Learn More
In July 1999, an at-sea experiment to measure the focus of a 3.5-kHz centered time-reversal mirror (TRM) was conducted in three different environments: an absorptive bottom, a reflective bottom, and a sloping bottom. The experiment included a preliminary exploration of using a TRM to generate binary-phase shift keying communication sequences in each of(More)
Time reversal, or phase-conjugation, refocuses energy back to a probe source location despite the complexity of the propagation channel. A probe source pulse is transmitted and a complicated multipath signal is measured by an array of source/receiver elements. The signal is time reversed and retransmitted into the ocean. The time-reversal process recombines(More)
Backscattering from the rough water-bottom interface can serve as a surrogate probe source in time reversal. A time-gated portion of the reverberation then is refocused to the bottom interface at the corresponding range @Lingevitch et al., J. Acoust. Soc. Am. 111, 2609–2614 ~2002!#. In this paper, reverberation nulling is investigated to enhance active(More)
Recent time-reversal experiments with high-frequency transmissions (3.5 kHz) show that stable focusing is severely limited by the time-dependent ocean environments. The vertical focal structure displays dynamic variations associated with focal splitting and remerging resulting in large changes in focal intensity. Numerical simulations verify that the(More)
A series of time-reversal experiments was performed in shallow water including a range-dependent slope environment. Time-reversal arrays implemented with center frequencies of 445 and 3500 Hz achieved sharp focal regions up to ranges of 30 and 13 km, respectively in 110–130-m shallow water. In this paper, resolution expressions are derived using an image(More)
Reverberation from rough ocean boundaries often degrades the performance of active sonar systems in the ocean. The focusing capability of the time-reversal method provides a new approach to this problem. A time reversal mirror (TRM) focuses acoustic energy on a target enhancing the target echo while shadowing the boundaries below and above the focus in a(More)
In recent years, we have demonstrated time-reversal mirrors (TRM) in the ocean. A focus of up to 30 km was achieved with low frequency (445 Hz) transmissions and the focal structure could be maintained over several days at a range of 15 km. However, the stable focus was limited to less than an hour with high frequency (3.5 kHz) transmissions due to the(More)
Marine Physical Laboratory, SIO, UCSD, La Jolla, CA 92093-0238, USA, e-mail: hcsong@mpl.ucsd.edu Marine Physical Laboratory, SIO,UCSD, La Jolla, CA 92093-0238, USA, e-mail: wak@mpl.ucsd.edu Marine Physical Laboratory, SIO, UCSD, La Jolla, CA 92093-0238, USA, e-mail: wsh@mpl.ucsd.edu SACLANT Undersea Research Centre, 19138 La Spezia, Italy, e-mail:(More)
We have performed a series of acoustic phase conjugation (PC) experiments in shallow water. A time reversal mirror (TRM) was implemented for center frequencies of 450 Hz and 3500 Hz. Very sharp focal regions out to ranges of 30 km were obtained. Analysis, including attenuation e ects, indicates that the di raction limit on the size of the focal region was(More)