of optical radiation and to provide spectral information
about the distribution of material components in a given scene, over a limited number of wave bands. By exploiting the
polarization of light to measure information about the vector nature of the optical field across a scene, collected
polarimetric images have the potential to provide additional information about the shape, shading, roughness, and
surface features of targets of interest. The overall performance of target detection algorithms could thus be increased by
exploiting these polarimetric signatures to discriminate man-made objects against different natural backgrounds. This is
achieved through the use of performance metrics, derived from the computed Stokes parameters, defining the degree of
polarization of man-made objects. This paper describes performance metrics that have been developed to optimize the
image acquisition of selected polarization angle and degree of linear polarization, by using the Poincare sphere and
Stokes vectors from previously acquired images, and then by extracting some specific features from the polarimetric
images. Polarimetric signatures of man-made objects have been acquired using a passive polarimetric imaging sensor
developed at DRDC Valcartier. The sensor operates concomitantly (bore-sighted images, aligned polarizations) in the
visible, shortwave infrared, midwave infrared, and the long-wave infrared bands. Results demonstrate the improvement
of using these performance metrics to characterize the degree of polarization of man-made objects using passive
polarimetric images.
Electro-optical imaging systems are frequently employed during surveillance operations and search and rescue missions
to detect various targets of interest in both the civilian and military communities. By incorporating the polarization of
light as supplementary information to such electro-optical imaging systems, it may be possible to increase the target
discrimination performance considering that man-made objects are known to depolarize light in different manners than
natural backgrounds. Consequently, many passive Stokes-vector imagers have been developed over the years. These
sensors generally operate using one single spectral band at a time, which limits considerably the polarization information
collected across a scene over a predefined specific spectral range. In order to improve the understanding of the
phenomena that arise in polarimetric signatures of man-made targets, a new passive polarimetric imaging system was
developed at Defence Research and Development Canada - Valcartier to collect polarization signatures over an extended
spectral coverage. The Visible Infrared Passive Spectral Polarimetric Imager for Contrast Enhancement (VIP SPICE)
operates four broad-band cameras concomitantly in the visible (VIS), the shortwave infrared (SWIR), the midwave
infrared (MWIR), and the longwave infrared (LWIR) bands. The sensor is made of four synchronously-rotating
polarizers mounted in front of each of the four cameras. Polarimetric signatures of man-made objects were acquired at
various polarization angles in the four spectral bands. Preliminary results demonstrate the utility of the sensor to collect
significant polarimetric signatures to discriminate man-made objects from their background.
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