The research of deep-sea water scattering strength measurement technology

摘要

There are many uneven “water masses”, layers, deep-sea creatures and seabed overflow bubbles in the deep sea. The scattering of incident acoustic waves on these scatterers contributes to the deep sea volume reverberation, and different seasons in different ocean regions contribute variously to scattering and their volume reverberation variesy. A research of volume reverberation in different seas and different times by measuring scattering strength of deep sea water, not only has an important role for performance prediction of active sonar system, but also makes a contribution to a better understanding of the acoustic characteristics of the deep sea. From the composition, classification, and characteristics of the main scatterers in the deep sea, this paper introduces the principle and method of scattering strength measuring, and then describes the composition and implementation of a scattering strength measurement sonar system. The scattering strength of each deep layer is measured by transmitting vertically downwards a narrow beam, and displaying the intensity value of scattering in an acoustic image. The sonar system is composed of transducer arrays, a power amplifier, a signal conditioner, a signal processor, and a sonar server. The system has been tested in the South China Sea, and has been used to measure the scattering strength at different time periods in a certain sea area, the depth of which is between 800 meters to 1400 meters, at a frequency of between 12kHz to 20kHz, when the ship speed was between 2kn to 6kn. Studies reveal that fishs within 100 meters of depth and the deep-sea creatures in the deep scattering layer are the major contributors to the volume reverberation. The deep scattering layer thickness is up to hundreds of meters, and the scatterer has obvious biological behaviour, namely deep during the daytime, and shallow at night. In addition, seabed overflow bubbles are also a kind of scatterer.