Kevin L Cockrell

Massachusetts Institute of Technology | MIT

Geoacoustic inversions using modal dispersion data is a very robust technique to estimate properties of the shallow water sediments. Accurate estimation of the modal arrival times is required for improving the accuracy of the inversion. A time-frequency analysis of the single hydrophone data is typically used to extract modal arrival times. This st...

While it is generally true that the waveguide invariant β is approximately equal to one in many shallow-water environments, the value of β observed in acoustic intensity striation patterns often deviates from the assumed value of one by 30% or more. The precise value of β, like the acoustic field itself, depends on source frequency, source and rece...

Driving large piles into the seafloor, as is done when constructing off-shore wind farms, produces high level underwater noise that can have an adverse effect on local marine life. This talk reviews an investigation of methods to mitigate this pile driving noise. A numerical model was used to simulate the structural vibrations in the pile and its c...

Much of the recent research in ocean acoustics has focused on developing methods to exploit the effects that the sea surface and seafloor have on acoustic propagation. Many of those methods require detailed knowledge of the acoustic properties of the seafloor and the sound speed profile (SSP), which limits their applicability. The range-frequency w...

The frequency dependence of a waveguide's Green's function can be summarized by a single parameter known as the waveguide invariant, β. Although it has been shown analytically that β≈1 for ideal waveguides, numerical and experimental results have shown that β≈1 for many realistic shallow water waveguides as well. There is not much prior work explai...

It is well known that a horizontal line array (HLA) can be used to observe a planewave signal from one source while rejecting noise from other sources. This talk discusses the selection of HLA processor weights when the goal is to observe waveguide invariant striations from one source while rejecting noise from other sources. It is shown that the a...

The waveguide invariant is typically defined using of normal modes or ray theory, but it can also be related to the wavenumber-integration method for calculating the acoustic field in a waveguide. In this letter, the Wiener-Khinchin Theorem is used to show that the autocorrelation of the wavenumber-integration kernel, when plotted versus wavenumber...

The waveguide invariant principle is used to estimate the range to a broadband acoustic source in a shallow-water waveguide using a single acoustic receiver towed along a path directly toward the acoustic source. A relationship between the signal processing parameters and the ocean-acoustic environmental parameters is used to increase the effective...

The waveguide invariant describes striations in a range versus frequency plot of a waveguide's Green's function. Analytic expressions for the waveguide invariant only exist for a few select waveguides, but experiments and simulations have shown that the waveguide invariant is approximately equal to unity for almost all realistic shallow-water waveg...

A range versus frequency spectrogram of an acoustic field due to a fixed source in a waveguide will exhibit striations whose slopes depend on the range to the acoustic source and the value of the waveguide invariant. While many authors have pointed out that the range to an acoustic source can be estimated from the slopes of the striations in the sp...

This talk addresses the problem of sequentially estimating the location of a moving acoustic source in a waveguide, given a series of acoustic field measurements from an array. The approach taken, in it's most general form, is known as sequential Bayesian estimation. A well known special case of sequential Baysian estimation is the Kalman filter. H...

Despite extensive effort by the ocean acoustics community to design signal processing techniques that take advantage of the waveguide structure of ocean environments (e.g., matched field processing), planewave beamforming remains the only technique robust enough to be used with autonomous vehicles processing data in real‐time. However, the waveguid...

It has been of recent interest to use autonomous underwater vehicles (AUVs) with towed arrays for source localization in ocean acousticwaveguides with uncertain environmental parameters. However, AUVs cannot implement source localization techniques designed to be robust against environmental mismatch because such techniques require more computation...

This paper provides an introductory description and User's Guide for the MIT MOOS-IvP Undersea Autonomous Network Architecture, based on the Nested Autonomy paradigm, as implemented and operated on the fleet of Bluefin21 autonomous Underwater vehicles applied by the Laboratry for Autonomous Marine sensing for research and development into distribut...