Wake acoustic measurements around a maneuvering ship

The underwater acoustic measurement around a maneuvering ship using Broad-band Underwater Recording Buoys (BURBs), was investigated. The BURB system composed of a set of four identical self-contained buoys with hyrodophones and GPS receivers was used for recording both underwater radiated noise and man-made acoustic transmissions. For pulse propagation tests, a Medium-frequency MultiMode Pipe Projector (MF-MMPP) was used to transmit 2 - 18 kHz × 10-ms duration LFM pulses. The transmitter was deployed at 5m depth from a small boat to freely drift on the opposite side of the ship wake from the BURBs and acoustic measurement was started 2 minutes before and 10 minutes after the ship passage. It was observed that wake effects affected shallow receivers more in comparison of deeper hydrophones. Resut shows that acoustic dropouts due to the masking effects of ship radiated noise and extinction effects from wake micro-bubbles are more pronounced in shallow acoustic paths.