Experimental study on underwater acoustic imaging of 2-D temperature distribution around hot springs on floor of Lake Qiezishan, China

An experimental study is performed on acoustic imaging of underwater temperature fields in Lake Qiezishan, located at Longling Country, Yunnan Province, China. There are hot springs and craters beneath Lake Qiezishan, which lies at 24°32′33″ north latitude and 98°47′44″ east longitude. Using the acoustic method, the temperature fields are recovered with the computed tomography of the measured time-of-flight data. Regarding the measuring system, hydrophones are used as transmitters and receivers. The signal correlation analysis is performed to obtain accurate acoustic wave transit time from the transmitted and received acoustic signals. Both the transmitter emission start time and the receiver capture start time are also estimated using a novel algorithm based on the time-of-flight measurements at different water temperature. The reconstruction of the 2-D temperature field which is an ill-posed problem, is conducted by total least-squares method. The reconstructed temperature distributions are rather approximations to the actual distributions measured with thermocouples. The preliminary results show that the potential of underwater acoustic imaging will be useful for the in situ monitoring of temperature distributions around sea-floor hydrothermal vents.