The U.S. Army is interested in developing low-cost, low-power, non-line-of-sight sensors for monitoring human
activity. One modality that is often overlooked is active acoustics using sources of opportunity such as speech or
music. Active acoustics can be used to detect human activity by generating acoustic images of an area at different
times, then testing for changes among the imagery.
A change detection algorithm was developed to detect physical changes in a building, such as a door changing
positions or a large box being moved using acoustics sources of opportunity. The algorithm is based on cross
correlating the acoustic signal measured from two microphones. The performance of the algorithm was shown
using data generated with a hand-held FM radio as a sound source and two microphones. The algorithm could
detect a door being opened in a hallway.