Application And Observation Of Coastal Acoustic Chromatography

Large-scale, continuous andreal-time measurements of flow and temperature field incoastal regions are essential for monitoring the coastal marine environment. However, in coastal areas of China, many ports, bays and large rivers make it difficult to perform conventional ocean observations due to theheavy shipping traffic and active fishing activities.Coastal acoustic tomography(CAT) is an application of oceanacoustic tomography to coastal regions.In this method, continuous observations of current velocity and temperature could be successfully conducted by deploying a few observation stations around the observation region without disturbing from shipping traffic and fisheries activities. So far few CAT experiments were conducted in China’s coastal regions.In this study, the CAT systems were used to observe the tidal bores in the Qiantang River, the tidal current and temperature structures in the Qiongzhou Strait. The main points of this study are as follows:(1)combining with CAT systems,conductivity temperature depth(CTD) and acoustic Doppler current profiler(ADCP) measurements, we successfully obtained tidal bores’ velocity, water level, temperature and other parameters during the observation.In addition, we analyzed the dynamic characteristics of tidal borebased on the observational data;(2) thenetwork observations for tidal current structure were carried out by using CAT systems in the Qiongzhou Strait. The horizontaldistribution of tidal current and residual current were reconstructed by the inverse method based on the travel time difference data. The results obtained by CAT were in good agreement with that measured by ADCP. The observation accuracies of China-made CAT systems wereclose to that of the matureimported CAT systems;(3) thetemperature tomography analyses were studied based on a 15-day dataset in the Qiongzhou Strait.Firstly, the position offsets, including a long-time averaged offset and a short-period fluctuation offset, were corrected for temperature estimation. Then, the horizontaldistribution of temperaturewith a 5-min interval was obtained in Qiongzhou Strait throughbuilding and solving the inverse problem. The temperature differences between the southern and northern coast of Qiongzhou Strait, and a long-time increase tendency of temperature due to the seasonal warming were wellcaptured. The temperatures obtained by the inverse analysis were in agreement with that measured by ADCP.In conclusion, the present study indicates that the CAT is an innovational technology to make upthe lack ofconventional instrument for measuring the current velocity and temperature in coastal regions. Itcould play an important role in monitoring the flow and temperature field incoastal regions for further understanding of coastal marine environment.