Sound source localization technique using a seismic streamer and its extension for whale localization during seismic surveys

Abstract

Marine seismic surveys are under increasing scrutiny because of concern that they may disturb or otherwise harm marine mammals and impede their communications. Most of the energy from seismic surveys is low frequency, so concerns are particularly focused on baleen whales. Extensive mitigation efforts accompany seismic surveys, including visual and acoustic monitoring, but the possibility remains that not all animals in an area can be observed and located. One potential way to improve mitigation efforts is to utilize the seismic hydrophone streamer to detect and locate calling baleen whales. This study describes a method to localize low frequency sound sources with data recoded by a streamer. Beamforming is used to estimate the angle of arriving energy relative to sub-arrays of the streamer which constrains the horizontal propagation velocity to each sub-array for a given trial location. A grid search method is then used to minimize the time residual for relative arrival times along the streamer estimated by cross correlation. Results from both simulation and experiment are shown and data from the marine mammal observers and the passive acoustic monitoring conducted simultaneously with the seismic survey are used to verify the analysis.

Estimating the location of baleen whale calls using dual streamers to support mitigation procedures in seismic reflection surveys

“…Previously, the TTR method was used to estimate sound source locations using data recorded by a single streamer on turns between track lines [ 20 ]. For monitoring purposes, it is also important to find the range of the calling animals when the streamer is being towed along straight track lines.…”

“… (a) single straight streamer, (b) actual single streamer, (c) actual dual streamers. The dashed lines are the lateral edges of the beamformer cone (see [ 20 ]), for each selected sub-array. The color shading shows the travel time residual (in seconds) from Eq 1 .…”

“…The travel time residual (TTR) method [ 20 ] is a grid-search technique that estimates the two-dimensional horizontal location of a sound source using data recorded by seismic streamers. Each streamer is divided into M sub-arrays, each comprising N hydrophones.…”

“…The method used in this study, the travel time residual method (TTR) [ 20 ], utilizes the full capabilities of long seismic streamers to estimate the horizontal location of low-frequency sound sources. Beamforming is used to estimate the angle of arriving energy relative to sub-arrays of the streamer, which constrains the horizontal propagation velocity to each sub-array for a given trial location.…”

“…A grid search method is then used to minimize the time residual for relative arrival times along the streamer estimated by cross correlation. This method was presented in a previous study [ 20 ] and used to find the location of low frequency sound sources (specifically airgun signals) using a single streamer during turns between track lines in a seismic survey off the coast of Washington state. In this paper, we extend the method to the use of dual streamers and we use it to locate low-frequency baleen whale calls during a seismic reflection survey off Alaska in order to assess the effectiveness of the mitigation procedures.…”