In-Flight Laser Sensor for Measurement of Acoustic Self-Radiation

We propose a system that utilizes an on-board laser to measure the acoustic radiation emitted by an air platform. Its immediate advantages are access to in/above-horizon acoustic radiation, good discrimination against ground reflections, high signal compared to background noise, and, at the same time, precise synchronization with helicopter operating state and rotor blade position.The technique is based on exploiting natural particles in the atmosphere. By remotely measuring the motion of the particles the laser measures the acoustic field radiated by the platform. In effect, the laser creates a virtual microphone positioned at the location of the laser probe volume, and being massless, there is no wind/flow noise. Multiple probe volumes can be arranged along the laser beam to create a linear array of such microphones. The laser beam can be steered to gather data at most angles of interest.