Article

Quantifying seismic survey reverberation off the Alaskan North Slope.

Marine Physical Laboratory, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0238, USA.
The Journal of the Acoustical Society of America (Impact Factor: 1.65). 11/2011; 130(5):3046-58. DOI: 10.1121/1.3628326
Source: PubMed

ABSTRACT Shallow-water airgun survey activities off the North Slope of Alaska generate impulsive sounds that are the focus of much regulatory attention. Reverberation from repetitive airgun shots, however, can also increase background noise levels, which can decrease the detection range of nearby passive acoustic monitoring (PAM) systems. Typical acoustic metrics for impulsive signals provide no quantitative information about reverberation or its relative effect on the ambient acoustic environment. Here, two conservative metrics are defined for quantifying reverberation: a minimum level metric measures reverberation levels that exist between airgun pulse arrivals, while a reverberation metric estimates the relative magnitude of reverberation vs expected ambient levels in the hypothetical absence of airgun activity, using satellite-measured wind data. The metrics are applied to acoustic data measured by autonomous recorders in the Alaskan Beaufort Sea in 2008 and demonstrate how seismic surveys can increase the background noise over natural ambient levels by 30-45 dB within 1 km of the activity, by 10-25 dB within 15 km of the activity, and by a few dB at 128 km range. These results suggest that shallow-water reverberation would reduce the performance of nearby PAM systems when monitoring for marine mammals within a few kilometers of shallow-water seismic surveys.

0 Bookmarks
 · 
123 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Several cetacean and pinniped species use the northeastern Chukchi Sea as seasonal or year-round habitat. This area has experienced pronounced reduction in the extent of summer sea ice over the last decade, as well as increased anthropogenic activity, particularly in the form of oil and gas exploration. The effects of these changes on marine mammal species are presently unknown. Autonomous passive acoustic recorders were deployed over a wide area of the northeastern Chukchi Sea off the coast of Alaska from Cape Lisburne to Barrow, at distances from 8 km to 200 km from shore: up to 44 each summer and up to 8 each winter. Acoustic data were acquired at 16 kHz continuously during summer and on a duty cycle of 40 or 48 min within each 4-h period during winter. Recordings were analyzed manually and using automated detection and classification systems to identify calls.
    Continental Shelf Research 09/2013; · 2.12 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Between 15 and 17 August 2010, a simple two-element vertical array was deployed off the continental slope of Southeast Alaska in 1200 m water depth. The array was attached to a vertical buoy line used to mark each end of a longline fishing set, at 300 m depth, close to the sound-speed minimum of the deep-water profile. The buoy line also served as a depredation decoy, attracting seven sperm whales to the area. One animal was tagged with both a LIMPET dive depth-transmitting satellite and bioacoustic "B-probe" tag. Both tag datasets were used as an independent check of various passive acoustic schemes for tracking the whale in depth and range, which exploited the elevation angles and relative arrival times of multiple ray paths recorded on the array. Analytical tracking formulas were viable up to 2 km range, but only numerical propagation models yielded accurate locations up to at least 35 km range at Beaufort sea state 3. Neither localization approach required knowledge of the local bottom bathymetry. The tracking system was successfully used to estimate the source level of an individual sperm whale's "clicks" and "creaks" and predict the maximum detection range of the signals as a function of sea state.
    The Journal of the Acoustical Society of America 09/2013; 134(3):2446-61. · 1.65 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Differing physical characteristics and levels of biological, environmental, and anthropogenic sounds contribute in varying levels of noise in different ocean environments. As a result, animals migrating over large ranges or widely distributed species are now exposed to a myriad of different acoustic environments, within which they must navigate, forage and reproduce. Given current increases in low-frequency (< 1000 Hz) anthropogenic noise, there is concern that resultant masking of communication and naturally occurring sounds may stress cetaceans already facing other forms of habitat degradation. As a critical first step to understanding the acoustic environments of coastal marine ecosystems, we examined month-long acoustic data from ten sites along the U.S. east coast that are either designated critical habitats or located along the migratory corridor of the North Atlantic right whale (Eubalaena glacialis): Gulf of Maine, Jeffreys Ledge, Massachusetts Bay, Cape Cod Bay, New York, New Jersey, North Carolina, South Carolina, Georgia (North), and Georgia (South). Data were collected using hydrophones positioned at depth to evaluate differences in the acoustic environment at these sites. High noise levels were observed at both major (New York, Boston) and non-major (Georgia) shipping ports located in or near the areas of study. Of the ten study sites, New Jersey and New York experienced the highest equivalent sound levels, while South Carolina and the Gulf of Maine presented the lowest. The majority of noise variability was found in low-frequency bands below 500 Hz, including the 71–224 Hz communication range utilized by long distance, contact-calling right whales and many other whale and fish species. The spatio-temporal variability of anthropogenic noise can be viewed as a form of habitat fragmentation, where inundations of noise may mask key sounds, resulting in a loss of “acoustic space” (overlapping frequency band and time of a whale’s vocalization), which could otherwise be occupied by vocalizations and other acoustic cues utilized by cetaceans. This loss of acoustic space could potentially degrade habitat suitability by reducing the geographic distance across which individuals acoustically communicate, and ultimately, over long timescales, disrupt aspects related to their natural behavior and ecology. Because communication plays a vital role in the life history of cetacean species, understanding temporal and geographical differences in ambient noise as part of cetacean ecology and habitat may elucidate future conservation strategies related to the assessment of noise impacts.
    Ecological Informatics 05/2014; · 1.98 Impact Factor

Full-text

Download
81 Downloads
Available from
May 21, 2014