Active stereo vision for improving long range hearing using a Laser Doppler Vibrometer

Laser Doppler Vibrometers (LDVs) have been widely applied for detecting vibrations in applications such as mechanics, bridge inspection, biometrics, as well as long-range surveillance in which acoustic signatures can be obtained at a large distance. However, in both industrial and scientific applications, the LDVs are manually controlled in surface selection, laser focusing, and acoustic acquisition. In this paper, we propose an active stereo vision approach to facilitate fast and automated laser pointing and tracking for long-range LDV hearing. The system contains: 1) a mirror on a Pan-Tilt-Unit (PTU) to reflect the laser beam to any locations freely and quickly, and 2) two Pan-Tilt-Zoom (PTZ) cameras, one of which is mounted on the Pan-Tilt-Unit (PTU) and aligned with the laser beam synchronously. The distance measurement using the stereo vision system as well as triangulation between camera and the LDV laser beam allow us to fast focus the laser beam on selected surfaces and to obtain acoustic signals up to 200 meters in real time. We present some promising results with the collaborative visual and LDV measurements for laser pointing and focusing in order to achieve long range audio detection.