Scholars@Duke
Jeffrey L. Krolik

Jeffrey L. Krolik

Professor of Electrical and Computer Engineering
Pierre R. Lamond Department of Electrical and Computer Engineering
jlk@duke.edu
Box 90291, Durham, NC 27708-0291
3465 CIEMAS, Durham, NC 27708

Scholarly Works - Journal articles

Ship Classification by Cyclostationary Analysis of Preimage Formation ISAR Data

Journal article IEEE Transactions on Radar Systems · January 1, 2026 Inverse synthetic aperture radar (ISAR) has proven valuable for imaging in maritime contexts. However, micro-Doppler (m-D) effects from rotating components on ships often blur ISAR imagery and complicate classification. On the other hand, m-D measurement c ... Full text Cite

Adaptive focusing for wideband beamforming in multipath environments.

Journal article The Journal of the Acoustical Society of America · January 2025 This paper addresses achieving the high time-bandwidth product necessary for low signal-to-noise ratio (SNR) target detection and localization in complex multipath environments. Time bandwidth product is often limited by dynamic environments and platform m ... Full text Cite

Athena – The NSF AI Institute for Edge Computing

Journal article AI Magazine · March 1, 2024 The National Science Foundation (NSF) Artificial Intelligence (AI) Institute for Edge Computing Leveraging Next Generation Networks (Athena) seeks to foment a transformation in modern edge computing by advancing AI foundations, computing paradigms, network ... Full text Cite

A wavefront adaptive sensing beamformer for ocean acoustic waveguides.

Journal article The Journal of the Acoustical Society of America · October 2023 This paper addresses robust adaptive beamforming for passive sonar in uncertain, shallow-water environments. Conventional beamforming is still common in passive sonar because adaptive beamformers suffer from signal mismatch in complex multipath environment ... Full text Cite

Vibrational Radar Backscatter Communications Theory and Bound

Journal article IEEE Transactions on Radar Systems · January 1, 2023 Vibrational radar backscatter communication (VRBC) utilizes millimeter-wave radar vibrometry to receive message signals from vibrating surfaces. So long as multiple transponding surfaces are separable by the system radar in angle and/or range, VRBC can sim ... Full text Cite

Waveguide-Invariant-Based Ranging and Receiver Localization Using Tonal Sources of Opportunity

Journal article IEEE Journal of Oceanic Engineering · April 1, 2020 Acoustic emissions from cargo ships transiting coastal waterways, measured by a single hydrophone, can be exploited to estimate both the time-varying source-receiver range and receiver location. In this paper, two parameter-search-based maximum-likelihood ... Full text Cite

Range-Velocity Estimation Bounds for Nonuniform Sonar Comb Signals

Journal article IEEE Transactions on Aerospace and Electronic Systems · December 1, 2018 This paper focuses on wideband Doppler-sensitive nonuniform frequency comb signals for sonar. Cramér-Rao bounds are derived for joint estimation of target range and velocity for comb signals with arbitrary frequency distribution in a fading channel with no ... Full text Cite

Synthetic aperture processing for passive co-prime linear sensor arrays

Journal article Digital Signal Processing A Review Journal · February 1, 2017 In this paper, we explore the use of synthetic aperture processing for optimizing the spatial covariance estimation capabilities of a moving linear co-prime sensor array. The linear co-prime sensor array geometry is a thinned linear array that is construct ... Full text Cite

MIMO space-delay adaptive processing for wide-area indoor human motion classification

Journal article IEEE Transactions on Aerospace and Electronic Systems · June 1, 2016 This paper develops space-delay adaptive processing (SDAP) for multiple-input, multiple-output (MIMO) arrays with application to classifying human motion in wide-area indoor environments. The proposed adaptive method resolves motion returns using joint spa ... Full text Cite

Multichannel Backscatter Communication and Ranging for Distributed Sensing With an FMCW Radar

Journal article IEEE Transactions on Microwave Theory and Techniques · July 1, 2015 This paper considers the adaptation of frequency modulated continuous wave (FMCW) radars for sensor data exfiltration in addition to their primary use in area surveillance. In particular, the application of wideband RF backscatter from semi-passive RF sens ... Full text Cite

Passive Towed Array Shape Estimation Using Heading and Acoustic Data

Journal article IEEE Journal of Oceanic Engineering · April 1, 2015 This paper addresses the problem of array shape estimation for passive towed sonar systems during platform maneuvers. Directional noise fields due to distant shipping lanes can be exploited as sources of opportunity for online array shape calibration. In t ... Full text Cite

MIMO adaptive beamforming for nonseparable multipath clutter mitigation

Journal article IEEE Transactions on Aerospace and Electronic Systems · October 1, 2014 The performance of ground-moving target indicator radars is often degraded in complex terrain by multipath spread-Doppler clutter. Multiple-input, multiple-output (MIMO) beamforming with limited training data has been previously proposed with separable tra ... Full text Cite

Simultaneous target and multipath positioning

Journal article IEEE Journal on Selected Topics in Signal Processing · February 1, 2014 This paper addresses the problem of target geo-localization in complex multipath environments such as indoor and urban settings. In both radar applications (where targets are non-cooperative) and navigation in GPS-denied areas using RF signals (where the s ... Full text Cite

Multichannel radar backscatter communication and localization

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 2014 This paper concerns the use of wideband RF backscatter from semi-passive RF tags for energy-efficient wireless telemetry. Using LFM (Linear Frequency Modulated) signals from a radar basestation, we present a method for joint ranging and communications with ... Full text Cite

MIMO RF probe for wide-area indoor human motion monitoring

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 2014 This paper addresses the problem of RF-based wide-area human motion monitoring in indoor multipath environments. A major challenge for conventional pulse-Doppler radar in mul-tipath scenarios is the difficulty in discriminating direct-path targets from gho ... Full text Cite

Exploiting array motion for augmentation of co-prime arrays

Journal article Proceedings of the IEEE Sensor Array and Multichannel Signal Processing Workshop · January 1, 2014 In this paper, we combine concepts from synthetic aperture processing and non-uniform linear array theory. Our objective is to use array motion to synthesize an array that can achieve the performance of a filled uniform linear array (ULA), but with fewer s ... Full text Cite

Cramer-Rao bounds for HF source geolocation with a vector sensor array

Journal article IEEE National Radar Conference Proceedings · January 1, 2014 Passive geolocation of a skywave HF source requires accurate estimation of azimuth and elevation angles together with correct ionospheric modeling. Arrays of polarimetric vector sensors have been proposed to reduce the array aperture required for this purp ... Full text Cite

Predicting the array gain of partially coherent planar HF arrays

Journal article IEEE National Radar Conference Proceedings · January 1, 2014 This paper concerns estimating the partially coherent signal gain of a large, fully-populated planar HF phasedarray using simulated data from a few widely distributed receive elements. Our approach involves estimating magnitude-squared coherence between se ... Full text Cite

Adaptive beamforming with augmentable arrays in non-stationary environments

Journal article 2013 5th IEEE International Workshop on Computational Advances in Multi Sensor Adaptive Processing Camsap 2013 · December 1, 2013 This paper introduces a near-field reduced rank adaptive beamforming method for nulling more interferers than sensors using fully augmentable arrays in wide sense stationary interference. Augmentable arrays, such as minimally redundant or co-prime, can exp ... Full text Cite

Adaptive phase-array calibration using MIMO radar clutter

Journal article IEEE National Radar Conference Proceedings · October 7, 2013 The goal of this paper is to develop methods for determining the calibrated array weights for uniform linear transmit and receive radar arrays necessary to achieve desired uniform sidelobe performance. The ability of current radar systems to suppress sidel ... Full text Cite

Heading and hydrophone data fusion for towed array shape estimation

Journal article Proceedings of Meetings on Acoustics · June 19, 2013 This paper addresses the problem of towed array shape estimation for passive, horizontal sonar arrays. Beamforming and localization techniques significantly degrade when an assumed linear array bends due to tow platform maneuvers or ocean currents. In this ... Full text Cite

Cramer-Rao performance bounds for simultaneous target and multipath positioning

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · January 1, 2013 This work considers the performance of none-light-of-sight (NLOS) target localization method using a distributed receiver array. The multipath propagation is modeled with single bounce reflection from unknown random scatters. A Simultaneous Target and Mult ... Full text Cite

Simultaneous Target and Multipath Positioning via multi-hypothesis single-cluster PHD filtering

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · January 1, 2013 This work considers the problem of tracking a RF source in dense multipath environments using a uniform linear receiver array (ULA) where multipath propagation is modeled as specular reflections from planar reflectors. A single cluster process is formulate ... Full text Cite

Maximum-likelihood spatial spectrum estimation in dynamic environments with a short maneuverable array.

Journal article The Journal of the Acoustical Society of America · January 2013 This work concerns the development of field directionality mapping algorithms for short acoustic arrays on mobile maneuverable platforms that avoid the left/right ambiguities and endfire resolution degradation common to longer non-maneuverable line arrays. ... Full text Cite

Simultaneous target and multipath positioning with MIMO radar

Journal article Iet Conference Publications · December 1, 2012 This paper presents an approach for jointly estimating target locations and uncertain multipath propagation channel parameters with a multi-input multi-output (MIMO) radar system. The multipath channel is modelled with geometrical features such as flat pla ... Full text Cite

Adaptive baseband interference suppression in multi-channel heterodyne radar receivers

Journal article Iet Conference Publications · December 1, 2012 In radar systems, heterodyne RF circuitry is commonly used to produce multi-channel in-phase and quadrature (I/Q) signals which are then beamformed and range-Doppler processed. Often such receivers are deployed in noisy environments, where interference sig ... Full text Cite

MIMO multipath clutter mitigation for GMTI automotive radar in urban environments

Journal article Iet Conference Publications · December 1, 2012 Ground-moving target indicator (GMTI) radar, commonly deployed on airborne platforms, is currently precluded on surface vehicles due to multipath spread-Doppler clutter in complex terrain. Multiple-input multiple-output (MIMO) radar techniques have been sh ... Full text Cite

Broadband field directionality mapping with spatially-aliased arrays

Journal article Proceedings of the IEEE Sensor Array and Multichannel Signal Processing Workshop · October 12, 2012 This paper addresses the problem of broadband spatial spectrum estimation using multiple spatially-aliased arrays. Unlike previous approaches using sparse arrays, the signals here are assumed to be uncorrelated between multiple arrays which, in fact, may b ... Full text Cite

Vehicular MIMO SAR imaging in multipath environments

Journal article IEEE National Radar Conference Proceedings · September 12, 2011 In this paper, multi-input multi-output (MIMO) forward looking synthetic aperture radar (FL-SAR) is developed for imaging from a moving ground vehicle in urban multipath environments. Conventional SAR is often seriously degraded by ghost artifacts with the ... Full text Cite

Space-time adaptive processing for range-folded spread-Doppler radar clutter mitigation

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · August 18, 2011 This paper concerns the detection of radar targets masked by Doppler-spread surface backscatter from points beyond the radar's maximum unambiguous range. Current methods for mitigating this so-called "range-folded" clutter, such as reducing the pulse-repet ... Full text Cite

A waveguide invariant adaptive matched filter for active sonar target depth classification.

Journal article The Journal of the Acoustical Society of America · April 2011 This paper addresses depth discrimination of a water column target from bottom clutter discretes in wideband active sonar. To facilitate classification, the waveguide invariant property is used to derive multiple snapshots by uniformly sub-sampling the sho ... Full text Cite

Target tracking in uncertain multipath environments using Viterbi data association

Journal article Fusion 2011 14th International Conference on Information Fusion · January 1, 2011 This paper addresses the problem of accurate geolocation of targets or emitters in an uncertain multipath propagation channel. We propose a new approach which exploits differences between target and multipath dynamics to jointly estimate target position an ... Cite

MIMO GMTI radar with multipath clutter suppression

Journal article 2010 IEEE Sensor Array and Multichannel Signal Processing Workshop SAM 2010 · December 20, 2010 This paper address ground-moving target indicator (GMTI) radar operation in the presence of strong multipath spread-Doppler clutter (SDC). Spacetime adaptive processing (STAP) for single-input-single-output (SIMO) radar is designed to mitigate direct-path ... Full text Cite

Time-varying spatial spectrum estimation with a maneuverable towed array.

Journal article The Journal of the Acoustical Society of America · December 2010 This paper addresses the problem of field directionality mapping (FDM) or spatial spectrum estimation in dynamic environments with a maneuverable towed acoustic array. Array processing algorithms for towed arrays are typically designed assuming the array i ... Full text Cite

An indoor s-band radar receive array testbed

Journal article IEEE National Radar Conference Proceedings · July 30, 2010 This paper describes a multi-channel S-band radar receive system designed as a laboratory testbed system for studying wideband radar array signal processing. The receive array was designed using a combination of low-cost commercial-of-the-shelf components ... Full text Cite

Software-defined calibration for FMCW phased-array radar

Journal article IEEE National Radar Conference Proceedings · July 30, 2010 This paper addresses the problem of calibrating a FMCW phased-array radar to meet design specifications both in slant-range and beam pattern. The software-defined method presented here, while generally applicable, is implemented on an S-band phased-array r ... Full text Cite

Quadrature slow-time MIMO radar with experimental results

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · January 1, 2010 Multiple-input multiple-output (MIMO) radar requires orthogonal waveforms to be transmitted on each transmit element or subarray. One practical problem that arises is the complexity and expense of the hardware needed to implement MIMO radar. Slow-time MIMO ... Full text Cite

An online method for time-varying spatial spectrum estimation using a towed acoustic array

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · January 1, 2010 This paper addresses the problem of time-varying field directionality mapping (FDM) or spatial spectrum estimation in dynamic environments with a maneuverable towed acoustic array. Array processing algorithms for towed arrays are typically designed assumin ... Full text Cite

Multiband chirp synthesis for frequency-hopped FMCW radar

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · December 1, 2009 This paper presents a method for increasing radar range resolution by stitching together non-contiguous frequency-hopped FMCW radar sweeps across different dwells. The work extends previous bandwidth extrapolation methods, designed for radar imaging of spa ... Full text Cite

MIMO enabled multipath clutter rank estimation

Journal article IEEE National Radar Conference Proceedings · September 11, 2009 Multiple-input multiple-output (MIMO) radar is an emerging technology that has the capability of providing range dependent transmit-domain degrees of freedom via receiver processing. When providing these additional degrees of freedom for target tracking, M ... Full text Cite

Adaptive radar detection in doubly nonstationary autoregressive doppler spread clutter

Journal article IEEE Transactions on Aerospace and Electronic Systems · July 20, 2009 The problem of adaptive radar detection in clutter which is nonstationary both in slow and fast time is addressed. Nonstationarity within a coherent processing interval (CPI) often precludes target detection because of the masking induced by Doppler spread ... Full text Cite

A graph-theoretic approach to constrained floor plan estimation from radar measurements

Journal article IEEE Transactions on Signal Processing · May 25, 2009 This paper proposes an approach to deducing the floor plan of a building using only a set of noisy room dimension measurements that have been obtained indirectly through radar probes. It is not assumed that the set of measurements is complete. The key feat ... Full text Cite

Sparse array imaging of change-detected ultrasonic signals by minimum variance processing

Journal article Aip Conference Proceedings · May 12, 2009 Spatially distributed arrays of permanently attached ultrasonic sensors are being considered for structural health monitoring systems. Most algorithms for analyzing the received signals are based upon change detection whereby baselines from the undamaged s ... Full text Cite

MIMO field directionality estimation using orientation-diverse linear arrays

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · January 1, 2009 This paper addresses the estimation of power versus azimuth and elevation using a sparse sensor array. In MIMO radar, clutter and noise field directionality can be measured both from the transmit array and to the receive array. In applications where sparse ... Full text Cite

Field directionality synthesis from multiple array orientations: A least squares approach

Journal article Oceans 2008 · December 1, 2008 Combining multiple beamforming outputs from different orientations of a linear array to obtain a full 2-D field directionality is investigated in this paper. A wavefield sampling method is proposed that could be effective at eliminating left-right ambiguit ... Full text Cite

Passive broadband source localization in shallow-water multipath acoustic channels

Journal article Oceans 2008 · December 1, 2008 This paper addresses the problem of direct-path passive broadband localization of a shallow-water acoustic source with a sparsely distributed set of sensors in the presence of uncertain multipath propagation. The classical approach to broadband source loca ... Full text Cite

Multipath spread-Doppler clutter mitigation for over-the-horizon radar

Journal article 2008 IEEE Radar Conference Radar 2008 · December 1, 2008 This paper discusses two adaptive spatial processing approaches that have been recently proposed for mitigating spread-Doppler clutter in skywave over-the-horizon (OTH) radar. The first is slow-time MIMO (SLO-MO) STAP which uses conventional waveforms that ... Full text Cite

Waveguide invariant broadband target detection and reverberation estimation.

Journal article The Journal of the Acoustical Society of America · November 2008 Reverberation often limits the performance of active sonar systems. In particular, backscatter off of a rough ocean floor can obscure target returns and/or large bottom scatterers can be easily confused with water column targets of interest. Conventional a ... Full text Cite

Radar clutter mitigation via space-time wavefront adaptive sensing

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · September 16, 2008 Space-time adaptive processing (STAP) in complex radar propagation and inhomogeneous clutter environments is often precluded because neither the target wavefront is sufficiently known nor is signal-free training data available. In recent work, wavefront ad ... Full text Cite

Beamspace slow-time MIMO radar for multipath clutter mitigation

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · September 16, 2008 This paper concerns beamspace multiple-input multiple-output (MIMO) space-time adaptive processing (STAP) to mitigate radar clutter subject to multipath propagation between transmit and receive arrays. Transmit beams are phase-coded to be orthogonal after ... Full text Cite

Waveguide invariant focusing for broadband beamforming in an oceanic waveguide.

Journal article The Journal of the Acoustical Society of America · March 2008 The performance of broadband sonar array processing can degrade significantly in shallow-water environments when interference becomes angularly spread due to multipath propagation. Particularly for towed line arrays near endfire, elevation angle spreading ... Full text Cite

MIMO STAP clutter mitigation performance demonstration using acoustic arrays

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · January 1, 2008 This paper demonstrates MIMO STAP radar techniques for Doppler-spread clutter mitigation using a 5-element transmit speaker array and a 16-element receive microphone array. Doppler-spread clutter is mitigated by "virtual" transmit beampattern nulling using ... Full text Cite

Theoretical passive sonar performance of a cluster of UUV towed line arrays employing orientation diversity

Journal article Oceans Conference Record IEEE · December 1, 2007 This paper characterizes the theoretical passive sonar performance of a cluster of small unmanned underwater vehicle (UUV) towed line arrays where the UUVs maneuver to maintain orientation diversity amongst the array bearing angles. A novel coordinated con ... Full text Cite

Wavefront adaptive sensing for radar spread clutter mitigation

Journal article 2007 2nd IEEE International Workshop on Computational Advances in Multi Sensor Adaptive Processing Campsap · December 1, 2007 In spatially inhomogeneous, Doppler-spread radar environments, adaptive processing is often precluded because neither the target wavefront is sufficiently known nor is signal-free training data available. This paper presents a new clutter mitigation method ... Full text Cite

Waveguide invariant focusing for broadband adaptive beamforming in a shallow water channel

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · August 6, 2007 Focusing methods are effective broadband techniques that can reduce the observation time required for adaptive beamforming. However, often focusing methods designed for planewave signals do not prevent broadband covariance matrix rank inflation for shallow ... Full text Cite

Waveguide invariant reverberation mitigation for active sonar

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · August 6, 2007 Reverberation often limits the performance of active sonar systems. A method of target detection and bottom-feature suppression has been developed exploiting waveguide-invariant phenomena and the frequency-selective fading properties of broadband reverbera ... Full text Cite

Electromagnetic Target Detection in Uncertain Media: Time-Reversal and Minimum-Variance Algorithms

Journal article IEEE Transactions on Geoscience and Remote Sensing · April 7, 2007 An experimental study is performed on imaging targets that are situated in a highly scattering environment, employing electromagnetic time-reversal methods. A particular focus is placed on performance when the electrical properties of the background enviro ... Full text Cite

Electromagnetic time-reversal source localization in changing media: Experiment and analysis

Journal article IEEE Transactions on Antennas and Propagation · February 1, 2007 An experimental study is performed on electromagnetic time reversal in highly scattering environments, with a particular focus on performance when environmental conditions change. In particular, we consider the case for which there is a mismatch between th ... Full text Cite

A graph-theoretic approach for constraining floor plan estimation from radar measurements

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · January 1, 2007 This paper addresses the problem of floor-plan estimation using a limited number of stand-off radar aspect angles, time-delay measurements and wall-penetrations. While most floor-plan estimation work has focused on local methods for reconstructing wall pos ... Full text Cite

Wavefront adaptive raymode processing for over-the-horizon HF radar clutter mitigation

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · January 1, 2007 Detection of surface targets using over-the-horizon radar (OTHR) is extremely challenging due to ionospherically induced Doppler spread clutter. In particular, low Doppler targets are often masked by ground clutter arriving via multipath propagation at dif ... Full text Cite

Slow-time MIMO STAP with improved power efficiency

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · January 1, 2007 This paper concerns a multiple-input multipleoutput (MIMO) generalization of space-time adaptive processing (STAP) to mitigate radar clutter subject to multipath propagation between transmit and receive arrays. Slow-time MIMO transmit channels are phase-co ... Full text Cite

A study of active sonar reverberation using ultrasonic experiments in a shallow-water tank

Journal article Oceans 2007 Europe · January 1, 2007 This paper describes a study of active sonar reverberation level (RL) estimates made using scaled ultrasonic water-tank data. Such laboratory experiments provide a means of upper bounding the performance of RL estimates made in real shallow-water ocean env ... Full text Cite

Comparative theoretical performance of maneuverable unmanned vehicles versus conventional towed-arrays for passive sonar

Journal article Oceans 2007 Europe · January 1, 2007 This paper considers the potential for passive acoustic target detection using a maneuverable unmanned underwater vehicle (UUV) equipped with towed line array. The objective is to assess target detection performance as a function of vehicle maneuverability ... Full text Cite

Single hydrophone passive localization of transiting acoustic sources

Journal article Oceans 2007 Europe · January 1, 2007 This paper presents a new method to estimate motion parameters of loud transiting acoustic sources with a single stationary hydrophone In shallow water environments. The parameters of Interest Include the time of Closest Point of Approach (CPA) and the rat ... Full text Cite

Exploiting multipath propagation for GMTI in urban environments

Journal article IEEE National Radar Conference Proceedings · December 1, 2006 This paper evaluates the potential for exploiting multipath propagation for improved radar detection of moving ground targets in dense urban environments. In particular, the radar coverage offered by exploiting non-line-of-sight (NLOS) propagation from an ... Full text Cite

Adaptive collaborative array trajectories for optimum passive detection

Journal article Oceans 2006 · December 1, 2006 Large static arrays can maximize their array gain for a fixed look direction when accurate signal wavefront modeling is available and stationary noise fields are present. However, a group of relatively agile shorter arrays towed by unmanned underwater vehi ... Full text Cite

Orientation diversity for an autonomous underwater vehicle cluster

Journal article Oceans 2006 · December 1, 2006 This paper presents a novel theory for the generation of vehicle heading sequences that simultaneously ensures orientation diversity both between vehicles and along a given vehicle's path, while at the same time bounding the cluster divergence, and transla ... Full text Cite

MIMO radar space-time adaptive processing for multipath clutter mitigation

Journal article 2006 IEEE Sensor Array and Multichannel Signal Processing Workshop Proceedings SAM 2006 · December 1, 2006 This paper describes a multiple-input-multiple-output (MIMO) generalization of space-time adaptive processing (STAP) to mitigate radar clutter subject to multipath propagation between transmit and receive arrays. Multipath clutter can occur when surface re ... Full text Cite

Single-snapshot beamformer performance using large arrays with faulty sensors

Journal article 2006 IEEE Sensor Array and Multichannel Signal Processing Workshop Proceedings SAM 2006 · December 1, 2006 Large sensor arrays are prone to element failures which can seriously degrade their performance. In the event of sensor failures, conventional non-adaptive re-design of array weights for the resulting non-uniform or even sparse array often leads to undesir ... Full text Cite

Target detection in abruptly non-stationary Doppler-spread clutter

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · December 1, 2006 This paper addresses the problem of target detection in the presence of Doppler spread clutter which is neither stationary during a coherent integration time (CIT) interval nor across different range bins. This phenomenology occurs, for example, in over-th ... Cite

Exploiting multipath propagation for GMTI in urban environments

Journal article CIE International Conference of Radar Proceedings · November 21, 2006 This paper evaluates the potential for exploiting multipath propagation for improved radar detection of moving ground targets in dense urban environments. In particular, the radar coverage offered by exploiting non-line-of-sight (NLOS) propagation from an ... Cite

Isolation and minimization of head motion-induced signal variations in fMRI data using independent component analysis.

Journal article Magnetic resonance in medicine · June 2006 Task-related head movement during acquisition of fMRI data represents a serious confound for both motion correction and estimates of task-related activation. Cost functions implemented in most conventional motion-correction algorithms compare two volumes f ... Full text Cite

Joint space-time interpolation for distorted linear and bistatic array geometries

Journal article IEEE Transactions on Signal Processing · March 1, 2006 This paper presents a new joint space-time interpolation technique (STINT) to improve the small sample support performance of space-time adaptive processing (STAP) with distorted linear monostatic arrays and linear bistatic array configurations. Brennan's ... Full text Cite

Improved motion correction of fMRI time-series corrupted with major head movement using extended motion-corrected independent component analysis

Journal article Lecture Notes in Computer Science Including Subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics · December 1, 2005 An extension of previously-described Motion-Corrected Independent Component Analysis (MCICA) for improved correction of significant patient head motion in fMRI data is proposed. For fMRI time-points corrupted with relatively large motion, i.e. on the order ... Full text Cite

An information-theoretic criterion for intrasubject alignment of FMRI time series: motion corrected independent component analysis.

Journal article IEEE transactions on medical imaging · January 2005 A three-dimensional image registration method for motion correction of functional magnetic resonance imaging (fMRI) time-series, based on independent component analysis (ICA), is described. We argue that movement during fMRI data acquisition results in a s ... Full text Cite

Electromagnetic time-reversal imaging of a target in a cluttered environment

Journal article IEEE Transactions on Antennas and Propagation · 2005 Electromagnetic time-reversal imaging is addressed for a target situated in a cluttered background. We first investigate the theory of electromagnetic time-reversal imaging, followed by an experimental demonstration. A transmitter-receiver antenna array is ... Full text Cite

Multipath delay estimation using the magnitude spectrum

Journal article IEEE Workshop on Statistical Signal Processing Proceedings · January 1, 2005 Four methods are presented by which the relative delay structure of a multipath signal can be estimated from the Fourier magnitude spectrum of the observation. The phase of the underlying source signal may be completely unknown. While the signal autocorrel ... Full text Cite

Robust range-rate estimation of passive narrowband sources in shallow water

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · January 1, 2005 This paper addresses the problem of range-rate estimation of narrowband passive sources in multipath environments. Although range-rate can be derived from a sequence of matched-field range-depth estimates, such an approach requires accurate modeling of the ... Full text Cite

Beamspace adaptive channel compensation for sensor arrays with faulty elements

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · January 1, 2005 Sensor failures in large uniform linear arrays cause significant degradation of the conventional beampattern. This paper proposes a beamspace adaptive channel compensation (B-ACC) method for interpolating the receiver channels based on a linear inverse the ... Full text Cite

Wide-band target depth estimation in a scattering ocean environment

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 2005 This paper concerns target depth estimation using wideband active sonar multipath returns. Detailed full-field modeling of target returns is complicated by spectral amplitude and phase distortions induced by unknown target scattering, uncertainty in the bu ... Full text Cite

Target detection using dynamically reconfigurable sensor arrays

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 2005 This paper addresses the problem of target detection with multiple dynamically reconfigurable sensor arrays (DRSA's). The limited spatial coherence of the signal wavefront and dynamic nature of the interference seriously limit target detection performance. ... Full text Cite

Adaptive sonar detection performance when the signal wavefront and noise covariance are uncertain

Journal article 2004 Sensor Array and Multichannel Signal Processing Workshop · December 1, 2004 This paper considers adaptive sonar array detection performance when both the multipath ocean environment and the noise field directionality are uncertain. Recent analytic results for adaptive matched-subspace detector (AMSD) performance with multi-rank si ... Cite

Motion-corrected independent component analysis for robust functional magnetic resonance imaging

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · October 7, 2004 Head movement during fMRI data collection can result in confusing artifacts when estimating task-related brain activations. In this paper, we propose an improved version of Motion-Corrected Independent Component Analysis (MCICA), which mitigates motion eff ... Cite

Array shape estimation and tracking using active sonar reverberation

Journal article IEEE Transactions on Aerospace and Electronic Systems · July 1, 2004 This paper concerns the problem of array shape estimation and tracking for towed active sonar arrays, using received reverberation returns from a single transmitted CW pulse. Uniform linear arrays (ULAs) deviate from their nominal geometry while being towe ... Full text Cite

Matched-field depth estimation for active sonar.

Journal article The Journal of the Acoustical Society of America · February 2004 This work concerns the problem of estimating the depth of a submerged scatterer in a shallow-water ocean by using an active sonar and a horizontal receiver array. As in passive matched-field processing (MFP) techniques, numerical modeling of multipath prop ... Full text Cite

A Generalized Karhunen-Loeve Basis for Efficient Estimation of Tropospheric Refractivity Using Radar Clutter

Journal article IEEE Transactions on Signal Processing · January 1, 2004 In this paper, we consider the problem of obtaining a reduced-dimension parameterization of a propagation medium for the purpose of estimating the medium from transmission data. The application addressed is microwave remote sensing of tropospheric index-of ... Full text Cite

Model-based space-time adaptive processing for active sonar

Journal article Conference Record Asilomar Conference on Signals Systems and Computers · January 1, 2004 In this paper, the problem of partially adaptive space-time adaptive processing (STAP) for towed active sonar arrays operating in a strong reverberation environment under extremely snapshot deficient conditions is considered. In particular, we propose a ro ... Full text Cite

Isolation and minimization of effects of motion on fMRI using multiple reference images

Journal article 2004 2nd IEEE International Symposium on Biomedical Imaging Macro to Nano · January 1, 2004 Cost functions implemented in most fMRI motion correction algorithms often fail to account explicitly for the signal variability between images not due to motion, but coming from brain activation. In this paper, we explore the performance of a newly propos ... Full text Cite

Inversion for refractivity parameters from radar sea clutter

Journal article Radio Science · 2003 This paper describes estimation of low-altitude atmospheric refractivity from radar sea clutter observations. The vertical structure of the refractive environment is modeled using five parameters, and the horizontal structure is modeled using six parameter ... Full text Link to item Cite

Robust altitude estimation for over-the-horizon radar using a state-space multipath fading model

Journal article IEEE Transactions on Aerospace and Electronic Systems · January 1, 2003 In previous work, a matched-field estimate of aircraft altitude from multiple over-the-horizon (OTH) radar dwells was presented. This approach exploits the altitude dependence of direct and surface reflected returns off the aircraft and the relative phase ... Full text Cite

A performance evaluation of autoregressive clutter mitigation methods for over-the-horizon radar

Journal article Conference Record of the Asilomar Conference on Signals Systems and Computers · January 1, 2003 Wide-area surveillance over-the-horizon radar (OTHR) requires minimizing the dwell time in each search region without compromising Doppler resolution of targets from clutter. Low-order autoregressive (AR) modeling of the clutter spectrum has been proposed ... Cite

Passive source localization in the presence of near-endfire interference

Journal article Conference Record of the Asilomar Conference on Signals Systems and Computers · January 1, 2003 We propose an approach for suppressing near-endfire interference in shallow water environments with a passive sonar system. Reduced azimuthal resolution near endfire limits the ability of conventional beamformers to discriminate between source and interfer ... Cite

Joint space-time interpolation for bistatic STAP

Journal article Conference Record of the Asilomar Conference on Signals Systems and Computers · January 1, 2003 We present a novel interpolation technique to improve the small sample support performance of airborne radar space-time adaptive processing (STAP) using bistatic configurations. Bistatic airborne radar operation increases the clutter rank and causes it to ... Cite

Space-time interpolation for adaptive arrays with limited training data

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 2003 This paper describes a method for improving the small sample support space-time adaptive processing (STAP) performance of distorted linear arrays. Receive arrays which deviate from a straight line may occur, for example, in conformal radar and towed sonar ... Cite

Track association for over-the-horizon radar with a statistical ionospheric model

Journal article IEEE Transactions on Signal Processing · November 1, 2002 Over-the-horizon (OTH) radar exploits the refractive nature of high-frequency radio-wave propagation through the ionosphere for the purpose of wide-area surveillance. In order to localize targets, however, multipath slant tracks from different ionospheric ... Full text Cite

The performance of matched-field track-before-detect methods using shallow-water Pacific data.

Journal article The Journal of the Acoustical Society of America · July 2002 Matched-field track-before-detect processing, which extends the concept of matched-field processing to include modeling of the source dynamics, has recently emerged as a promising approach for maintaining the track of a moving source. In this paper, optima ... Full text Cite

VLT optical and near-infrared observations of the z=6.28 quasar SDSS J1030+0524

Journal article Astron. J. (USA) · 2002 We present new VLT spectroscopic observations of the most distant quasar known, SDSS J103027.10+052455.0, at z=6.28, which was discovered by the Sloan Digital Sky Survey. We confirm the presence of a complete Gunn-Peterson trough caused by neutral hydrogen ... Full text Link to item Cite

Sloan Digital Sky Survey: early data release

Journal article Astron. J. (USA) · 2002 The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey that will eventually cover approximately one-quarter of the celestial sphere and collect spectra of ≈106 galaxies, 100000 quasars, 30000 stars, and 30000 serendipity targets. In ... Full text Link to item Cite

Passive localization in range-rate of shallow-water moving targets, by sequential importance sampling

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 2002 We examine the problem of passive localization of moving targets in shallow-water environments. In contrast with standard Matched Field Processing approaches, we localize targets in range-rate, rather than in range. This approach avoids smearing of target ... Full text Cite

MAP sequence estimation of microwave refractivity from radar clutter via a particle filtering implementation of the viterbi algorithm

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 2002 This paper addresses the problem of predicting microwave propagation loss under ducting conditions by means of estimating the range and height varying index of refraction from observations of radar sea clutter returns. Specifically, the Fourier split-step ... Full text Cite

Maximum A posteriori refractivity estimation from radar clutter using a Markov model for microwave propagation

Journal article International Geoscience and Remote Sensing Symposium IGARSS · December 1, 2001 This paper addresses the problem of estimating range-varying parameters of the height-dependent index of refraction over the sea surface in order to predict ducted microwave propagation loss. Refractivity estimation is performed using a Markov model for mi ... Cite

Multichannel system identification methods for sensor array calibration in uncertain multipath environments

Journal article IEEE Workshop on Statistical Signal Processing Proceedings · December 1, 2001 This paper concerns the problem of estimating the array element relative gain and phase responses using sources of opportunity in an uncertain multipath environment. Unlike previous methods, which assume uncorrelated source wavefronts, we propose to perfor ... Cite

Broad absorption line quasars in the Sloan Digital Sky Survey with VLA FIRST radio detections

Journal article Astrophys. J. (USA) · 2001 We present 13 broad absorption line (BAL) quasars, including 12 new objects, identified in the Sloan Digital Sky Survey (SDSS) and matched within 2" to sources in the FIRST radio survey catalog. The surface density of this sample of radio-detected BAL quas ... Full text Link to item Cite

Refractivity estimation from radar clutter by sequential importance sampling with a Markov model for microwave propagation

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 2001 This paper address the problem of estimating range-varying parameters of the height-dependent index of refraction over the sea surface in order to predict ducted microwave propagation loss. Refractivity estimation is performed using a Markov model for micr ... Cite

Robust altitude estimation for over-the-horizon radar using a state-space model for multipath fading

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 2001 In previous work, a matched-field estimate of aircraft altitude from multiple over-the-horizon radar dwells was presented. This approach exploits the altitude dependence of direct and surface reflected returns off the aircraft and the relative phase change ... Cite

Application of maximal invariance to the ACE detection problem

Journal article Conference Record of the Asilomar Conference on Signals Systems and Computers · December 1, 2000 Three simple adaptive detection statistics frequently appearing in the radar detection literature, which employ a sample covariance estimate for clutter suppression, are Kelly's GLRT, the adaptive matched filter (AMF), and the adaptive cosine estimator (AC ... Cite

Intensive HST, RXTE, and ASCA monitoring of NGC 3516: evidence against thermal reprocessing

Journal article Astrophys. J. (USA) · 2000 During 1998 April 13-16, the bright, strongly variable Seyfert 1 galaxy NGC 3516 was monitored almost continuously with HST for 10.3 hr at ultraviolet wavelengths and 2.8 days at optical wavelengths, and simultaneous RXTE and ASCA monitoring covered the sa ... Full text Link to item Cite

Relationships between adaptive minimum variance beamforming and optimal source localization

Journal article IEEE Transactions on Signal Processing · January 1, 2000 For many years, the popular minimum variance (MV) adaptive beamformer has been well known for not having been derived as a maximum likelihood (ML) estimator. This paper demonstrates that by use of a judicious decomposition of the signal and noise, the log- ... Full text Cite

Adaptive temporal processing for equatorial spread Doppler clutter suppression

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 2000 The detection performance of skywave HF over-the-horizon radars is fundamentally limited by ionospheric motion which causes spreading of surface clutter returns in Doppler space. This work presents an adaptive temporal processing approach for suppressing r ... Full text Cite

Optimal subspace selection for non-linear parameter estimation applied to refractivity from clutter

Journal article IEEE Signal Processing Workshop on Statistical Signal and Array Processing Ssap · January 1, 2000 We consider the problem of constructing an optimal reduced-rank subspace for parameter estimation, in models where the data is a non-linear function of the parameters. The solution which minimizes mean-squared error is a compromise between the prior distri ... Cite

Barankin bounds for source localization in an uncertain ocean environment

Journal article IEEE Transactions on Signal Processing · December 1, 1999 Ambiguity surfaces for underwater acoustic matched-field processing are prone to having high secondary peaks. This leads to anomalous source localization estimates below a threshold signal-to-noise ratio (SNR) at which the performance rapidly departs from ... Full text Cite

Using radar sea echo to estimate surface layer refractivity profiles

Journal article International Geoscience and Remote Sensing Symposium IGARSS · December 1, 1999 A method for inferring the evaporation duct height from sea clutter is described. The method is based on the observation that the signal from the evaporation duct manifests itself in the slope of the clutter power, while the horizontal variability of the s ... Cite

Using radar sea clutter to estimate refractivity profiles associated with the capping inversion of the marine atmospheric boundary layer

Journal article International Geoscience and Remote Sensing Symposium IGARSS · December 1, 1999 This paper addresses the problem of estimating refractivity profile parameters, associated with the capping inversion of the marine boundary layer, which characterize ducted microwave propagation. The approach presented here provides synoptic measurement o ... Cite

Theoretical performance limits on tropospheric refractivity estimation using point-to-point microwave measurements

Journal article IEEE Transactions on Antennas and Propagation · November 1, 1999 Ducted propagation above the ocean surface can seriously impact shipboard radar and communications. Point-to-point microwave measurements have been proposed as a means of estimating tropospheric refractivity for the purposes of characterizing surface-based ... Full text Cite

Matched-field estimation of aircraft altitude from multiple over-the-horizon radar revisits

Journal article IEEE Transactions on Signal Processing · April 1, 1999 Over-the-horizon (OTH) radar uses the refractive properties of the ionosphere for wide-area surveillance of targets at long ranges. Currently, OTH radars can localize targets in latitude and longitude but have difficulty estimating target altitude, which i ... Full text Cite

Ultraviolet imaging polarimetry of narrow-line radio galaxies

Journal article Astrophys. J. (USA) · 1999 In an examination of the unification of radio galaxies and quasars, the authors obtained UV polarization images of eight narrow-line radio galaxies (NLRGs) with the Faint Object Camera on board the Hubble Space Telescope (HST). By observing in the rest ult ... Full text Link to item Cite

Imaging a quasar accretion disk with microlensing

Journal article Astrophys. J. (USA) · 1999 Shows how analysis of a quasar high-magnification microlensing event may be used to construct a map of the frequency-dependent surface brightness of the quasar accretion disk. The same procedure also allows determination of the disk inclination angle, the ... Full text Link to item Cite

Multipath track association for over-The-horizon radar using a bootstrapped statistical ionospheric model

Journal article Conference Record of the 33rd Asilomar Conference on Signals Systems and Computers · January 1, 1999 Over-The-horizon (OTH) radar uses the refractive properties of high-frequency radiowave propagation through the ionosphere for wide-Area surveillance at long ranges. Ionospheric propagation often gives rise to multiple raymodes between the OTH radar and a ... Full text Cite

Efficient computation of the Bayesian Cramer-Rao bound on estimating parameters of Markov models

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1999 This paper presents a novel method for calculating the Hybrid Cramer-Rao lower bound (HCRLB) when the statistical model for the data has a Markovian nature. The method applies to both the non-linear/non-Gaussian as well as linear/Gaussian model. The approa ... Cite

Matched window processing for mitigating over-the-horizon radar spread Doppler clutter

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1999 Ionospheric motion causes spreading of surface clutter in Doppler space which fundamentally limits the detection performance of skywave HF over-the-horizon radars. This paper presents a technique which reduces the effect of so-called `coincident' spread Do ... Full text Cite

Learning neural networks for detection and classification of synchronous recurrent transient signals

Journal article Signal Processing · February 26, 1998 This paper proposes a neural network solution to the classical signal processing problem of detection of a synchronous recurrent transient signal in noise. If a signal exists, it is assumed to be one of M known signals which may sometimes occur (probabilis ... Full text Cite

Photon damping of waves in accretion disks

Journal article Astrophys. J. (USA) · 1998 MHD turbulence is generally believed to have two important functions in accretion disks: it transports angular momentum outward, and the energy in its shortest wavelength modes is dissipated into the heat that the disks radiate. The authors examine a pair ... Full text Link to item Cite

Over-the-horizon radar target localization using a hidden Markov model estimated from ionosonde data

Journal article Radio Science · January 1, 1998 Uncertainty about the downrange ionospheric conditions is a well-known source of localization errors in over-the-horizon radar. Statistical modeling of ionospheric parameters has recently been proposed in order to derive a maximum likelihood (ML) localizat ... Full text Cite

Multi-dwell matched-field altitude estimation for over-the-horizon radar

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1998 In previous work, electromagnetic matched-field processing was proposed for estimating aircraft altitude with over-the-horizon radar using a single radar dwell. Although this approach exploits the altitude dependence of unresolved multipath returns in comp ... Full text Cite

The performance of maximum likelihood over-the-horizon radar coordinate registration

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1998 A well-known source of target localization errors in over-the-horizon radar is the uncertainty about downrange ionospheric conditions. Maximum likelihood (ML) coordinate registration, using statistical modeling of ionospheric parameters, has recently been ... Full text Cite

Maximum likelihood coordinate registration for over-the-horizon radar

Journal article IEEE Transactions on Signal Processing · December 1, 1997 Over-the-horizon radar exploits the refractive and multipath nature of high-frequency propagation through the ionosphere to achieve wide-area surveillance. The coordinate registration process converts the group delays and azimuths (i.e., slant coordinates) ... Full text Cite

Robust wideband matched-field processing with a short vertical array

Journal article Journal of the Acoustical Society of America · February 1, 1997 This paper addresses the problem of matched-field passive localization of broadband underwater acoustic sources with a short vertical array. In previous work, incoherent averaging of narrow-band Bartlett ambiguity surfaces has been proposed to improve the ... Full text Cite

Robust maximum-likelihood source localization in an uncertain shallow- water waveguide

Journal article Journal of the Acoustical Society of America · January 1, 1997 This paper addresses the problem of matched-field source localization in the presence of uncertainties in the ocean environment. Because signal wavefront mismatch can cause anomalous source location estimates, development of robust localization methods is ... Full text Cite

A powerful nuclear starburst in the Seyfert galaxy Markarian 477: implications for the starburst-active galactic nucleus connection

Journal article Astrophys. J. (USA) · 1997 There have been many suggestions that starbursts may play an important rôle in Seyfert galaxies. Analyses of the UV, optical, and near-IR “featureless continuum” (FC) in type 2 Seyfert nuclei have provided indirect evidence that-the FC ma ... Full text Link to item Cite

Electromagnetic matched-field processing for target height finding with over-the-horizon radar

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1997 The refraction of over-the-horizon skywave radar signals by the ionosphere facilitates wide-area surveillance. While current systems measure target ground range, azimuth, and velocity they do not estimate target altitude, which is important for classificat ... Cite

Robust beamformer weight design for broadband matched-field processing

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1997 Matched-field beamforming has been proposed for localizing wideband acoustic sources in uncertain underwater channels. While adaptive matched-field beamforming provides adequate sidelobe suppression for stronger sources, at low signal-to-noise ratios it co ... Cite

Barankin bound for source localization in shallow water

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1997 Matched-field methods are known to have a severe ambiguity problem. In low signal-to-noise-ratios (SNR's), where the estimator cannot distinguish between the ambiguity function peak near the true source location and ambiguous ones, its mean square error de ... Cite

The performance of matched-field beamformers with mediterranean vertical array data

Journal article IEEE Transactions on Signal Processing · December 1, 1996 Minimum variance (MV) adaptive beamforming has been widely proposed for inatclied-field processing because it provides a means of suppressing ambiguous beampattern sidelnbes. A difficulty with MV methods however is their sensitivity to signal wavefront mis ... Full text Cite

The Performance of Matched-Field Beanformers with Mediterranean Vertical Array Data

Journal article IEEE Transactions on Signal Processing · December 1, 1996 Minimum variance (MV) adaptive beamforming has been widely proposed for matched-field processing because it provides a means of suppressing ambiguous bcampattem sidelobcs. A difficulty with MV methods, however, is their sensitivity to signal wavefront mism ... Cite

Performance bounds on acoustic thermometry of ocean climate in the presence of mesoscale sound-speed variability

Journal article Journal of the Acoustical Society of America · January 1, 1996 The ability to measure climatic changes in ocean temperature is fundamentally limited by the presence of mesoscale variability. Because ocean acoustic propagation can be used to measure the range-averaged temperature profile, long-range acoustic transmissi ... Full text Cite

High resolution adaptive beamforming for three-dimensional acoustic imaging of zooplankton

Journal article Journal of the Acoustical Society of America · January 1, 1996 This paper investigates the use of adaptive beamforming techniques to increase the performance of a sonar imaging system developed at the Scripps Institution of Oceanography to monitor the migration of zooplankton. The original system, known as Fish Televi ... Full text Cite

Is the Accretion Flow in NGC 4258 Advection Dominated?

Journal article Astrophysical Journal · 1996 Cite

Robust matched-field beamforming with benchmark shallow-water acoustic array data

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1996 In this paper, four robust matched-field beamforming methods are evaluated using benchmark shallow-water Mediterranean data. While the Bartlett beamformer, reduced minimum variance beamformer (RMV), and minimum variance beamformer with neighborhood locatio ... Cite

Robust maximum likelihood source localization by exploiting predictable acoustic modes

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1996 This paper presents a robust Maximum-Likelihood estimator for matched-field source localization in the presence of uncertainties in the ocean environment. The method is based on a decomposition of the field into predictable and unpredictable subspaces of t ... Cite

Fundamental limits on acoustic source range estimation performance in uncertain ocean channels

Journal article Journal of the Acoustical Society of America · January 1, 1995 Matched-field methods which exploit complex multipath propagation models to localize underwater acoustic sources are particularly sensitive to errors in the assumed environmental parameters. In this paper, the Cramer-Rao lower bound (CRLB) is used to deter ... Full text Cite

Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. IV. Multiwavelength analysis

Journal article Astrophys. J. (USA) · 1995 For pt.III see ibid., vol.438, no.1, p.108-19 (1995). Simultaneous X-ray, ultraviolet, optical, infrared, and radio monitoring data were used to test and constrain models of continuum emission from the BL Lac object PKS 2155-304. Intensively sampled ultrav ... Full text Link to item Cite

The nature of the ultraviolet continuum in type 2 Seyfert galaxies

Journal article Astrophys. J. (USA) · 1995 Type 2 Seyfert nuclei are well known to contain a “featureless continuum” which makes a significant contribution in the optical and ultraviolet. However, the nature of this featureless continuum is not clear. Optical spectropolarimetry shows th ... Cite

Cramer-rao bound on acoustic measurement of ocean climate change in the presence of mesoscale sound-speed variability

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1995 The ability to measure climate-related mean changes in ocean temperature is fundamentally limited by the presence of mesoscale variability. In this paper, the Cramer-Rao Lower Bound on the estimation of the mean depth-dependent temperature profile is evalu ... Cite

A Multiple Time Scale Modularized Adaptive Beamformer

Journal article IEEE Transactions on Signal Processing · January 1, 1994 This paper analyzes the cascaded equivalent form of the min imum variance distortionless response (MVDR) beamformer. A unique feature of the modularized MVDR (M2 VDR) beamformer is the ability to distribute adaptive degrees of freedom (DOF) amon ... Full text Cite

The intrinsic nuclear spectrum of NGC 1068

Journal article Astrophys. J. (USA) · 1994 Infers the intrinsic optical, UV and X-ray continuum of the obscured Seyfert nucleus of NGC 1068, using small aperture and polarized flux data to separate host galaxy contamination from reflected nuclear light. In support of popular unification models, the ... Full text Link to item Cite

Spatial correlation of rough seabed scattering of surface-generated ambient noise

Journal article Journal of the Acoustical Society of America · 1994 Cite

Sensor array processing performance evaluation via bootstrap resampling

Journal article Journal of the Acoustical Society of America · January 1, 1994 This paper examines bootstrap resampling methods for evaluating the performance of source localization methods on real sensor array data without precise a priori knowledge of true source positions and the underlying data distribution. Bootstrap resampling ... Full text Cite

On the Mean-Square Error Performance of Adaptive Minimum Variance Beamformers Based on the Sample Covariance Matrix

Journal article IEEE Transactions on Signal Processing · January 1, 1994 This correspondence examines the mean-square error (MSE) performance of two common implementations of adaptive linearly constrained minimum variance (LCMV) beamformers that employ the sample covariance matrix. The Type I beamformer is representative of blo ... Full text Cite

The Spatial Correlation Of Rough Seabed Scattering Of Surface-Generated Ambient Noise

Journal article Journal of the Acoustical Society of America · January 1, 1994 This article considers the effect of rough seabed scattering on the spatial correlation of low-frequency ambient noise. Extending the study presented by Liu et al. [J. Acoust. Soc. Am. 93, 753-769 (1993)], it is shown here that seabed roughness may alter t ... Full text Cite

X-ray light curves of active galactic nuclei are phase incoherent

Journal article Astrophys. J. (USA) · 1993 The authors compute the Fourier phase spectra for the light curves of five low-luminosity active galactic nuclei observed by EXOSAT. There is no statistically significant phase coherence in any of them. This statement is equivalent, subject to a technical ... Full text Link to item Cite

Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. I. The IUE campaign

Journal article Astrophys. J. (USA) · 1993 Daily monitoring with the IUE satellite has revealed dramatic, large-amplitude, rapid variations in the ultraviolet flux. Many smaller, rapid flares are superposed on a general doubling of the intensity. During the 5d period when sampling was roughly conti ... Full text Link to item Cite

Matched-field minimum variance beamforming in a random ocean channel

Journal article Journal of the Acoustical Society of America · October 14, 1992 Matched-field source localization methods that employ deterministic full- wave acoustic propagation models can be seriously degraded due to the presence of random inhomogeneities in the ocean channel. In this paper, a minimum variance (MV) matched-field be ... Full text Cite

Cross-talk artifacts in spatial spectrum estimation with a sensor array

Journal article Journal of the Acoustical Society of America · January 1, 1992 Cross-talk between output channels is a common problem that can occur in the wet-end or dry-end electronic cabling of a sensor array. This paper examines artifacts in spatial spectral estimates caused by cross-talk between sensor output channels. It is sho ... Full text Cite

Matched field source localization in an uncertain environment using constraints based on sound-speed perturbations

Journal article Oceans Conference Record IEEE · December 1, 1991 Matched field source localization methods can be seriously degraded due to errors in modeling the propagation characteristics of the ocean channel. A maximum likelihood (ML) matched field beamformer is presented which achieves greater robustness to model m ... Cite

Broadband source localization in a slowly time-varying environment by multichannel Kalman filtering

Journal article IEEE Pacific Rim Conference on Communications Computers and Signal Processing Conference Proceedings · December 1, 1991 An adaptive multichannel (AMC) strategy is generalized to operate in a nonstationary environment. A recursive means of generating cross spectral density matrix (CSDM) estimates is presented in terms of a Kalman filter formulation. The Kalman filter is deri ... Cite

The Performance of Minimax Spatial Resampling Filters for Focusing Wide-Band Arrays

Journal article IEEE Transactions on Signal Processing · January 1, 1991 In recent research, coherent focusing of wideband data received by a linear array of sensors has been achieved by adjusting the spatial sampling rate, or “spatially resampling” the array outputs, as a function of temporal frequency. Spatial resampling perm ... Full text Cite

The application of adaptive multichannel spectral estimation for broadband array processing

Journal article Proceedings ICASSP IEEE International Conference on Acoustics Speech and Signal Processing · January 1, 1991 An alternative means of reducing the observation time required to make high-resolution broadband spatial spectral estimates is presented which precludes the need for preliminary periodogram cross spectral density matrix (CSDM) estimates. The methods descri ... Full text Cite

A bootstrap approach for evaluating source localization performance on real sensor array data

Journal article Proceedings ICASSP IEEE International Conference on Acoustics Speech and Signal Processing · January 1, 1991 Bootstrap methods for evaluating the performance of source localization methods on real sensor array data without precise a priori knowledge of true source positions and the underlying data distribution are examined. Bootstrap resampling methods are used t ... Full text Cite

The detection performance of coherent wideband focusing for a spatially resampled array

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · December 1, 1990 Using output deflection as a criterion, the detection performance of the SRMV (spatially resampled minimum variance) and ICMV (incoherent minimum variance) spatial spectral estimates are examined. The SRMV method is shown to provide improved detection perf ... Cite

Focused Wide-Band Array Processing by Spatial Resampling

Journal article IEEE Transactions on Acoustics Speech and Signal Processing · January 1, 1990 This correspondence presents a new approach for coherently focusing wide-hand data received by a linear array of sensors. The proposed preprocessing consists of adjusting the spatial sampling rate or “spatially resampling” the array outputs as a function o ... Full text Cite

Focussed partially adaptive broadband beamforming via spatial resampling

Journal article undefined · December 1, 1989 Summary form only given. A focusing technique that can reduce each wideband interferer in multigroup scenarios to essentially a rank-one representation without preliminary estimates of the group locations has been developed. The method is based on adjustin ... Cite

Implementation considerations for a doubly-steered, coherently-focussed high-resolution broadband beamformer for source location estimation

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · December 1, 1989 It is demonstrated that the doubly steered, coherently focused broadband beamformer implementation is a practically viable technique for source location estimation in an underwater acoustic environment. Various simple relationships among the key parameters ... Cite

Robust incoherent matched field processor for source localization in uncertain multipath fields

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · December 1, 1989 Matched-field source localization methods are seriously degraded because of errors in modeling the propagation characteristics of the ocean channel. A generalized minimum-variance distortionless-response (MVDR) method that is more robust to model mismatch ... Cite

Multiple Broad-Band Source Location Using Steered Covariance Matrices

Journal article IEEE Transactions on Acoustics Speech and Signal Processing · January 1, 1989 This paper presents an approach for reducing the threshold observation time required to achieve high-resolution localization of multiple broadband sources. The proposed techniques are based on a spacetime statistic called the steered covariance matrix (STC ... Full text Cite

Source Location Bias In The Coherently Focused High-Resolution Broadband Beamformer

Journal article IEEE Transactions on Acoustics Speech and Signal Processing · January 1, 1989 A simple expression for the source location (angle of arrival) bias is developed for Wang and Kaveh's focused broadband beamformer. It is shown to depend on the source temporal frequency spectrum only through its centroidal frequency. The bias is zero if t ... Full text Cite

Dominant-mode steered linear prediction for high resolution broadband source location

Journal article undefined · December 1, 1988 The authors develop a linear predictive approach for high-resolution broadband bearing estimation in low signal-to-noise ratio environments. The proposed technique is based on a space-time statistic called the steered covariance matrix (STCM). In broadband ... Cite

Time Delay Estimation of Signals with Uncertain Spectra

Journal article IEEE Transactions on Acoustics Speech and Signal Processing · January 1, 1988 This paper presents a method of improving the performance of generalized correlation (GC) methods for time delay estimation when a priori knowledge of the received source spectrum is limited. The treatment is restricted to finite-time observation of a sing ... Full text Cite

HIGH-RESOLUTION BROADBAND BEAMFORMING USING A DOUBLY-STEERED COHERENT SIGNAL-SUBSPACE APPROACH.

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1988 H. Wang and M. Kaveh's (1985) wideband coherent signal-subspace technique is shown to have a straightforward correlation domain interpretation, with their simplified, so-called focused covariance matrix being a slice through the generalized correlation mat ... Cite

MINIMUM VARIANCE SPECTRAL ESTIMATION FOR BROADBAND SOURCE LOCATION USING STEERED COVARIANCE MATRICES.

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1988 An approach is presented for reducing the threshold observation time required to perform high resolution broadband bearing estimation. The proposed technique is based on a space-time statistic called the steered covariance matrix (STCM). In broadband setti ... Cite

Adaptive Lattice Filter for Multiple Sinusoids in White Noise

Journal article IEEE Transactions on Acoustics Speech and Signal Processing · January 1, 1987 In this paper we present an analytical study of the lattice filter for an input time series consisting of multiple sinusoids in white noise. For this model, the method of undetermined coefficients is applied to derive the convergent solution. Further, expr ... Full text Cite

TIME DELAY ESTIMATION VIA GENERALIZED CORRELATION WITH ADAPTIVE SPATIAL PREFILTERING.

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · December 1, 1986 The use of adaptive beamforming prior to generalized correlation (GC) is demonstrated as a means of time-delay-estimate (TDE) bias reduction in interference-dominated environments. Analysis of GC TDE bias with both minimum-variance distortionless response ... Cite

APPLICATION OF THE LMS ADAPTIVE LINE ENHANCER IN TIME DELAY ESTIMATION.

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · December 1, 1985 It is demonstrated that the LMS adaptive line enhancer (ALE) can be used to enhance estimation performance in situations where source signal spectra have tonal components. Time-delay estimation obtained by using ALEs as prefilters followed by a cross corre ... Cite

Constrained time delay estimation via zero-crossing methods

Journal article Adaptive Methods in Underwater Acoustics. Proceedings of the NATO Advanced Study Institute · 1985 A constrained processor (CP) for time delay estimation is presented which employs a predefined set of candidate log-likelihood score functions. In spatially white ambient noise, the CP can achieve nearly minimum variance time delay estimates without a prio ... Cite

COMPARATIVE STUDY OF THE LMS ADAPTIVE FILTER VERSUS GENERALIZED CORRELATION METHODS FOR TIME DELAY ESTIMATION.

Journal article ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings · January 1, 1984 Cite

Computationally efficient Monte Carlo estimation algorithms for matched field processing in uncertain ocean environments

Journal article J. Comput. Acoust. (Singapore) In this paper, Monte Carlo estimation techniques are presented for computationally efficient implementation of two methods for matched field source localization in uncertain ocean channels. In the Optimal Uncertain Field Processor (OUFP), Monte Carlo integ ... Cite

Highlights of statistical signal and array processing

Journal article IEEE Signal Process. Mag. (USA) The Statistical Signal and Array Processing Technical Committee (SSAP-TC) deals with signals that are random and processes an array of signals simultaneously. The field of SSAP represents both solid theory and practical applications. Starting with research ... Full text Link to item Cite

Two-dimensional hydrodynamic simulations of convection in radiation-dominated accretion disks

Journal article Astrophys. J. (USA) The standard equilibrium for radiation-dominated accretion disks has long been known to be viscously, thermally, and convectively unstable, but the nonlinear development of these instabilities - and hence the actual state of such disks - has not yet been i ... Full text Link to item Cite

Ultraviolet-optical observations of the Seyfert 2 galaxies NGC 7130, NGC 5135, and IC 3639: implications for the starburst-active galactic nucleus connection

Journal article Astrophys. J. (USA) The authors present and discuss Hubble Space Telescope (HST) (WFPC2 and FOC) images and ultraviolet (GHRS) spectra plus ground-based optical spectra of three Seyfert 2 nuclei (NGC 7130, NGC 5135 and IC 3639). These galaxies, together with Mrk 477 (Heckman ... Full text Link to item Cite