Abstract
Underwater noise from impact pile driving of 512 -m-long conductor casings was measured at a deep-water offshore oil platform in the Santa Barbara Channel. Beamforming measurements, obtained with a vertical array, confirmed that the primary wave front generated by hammering the conductor casing was a Mach cone propagating at an angle of 17.6° below the horizontal. Analysis of the processed array data also revealed the presence of high-frequency secondary waves at angles steeper than 45° below the horizontal. These secondary waves, which appeared to be generated near the sea-surface, dominated the acoustic spectrum of the pulses at frequencies above 1 kHz. Shallow hydrophone measurements outside the Mach cone showed clear evidence of a surface shadow zone, which was caused by the strong downward directivity of the source. Although reflected waves, diffraction, and secondary waves still produced sound inside the surface shadow zone, sound levels were 10-15 dB lower in this region. Long-term hydrophone measurements showed that there was little difference (±1 dB) in mean sound levels from impact hammering of different conductors installed at the same platform over three months.
Highlights
Regulators in the United States (U.S.) and other jurisdictions typically require that operators of marine pile driving equipment establish exclusion zones around their activities, based on maximum acceptable noise exposure guidelines for marine animals.[4,5]
Many noise studies have been carried out on structural piles driven near shore in shallow water, such as those associated with piers[6] and bridges.[7,8]
Offshore pile driving measurements have been mainly associated with wind farm construction,[9,10] but these have been limited to relatively shallow water depths (
Summary
Marine impact pile driving generates high underwater sound pressures that could exceed disturbance or injury thresholds for marine wildlife.[1,2,3] Regulators in the United States (U.S.) and other jurisdictions typically require that operators of marine pile driving equipment establish exclusion zones around their activities, based on maximum acceptable noise exposure guidelines for marine animals.[4,5] Many noise studies have been carried out on structural piles driven near shore in shallow water, such as those associated with piers[6] and bridges.[7,8] Offshore pile driving measurements have been mainly associated with wind farm construction,[9,10] but these have been limited to relatively shallow water depths (100 m) pile driving
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