Tron Vedul Tronstad

Modeling Propagation of Seismic Airgun Sounds and the Effects on Fish Behavior

High activity of seismic surveying in Norwegian waters has caused concerns about the impact the acoustic noise from the seismic airguns may have on marine life. There is evidence that this noise can cause reactions on the behavior of the fish resulting in reduced catches. To mitigate the problem and the conflict of interest between the fishing industry and the seismic exploration interest, the Norwegian Petroleum Directorate (NPD) commissioned SINTEF Information and Communication Technology (ICT, Trondheim, Norway) and the Department of Biology, University of Oslo (Oslo, Norway) to develop an acoustic-biological model to predict the impact of seismic noise on the fish population. The ultimate goal is to develop an acoustic-biological model to use in the design and planning of seismic surveys such that the disturbance to fishing interest is minimized. This acoustic module of the model is based on ray theory and can deal with range-dependent bathymetry and depth-dependent sound-speed profiles. The bottom is modeled as a sedimentary fluid layer over a solid elastic rock and the model requires the thickness and seismoacoustic properties of the sediments layer and the rock with compressional speed, shear speed, and absorption. The model simulates the total sound field, both in the time domain and in the frequency domain, out to very large distances. Calculated sound exposure levels are compared with startle response levels for cod. Preliminary conclusions indicate a required distance in the range of 5-10 km, but dependent on the depth and the season. In additions, under certain conditions, there will appear regions with hot spots where the sound level is significantly higher due to caustics and focusing of sound. Modeled results are compared with results obtained from a joint seismoacoustic survey conducted in summer 2009 at Vesterålen-Lofoten area (Nordland VII). In this experiment, signals were recorded at fixed hydrophone positions as the seismic vessel approached from a maximum distance of 30 km toward the receiving positions. The same situation was modeled using available geological and oceanographic information as input to the acoustic model. The agreement between the real and recorded signals and the model results is good. This indicates that in the future acoustic-biological models may be used in the design and planning of seismic surveys such that the disturbance to fishing is minimized.

Bathymetric and seasonal effects on the propagation of airgun signals to long distances in the ocean

Marine seismic exploration uses air guns or air gun arrays to generate high energy, short duration acoustic pulses deep into the ocean floor but some of the seismic/acoustic energy remains in the water column and can propagate to considerably distances. This may cause disturbance to marine life and there is evidence that this noise can cause reactions on the behavior of fish resulting in reduced catches. This has resulted in severe conflict of interest between the petroleum and the fishing industry. The ultimate goal of the work that is presented here is to be able to estimate the minimum distance from a seismic survey to avoid significant negative effects on fish behavior and fish catch. We have developed a propagation model, based on ray theory that can deal with range dependent bathymetry and depth dependent sound speed profiles. This paper describes briefly the model and its capabilities, followed by the presentation of several relevant examples of propagation over range dependent bathymetry with typical sound speed profiles from different geographical locations and seasons. The main conclusion is that both the bathymetry, the geo-acoustic properties of the bottom and the oceanographic conditions have significant impact on the propagation of seismic noise. The focusing of sound, caused by the bathymetry and/or sound speed profile, may create regions with hot spots where the sound level is significantly higher than normally expected. Common range dependent sound propagation methods for cylindrical and spherical spreading, e.g. −10log(r) and −20log(r), are also compared to the modeled results.

The efficacy of sound regulations on the listening levels of pop concerts

ABSTRACT This analysis of new and previously collected data was done to validate the efficacy of recommendations for limits regarding sound exposure levels at live pop concerts. After the World Health Organization (WHO) recommended limiting the sound levels at such concerts to avoid noise induced hearing damage among the audience, the actual levels at concerts where these recommendations are observed, have stabilized around 100 dBA. This is a level that is considered acceptable by WHO. At concerts where there are no limitations, however, the sound levels in the audience area are still increasing far beyond safe limits and thus the exposure may represent a serious threat to peoples hearing.

Statistical tool to detect small hearing threshold shifts

Abstract Objective: The aim of this study is to present a new tool that can be used in the prevention of noise-induced hearing loss. Even in most countries where noise levels are well regulated, many workers are still exposed to high levels of noise and suffer from permanent threshold shifts. It is necessary to develop a new strategy to prevent such damage. Method: A statistical process control (SPC) scheme is presented that is able to detect both large and small hearing threshold shifts. Monte Carlo simulations were used to assess the performance of this hearing monitoring scheme. Different hearing threshold shifts were simulated to evaluate the performance of a variety of hearing development scenarios. Results: It is possible to detect hearing threshold shifts smaller than the standard deviation of the hearing tests performed. This means that permanent hearing threshold shifts smaller than 5 dB can be detected and acted on. Outliers can also be automatically detected and treated, increasing the robustness of the monitoring scheme. Conclusion: The proposed statistical framework can be used as an early warning indicator of noise-induced hearing loss with the aim of improving workers’ safety. Individual counteractions can be implemented, reducing the risk of further damage.

Sound exposure during outdoor music festivals

Most countries have guidelines to regulate sound exposure at concerts and music festivals. These guidelines limit the allowed sound pressure levels and the concert/festival’s duration. In Norway, where there is such a guideline, it is up to the local authorities to impose the regulations. The need to prevent hearing-loss among festival participants is self-explanatory, but knowledge of the actual dose received by visitors is extremely scarce. This study looks at two Norwegian music festivals where only one was regulated by the Norwegian guideline for concert and music festivals. At each festival the sound exposure of four participants was monitored with noise dose meters. This study compared the exposures experienced at the two festivals, and tested them against the Norwegian guideline and the World Health Organization’s recommendations. Sound levels during the concerts were higher at the festival not regulated by any guideline, and levels there exceeded both the national and the Worlds Health Organization’s recommendations. The results also show that front-of-house measurements reliably predict participant exposure.