We investigated tradeoffs between accuracy and battery-energy longevity of acoustic beamforming on disposable sensor nodes subject to varying key parameters: number of microphones, duration of sampling, number of search angles, and CPU clock. Beyond finding the most energy efficient implementation of the beamforming algorithm at a specified accuracy, we enable application-level selection of accuracy based on the energy required to achieve this accuracy. We measured the energy consumed by the HiDRA node, provided by Rockwell Science Center, employing a 133-MHz StrongARM processor. We compared the accuracy and energy of our time-domain beamformer to a Fourier-domain algorithm provided by the Army Research Laboratory (ARL). With statistically identical accuracy, we measured a 300x improvement in energy efficiency of the CPU relative to this baseline. We present other algorithms under development that combine results from multiple nodes to provide more accurate line-of-bearing estimates despite wind and target elevation.
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