Many of the institutions visited mentioned that they were involved in various acoustics applications. The brevity of the discussions did not allow documentation of many of the technical details. Because of this lack of complete information the following discussions may be brief, but the associated tables will help to clarify where applications were mentioned. When possible, more detailed information will be presented. For more information, contact the specific institute representatives named in the site reports (Appendices B through F).
. Although the institute has nine departments, the WTEC visit was primarily concerned with the institute's work in devices for oceanographic research. While several of the departments contribute to marine related research, the majority of that work is done in the Department of Wave Phenomena. The institute's Acoustic Ocean Sounding laboratory has been using a towed fish, equipped with two transducers, in the Barents Sea to do sound path research at 100 Hz and 300 Hz frequencies at output powers of 100 W and 300 W, respectively. In conjunction with these acoustic sources, an array consisting of 12 hydrophones is used for receiving the acoustic signals. The array, 70 m in length, can be towed from a ship or mounted on the sea floor where it is battery powered (operating depth of 500 m). The array has sensors to measure depth and tilt angle to compensate for these variables in signal processing. Through the use of buoys, the received data can be transmitted to a remote location up to 10 miles away.
Using this system, researchers have sent acoustic signals over a 500 km path to determine losses for both vertical and horizontal paths. This work has been used in conjunction with acoustic tomography efforts in the United States. The institute hopes to continue this work in the Arctic Basin for long-range tomography experiments. The institute also hopes to do some shallow water work with this system in the Barents Sea.
Atmosphere - Ocean Communications. An interesting application was discussed where communications between an aircraft and a submarine would be accomplished using high-powered lasers and acoustics. The aerial platform would use a very high-powered, modulated laser directed at a very small area of the ocean surface. The power output of the laser would be high enough to create mechanical surface roughness that could be sensed by the submerged platform. Through analysis of the generated surface roughness, the information transmitted would be detected.
Conversely, the submerged platform would use an upward directed very high frequency sound source to create similar roughness on the sea surface. This roughness would then be detected by a cross-polarized radar. This concept has been tested from a low flying aircraft.
The Andreev Acoustics Institute is a research institute and considers first principles related to acoustic applications. Although the institute does not build systems, it becomes involved in the testing and evaluation of systems after they have been developed.
The institute focuses on basic research of sound propagation in the sea, although it is now considering air acoustics as well as a number of other application areas. The institute is involved with scientific research, not prototype development. It is involved in five areas of acoustic research: (1) ocean, (2) oil and gas, (3) medical, (4) ecological, and (5) air acoustics. This is a technical institute and, as such, previously worked only on problems provided by the user community. Recently it has been given more freedom to choose its research directions, but has far less support to accomplish that research.
The following nine acoustic applications were mentioned, a few of which were discussed in some technical depth:
. The institute is interested in undersea transponders with extended durations. Some work has been undertaken directed at the development of transponders that would extend their endurance through the use of a sleep mode. One year or more lifetime with wake up mode is expected.
The institute has been investigating the design of a multibeam receiver for obtaining accurate range and bearing determination using transponders. Investigations suggest bearing accuracies of 1°. The institute has not built these receivers, but has completed the design investigations.
Bottom Referenced Positioning System. This project uses bathymetric data to monitor the movement of slow moving objects such as oil rigs. Andreev Institute compared data acquired from a multibeam sonar with previous data to get motion accuracy of ±1 cm. The institute has a multibeam sonar of 100 1° beams.
Bore Hole Reentry System. Andreev Institute is considering using stationary arrays to monitor the positions of oil drilling heads. Processing will eliminate the noise associated with the drilling process and allow for range and bearing to drill head.
Sound Vision System. This effort is focused on medical applications. An acoustic imaging systems was discussed that uses 1 MHz and a 100 x 100 array with 1° beams. The beams are electronically formed from the array data.
Parametric Sonar Systems. The institute is working on parametric sonar techniques for different applications. One such application is for oil exploration; the sediment is used to mix carriers around 300 kHz to get a 600 Hz difference in frequency for subbottom profiling/seismic analysis.
Pulsed Acoustics for Pollution Monitoring. The institute's scientists believe that they can obtain pollutant concentrations by analyzing received pulses over small volumes of water (1 to 10 m) paths. They have run some experiments to obtain understanding of changes in concentrations of pollutants to 1 part per 1E8.
Matched Field Processing. The institute has been working on matched field processing for years, and is now applying that technique to various problems. They are working on, or at least interested in:
Communications. The institute's scientists and engineers have worked on some communication systems that they cannot discuss. They have looked at some filter processing techniques being applied to underwater communications. They believed that there was a need for long range communications at low data rates (2,000 km to 3,000 km). The same techniques can be applied to shorter ranges with correspondingly higher data rates (e.g., 20 Hz ±10 for ranges of 1,000 km to 2,000 km using a receiver with 18 bit resolution). With regard to bore head telemetry, the institute wants to use its techniques for implementing a low data rate telemetry system from the drill head to the surface without cables.
Marine Mammals Research. Andreev is researching dolphins' and other marine animals' sonar capabilities, with an interest in understanding what can be applied to sonar systems. Marine mammals such as the dolphin have a sonar system that is a "whole" system, that is, the physiological characteristics of the animal as well as its behavior are part of the entire sonar system. Much may be learned from this: it has been said that 5 to 100 neurons can sometimes have the equivalent processing capability of a million computers.
The institute is investigating some basic issues associated with neural networks, specifically, how a group of neurons with msec response times can be connected so that the group can detect msec variations. The research effort in this area is not large.
The Marine Hydrophysical Institute is principally focused on the study of physical oceanography. Scientists there have a substantial design, development, and manufacturing capability to support the development of instrumentation required for their activities. There is an acoustics facility at Odessa, but there was not enough time for the team to visit it.
The institute has developed a number of acoustic current meters for its needs. It has concentrated on acoustic current meters that measure velocity components at a point rather than utilizing the range gated Doppler system concept. No other unique applications of acoustic technology were reported; however, others may well exist.
The Shirshov Institute is involved with the production of platform and instrumentation systems needed to support its oceanographic research. Since there was limited availability of Western equipment, the institute's scientists and engineers were forced to develop their own instruments. While this activity was driven by necessity, it also helped to stimulate the development of some unique devices. The applications mentioned were:
Sonar Information Processing. The little about sonar information processing that was discussed appeared to be related to side scan sonar imagery.
Transducer Elements for Side Scan Sonar and Acoustic Imaging. The work on side scan sonar transducers and imaging systems focused on the development of transducers rated for 6,000 m.
Hydroacoustic Beacon/Transponder. This effort focused on the development of a beacon/transponder system for attachment to divers and marine mammals. In both cases, physiological and location data could be sent back to a remote station. It was suggested that this system could be used to control the activities of marine mammals via long distance communications.
Geophysical Towed Arrays. Mr. Merklin discussed his development of a smaller, lower-cost geophysical seismic system. Pointing out that existing 3-D systems are large and expensive, his goal is to achieve similar results with much less complexity by developing a 5 km towed array using sensors that are only 20 to 25 mm in diameter. A microjet transmitter would transmit a complex broadband signal as a source for seismic analysis of returns.
Additional InformationAdditional information can be obtained from a publication developed by the Office of Naval Research, European Office (NAVSO P-3678). This publication mentions acoustic applications under investigation at the Laboratory of Acoustic Noise and Sound Fluctuations and the Acoustic Wave Propagation Laboratory of the institute. These include free-floating acoustic recording capsules, bottom tomography, various arrays, and a portable acoustic positioning system with baseline distances in the 20 to 25 km range.
Discussions during the WTEC team's visit focused on the Department of Hydrophysics and Hydroacoustics for work related to acoustic applications, where most of this institute's ocean-related work takes place. Although little technical detail was discussed, several projects were mentioned, including:
. One example of work on low frequency sources was the testing of a compact electromagnetic monopole source in conjunction with the Woods Hole Oceanographic Institute (published in WHOI-93-09). The titanium source, developed at IAP RAS, has a mass of 123 kg and a diameter of .54 m. The system has a center frequency of 225 Hz, a bandwidth of about 50 Hz, an associated pulse resolution of about 200 msec, and a sources level of 198 Db re 1 mPa at 1 m, with an efficiency of about 50 percent. This source is being considered for use in monitoring the ocean to understand more about global ocean processes and their impact on the world's climate.
Mobile Linear Array. This 200 m long mobile linear array consists of 64 hydrophones spaced 3 m apart (300 m operating depth). The system is capable of making very accurate acoustic spectrum measurements from 20 to 300 Hz. The upper range can be extended to 2,000 Hz. Included with this system, which is available for sale at $20,000, is signal processing software, which otherwise costs an additional $12,500.
Acoustic Doppler Current Profiler. This instrument is a three-beam (30° beams oriented 30° off vertical in 120° azimuthal increments), 220 kHz system for operation in water depths to 400 m (200 to 300 m for current profiling, and 300 to 400 m for ship velocity measurements). The system is configured with an IBM/AT for processing. It is believed to be superior to the RD Instruments system.
NIIVK was represented as the institute responsible for designing computer hardware and systems software. In accomplishing this task, NIIVK scientists developed algorithms for sonar systems. Much of this work was originally classified (and some still remains so) but is now unclassified. Efforts are underway to commercialize several acoustic applications that have evolved from the work at NIIVK. The following describes some of those concepts.
Fish Monitoring Sonar System. This system is designed for low-tonnage vessels fishing in any open ocean areas. It is aimed at detecting pelagic and bottom fish shoals to determine their location while the vessel is operating at full speed in seas up to sea state 4. The system is used in low-tonnage vessels for fish objects detection (fish, crustaceans, mollusks) in active and/or passive (on receiving bioacoustic signals) sonar mode.
The unique feature of the system is its use in a passive sonar mode, which assists in the detection and classification of living resources on or in the bottom layer, which is a favorite location of crustaceans and mollusks. The Fish Monitoring Sonar System includes a receiving-transmitting transducer (antenna); a signal processor; and displaying, recording, and control devices. The use of a standard recorder and a standard display is possible, as well. Receiving-transmitting and control devices should be installed in a pilot house.
The sonar system range is nominally 15 km, but depends on sea depth, sound speed dependence, bottom and surface acoustic parameters, and equivalent radius of a fish shoal.
At 1 Pa total acoustic noise (reduced to reference conditions: 1 kHz frequency, 1 Hz bandwidth, and a concentration factor equal to 1) at the site of the transducer, the range for a shelf zone must be more than 6,000 m for pelagic fish shoals (at an equivalent sphere radius R = 2 m), and 200 m for a single fish at a bottom layer (R = 0.1 m). R is given for a frequency of 15 kHz. At a signal occurrence probability equal to 0.4, a signal detection probability must be not less than 0.8.
Depending on operational needs, fish shoal search may be carried out in sector or in circular view mode. In the sector scan mode, the system scans ± 165° in the azimuth plane and 0 to 90° in the elevation plane (bottom direction). Accuracy of fish object location in the azimuth and elevation guidance mode is not less than 3 percent. Less precision is permitted in the search mode.
Classification of objects detected in passive mode is implemented automatically. The probability of species and subspecies valid classification achieves 0.7 to 0.8 for relatively high values of signal/noise ratio. The results of the classification are displayed in a form suitable for operator perception.
A receiving-transmitting antenna is a 0.9 m height and near 2 m diameter cylinder. The antenna is installed under a keel in a glass-fiber-plastic or a metal sonar dome. The antenna may also be placed in a lifting-sliding facility or may be lowered from a helicopter. This facility must lower the antenna 1 m lower than a keel. In an idle state the antenna should be retracted into a trunk inside a vessel hull. The antenna displacement control is remote, automatic, and manual.
Display, signal, and control processors are based on 286 (386, 486) and TMS 320C30 processors. The required performance of the signal processor is about 800 MDPS.
Compact Sonar System for the Nearest Water Area Viewing. This compact sonar system is designed for underwater apparatus used in shelf zones for applications such as exploration of mineral deposits, laying cable, surveying platform sites, and investigating ice covers. General system specifications are given in Table 6.2.
This parametric sonar system has a transmitting array of 0.2 square meters in the angular sector. A parallel-sequential spatial view is obtained by the system.
General System Specifications -- Nearest Water Area Viewing
The receiving array (0.6 square meters) receives a noise and valid signal mixture. The amplified, filtered, and digitized signals are sent to the computing facilities. Signal processing includes the following:
The processing results are displayed. An operator analyzes the image and, taking into account primary classification data, identifies the object under observation.
Design specifications of this system are available. The main design concepts have been analyzed, simulated, and tested in natural conditions, and the array breadboarding has been accomplished. Proposals for cooperation with foreign participants are being sought.
Multiship Fish Monitoring Sonar System. This compact system is designed for fish shoals search and classification in the shelf zone and in the open ocean. General system specifications are given in Table 6.3.
The pseudo random signal transmitting antenna is towed by the most forward fishing vessel. The receiving array is towed by one or two fishing ships, moving parallel with the major vessel. The arrays receive a noise and valid signal mixture. These signals are amplified, filtered, digitized, and sent to the computing facility. Signal processing includes:
General System Specifications -- Multiship Fish Monitoring
The processing results are displayed. An operator analyzes the image and, taking into account initial classification data, identifies the object under observation. Data concerning new objects are then loaded into the classification database.
Scientific analysis of detection methods and underwater moving objects classification are available. Proposals for cooperation are being sought.
Sonar System for Beam Structure Parameters of Undersea Acoustic Fields. This system is aimed at acquiring parameters of undersea acoustic fields and comparing empirical data with calculated parameters. The system can measure the following:
General system specifications are given in Table 6.4.
The antenna, installed at the transmitting ship, transmits a pseudorandom signal. The array at the receiving ship can be placed in the vertical or horizontal position. It receives a noise and valid signal mixture. Amplified, filtered, and digitized signals are sent to the computing facilities. The computer evaluates the beam structure parameters of sea acoustic fields. The use of special algorithms provides beam super resolution. Computer system software includes beam structure evaluation of acoustic fields and the comparison of theoretical and experimental results.
In order to make measurements more accurate, the receiving array is automatically calibrated at regular intervals. Processing results are displayed and loaded into a database. This measurement method has been experimentally verified in the Atlantic Ocean. Proposals for cooperation are being sought.
General System Specifications -- Beam Structure Parameters
The university has some interest in an ultrashort baseline underwater tracing system with a range of 1 km. Not much was discussed relating to other acoustic applications, although there may be other work underway.
Oceanpribor is the largest Russian company specializing in the design and manufacture of hydroacoustic systems. The company has developed and is selling transponders and transducers as well as hydroacoustic systems for various applications under the trademark "Korvet." Hence the company is sometimes known as Korvet Oceanpribor. Table 6.5 summarizes some of its offerings.
The bureau's primary function is to design, build, and test samplers, sensors, and instrumentation for oceanographic research. Its activities in acoustic applications seem consistent with the types of instruments commonly found in the ocean community. The following applications/acoustic instruments were mentioned:
TECHNOPOLE is a trade group that represents several startup companies that have spun off the technologies developed at Atoll Scientific Research Institute in Dubna. Four companies discussed their products and ideas for products, as summarized below.
Geoton (in existence for about two years) presented a multichannel seismic system to explore for oil and gas. The unique feature of the Geoton system is its multichannel capability for data acquisition and processing. Up to 10,000 channels are possible in the system, which can enable three-dimensional views and greater accuracy for location of test drilling sites. Geoton claims that this will reduce the number of test wells by one-third. With the Geoton system in place it is also possible to estimate undepleted reserves in productive oil and gas fields.
Oceanpribor's Transponders, Antennae and Systems
Geoton has built components for its system and tested them in the laboratory. Systems have been developed around the TMS 320 processor using algorithms developed solely in Russia, since the company has had no access to the computer technology of the West. The Institute of Oil and Gas has deployed and tested a 12-channel system with good results. Although Geoton does not manufacture, it will form partnerships with other Russian companies to produce the system. Geoton representatives believe they are well positioned to serve companies that will be conducting oil and gas exploration in the fields of Siberia, and are looking for clients with that same interest.
The ROS Company, which may be the oldest of the four companies, was a company with a product that was developed and ready for sale: a seabed passive sonar system. This low-frequency system uses from less than 1 Hz up to 5 kHz, and has a sensitivity of 250 microvolt/Pa.
The wet part of the system consisted of multiple hydrophone arrays, each array in a straight line with multiple arrays ganged onto an underwater data transmission line. The arrays might have 30 or 80 hydrophones. From four to eight arrays would make up the underwater systems. Analog to digital signal conversion was provided at each hydrophone, and electronic to optical signal conversion occurred in a regenerator at the array level to enable fiber optic transmission to the shore station.
The dry part of the system consisted of a remote-controlled power supply and an acoustic data analysis and display system that used an 80486 microcomputer. Very efficient data sampling, and compression and analysis algorithms were claimed for the system, which together with TMS 320 S-30 chips for each four arrays enabled effective and timely processing with a 486 microcomputer. Frequency, bearing, time, and target location (depending on array layout) could be displayed for up to five simultaneous targets per display. A database for classification of shipping targets is available from ROS. Larger projection displays could be incorporated if desired. The wet system could be retrieved and redeployed. The dry system is compact enough to reside in a mobile van. Other characteristics are in Figure Dubna.1 in the TECHNOPOLE/Dubna site report (see Appendix B). Figures Dubna.2 and Dubna.3, also in the site report, are photos that show the hydrophone piezoceramic of about 1.5 inch diameter, and the hydrophone housing, which is approximately 12" x 5" x 2", and contains the hydrophone and the a/d signal converter.
The Peleng Company specializes in high power, low frequency (below 1,000 Hz) acoustic emitters. Mr. Polevik is a senior scientist there with many years of experience in emitter design, and holds approximately 80 patents for acoustic devices. He discussed the design of sparker, boomer, electrodynamic, and hydraulic-type emitters. Finally, he discussed the characteristics of a patented cylindrical emitter, created especially for use in seismic operations.
The problem of more durable electrodes in the sparker device has been solved by encapsulating them in a special liquid in which the high powered electric discharge takes place. The power in a single pulse from this large device, which is 1.2 m by .6 m and weighs 300 kg, is 5 kJ, which is hydraulically transmitted through the encapsulation to the surrounding sea. The operational depth of the device is up to 200 m.
High Powered Boomer-Type Induction Pulsing Emitter. A high powered boomer-type induction pulsing emitter with a tunable frequency response was described. The device was tunable to provide maximum amplitude in the low frequencies -- 50 to 700 Hz. It was claimed to be the first such design available for deep water use, that is, up to 300 m.
Pulse Resonant Transmitter With High Frequency Response. A working model of a new pulse resonant transmitter with high frequency response has been completed. The transmitter has a flat characteristic curve in the 10 to 300 Hz range through the use of reactive compensation, and has output power in the 3 kJ range. The transmitter is electrohydraulic; it is purely electric at low power and can be purely hydraulic at high power.
Low Frequency Active Array. A developmental concept was discussed for a low frequency active array of cylindrical shapes that might be used for searching out oil and gas fields. The array would be arranged to fit down an oil and gas well casing and would operate in the 50 to 100 Hz range with control to produce a directed beam pattern along a horizontal plane. The total system would also include a multichannel receiver array.
A senior scientist from INFRAD described the ARGUS system, which is being developed in partnership with other companies in the Dubna region. The ARGUS system proposes using sonar emission tomography to detect fish shoals, currents and underwater waves, and sediment fallout rates. The proposed system would be purely passive and would have a maximum depth of 1,000 m, with a monitoring base line of 150 m that lies up to 200 km offshore. The pattern of surface noise would be understood through array processing as fish, currents, or sediment, and could be characterized as to depth, density, and school size of fish. The processing by each array would require the characteristics of the conditions in situ. The spokesperson for INFRAD explained that for about one year, there had been basic work exploring the fine structure of hydroacoustic fields to support the concept of sonar tomography, but as yet there had been no funding to support experiments.
The discussions at Heriot-Watt University focused on two groups involved with research directly related to undersea systems. The Ocean Systems Laboratory, headed by Professor George Russell, is investigating several different areas, three of which focus on sonar applications. The second group, headed by Dr. L.M. Linnett, was investigating sonar signal processing. The following topics were discussed:
Multisensor Fusion. This investigation studies methods of sensing three-dimensional environments in which subsea robotics activities take place, providing the precise positional information required by combining signals from optical sensors and acoustic sensors to increase realizable accuracies.
Subsea Communications. These studies investigate mathematical models of underwater acoustic propagation channels and the validation of these models through field demonstrations. The purpose of these efforts is to provide design information for high data rate communications for autonomous underwater vehicles.
Digitally Focused Sonar System. This project seeks to develop methods of creating high definition images by the digital processing of signals from sonar arrays, with application to the detailed survey of seabed features, texture classification, object detection by surface vessels and underwater vehicles, obstacle avoidance, and navigation of AUVs.
Object Detection. The group's years of work on object detection has advanced to a stage where excellent detection rates have been achieved for many different seabed types. The work is now aimed at assessing the probability of detection against different backgrounds.
Pipeline Inspection. A system has been developed for inspecting subsea pipelines using side scan sonar techniques to detect spans (unsupported sections of a pipe). A system that performs real-time processing of the data has been successfully produced.
Seabed Characterization. This work has reached the stage where excellent characterization of complex seabeds from side scan sonar records has been achieved. The present aim is towards a database of seabed types covering most areas of the seabed. With the increase in data rates from sonar equipment, the ability to accurately analyze data quickly is essential. To this end, a system has been developed for performing on-line segmentation of seabed types. This has application in hydrography where it is possible to perform seabed comparison over very short time scales. This could be of major importance in times of conflict.
Sonar Data Compression. With the increase in resolution of modern sonars, gigabytes of data are now being gathered in side scan surveys. Techniques have been developed that are capable of compressing the information by many orders of magnitude. This has obvious benefits for the storage, manipulation, and transmission of such data. Work is continuing on techniques for real-time handling of acoustic data.
Sonar Simulation. The group is developing mathematical and graphical techniques for synthesizing side scan data. The aim is to develop a system to allow the study of the sonar process, which will aid analysis and detection work.
The Marine Technology Directorate (MTD) is a United Kingdom-based association with international membership. The members have significant interests and capabilities in ocean-related technologies and come from industry, government, research establishments, academic institutions, the United Kingdom's Science and Engineering Research Council, and the Royal Academy of Engineering.
MTD funds research programs that relate to undersea vehicle technology. One, the Technology for Unmanned Underwater Vehicles (TUUV) program, covers a broad spectrum of technology problems in six main areas: sensing, control, communication, navigation, propulsion, and analysis. Three of those projects reflect types of activities related to acoustic applications in the undersea environment. MTD advances research and development through its funding of marine research. MTD also encourages communication in the marine community by organizing discussions with companies whose interests relate to the objectives of the WTEC study. A description of three TUUV projects funded by MTD follows:
Techniques for Processing Side Scan Sonar Data from Large Data Sets (Heriot-Watt University). In recent years, there has been an increase in the demand for high quality side scan sonar data for mapping sediments on the seafloor. Coupled with this demand has been increasingly sophisticated sonar equipment capable of obtaining high resolution images of the seafloor. These factors have led to an abundance of data that must be examined by trained personnel in a subjective and time-consuming process. Techniques must be developed to more fully automate this process.
A New Underwater Vision System (Strathclyde University). The goal of this project is to investigate a new vision system for working underwater. It combines the complementary characteristics of stereo optics with three-dimensional acoustic imaging. A 2-D matrix ultrasonic array, fixed relative to a pair of underwater cameras operating in stereo mode, will generate spatial and depth information to a target. This data will then be used to update and optimize a stereo matching algorithm to provide accurate 3-D optical vision. The objectives of the project are: (1) to merge acoustic data with 3-D optical data; (2) to design and evaluate a 2-D matrix ultrasonic array; (3) to create and implement stereo matching algorithms by fusing acoustic and optical data; and (4) to evaluate a prototype system.
High Data Rate Subsea Acoustic Communications for UUVs (Newcastle University). The goal of this project is to better understand the potential for using acoustics to achieve 20 kbits/sec data transmission in shallow water environments. The objectives of this effort are: (1) to determine the fundamental limitations relating to the use of m-ary phase shift keying (PSK), beamforming, and adaptive equalization in the subsea environment; (2) to develop a half-duplex acoustic telemetry link using simultaneous beamforming at the transmitter and receiver; and (3) to demonstrate the practicality of high data rate acoustic communications systems operating in real conditions.
Tritech produces a range of advanced, high performance, and compact scanning sonar heads, all of which can be operated from the SCU-3 Multitasking Surface Control Unit. The heads are available in three different frequencies to satisfy the majority of underwater requirements. The ST 325 long range scanning sonar is used throughout the world. It is an all-around sonar with a 200 m range capability. It is generally used for obstacle avoidance and navigation on small and large vehicles. The ST 525 high resolution, imaging sonar combines long range (100 m) with high resolution making it suitable for most ROV applications, including target acquisition and debris survey. The ST 725 very high resolution sonar is a high resolution, mid-range (50 m) imaging sonar used where higher resolution images are needed in preference to long operation.
The scanning heads for these sonar systems are available in three different configurations (vertical, horizontal, and big top) to allow installation in available spaces. The big top version has a larger transducer than the standard vertical and horizontal heads. This design produces a narrower and more concentrated sonar beam, resulting in higher angular resolution beam patterns.
Specifications of Tritech Sonars
The sonar heads share a common power supply requirement and data communication protocol that enable the connection of multiple devices, including sonar, profilers, and altimeters, to the SCU-3 via a single twisted pair.
The SCU-3 is a powerful yet simple to operate multitasking acoustic processor. In addition to controlling ST sonars, it also operates Tritech ST 1000 scanning profilers, displays real-time video, and shows information from other sensors, such as a TSS 340 Pipetracker and eastings and northings from a navigation computer, all on the same monitor simultaneously. Data may be logged to and replayed from disk.
Images may be taken from SCU-3 and entered into desktop publishing packages to assist in creating post-operation reports.
The SEABAT 9001 system is a multibeam sonar system that carries out profiling operations. It consists of a low weight (5 kg in water) multibeam sonar head, a 19-inch rack mounted processor, a high resolution monitor, and a track-ball with which to control the system (all functions are menu driven).
The SEABAT 9001 transmits a 90° x 1.5° fan beam consisting of sixty 455 kHz individual beams (1.5° x 1.5°) in one single pulse. All the beams are formed using a curved face transducer that minimizes background noise.
Because a single pulse is transmitted, undistorted profiles are generated, accurately portraying even the most complex sea bed features. Also, due to the single transmission pulse, the full 90° profile is updated at 30 times per second at 25 m range or below, reducing to 7 times per second at 100 m.
The SEABAT 9001 exports the X/Z coordinates as a data stream twice per second to be integrated with roll, heave, pitch, and heading sensor information via a data acquisition program to provide an XYZ data stream that is combined with the positioning information supplied via the navigation program and passed through a digital terrain modelling program to provide the specified charts.
The SEABAT 6012 is a 455 kHz electronically scanning minisonar. It was especially designed as a principal ROV sensor for mine warfare. It is a 90° forward-looking sonar used for detection, relocation, and classification of mine-like objects located on the seabed or in the mid-water column.
The SEABAT 6012 functions in real-time with a visual window of 90° horizontally and 15° vertically. This, in effect, is similar to a wide angle camera view. Because the SEABAT displays static and moving objects dynamically in real-time, the sonar head can be set on a pan and tilt mount, as you would a video camera, to follow an area of interest while maintaining orientation. This is particularly useful when monitoring installation or positioning procedures in visibility that precludes the use of video.
The 6012 has a maximum usable range of 200 m and a minimum set range of 2.5 m. The speed of update is controlled by the range selected and is dependent on the speed of sound through water. For example, at ranges from 2.5 to 25 m, the update is 30 times per second. The image displayed is optically correct, with the objects viewed appearing without dimensional distortion. This remains the case regardless of the speed of movement of the supporting platform or the object being viewed. The SEABAT 6012 has been operated satisfactorily at towed speeds of up to 10 kt.
Marconi UDI [now Fugro UDI Limited] is a relatively small company focused on the development and application of sonar systems. The company has a strong focus on the development of acoustic transducers, and has expanded that focus into different projects. Marconi has a modular building block concept where the company packages standard blocks of transducers into large arrays. The following summaries describe some of the systems discussed.
Sonavision 4000. Sonavision 4000 is the first commercial high frequency scanning sonar to use UDI's newly developed composite array technology. The use of these arrays results in a wider bandwidth and much greater efficiency in the conversion of electrical energy into mechanical energy.
The Sonavision 4000 transmitter and receiver electronics are fully tunable via software from 150 kHz to 1.5 MHz. Therefore various beam angles and frequencies are available, that is, 1 MHz profile and 2,000 kHz long range search. See Table 6.7 for specifications.
In one application, the standard Sonavision 4000 sonar product was modified to take a 1.2° 500 kHz sonar array. The computer graphics card in the display system was modified to store up to 10 sonar pictures and the OS9-based control software was adjusted accordingly. Software was also supplied for personal computer control of the sonar system, enabling the operator to store sonar images to disc.
1-3 Connectivity Piezoelectric Materials for High Frequency Sonar. UDI and Strathclyde University have spent three years developing new materials for sonar applications. In brief, the material consists of piezoelectric ceramic pillars embedded in a polymer matrix. In general, the combination of long, tall ceramic pillars and polymer materials enhances the electromechanical conversion efficiency and reduces the acoustic impedance to provide a better match to water. The results have enabled phased arrays to be manufactured at a fraction of their price, and for special sonar transducers to be supplied at little additional cost to clients.
Specifications of Sonavision 4000 at 500 kHz
Cavitation Cleaning Sonar. UDI built a technical demonstrator sonar consisting of a 400 mm diameter multi-ring 270-element phased array, and racks of 45 power amplifiers. The system was designed to produce a focused beam capable of cavitating a small volume of water. The cavitation effect can be used to clean rust off metals. Investigations are underway into its capabilities against marine growth.
Mirror Sonar. The company participated in the design and manufacture of the arrays and subsea electronics for a low cost mirror sonar. High frequency multi-element sonar receive and transmit arrays were designed and built into a focused acoustic mirror housing. Electronics from UDI's modular sonar designs were incorporated to provide a 24-channel sonar system.
Modular Arrays. UDI has developed a modular construction technique for a sonar phased array. Using this technique, 8 array modules of 16 elements each were mounted onto a frame, producing a 128 element array. Electronic pods containing power amplifiers and preamplifiers were also delivered. Electronics costs were kept to a minimum by using UDI standard sonar building blocks that use surface mount devices.
In conjunction with its product development, Marconi Underwater Systems has developed acoustic systems. During the visit of the WTEC team, a few of those applications were discussed briefly, as summarized below.
Communication Between Divers and Between Diver and Surface. A sealed divers electronic module (DEM) has been designed for use down to 100 m. Divers using gloves can carry out simple battery changes. Communication is achieved using high frequency acoustic waves transmitted through water between acoustic transducers attached to the DEMs. Each DEM uses a single sideband, a suppressed carrier, transmitters, and receivers.
A two-way simplex communication is available; each transmission is preceded by a short tone-burst. The operation of the press-to-talk (PTT) switch causes the changeover from receive to transmit. To enable diver-to-surface communication, an adaptive headset is used for the surface operator, while the diver uses bone conduction earphones and microphones.
A minimum effective distance of 1 km can be achieved when the DEM is selected at long range. A facility exists to reduce the effective range to short range (less than 100 m), depending on prevailing propagation conditions for use in complex missions. Any number of divers can be involved with the controlling surface station.
A Hull Mounted High Definition Scanning Sonar for Surveying Inshore Coastal Waters. The transmitting and receiving arrays assembled within the sonar head are mounted beneath the vessel. The scanned sector can be depressed to any angle from the horizontal and can be rotated to any position in azimuth, in either the vertical or horizontal mode.
The sonar head is mounted on a dynamic, stable platform that relates the beam to a fixed spatial reference independent of roll, pitch, and yaw by the vessel. The 60° insonified sector is scanned electronically by a very narrow beam to generate a high definition video image. Each echoed pulse represents angle and range data for processing by the computer. The received echoes are digitized and subjected to modern image processing techniques. These enhance the composite video and eliminate flicker. Performance has been demonstrated up to speeds of 10 kt and sea state 4.
The Mark II Hydrosearch outputs standard CCIR TV format. This permits the use of a wide range of devices, such as TV monitors, line scan recorders, video recorders, and output printers.
Bathyscan Swath Echo Sounding System. Bathyscan is a 100/300 kHz swath echo sounder based on the principle of acoustic interferometry. In the 100 kHz mode the system will operate in continental shelf water depths and can map a swath up to 500 m wide, while at 300 kHz it offers high resolution surveys in rivers, harbors, and estuaries.
Advanced Models of Sound Propagation in the Ocean. Marconi Underwater Systems is engaged in research on the propagation of sound in the oceans in order to further develop the company's knowledge of the complex underwater environment. Computer models of sound propagation play an important part in this research and allow the user to predict the distribution of sound intensity given prior knowledge of the physical properties of the ocean, such as its sound speed profile.
IFREMER, a French government agency with scientific, industrial, and commercial roles, directs, funds, and promotes ocean research and development. The agency often develops system concepts, then works with industry to build the system and evaluate its operation. The Toulon facility is focused on the operation of many of the developed systems. The Brest facility, however, has established an acoustics development laboratory. The following applications were mentioned, although few details were gathered during this visit: (1) acoustic data transmission; (2) acoustic determination of seabed characteristics; (3) development of very low frequency transducers; and (4) array processing (acoustic tomography).
Further information is readily available by contacting the Brest laboratory.