Water Temperature Observation by Coastal Acoustic Tomography in Artificial Upwelling Area

Abstract

Artificial upwelling is a geoengineering method to repair and improve marine ecosystems, and its operation requires long-term and continuous temperature field observation. However, existing methods are rarely seen to accomplish such observation. In this study, we investigate the coastal acoustic tomography (CAT) to obtain the long-term horizontal temperature field of an artificial upwelling area in an anechoic tank. We conduct four sets of experiments with different CAT station numbers and compare their data with those collected from temperature sensors. By analyzing the travel time from the CAT experiments, the horizontal temperature field of the upwelling area could be mapped. The CAT results and the comparison results show that the surface temperature of the observed area decreases by approximately 3 °C after upwelling, while the temperature of where the CAT is deployed decreases by about 1 °C; the temperature is lowest at the center of the upwelling area. Increasing the number of stations and station spacing would improve the temperature mapping accuracy. Therefore, the feasibility of using the CAT system to observe artificial upwelling is proved valid. This study indicates the potential application of CAT in temperature field observation in artificial upwelling area in the sea.

Short-Range Water Temperature Profiling in a Lake with Coastal Acoustic Tomography

“…A significant number of experiments have been conducted to measure range-average temperatures or map temperature distribution vertically and horizontally with CAT [15][16][17][18]. However, few researchers have attempted the short-range temperature observation, which may be used to monitor specific targets in small ranges, such as artificial upwelling and hydrothermal areas [15,19]. A higher frequency sound wave is needed for a high requirement of time resolution in short-range acoustic tomography research.…”

“…CAT can conduct real-time field observations with multi-station networking, which is a prominent advantage in comparison with fixed-point and sensor array measurements [ 10 , 11 , 12 , 13 , 14 ]. A significant number of experiments have been conducted to measure range-average temperatures or map temperature distribution vertically and horizontally with CAT [ 15 , 16 , 17 , 18 ]. However, few researchers have attempted the short-range temperature observation, which may be used to monitor specific targets in small ranges, such as artificial upwelling and hydrothermal areas [ 15 , 19 ].…”

Layer-Averaged Water Temperature Sensing in a Lake by Acoustic Tomography with a Focus on the Inversion Stratification Mechanism

“…The CAT system developed by the Hiroshima University Acoustic Tomography Group has been widely used for oceanographic observation since 1995 [6]. Plenty of experiments have been conducted to measure depth-averaged water temperature or map temperature distribution vertically and horizontally with the CAT system [7][8][9][10][11][12][13]. Syamsudin et al obtained a five-layer-averaged water temperature and flow velocity of the vertical profile successfully in the Bali Strait using two acoustic systems.…”

Mapping Small-Scale Horizontal Velocity Field in Panzhinan Waterway by Coastal Acoustic Tomography

“…As a consequence, the application of CAT in shallow waters such as the marine ranch, artificial upwelling, and Autonomous Underwater Vehicle (AUV) observation has been widely investigated, and particularly the short-range velocity measurements have gradually been an important focus of research. The observation area of those specific targets is usually within 1 km (much smaller than the traditional CAT observation range) [ 28 , 29 , 30 ]. Luo et al [ 31 ] conducted a field experiment in Delaware Bay with two CAT stations at a distance of 387 m to observe the average velocity along the propagation path.…”