Eva-Marie Nosal

Sperm whale three-dimensional track, swim orientation, beam pattern, and click levels observed on bottom-mounted hydrophones.

In an earlier paper [Nosal and Frazer Appl. Acoust. 61, 1187-1201 (2006)], a sperm whale was tracked in three-dimensions using direct and surface-reflected time differences (DRTD) of clicks recorded on five bottom-mounted hydrophones, a passive method that is robust to timing errors between hydrophones. This paper refines the DRTD method and combines it with a time of (direct) arrival method to improve the accuracy of the track. The position and origin time of each click having been estimated, pitch and yaw are then obtained by assuming the main axis of the whale is tangent to the track. Roll is then found by applying the bent horn model of sperm whale phonation, in which each click is composed of two pulses, p0 and p1, that exit the whale at different points. With instantaneous pitch, roll, and yaw estimated from time differences, amplitudes are then used to estimate the beam patterns of the p0 and p1 pulses. The resulting beam patterns independently confirm those obtained by Zimmer et al. [J. Acoust. Soc. Am. 117, 1473-1485 (2005); 118, 3337-3345 (2005)] with a very different experimental setup. A method for estimating relative click levels is presented and used to find that click levels decrease toward the end of a click series, prior to the creak associated with prey capture.

Localization and Subsurface Position Error Estimation of Gliders Using Broadband Acoustic Signals at Long Range

Broadband acoustic source transmissions recorded on Seagliders at ranges up to 700 km are used to estimate subsurface glider position. Because the sources transmitted at 9-min intervals the glider moved appreciably between source receptions. Source-glider ranges estimated from acoustic arrivals were combined using least squares analysis to estimate glider position and velocity during each reception period. The analysis was applied to 387 sets of source transmissions using three different flight models of glider subsurface motion for initial position input values. The offsets between the position estimated from the flight models and the acoustically derived position resulting from the inversions were 600-900-m root mean square (rms) depending upon the model and input parameters. The offsets were tripled if the positions from the flight models were not corrected for a dive-averaged current (DAC). Estimates of a posteriori errors ranged from 78-105-m rms and from 9.1-11.6-cm/s rms for glider position and velocity, respectively. Data residuals were on the order of 50-m rms, a dramatic reduction from 178-m rms, which was documented for the case neglecting the motion of the glider between subsequent source transmissions (Van Uffelen , J. Acoust. Soc. Amer., vol. 134, pp. 3260-3271, 2013). Overall horizontal glider speed was estimated to be approximately 21-cm/s rms.

Acoustic Seagliders in PhilSea10: Preliminary results

In November 2010, four acoustic Seagliders were deployed in the Northern Philippine Sea in the vicinity of an acoustic tomography array as part of the PhilSea10 project with the goal of characterizing this oceanographically complex and highly dynamic region. The gliders were flown between the moored transceivers of the pentagonal tomography array with a radius of approximately 330 km until their recovery in April 2011. During this mission they collected oceanographic and acoustic data in the upper 1000 m of the water column. Temperature, salinity, and pressure data collected by the Seagliders provide a time-evolving characterization of the sound-speed environment in the variable upper ocean between the transceivers. The gliders were also equipped with an integrated Acoustic Recorder System (ARS). The ARS was scheduled to record transmissions from the moored acoustic tomography sources, measuring the arrival structure between the various moorings in order to near-continuously map the arrival pattern as a function of range and depth. Spectrograms show the arriving linear frequency modulated signals from the sources, as well as other ocean sounds. With travel times determined from this data, we will determine whether, given the joint nature of the combined positioning/tomography problem, it is possible to use Seagliders equipped with an acoustic receiver as mobile nodes in the tomography array, thereby enhancing the resolution of the tomography system.

Compressional Wave Speed Dispersion and Attenuation in Carbonate Sediments, Kaneohe Bay, Oahu, HI

In situ compressional wave speed and attenuation measurements between 20 and 100 kHz were made at two carbonate sediment sites in Kaneohe Bay, on the windward side of the Hawaiian island of Oahu. Velocities increased with frequency from 1691 to 1708 m/s at a coarse sediment site (HC, porosity=0.45) and from 1579 to 1585 m/s at a fine-grained sediment site (HF, porosity=0.56). Effective attenuation increased with frequency from 15 to 75 dB/m at HC and from 22 to 62 dB/m at HF. Values of sound speed at these sites are within the range of those reported in the literature for silicate sands of the same porosity. Attenuation values of these reef-derived carbonate sands are higher than many of those reported in the literature for silicate sands and they appear to be linearly related to frequency (¿=0.65f). Sound-speed and attenuation data were compared to predictions of two sediment geoacoustic models, Biot-Stoll and grain shearing (GS). In both models, two unknown parameters were varied to find best fits at each site to: 1) both attenuation and sound-speed data and 2) sound-speed data only. Both models yielded similar fits, which differ significantly from the measured data.

Single-hydrophone automated passive acoustic ranging of fin whales at Station ALOHA

This paper presents a technique for performing passive underwater acoustic ranging with data from a single hydrophone and builds upon earlier localization approaches which estimate the sound source position using times of arrival of acoustic energy traveling along direct and/or interface-reflecting paths between source and receiver. In this work, measured time differences between interface-reflecting and direct path arrival times are compared with a set of model-predicted time differences calculated over a set of candidate source ranges in a way that does not require measured arrival paths to be labeled (e.g., direct, surface bounce, bottom bounce, etc.). The modeled set with the best match to the measured data indicates the best estimate of source range. To enable the processing of multi-year data sets, the detection and localization steps are automated and, where possible, multi-threaded to improve computational efficiency on multi-core computer processors. This approach is demonstrated using 20-Hz fin whale (Balaenoptera physalus) calls recorded by the ALOHA Cabled Observatory (ACO), 100 km N of Oahu (Hawaii) in 4782 m of water.This paper presents a technique for performing passive underwater acoustic ranging with data from a single hydrophone and builds upon earlier localization approaches which estimate the sound source position using times of arrival of acoustic energy traveling along direct and/or interface-reflecting paths between source and receiver. In this work, measured time differences between interface-reflecting and direct path arrival times are compared with a set of model-predicted time differences calculated over a set of candidate source ranges in a way that does not require measured arrival paths to be labeled (e.g., direct, surface bounce, bottom bounce, etc.). The modeled set with the best match to the measured data indicates the best estimate of source range. To enable the processing of multi-year data sets, the detection and localization steps are automated and, where possible, multi-threaded to improve computational efficiency on multi-core computer processors. This approach is demonstrated using 20-Hz fin ...

Multi-channel cross-correlation used to estimate time delays

Many marine mammal localization techniques rely on estimating the time of arrival delays of a call between the hydrophones of an array. This is commonly achieved by cross-correlating (some version of) received signals between hydrophone pairs. This process is complicated in cases with noise, multiple animals, and multipath arrivals. In this talk, I explore and demonstrate the potential of a multi-channel cross-correlation technique to help establish time delay estimates. Possible extensions to signal enhancement for detection and classification purposes are also discussed. [This work was supported by ONR Award No. N00014-16-1-2598.]Many marine mammal localization techniques rely on estimating the time of arrival delays of a call between the hydrophones of an array. This is commonly achieved by cross-correlating (some version of) received signals between hydrophone pairs. This process is complicated in cases with noise, multiple animals, and multipath arrivals. In this talk, I explore and demonstrate the potential of a multi-channel cross-correlation technique to help establish time delay estimates. Possible extensions to signal enhancement for detection and classification purposes are also discussed. [This work was supported by ONR Award No. N00014-16-1-2598.]

Impulsive source separation with application to sperm whale clicks

This paper proposes a new method for impulsive source separation in multi-input single-output (MISO) systems based on impulse spacing. The primary application of the method is the classification of click trains from multiple marine mammals. The impulse spacing can be modeled as a renewal process, so to classify sources, an algorithm is developed to maximize the likelihood of click assignment based on the impulse spacing distributions. A theoretical lower bound on the performance is derived and the algorithm shown to get reasonably close to the bound. Additionally, the algorithm is further extended for use when the impulse spacing distribution parameters are unknown. The algorithm is tested with recordings of sperm whales, and the separation is shown to be accurate.

Passive Acoustic Monitoring of Surface Vessel Activity

Monitoring human activity in remote marine areas is a challenging problem to which acoustic methods present a promising solution. This paper develops and demonstrates automated passive acoustic methods to estimate ranges to surface vessels using a single seafloor-mounted hydrophone. Surface vessels that use echosounders (to navigate or find fish, for example) are especially well suited for passive acoustic monitoring since they use high-energy, narrow-band, short-duration pulses. Examples of surface vessel ranges estimated using echosounder pulses recorded on a seafloor-mounted hydrophone are presented.Copyright