Properties influencing the transmission loss and mitigation of the underwater sound from marine pile driving

Abstract

The transmission loss of underwater sound generated by impact or vibratory pile driving, combined with the potential mitigation of this sound, ultimately determine the regulatory zone-of-impact on marine life. For impact pile driving the pile source assumes properties of a “phased array” as shown in Reinhall and Dahl [J. Acoust. Soc. Am. 130, 1209–1216 (2011)], where sound radiation arises from the state of radial expansion which travels down the pile at a speed which is supersonic relative to the speed of sound in water. The acoustic field that develops is shown to be the dominant contributor to peak underwater sound pressure. An important range scale can be identified that is useful for both guiding measurements, and for transmission loss modeling. For vibratory pile driving, measurements made at close range (within about a one water depth) show considerable low-frequency content that can be below the cut-off frequency of the waveguide. Some key properties of impact and vibratory pile driving will be di...