Design and Demonstration of an Infrared Passive Ranger

Jörne important targets can provide superior visibility in the infrared (IR) owing to thermal contrast. Current passive IR imaging systems designed for naval defense can yield highly accurate estimates of target angle, but not range data. This article describes the design and demonstration of a novel method for passively acquiring target range with an IR adaptation of an optical rangefinder. The concept uses a stereo perspective combined into a single lens and imaging camera. Tests with a laboratory prototype demonstrate that range error of only a few percent can be achieved at target ranges of 15 nmi or more, and with a stereo perspective baseline of 10 ft or less. One important attribute of the IR ranger is its completely passive nature; no energy is emitted to measure range and angular position. This could be especially important for certain military and surveillance applications. (