Kevin D. LePage

Bayesian Tracking in Underwater Wireless Sensor Networks With Port-Starboard Ambiguity

Port-starboard ambiguity is an important issue in underwater tracking systems with anti-submarine warfare applications, especially for wireless sensor networks based upon autonomous underwater vehicles. In monostatic systems this ambiguity leads to a ghost track of the target symmetrically displaced with respect to the sensor. Removal of such artifacts is usually made by rough and heuristic approaches. In the context of Bayesian filtering approximated by means of particle filtering techniques, we show that optimal disambiguation can be pursued by deriving the full Bayesian posterior distribution of the target state. The analysis is corroborated by simulations that show the effectiveness of the particle-filtering tracking. A full validation of the approach relies upon real-world experiments conducted by the NATO Science and Technology Organization - Centre for Maritime Research and Experimentation during the sea trials Generic Littoral Interoperable Network Technology 2011 and Exercise Proud Manta 2012, results which are also reported.

Bottom reverberation in shallow water: Coherent properties as a function of bandwidth, waveguide characteristics, and scatterer distributions

Shallow water presents a difficult, reverberation-limited environment for active SONAR operations. It is important to understand the predictable structure of shallow-water reverberation in order to aid the design of processors and detectors which work properly in these environments. In this paper, the temporal characteristics of monostatic reverberation are predicted as a function of source bandwidth, source–receiver depth, and the propagation characteristics of range-independent shallow water. Results show that at early time, reverberation can be highly coherent across a vertical line array, violating the homogeneous noise assumption, while at late time the reverberation becomes increasingly uncorrelated. This is shown to be due to the insonification of independent bottom patches at late time. It is also shown that this decorrelation of the reverberation is dependent both on the propagation characteristics of the particular shallow-water environment, the correlation length scale of the scatterers, and th...

Single snapshot DOA estimation using compressed sensing

This paper deals with the problem of estimating the Directions of Arrival (DOA) of multiple source signals from a single observation of an array data. In particular, an estimation algorithm based on the emerging theory of Compressed Sensing (CS) is analyzed and its statistical properties are investigated. We show that, unlike the classical Fourier beamformer, a CS-based beamformer (CSB) has some desirable properties typical of the adaptive algorithms (e.g. Capon and MUSIC). Particular attention will be devoted to the super-resolution property. Theoretical arguments and simulation analysis are provided in order to prove that the CSB can achieve a resolution below the classical Rayleigh limit.

Single-snapshot DOA estimation by using Compressed Sensing

This paper deals with the problem of estimating the directions of arrival (DOA) of multiple source signals from a single observation vector of an array data. In particular, four estimation algorithms based on the theory of compressed sensing (CS), i.e., the classical ℓ1 minimization (or Least Absolute Shrinkage and Selection Operator, LASSO), the fast smooth ℓ0 minimization, and the Sparse Iterative Covariance-Based Estimator, SPICE and the Iterative Adaptive Approach for Amplitude and Phase Estimation, IAA-APES algorithms, are analyzed, and their statistical properties are investigated and compared with the classical Fourier beamformer (FB) in different simulated scenarios. We show that unlike the classical FB, a CS-based beamformer (CSB) has some desirable properties typical of the adaptive algorithms (e.g., Capon and MUSIC) even in the single snapshot case. Particular attention is devoted to the super-resolution property. Theoretical arguments and simulation analysis provide evidence that a CS-based beamformer can achieve resolution beyond the classical Rayleigh limit. Finally, the theoretical findings are validated by processing a real sonar dataset.

Statistics of broad-band bottom reverberation predictions in shallow-water waveguides

A new coherent reverberation model developed at the Naval Research Laboratory, Washington, DC, and the Supreme Allied Commander Atlantic Undersea Research Centre, La Spezia, Italy, is exercised in the 17-750-Hz band to estimate the degree of non-Rayleighness of shallow-water reverberation envelopes as a function of waveguide multipath, system bandwidth, directivity, and frequency. Findings suggest that reverberation from diffuse, but non-Gaussian, scatterer distributions is significantly more Rayleigh for multipath environments than for equivalent environments excited by a single or small number of modes or for broadside receiver array processing that extracts narrow angles of reception. These findings suggest that the problem of non-Rayleigh reverberation in shallow-water waveguides can be ameliorated through the use of tuned ensonification and reception schemes, which retain high probabilities of detection while reducing the associated probability of false alarm.

Modeling of low‐frequency transmission loss in the central Arctic

The magnitude of low‐frequency (10−100 Hz) propagation loss in the central Arctic is known to be larger than predicted by most free surface scattering theories. This high loss is introduced primarily by scattering at the ice canopy, with which the acoustic path interfers regularly due to the presence of a strongly upward refracting surface duct. While distinct feature scattering theories such as boss or elastic keel models predict higher losses, these results are typically too frequency dependent to agree with the data over the entire band of interest. Perturbation theory gives close to the correct frequency dependence, but historically predicts too little loss when the dynamics of the ice canopy is neglected or the ice is assumed to be locally reacting. In this paper it is proposed that when perturbation theory is extended to include scattering of incident acoustic energy into propagating elastic modes in the ice, the resulting expressions correctly predict low‐frequency losses measured in the Arctic.

Boundary characterization experiment series overview

Ocean acoustic propagation and reverberation in continental shelf regions is often controlled by the seabed and sea surface boundaries. A series of three multi-national and multi-disciplinary experiments was conducted between 2000-2002 to identify and measure key ocean boundary characteristics. The frequency range of interest was nominally 500-5000 Hz with the main focus on the seabed, which is generally considered as the boundary of greatest importance and least understood. Two of the experiments were conducted in the Mediterranean in the Strait of Sicily and one experiment in the North Atlantic with sites on the outer New Jersey Shelf (STRATAFORM area) and on the Scotian Shelf. Measurements included seabed reflection, seabed, surface, and biologic scattering, propagation, reverberation, and ambient noise along with supporting oceanographic, geologic, and geophysical data. This paper is primarily intended to provide an overview of the experiments and the strategies that linked the various measurements together, with detailed experiment results contained in various papers in this volume and other sources

Bistatic synthetic aperture imaging of proud and buried targets from an AUV

The use of autonomous underwater vehicles (AUVs) for the detection of buried mines is an area of current interest to the Mine CounterMeasures (MCM) community. AUVs offer the advantages of lower cost, stealth, reduced operator risk, and potentially improved coverage rates over more traditional mine hunters. However, AUVs also come with their own set of difficulties, including significant error in navigation and low communication rates with the mother platform and each other. In the case of bistatic detection scenarios, AUVs will therefore have difficulty knowing where exactly in space they are and the trigger time of sources on other platforms, be they ships or other AUVs. However, the potential improvement in detection and coverage rates offered by bistatic sonar concepts makes resolution of these issues a high priority. In this paper, the problems of inaccurate navigation and source timing information are addressed for the Generic Oceanographic Array Technology data set. In this experiment, conducted off Marciana Marina during June 1998, a MIT AUV with a SACLANTCEN acoustic array and acquisition system was used together with a TOPAS parametric sonar to explore issues of buried target detection using AUVs. In this paper, solutions to the navigation and timing problems are proposed which enable the effective use of bistatic synthetic aperture sonar (SAS) concepts for the detection of buried objects in the mid-frequency regime of 2-20 kHz.

Spectral integral representations of monostatic backscattering from three-dimensional distributions of sediment volume inhomogeneities

A theory is developed for generating short time, monostatic reverberation realizations caused by three-dimensionally distributed volume inhomogeneities in stratified media. A wave number integral approach to treating the propagation to and from the scatterers, combined with a two-dimensional spectral representation of the azimuthally averaged scatterer realizations and a novel numerical implementation, combine to yield an efficient, high fidelity reverberation simulator for predicting monostatic backscatter from horizontally stratified sediments.

A non-myopic, receding horizon control strategy for an AUV to track an underwater target in a bistatic sonar scenario

We investigate how to improve the autonomy of AUVs to operate effectively in a multistatic network for littoral surveillance. We present a novel algorithm to control the movement of an AUV towing a line array acting as a receiver node in the network. The proposed algorithm uses a non-myopic, receding horizon policy to control the AUV heading to minimize the expected target position estimation error of a tracking filter. Minimizing this error is typically of the utmost interest in target state estimation since it is one way of maintaining track. Methods to simplify the resulting decision tree are used together with a branch and bound technique to solve an optimization problem at each ping time with the low computational power available onboard AUVs. Results from COLLAB13 sea trials are reported and show both the feasibility of running the algorithm in real-time on an onboard computer and the benefits of using the proposed algorithm over conventional predefined paths. These results represent, to the best of our knowledge, the first successful demonstration at sea of a complex non-myopic algorithm running in real-time on AUVs in a realistic multistatic littoral surveillance scenario.