Analysis Plan for Narrowband/Narrowbeam Ambient Noise
TETRA TECH INC ARLINGTON VA
Traditionally, the acoustic modeling and measurement program conducted by LRAPP has concentrated on two aspects of acoustic environment characterization estimationprediction of the energy level output of the beamformer due to a point source signal propagating between a given point and the receiving array and analyzing the ambient noise amplitude spatial distribution for specific band-limited frequencies, typically 13 octave segments. When narrowband noise has been investigated, it has normally been at least 1 Hz in bandwidth, although there have been more frequent uses made of narrowband bandwidths lately, on the order of 110-1Hz. The noise has been characterized in terms of its most elementary statistical properties, that is, its mean value almost exclusively, in these bandwidths. Among the systems being introduced into operation or in advanced stages of R and D currently are SPEAR, SIMS Signal Imaging and Measurement System, and SVAA Super Vernier Auto Alert. Generically speaking, these systems include such features as very narrow bandwidths on the order of a few mHz, line trajectory formation, and automatic threshold counting and decision processes. In the case of such narrowband detection, it is likely that narrowband lines from merchant shipping may constitute a major portion of the ambient background, even to the point of appearing flat in a sufficiently narrow bandpass. The impact of such cases upon narrowband noise statistics and detection performance is of great interest. Since such signals may in fact comprise the dominant features of the noise background.