Progress on MEMS-scanned ladar

The Army Research Laboratory (ARL) has continued to research a short-range ladar imager for use on small unmanned ground vehicles (UGV) and recently small unmanned air vehicles (UAV). The current ladar brassboard is based on a micro-electro-mechanical system (MEMS) mirror coupled to a low-cost pulsed erbium fiber laser. It has a 5-6 Hz frame rate, an image size of 256 (h) x 128 (v) pixels, a 42 degrees x 21 degrees field of regard, 35 m range, eyesafe operation, and 40 cm range resolution with provisions for super-resolution. Experience with driving experiments on small ground robots and efforts to extend the use of the ladar to UAV applications has encouraged work to improve the ladar's performance. The data acquisition system can now capture range data from the three return pulses in a pixel (that is first, last, and largest return), and information such as elapsed time, operating parameters, and data from an inertial navigation system. We will mention the addition and performance of subsystems to obtain eye-safety certification. To meet the enhanced range requirement for the UAV application, we describe a new receiver circuit that improves the signal-to-noise (SNR) several-fold over the existing design. Complementing this work, we discuss research to build a low-capacitance large area detector that may enable even further improvement in receiver SNR. Finally, we outline progress to build a breadboard ladar to demonstrate increased range to 160 m. If successful, this ladar will be integrated with a color camera and inertial navigation system to build a data collection package to determine imaging performance for a small UAV.