InterResources
InterResources Inc. has redesigned the Polatrak Deep-C-Meter to allow more flexibility of operation. The equipment now has a separate dual readout in a pressure housing that can be mounted anywhere within camera sight on the vehicle. The probe, a standard Polatrak ROV II tip contact probe, is connected back with a flying lead. A new compliant tee-handle mount makes it easy for the manipulator to handle.

Thales Geo-Solutions successfully proved the instrument on a Sea-Lion ROV, using it to perform an in-service inspection on a SPAR structure for Kerr McGee. The 10,000-foot (3,000m) depth rating and simple interfacing make it ideal for subsea structures where only a few CP readings are required. The two or three hours saved in interfacing time more than pay for the unit on its first job.

The probe unit can be used as a stand-alone, wired through the umbilical as required, and can then be used as a proximity probe for platform inspections. Owners of the original Deep-C-Meter can have their equipment upgraded at a nominal cost. InterResources and its sister company, Deepwater Corrosion Services, have developed a new low-cost survey system called the Polatrak CP Snake. The equipment is a snake-like apparatus that is towed on the seabed to make lateral passes over the pipeline under survey. Inside the snake are a depth sensor and a gradiometer that tell the operator when the equipment crosses the pipeline, then data are read from an array of reference electrodes in much the same way that conventional ROV surveys work.

The survey does require periodic remote field calibration, normally achieved after the survey using a separate diver or ROV spread. The system allows the potential of the pipeline to be plotted at every crossing point, more than enough information to verify the condition of the pipeline.

The CP Snake combines the low cost of trailing wire surveys with the improved accuracy of multiple electrode surveys, and has the advantage of being able to operate from a small survey vessel. The Snake was used successfully in the Java Sea and Cook Inlet in 2001, and will be working in the Gulf of Mexico in 2002. It is available for sale or lease. Visit www.stoprust.com or email jbritton@stoprust.com.

Oceanic Imaging Consultants
Dr. Thomas B. Reed IV first got his feet wet while working with seafloor mapping data using the SeaMARC II sidescan sonar and swath bathymetry system at the University of Hawaii in the early 1980s. In 1993, as a spin-off of research done at the university, Oceanic Imaging Consultants, Inc. (OIC)was founded to answer the growing need for commercially available seafloor mapping software, services, and systems.

OIC got its start by developing a commercial software package to process such data originally for University of Hawaii users. However, commercial, military, and government users became increasingly interested, looking to get away from manual charting to a faster, more automated way of making maps of waterways, harbors, and routes for pipelines and cables.

In 1994, OIC began work on a system to both acquire and process sonar data in real time, largely alleviating the need for extensive and time-consuming processing of data after the survey is completed. This system, known as GeoDAS (Geophysical Data Acquisition Software), has become OIC's flagship product. Along with the OICToolkit post-processing package, it provides the only complete, commercially available software package for all phases of sonar data acquisition and processing. GeoDAS offers a wide range of sensor support, including side scan, multibeam, interferometric sonars, the Raytheon laser line scan, and electronic still cameras. It can acquire, log, and process sonar data, along with all associated navigation, attitude, and meta-data, providing final-safe logging while still offering real-time processing and data interactivity second to none. This unique processing capability adds to the immediacy of seeing your survey progress in real time, assuring improved survey quality and reduced cost due to reducing unnecessary overlap.

GeoDAS Version 4, their latest release, represents a major upgrade in data accuracy. The move to "double point" precision allows centimeter resolution for all logged, playback, and mosaicked outputs. GeoDAS supports datum conversion and projection, not just UTM.

Other significant improvements and features include a graphically rich interface, targeting, the client-server mode, datum conversion module including state plane coordinates, tidal and draft correction, and a console configurable data format input and output listing. Ultimately, GeoDAS allows the user to "see" what is on the ocean bottom, and where it is in the world.

In 1998, Oceanic Imaging Consultants, Inc. was awarded a contract by Hawaii's Center for Excellence in Research of Ocean Sciences (CEROS) for the development of a real-time terrain visualization, 3-D virtual reality product. The goal was to allow an ROV operator to successfully maneuver in zero visibility conditions.

The result, ROVer's Eye, is designed to aid in the navigation of the seabed terrain and to avoid hazards unseen by normal visual means. ROVer integrates a high speed 3-D rendering package with GeoDAS's real-time processing and target analysis package to provide an interactive immersive experience. Underwater vehicle operators can work not only with existing models, but see new data from on-board sensors evolve into the current model in real time. ROVer accommodates simultaneous inputs from side scan, bathymetry, and navigation systems, while accessing a database of existing data, targets and as-built structure models. The combination of synoptic swath data with detail-rich target imagery in a fully geo-coded environment provides a new level of data interpretation experience.

OIC is a leader in the development of seafloor-imaging software for underwater mapping applications for the world's military, commercial, and academic markets. The company provides consulting and data processing services including the scientific analysis and interpretation of sonar data. OIC also provides complete turnkey systems, including software bundled with a workstation and/or sonar of the client's choice. For more, visit us at www.oceanicimaging.com or email info@oicinc.com.

Coda's Version 3 for Linux
Coda Technologies has released the latest version of their Codasoft geophysical software. Developed for the Linux operating system, version 3 of Coda's data acquisition and post-processing software suite is a major step forward for the hydrographic survey industry.

Coda's software was previously only available as part of an integrated Unix-based hardware and software system. This Linux release will, for the first time, allow Coda to supply a software-only solution to any customer for acquiring and processing sonar and shallow seismic data. Coda systems can read all common sonar data formats, allowing customers to acquire side scan and sub-bottom data on a variety of manufacturers' systems, but post-process using Codasoft play, geoKit, and mosaic modules. Several customers around the world have already adopted this approach.

While retaining reliability, functionality, and true integration capabilities, version 3 also includes a number of new features developed in response to customer feedback. These new features include improved file management, recording to networked devices, additional data recording and output formats, support of new printers, compatibility with an even wider range of sonars, and a host of improvements to data processing and interpretation. The version 3 functionality builds on the notable additions in version 2, which included improvements to recording, storage media, data transfer routines, data processing, and navigation.

Version 3 will still be available on Coda's traditional Unix platform, with the Codasoft play module and the analysis and reporting modules, geoKit, mosaic and pipeInspect, available immediately for the Linux platform.

Coda's first sale of the new version 3 went to the Geological Survey of Ireland (GSI). The sale consisted of an office playback system with Cosasoft play and Codasoft geoKit software, allowing playback and interpretation of GSI's large collection of data.

The Geological Survey of Ireland is the National Earth Science Agency. Founded in 1845, it is responsible for providing geological advice and information, and acquiring and interpreting data for this purpose. Long-term surveying programs guide the gathering of data, with reports and information produced for direct use by a wide range of external customers.

"The Linux release of our software has been a catalyst in the upsurge in Coda's sales over the past few months," explains Jason Reid, Commercial Director. "There has been even keener interest in our Microsoft Windows-compatible version, which is on schedule for release this year."

DWS International
DWS International Inc. is based in Corpus Christi, Texas. Their Marine Integrated Survey Systems (MISS) are utilized worldwide in both commercial and government applications. These systems evolved from reconditioning used equipment and integrating these subsystems with other state-of-the-art systems to provide a highly competitive, economic solution to our clients needs.

DWS was awarded a multi-year contract with the US Navy to provide the MISS-100 Marine Integrated Seismic Systems on the Pathfinder class vessels. The MISS-100 is designed as a portable roll-on/roll-off system that can be brought on board the vessel as required for various seismic surveys. Together, the air guns and compressor subsystem provide a pneumatic seismic source which is received by the towed hydrophone array and processed by the data acquisition and processing subsystem. The marine enclosure houses the compressor subsystem, which provides high-pressure air to the air guns.

The MISS systems are flexible in operating scenarios allowing for survey speeds over 8 knots with a wide range of water depths and can provide simultaneous towing of multiple sensors on a single tow cable. This unique design has provided for economical system upgrades to software, firmware, and entire subsystems, expanding the system's versatility and lowering the capital asset cost.

The latest MISS-100 system for T-AGS 65 utilizes the latest technology advances in seismic acquisition and processing techniques. These advancements improved the Navy's ability to acquire quality data under demanding operational scenarios, while reducing the operational cost and environmental risk.

Other versions of the MISS series include 2D and 3D digital marine seismic systems, harbor monitors, marine magnetics and gradiometers, integrated navigation systems, dynamically focused multi-beam side scan sonar, and bathymetric multi-beam survey systems. Each system is custom designed to provide a total solution within the client's economic parameters.

GeoAcoustics
GeoAcoustics is a manufacturer of underwater acoustic survey equipment based in Great Yarmouth, Norfolk, UK. They sell to a client base that spans over 50 countries. Sales offices in Singapore and Boston are ably assisted by a worldwide network of dedicated and knowledgeable agents.

The GeoAcoustics equipment range has always included side scans, sub-bottom profilers, and topside processing equipment, but recent developments have opened up exciting new markets. GeoSwath, which has created a storm of activity within the industry since its introduction a few short months ago and GeoPrinter, which has provided the survey community with a low cost, high reliability thermal printer, are recent additions to the company's catalog.

The complete product range uses sophisticated technology, but is based upon the simple philosophy of ease of operation and reliability. This has resulted in increasing sales every year since the company was formed in 1991. Customers can buy equipment safe in the knowledge that later purchases will be fully compatible with existing equipment, and are appreciative of GeoAcoustics' modular approach to system integration.

The GeoPulse range of profilers, including the Pinger and Boomer, along with the Dual Frequency Sidescan, are recognized as industry standards. Newer additions to the range are also quickly gaining the respectability.

The Deep Tow 2000 system was developed as a result of demand for survey capability in deep waters. The system combines the latest developments in chirp sub-bottom profiling together with high-resolution side scan and optional magnetometer. It is proving to be a big hit with deepwater operators. The GeoSwath shallow water long-range swath bathymetry system is capable of providing seabed contour data at ranges of up to 12 times water depth. This system has the added advantage of producing real-time side scan data.

The GeoPro topside sonar processors range from the entry level LC to the sophisticated GeoPro 4 four-channel version. These systems complement existing side scan and sub-bottom profiling systems and add an array of enhancement, display, and storage features to any survey task.

GeoAcoustics' GeoPrinter is an affordable thermal graphic recorder. This system is already clocking hundreds of survey hours with a host of clients. A fast CSI or parallel interface makes this the ideal tool for real-time acquisition or fast playback.

Andrews Survey
Since the removal of Selective Availability (SA) by the US Department of Defense on March 1, 2000, stand-alone (without differential corrections) GPS accuracy has improved considerably. Andrews Survey has found that clients are indicating that a practical accuracy of +/-5m is quite acceptable for marine operations reports. This is particularly so for anchor tug positioning during rig moves, positioning marker buoys, and other practical uses that do not require sub-meter accuracy. To observe the difference made by the removal of SA from the

GPS signals, Andrews Survey has established a GPS monitoring station at their new Ann Street base in central Aberdeen. The company has carried out a series of tests to monitor and log stand-alone GPS against a known reference point. A total of 188,000 observations were logged over a 23-day period. The result was that 99.8 percent of the readings were accurate to less than 5m.

In addition to these tests, other technical advances being made with worldwide GPS enhancement techniques from C-Nav and EGNOS / WAAS systems, are also well advanced. Andrews Survey is currently evaluating the performance of several systems for possible future utilization by the company.

Aquatec Subsea
Aquatec Subsea's new Aqualogger 510T is a self-contained temperature logger capable of storing 65,000 temperature readings to better than 0.1 degree C accuracy. The 510T model is an evolution of the company's 500TX, of which more than 200 were manufactured in the last year.

The new version is housed in a rugged plastic pressure case that may be opened for battery replacement ­ typically after several years of use. Programming and data download are achieved through an electromagnetic link, so the case remains sealed for normal use.

Nearly 100 of the new loggers will be deployed this year in the waters off Los Angeles as part of a long-term study of the temperature distribution along that part of the California coastline.

Aquatec Subsea's Aquascat Acoustic Backscatter System represents a significant step forward in acoustic analysis of sediment dynamics near the seabed. Its primary use is measuring vertical profiles of the load and particle size distribution of suspended material in the water column.

However, it is also finding applications in high-resolution altimetry and observation of seabed morphology. The Aquascat accommodates up to four high frequency acoustic transducers. Scattered acoustic energy from suspended particles in the water column and from the seabed is acquired and processed digitally at full bandwidth before compression. This allows the system to operate with enhanced spatial resolution as fine as 2.5mm.

The Aquascat is available in a laboratory version, or in a fully-housed subsea pressure case. The instrument incorporates a rugged hard disk to store the large quantity of data that is generated over a typical three- or four-month deployment. The onboard DSP also processes and compresses data to maximize use of the storage space. A USB interface ensures that the data can quickly be retrieved to the user's PC, where a suite of data display software can be used to inspect downloaded files. With recent sales to universities and research institutions in Britain, Europe, and the USA, the capabilities of the Aquascat are expanding rapidly, as improvements in processing and versatility are developed to suit client needs.

EPC Labs
EPC Labs, Inc., of Danvers, Massachusetts, has introduced two new thermal recording systems that offer unique ways of acquiring and storing side scan sonar and sub-bottom data. The MP-1086 and 1086NT build upon the company's popular 1086 Series. An application-programming interface (API) offers an easy way for users to interface the printer.

The MP-1086 is a multi-purpose recording system that serves as a continuous gray scale printer, analog tow fish interface, mass storage device, and signal processor. The analog tow fish interface allows users to connect commonly used side scan sonar directly to the MP-1086, with no need for any external components. Photographic imagery is produced using EPC's direct thermal printing expertise. Data can easily be logged for post-processing directly to a 2.2 GB removable storage, or exported over a network interface in XTF format.

The 1086NT builds upon the industry standard GSP-1086-2 500 Series by incorporating the Network Interface and adding several other new features like a 32-bit architecture, 256 shades of gray, speed correction, and control panel enhancement. The network interface in both the MP-1086 and 1086NT provides a simple LAN-based RJ45 connection between a host NT workstation and one or more recorders.

In order to greatly reduce the development cycle, EPC offers a high-level API which can be linked to user-level code. The tiny library provides an extremely intuitive and self-documented interface to the recorder. Advanced spooling algorithms, multi-threaded operations, and inter-process communication techniques are all employed with the DLL so that the host developer is relieved of such time-consuming coding. The end result is a rich, high-level function set that allows integration of solid driver code in a matter of days instead of weeks.

Topside manufacturers will find the simplicity of the physical connection very attractive. Operators can use a normal LAN connection to a 100-speed hub or opt for a simple crossover cable connection between a portable and a recorder. Either way, the API provides a simple function for querying the network and returning a list of available recorders. Furthermore, the transmission characteristics and raw speed of the Ethernet interface far surpass standard parallel methods commonly used today.

The new software also addresses the age-old problem of pacing a continuous printer during real-time data acquisition. The host software can register a user-defined callback with the library to notify it when particular events have occurred. Using this advanced method, the developer can write highly efficient data transmission routines that circumvent the not-so-real-time tendencies of the NT operating systems. EPC is planning on implementing the same high-level interface for its high-speed wide-bed printer, the Model 9206.

Tritech International
Following years as a leader in mechanical scanning profilers, Tritech International Limited has taken mechanical profiling to a new level. Their new Super SeaKing Dual Frequency Profiler (DFP) offers improvements that are only available when using composite transducer technology.

The new 600kHz/1.2Mhz transducer was designed with increased side lobe suppression as well as narrower beamwidth characteristic, offering users the opportunity to carry out profile work more accurately than was previously achievable when using a mechanical scanning profiler. In addition, the new circuitry in the Super SeaKing DFP, in conjunction with this composite transducer technology, allows increased range performance.

When redesigning the Super SeaKing DFP, Tritech elected to fit a hard boot over the transducer. This offers increased protection to the transducer without reducing the signal strength. This new mechanical profiler is likely to replace the current SeaKing DFP as a favorite among operators and is available for sale or rental.

RS Aqua
RS Aqua is the distributor for the Capsum GmbH Methane Sensor, known as METS. This sensor was developed at the German GKSS laboratories and units have already been supplied to customers in the USA, China, UK, Germany and Brazil. METS has applications in the fields of deep ocean research, methane hydrate exploration, leakage detection, and waste monitoring. The sensor, which can be supplied in versions rated to 11,480 feet (3,500m), is ideally suited for mounting aboard ROVs, AUVs, towed vehicles, and seabed landers.

RS Aqua is the European distributor for Novatech Designs, a manufacturer of xenon flash and VHF radio location beacons. These devices are used to identify and locate all sorts of underwater packages including AUVs, ROVs, seabed landers, and general instrumentation bundles. They can sit dormant for periods up to one year and then activate reliably upon surfacing. NERC's AutoSub team at the Southampton Oceanography Centre experimented with a cheaper alternative to the Novatech product and suffered the consequences. When a recent requirement arose to restock supplies, they headed straight to RS Aqua Ltd with a Novatech order for the Autosub.

RS Aqua also handles Neptune Sciences' Sentry range of wave buoys. There are two versions covering directional and non-directional measurements. The Sentry range was developed for the US Navy to provide input to environmental data predictions during operational landings. The standard Wave Sentry buoy measures, stores, and transmits (UHF radio) full directional wave data. Its hand-held stable mate, Mini Wave Sentry, provides amplitude and period data along with current drift determined via an on-board GPS sensor.

Since their introduction to the UK market, Sentry buoys have been used by the Royal Navy during the Oman training program, by the RNLI in support of lifeboat trials, and by Ocean Power Delivery as part of their wave energy project.

RS Aqua reports that an increasing number of Vessel Traffic Management System manufacturers are now specifying Aanderaa current and meteorological equipment for integration with their port and harbor installations. Aanderaa's Doppler current profiler, coupled with the AWS 2700 met station, provides a comprehensive, modular, and robust package covering currents, waves, tides, wind, visibility and all other met parameters. The key features that make the Aanderaa equipment so attractive are high accuracy, robustness, modularity and ease of interfacing.

RS Aqua also handles Saab Rosemount's WaveRadar Rex offshore wave sensor, which has a new local display module enabling operators to monitor the output from the sensor during installation and servicing. In addition to the most common usage as an input to platform-based met-ocean monitoring systems for the offshore industry, WaveRadars have been used to monitor structural stress at offshore wind farms and in support of coastal erosion studies.

SEA's Submetrix Sonars
The SEA Group has been developing and implementing engineering solutions for marine sonars for over 12 years, and the Submetrix expertise in developing, manufacture, and operation of interferometric sonars goes back over 9 years. The Submetrix 2000 Series Sonars, manufactured by SEA in the UK, are shallow water hydrographic survey sonars with versions available for up to 650 feet (200m) water depth.

The Submetrix Sonars use interferometric (phase measuring) multibeam technology with simultaneous side scan imaging. The sonars are designed for deployment on inshore vessels, as well as being suitable for larger survey platforms. They can also be adapted for unmanned vessels such as AUVs. For example, QinetiQ in the UK has developed the MIMIR unmanned surface vessel, which in late 2001 was fitted with a 2000 Series derivative for its initial program of environmental mapping work off the UK South coast.

The basic Submetrix 2000 Series system consists of a PC-based data acquisition and processing unit with real-time and post-processing software, two transducers, and associated cabling. A motion reference unit, gyrocompass, and DGPS positioning system can be interfaced to the basic system to provide a complete data acquisition package. Survey data is stored on the internal hard drive and DVDR is used as a removable storage medium.

The Submetrix sonars are compact and robust systems that can be easily transported and quickly mobilized for near-shore work and surveys of dams and rivers. The size of the transducer head makes it possible for two men to deploy the sonar on most vessels in a couple of hours using the Submetrix temporary bow mount.

The 2000 Series were developed as seafloor visualization sonars capable of mapping of the seabed environment in shallow waters, particularly from small vessels of opportunity. Visualizing the sea bottom in shallow waters requires high resolution up to the edge of the swath, wide swaths even in very shallow waters, a swath width that is not affected by roll, and an ability to survey up to the shoreline in rapidly shoaling waters (e.g. river banks).

These are all features of the Submetrix sonars, and the shallow grazing angles and banks that occur in near-shore and river surveys are best suited to the interferometric multibeam technology.

Simultaneous co-registered side scan is an integral part of the Submetrix sonars, with the same transducer giving the side scan image and the bathymetry. This verifies full ensonification of the seafloor across the whole swath, and the side scan image gives confidence of detection of even small features on the seafloor. The amplitude imaging combined with the bathymetric depth imaging is a great aid in feature identification and in environmental mapping.

The Submetrix 2000 Series Sonars have been particularly successful in environmental and research seabed visualization roles in shallow coastal waters and inland waters.

Examples of users include:

• United States Geological Survey, Woods Hole ­ large area mapping of the shallow waters off the USA East Coast.
• The Environment Agency (UK) ­ surveys for environmental modeling off the English coasts.
• St Andrews University ­ Monitoring work on Scottish Reservoirs, and benthic habitat work off the Scottish East coast.
• National University of Ireland ­ Marine Archaeological work in rivers, lakes and offshore in Norway and Ireland.
• Korean Ocean Research and Development Institute ­ sediment transport research in the Yellow Sea.
• North Carolina State University ­ Sediment transport monitoring off the North Carolina coast.

Oceano and Thales Sign License Agreement
Oceano Technologies and Thales Underwater Systems (formerly Thomson Marconi Sonar) have signed an exclusive licence agreement entitling Oceano Technologies (formerly MORS Environment) to manufacture and sell the Posidonia USBL positioning system.

Posidonia was developed jointly between Thales Underwater Systems' civil department and Oceano Technologies, with the support of IFREMER and the Regional Group for Acoustics Research G2RA. Posidonia will be manufactured at Oceano Technologies' premises in Brest.

The system was originally designed to position the IFREMER ROV Victor 6000 down to 19,680 feet (6,000m) water depths. Posidonia is the only ultra-short baseline positioning system to offer accuracies of 0.3 percent rms of slant range down to 19,680 (6,000m), and operational slant ranges up to 26,240 feet (8,000m). It is also designed to operate in noisy environments and minimize the problems of reverberation and multiple acoustic paths.

Ocean Data Equipment
Ocean Data Equipment Corporation (ODEC) has released their StrataBox Marine Geophysical Instrument. For a limited time, ODEC is offering the StrataBox for $11,992.00, a 20 percent discount off the normal price of $14,990.00. This discount is valid only on deliveries made by March 31, 2002.

The system includes a transducer, sensor unit, and PC Acquisition Software. The StrataBox is a portable high-resolution marine sediment imaging instrument capable of delivering 6cm of marine sediment strata resolution, with bottom penetration of up to 40m. It is designed exclusively for inshore and coastal geophysical marine surveys in up to 492 feet (150m) of water depth. The sensor is compact, interfaces to a standard laptop PC, and comes complete with a lightweight and efficient acoustic transducer and PC software. Ease of use, portability, and cost efficiency make this device a good choice for shallow water marine geophysical applications. ODEC is based in Rhode Island.

Leica Geosystems
Leica Geosystems is now offering CheckMate automatic integrity monitoring with their System 500 series GPS surveying receivers. CheckMate provides automatic, continuous real-time kinematic (RTK) integrity monitoring for 99.9 percent reliability in centimeter-level accuracy GPS surveying.

With CheckMate, Leica's System 500 continually calculates two separate sets of RTK ambiguities. By comparing the two, the system ensures that the correct ambiguity solutions are always being applied. Whenever it detects a disagreement between the two ambiguity sets, it sounds an audible alarm, displays a visual message, and automatically reverts to precise differential code positioning while it restarts the ambiguity search routine from the beginning - all in less than ten seconds.

Leica is offering a special promotion to introduce System 500 with CheckMate to the North American market, including 2.99 percent financing with no payments and no interest for 12 months, a GPS receiver trade-in credit, and a $2,500 discount on the purchase of a Leica TCRA1102 robotic total station when buying a System 500.

Since its initial introduction in 1999, Leica's System 500 has provided cost-effective single- and dual-frequency real-time solutions for a wide range of applications.

C-Max
C-Max introduced the CM800 system in 1994 and more than 100 of these systems are in use around the world today. The CM800's features included an industrial PC for the top-end display and recording, 3.5-inch magneto-optical (MO) disks as the recording, a custom splash-proof keypad for control and annotation, and the option of a fiber optic tow cable for intermediate depths.

At the time, these features were unique in a side scan sonar. Since that time, the PC has become ubiquitous for sonar processing and MO disks have progressed from 128MB capacity to 1.3GB. However, the CM800's keypad and the slim fiber optic tow cable option remain unique.

The challenge for C-Max was to improve on the CM800 and at the same time address the growing market for systems with deepwater capability. The key to achieving these aims has been the redesign of the tow cable telemetry, the subsystem that brings the sonar data up the tow cable and sends commands down to the towfish.

In the CM800, the telemetry system was restricted to fiber optic cables up to 3km long or electrical tow cables up to 500m. A disadvantage of the fiber optic tow cables, apart from their cost, was the fact that they did not carry power and, therefore, batteries were needed in the towfish.