The new development of the autonomous sources for ocean acoustic navigation, tomography and communications

A tunable high-Q resonator sound source with exceptional demonstrated performance has been developed by Teledyne Marine. The sound source is efficient, powerful, and has unlimited operational depth, as well as a minimum level of high frequency harmonic content. The projector transmits a digitally synthesized frequency swept signal and the mechanical actuator tunes a high-Q organ pipe to match the frequency and phase of a reference signal. High-efficiency tunable sound sources have been deployed in the ocean over the past 15 years, and have been successfully used for ocean acoustic tomography and long range navigation. A few examples are Pacific Ocean, Pioneer Seamount (2001); MOVE Experiment (2004-2005); Pacific Ocean, Hoke Seamount (2002-2004); NPAL04, SPICE04, Pacific Ocean (2004-2005); Fram Strait 2008-2016; Philippine Sea (2009, 2010-2011); Newfoundland, Canada (2014-2015), Arctic (2016-2017). Recently, it was shown that a bottom-deployed swept frequency array can be used for high-resolution seismic imaging of deep geological formations. The long-term operating experience of the sound sources requires the development of an improved sound source system. A recent development of a sound source system is considered in this paper. A finite-element analysis that shows the structural acoustics of the tunable resonator has been conducted to improve the acoustics of the sound source. The analysis gave a better solution for a tuning mechanism with a very wide frequency range. It has been shown that the organ-pipe resonator can be tuned in an octave frequency range. The system variant for a 500-1000 Hz frequency range was built and tested. In many oceans acoustic experiments, such as underwater acoustic communication or navigation, the frequency sweep is not the optimal waveform. In these applications signals with an arbitrary form are more preferable and should have a broadband frequency response with a bandwidth of at least 100 Hz. The experimental testing of such sound source has shown that the bandwidth of a tunable resonant peak is expanding with the frequency and at the end of the frequency band the resonant frequency response became reasonably broadband. The finite element analysis has shown how to expand the tunable resonant frequency response at the end of the high frequency band even more. Such hybrid sound source combines the advantages of high efficiency and large frequency range of a tunable system with ability to transmit the broadband arbitrary waveform signals at the end of its frequency range. A hybrid sound source has been designed and built, which can sweep a frequency range of 500-1000 Hz and also has a broadband transduction at 850-1000 Hz. Such property allows the sound source to operate with a frequency sweep from 500 to 1000 Hz and to use the upper end of the band to transmit broadband arbitrary waveforms. The frequency sweep is quite useful for high precision navigation and the broadband dual-resonant frequency response is necessary for underwater communications and timing. The sound source is controlled by a DSP controller. In addition the source includes a chip scale atomic clock (CSAC), 8 channels acoustic receiver array, 7 kWh battery, and a programmable interface to provide a customized transmission schedule. An external serial port connector is available to connect to a dual port underwater acoustic modem for remote communication, acoustic modem, and navigation interrogator. The sound source has a high-voltage DC-DC converter and a high voltage H-bridge driven by pulse-width modulated signal from DSP controller. The magnetic phase matching circuit uses a variable inductor for precise phase compensation in a very broad frequency band. The pressure housing for electronics and batteries is rated for 3000 m depth. Aluminum cage is used for system protection during transportation and deployment. Teledyne Marine Systems continue innovating solutions for ocean acoustic tomography, navigation, and seismo-acoustic applications.