Low-frequency propagation and noise in the intertidal zone

Measurements of ambient noise and short-range propagation (<2m) were made in the intertidal zone with water depths ranging from 50 to 80 cm using vector sensors. The sites selected for the measurements were known nesting areas for plainfin midshipman (Porichthys notatus). Males of this species produce continuous acoustic advertisement calls with fundamental frequencies in the 70 to 100 Hz range. The temporal and spectral structure of these calls must convey information regarding the source’s range, direction, and/or fitness over the maximum detectable range in a complex environment. Both fundamental and harmonic components appear to be above a rapid low-frequency increase in the noise floor due to local wave motion and below the frequency range of several observed noise transients at times with modest wind speeds (<5 mph) and small wave heights (<20cm). There is little evidence of significant propagation differences between specific frequencies within the band of interest.