Vessel Noise from Western Geophysical's
1998 Programme in Alaska

Lawson[1] describes some detailed measurements that were made of the noise generated by three vessels during a 1998 seismic programme conducted for Western Geophysical in Alaska. A boat-based hydrophone was used to measure vessel sounds at several distances from the vessels Arctic Star and Saber Tooth. An air-dropped sonobuoy was used to measure sounds at a single, longer distance of 3 km from the Western Frontier. All three vessels were in shallow water and underway at the times of the recordings. No airgun was in use when the measurements were made.

The figures below show both the 1/3 octave band levels and the spectral densities for the three vessels. The background noise level is also shown. For the Saber Tooth and the Arctic Star, which were recorded at several ranges, the levels decreased consistently with range, as expected. At frequencies below 100-125 Hz, the received levels decreased rapidly with decreasing frequency. The authors attribute this to the low-frequency cutoff effect of shallow water. At frequencies above 100 Hz the noise from the Arctic Star was consistently higher than the Saber Tooth, despite the fact that the Saber Tooth was moving more rapidly. Arctic Star is a conventional vessel with propellers whereas Saber Tooth is a shallow draft vessel with water jet propulsion.

Artic Star noise spectra Sabre Tooth noise spectra

Source Levels were estimated by 1/3 octave band, for frequencies of 100 Hz to 10 kHz. At lower frequencies the rate of attenuation was too great for the Source Level to be estimated. The narrowband spectra did not exhibit tonal structure, which was put down to the high attenuation rate at low frequencies, and the low tonal noise level of water jet propulsion systems.

The figure below illustrates broadband SPL versus range for the three vessels recorded in 1998, with the 1996 data for Peregrine.

Vessel transmission loss
  1. Lawson J W (1999)
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