My Joy of Life
A recent experiment1 first demonstrated an acoustic time-reversal mirror ~TRM! in the ocean. A TRM2,3 also referred to as the process of phase conjugation in the frequency domain,4–8 focuses sound from a source–receive array
~SRA! back to the probe source ~PS! which ensonified the SRA. The SRA receives the probe-source field, time reverses it ~phase conjugation in the frequency domain!, and then uses the time-reversed data as the excitation for an array of sources which are collocated with the receiving hydrophones.
If the ocean environment does not change significantly during the two-way travel time, the phase-conjugate field will refocus, regardless of the complexity of the medium, with the caveat that excessive loss in the system degrades the process. The focus is both spatial and temporal, recombining the multipaths from the first part of the transmission.9 Since this process offers an approach to compensate for multipath interference and other distortion through a complex medium, it may be applicable to various adaptive sonar and communication concepts.
This paper describes a second phase-conjugation experiment conducted in May 1997. The new results reported in this paper include: ~1! extending the range of focus from the earlier result of 6 km out to 30 km, ~2! validating a new technique to refocus at ranges other than that of the probe source, and ~3! demonstrating that probe-source pulses 1 day, 2 days, and as much as 1 week old can be successfully refocused. I. EXPERIMENTAL GEOMETRY
The second TRM experiment was performed off the west coast of Italy in May 1997 at the same location as the previous experiment.1
Figure 1 is a schematic of the experiment, and indicates
~SRA! back to the probe source ~PS! which ensonified the SRA. The SRA receives the probe-source field, time reverses it ~phase conjugation in the frequency domain!, and then uses the time-reversed data as the excitation for an array of sources which are collocated with the receiving hydrophones.
If the ocean environment does not change significantly during the two-way travel time, the phase-conjugate field will refocus, regardless of the complexity of the medium, with the caveat that excessive loss in the system degrades the process. The focus is both spatial and temporal, recombining the multipaths from the first part of the transmission.9 Since this process offers an approach to compensate for multipath interference and other distortion through a complex medium, it may be applicable to various adaptive sonar and communication concepts.
This paper describes a second phase-conjugation experiment conducted in May 1997. The new results reported in this paper include: ~1! extending the range of focus from the earlier result of 6 km out to 30 km, ~2! validating a new technique to refocus at ranges other than that of the probe source, and ~3! demonstrating that probe-source pulses 1 day, 2 days, and as much as 1 week old can be successfully refocused. I. EXPERIMENTAL GEOMETRY
The second TRM experiment was performed off the west coast of Italy in May 1997 at the same location as the previous experiment.1
Figure 1 is a schematic of the experiment, and indicates