Experimental Study And Application Of New Wave Measurement Using Passive Acoustics

Surface waves are one of the most common phenomena in the sea, which act as important dynamics in beach evolution and must be properly addressed in both design and construction of coastal structures. It also plays a principle role in marine economy, marine resources exploitation and utilization, marine military affairs, as well as location, planning, designing, construction and daily operations of ocean engineering. The observation and computation of ocean waves not only helps to understand its formation and growth mechanism, find out its internal structures and external characteristics, but provides essential parameters for ocean engineering, such as designing of ports & bridges, construction of oil platforms, etc. Nowadays, the developing of science & technology and particularity of marine environments give rise to higher aspiration for the performance of wave measurement instruments.Based on the current development of wave measurements and requirements of in situ observations, as well as the truth that a hydrophone has unanimous signals with a simultaneous pressure sensor after bandpass filtering with the passband of wave frequency, a new wave measurement using underwater passive acoustics is proposed, which is quick, convenient, economic, and practical. It estimates the spectrum of filtered signals, and amend it with a transfer function and a compensation factor to get the surface spectrum, then obtain statistical wave parameters like significant wave height and period. A portable wave measurement system is then specially designed and developed by use of virtual instrumentation, which is efficient and user friendly. After the laboratory validation, the system is used in field measurements in Laizhou Bay and Zhifu Island, respectively. It shows a good result comparing to the simultaneous pressure sensor data. The system is easily extendable, which meets the variability of ocean measurements. It is then extended to explore the relation between wave breaking and groupiness, since it can get breaking events and envelopes simultaneously by using only one hydrophone, which makes the results more reliable and reasonable.The system is also applied to detection of surface weather from underwater, based on the theoretical model of wave breaking statistics:to predict wind speed at sea surface by measuring the mean wave period and breaking probability using a hydrophone; to predict the precipitation by analyzing the variance of sound spectrum level. Taking its advantage of operating safe and non-intrusively, the system is concealed and easy to move, especially suitable for submarines.