Proceedings Article | 12 August 2009
KEYWORDS: Polarimetry, Long wavelength infrared, Thermography, Polarization, Cameras, Roads, Calibration, Polarizers, Imaging systems, Staring arrays
We report test results of a study to assess the applicability for using passive polarimetric imaging in the
long-wave infrared (LWIR) to detect regions of recently altered road-type surfaces, e.g., soil, gravel,
asphalt, etc. The field test was conducted at the U.S. Army Research Laboratory, Adelphi, MD, on a test
surface best described as a well traveled dirt road consisting of a gravel clay-soil mixture that was well
compacted. During this initial proof-of-concept test, a LWIR polarimetric camera system was positioned
at a slant-path of 10 degrees with respect to the line-of-site (LOS) and the natural lay of the surface,
approximately 15 meters from the target test-bed. Stokes images, S0, S1, and S2, were recorded using the
LWIR polarimeter that utilizes a spinning achromatic retarder design mated to Mercury Cadmium
Telluride (MCT) focal plane array (FPA). Various surrogate targets were buried near the surface and great
care was taken to camouflage the area to eliminate any "visible" signs of disturbance. Thermal gradients
resulting from the unearthing of cool soil were allowed to dissipate. Two metrics were used to evaluate
performance, i.e., conventional receiver operating characteristic (ROC) curve analysis and an effective
contrast ratio between the target and background. Results showed particularly good detectability in the S2
imagery, with less in S1, and no detectability in S0, i.e., the conventional LWIR thermal image.
