# Kay L GembaNaval Postgraduate School | NPS · Department of Physics

Kay L Gemba

Doctor of Philosophy

## About

72

Publications

33,977

Reads

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472

Citations

Citations since 2017

Introduction

Kay Gemba works in the Department of Physics, United States Naval Postgraduate School. His research interests are in Acoustical Oceanography, Statistical Signal Processing, and Inverse Theory.

Additional affiliations

May 2020 - September 2021

February 2018 - May 2020

January 2015 - January 2018

## Publications

Publications (72)

This manuscript discusses the utility of maximal period linear binary pseudorandom sequences [also referred to as m-sequences or maximum length sequences (MLSs)] and linear frequency-modulated (LFM) sweeps for the purpose of measuring travel-time in ocean-acoustic experiments involving moving sources. Signal design and waveform response to unknown...

The use of knowledge-aided covariance is considered for processing underwater acoustic array data in snapshot-deficient scenarios. The knowledge-aided formalism is a technique that combines array data with a known covariance to produce an invertible estimate. For underwater acoustics, simulations of ambient noise provide the a priori covariance all...

The 75 Hz Kauai-Beacon source is well-situated for observing the North Pacific Ocean acoustically, and ongoing efforts enable transmissions and analysis of broadband signals in 2023 and beyond. This is the first demonstration of acoustic receiving along paths to Wake Island (∼3500 km) and Monterey Bay (∼4000 km). The 44 received m-sequence waveform...

This paper discusses the value added by using a single vector sensor over a conventional pressure-only hydrophone for geoacoustic inversions. Inversion methods based on genetic algorithms are used to estimate the seabed properties. Synthetic signals of impulsive arrivals first are modeled using KRAKEN and RAM propagation models, each being modified...

For underwater source localization, accurate estimation of the time of flight (or travel time) is required and the observed waveform may include Doppler (waveform dilation). The source waveform, thus, needs to be sensitive to estimate both time of flight and Doppler. In this study, we compare two waveforms : Linear Frequency Modulated sweeps (LFMs)...

This video presentation is dedicated to the career and legacy of Jeffrey A. Nystuen.

No PDF available
ABSTRACT
The Departments of Physics and of Electrical and Computer Engineering at the Naval Postgraduate School offer graduate programs in acoustics leading to MS and PhD degrees in applied physics and engineering acoustics. Engineering acoustics degrees can be completed in either traditional or distance learning modes. The departm...

No PDF available
ABSTRACT
Long distance underwater acoustic propagation is of interest for a variety of applications including underwater navigation, yet modeling such propagation is challenging due to the large degree of environmental uncertainty. In this presentation, the propagation of 75 Hz center frequency maximum length sequence (MLS) signals...

Ocean sound speed and its uncertainty are estimated using travel-time tomography at ranges up to 2 km using a moving source in ∼600 m water depth. The experiment included two 32-element vertical line arrays deployed about 1 km apart and a towed source at ∼10 m depth transmitting a linear frequency modulated waveform. The inversion accounts for unce...

A library of broadband (100–1000 Hz) channel impulse responses (CIRs) estimated between a short bottom-mounted vertical line array (VLA) in the Santa Barbara channel and selected locations along the tracks of 27 isolated transiting ships, cumulated over nine days, is constructed using the ray-based blind deconvolution algorithm. Treating this CIR l...

No PDF available
ABSTRACT
A moving source tomography experiment was conducted in 2016 off the coast of Southern California. From the travel time data extracted from the experiment, ocean sound speed and its uncertainty were estimated. The moving source poses extra complexity and adds components that need to be accounted for in a successful inversio...

No PDF available
ABSTRACT
We consider passive localization and tracking of an underwater acoustic source from measurements provided by a vertical line array. A focalization approach is introduced that probabilistically associates detected directions of arrival (DOAs) to modeled DOAs and jointly estimates the time-varying source location. Modelled D...

This paper presents a Bayesian estimation method for the passive localization of an acoustic source in shallow water. Our probabilistic focalization approach estimates the time-varying source location by associating direction of arrival (DOA) observations to DOAs predicted based on a statistical model. Embedded ray tracing makes it possible to inco...

Localizing and tracking an underwater acoustic source is a key task for maritime situational awareness. This paper presents a sequential Bayesian estimation method for passive acoustic source localization in shallow water. The proposed probabilistic focalization approach associates detected directions of arrival (DOAs) to modeled DOAs and jointly e...

This paper introduces the maximal eigengap estimator for finding the direction of arrival of a wideband acoustic signal using a single vector-sensor. We show that in this setting narrowband cross-spectral density matrices can be combined in an optimal weighting that approximately maximizes signal-to-noise ratio across a wide frequency band. The sig...

No PDF available
ABSTRACT
A scaled experiment in a water tank was conducted to study effects of medium heterogeneities on underwater acoustic propagation while controlling the so-called fluctuations. An ultrasonic wave is transmitted (a pulse train at center frequency f = 2.25 MHz) throughout an acoustic lens presenting a plane input face and a ran...

A multiple constraint method (MCM) specifically designed to accommodate the uncertainty of array tilt is developed for matched field processing (MFP). Combining the MCM with the white noise gain constraint method results in a processor that is tolerant to both array tilt and environmental mismatch. Experimental results verify the robustness of the...

Ocean acoustic travel-time-tomography attempts to map heterogeneities such as ocean temperature with mesoscale resolution. The Santa Barbara Channel Experiment in 2016 (SBCEx16) contained both controlled and uncontrolled (i.e., ships of opportunity) sources, in addition to environmental data collected by a variety of sensors. The path to developing...

No PDF available
ABSTRACT
Ed Sullivan’s legacy includes significant contributions to the field of signal processing. Inspired by his Bayesian approach, we present results for a method coined Sparse Bayesian learning (SBL) to estimate source parameters. Previously, SBL has been applied to the matched field processing application [K. L. Gemba, S. Nan...

Sparse Bayesian learning (SBL) has emerged as a fast and competitive method to perform sparse process- ing. The SBL algorithm, which is developed using a Bayesian framework, iteratively solves a non-convex optimization problem using fixed point updates. It provides comparable performance and is significantly faster than convex optimization techniqu...

Sparse linear arrays such as co-prime and nested arrays can resolve more sources than the number of sensors. In contrast, uniform linear arrays (ULA) cannot resolve more sources than the number of sensors. This paper demonstrates this using Sparse Bayesian learning (SBL) and co-array MUSIC for single frequency beamforming. For approximately the sam...

The uncertainty of estimating relative channel impulse responses (CIRs) obtained using the radiated signature from a ship of opportunity is investigated. The ship observations were taken during a 1.4 km (11 min) transect during the Noise Correlation 2009 (NC09) experiment. Beamforming on the angle associated with the direct ray-path yields an estim...

No PDF available
ABSTRACT
The paper considers direction of arrival (DOA) estimation from long-term observations in a noisy environment. In such an environment the noise source might evolve, causing the stationary models to fail. Therefore a heteroscedastic Gaussian noise model is introduced where the variance can vary across observations and sensor...

Using simulations and data, we localize a quiet source in the presence of an interferer. The SWellEx-96 Event S59 consists of a submerged source towed along an isobath over a 65 min duration with an interferer traversing the source track. This range independent, multi-frequency scenario includes mismatch, non-stationary noise, and operational uncer...

The uncertainty of estimating relative channel impulse responses (CIRs) obtained using the radiated signature from a ship of opportunity is investigated. The ship observations were taken during a 1.4 km (11 min) transect in a shallow water environment during the Noise Correlation 2009 (NC09) experiment. Beamforming on the angle associated with the...

Sparse Bayesian learning (SBL) employs Gaussian priors with unknown parameters to solve an underdetermined system of linear equation. It provides comparable performance and is significantly faster than convex optimization techniques used in sparse processing. In this paper we extend SBL to process observations from multiple dictionaries when the sp...

An experiment was performed in the Santa Barbara Channel (SBCEx16) using four vertical line arrays (VLAs) of hydrophones placed midway between the in- and out-going shipping lanes of a maritime highway. The goal of this experiment was to study whether these sources of opportunity can be used for passive tomographic purposes. In addition to the cont...

This paper summarizes the ongoing investigations surrounding the use of a ray-based blind deconvolution algorithm to recover arrival time information from sources of opportunity, such as shipping vessels, recorded on vertical line arrays (VLAs) in ocean waveguides. The deconvolution is primarily performed by using an estimate of the unknown source...

Previously, we demonstrated using the Noise-09 data set that it is possible to estimate the relative channel impulse responses (CIR) over a 1.5 km transect independently at 3 vertical line arrays (VLAs). This vessel provided sufficient SNR and bandwidth for the uncertainty of the direct arrival time to reach 5 microseconds. The time evolution of th...

The multi-snapshot, multi-frequency sparse Bayesian learning (SBL) processor is derived and its performance compared to the Bartlett, minimum variance distortionless response, and white noise constraint processors for the matched field processing application. The two-source model and data scenario of interest includes realistic mismatch implemented...

Passive acoustic tomography exploits the acoustic energygenerated by sources with unknown spectral content such as sources of opportunity (e.g., cargo ships) to study the ocean. The recording at each sensor within a vertical line array (VLA) is the channel impulse response (CIR) convolved with the noisegenerated by the moving random radiator. Using...

An experiment was performed in the Santa Barbara Channel using four vertical acoustic receive arrays placed between the sea lanes of in- and outgoing shipping traffic. The purpose of the experiment was to determine whether these sources of opportunity can be utilized for tomographic inversion of water column properties. The environment was continuo...

Compressive sensing has been applied to underwater acoustic problems. Using multi-frequency sparse Bayesian learning (SBL), we present simulation and data results (SWellEx-96 Event S5) including mismatch. Mismatch is defined as a misalignment between the actual source field observed at the array and the modeled replica vector. Results for a multipl...

Sparse Bayesian learning (SBL) has emerged as a fast and competitive method to perform sparse processing. The SBL algorithm, which is developed using a Bayesian framework, approximately solves a non-convex optimization problem using fixed point updates. It provides comparable performance and is significantly faster than convex optimization techniqu...

Sparse Bayesian learning is a sparse processing method used for solving high-dimensional, underdetermined linear equations. Often the sensing matrix in the system of equations is assumed known and in presence of perturbations in this matrix performance of sparse processing degrades. We develop a sparse Bayesian learning method that accounts for per...

Matched field processing is a generalized beamforming method that matches received array data to a dictionary of replica vectors in order to locate one or more sources. Its solution set is sparse since there are considerably fewer sources than replicas. Using compressive sensing (CS) implemented using basis pursuit, the matched field problem is ref...

The impulse response (IR) of an acoustic channel can be obtained by cross-correlating the received signal with the broadband excitation signal in unfavorable noise conditions. However, the decon-volved IR is colored by the IRs of the combined electrical equipment. This letter presents a time domain approach using pre-computed filters to whiten the...

Passive acoustic tomography exploits the acoustic energy generated by sources with unknown spectral content such as sources of opportunity (e.g., cargo ships) to study the ocean. However, separating the channel impulse response (CIR) from a possibly moving, random radiator is non-trivial for coherent processing and the amount of unknown variables m...

Compressive sensing based techniques have recently been applied successfully to underwater acoustics problems such as beamforming and matched field processing. Sparse Bayesian Learning (SBL) is one of the fast compressive sensing methods and is formulated using Bayesian statistics. In the SBL framework, source amplitudes are modeled as complex Gaus...

Compressive sensing based techniques have been applied successfully to underwater acoustics problems. We present data results using a robust multi-frequency sparse Bayesian learning (SBL) algorithm that can account for model mismatch leading to errors in the replica vector dictionary. We use the SWellEx-96 Event S5 data set to demonstrate SBL capab...

Matched field processing is a generalized beamforming method which matches received array data to a dictionary of replica vectors to locate and track a source. Its solution set generally is sparse since there are considerably fewer sources than replicas. The problem is also underdetermined since the number of sensors are less than the number of uni...

Matched field processing is a generalized beamforming method which matches received array data to a dictionary of replicas to locate and track a source. The solution set generally is sparse since there are considerably fewer sources than replicas. This underdetermined problem can be solved with sparse processing (SP) which potentially is attractive...

The ability to accurately characterize an underwater sound source is an important prerequisite for many applications including detection, classification, monitoring and mitigation. Unfortunately, anechoic underwater recording environments, required to make ideal recordings, are generally not available. Current methods adjust source recordings with...

The use of passive acoustics to detect self-contained underwater breathing apparatus (SCUBA) divers is useful for nearshore and port security applications. While the performance of a detector can be optimized by understanding the signal's spectral characteristics, anechoic recording environments are generally not available or are cost prohibitive....

A goal of the Center for Island, Maritime, and Extreme Environment Security is to develop passive acoustic methods to monitor harbor and near-shore environments. To study detection of open circuit SCUBA divers, several regulator configurations were recorded and characterized under ideal conditions in a pool environment. Sound Pressure Levels (SPL)...

A passive acoustic system aimed at tracking sound sources in harbor and near‐shore environments is currently being developed. At the expense of decreased directivity for the same number of elements, volumetric arrays have an advantage over line or planar arrays since beam patterns can be steered both vertically and horizontally. In this paper, the...

The purpose of this project is to extend a previously developed synthesis level multidisciplinary design and optimization (MDO) method for a Trimaran and apply it to preliminary design stage of a catamaran vessel concept. The synthesis method integrates stability, powering, structural weights, payload, ship cost and hydrodynamic performance of a sh...

The paper discusses the development of a 2000 N thrust liquid oxygen/propylene rocket engine designed to power the upper stage of a Nanosat Launch Vehicle (NLV). The prelim-inary design is intended for space operations with an expansion ratio of 70. The targeted combustion efficiency is 95% and nozzle efficiency is 98%, corresponding to a specific...

The paper discusses the development of a 2000 N thrust liquid oxygen/propylene rocket engine designed to power the upper stage of a Nanosat Launch Vehicle (NLV). The preliminary design is intended for space operations with an expansion ratio of 70. The targeted combustion efficiency is 95% and nozzle efficiency is 98%, corresponding to a specific i...

The paper discusses the development and testing of a 2000 N thrust liquid oxygen/propylene rocket engine designed to power the upper stage of a Nanosat Launch Vehicle (NLV). The preliminary design is intended for space operations with an expansion ratio of 70. The targeted combustion efficiency is 95% and nozzle efficiency is 98%, corresponding to...

In quantum mechanics with minimal length uncertainty relations the Heisenberg-Weyl algebra of the one-dimensional harmonic oscillator is a deformed SU(1,1) algebra. The eigenvalues and eigenstates are constructed algebraically and they form the infinite-dimensional representation of the deformed SU(1,1) algebra. Our construction is independent of p...

This report summarizes the Prometheus project, which is currently being developed by the National Aeronautics and Space Agency (NASA), and focuses in detail on the Nuclear Electric Propulsion (NEP) system.. The Jupiter Icy Moon Orbiter (JIMO), the first spacecraft designed in the Prometheus project, is a robotic spacecraft with the
mission to explo...

It is well known that an objects shape plays a critical role in the drag produced while subjected to a free stream flow. This experiment was conducted to become more familiar with the effects an object' shape has on drag. Utilizing a single component balance in a subsonic windtunnel, testing was conducted at different flow speeds to measure corresp...

A basic understanding of flow characteristics over a flat plate is essential to a complete study of Aerodynamics. This experiment was conducted in the California State University of Long Beach, CSULB, windtunnel to gain a better understanding of the parameters and characteristics of fluid flow over a flat plate. Readings of the boundary layer were...