Artificial Upwelling Observation With Coastal Acoustic Tomography

Our country is a large marine country with more than 18,000 kilometers of coastline and vast sea areas.The oceans provide us abundant fishing resources and great potential for oil and gas development.With the continuous deterioration of the marine ecological resources in our country,there is an urgent need for an effective way to improve this trend.Artificial upwelling flow,an earth engineering method,is an ideal solution to reduce the carbon dioxide content of the air and enhance marine primary productivity.However,due to the lack of long-term time series observation data,there are still few scientific studies on currents and temperature distribution patterns and evolution mechanisms of artificial upwelling at home and abroad.This situation has severely restricted the research and development of artificial upwelling technology.By placing fewer instruments on the periphery of the observation area,acoustic tomography technology can simultaneous observation for a wide range and a long-term,acoustic tomography is not restricted by shipping and fishing activities which can provide continuity,real-time,three-dimensional,and economical observations.It is an ideal way to monitor artificial upwelling.This paper analyzes the theory and feasibility of applying coastal acoustic tomography to observe artificial upwelling in a small area.The basic knowledge of sound propagation in underwater was introduced.The sound propagation route and signal propagation loss in the artificial upwelling sea area were simulated,and a method to improve signal to noise ratio was proposed.From the aspect of theoretical calculations,the temperature field and inversion method of the flow field in artificial upwelling area are introduced in detail.Assessment of noise in artificial upwelling seas through access information about nearshore,numerical simulation of temperature field in artificial upwelling sea area.Theoretically,the accuracy requirements of measuring current and temperature in the artificial upwelling sea area are calculated,several methods for improving the accuracy are proposed,and introduce the working principle and use method of cosatal acoustic tomography instruments.The application characteristics of coastal acoustic tomography in the observation of small-scale water bodies were studied.In the past,acoustic tomography experiments and applications were usually conducted on large-scale and meso-scale oceanic phenomena,and small scales were rarely observed.To further clarify the application characteristics of coastal acoustic tomography in the actual observation of small-scale water bodies and provides guidance for small-scale observational applications of coastal acoustic tomography.Several small-scale observation experiments have been conducted in a large section experimental sink at Zhejiang University.The operating characteristics of the system are summarized by changing the conditions such as flow rate,temperature,and area range.At the same time,the feasibility and stability of the observation of the acoustic tomography system in a small range of environmental conditions were verified.In order to test the observational effect of the coastal acoustic tomography system on artificial upwelling and to prepare for the observation of artificial upwelling in the next stage,an artificial upwelling flow temperature tomography experiment was performed in the muffler basin of the Ocean University of Zhejiang University.The experiment observed the static water and the artificial upwelling for 5 hours.The results obtained by high frequency acoustic chromatography and temperature chains are basically consistent.Shows the feasibility of using a high-frequency sound tomography system to observe the temperature of artificial upwelling.