Abstract:

Detection and identification of vehicles obscured by forest canopy is a particularly challenging military problem. Imaging techniques (laser radar imaging a target through gaps in foliage, for example) require extensive data, making this approach pro cessing-intensive and time consuming. A new method for detection of a vehicle obscured by forest canopy by remotely sensing the vibration of foliage with a laser Doppler vibrometer has been proposed. The method uses the effect of coupling of sound waves from the vehicle's engine through the air to tree leaves, causing them to vibrate. The presence of a vehicle can be determined by the spectrum of the leaves' vibrations. The feasibility of the proposed method has been studied experimentally. The acoustical impedance of various types of leaves was measured in the laboratory and outdoor settings. The results show that the vibration response of a leaf to the sound from an idling vehicle is high enough to be reliably sensed with an LDV in a wide frequency band. The vibrations of leaves excited with simulated vehicle acoustic stimuli were successfully measured with an LDV in the laboratory and outdoor environment. A real vehicle masked by foliage was successfully detected by the proposed method.