Range-dependent flexibility in the acoustic field of view of echolocating porpoises (Phocoena phocoena)

Funding: Det Frie Forskningsrad (MJ)Toothed whales use sonar to detect, locate, and track prey. They adjust emitted sound intensity, auditory sensitivity and click rate to target range, and terminate prey pursuits with high-repetition-rate, low-intensity buzzes. However, their narrow acoustic field of view (FOV) is considered stable throughout target approach, which could facilitate prey escape at close-range. Here we show that, like some bats, harbour porpoises can broaden their biosonar beam during the terminal phase of attack but, unlike bats, maintain the ability to change beamwidth within this phase. Based on video, MRI, and acoustic-tag recordings, we propose this flexibility is modulated by the melon and implemented to accommodate dynamic spatial relationships with prey and acoustic complexity of surroundings. Despite independent evolution and different means of sound generation and transmission, whales and bats adaptively change their FOV, suggesting that beamwidth flexibility has been an important driver in the evolution of echolocation for prey tracking.Publisher PDFPeer reviewe

Single mode excitation in the shallow water acoustic channel using feedback control

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1996The shallow water acoustic channel supports far-field propagation in a discrete set of modes. Ocean experiments have confirmed the modal nature of acoustic propagation, but no experiment has successfully excited only one of the suite of mid-frequency propagating modes propagating in a coastal environment. The ability to excite a single mode would be a powerful tool for investigating shallow water ocean processes. A feedback control algorithm incorporating elements of adaptive estimation, underwater acoustics, array processing and control theory to generate a high-fidelity single mode is presented. This approach also yields a cohesive framework for evaluating the feasibility of generating a single mode with given array geometries, noise characteristics and source power limitations. Simulations and laboratory waveguide experiments indicate the proposed algorithm holds promise for ocean experiments.Josko Catipovic funded my research for summer of 1992 on the Office of Naval Research Grant Number N00014-92-J-1661 and from June 1993 through August 1995 on Defense Advanced Research Projects Agency Grant Number MDA972-92-J- 1041. The Office of Naval Research Grant N00014-95-1-0362 to MIT supported the computer facilities used to do much of this work

Efficient inversion methods in underwater acoustics

This dissertation describes efficient methods developed and implemented for source localization and sound speed and bottom depth estimation using sound propagation in the ocean. The proposed inversion techniques are based on the linearization of the generally non-linear inverse problem of parameter estimation in underwater acoustics. These techniques take into account properties of the ocean environment and are accurate in their estimation results without being prohibitively computationally intensive. For the inversion, select ray paths are taken into account: the direct, first surface bounce, and first bottom bounce. Ray travel time derivatives with respect to parameters that affect path arrival times are obtained analytically. These derivatives and a first order expansion are then used to find estimates of unknown parameters through replica and true paths; replica paths are generated using ray theory for underwater sound propagation and true paths are identified from measured time series. The linearization scheme works efficiently for the estimation of geometric parameters such as the source and receiver location coordinates and the depth of the water column. It is also successful in estimating the sound speed profile in the ocean using empirical orthogonal functions. In this work, the linearization inversion technique is applied to marine mammal tracking, and it is also used with real data collected during the Haro Strait experiment for source and receiver localization. For the Haro Strait data, inversion using linearization is also compared to matched-field processing, which estimates source location and geoacoustic parameters through a full field matching approach

Acoustic Oceanographic Buoy Test during the MREA’03 Sea Trial

Rep 04/03 - SiPLAB 10/Nov/2003Environmental inversion of acoustic signals for bottom and water column properties is being proposed in the literature as an interesting concept for complementing direct hydrographic and oceanographic measurements for Rapid Environmental Assessment (REA). The acoustic contribution to REA can be cast as the result of the inversion of ocean acoustic properties to be assimilated into ocean circulation models specifically tailored and calibrated to the scale of the area under observation. Traditional ocean tomography systems and methods for their requirements of long and well populated receiving arrays and precise knowledge of the source/receiver geometries are not well adapted to operational Acoustic REA (AREA). An innovative concept that responds to the operational requirements of AREA is being proposed under a Saclantcen JRP jointly submitted by the the Universit´e Libre de Bruxelles (ULB), SiPLAB/CINTAL at University of Algarve, the Instituto Hidrogr´afico (IH) and the Royal Netherlands Naval College (RNLNC) and approved by Saclantcen in 2003 under the 2004 SPOW. That concept includes the development of water column and geo-acoustic inversion methods being able to retrieve environmental true properties from signals received on a drifting network of Acoustic-Oceanographic Buoys (AOB). A prototype of an AOB and a preliminary version of the inversion code, was tested at sea during the Maritime Rapid Environment Assessment’2003 sea trial (MREA’03) and is described in this report together with the results obtained.This report presents the AOB system and the results obtained during its testing in the MREA’03 sea trial. The MREA’03 sea trial took place off the Italian coast, near Elba I. in the period 26 May - 27 June 2003. The authors of this report would like to thank: the SACLANT Undersea Research Centre for the opportunity for participating in the sea trial • the scientist in charge Dr. Emanuel Coelho; the collaboration of Saclantcen personnel; the master and crew of the R/V Alliance; the contribution of Prof. J.-P. Hermand from ULB for the discussions and pictures shown in this report

Broadband source localization with a single hydrophone

Source localization with vertical arrays in shallow water has been a topic of intense research in the last 20 years. Although horizontal arrays can (and have) been used, vertical arrays are better suited for extracting signal modal structure and thus provide a source-location estimate in range and depth. It is well known that broadband signals have a localization capability superior to that of narrowband signals. One question that remains largely unresolved is whether frequency extent can compensate for the spatial diversity provided by sensor arrays, i.e., at the limit, can a broadband signal be localized with a single sensor ? This communication presents theoretical, simulated, and practical evidence that a multipath-delay maximum-likelihood estimator does provide enough signal to background discrimination for localizing a 500 Hz bandwidth signal at 5 km range in a 130 m depth shallow water channel with a single hydrophone. The real data used in this study was collected during the INTI-MATE'96 experiment which was conducted off the west of Portugal in June 1996 during an internal tide tomography experiment. Comparison with localization results provided by direct match between the received and the model-generated arrival patterns will be discussed

A prony algorithm for shallow water waveguide analysis

Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1987Low frequency acoustic propagation in shallow water is examined from a normal mode context. By modelling the far field pressure field as a modal sum, propagating mode characteristics of wavenumber, initial phase, attennation and amplitude may be estimated using a high resolution parameter modeling technique. The advantages of such an algorithm are the resolution of closely spaced modes in a range independent environment and the ability to analyze range dependent waveguides. This thesis presents the application of a Prony algorithm to the shallow water environment. The algorithm operates directly on the signal matrix. Synthetically generated, range independent pressure fields are used to analyze the technique'S performance and to observe its sensitivity to variations in model specifications. Noise is added to determine the threshold of acceptable performance. As a consequence of field data tests, further enhancements to the algorithm are suggested. Range dependent performance is evaluated on a coastal wedge example and geoacoustic parameter shift example

Long distance passive localization of vocalizing sei whales using an acoustic normal mode approach

Author Posting. © Acoustical Society of America, 2012. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 131 (2012): 1814-1825, doi:10.1121/1.3666015.During a 2 day period in mid-September 2006, more than 200, unconfirmed but identifiable, sei whale (Balaenoptera borealis) calls were collected as incidental data during a multidisciplinary oceanography and acoustics experiment on the shelf off New Jersey. Using a combined vertical and horizontal acoustic receiving array, sei whale movements were tracked over long distances (up to tens of kilometers) using a normal mode back propagation technique. This approach uses low-frequency, broadband passive sei whale call receptions from a single-station, two-dimensional hydrophone array to perform long distance localization and tracking by exploiting the dispersive nature of propagating normal modes in a shallow water environment. The back propagation approach is examined for accuracy and application to tracking the sei whale vocalizations identified in the vertical and horizontal array signals. This passive whale tracking, combined with the intensive oceanography measurements performed during the experiment, was also used to examine sei whale movements in relation to oceanographic features observed in this region.Office of Naval Researc

Performance analysis of adaptive equalization for coherent acoustic communications in the time-varying ocean environment

Author Posting. © Acoustical Society of America, 2005. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 118 (2005): 263-278, doi:10.1121/1.1907106.Equations are derived for analyzing the performance of channel estimate based equalizers. The performance is characterized in terms of the mean squared soft decision error of each equalizer. This error is decomposed into two components. These are the minimum achievable error and the excess error. The former is the soft decision error that would be realized by the equalizer if the filter coefficient calculation were based upon perfect knowledge of the channel impulse response and statistics of the interfering noise field. The latter is the additional soft decision error that is realized due to errors in the estimates of these channel parameters. These expressions accurately predict the equalizer errors observed in the processing of experimental data by a channel estimate based decision feedback equalizer (DFE) and a passive time-reversal equalizer. Further expressions are presented that allow equalizer performance to be predicted given the scattering function of the acoustic channel. The analysis using these expressions yields insights into the features of surface scattering that most significantly impact equalizer performance in shallow water environments and motivates the implementation of a DFE that is robust with respect to channel estimation errorsThis work has been supported by ONR Grant Nos. N00014-00-1-0048 and N00014-02-C-0201

Investigation of mode filtering as a preprocessing method for shallow-water acoustic communications

Author Posting. © IEEE, 2010. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 35 (2010): 744-755, doi:10.1109/JOE.2010.2045444.Acoustical array data from the 2006 Shallow Water Experiment (SW06) was analyzed to show the feasibility of broadband mode decomposition as a preprocessing method to reduce the effective channel delay spread and concentrate received signal energy in a small number of independent channels. The data were collected by a vertical array, which spans the water column from 12-m depth to the bottom in shallow water 80 m in depth. Binary-sequence data were used to phase-shift-keyed (PSK) modulate signals with different carrier frequencies. No error correction coding was used. The received signals were processed by a system that does not use training or pilot signals. Signals received both during periods of ordinary internal wave activity and during a period with unusually strong internal wave solitons were processed and analyzed. Different broadband mode-filtering methods were analyzed and tested. Broadband mode filtering decomposed the received signal into a number of independent signals with a reduced delay spread. The analysis of signals from the output of mode filters shows that even a simple demodulator can achieve a low bit error rate (BER) at a distance 19.2 km.This work was supported by the U.S. Office of Naval Research (ONR)

Shallow water tomography in a highly variable scenario

In October 2000, SiPLAB and the Instituto Hidrografico (IH - PN) conducted the IN-TIFANTE'00 sea trial in a shallow area off the Peninsula of Troia, approximately 50 km south from Lisbon, in Portugal. The experiment itself and results obtained in most of the data set have been reported at various occasions in the last two years. This paper focuses on the data acquired during Event 2, where the acoustic propagation path was approximately range independent and the source ship was held on station at a constant range of 5.8 km from the vertical line array. Although these conditions were, in general, relatively benign for matched-field tomography, retrieval of water column and bottom parameters over a 14-hour-long recording revealed to be extremely difficult. This paper analysis in detail the characteristics of this data set and determines the causes for the observed inversion difficulties. Is is shown that the causes for the poor performance of the conventional methods are mainly the tide induced spatially correlated noise and the relative source-receiver motion during time averaging. An eigenvalue-based criterion is proposed for detecting optimal averaging time. It is shown that this data selection procedure together with hydrophone normalization and an appropriate objective function provide a better model fit and consistent inversion results and thus a better understanding of the environmental variability