Infrared polarisation measurements of targets and backgrounds in a marine environment

The infrared (IR) radiation emitted or reflected in an off-normal direction from a smooth surface is partially polarised. This principle can be used for enhanced discrimination of targets from back.-rounds in a marine environment. It has been shown that (man-made) targets do not demonstrate a pronounced polarisation effect when observed from near normal direction whereas C the sea back-round radiation has a certain degree of polarisation in slant observation path. A measurement setup has been constructed for collecting polarised IR imagery. This setup contains a rotating polarisation filter that rotates synchronously with the frame sync of the camera. Either a long wave IR (LWIR) or a mid wave IR (MWIR) camera can be mounted behind the rotating polarisation filter. The synchronisation allows a sequence of images to be taken with a predefined constant angle of rotation between the images. Out of this image sequence three independent Stokes images are constructed, containing the normal intensity part, the vertical/horizontal polarisation and the diagonal polarisation. Upto 20 full linearly polarised images can be acquired per second. Measurements are taken at the North Sea coast with this setup. The recorded images are analysed to determine the influence C of polarisation on the detection of small targets in such an environment. Furthermore differences between polarisation contrasts in MWIR are analysed.