Forward‐scatter barrier with a time‐reversal mirror

The classic difficulty in constructing an acoustic trip line barrier is that the forward‐scattered field from the target must be extracted from the (usually) much more intense direct blasting arriving beam, i.e., ‘‘looking into the sunlight effect.’’ During the time‐reversal experiment conducted in May 2000, we investigated the forward‐scatter barrier concept using a six‐element transponder at 65‐m depth drifting along with a ship, which traversed the trip line between two moored vertical arrays separated by 5 km in 110‐m water depth. A 10‐ms cw pulse from a probe source (PS) located at the bottom of the vertical receive array (VRA) is received and time‐reversed at the source/receive array (SRA). The transmitted time‐reversed signal is then refocused at the PS location of the VRA. This time‐reversed signal is also captured by the transponder simulating the forward‐scatter target and is retransmitted to the VRA with various amplitudes simulating different forward‐scatter target strengths. With an appropria...