Bistatic Sonar Research Articles

An Improved Algorithm of Bearing-Only Localization and Optimal Position Performance of Multistaic Sonar

To improve the localization accuracy of bistatic sonar in such districts as baseline district, and side districts of transmitting and receiving stations, the most effective method is to increase the number of transmitting and receiving stations, which forms a multistatic sonar system. The mature algorithm of multistatic sonar system which contains three measurements in one subset, calls the multistatic bearing-only localization (BOL) algorithm. This paper proposes a new algorithm of improving the bearing-only localization algorithm. The simulation results show that the proposed localization algorithm exhibits higher accuracy compared with the BOL algorithm and provides less time than it.

Source ranging with an underwater geographic point in non-cooperative bistatic sonar

Active sonar is divided into monostatic and bistatic sonar according to the relative positions of the source and the receiver. Bistatic sonar on modern submarines is classified into cooperative and non-cooperative operations. Cooperative operation uses an active signal of a friendly ship; therefore, source information is known a priori, whereas non-cooperative operation utilizes an active signal of the enemy, and hence, it is difficult to acquire source information, such as a source range, which is important for bistatic sonar operation. In order to overcome this difficulty, this paper proposes an estimation method for the source range that employs geographic information, and the utility of the source range estimation is evaluated. For the evaluation, we consider three error components. Then, the validity of the scheme is confirmed through theoretical error analysis and simulation study. The results show that geographic points that satisfy certain specific conditions can be used to estimate the source range within a range of tens of km in the simulation. Finally, we confirm that the receiver could estimate the source range from far away using non-cooperative bistatic sonar.

Source Information Estimation Using Enemy's Single-Ping and Geographic Information in Non-cooperative Bistatic Sonar

Bistatic sonar operations on modern submarines are classified into cooperative and non-cooperative operations. In the cooperative operation, an active signal of a friendly ship is used and the source information is known a priori. In the non-cooperative operation, an active signal of the enemy is used, which makes it difficult to acquire the source information. The source information consists of the range, speed, course, and frequency of ping, which gives advantage to operating bistatic sonar. This paper suggests a novel method of estimating the source information with geographic information in the sea and the single-ping of the enemy. The source range is given using one geographic point. The source speed, course, and the frequency of the enemy's source signal are given using two geographic points. The performance of the proposed method is validated through simulation studies.

Space-time-frequency analysis of the scattered acoustic wave field from elastic shells recorded by bistatic sonar systems.

An ongoing challenge for underwater sonar systems is to discriminate a man made target (shell) from surrounding clutter returns and to provide robust classification features for the estimation of the physical target characteristics (e.g., shell thickness and material properties). To this end, time-frequency analysis, and, in particular, Wigner–Ville analysis, has been shown to provide a robust processing tool for interpreting the evolutional time dependent aspect of the scattered acoustic wave field from elastic shells. The design of a robust space-time-frequency bistatic sonar system to enhance the target detection of shells with the use of a sensor array will be presented. Practical implications for bistatic mine countermeasure sonar systems, using a network of autonomous underwater vehicles, will be discussed.

Performance comparison of target localization for active sonar systems

The performance comparison of target localization for active sonar and effective fusion algorithms for target localization of multistatic sonar is investigated. Active sonar can be categorized into monostatic, bistatic, and multistatic, depending on the number of receiver elements. Target localization performance depends on the system configuration. The target localization performance of the monostatic, bistatic, and multistatic sonar systems is compared assuming that each element can receive both range and azimuth information of the target. In addition, we propose the weighted least square (WLS) algorithm, which incorporates judicial weighting to the conventional least square (LS) method, and an efficient sensor arrangement rule for target localization in the multistatic sonar system. The representative experimental results demonstrate that the target localization performance of multistatic sonar configuration is superior in terms of root-mean-square error (RMSE), to monostatic sonar and bistatic sonar by 35.98% and 37.45%, respectively, while the proposed WLS algorithm showed an improvement of 2.27% compared with the LS method.

Time‐reversed maximal‐length sequences for outdoor, underwater sound propagation, and room‐acoustic artificial reverberation simulations.

Pseudorandom properties of maximal‐length sequences (M‐sequences) have long been exploited for acoustic measurements. Time‐reversed M‐sequence pairs also possess unique correlation properties, including a two‐valued autocorrelation function and a low‐valued cross‐correlation function, which make them excellent candidates for acoustic measurements using simultaneous dual‐sources [N. Xiang and M. R. Schroeder, J. Acoust. Soc. Am. 113, 2754–2761 (2003)]. The application of time‐reversed M‐sequences was originally inspired by the outdoor acoustic tomography. This paper reports on a recent underwater experiment using the time‐revered M‐sequence pairs in a quasibistatic sonar system. Different from the baseband simultaneous acoustic excitations in outdoor sound propagation, the underwater application in the bistatic sonar requires ultrasonic amplitude modulation technique in order to exploit the desired correlation properties. Their excellent pseudorandom and correlation properties have also been exploited in room‐acoustic applications. In addition to simultaneous dual‐source room impulse response measurements, this paper also reports on creating artificial enveloping reverberations using time‐reversed M‐sequences.

Direct wave suppression using wavelet transform for bistatic sonar

The bistatic sonar is often influenced by the direct wave, especially when the target approaches the baseline of the system. The direct wave is above 50dB higher than the scattering signal level. The paper analyzes the effect of the direct wave, and proposes a new method based on wavelet transform for direct wave suppression. The strong direct wave is well eliminated while maintaining the weak scattering signal almost unchanged. The basic idea is that the direct wave is firstly removed form the received signal after wavelet transform. Then the signal is reconstructed in time domain, finally the cross-correlation is achieved to shown the doppler frequency shift of the weak scattering signal. Computer simulation is given. The cross-correlations of the received signal for both before and after the direct wave suppression are compared. It shows that the influence of the direct wave is correctly removed, the time delay and Doppler frequency shift are shown in the figure and the target is detectable.

Intensity processing of vector sensors in the bistatic regime

Acoustic intensity processing of signals from directional frequency analysis and recording (DIFAR) acoustic subsystems is used to enhance the detection of submerged bodies in bistatic sonar applications. In some directions, the scattered signals may be completely dominated by the incident blast from the source, depending upon the geometry, making the object undetectable by traditional scalar pressure measurements. Previous theoretical derivations suggest that acoustic vector intensity sensors, and the associated intensity processing, are a potential solution to this problem. Deep-water experiments conducted at Lake Pend Oreille in northern Idaho are described. A large body of revolution is located between a source and a number of SSQ-53D DIFAR sonobuoys positioned from 5 to 30 body lengths away from the scattering body. Scalar pressure measurements change by less than 0.5 dB when the scattering body is inserted in the field. However, the phase of the acoustic intensity component formed between the omnipressure and directional channel orthogonal to the direction of incident wave propagation varies by as much as 75. This metric is shown to be a repeatable and strong indicator of the presence of the scattering body. [Work supported by ONR, code 321MS.]

Acoustic sampling volume of a bistatic sonar

The expression for the acoustic sampling volume of a monostatic sonar [K. G. Foote, J. Acoust. Soc. Am. 90, 959 (1991)] is generalized to the case of a bistatic sonar, with separate, non-collocated transmitting and receiving transducers. The bistatic sampling volume is the integral of a counting function over the physically accessible space. The argument of the counting function, a Heaviside step function, is the difference between the scattering amplitude, or other measure of scattering strength, and a noise-dependent threshold. When this difference is positive, the integrand is unity; when zero, one-half; when negative, zero. Both the sampling volume and a related quantity, the equivalent beam angle, are evaluated numerically for several bistatic geometries, transducer shapes, and narrowband frequencies for the cases of point scatterers and directional scatterers. The application of the bistatic acoustic sampling volume to the quantification of suspended particulate matter and aquatic organisms is discussed.

Time domain beamforming ASIC for a handheld bistatic imaging sonar system

A high-resolution, handheld imaging sonar system has been developed by Teratech Corporation for the U.S. Navy. This is a 192-channel, dual-frequency bistatic sonar for Navy divers performing search and survey missions for underwater explosives. The goal is to provide the most compact and energy-efficient imaging system for the divers. The low power and small volume are a result of the development of Teratech’s Charge Domain Processing (CDP) technology. This technology has led to the development of a low-power 64-channel beamformer chip. As a result, only three beamformer chips are needed for the 192-element array. Until now, implementation of small, low-power sonar systems containing this many elements and forming enough beams to create an image was considered impossible. Test results and acoustic images obtained in Teratech’s acoustic test tank will be presented. [Work sponsored by ONR and OSD Small Business Innovative Research Program, Program Manager, Mr. Bruce Johnson, Naval Explosive Ordnance Disposal Technology Division.]

Development of a handheld bistatic imaging sonar system for underwater search and survey

A high resolution, handheld imaging sonar system is under development by Teratech Corporation for the U.S. Navy. This is a 192 channel, dual frequency bistatic sonar for Navy divers performing search and survey missions for underwater explosives. Our goal is to provide the most compact and energy efficient imaging system for the divers. The system consists of a self-contained handheld unit and a head mounted display integrated into the divers mask. The low power and small volume are a result of the development of Teratechs Charge Domain Processing (CDP) technology. This technology has led to the development of a low power 64-channel beamformer chip. As a result, only three beamformer chips will be required for the 192 channels. Until now, the implementation of small, low power sonar systems containing this many elements and forming enough beams to create an image was considered impossible. Progress in the development of this product will be presented. In-water testing is planned for late summer 2003. Experimental results and test images available will be presented at the conference. [Work sponsored by ONR and OSD Small Business Innovative Research Program, Program manager, Mr. Bruce Johnson, Naval Explosive Ordnance Disposal Technology Division.]

Wave Kinematics at High Sea States

Abstract Measurements of currents close to the ocean surface and within the crests of large, steep waves have been acquired with an incoherent bistatic sonar mounted on the seafloor. The sonar uses a single narrow-beam transmitter/receiver and three fan-beam receivers set in a triangular configuration around the source. Acoustic pulses transmitted from the seafloor are scattered by bubble clouds and the sea surface to the four receivers and may be transformed into velocity components as a function of elevation. Individual estimates of the currents at, and close to, the surface are made with sufficient temporal resolution to identify kinematics in the crests of large waves. Observations acquired in the Danish sector of the North Sea are examined to evaluate both the potential merits and limitations of the measurement approach. At lower wind speeds, sidelobe scatter from the surface reaches the receiver simultaneously with the volume scattered signal arriving from a few meters beneath, contaminating the vel...

Bistatic scattering: A new way to improve sonar detection capabilities?

In the field of seabed sonar imagery, it is necessary to establish local scattering models to improve the performances of the detection or recognition algorithms. In this paper, we present the Probability Density Function (PDF) of the acoustic intensity scattered by a natural profile as a function of the bistatic angle. To do this we have developed a 1-D bistatic scattering model called NEWS (Numerical Estimation for Waves Scattering) that incorporates physical phenomenons like multiple reflections, shadow and the reflection coefficient of the profile. Moreover, NEWS takes into account acquisition parameters like sensors characteristics and their positions in relation to the center of the illuminated area. Gaussian spectra for the profile height fluctuation are considered. Five hundred profiles are generated. For each profile NEWS’s algorithm gives the angular distribution of the scattered field in amplitude and in phase for all geometries and as a function of incident and scattered wave. The acoustic intensity is then treated as a random variable, and histograms are established. The PDF of the scattered intensity is compared to the K, Weibull and lognormal distributions and we examine the statistical informations providing by bistatic sonar.

Ultrasonic scattering in highly turbulent clear water flow

Abstract Experiments have been made to investigate the source of ultrasonic scattering in clear turbulent water. Microstructure scattering in open-channel is related to turbulence parameters by adapting the Batchelor spectrum and theory valid in a steady uniform flow. Quantitative verification of this relationship is carried out by experiments with a coherent Doppler sonar, from which the profiles of the turbulence parameters are determined. Results from both multi-beam monostatic sonar and bistatic sonar show that the theoretically predicted scattering cross section profile coincides with the observed one under the assumption that fine air bubble microstructures dominate the scattering process. The scattering from temperature microstructures is too small to account for the observed scattering. Experiments made in a grid-stirred tank filled with normal tap water and with degassed water further confirm the hypothesis that the concentration variation of fine air bubbles is responsible for the scattering observed by high-frequency sonar in clear water open-channel flow.

Shallow water active sonar environmental acoustic issues

The propagation and reverberation of sound in shallow water under downward refracting conditions is governed by the geoacoustic and scattering properties of the bottom. The active bistatic sonar equation for this case is developed and it is shown that, when the transmission to the target and the bottom are approximately the same for reverberation-limited conditions, a simpler parametric form of this equation results. That is, the signal excess depends on the effective bottom backscattering strength, the coherent signal gain, and a reverberation area for a given target strength and threshold. A parametric analysis is presented that focuses on the frequency-dependent characteristics of the bottom backscattering strength and the effect of coherence on receiving array aperture. Recent reverberation and signal coherence measurements are reviewed and the needs for additional studies delineated. The coherence issue for the waveguide is stressed and the measurement problem of coherence is discussed and compared to the measurement of signal versus the receiver length in wavelengths.

Adaptive predictor of surface reverberation in a bistatic sonar

A bistatic sonar employing LMS adaptive spatial prediction is used to process against surface reverberation from the convergence zone (CZ). Hydrophones (120, 130) spatially separated from the primary array (100) are used as references. The critical behavior exploited by the invention is that since the reverberation may be viewed as an extended source for the reverberation, the correlation drops off with separation between the reference and primary sensors, while it stays a constant for the plane wave target return. The reverberation is nonstationary functionally dependent on the signal (even though the back scatter is statistically uncorrelated with the signal), and spatially extended over the sector of the CZ annulus cut out by the transmitter azimuth beamwidth. The detection of the target is based on the sudden appearance of one strong target point source (50) within a densely packed region of weak point sources that have been constantly present and whose sum is much larger than the target. The use of more than a single reference leads to a minimal improvement in detection performance and may actually degrade performance due to increased algorithm noise. Detection performance tends to increase with increasing separation distance between the primary and the reference hydrophone.