Abstract
In this paper, we describe the development of a continuous real-time system capable of measuring seafloor crustal deformation using the GNSS/Acoustic technique and a moored buoy. A program was implemented on the buoy to automatically distinguish the onset of a direct acoustic wave even if that wave had been contaminated with reflected waves and to compress the acoustic data prior to transmission over a satellite link to the ground base station. We conducted an operations test for a total of 106 d and found that the acoustic ranging and data transmissions were frequently interrupted by an unstable power supply, resulting in only 21 % of the transmitted data being received at the ground base station. Nevertheless, the acoustic ranging measurements continued successfully as long as power was supplied.
Highlights
A system for seafloor crustal deformation measurement using the global satellite navigation system (GNSS) and acoustic techniques has been developed over the last 20 years (e.g., Spiess et al, 1998; Fujimoto, 2006; Fujita et al, 2006; Tadokoro et al, 2006; Ikuta et al, 2008)
Other researchers have evaluated the use of the Wave Glider (Liquid Robotics, Inc.) as a novel platform for GNSS/Acoustic measurements (Chadwell, 2013; Sathiakumar et al, 2016)
Examples of the acoustic waveform recorded in the buoymounted acoustic ranging controller are shown in Figure 8, where it can be seen that the buoy-based acoustic ranging system provided high quality waveforms based on the high maximum value of the absolute cross-correlation function (CCF) between the received and transmitted signals (Figure 9)
Summary
A system for seafloor crustal deformation measurement using the global satellite navigation system (GNSS) and acoustic techniques has been developed over the last 20 years (e.g., Spiess et al, 1998; Fujimoto, 2006; Fujita et al, 2006; Tadokoro et al, 2006; Ikuta et al, 2008). Examples of the acoustic waveform recorded in the buoymounted acoustic ranging controller are shown, where it can be seen that the buoy-based acoustic ranging system provided high quality waveforms based on the high maximum value of the absolute cross-correlation function (CCF) between the received and transmitted (reference) signals (Figure 9). This situation is different from those of conventional observations made using moving vessels with acoustic transducers mounted on a rod. This was identified as a limitation of the present algorithm
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