No abstract

Plume is closely related to the presence of gas hydrates which can often be found in plume development area. By acoustic detection, plumes of bubbles in the seawater from shallow gas have been found by marine surveying instruments in some areas over the world. Based on the existed theory of plume porosity, acoustic echo profile of sedbed seep plumes are numerically calculated. Within the simulation results, according to the pattern of gas bubble change and movement in the seawater, process of methane plumes generation is simulated and directs the distribution of bubble radius and plume boundary as depth. Acoustic features of plume bubbles seeping from shallow gas are shown to be consistent with the field results.

Sound pressure is an important parameter of marine background noise monitoring. A laser interferometric hydrophone is designed based on Michelson interferometry. By tracking compensation method, immunity from interference of the hydrophone is improved. Error analysis shows that the vibrating membrane is the main source of the sound pressure error, which can be eliminated to a certain extent by a vibrating membrane materials selection. Offshore data show that hydrophone pressure measurement of high precision, and with a good frequency response. By comparison with the theoretical model to some extent also verified the accuracy of data. In coastal waters, wind noise and ship radiate noise is the main noise source of marine ambient noise. Here, marine ambient noise spectrum of three wind speed were calculated, and with Kundsen curves were compared. Results show that measured data and Kundsen curve fitting is better. In addition, the measurement of vessel radiation noise is mainly concentrated in frequency range of 350~500Hz.

A low frequency and high-precision microbarograph monitoring system is developed based on the Michelson interference of unequal-arm type, a method of signal modulation and compensation is presented, it improves the system’s anti-jamming capability and measurement accuracy. Experiments show that the monitoring system has a high accuracy and a wide dynamic range, especially for monitoring low-frequency signal.