Polarized thermal light gives soldiers detailed night vision
A new thermal imaging system being developed for the US Army Laboratory by physicist Dr Kristan Gurton and electronics engineer Sean Hu uses polarized infrared light to reveal details like facial features. The technology will allow soldiers to pick out details such as tripwires, booby traps, buried landmines, mortars and UAVs in flight – even in total darkness.
Night vision technology has revolutionized warfare by enhancing the ability of soldiers to carry out their missions beyond daylight hours. Thermal imaging is particularly useful because it works in complete darkness and needs no external illumination.
Where photomultiplier systems rely on reflected infrared light and require an outside source – often a lamp on the night vision scope itself – thermal imaging uses the infrared radiation emitted by any object that has a temperature above absolute zero. This radiation varies in intensity with the temperature of the object, allowing a thermal camera to build up false color images of people, landscapes, and objects in both day and night conditions.
The problem is that thermal imaging is prone to ghosting effects, which blur details and make faces look like blank masks. But when polarized infrared light is added using facial recognition algorithms, the details return with surprising clarity.
"Researchers have known for about 30 years that man-made objects emit thermal radiation that is partially polarized, for example, trucks, aircraft, buildings, vehicles, etcetera, and that natural objects like grass, soil, trees and bushes tend to emit thermal radiation that exhibits very little polarization," says Gurton. "We have been developing, with the help of the private sector, a special type of thermal camera that can record imagery that is based solely on the polarization state of the light rather than the intensity. This additional polarimetric information will allow soldiers to see hidden objects that were previously not visible when using conventional thermal cameras."
But, Gurton says, making the concept a reality has been elusive because previous approaches have been overly complicated.
"Early on, researchers attempted to place micro-polarizers on individual micron-size pixels of the infrared Focal-Plane Array (FPA). Both the FPA and micro-pixel polarizers technology in the 80s and 90s were fairly unsophisticated. During my first contract, I stressed a KISS approach ... and I insisted that competing companies avoid the so-called micro-pixel approach and propose very simple concepts in order to produce a calibrated research-grade thermal polarimetric camera system that would actually work. For this new design, we settled on a simple rotating element approach, which is still the gold standard today."
However, Gurton contends that if the technology is to be successfully commercialized, the micro-pixel FPA approach will need to be readapted and perfected. In addition, the camera and other systems will need better miniaturization.
"Our primary goal was to develop a new type of camera system that could detect objects that were difficult, or impossible, to see using current state-of-the-art thermal cameras," says Gurton. "We are working with the private sector on a two-prong approach in which both research grade and ruggedized commercial grade polarimetric cameras are being developed. It's our hope that in the future, all deployed Department of Defense thermal imaging systems will have a polarimetric ability that can be implemented with a simple press of a button."
The video below shows how the polarized layers are combined with the unpolarized ones to form a final image.
Source: US Army Research Laboratory