Sonobuoy System Research Articles

Development of Synthetic Signal Generator and Simulator for Performance Evaluation in Multiple Sonobuoy System

Development of Synthetic Signal Generator and Simulator for Performance Evaluation in Multiple Sonobuoy System

Bistatic sonobuoy deployment strategies for detecting stationary and mobile underwater targets

The problem of determining effective allocation schemes of underwater sensors for surveillance, search, detection, and tracking purposes is a fundamental research area in military operations research. Among the various sensor types, multistatic sonobuoy systems are a promising development in submerged target detection systems. These systems consist of sources (active sensors) and receivers (passive sensors), which need not be collocated. A multistatic sonobuoy system consisting of a single source and receiver is called a bistatic system. The sensing zone of this fundamental system is defined by Cassini ovals. The unique properties and unusual geometrical profile of these ovals distinguish the bistatic sensor allocation problem from conventional sonar placement problems. This study is aimed at supporting decision makers in making the best use of bistatic sonobuoys to detect stationary and mobile targets transiting through an area of interest. We use integral geometry and geometric probability concepts to derive analytic expressions for the optimal source and receiver separation distances to maximize the detection probability of a submerged target. We corroborate our analytic results using Monte Carlo simulation. Our approach constitutes a valuable “back of the envelope” method for the important and difficult problem of analyzing bistatic sonar performance.

Work Domain Analysis for the Interface Design of a Sonobuoy System

Modern sonar systems have greatly improved their sensor technology and processing techniques, but little effort has been put into display design for sonar data. The enormous amount of acoustic data presented by the traditional frequency versus time display can be overwhelming for a sonar operator to monitor and analyze. In addition to their normal sonar tasks, sonobuoy system operators manage the deployment of sonobuoys and ensure proper functioning of deployed sonobuoys. This paper describes a work domain analysis carried out as part of an interface design project targeting the sonobuoy system on board a maritime patrol aircraft. The domain of sonobuoy management and the domain of tactical situation awareness were modeled separately to address the two different aspects of the operator's work. Information requirements were drawn from the two models. Some of these requirements have significant implications for new design ideas that were previously overlooked in displays for sonobuoy systems.

Air-deployable sonobuoy array concepts and their performance against high-frequency noise anisotropy

High-frequency sonobuoy arrays with vertical aperture were developed and tested to exploit the noise anisotropy for enhanced array gain [Ferat and Arvelo, J. Acoust. Soc. Am. 114, 2462–2463 (2003)]. Afterwards, an inexpensive and conformal piezoelectric wire material was employed in the design and construction of a volumetric array [Arvelo et al., J. Acoust. Soc. Am. 116, 2650 (2004)]. However, detection performance of air-deployed sonobuoys is severely affected by noise interference through the beamformers sidelobes. An improved sonobuoy system design with in-buoy processing for sidelobe suppression is introduced and its detection performance in anisotropic wind noise with nearby shipping interference is evaluated and compared against previous designs in selected environmental conditions. The high-frequency array gain for increased vertical aperture will be compared against the gain for increased horizontal aperture to explore coherence limitations. The effects of array tilt, as well as interelement amplitude, phase, and topology errors, on the performance deterioration of the new design will also be addressed. [This effort is supported by the Maritime Sensing (MS) Program of the Office of Naval Research (ONR Code 321).]

Sei whale sounds recorded in the Antarctic

Sei whales are the least well known acoustically of all the rorquals, with only two brief descriptions of their calls previously reported. Recordings of low-frequency tonal and frequency swept calls were made near a group of four or five sei whales in waters west of the Antarctic Peninsula on 19 February 2003. These whales also produced broadband sounds which can be described as growls or whooshes. Many of the tonal and frequency swept calls (30 out of 68) consist of multiple parts with a frequency step between the two parts, this being the most unique characteristic of the calls, allowing them to be distinguished from the calls of other whale species. The average duration of the tonal calls is 0.45 +/- 0.3 s and the average frequency is 433 +/- 192 Hz. Using a calibrated seafloor recorder to determine the absolute calibration of a sonobuoy system, the maximum source level of the tonal calls was 156 +/- 3.6 dB re 1 microPa at 1 m. Each call had different character and there was no temporal pattern in the calling.

Geometrical interpretation of the localization performance of a sonobuoy system

This is an explorative paper which focuses on the accuracy of locating an underwater acoustic source using the broadband information collected at arbitrarily positioned, submerged, omnidirectional hydrophones. The paper presents expressions for the localization-error covariance of an optimally weighted least-square-error estimator for two sources of error: ocean acoustic noise and sensor perturbations. The performance measure used for comparisons is the mean square euclidean localization error, which is the trace of the localization-error covariance matrix. Comparisons of performance are made between two specific systems: one based on two sensors and the other based on three sensors. The main contribution of the paper is the explanation of the improved performance obtained by using a geometric approach to visualize the localization error. This geometric interpretation method is demonstrated by an explanation of the principles involved in the dramatic improvement in the mean square euclidean error obtained by adding a third sensor to a two-sensor system. The geometric interpretation is an approach based on the eigen structure of the sensor-system covariance matrices. This is a very useful tool for visualizing the localization error for any arbitrary source-sensor configuration.

Seismic investigation of the Coast Plutonic Complex – Insular Belt boundary beneath the Strait of Georgia

The Strait of Georgia, a topographic depression between Vancouver Island and the mainland of British Columbia, is considered to be the boundary between two tectonic provinces: the Coast Plutonic Complex on the east and the Insular Belt to the west. The allochthonous nature of the Insular Belt has been established, mainly on the basis of paleomagnetic measurements. Various tectonic models to explain the geological differences between the two provinces have been proposed. One of these suggests that the boundary is an old transform fault zone and is represented currently by a thrust fault along the eastern side of the Strait of Georgia. Other models propose that the Coast Plutonic Complex is a feature superimposed by tectonic and metamorphic events after the accretion of the Insular Belt. Such models do not require a major crustal discontinuity along the Strait of Georgia.In May 1982, a seismic refraction survey using a 32 L air gun and a radio telemetering sonobuoy system was carried out in the Strait of Georgia with the objective of investigating the nature of this boundary and determining the upper crustal structure. Three reversed profiles across the strait were shot; these are supplemented by several high-resolution reflection profiles from previous experiments. Two-dimensional models of the crustal structure across the strait have been constructed using a forward modelling ray trace and synthetic seismogram algorithm to match the travel times and amplitude characteristics of the data.Three basic layers or strata form the models, for which the maximum depth of reliability is 3 km. The first layer consists of unconsolidated sediments and Pleistocene glacial deposits, and the second represents Late Cretaceous – early Tertiary basin fill sediments that form the Nanaimo Group, the Burrard–Kitsilano formations, and the Chuckanut Formation. The third layer is likely the extension of the Coast Plutonic Complex beneath the strait, but the westerly limit of this unit is undetermined because of seismic properties similar to those of the Insular Belt volcanics. A local fault is located ~15 km northeast of Galiano Island on the west side of the strait. However, our study shows no evidence for a major fault along the strait. Thus those aspects of tectonic models that require the existence of a major transform or transcurrent fault boundary along the Strait of Georgia. may have to be revised.

Sonobuoy system

Sonobuoy system

A single-ship telemetric seismic refraction system

A telemetering, recoverable, sonobuoy system for seismic refraction surveying using a single ship is described. The novel feature of the system is two-way telemetry between ship and buoys, enabling the setting of gain controls in the buoys and conservation of battery power between recording periods. This makes it possible to have several widely separated buoys simultaneously record the shots. Thus a reversed or multiple-reversed profile is obtained from a single line of shots. By careful design of the telemetry system, a maximum range of 50 km is achieved with an antenna height of only 50 ft on the ship.

Deep-sea sediment velocity determination made while reflection profiling

A technique for routinely determining the velocity structure of the sediment column with an average error of less than 100/m sec during normal reflection profiling is described. An expendable passive sonobuoy is launched while the ship is underway. A variable angle reflection profile is recorded on one channel of the seismic profiler, and a vertical reflection profile is obtained on the other, providing dip and topographic corrections for the variable angle data. The velocity structure is determined by means of a modified T2/X2 solution programmed for a digital computer. The sonobuoy system has the advantage of being free of towing noise, permitting the use of lower frequencies, which in some areas results in greater penetration than is possible with a towed array. The accuracy and reliability of the system and the problems relating to velocity gradients are discussed. The examples discussed cover a wide range of conditions and geographic locations.