Phenomenology studies using a scanning fully polarimetric passive W-band millimeter-wave imager
2011
We present experimental results obtained from a scanning passive W-band fully polarimetric imager. Passive millimeter
wave imaging offers persistent day/nighttime imaging and the ability to penetrate dust, clouds and other obscurants, as
well as thin layers of clothing and even dry soil. The selection of the W-band atmospheric window at 94 GHz offers a
compromise as there is sufficient angular resolution for imaging applications using modestly-sized reflectors appropriate
for mobile as well as fixed location applications. The imager is based upon an F/2.1 off-axis parabolic reflector that
exhibits -34 dB of cross polarization suppression. The heterodyne radiometer produces a 6 GHz IF with 4 GHz of
bandwidth resulting in an NEDT of < 200 mK. Polarimetric imaging reveals the presence of man-made objects due to
their typically anisotropic nature and the interaction of these objects with incident millimeter wave radiation. The
phenomenology studies were undertaken to determine the richest polarimetric signals to use for exploitation. In addition
to a conventional approach to polarimetric image analysis in which the Stokes I, Q, U, and V images were formed and
displayed, we present an alternative method for polarimetric image exploitation based upon multivariate image analysis
(MIA). MIA uses principal component analysis (PCA) and 2D scatter or score plots to identify various pixel classes in
the image compared with the more conventional scene-based image analysis approaches. Multivariate image
decomposition provides a window into the complementary interplay between spatial and statistical correlations
contained in the data.
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