Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008geoji.174..505b&link_type=abstract
Geophysical Journal International, Volume 174, Issue 2, pp. 505-524.
Astronomy and Astrophysics
Astronomy
1
Controlled Source Seismology, Body Waves, Wave Propagation, Antarctica, Arctic Region, Atlantic Ocean
Scientific paper
Air guns and air-gun arrays of different volumes are used for scientific seismic surveys with R/V Polarstern in polar regions. To assess the potential risk of these research activities on marine mammal populations, knowledge of the sound pressure field of the seismic sources is essential. Therefore, a broad-band (0-80 kHz) calibration study was conducted at the Heggernes Acoustic Range, Norway. A GI (2.4 l), a G (8.5 l) and a Bolt gun (32.8 l) were deployed as single sources, 3 GI (7.4 l), 3 G (25.6 l) and 8 VLF™ Prakla-Seismos air guns (24.0 l) as arrays. Each configuration was fired along a line of 3-4 km length running between two hydrophone chains with receivers in 35, 100, 198 and 263 m depth. Peak-to-peak, zero-to-peak, rms and sound exposure levels (SEL) were analysed as functions of range. They show the typical dipole-like directivity of marine seismic sources with amplitude cancellation close to the sea surface, higher amplitudes in greater depths, and sound pressure levels which continuously decrease with range. Levels recorded during the approach are lower than during the departure indicating a shadowing effect of Polarsterns's hull. Backcalculated zero-to-peak source levels range from 224-240 dB re 1 μPa @ 1 m. Spectral source levels are highest below 100 Hz and amount to 182-194 dB re 1 μPa Hz-1. They drop off continuously with range and frequency. At 1 kHz they are ~30 dB, at 80 kHz ~60 dB lower than the peak level. Above 1 kHz amplitude spectra are dominated by Polarstern's self-noise. From the rms and sound exposure levels of the deepest hydrophone radii for different thresholds are derived. For a 180 dB rms-level threshold radii maximally vary between 200 and 600 m, for a 186 dB SEL threshold between 50 and 300 m.
Boebel Olaf
Breitzke Monika
El Naggar Saad
Jokat Wilfried
Werner Berthold
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