Joal J. Newcomb

Assessing the Deepwater Horizon oil spill impact on marine mammal population through acoustics: Endangered sperm whales

Long-term monitoring of endangered species abundance based on acoustic recordings has not yet been pursued. This paper reports the first attempt to use multi-year passive acoustic data to study the impact of the Deepwater Horizon oil spill on the population of endangered sperm whales. Prior to the spill the Littoral Acoustic Demonstration Center (LADC) collected acoustic recordings near the spill site in 2007. These baseline data now provide a unique opportunity to better understand how the oil spill affected marine mammals in the Gulf of Mexico. In September 2010, LADC redeployed recording buoys at previously used locations 9, 25, and 50 miles away from the incident site. A statistical methodology that provides point and interval estimates of the abundance of the sperm whale population at the two nearest sites is presented. A comparison of the 2007 and the 2010 recordings shows a decrease in acoustic activity and abundance of sperm whales at the 9-mile site by a factor of 2, whereas acoustic activity and abundance at the 25-mile site has clearly increased. This indicates that some sperm whales may have relocated farther away from the spill. Follow-up experiments will be important for understanding long-term impact.

Three-dimensional seismic array characterization study: experiment and modeling.

In the summer of 2003, the Littoral Acoustic Demonstration Center conducted an acoustic characterization experiment for a 21-element marine seismic exploration airgun array of total volume of 0.0588 m(3) (3590 in.(3)). Two Environmental Acoustic Recording System buoys, one with a desensitized hydrophone, were deployed at a depth of 758 m in a water depth of 990 m, near Greens Canyon in the Gulf of Mexico. Shots over a grid were recorded and calibrated to produce absolute broadband (up to 25 kHz) pressure-time dependencies for a wide range of offsets and arrival angles in the water column. Experimental data are analyzed to obtain maximum received zero-to-peak pressure levels, maximum received sound exposure levels, and pressure levels in 13-octave frequency bands for each shot. Experimental data are quantitatively modeled by using an upgraded version of an underwater acoustic propagation model and seismic source modeling packages for a variety of ranges and arrival angles. Experimental and modeled data show good agreement in absolute pressure amplitudes and frequency interference patterns for frequencies up to 1000 Hz. The analysis is important for investigating the potential impact on marine mammals and fish and predicting the exposure levels for newly planned seismic surveys in other geographic areas.

Chirp sonar sediment characterization at the northern Gulf of Mexico Littoral Acoustic Demonstration Center experimental site

Chirp sonar subbottom surveys have been conducted during a recent Littoral Acoustic Demonstration Center (LADC) experiment to invert bottom geoacoustic properties in the Northern Gulf of Mexico. Sediment properties such as density, porosity, and sound-speed profiles are inverted by using reflection amplitude and phase data obtained from a shallow-towed 2-12 kHz chirp sonar. High-quality subbottom images have been obtained with submeter resolution and up to 60 m penetration resolving several seafloor fault and diapir systems in the area. The attenuation coefficient is also estimated using the frequency shift method that seems to be relatively insensitive to reflection and transmission effects. The sound-speed and density structures of the LADC acoustic propagation tracks are efficiently mapped and made available for the numerical simulation studies of ambient noise and marine mammal acoustic propagation. The inversion results compare favorably with the previously reported sediment core data indicating that an accurate and rapid estimation of acoustical and physical properties of marine sediments is feasible.

Measurements of ambient noise and sperm whale vocalizations in the northern Gulf of Mexico using near bottom hydrophones

The Littoral Acoustic Demonstration Center (LADC) consisting of the University of Southern Mississippi (USM), the University of New Orleans (UNO), and the Naval Research Laboratory at Stennis Space Center (NRL-SSC), with guidance and technical assistance from the Naval Oceanographic Office (NAVOCEANO), was formed to do ambient noise and marine mammal acoustic measurement and analysis. Three Environmental Acoustic Recording System (EARS) buoys, designed and produced by NAVOCEANO, were deployed by LADC in the northern Gulf of Mexico (GoM) in the summer of 2001. These bottom-moored omni-directional hydrophone recording systems were modified by NAVOCEANO to sample almost 12 kHz, so that the vocalizations of sperm whales could be recorded. The Sperm Whale Acoustic Monitoring Program (SWAMP) was conducted during that summer by the Minerals Management Service and its collaborators. The EARS buoys recorded during the entire 36 days of SWAMP from 17 July through 21 August of 2001. The EARS buoy hydrophones, 50m above the bottom, were placed on a downslope line, ending at the largest concentration of sperm whale sightings in the northern GoM, in 600m, 800m, and 1000m water depths. The moorings were instrumented with self-recording environmental sensors to obtain time series data of temperature, conductivity, and pressure at specified depths spanning the water column. Four cruises were made to deploy and recover the buoys and to collect a suite of environmental measurements, including CTD and XBT casts and a chirp sonar survey for bottom properties to support propagation modeling. In between the first and second cruises, Tropical Storm Barry moved through the area and changes in the oceanographic properties were observed. Each EARS buoy recorded a bandwidth of 5859 Hz for 36 days. These data clearly reveals sperm whale vocalizations, passing ships, and seismic airguns. Marine mammal vocalizations and airgun signatures have been isolated and are being analyzed. Spectral levels for ten minute averages of ambient noise on four different days show moderate shipping levels except during the passage of the tropical storm. A plateau in the noise spectrum from 200 to 1000Hz on one day is due to the presence of sperm whales. Spectrograms show sperm whale clicks and creaks and the seismic airgun signal is very clear.

Measurements of Ambient Noise during Extreme Wind Conditions in the Gulf of Mexico

The Littoral Acoustic Demonstration Center (LADC) deployed three Environmental Acoustic Recording System (EARS) buoys in the northern Gulf of Mexico during the summer of 2002 (LADC 02). The hydrophone of each buoy was approximately 50 m from the bottom in water depths of 645 m to 1034 m. During LADC 02 Tropical Storm Isidore and Hurricane Lili passed within approximately 73 nmi and 116 nmi, respectively, west of the EARS buoys. The proximity of these storm systems to the EARS buoys, in conjunction with wind speed data from three nearby National Data Buoy Center weather (NDBC) buoys, allows for the direct comparison of underwater ambient noise levels with high wind speeds. These results are compared to the G. M. Wenz spectra at frequencies from 1 kHz to 5.5 kHz. Anomalously high levels of ambient noise may be due to banding effects of the storms. Results of the ambient noise analysis will be presented. (Research supported by ONR PE62435N).

Localization to verify the identification of individual sperm whales using click properties.

Previous research to identify individual sperm and beaked whales from the properties of their echolocation and coda clicks using cluster analysis has been reported. Although reasonably consistent and robust results showing distinct classes (each corresponding to an individual) have been obtained with both self‐organizing maps and K‐means, no independent verification of these identifications has previously been available. However, data from a July 2007 experiment in the Gulf of Mexico should provide enough geometry information to verify some identifications. The Littoral Acoustic Demonstration Center deployed six environmental acoustic recording system buoys, measuring to 96 kHz for 9 days, to record sperm and beaked whale clicks in the northern Gulf of Mexico. Three buoys were in close proximity to enable multisensor detections of single clicks for possible localization, tracking, or bearing estimation sufficient to confirm the identification of individuals from cluster analysis. Displays of cluster class...

Source characterization study 2007: The three‐dimensional primary field of a seismic airgun array.

During September 2007 the Littoral Acoustic Demonstration Center collected acoustic and related data from three moored arrays and ship‐deployed hydrophones spanning the full water column to measure the 3‐D acoustic field of a seismic airgun array. A seismic source vessel shot a series of lines to give detailed angle and range information concerning the field of the primary arrival. The data were collected in the western Gulf of Mexico between the East Break and Alamos Canyon regions. Peak pressures, sound exposure levels, total energy spectra, one‐third octave band, and source directivity analyses are measures used to characterize the field. Three‐dimensional maps of these quantities are generated to show dependence on emission and azimuthal angles and range. Three‐dimensional visualizations are being developed using a visualization cave and software for 2‐D cave emulation. [Research supported by the Joint Industry Programme through the International Association of Oil and Gas Producers.]

The source characterization study 2007: A detailed three dimensional acoustic field measurement of a seismic airgun array.

In September 2007 the Littoral Acoustic Demonstration Center (LADC) collected acoustic and related data from three moored arrays and ship‐deployed hydrophones spanning the full water column to measure the three‐dimensional acoustic field of a seismic airgun array. The seismic source vessel shot a series of lines to give a detailed angle and range information concerning the field. The data were collected in the western Gulf of Mexico between the East Break and Alamos Canyon regions. Peak pressures, sound exposure levels, total shot energy spectra, and one‐third octave band analyses are measures used to characterize the field. Three dimensional maps of these quantities are generated to show dependence on emission and azimuthal angles and range. Both the direct and indirect fields are characterized. Moveout analysis is done to delineate arrivals and to detect ducted and interface waves. [Research supported by the International Association of Oil and Gas Producers.]

Propagation modeling for sperm whale acoustic clicks in the northern Gulf of Mexico

Simulations of acoustic broadband (500–6000 Hz) pulse propagation in the northern Gulf of Mexico, based on environmental data collected as a part of the Littoral Acoustic Demonstration Center (LADC) experiments in the summers of 2001 and 2002, are presented. The results of the modeling support the hypothesis that consistent spectrogram interference patterns observed in the LADC marine mammal phonation data cannot be explained by the propagation effects for temporal analysis windows corresponding to the duration of an animal click, and may be due to a uniqueness of an individual animal phonation apparatus. The utilization of simulation data for the development of an animal tracking algorithm based on the acoustic recordings of a single bottom‐moored hydrophone is discussed. The identification of the bottom and surface reflected clicks from the same animal is attempted. The critical ranges for listening to a deep‐water forging animal by a surface receiving system are estimated. [Research supported by ONR.]

Near‐bottom hydrophone measurements of ambient noise and sperm whale vocalizations in the northern Gulf of Mexico

Three bottom‐moored hydrophones, 50 m above the bottom, were placed on a downslope line, ending at the largest concentration of sperm whale sightings in the northern Gulf of Mexico, in 600 m, 800 m, and 1000 m water depths. These depths were chosen after upslope propagation modeling, using historical databases, showed transmission losses greater than 110 dB at hydrophones near the bottom in water shallower than 600 m for a 500 m deep source at the 1000 m contour. These autonomously recording hydrophones were environmental acoustic recording system (EARS) buoys obtained from the Naval Oceanographic Office. They were capable of recording signals up to 5500 Hz continuously for 36 days and were deployed from July 17 through August 21. During this period a major marine mammal exercise was being conducted at the surface by the Minerals Management Service and the National Marine Fisheries Service, with other government and university scientists, in which temporary acoustic recording devices were attached to the ...