Multispectral polarization active imager in the visible band

We present the concept of a Multispectral Polarization Active Imager operating in the visible range. The acquisition of three degree of polarization (0% < Dp < 100%) images and three intensity images at different wavelengths (RGB) enables to get information about the spectral signature of targets as well as their polarization properties. A theoretical analysis and an experimental validation of this technique are presented. The device is operating in a monostatic configuration, using a white light source to illuminate the target. The reception system consists of a liquid crystal achromatic polarization rotator followed by a liquid crystal color filter and a CCD camera, all driven by a computer. The three polarization images can be merged in one by using a RGB coding in order to visualize the whole polarization information. Results with different targets will be presented, emphasizing polarization effects about backscattering. In particular the degree of polarization is found to be highly correlated to the reflectance of diffuse materials like paints, papers and other coatings. A first interpretation is given to explain this phenomenon. Application to identification of targets with low sensitivity to irradiance can be envisaged thanks to multispectral polarization signature.