The continuous water temperature monitoring by using Acoustic Tomography Technology

Acoustic Tomography (AT) Technology transmits reciprocal acoustic waves to measure the flow characteristics such as flow velocity, water temperature, suspended sediment concentration, salinity and the flow direction in rivers, dam storages, lakes, seas and the oceans. Although, this technique is widely applied in developed countries, it was not used in Iran yet. This research shows the first acoustic tomography experiment in Iran for measuring the flow velocity in a shallow lake located in the western of Shiraz City. Reciprocal sound transmissions were performed between the two acoustic stations located on both sides of the lake. The length of sound transmission line was 262m and the central frequency was set to 30 kHz. The experiment period was 20 minutes and the acoustical data was collected at time intervals of 40s. The surface temperature was measured by a Temperature Sensor (accuracy= 0.1 oC) at four positions along the acoustical ray path. The results showed the arrival time of acoustic waves were approximately constant and it was 177 ms. Finally, the depth- and range-averaged sound speed and the water temperature along the ray path were estimated from the mean travel time. The temperature varied between 19.7 to 19.9 oC that was confirmed by Temperature Sensor data. The temperature resolution of AT technique was estimated around 0.04 oC that shows the more accuracy than the Temperature Sensor. The result of this study showed the ability of acoustic tomography technique to monitor the water temperature in natural aquatic environments.