Field demonstration and characterization of a 10.6 micron reflection tomography imaging system

A field experiment to investigate an imaging technique based on reflection tomography has been performed at the Air Force Research Laboratory. The experiment, called HILT (Heterodyne Imaging Laser Testbed), involves the illumination of objects with short pulses of laser radiation, and the measurement of the temporal characteristics of return pulses scattered by the object. Return pulses, referred to as projections, provide range resolved information characteristic of the object surface shape and viewing angle. By obtaining multiple projections at different viewing angles, a tomographic reconstruction of the object's surface can be obtained. Recent testing has produced images of targets at a range of 990 meters using 1.4 ns pulses from a 10.6 mu CO2 laser. A heterodyne detection technique was utilized to record the weak return signals. The results obtained from this system are believed to be the first LADAR range resolved reflection tomographic images of diffuse objects in a field environment, and the first use of a heterodyne detection system for LADAR reflection tomography. A description of the system is provided and experimental results are presented.