A novel technique to improve measurements in time-of-flight based acoustic tomography

Abstract

Understanding the changes in oceanographic conditions is important for many applications; from weather forecasting, studying the impacts of climate change and for safety considerations during operations at sea, such as offshore oil installations or offshore wind turbine sites. Many oceanographic parameters, such as temperature, current speed, salinity and pressure, can be derived using acoustic tomography techniques, which determine the time-of-flight between two points and then calculate the properties based on the bi-directional travel times. Initial work in the field of time-of-flight acoustic tomography had focused on the mesoscale (100-1000s of kilometers). More recently, smaller scale systems have been tested that cover systems in the 100s of meters. This new range presents new challenges such as multipath propagation and the impact of timing errors on the scale of milliseconds. If these systems are to become successful, it will be essential to improve upon the precision and accuracy of the measurements obtained. A new approach has been proposed and system developed to test its merits. This system utilizes an additional, third hydrophone to observe the waveform in the aqueous environment which is used in place of an ideal waveform in the data analysis. Where possible, to reduce sources of error, shore-side laboratory equipment was utilized for their robust prior testing and manufacturing quality and physical connections were utilized to prevent timing error.