MEMS-scanned ladar for small unmanned air vehicles

This paper presents research at the Army Research Laboratory (ARL) on a laser radar (LADAR) imager for surveillance from small unmanned air vehicles (UAV). The LADAR design is built around a micro-electro-mechanical system (MEMS) mirror and a low-cost pulsed erbium fiber laser to yield a low-cost, compact, and low-power system. In the simplest sense the LADAR measures the time-of-flight of a short laser pulse to the target and return as a means to determine range to a target. The two-axis MEMS mirror directs the light pulse to a point in the scene and establishes the angular direction to a pixel. The receiver looks over the entire region scanned by the laser and produces a voltage proportional to the amount of laser light reflected from the scene. The output of the receiver is sampled by an analog-todigital convertor. The net result is a data file containing a range and a horizontal and vertical angle that identifies the position of every image voxel in the scene and its amplitude. This data is displayed on a computer using standard and stereo techniques to render a three-dimensional image of the scene. At this time, the LADAR operating parameters are set to form images of 256 (h) x 128 (v) pixels over a 15 degrees x 7.5 degrees field of view and 50 m range swath at a 5-6 Hz frame-rate to 160 m range. In the prior year, we built an initial flight package that we have flown in an auto-gyro that yielded encouraging imagery of ground targets at an altitude of roughly 100 m. Here we discuss progress to improve the performance of the LADAR to image at an altitude of 160 m and increase its mechanical robustness for extensive data collection activities.