Lifting the Fog

Objects shrouded by smoke, fog, dust or camouflage can be isolated and identified by a special camera developed by Office of Naval Research-funded researchers. This device aids human vision, which does not have the capability of seeing very far into the infrared region of the electromagnetic visual spectrum. Bees, for example, can see light invisible to humans, but they also cannot see the yellow-to-red part of the spectrum, which appears as black to the bee. It is the polarization signature of a flower that attracts the bees.

This innovative camera system, in addition to exposing battle targets and threats, could potentially be used commercially for mineral identification, agriculture, and can even discern the precise shade of a ripe grape, alerting wineries to the perfect moment to harvest.

The camera has an Acousto-Optic Tunable Filter (AOTF) which controls the diffraction of light passing through the camera. The AOTF can sort through the entire light spectrum including the infrared regions of the spectrum.

Before light passes through the AOTF, a device called a variable retarder selects the optimal type of polarization to increase image contrast. The patented combination of the AOTF and retarder enables objects to become visible through conditions such as smoke or fog. The camera, called a spectro-polarimetric camera, currently has a charged-coupled device imaging chip that covers a spectral range from 450 to 1,000 nanometers.

"The ability to capture the entire light spectrum and polarization of the light in a system with an agile tunable filter is an exciting development," said Dr. Thomas McKenna, the ONR program manager overseeing the research work by Carnegie Mellon University.