Estimation of clock errors in underwater acoustic instruments

All underwater acoustic sensors require accurate on-board clocks for subsequent data analysis and interpretation. Unfortunately, most clock oscillators change their frequency over time, which occurs due to environmental changes, aging, and other factors. Typically, clock errors are accounted for by referencing the instrument clock to a known accurate clock (such as GPS) before and after the deployment and applying a correction during data post-processing. This method, however, does not accurately estimate clock errors during a specific experimental event. A method to estimate clock performance during the specific event of interest has been developed. It is shown that advanced signal processing techniques can be used to accurately reconstruct the motion of the acoustic source, which, in turn, can improve the accuracy of the acoustic receivers deployed on the seafloor in the deep ocean. A small subset of data collected on the last day of the Ocean Bottom Seismometer Augmentation in the North Pacific (OBSANP) Experiment in June–July 2013 is analyzed for the demonstration of these techniques. [Work supported by the MITRE Corporation’s R&D Program.]All underwater acoustic sensors require accurate on-board clocks for subsequent data analysis and interpretation. Unfortunately, most clock oscillators change their frequency over time, which occurs due to environmental changes, aging, and other factors. Typically, clock errors are accounted for by referencing the instrument clock to a known accurate clock (such as GPS) before and after the deployment and applying a correction during data post-processing. This method, however, does not accurately estimate clock errors during a specific experimental event. A method to estimate clock performance during the specific event of interest has been developed. It is shown that advanced signal processing techniques can be used to accurately reconstruct the motion of the acoustic source, which, in turn, can improve the accuracy of the acoustic receivers deployed on the seafloor in the deep ocean. A small subset of data collected on the last day of the Ocean Bottom Seismometer Augmentation in the North Pacific (OBSANP...