Active sonar systems can provide good target detection potential but are limited in shallow water environments by the high level of reverberation produced by the interaction between the acoustic signal and the ocean bottom. The nature of the reverberation is highly variable and depends critically on the ocean and seabed properties, which are typically poorly known. This has motivated interest in techniques that are invariant to the environment. In passive sonar, a scalar parameter termed the waveguide invariant, has been introduced to describe the slope of striations observed in lofargrams. In this work, an invariant for active sonar is introduced. This active invariant is shown to be present in the time-frequency structure observed in sonar data from the Malta Plateau, and the structure agrees with results produced from normal mode simulations. The application of this feature in active tracking algorithms is discussed.
"A summary of the underlying theory and the results will be provided in Section II. Experimental data from the Malta Plateau has shown striation patterns in active sonar field experiments as outlined by Quijano  and thus motivated further research on this topic in simulations, experiments and potential applications. "
[Show abstract][Hide abstract] ABSTRACT: Physics-based detection algorithms can improve discrimination of sonar targets from competing bottom reverberation, but are vulnerable to environmental uncertainties. Recent research in the underwater community has identified an environmentally robust time-frequency signature for improved target discrimination. Application of this “invariant” requires processing algorithms to identify striations in a spectrogram and to quantify the associated track certainty. In this paper, two robust invariant-based algorithms are presented and demonstrated with underwater data. The first algorithm uses a Kalman Filter to estimate the time-frequency striations in sonar spectrograms. The second computes a “likeliness” metric to measure discrimination between target and non-target detections.
Signals, Systems and Computers (ASILOMAR), 2010 Conference Record of the Forty Fourth Asilomar Conference on; 12/2010
"The performance of the algorithms was evaluated by estimating frequency patterns from simulated spectra and injecting clutter at various levels to quantify noise performance. While this provided an assessment of the efficacy of the proposed IEKF, it did not provide a data demonstration of the striation patterns in truly bistatic geometries (Quijano and Zurk  "
[Show abstract][Hide abstract] ABSTRACT: Target tracking in multistatic active sonar systems is often limited in shallow-water environments due to the high level of bottom reverberation that produces false detections. Past research has shown that these false alarms may be mitigated when complete knowledge of the environment is available for discrimination, but these methods are not robust to environmental uncertainty. Recent work has demonstrated the existence of a waveguide invariant for active sonar geometries. Since this parameter is independent of specifics of the environment, it may be used when the environment is poorly known. In this paper, the invariance extended Kalman filter (IEKF) is proposed as a new tracking algorithm that incorporates dynamic frequency information in the state vector and uses the invariance relation to improve tracker discrimination. IEKF performance is quantified with both simulated and experimental sonar data and results show that the IEKF tracks the target better than the conventional extended Kalman filter (CEKF) in the presence of false detections.
[Show abstract][Hide abstract] ABSTRACT: Random variability in shallow water will induce variability in a propagating acoustic field. The long-term goal of this research is to quantify how random variability in the ocean environment translates into random variability in the acoustic field and the associated signal processing algorithms. In the present funding cycle, the emphasis is on the effects of linear and non-linear internal waves on acoustic propagation in the mid-frequency (1-10 kHz) band. OBJECTIVES The specific objective for the current funding cycle is to understand the generation of new acoustic paths that occur due to the passage of non-linear internal waves. APPROACH During the Shallow Water 2006 Experiment (SW06), mid-frequency acoustic transmission data were collected over a continuous 7-hour period at range 550 m. The relatively short range was deemed desirable for isolating the effects of shallow water internal waves on acoustic propagation. At the SW06 site, both linear and non-linear internal waves were potentially important. Linear internal waves often are modeled as a background random process introducing small changes in the sound speed that cause fluctuations in the acoustic field. At range 550 m, mid-frequency transmissions between 1 and 10 kHz were thought to span the transition between the regimes where classical weak-and strong-scattering theories for random media would apply . Non-linear internal waves are often modeled as a more event-like process causing strong, localized changes in the sound speed. Packets of non-linear internal waves are not unusual and it was anticipated that a 550 m acoustic path might permit individual waves in the packet to be isolated. Our approach is to use a statistical model for the acoustic fluctuations introduced by random background internal waves, and a more deterministic model for the acoustic effects introduced by passage of more event-like non-linear internal waves.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.