DUMMY'S GUIDE TO MARINE TECHNOLOGY - AUVAC

Glossary of Marine Technology TermsThis glossary was originally developed by MTS member Brock Rosenthal as the“Dummy's Guide to Marine Technology.” We will continue to build on Brock's work byadding terms when appropriate. If there is a term that you would like to see added to theGlossary, please e-mail us at mtsprograms@erols.com.AAcoustic Current MetersAcoustic Doppler Current MetersAids to NavigationArc LightsAUVs (Autonomous Underwater Vehicles)BBatteriesBottom SamplersBulkhead ConnectorsBuoysCCablesCable GlandsCamerasChemical SensorsCompassesConductivityConductorsConnectorsCorrosionCTDs (Conductivity Temperature Depth)Current MetersDData Collection PlatformsData LoggersData MultiplexingData TelemetryDrifting BuoysDynamic PositioningEEcho SoundersElectromechanical Current MetersFFiber Optic ConnectorsFiber Optic GyrocompassesFloatsFlotationFluorometersFlux Gate CompassGGeophysical InstrumentsGPS (Global Positioning System)HHigh-Frequency RadarHydrophonesIIncandescent LightsInertial Navigation SystemsInsulationJJacketLLaunch and Recovery SystemsLEDsLightingLinear Cable EnginesMMagnetic CompasMagnetometersMarker BuoysMeterological SensorsMet SensorsMoored Buoys

Glossary of Marine Technology Terms 2Motion SensorsNNephelometersOOptical SensorsOverhauser MagnetometersPPan & TiltsPhysical Oceanographic SensorsPressure-Balanced Oil-Filled ConnectorsPressure HousingsProton MagnetometersRReleasesRemote SensingResistance Temperature DetectorsRing Laser GyrosRopes and Tension MembersROVs (Remotely Operated Vehicles)SScourSealsSeawater BatteriesSediment TrapsSelf-deployed buoysShip MooringsSlip RingsSonarSpectrofluorometersSpectrophotomersSpinning Mass GyrocompassStrength memberSubmersiblesSubsurface buoysSubsurface Drifting BuoysSurface Supplied Air DivingTTether Management SystemsThermistorsTide GaugesTraction WinchesTransmissometersTowed VehiclesUUnderwater Acoustic ImagingUnderwater Position & TrackingWWater SamplersWave GaugesWinchesReferences

Glossary of Marine Technology Terms 3AAUVs, or Autonomous Underwater Vehicles,are underwater robotic vehicles that do not havea tether to the surface. They are preprogrammedto operate over a particular courseor to respond to sensor data or perhaps acousticcommands. Applications include surveying,scientific data collection and mine-hunting.BBatteries: All types of batteries used topside(out of water) can also be used undersea. Thereare a few factors unique to using batteriesunderwater. One is that some batteries canproduce gases that are potentially explosive. Inthe open air this is usually not a problembecause the small volume of off-gases is quicklydiluted. However, in sealed pressure housing,gas build-up can cause problems ranging fromwater leaks to explosive failure. Pressure reliefvalves can safely vent gas to eliminate theseproblems.Some batteries and other subsea electronics usepressure-balanced, oil-filled packaging. In thismethod, all air spaces and voids in a housing arefilled with oil or hydraulic fluid. A flexiblemembrane on the housing transmits ambientwater pressure through the housing. Because thepressure inside the housing is the same as theoutside water pressure, it is said to be equalized.Since there is no pressure gradient, a heavypressure-proof housing is not required.Seawater batteries utilize seawater as anelectrolyte. Most use electrodes of magnesiumfor anodes, and oxygen dissolved in the seawater as oxidant. Advantages of seawaterbatteries are that they have a very long shelf lifewhile dry, can be used to very deep depths, havehigh energy densities, and have long dutycycles. Disadvantages are that the cell voltagesare low, necessitating DC/DC converters andthat the output power can be influenced byfactors such as the water circulation, quantity ofdissolved oxygen, temperature and salinity.Bottom Samplers are sediment samplingdevices. There are many different types ofbottom samplers. A box corer can be droppedinto the mud to bring back a block of nearsurfacesediment. A piston corer can return acylinder of sediment up to 100 feet (33 meters)long that may encompass several million yearsof sedimentary history. For researchersespecially interested in the seawater-seafloorinterface, a gravity corer can return cores up to20 feet (6 meters) long with little core-topdisturbance. Vibracorers use a motor thatproduces a high-frequency oscillatory vibrationto help propel a long core barrel intounconsolidated sediments.Buoys: There are two main classes of buoys:drifting and moored.As the name implies, drifting buoys are notanchored to the seafloor. They are typically usedto study currents and circulation patterns. Adrogue (a cylindrical or funnel-shaped device) issometimes added to have the surface buoyfollow a subsurface current.Subsurface drifting buoys, or floats, usuallyhave variable buoyancy engines to descend to apredetermined depth where they follow thiscurrent and possibly collect environmental data.The buoyancy engine is programmed tooccasionally bring the float to the surface whereit can telemeter its data back to shore. (Atelemeter is an electrical apparatus formeasuring a quantity—such as pressure, speed,or temperature—and transmitting the resultespecially by radio to a distant station.)Trajectories of individual floats show how the

Glossary of Marine Technology Terms 4water moves horizontally, and trajectories ofgroups of floats show how the water is mixed byeddies. This information is important forunderstanding how water tracers and pollutantsare transported by the ocean. The AdvancedResearch and Global Observation Satellite(ARGOS) program is a large multinationaleffort to put thousands of floats in the world’soceans.Moored buoys are used for many purposes.Some of the most common uses are: Aids to Navigation (ATON)—used tomark hazards to mariners, harborentrances and other navigable channels. Data Collection Platforms—Mooredbuoys make excellent platforms forcollecting data at one location anywherein the ocean on time scales ranging fromweeks to years. Sensors and instrumentscan be mounted anywhere from theseafloor on up to masts installed on thetop of the mooring float Marker Buoys—used to relocateobjects on the seafloor Ship Moorings—typically used to moorlarge commercial or military ships whendock space is not available or near-shorewaters are too shallow. Also used foroffshore loading and unloading of tankerships.Other special types of buoys are:Subsurface buoys: used when surfacemeasurements are not required. They alsoeliminate vandalism, which can be a bigproblem with surface buoys.Self-deployed buoys have the anchor, line andsensors packaged in a compact assembly. Airdeployed buoys are dropped from a plane.Moored buoys come in a wide variety of shapesand sizes. Hull forms include disk, sphere, cone,boat hull and spar. The typical moored buoyconsists of: Tower for mounting antennas, sensorsand solar panels Float, usually has a well containingbatteries Bridle for attaching the mooring line Mooring line to connect the bridle to theanchor AnchorMoored buoys are important to the marinetechnologist because they make excellentplatforms for collecting data anywhere in theocean on time scales ranging from weeks toyears. Sensors and instruments can be mountedanywhere from the seafloor on up to mastsinstalled on the top of the mooring float.Anchors are connected to holding lines withacoustic couplings that are released to recall theinstruments. Flotation holds the instruments andtheir tether line upright in the water column andbrings them to the surface on release.CCables can be electrical, fiber optic, or acombination of the two. Underwater electricalcables date back to the advent of the telegraphthe mid 1840s. Hemp, tar and jute were usedaround conductors. The advent of plastics andother synthetic materials brought about a varietyof new cable designs. The components of atypical underwater electrical cable are: Conductors—the metallic component ofcables through which electrical power orelectrical signals are transmitted.

Glossary of Marine Technology Terms 5 Insulation—material applied around aconductor to provide electrical isolation. Strength member—bears tensile load,ensuring that it does not transfer to theconductors. Internal strength membersare made from various polymers.External strength members, referred toas armoring, are usually made from steelwire. Jacket—outer polymer layer protectingthe parts inside.There are two basic types of fiber used:SingleMode (SM) and MultiMode (MM).SingleMode fiber is generally used where thedistances to be covered are greater. There aregenerally five elements that make up theconstruction of a fiber-optic strand: the opticcore, optic cladding, a buffer material, a strengthmaterial and the outer jacket. Underwater opticcables have a heavy outer jacket and/orarmoring. Many designs protect the fibers byrunning through a flexible steel tube that isfilled with a gel compound that cushions thefiber and impedes or blocks water penetration.The optic core is the light-carrying element atthe center of the optical fiber. It is commonlymade from a combination of silica andgermania. Surrounding the core is the opticcladding made of pure silica . It is thiscombination that makes the principle of totalinternal reflection possible. The difference inmaterials used in the making of the core and thecladding creates an extremely reflective surfaceat the point in which they interface. Light pulsesentering the fiber core reflect off thecore/cladding interface and thus remain withinthe core as they move down the line.Cameras are used underwater for all sorts ofinspections and documentation. Most types ofcameras that can be found topside can be housedand used underwater. They are used by divers,on subsea vehicles and as stand-alone devices.Film cameras are rarely used any more becauseof the limited amount of images that can bestored before the camera must be brought to thesurface so the film can be changed. Thus, forstill images, digital cameras are usuallypreferred. Video camera types include color,black and white, and low light. For low light,imaged-intensified CCD cameras are used, asare tube-type cameras known as SITs (siliconeintensified targets). Dome port optics are used insome cameras to correct the distortions causedby looking through a flat window underwater.Features to consider when selecting anunderwater camera include, fixed vs. zoom lens,field of view, depth capability, resolution andsensitivity.Chemical Sensors are commonly used todetect hydrocarbons, nutrients (nitrate, nitrite,ammonia, urea, phosphate, silicate, and iron) aswell as pH and dissolved oxygen in and onwater. A variety of sensing techniques areemployed including optical methods.Compasses: Magnetic compasses consist of asmall, lightweight magnet balanced on a nearlyfrictionless pivot point. Magnetic compasseshave several problems when used on movingplatforms like ships. They must be level, theycorrect rather slowly when the platform turns,they are influenced by ferrous metals and theyindicates magnetic north rather than true north .For these reasons, most ships and airplanes usegyroscopic compasses.A spinning mass gyrocompass has a spinningbody with three axes of angular freedom

Glossary of Marine Technology Terms 6constituting a gyroscope. They can take up toseveral hours to spin up and stabilize.A flux gate compass consists of a field sensor,usually an inductor, mounted to a gimbaledplatform that is intended to sense the horizontalcomponent of the earth’s magnetic field.Fiber Optic Gyrocompasses (FOGs) and RingLaser Gyros (RLGs) work by shining lightthrough two coils of optical fiber. The inputlight beam is split into two beams that travel thesame path but in opposite directions: oneclockwise and the other counter-clockwise. Thebeams are recombined and sent to the outputdetector. In the absence of rotation, the pathlengths will be the same and the output will bethe total constructive interferences of the twobeams. If the apparatus rotates, there will be adifference in the path lengths traveled by thetwo beams, resulting in a net phase differenceand destructive interference. The net signal willvary in amplitude, depending on the phase shift;therefore, the resulting amplitude is ameasurement of the phase shift, andconsequently, the rotation rate. Because thereare no moving parts, there is no friction, andhence no drift.Flux gates are small, light weight and relativelyinexpensive. Spinning mass gyros can be moreaccurate but are large and heavy by comparison.FOGS are intermediate in size and offer thehighest accuracy, along with the highest pricetag. For more information, seehttp://www.autonav.com/html/anav4009.htmConnectors are used to join a cable to a devicesuch as an underwater vehicle, instrument orbattery; or to join two cables together. They canbe used for electrical conductors or opticalfibers, or both. There are many types ofunderwater connectors, some can be matedwhen wet, others must be dry. Some of thecommon types are: Cable Glands—actually not a connectorat all but a rubber grommet in a housingthat seals around a cable. They areinexpensive and easy to install but arenot reliable for long-term immersions orin dynamic situations where the cablewill be subject to flexing. Rubber Molded—neoprene rubberconnectors molded to cables or ontometal bulkhead posts use compressionseals or o-rings seals molded in femalesockets. There are several commonstyles. Some have a vent hole forpurging water when wet mated.Advantages are inexpensive and deepdepth ratings; however, rubber candegrade with long-term exposure tosunlight and certain chemicals. It is notavailable in high-contact counts. Epoxy—glass filled epoxy constructionbulkhead connectors with rubber moldedmating cable connector. Inexpensive butnot good for applications where epoxypart is subject to shock or impact. Metal Shell—some utilize rubbermolded connectors bonded to an outermetal shell for increased robustness.Other types utilize an insert in shell.Wide variety of configurations available,including high contact counts. Glass to Metal Seal—hermetic sealingof pins to glass puck makes for a veryreliable pressure proof seal but at highercost. Pressure-Balanced Oil-Filled (PBOF)connectors, typically can be wet mated

Glossary of Marine Technology Terms 7at any depth, because they are pressureequalized.Connectors that mount to a pressure housing areknown as bulkhead connectors. They typicallyhave one or more o-rings for sealing. BCR-typebulkhead connectors thread into a tapped hole orare retained in a thru hole by a nut and washer.FCR types have a flange that attaches withmounting screws or bolts. In-line connectors areinstalled on the end of the cable. They are oftenknown as CCRs and CCPs, where R stands forreceptacle (female sockets) and P stands forplug (male pins). Dummy connectors are usedto keep contacts clean when connectors areunmated.Fiber optic connectors are available in bothdry mate and wet mate styles, as are hybridconnectors, which have electrical and opticalcontacts.Corrosion results when two dissimilar metalsare in contact with each other and are immersedin a conductive solution (i.e., seawater).Corrosion can cause structural failure ofmaterials or cause sealing surfaces to leak; thus,it is a very important engineering concern. Therate of corrosion is determined by severalfactors, including: Valence of the metals Salinity of the water Temperature Oxygen levelSeveral techniques are used to minimize oreliminate corrosion. These include: Replace one of the metals with a plasticmaterial. For machined parts, Delrin(acetyl) is a good choice. For pipes, PVCis available in many sizes. Isolate the metals from each other.Plastic washers are often used withmetallic hardware. Use sacrificial anodes. Zinc anodes areavailable in an assortment of sizes andshapes in most marine hardware stores. Passify the metal. Various processes areavailable for different metals that helpprotect it from corrosion. For aluminumit’s anodize, for titanium it’s Tiodize, forstainless steel it’s passification. Paint—coating the entire surface of anobject eliminates contact with seawaterand hence prevents corrosion. However,any scratch or pin hole in the paint willput the metal in contact with water, so itis usually advisable to have the metalpassified before painting. Most corrosion occurs as an oxidation ofa metal, and thus freely availabledissolved oxygen is required. Crevicecorrosion is an anaerobic process thatoccurs in low-oxygen-level waters or incracks and crevices where there is littleexchange of water.CTDs (conductivity temperature depth)measure how the electrical conductivity andtemperature of the water column changesrelative to depth. Conductivity and temperatureinformation is valuable, because the speed ofsound in seawater can be derived from thesevariables. This is used to correct devices thatuse sound underwater. CTD data can also beused to calculate water density. Oceanographersuse CTDs to study the physical properties ofwater, which can help them understand currents,mixing, biological processes and otherphenomena. For this reason they are one of the

Glossary of Marine Technology Terms 8most common instruments used by marinescientists.A CTD may be deployed by itself, attached to asubmersible, or as part of a larger metal watersampling array known as a rosette, or carousel.Multiple water sampling bottles are oftenattached to the rosette to collect water atdifferent depths of the cast.Current Meters are devices that measurewater velocity and direction. Measuring currentsis a fundamental practice of physicaloceanographers. By determining how oceanwaters move, scientists can determine howorganisms, nutrients and other biological andchemical constituents are transported throughoutthe ocean. There are several common types ofcurrent meters: Mechanical current meters are likeunderwater pin wheels. The rate atwhich the wheel spins is used tocalculate the current flow. A drawbackto mechanical meters is that they do notwork well in weak currents. Electromechanical current meters arebased on the principle that a voltage isproduced when a conductor (the water)moves through a magnetic field. Themagnetic field is produced by a coil andthe voltage is picked up by electrodes onthe surface of the instrument. By havingtwo orthogonal pairs of electrodes, twoaxis flow velocities are obtained from asingle probe. The sensor has no movingparts and the system is capable ofmeasuring fast changing flows over awide dynamic range. Acoustic current meters, sometimescalled sing arounds, measure how long ittakes for sound pulses to travel around aprescribed area. By comparing the phaseshift of the signals, very precisemeasurements can be taken. Acoustic Doppler Current Metersmeasure the Doppler shift of soundbouncing off reflectors suspended in thewater. They can be used to take a pointmeasurement at a specific distance fromthe instrument, or to take a series ofmeasurements known as a profile.Doppler current meters can be mountedin the hulls of ships, installed on buoysor mid-water mooring lines, or mountedon the seafloor looking up towards thesurface. High-Frequency Radar is used tomeasure surface currents. HF Radar canmap areas of tens to hundreds of squarekilometers from shore-based antennae.DData Loggers are used to acquire and storeinformation from sensors. The entire spectrumof data storage devices used topside have andcan be housed in pressure vessels. These includehard disk drives, flash memory, video tape, etc.When brought to the surface, the logged datacan be transferred to a computer or the memorycan be removed for archiving. Factors toconsider when selecting a data logger includehow many sensors will be measured, for howlong at what sampling rate, how much power isavailable, how much space is available, etc.Environmental sensors and transducers oftenmeasure things such as temperature, pressure,sound or light, as voltages or current levels.These analog signals must be converted todigital ones for use by computers. Theconversion, known as A/D conversion, is doneby electronic sampling of the analog signals.

Glossary of Marine Technology Terms 9This function is often performed by a dataacquisition board in a data logger. The boardmay have several input channels to take in datafrom more then one sensor.Data Multiplexing is the practice of sendingmultiple signals or streams of information on acarrier at the same time in the form of a single,complex signal and then recovering the separatesignals at the receiving end.In analog transmission, signals are commonlymultiplexed using frequency-divisionmultiplexing (FDM) in which the carrierbandwidth is divided into sub channels ofdifferent frequency widths, each carrying asignal at the same time in parallel.In digital transmission, signals are severalcommon multiplexing techniques. These includetime-division multiplexing (TDM) in which themultiple signals are carried over the samechannel in alternating time slots; frequency-shiftkeying (FSK) in which the frequency of thetransmitted signal is varied and phase-shiftkeying (PSK) in which the phase of atransmitted signal is varied to conveyinformation.Electrical signals can also be converted tooptical signals. A fiber optic transmitter consistsof an interface circuit, a source drive circuit andan optical source. The interface circuit acceptsthe incoming electrical signal and processes it tomake it compatible with the source drive circuit.The source drive circuit intensity modulates theoptical source by varying the current through it.The optical signal is coupled into an opticalfiber through the transmitter output interface.Multiple optical signals can be carried togetheras separate wavelengths of light in amultiplexed signal using dense wavelengthdivision multiplexing (DWDM). Very high datarates can be achieved with DWDM.Data Telemetry is the process of measuringdata at the source and transmitting itautomatically. There are many ways totelemeter data back to shore such as by cellphone, radio transmitter, microwave andsatellite. There are several satellite servicesavailable (ARGOS, Inmarsat, Irridium, GOES,Orbcomm ) that can receive data from mostanywhere on the planet. Data can be transmittedfrom a variety of platforms, including mooredbuoys, drifting floats, and even marine animals.Acoustic modems are used to telemeter datathrough the water column from a source to areceiver. They rely on coded pulses of sound.Acoustic modems are often used with seafloorsensors to telemeter data to a surface buoy orsurface ship. From there the data can be relayedto shore using one of the previously mentionedmethods of telemetry.Dynamic Positioning is a method to keep aship, platform or subsea vehicle stationary overa fixed spot on the seafloor. Such stationkeeping is desirable for many tasks includingcoring, drilling, lifting, sampling and diversupport. DP systems use thrusters in the bowand stern to maintain position. A computer isused to direct power to each thruster whennecessary based upon input from GPS, compass,motion sensors, wind sensors, current meters,acoustic navigation equipment and othersystems. More information on this subject maybe found at http://www.imcaint.com/divisions/marine/reference/intro.htmlEEcho Sounders are used to measure waterdepth by sending an acoustic pulse to theseafloor and measuring how long it takes to be

Glossary of Marine Technology Terms 10reflected back to the surface. Single beam echosounders have a single transducer to transmitand receive sound. Multi-beam echo soundershave many transmit/receive hydrophones andthus cover a much larger area on the seafloor.This greater coverage makes it much quicker tosurvey a given area. Interferometry-based swathbathymetry survey systems offer wide-area,high-data-density coverage and are particularlysuited to surveys in shallow coastal regionsThe term “interferometry” is generally used todescribe swath-sounding sonar techniques thatuse the phase content of the sonar signal tomeasure the angle of a wave front returned froma sonar target. This technique may be contrastedwith multibeam (and single beam) systems,which look for an amplitude peak on each beamin order to detect the sea-bed, or other targets,across the swath.FFlotation: In marine technology, flotation canbe divided into materials intended for use on thesurface and those for use underwater. Forsurface flotation, buoys are fabricated out ofsteel or other metals, molded plastic or plasticfoams. Ionomer foam is a popular materialbecause of its reduced weight and highdurability.Underwater, subsea flotation is often needed toachieve neutral buoyancy for subsea vehiclesand platforms or to provide a positively buoyantupward force. Because of the compressive forceof water pressure, subsea flotation is a morechallenging problem then it is on the surface.For shallower depths, foamed materials may beused. Foams compress as they descend into thedepths and thus the amount of buoyancy theyprovide is not constant. Ultimately at somedepth they will become so compressed that theywill lose all of their buoyancy. For deeperdepths, non-compressible materials that are lessdense then water should be used.The bathycaphe Trieste solved this problem byusing a large volume of aircraft fuel, which isless then water and compresses very little. In1963, under the supervision of Dr. AndreasRechnizter, this submersible carried Don Walshand Jacque Piccard to the deepest point in theworld—The Challenger Deep.In more recent years, non-compressible foamsmade from a matrix of small glass spheresembedded in epoxy have been used. Known assyntactic foam, this material can be cast intoshapes and sanded or machined. Syntactic isavailable in various densities with differentdepth ratings. Hollow ceramic spheres are alsoavailable for deepsea flotation.Subsea buoys are made from a variety ofmaterials, ranging from PVC plastic pipes withend caps to titanium spheres. Glass spheres arepopular for deep depths, because they arerelatively inexpensive. Plastic “hard hats” areoften used to protect the glass.GGeophysical Instruments are used byscientists and those seeking hard minerals andhydrocarbon deposits to study those parts of theearth hidden from direct view. Instruments usedunderwater include magnetometers (which aredescribed in this glossary under their ownlisting), gravimeters, and seismometers.Seismic devices are another class of underwatergeophysical equipment used to generate shockwaves so reflected signals can be used to detectstructures under the sea floor. Dynamite wasoriginally used to generate shock waves. Todaymechanical devices such as air guns, bubble

Glossary of Marine Technology Terms 11pulsers, boomers and sparkers are utilized. Thereflected signals are detected by hydrophonesthat can either be placed on the seafloor ortowed behind a ship. Streamer cables are arraysof hydrophones that are wired together andcontained in oil-filled plastic hose.In recent years three dimensional (3D) and threedimensional times series (4D) seismic surveytechniques have been developed. The newesttechnique in this field is Continuous SourceElectro-magnetic Measurements (CSEM).CSEM involves towing a source of lowfrequency electromagnetic signals to an array ofseafloor receivers. The received data is used todetermine the resistivity structure of thesubsurface. This is of interest, because there is asignificant contrast between resistivehydrocarbons reservoirs and conductive salinewater saturated layers.GPS (Global Positioning System): Users of aglobal positioning system can calculate theirlocation anywhere on the earth. Two “public”GPS systems are The NAVSTAR system,owned by the United States and managed by theDepartment of Defense, and the GLONASSsystem, owned by the Russian Federation.Global Positioning Systems are space-basedradio positioning systems that provide 24-hour,three-dimensional position, velocity and timeinformation to suitably equipped usersanywhere on the surface of the Earth. The GPSsignals do not penetrate through water, sosubsea vehicles must surface to get a GPS fix.The system works by a constellation of satellitesthat transmit timing information, satellitelocation information and satellite healthinformation. The user requires a special radioreceiver - a GPS receiver - to receive thetransmissions from the satellites. The GPSreceiver contains a specialized computer thatmakes calculations based on the satellite signals.The user gets 24-hour, three-dimensionalposition, velocity and time information and doesnot have to transmit anything to the satellite.Standard GPS has accuracy on the order of 10meters. Differential GPS uses a correctionsignal from a regional source and has typicalaccuracies of 2-3 meters. Real-Time Kinematic(RTK) GPS is a technique that uses a local basestation that is surveyed in and that transmits alocal correction signal to a roving receiver. RTKcan yield positional accuracies of up to 10centimeters.HHydrophones: Underwater hydrophonesdetect acoustic signals in the ocean just asmicrophones collect sound in the air. Mosthydrophones are based on a special property(piezoelecticity) of certain ceramics thatproduce a small electrical current whensubjected to pressure changes. When submergedin water, a ceramic hydrophone produces smallvoltagesignals over a wide range of frequenciesas it is exposed to underwater soundspropagating from any direction. By amplifyingand recording the electrical signals produced bya hydrophone, sound in the sea can be measuredwith great precision. Although a singlehydrophone records sound arriving from anydirection, several hydrophones can besimultaneously deployed in an array, and theresulting signals can then be manipulated to“listen” in any direction with even greatersensitivity than a single hydrophone element.Whether within an array or as a single element,the hydrophone is the basic sensor ofunderwater acoustics. Things to consider whenselecting a hydrophone include receivingresponse, beam width, and depth rating.

Glossary of Marine Technology Terms 12IInertial Navigation SystemsWhen you spin a gyroscope, its axle wants tokeep pointing in the same direction. If youmount the gyroscope in a set of gimbals so thatit can continue pointing in the same direction, itwill. This is the basis of the gyrocompass. If youmount two gyroscopes with their axles at rightangles to one another on a platform, and placethe platform inside a set of gimbals, theplatform will remain completely rigid as thegimbals rotate in any way they please. This isthis basis of inertial navigation systems (INS).In an INS, sensors on the gimbals’ axles detectwhen the platform rotates. The INS uses thosesignals to understand the vehicle’s rotationsrelative to the platform. If you add to theplatform a set of three sensitive accelerometers,you can tell exactly where the vehicle is headingand how its motion is changing in all threedirections. With this information, a ship'sautopilot or an AUV’s guidance system cankeep the vehicle on its intended course.LLighting is used underwater to provideillumination for divers, for submersible pilotsand passengers, and for cameras. Three generalclasses of lights exist: incandescent, arc, andLEDs.Incandescent lights work by heating a filamentto the point where it radiates light. Quartzhalogen lights are the most commonly usedincandescent. The name derives from the quartzglass bulb used that is filled with a halogen gaswhich is used to redeposit evaporated filamentmaterials back on the filament. Incandescentlights are inexpensive but bulbs are fragile andhave relatively short life times.Arc lights, or gas discharge lights, utilizeelectrodes to heat a mixture of gases until aluminous plasma is produced. Depending on thegas mixture, different qualities of light can beproduced. Examples are HID, HMI, and Xenon.Since gas discharge lights have no filament tobreak, they are more robust then incandescentsand usually have longer burn life. Additionally,they are much more efficient at convertingelectrical power into light, an importantconsideration if utilizing battery power. Powerlimiting electronics called ballasts are required.These can be housed with the light fixture orremoted to a separate electronics bottle. Inaddition to the drawback of having a ballast,some arc lights require several minutes to warmup to full power and need to cool down beforere-starting.LEDs are small, low-cost, solid-state devices.They have very long life times and have nofilaments to break nor do they require a ballast.They are available in a variety of color outputsincluding white. Because of their small size,they can be easily incorporated directly into acamera housing.MMagnetometers are used to measureanomalies in the earth’s magnetic field. Thesecan be due to local geologic features or manmadeobjects in the area (i.e., ship wrecks).Underwater magnetometers are typically towedbehind a ship.Proton magnetometers operate on the principalthat the protons in all atoms are spinning on anaxis aligned with the magnetic field. Ordinarily,protons tend to line up with the earth's magneticfield. When subjected to an artificially-inducedmagnetic field, the protons will align themselveswith the new field. When this new field isinterrupted, the protons return to their originalalignment with the earth's magnetic field. Asthey change their alignment, the spinning

Glossary of Marine Technology Terms 13protons precess, or wobble, much as a spinningtop does as it slows down. The frequency atwhich the protons precess is directlyproportional to the strength of the earth’smagnetic field.Overhauser magnetometers use electronprotoncoupling to produce stronger precessionsignals than conventional proton precessionmagnetometers. Optically pumpedmagnetometers (Cesium, Potasium, andRubidium) make even more precisemeasurements of magnetic fields bydetermining the frequency of radio wavesrequired to change the transparency of a glassvapor cell containing gaseous metal that isexposed (or pumped) to polarized light of veryspecific wavelength.Meterological Sensors (met sensors):Exchanges across the air-sea interface, includingheat and fresh water, couple the ocean andatmosphere and are of major interest in studiesof global climate. Met sensors on either researchvessels or buoys include those used to measuresea surface temperature, air temperature, windspeed and direction, barometric pressure, solarand long-wave radiation, humidity andprecipitation. From these measurements,accurate estimates of air-sea fluxes can be made.Motion Sensors measure heave, pitch and roll –typically on surface vessels. Correcting forvessel motion is critical for multi-beamhydrographic surveys, for high-accuracyacoustic positioning systems and for otherapplications. Most are based on three orthogonalaccelerometers of which there are several typeshaving different accuracies at different costs.Older systems, some of which are still in use,are based on pendulums.For less dynamic or static applications, tiltsensors can be used to measure the angle ofinclination. These are commonly used on subseavehicles or instruments resting on the seafloor.Electrolytic tilt sensors use a sealed glass vialpartially filled with a conductive fluid. Severalmetal electrodes go through the glass into thefluid filled chamber. As the sensor tilts, thesurface of the fluid remains level due to gravity.The fluid is electrically conductive, and theconductivity between the two electrodes isproportional to the length of electrode immersedin the fluid. Electrically, the sensor is similar toa potentiometer, with resistance changing inproportion to tilt angle. Single and dual axissensors are available.OOptical Oceanographic Sensors measurethe optical properties of water such asabsorption, attenuation, scattering, fluorescenceand volume scattering function. The instrumentsused to measure these parameters include:Transmissometers are devices for measuringtransmission or beam attenuation. They work byshining a narrow, collimated beam of lightthrough the water. A receiver with a narrowfield of view measures how much light arrivesat the other end of a set distance. Light that islost to absorption or is scattered will not bedetected.Nephelometers, or turbidity sensors, measurelight scattering to determine the overallconcentration of particles suspended in water.Fluorometers provide an indication of theconcentration of a given material by measuringthe amount of fluorescence attributed to thematerial. For example, a fluorometer providesan excitation beam at a wavelength that isknown to cause fluorescent emission from

Glossary of Marine Technology Terms 14chlorophyll and measures light at a wavelengththat matches the chlorophyll emission. As aresult, the amount of chlorophyll-containingbiomass can be estimated.Spectrofluorometers are fluorometers that usemultiple excitation wavelengths and multipleemission wavelengths to isolate and determinerelative concentrations of different materials inthe water.Spectrophotomers measure the scattering oflight. The volume scattering function (VSF)describes the directional dependence of thisscattering. The VSF is an “inherent opticalproperty” of water that is used by opticaloceanographers to predict light propagation,image degradation, remote-sensed ocean color,biological environment, etc. in water.PPan & Tilts are positioning devices used toremotely move cameras, lights, sonars and otherdevices. Pan refers to movement along thehorizontal axis and tilt refers to movement in thevertical axis. A scanner is a one-axis positioner.Physical Oceanographic Sensors are usedto measure the basic physical properties ofseawater. The most common are conductivity,temperature, and pressure (depth). Togetherthese three sensors form a CTD, a commonoceanographic instrument (described under itsown listing in this glossary).Conductivity is the measurement of the water’sability to conduct electric current. It is oftenused as a proxy for measuring salinity. Thebasic unit of conductance is Siemens(represented by an S), formally called the mho(omh spelled backwards). The principle bywhich instruments measure conductivity issimple. After an electrode consisting of twoconductive plates is placed in the water, asinewave voltage is applied across the platesand the current is measured. Electrodes areprone to corrosion, and the pumps that supplythem with water can foul.Electrodeless conductivity sensors use inductivecoils. The inductive conductivity sensor consistsof two high-grade toroids (coils) that areincorporated concentrically and adjacent to oneanother in a polymer or ceramic body. Thesecoils form a current transformer. The sensor isdesigned so part of the liquid media forms aclosed conductive current path passing throughthe toroids. The primary coil is activated with asinusoidal alternating voltage, which induces analternating voltage in the liquid loop (samplemedium). In liquids that conduct electricity, thiscauses a current flow that is proportional to theconductivity of the sample medium. The liquidloop is also acting as the primary winding of thesecondary coil, which functions as a currenttransformer. This current is rectified to thecorrect phase and amplified.Temperature is typically measured by one oftwo types of devices:Resistance temperature detectors (RTDs) aremade of coils or films of metals (usuallyplatinum). When heated, the resistance of themetal increases; when cooled, the resistancedecreases. Passing current through an RTDgenerates a voltage across the RTD. Bymeasuring this voltage, you determine itsresistance, and thus its temperature. RTDs arepopular because of their excellent stability, andbecause they exhibit the most linear signal withrespect to temperature of any electronictemperature sensor. They are generally moreexpensive than alternatives, however, becauseof the careful construction and use of platinum.

Glossary of Marine Technology Terms 15RTDs are also characterized by a slow responsetime and low sensitivity.Thermistors (thermally sensitive resistors) aresimilar to RTDs in that they are electricalresistors whose resistance changes withtemperature. Thermistors are manufacturedfrom metal oxide semiconductor material whichis encapsulated in a glass or epoxy bead.Thermistors have a very high sensitivity,making them extremely responsive to changesin temperature. Thermistors are generally lessexpensive and less accurate then RTDs.There are many ways to sense pressure (depth).Most pressure sensors require the transductionof pressure information into a physicaldisplacement. Measurement of pressure requirestechniques for producing the displacement andmeans for converting such displacement into aproportional electrical signal.One common element used to convert pressureinformation into a physical displacement is thediaphragm. A diaphragm is like a spring, andtherefore extends or contracts until a force isdeveloped that balances the pressure differenceforce. The bellows is another device much likethe diaphragm that converts a pressuredifferential into a physical displacement, exceptthat here the displacement is much more astraight-line expansion. Other pressure sensortransducers consist of a ceramic disk thatchanges its capacitance linearly with appliedpressure. This variation is measured by anelectronic circuit and is converted to a voltageoutput, to give an accurate pressuremeasurement reading. Integrated circuitmanufacturers have developed compositepressure sensors that are particularly easy to use.These devices commonly employ asemiconductor diaphragm onto which asemiconductor strain gauge and temperaturecompensationsensor have been grown.Appropriate signal conditioning is included inintegrated circuit form, providing a DC voltageor current linearly proportional to pressure overa specified range.The most accurate measurements of pressureuse a transducer made of a single quartz crystalwhose frequency of oscillation varies withpressure-induced stress. Quartz crystals werechosen for the sensing elements because of theirremarkable repeatability, low hysteresis andexcellent stability. Accuracies of ±0.01% of fullscale are readily achieved. When operating indeep water (i.e., >10,000 feet), a smalldifference in accuracy can equate to a largedifference in depth measured.Pressure HousingsPressure housings are used to encloseelectronics underwater. There are two primarytypes of housings.Pressure compensated housings are fluid filledand are maintained at ambient pressure. Aflexible diaphragm is typically used to transmitthe external pressure to inside the housing.Benign substances such as mineral oil orsilicone oil are used for the compensating fluidwhich must completely fill the inside of thehousing leaving no air pockets. Componentsthat are air or gas filled cannot be used, becausethey will implode under pressure.One-atmosphere housings maintain constantpressure inside. Typically they are air filled, butsometimes dry nitrogen or other gases are usedto prevent condensation. Cylindrical- andspherical-shaped housing designs are strongest.Rectangular and other shapes are usually onlyused in shallow water applications. Commonmaterials selected for immersion in seawater are

Glossary of Marine Technology Terms 16anodized aluminum, stainless steel, titanium andplastic.Cylinders are the most common housinggeometry. Flat or hemispherical end caps aretypically retained with bolts or are threaded intothe main tube. Glass spheres are also sometimesused for pressure housings. The clarity of theglass can be taken advantage of by opticalsensors and controllers.Things to consider when designing or selectingan underwater pressure housing include depthrating, safety margin and material selection.RReleases: A common task is to recover anobject that is weighted down or anchored to theseafloor. To do this without divers or an ROV, arelease is utilized. There are several types ofreleases.Galvanic releases rely on seawater to corrode awire or link. Generally these are inexpensive butthe rate of corrosion can differ from place toplace and thus the time to release is notcontrolled with great precision.Burn wire releases utilize a timing device toactivate an electrical current that will burn out awire, which in turn causes the payload to bereleased.Timed releases use some sort of mechanicaldevice that is activated by a timer.The drawback to all these methods is that therelease time must be set before the device isdeployed. Thus, there is no way to change therelease time if inclement weather or other issueschange one’s schedule. Acoustic releases solvethis problem, because they are activated whenthey receive an acoustic tone of a specificfrequency. Typically this is done by someone ina boat who is in the vicinity of the object to bereleased. Acoustic releases are available withdifferent frequencies that have different ranges.Other considerations in selecting a release arebattery life, depth rating and strength rating.More sophisticated acoustic releases use a codedpulse to prevent being accidentally activated if apassing ship or some other source in the areahappens to emit noise at the release frequency.Remote Sensing is ocean data collected bysensors on satellites or aircraft. The term impliesthat the sensor is placed at some considerabledistance from the sensed target, in contrast toclose-in measurements made by “in situ"sensing. Commonly measured parameters areocean color, sea surface temperature and seasurface altitude.Ropes and Tension Members are used tocarry loads on moorings, towed sleds anddevices lowered over the sides of ships. Fiberropes, wire ropes and chains are examples offlexible tension members. Synthetic fiber ropesare made from Nylon, Dacron, Polypropylene,Kevlar, Vectran and Spectra. Considerations inselecting a material are strength,weight/buoyancy, and stretch. Synthetic fiberropes can be terminated by eye splicing or bysocketing with epoxy.Wire ropes are typically made from highstrengthcarbon steel but stainless steel andother alloys are sometimes used. They are muchmore cut-and-abrasion resistant then fiber ropes.They are terminated with eyes, swaged sockets,and zinc- or resin-poured sockets.Chains made of steel can provide even higherlevels of strength and cut/abrasion resistance.They are typically terminated with shackles but

Glossary of Marine Technology Terms 17other fittings such as links, rings, and swivelsare also used.ROVs or Remotely Operated Vehicles areunderwater robots used for a wide variety oftasks, ranging from simple inspection tomaintenance and repair work. These tasks areperformed on offshore oil rigs, ship hulls, docks,mooring buoys, dams, bridges and power plants,and in water tanks. ROVs are lowered on acable either alone or in a protective cage andthen operated on a slack tether that decouples itfrom the ship’s surface motion. Video camerasserve as “eyes” for the operator who controls thevehicle via the cable. An ROV can explore, takephotographs, collect samples, or handleinstruments, operating around the clock formany consecutive days. Job-specific tool skidsare sometimes mounted under larger vehicles.A good write up on ROVs and their history maybe found at the MTS ROV committee Web sitehttp://www.rov.org/info.cfm.SScour is the destructive effect that flowingwater has on a submerged object. When a manmadeobject such as a bridge pier, pipeline,cable, etc. is submerged in flowing water, thelocal effect is to increase the current velocityaround the object. This increased velocity hasthe tendency to remove or scour away thebottom material that supports the structure.Seals: The type of seals discussed here are notmarine mammals or navy commandos. Seals area means for keeping water out of pressurehousings. Types of seals used in the marineenvironment include gaskets, shaft seals, lipseals, stuffing tubes and gland seals. The o-ringis the most commonly-used type of sealunderwater. It is a solid piece of elastomericmaterial shaped like a doughnut or torus. Whenpressed between mating surfaces, an o-ringblocks the passage of liquids or gases. The o-ring is the most widely used seal due to itssimplicity, low cost, ease of installation, andsmall space requirements without supportingstructures. An O-ring can be considered anincompressible viscous fluid with very highsurface tension. This “fluid” is forced bymechanical or hydraulic pressure to flow intothe sealing cavity, blocking the flow of the lessviscousfluid being sealed. Properly installed,the O-ring is squeezed about 10% to 15% of itsoriginal cross-sectional diameter. Thecompression absorbs the tolerance stack upbetween mating surfaces (or between shaft andgland in dynamic applications) and forces theelastomer into microscopic surface grooves onmating parts.Successful use of o-rings depends upon propergroove dimensions and selection of the rightelastomeric compound. Compounds are chosenfor their resistance to chemicals andtemperatures. Common materials utilizedinclude Nitrile, neoprene, flurocarbon (Viton),silicone, fluorosilicone, and urethane.Today's dynamic o-ring in a short rectangulargroove was the result of experimental work inthe early 1930s by Niels Christensen (seehttp://www.uh.edu/engines/epi555.htm). In theearly 1940s, the o-ring became the standard sealfor U.S. Air Force hydraulic systems. Thisestablished the basic sizes and designinformation. Today, billions of o-rings aresealing every conceivable apparatus all over theworld, in the air, on land and sea, and in outerspace.Sediment Traps are used to collect samples ofparticles sinking through the water column.Scientists can learn the rate of sedimentation

Glossary of Marine Technology Terms 18and about the organisms that populate the watercolumn using sediment traps.Slip Rings are electromechanical devices thatallow the transmission of power and electricalsignals from a stationary to a rotating structure.Also called a rotary electrical joint, collector orelectric swivel, a slip ring can be used in anyelectromechanical system that requires unrestrained,intermittent or continuous rotationwhile transmitting power and/or data. They arecommonly used on cable winches. For fiberoptic conductors the Fiber Optic Rotary Joints(FORJs) are used in place of slip rings.Sonar (SOund NAvigation and Ranging) isused for many purposes. Passive sonars detectnoise from marine objects, such as submarines,ships and marine animals. Active sonars emit apulse of sound or “ping,” into the water and thenlisten for an echo when the signal is reflectedoff an object. To measure the distance to anobject, one measures the time from emission ofa pulse to reception. Some common sonardevices are:Side Scan Sonar—as the name implies, is asonar that looks out sideways. It is used to mapseafloor topography or to locate objects on thebottom or in the water column. It consists of atow fish with a transducer running along eachside. Acoustic pulses are transmitted orthogonalto the axis of the tow fish. The receivermeasures the time it takes for the pulses toreturn and their strength. These are combinedtogether to create a “shadow picture” thatdepicts the shape and texture of the seafloor andany objects laying on it. A good review of sidescan sonars can be found athttp://inventors.about.com/gi/dynamic/offsite.htm?site=http://www.instituteformarineacoustics.org/SonarPrimer/SideScanSonar.htmScanning Sonars—also known as forwardlookingsonars and sector scanning sonars, areused for navigation on subsea vehicles. Thetransducer sweeps back and forth to paint apicture of what is in front of the vehicle.Sonar altimeters are underwater echo sounders.They measure height off the seafloor from asubsea vehicle. Altimeters are also used to studysediment transport and to monitor scouringaround bridge pilings.Sub-Bottom Profilers use low-frequency sonar(2 to12kHz) to penetrate the seafloor. Soundpulses are reflected from the boundariesbetween sediment layers. This information canbe used for geological studies and to find buriedobjects such as shipwrecks, mines and lostequipment.In side scan sonar surveying, it is desirable tocover the seabed quicker and at higherresolutions. This causes great difficulty forconventional side scan technology. There areonly two choices—using higher frequencies (toachieve narrower beams and thus higherresolutions) or using longer apertures to achievethe same effect. The downside to this approachis either shorter operational ranges with higherfrequencies (compromising coverage rates) orproblems associated with handling large towfish. Similarly, as the imagery is tied to thesonar beam width, the resolution ofconventional side scan degrades with range.Two techniques have been developed to getaround these obstacles. Multi-beam side scansonars use several transducers along each sideof the tow fish. With beam steering andfocusing techniques, several simultaneousadjacent parallel beams are generated per side.This allows for 100 % coverage at very hightow speeds with extraordinary resolution andimage clarity. Another method, Synthetic

Glossary of Marine Technology Terms 19Aperture Sonar (SAS) synthesises a longaperture image by adding successive sonarreturns, which are processed to compensate forthe movement between returns and otherfactors. The results are much improvedresolutions.Submersibles: Manned submersibles are noncombatantcraft capable of independentoperation on and under the water’s surface.Manned submersibles have their own propulsionpower and a means for direct viewing for theoccupants who are in a dry one-atmospherecabin. Manned submersibles have a long historygoing back hundreds of years and now employmany of the technologies described in thisglossary. Today they are primarily usedforscientific research, exploration and tourismMajor subsystems include the pressure hull,viewing ports, life support systems,exostructure, ballast/trim, propulsion, batteriesand fairings/sail. Operational instrumentationtypically includes lights, cameras, sonar, thruwatercommunications, and often a manipulator.Navigation equipment consists of a pressuresensor, tilt sensor, gyrocompass, dopplervelocity log (DVL), underwater trackingsystem, altimeter and perhaps an inertialnavigation system that would integrate the datafrom all the other sensors. In addition, missionspecificscientific equipment is often added.The MTS Manned Submersibles Committeeweb site athttp://www.mtsociety.org/pro_committees/mannedsubmersibles/default.html has a suggestedreading list and links to many valuableresources. Also, the out-of-print classic“Manned Submersibles” by Frank Busby isavailable on-line athttp://busby.psubs.org/html/page-001.html . Acomprehensive compilation of American subsby Will Forman is The History of AmericanDeep Submersible Operations.Surface-Supplied Air Diving: Diverstethered to a surface-supplied-air-diving systemcan achieve dives up to 190 feet of seawater(FSW) in air diving and 300 FSW in mixed gasdiving. Air is supplied via an air compressor orhigh-pressure air flasks. A surface-supplied-airdiving system can permit a diver to stay downfor a longer period of time than a SCUBAsystem would allow.TTide Gauges are used to measure changes insea level. This is important to know for manyreasons, including the correction echo sounderdata used in making hydrographic charts.The first known tide measuring devices wereused by the Egyptians 5,000 years ago, makingtide gauges the first known marine technology.Wooden or reed sticks and later marble columnsplanted in the river bottom were sufficientlylong enough to extend above the waterlinewhere the fluctuating level of the Nile Rivercould be measured against markings. Thehydrological information collected is one thelongest scientific time-series data sets evercollected. Today, tide staffs are still widelyused.Mechanical tide recording devices have beenused for more then a century. These devicestypically consist of a wire hung over a pulleywheel. At one end, there is a metal float and atthe other end a counter weight. As the tidefluctuates, the wire turns the pulley that isgeared to a pen that runs over a paper chart heldin tension over a platen. The paper is movedfrom a supply spool to a take-up spool by aclock-driven mechanism. The recorder is placedin a shelter or in a security box on top of a

Glossary of Marine Technology Terms 20stilling well. A stilling well consists of a pipeattached vertically to a pier or other structure. Ithas a sealed bottom with an inlet hole of about1/50 of the diameter of the well. This “stills”wave action, allowing an accurate measurementto be taken.Modern electronic tide gauges use pressuresensors and data loggers. For information on thedifferent type of pressure sensors used, see thesection on this subject in this glossary.Long-term tide gauge records can be used todetermine changes in mean sea level. However,with tide gauges alone, it is impossible todistinguish between any “true” sea levelvariations and vertical land movements at thetide gauge site. GPS monitoring can be used todecouple vertical land movements from changesin relative sea level, so that tide gauges canprovide estimates of changes in “absolute sealevel.”Towed Vehicles: Many types of underwatertowed vehicles have been developed foroceanographic real-time surveys. They offer thecapability of moving in wide area with stableattitude at speeds much faster then ROVs andAUVs. Towed vehicles are used for such tasksas monitoring the oceanographic environment,surveying the seabed and inspecting pipelineson the seabed. Some types can be steered andothers can be winched in and out.UUnderwater Acoustic Imaging is used toproduce high-quality images in water wherevisibility is too poor to use optical methods. Inunderwater acoustic imaging, electrical energy(electricity) is sent to a crystal, which causes thecrystal to vibrate. The sound of the vibration(mechanical energy) travels out into the watercolumn until it hits an object and is reflectedback to the crystal. After the energy returns tothe crystal, a computer converts it to an image.Underwater Positioning & TrackingSystems are used to identify the location of anobject or vehicle underwater. Since radios donot transmit through water, GPS cannot be usedunless an antenna is cabled to the surface.Several acoustic methods have been developedfor the purpose of underwater navigation. Theseinclude:Long Base Line (LBL) uses severaltransponders on the seafloor. The distancebetween each transponder is measured. Atransducer on the vessel, ROV, AUV or towfish, interrogates each transponder and theranges to each are measured. From thisinformation, the position of the subsea platformcan be determined by triangulation.Short Base Line (SBL) is similar to LBLexcept the array of transponders is spread alongthe underside of the vessel.Ultra Short Base Line (USBL) uses only onetransponder and one multi-element hydrophoneon the surface. The measurement of the angle tothe transducer is made across the face of thehydrophone (the ultra short base line). Inaddition to the angle, the range is determined bymeasuring the amount of time it takes for apulse to travel from the hydrophone and to bereturned by the transponder. So range andbearing to the target are determined.LBL is the most accurate of the methodsdescribed and is more common in deeper water,because the accuracy of SBL and USBLdegrade with range. The disadvantage of LBL isthe time and expense required to deploy andsurvey in the seafloor transponders. USBL is the

Glossary of Marine Technology Terms 21least expensive method and the easiest to use.SBL falls somewhere in between the two.WWater sampling devices range from a bucketdropped over the side of a ship to large waterbottles sent thousands of meters toward theseafloor on a wire. Probably the most commonlyused water sampler is known as a CTD/rosette:it is a framework designed to carry 12 to 36sampling bottles (typically ranging from 1.2- to30-liter capacity) and a conductivity/temperature/depth sensor that sends informationto the laboratory so that the water bottles can beclosed selectively as the instrument ascends.Alternatively a single water bottle can beequipped with a spring-loaded release andlowered on a line. When the desired depth isreached, a messenger weight is slid down theline and trips the release allowing, the end capsto snap close on the bottle. The largest waterbottles, called Gerard barrels, collect 250 liters.Particles in the water samples may be quantifiedwith a transmissometer sent down the wire orattached to a CTD/rosette. Aboard the ship, aflow cytometer may be used to analyze particlesin the form of single-celled organisms foroptical properties indicative of their physiologyand structure.Wave Gauges are made in several ways.Electric wave staffs measure wave height bychanges in resistance. More common is using apressure sensor with a current meter in atechnique called PUV. Wave height is measuredas changes in pressure. With an array of three ormore sensors, wave direction can be determined.Another method uses Doppler current meters toform a virtual wave array. This is done bybottom mounting an upward-looking, multiplebeamedDoppler so it can measure the range tothe surface as well as the orbital wave velocitiesin a series of bins extending away from theinstrument. These manifold measurements allowone to differentiate among multiple sources ofwaves—something that a single point sensorcannot do.Wave heights can also be measured fromvessels or piers using microwave altimeters.An accelerometer is used to remove ship motionfrom the wave amplitude measurement.Buoys can be used to measure waves if theyhave an elastic mooring line that allows them totravel with the waves. By using three orthogonalaccelerometers, the buoy motion can be used tomeasure wave height and direction. Anothertechnique uses the Doppler shift of GPS signalsto determine buoy movement. By analyzing thesignal from several GPS satellites, wave heightand direction can be determined.A good primer on wave theory andmeasurement may be found athttp://cdip.ucsd.edu/?nav=documents&sub=index&xitem=waves#gaugingFor info on wave measurement instruments usedat the Scripps Institution of Oceanography, seehttp://cdip.ucsd.edu/?nav=documents&sub=index&xitem=gaugeWinches are devices used to pay out, pull in,and store cable. They consist of a movable drumaround which a cable is wound so that rotationof the drum produces a drawing force at the endof the cable. Winches can be powered by diesel,hydraulic or electrical power. A reel is a handpoweredwinch. Winches are selected by cablecapacity, line speed, strength (line pull) andmaterial (typically steel or aluminum). Optionsinclude remote controls, level winds, variablespeed drives, brakes, clutches (for freespooling), cable counters and heave

Glossary of Marine Technology Terms 22compensation. There are many special types ofwinches for specific applications, includingthose for ROV umbilicals, diver hoses, andCTDs. Slip rings are used with winches totransfer electrical power. Other related devicesinclude: Traction Winches are used fortensioning the cable so there will be nospooling problems due to slack line. Launch and Recovery Systems(LARS) are used for ROVs, AUVs, andsubmersibles. Linear cable engines (LCE) can pullany size cable, chain or pipe and can pullthe material to be deployed from astorage tank or even from an organized“pile” on the deck of a ship. They havethe ability to grip nearly any surface andpass or “climb over” joints or otherobjects Tether Management Systems (TMS)are essentially under winches used withROVs, particularly in deeper water. Aheavy duty lifting cable connects theTMS to the surface allowing a lighterweight umbilical to be used with theROV.

Glossary of Marine Technology Terms 23REFERENCESNational Science Foundation Ocean Sciences program information:http://www.geo.nsf.gov/oce/whatis/tools.htmNOAA Ocean Explorer observation tools site has pages on ADCPs, ocean acoustics, GIS,satellites, sonars, CTDs, drifting buoys and more:http://oceanexplorer.noaa.gov/technology/tools/tools.htmlNational Academy of Science ocean acoustics tutorialhttp://www.beyonddiscovery.org/content/view.article.asp?a=219NOAA ocean acoustics tutorialhttp://pmel.noaa.gov/vents/acoustics/tutorial/tutorial.htmlUnderwater acoustics and sonar primer:http://inventors.about.com/gi/dynamic/offsite.htm?site=http://www.instituteformarineacoustics.org/SonarPrimer/SideScanSonar.htmDr. Bob Stewart of Texas A&M has several excellent web resources. One covers a wide range ofocean topics: http://oceanworld.tamu.edu/index.htmlAnother has an on-line introduction to physical oceanography textbook:http://oceanworld.tamu.edu/resources/ocng_textbook/contents.htmlAnd another has online general oceanographic textbook for high school and college students.http://oceanworld.tamu.edu/home/oceanography_book.htm