Measurement and Extraction of Recurring Waveforms: For Applications to Active Transmissions, Flow-Noise, and Helicopter-Radiated Noise Problems

摘要

Physical acoustic sources that radiate transient waveforms represent a large class of noise generators. Active transmissions, flow-noise, and helicopter-radiated noise under certain flight situations depending on the source-observer orientation are members of this class. The objective of this paper is to present a signal processing methodology to extract time domain recurring waveforms from data. The recurring waveforms, on the one hand, may represent a source of interference that is to be eliminated as much as possible. But, on the other hand, these recurring waveforms may represent a desired signal that is to be extracted from a background of undesired noise. Both cases are shown in the paper to be different aspects of the same problem. Initially, the methodology is based on a physical property of equally spaced and identical recurring waveforms. These results are then generalized, because in practice, either by design or by other causes, the recurring waveforms may not be equally spaced and identical. The method is then applied to extract equally spaced and nearly identical waveforms which were produced by an approaching helicopter. (Author)