Modellierung der Schallausbreitung im Südozean zur Abschätzung des Gefährdungspotenzials seismischer Forschungsmessungen für marine Säuger

• Main Author: Breitzke, Monika
• Format: Conference Object
• Language: unknown
• Published: 2010
• Subjects: Antarctic; Southern Ocean; The Antarctic; Weddell; Weddell Sea; Alfred Wegener Institute; Antarc*; Polarforschung
• Online Access: https://epic.awi.de/id/eprint/21973/; https://hdl.handle.net/10013/epic.34217

Modelling sound propagation in the ocean is an essential tool to assess the potential risk of air-gun shots on marine mammals. Based on a 2.5D finite-difference code (Bohlen, 2002) a full waveform modelling approach is presented, which determines both sound exposure levels of single shots and cumulative sound exposure levels of multiple shots fired along a seismic line. Point source approximations of compact air-gun clusters typically deployed by R/V Polarstern in polar regions are used as sound sources. Marine mammals are simulated as static receivers.Applications to deep (3000 m) and shallow (400 m) water models including constant and depth-dependent sound velocity profiles of the Amundsen/Bellingshausen and the Weddell Sea show dipole-like directivities in case of single shots and tubular cumulative sound exposure level fields beneath the seismic line in case of multiple shots. Compared to a semi-infinite model an incorporation of sea floor reflections enhances the seismically induced noise levels close to the sea surface. Refraction due to sound velocity gradients and sound channelling in near-surface ducts are evident, but affect only low to moderate levels. Hence, exposure zone radii derived for different hearing thresholds are almost independent of the sound velocity structure. With decreasing thresholds radii increase according to a spherical 20 log10 r law in case of single shots and according to a cylindrical 10 log10 r law in case of multiple shots. A doubling of the shot interval diminishes the cumulative sound exposure levels by -3 dB and halves the radii. The ocean bottom properties only slightly affect the radii in shallow waters, if the normal incidence reflection coefficient exceeds 0.2.A detailed description of this modelling study can be found in Breitzke & Bohlen (2010). It is a contribution to a risk assessment on the impact of seismic research surveys on marine mammals in the Antarctic Treaty area (Boebel et al., 2009) prepared by the Alfred-Wegener-Institute for Polar and Marine Research (AWI) for the German Federal Environment Agency (UBA). ReferencesBoebel, O., Breitzke, M., Burkhardt, E. & Bornemann, H. 2009.Strategic assessment of the risk posed to marine mammals by the use of airguns in the Antarctic Treaty area, Information Paper IP 51 , Agenda Item: CEP 8c, Antarctic Treaty Consultative Meeting XXXII, Baltimore, USA , 273 pp. Bohlen, T. 2002. Parallel 3-D viscoelastic finite difference seismic modelling, Computer & Geosciences, 28, 887 - 899.Breitzke, M. & Bohlen, T. 2010. Modelling sound propgation in the Southern Ocean to estimate the acoustic impact of seismic research surveys on marine mammals, Geophysical Journal International, in press.