IR polarimetry and far IR imaging

The exploitation of infrared polarimetry has been shown to yield good results when applied to target discrimination in military applications and to civilian remote sensing problems. Similarly, numerous workers have shown that imaging sensors operating in the far infrared spectral bands may be useful in such counter-terror applications as concealed weapon and biological and chemical agent detection. Unfortunately, these detection and discrimination techniques have not been exploited because of the lack of suitable sensors capable of making the necessary measurements with acceptable sensitivity. In this paper we present and discuss several methods for measuring the polarization signature of a target scene using sensors with no moving parts. We also present and analyze a far infrared imaging system based on an uncooled bolometer focal plane array. The methods of measuring polarization signature with no moving parts include a coherent in-phase and quadrature approach suitable for both broad- and narrow-band sensors, a broadband sensor using channeled spectropolarimetry, a variant of this latter method that involves correlation of the spectral signatures with those of known targets, and another variant that uses an electro-optic or an acousto-optic modulator. A focal plane array of uncooled bolometers has been proposed before as a far infrared imaging system. One problem with such devices is that they are not sensitive enough to detect the low-intensity emission from a room-temperature blackbody in the far infrared bands. A potential solution to this problem is to use a high- or low-temperature blackbody to illuminate the scene to be imaged. In this paper, methods of measuring the infrared polarimetric signature and the far-infrared spatial signature of a scene will be presented and discussed.