Comparison of Narrow-Band and One-Third Octave Ambient Noise Measurements

摘要

In preparation for the eventual testing of a drifting environmental acoustic buoy, the ambient noise in an area off the Monterey, California coast was measured using two analysis methods. Narrow band processing (9 Hz) was compared to 1/3 octave band processing for frequencies up to 2500 Hz. Noise generation due to shipping and local wind was examined for the contribution of each to the noise spectrum. Noise spectrum levels measured using either approach agreed within 2dB, usually within 1 dB. Local and distant shipping varied on a daily basis and appeared to coincide with port activity. The mean variability at 50 Hz was 5 dB for hourly records influenced by individual ships. Distant shipping at 50 Hz showed a 2-3 dB variation. Also, this study shows that mean ambient noise curves may be used to estimate wind speed using the ambient noise at 1700 Hz, provided there are no local ships within 16 km. Ships at greater range appear to contribute little to the wind-dependent spectrum at 1700 Hz.