《航海学》课程参考文献（地文资料）CHAPTER 30 HYDROGRAPHY AND HYDROGRAPHIC REPORTS

CHAPTER 30HYDROGRAPHYANDHYDROGRAPHICREPORTS3000.Introductionfactors. Cartography is the final step in a long processwhichleadsfromrawdatatoausablechartforthemarinerBecause the nautical chart is so essential to safe navi-The mariner,in addition tobeing theprimary user ofgation, it is important for the mariner to understand thehydrographicdata, is also an important sourceofdata usedcapabilities and limitations ofboth digital and paper chartsin the production and correction of nautical charts.ThisPrevious chapters have dealt with horizontal and verticalchapter discusses the processes involved in producingadatums, chart projections, and other elements of carto-nautical chart, whether in digital or paper form, from thegraphic science.This chapter will explain some basicinitial planning of a hydrographic survey to thefinal print-concepts of hydrography and cartography which are impor-ing.With this information, the mariner can better evaluatetant to the navigator, both as a user and as a source of datathe information which comes to his attention and can for-Hydrography is the science of measurement and descrip-ward it in a form that will be most useful to chartingtion of all of the factors which affectnavigation, includingagencies,allowing themtoproduce more accurate anduse-depths,shorelines, tides, currents,magnetism,and otherful charts.BASICSOFHYDROGRAPHICSURVEYING3001.PlanningTheSurveyif it meets the expected accuracy standards, so the tidegauges can be linked to the vertical datum used for the sur-Thebasic documents used to produce nautical chartsvey.Horizontal control is reviewed to checkfor accuracyare hydrographic surveys.Much additional information isand discrepancies and to determine sites forlocal position-included, but the survey is central to the compilation of aing systems tobe used in the survey.chart. A survey begins long before actual data collectionLine spacing refersto the distance between tracks to bestarts. Some elements which must be decided are:runby the survey vessel. It is chosen to provide thebest cov-erageofthe areausingtheequipment available.Line spacing.Exactareaofthesurvey..Typeof survey(reconnaissance or standard)andis afunction of the depthofwater,thesound footprint ofthescale to meet standards of chartto be produced.collection equipment to beused, and the complexity of the:Scope of the survey (short or longterm)bottom.Oncelinespacingischosenthehydrographercan·Platforms available (ships, launches,aircraft, leasedcomputethetotal miles of surveytracktobe run and haveanvessels,cooperativeagreements)idea ofthetime required for the survey,factoring in the ex:Support work required (aerial or satellite photogra-pectedweather and other possible delays.The scale ofthephy,geodetics,tides)survey,orientation to the shorelines in the area,and the meth-.Limiting factors (budget, political or operational con-odof positioningdetermine line spacing.Planned tracks arestraints,positioning systemslimitations, logistics)laid out sothattherewill benogaps between sound linesandOnce these issues are decided, all information avail-sufficient overlaps between individual survey areas.able in the survey area is reviewed. This includes aerialLines with spacinggreater than the primary survey'sphotography,satellite data, topographic maps, existing nau-linespacing arerun atrightangles totheprimarysurveyde-tical charts,geodetic information,tidal information,andvelopment to verify data repeatability.These are calledanything else affecting the survey.The survey plannerscross check lines.thencompilesoundvelocityinformation,climatology,waOthertaskstobecompletedwiththesurveyincludebottomter claritydata, anypast surveydata,and informationfromsampling,seabedcoring,productionofsonarpicturesofthesealights lists,sailing directions,and notices to mariners.Tidalbed, gravity and magnetic measurements (on deep oceaninformation is thoroughly reviewed and tide gauge loca-tions chosen.Local vertical control data is reviewed to seesurveys),and sound velocity measurements in the water column411

411 CHAPTER 30 HYDROGRAPHY AND HYDROGRAPHIC REPORTS 3000. Introduction Because the nautical chart is so essential to safe navi￾gation, it is important for the mariner to understand the capabilities and limitations of both digital and paper charts. Previous chapters have dealt with horizontal and vertical datums, chart projections, and other elements of carto￾graphic science. This chapter will explain some basic concepts of hydrography and cartography which are impor￾tant to the navigator, both as a user and as a source of data. Hydrography is the science of measurement and descrip￾tion of all of the factors which affect navigation, including depths, shorelines, tides, currents, magnetism, and other factors. Cartography is the final step in a long process which leads from raw data to a usable chart for the mariner. The mariner, in addition to being the primary user of hydrographic data, is also an important source of data used in the production and correction of nautical charts. This chapter discusses the processes involved in producing a nautical chart, whether in digital or paper form, from the initial planning of a hydrographic survey to the final print￾ing. With this information, the mariner can better evaluate the information which comes to his attention and can for￾ward it in a form that will be most useful to charting agencies, allowing them to produce more accurate and use￾ful charts. BASICS OF HYDROGRAPHIC SURVEYING 3001. Planning The Survey The basic documents used to produce nautical charts are hydrographic surveys. Much additional information is included, but the survey is central to the compilation of a chart. A survey begins long before actual data collection starts. Some elements which must be decided are: • Exact area of the survey. • Type of survey (reconnaissance or standard) and scale to meet standards of chart to be produced. • Scope of the survey (short or long term). • Platforms available (ships, launches, aircraft, leased vessels, cooperative agreements). • Support work required (aerial or satellite photogra￾phy, geodetics, tides). • Limiting factors (budget, political or operational con￾straints, positioning systems limitations, logistics). Once these issues are decided, all information avail￾able in the survey area is reviewed. This includes aerial photography, satellite data, topographic maps, existing nau￾tical charts, geodetic information, tidal information, and anything else affecting the survey. The survey planners then compile sound velocity information, climatology, wa￾ter clarity data, any past survey data, and information from lights lists, sailing directions, and notices to mariners. Tidal information is thoroughly reviewed and tide gauge loca￾tions chosen. Local vertical control data is reviewed to see if it meets the expected accuracy standards, so the tide gauges can be linked to the vertical datum used for the sur￾vey. Horizontal control is reviewed to check for accuracy and discrepancies and to determine sites for local position￾ing systems to be used in the survey. Line spacing refers to the distance between tracks to be run by the survey vessel. It is chosen to provide the best cov￾erage of the area using the equipment available. Line spacing is a function of the depth of water, the sound footprint of the collection equipment to be used, and the complexity of the bottom. Once line spacing is chosen, the hydrographer can compute the total miles of survey track to be run and have an idea of the time required for the survey, factoring in the ex￾pected weather and other possible delays. The scale of the survey, orientation to the shorelines in the area, and the meth￾od of positioning determine line spacing. Planned tracks are laid out so that there will be no gaps between sound lines and sufficient overlaps between individual survey areas. Lines with spacing greater than the primary survey’s line spacing are run at right angles to the primary survey de￾velopment to verify data repeatability. These are called cross check lines. Other tasks to be completed with the survey include bottom sampling, seabed coring, production of sonar pictures of the sea￾bed, gravity and magnetic measurements (on deep ocean surveys), and sound velocity measurements in the water column

412HYDROGRAPHYANDHYDROGRAPHICREPORTS3002.Echo Sounders In Hydrographic Surveyingso that all soundings can be corrected for tideheight andthus reduced to the chosen vertical datum.Tide correctionseliminatetheeffect of thetides on thecharted watersandEchosounders were developed in the early1920s,andensure that the soundings portrayed on the chart are thecomputethedepth ofwaterbymeasuringthetime ittakesminimum availabletothemarineratthe soundingdatumfora pulse of sound to travel from the source to the sea bot-Observed,not predicted, tides are used to accountforbothtom and return. A device called a transducer convertsastronomically and meteorlogically induced water levelelectrical energy into sound energy and vice versa.Forbasicchanges during the survey.hydrographic surveying,thetransduceris mountedperma-nently in thebottom ofthe survey vessel, which then follows3003.Collecting SurveyDatathe planned trackline, generating soundings along the track.Themajordifferencebetweendifferenttypesof echoWhile sounding data is beingcollected alongtheplannedsounders is in the frequencies they use.Transducers can betracklines bythesurvey vessel(s),a variety of other relatedacclassified according to theirbeam width, frequency,and pow-tivities are taking place. A large-scale boat sheet is producederrating.Thesoundradiatesfromthetransducerinaconewith many thousands of individual soundings plotted. A com-withabout 50%actuallyreachingto sea bottom.Beamwidthplete navigation journal iskeptofthe survey vessel'sposition,isdetermined bythefrequencyofthepulseand the sizeofthecourse and speed.Side-scan sonarmay bedeployed to investi-transducer.In general, lowerfrequencies produce a widergate individual features and identify rocks, wrecks, and otherbeam,and ata givenfrequencya smallertransducer will prodangers. Time is the parameter which links the ship's positionduce awiderbeam.Lowerfrequencies alsopenetrate deeperwith the various echograms,sonograms,journals,and boatintothewaterbuthavelessresolutionindepthHigherfre-sheets that make up the hydrographic data package.quencieshavegreater resolution indepth,but less range,sothe choice is a trade-off. Higher frequencies also require a3004.ProcessingHydrographicDatasmallertransducer.Atypicallowfrequencytransduceroper-ates at 12kHz and a high frequency one at200kHzDuring processing, echogram data and navigationalTheformulafordepthdeterminedbyanecho sounderisdataarecombined withtidaldataand vessel/equipmentcor-V×T+K+DrD=rections to produce reduced soundings.This reduced dataiscombinedonaplotof thevessel'sactualtracktheboatwhere D is depth from the water surface,V is the aver-sheetdatatoproduceasmoothsheet.Acontouroverlayisage velocity of sound inthe water column,T is round-tripusuallymade totestthelogic of all thedata shown.All ano-timeforthepulse,Kisthe system indexconstant,andD,ismolous depths are rechecked in either the survey records orthedepthofthetransducerbelowthesurface(whichmaynotin thefield.Ifnecessary,sonardata arethen overlayed toan-be the same as vessel draft). V, Dr, and T can be only gener-alyze individual features as related to depths.It may takeallydetermined,and Kmust bedeterminedfrom periodicdozens of smooth sheetsto cover the areaofa complete sur-vey.The smooth sheets arethen ready for cartographers.calibration, In addition, T depends on the distinctiveness ofwho will choose representative soundings manually or usingthe echo, which may vary according to whether the sea bot-automated systemsfrom thousands shown,to produceatom ishard or soft.Vwill varyaccordingtothedensityofthenautical chart.Documentationoftheprocess is such thatanywater, which is determined by salinity,temperature, andpressure,and may vary both in terms of area and time.Inindividual sounding on any chart can betraced back to itsoriginal uncorrected value.See Figure 3004.practice, average sound velocity is usually measured on siteand the samevalue usedfor an entire survey unless variationsinwatermassareexpected.Suchvariations couldoccur,for3005.RecentDevelopments InHydrographic Surveyingexample,in areas ofmajor currents.While V is a vital factorindeepwatersurveys,itisnormalpracticetoreflecttheechoTheevolutionof echo sounders has followed the samesounder signal offa plate suspended under the ship at typicalpattern of technological innovation seen in otherareas.Indepthsfor the survey areas in shallowwaters.TheKparam-the 1940s lowfrequency/wide beam sounderswere devel-eter, or index constant, refers to electrical or mechanicalopedforshipstocoverlargeroceanareasinlesstimewithdelavsinthecircuitryandalsocontainsanyconstantcorrec-some loss of resolution.Boats used smaller sounders whichtion due to the change in sound velocity between the upperusuallyrequiredvisualmonitoringofthedepth.Later,nar-layers of water and the average used for thewholeproject.row beam soundersgave ship systemsbetterresolutionFurther.vesselspeedisfactoredinandcorrectionsarecom-using higher frequencies,but with a corresponding loss ofputed for settlement and squat, which affect transducerarea.These were then combined into dual-frequency sys-depth.Vessel roll,pitch,and heaveare also accountedfor.Fitems.All echo sounders,however,used a singletransducernally,theobservedtidaldataisrecordedinordertocorrectwhichlimited surveys to singlelines ofsoundings.Forboatthe soundings during processingequipment,automaticrecordingbecamestandardTides are accurately measured during the entire surveyThe last three decades have seen the development ofmulti-

412 HYDROGRAPHY AND HYDROGRAPHIC REPORTS 3002. Echo Sounders In Hydrographic Surveying Echo sounders were developed in the early 1920s, and compute the depth of water by measuring the time it takes for a pulse of sound to travel from the source to the sea bot￾tom and return. A device called a transducer converts electrical energy into sound energy and vice versa. For basic hydrographic surveying, the transducer is mounted perma￾nently in the bottom of the survey vessel, which then follows the planned trackline, generating soundings along the track. The major difference between different types of echo sounders is in the frequencies they use. Transducers can be classified according to their beam width, frequency, and pow￾er rating. The sound radiates from the transducer in a cone, with about 50% actually reaching to sea bottom. Beam width is determined by the frequency of the pulse and the size of the transducer. In general, lower frequencies produce a wider beam, and at a given frequency, a smaller transducer will pro￾duce a wider beam. Lower frequencies also penetrate deeper into the water, but have less resolution in depth. Higher fre￾quencies have greater resolution in depth, but less range, so the choice is a trade-off. Higher frequencies also require a smaller transducer. A typical low frequency transducer oper￾ates at 12 kHz and a high frequency one at 200 kHz. The formula for depth determined by an echo sounder is: where D is depth from the water surface, V is the aver￾age velocity of sound in the water column, T is round-trip time for the pulse, K is the system index constant, and Dr is the depth of the transducer below the surface (which may not be the same as vessel draft). V, Dr, and T can be only gener￾ally determined, and K must be determined from periodic calibration. In addition, T depends on the distinctiveness of the echo, which may vary according to whether the sea bot￾tom is hard or soft. V will vary according to the density of the water, which is determined by salinity, temperature, and pressure, and may vary both in terms of area and time. In practice, average sound velocity is usually measured on site and the same value used for an entire survey unless variations in water mass are expected. Such variations could occur, for example, in areas of major currents. While V is a vital factor in deep water surveys, it is normal practice to reflect the echo sounder signal off a plate suspended under the ship at typical depths for the survey areas in shallow waters. The K param￾eter, or index constant, refers to electrical or mechanical delays in the circuitry, and also contains any constant correc￾tion due to the change in sound velocity between the upper layers of water and the average used for the whole project. Further, vessel speed is factored in and corrections are com￾puted for settlement and squat, which affect transducer depth. Vessel roll, pitch, and heave are also accounted for. Fi￾nally, the observed tidal data is recorded in order to correct the soundings during processing. Tides are accurately measured during the entire survey so that all soundings can be corrected for tide height and thus reduced to the chosen vertical datum. Tide corrections eliminate the effect of the tides on the charted waters and ensure that the soundings portrayed on the chart are the minimum available to the mariner at the sounding datum. Observed, not predicted, tides are used to account for both astronomically and meteorlogically induced water level changes during the survey. 3003. Collecting Survey Data While sounding data is being collected along the planned tracklines by the survey vessel(s), a variety of other related ac￾tivities are taking place. A large-scale boat sheet is produced with many thousands of individual soundings plotted. A com￾plete navigation journal is kept of the survey vessel’s position, course and speed. Side-scan sonar may be deployed to investi￾gate individual features and identify rocks, wrecks, and other dangers. Time is the parameter which links the ship’s position with the various echograms, sonograms, journals, and boat sheets that make up the hydrographic data package. 3004. Processing Hydrographic Data During processing, echogram data and navigational data are combined with tidal data and vessel/equipment cor￾rections to produce reduced soundings. This reduced data is combined on a plot of the vessel’s actual track the boat sheet data to produce a smooth sheet. A contour overlay is usually made to test the logic of all the data shown. All ano￾molous depths are rechecked in either the survey records or in the field. If necessary, sonar data are then overlayed to an￾alyze individual features as related to depths. It may take dozens of smooth sheets to cover the area of a complete sur￾vey. The smooth sheets are then ready for cartographers, who will choose representative soundings manually or using automated systems from thousands shown, to produce a nautical chart. Documentation of the process is such that any individual sounding on any chart can be traced back to its original uncorrected value. See Figure 3004. 3005. Recent Developments In Hydrographic Surveying The evolution of echo sounders has followed the same pattern of technological innovation seen in other areas. In the 1940s low frequency/wide beam sounders were devel￾oped for ships to cover larger ocean areas in less time with some loss of resolution. Boats used smaller sounders which usually required visual monitoring of the depth. Later, nar￾row beam sounders gave ship systems better resolution using higher frequencies, but with a corresponding loss of area. These were then combined into dual-frequency sys￾tems. All echo sounders, however, used a single transducer, which limited surveys to single lines of soundings. For boat equipment, automatic recording became standard. The last three decades have seen the development of multi￾D V T × 2 -KDr = + +

413HYDROGRAPHYANDHYDROGRAPHICREPORTSANDNAVIGATIONeSOUNDINGBOATSHEETSONOGRAMSECHOGRAMSomJOURNALSCALECORRECTSOUNDINGSPLOTSIDE SCAN TRACKSPLOTPOSITIONSONTRACK SHEETON SONAR COVERAGESHEETENTER0000TIOALDATUMREDUCERSTRACKSHEETReducedsoundingsequals scaledFeature analysissoundings plusandevaluationvarious correctionsSOUNDING SHEET家查欢临TRACK SHEETPencil and inksoundingsANDEOCORRECTIONSREVIEWANDEDITFigure 3004. The process of hydrographic surveying

HYDROGRAPHY AND HYDROGRAPHIC REPORTS 413 Figure 3004. The process of hydrographic surveying

414HYDROGRAPHYANDHYDROGRAPHICREPORTSidepiempaeEW00O000800m50043294386440244824539457345824578457846244727476247744758475847784778479047974806482148304843487948888000m500mFigure3005.Swathversussingle-transducersurvevs

414 HYDROGRAPHY AND HYDROGRAPHIC REPORTS Figure 3005. Swath versus single-transducer surveys

415HYDROGRAPHYANDHYDROGRAPHICREPORTSple-transducer, multiple-frequency sounding systems which areofthissystem isfixed bythedistancebetweenthetwooutermostable to scana wide areaofseabed.Two general types are in use.transducers and is not dependent on waterdepthOpen waters are best surveyed using an array of transducersA recent development is Airborne Laser Hydrogra-spread out athwartships across the hull of the survey vessel.phy (ALH).An aircraft flies over the water,transmitting aTheymayalso be deployed from an array towed behind the ves-laserbeam.Part of thegenerated laserbeam is reflectedbysel at some depthto eliminate corrections for vessel heave,roll,the water's surface,which isnoted by detectors.The rest pen-and pitch. Typically,as many as 16 separate transducers are ar-etratestothe seabottom and is alsopartiallyreflected,this israyed,sweepingan arc of90Thearea coveredbythese swathalso detected,Water depth can be computed from the differ-surveysvstemsisthusafunctionofwaterdepth.Inshallowwaenceintimesofreceiptofthetworeflectedpulses.Twoter, track lines must be much closer together than in deep water.different wavelength beams can also beused, one which re-This is fine with hydrographers, because shallow waters needflectsoffthesurfaceofthewater,andonewhichpenetratesmorecloselyspaceddatatoprovideanaccurateportrayaloftheand isreflectedofftheseabottom.Theobviouslimitationofbottom oncharts.The second type ofmultiplebeam system usesthis system is water clarity.However, no other system cananarrayofvertical beamtransducersriggedoutonpolesabeamsurvey at 200 or so milesper hour while operating directlythe survey vessel with transducers spaced to give overlappingover shoals,rocks,reefs,and other hazardstoboats.Bothpolar andmany tropical waters are suitableforALH systems.coveragefor thegeneral waterdepth.This is anexcellent configurationforveryshallowwater,providingverydenselyspacedDepth readings up to40meters havebeen made,and at cersoundingsfromwhichanaccuratepictureofthebottomcanbetain times of the year, some 80% of the world's coastalmadeforharborand small craft charts.Thewidthoftheswathwaters are estimated to be clear enough for ALH.HYDROGRAPHICREPORTS3006.ChartAccuraciesagencies requiresactive participationbymariners indata col-lection and reporting Examples of the type of informationrequired are reports of obstructions, shoals or hazards to navi-Thechart results froma hydrographic survey canbenogation,sea ice,soundings,currents,geophysicalphenomenamore accuratethanthe surveythe survey's accuracy,inturn, issuch as magnetic disturbances and subsurfacevolcanic eruplimited by the positioning system used. For many older charts.thepositioning system controllingdata collection involved us-tions, and marine pollution In addition, detailed reports ofharborconditionsandfacilitiesinbothbusyandout-of-the-ingtwo sextants to measurehorizontal angles between signalsestablishedashore.Theaccuracyofthismethod,andtoalesserway ports and harbors helps charting agencies keep their products current.Theresponsibility for collecting hydrographicextenttheaccuracyofmodern,shorebasedelectronicpositioning methods, deteriorates rapidly with distance.This oftendata by U.S.Naval vessels is detailed in various directives anddeterminedthemaximum scalewhichcouldbeconsideredforinstructions.Civilianmariners.becausetheyoftentraveltoathe final chart. With the advent ofthe Global Positioning Sys-widerrangeof ports,alsohavean opportunityto contributesubstantialamountsofinformation.tem(GPS)andtheestablishmentofDifferentialGPSnetworksthemariner cannownavigatewithgreater accuracythancould3008.ResponsibilityForInformationthe hydrographic surveyor who collected the chart source dataTherefore,exercisecarenottotakeshoal areasorotherhazardscloseraboard than was past practice because they may notbeTheDefenseMappingAgency,theU.S.NavalOcean-ographic Office (NAVOCEANO), the U.S. Coast Guardexactly where charted. This is in addition to the caution theand theCoast andGeodeticSurvey(C&GS)aretheprimarymarinermustexercisetobesurethathisnavigationsystemandchart are on the same datum.The potential danger to themari-agencies which receive,process, and disseminatemarinener increaseswithdigital charts becausebyzooming in,hecaninformationintheU.S.increasethechart scalebeyondwhat canbesupportedbytheDMA provides charts and chart update (Notice to Mari-source data.Theconstant and automatic update of the vesselsners)and other nautical materials for the U.S.military servicesposition onthe chartdisplay cangivethe navigatorafalsesenseand for navigators in general in waters outside the U.S.NAVOCEANO conducts hydrographic and oceano-ofsecurity,causinghimtorelyontheaccuracyofachartwhenthesourcedatafrom whichthechart was compiledcannot supgraphic surveys of primarily foreign or internationalportthe scale ofthechartdisplayed.waters,and disseminates informationtonavalforces,governmentagencies,and civilians.The Coast and Geodetic Survey (C&GS) conducts hy-3007.NavigationalAndOceanographicInformationdrographic and oceanographic surveys and provides chartsMariners at sea,because of their professional skills andfor marine and air navigation in the coastal zones of thelocation,representa uniquedata collection capability unob-United States and itsterritoriestainable by any government agency.Provision of high qualityThe U.S. Coast Guard is charged with protecting safetynavigationalandoceanographic informationbygovernmentof life and propertyat sea,maintaining aids to navigation

HYDROGRAPHY AND HYDROGRAPHIC REPORTS 415 ple-transducer, multiple-frequency sounding systems which are able to scan a wide area of seabed. Two general types are in use. Open waters are best surveyed using an array of transducers spread out athwartships across the hull of the survey vessel. They may also be deployed from an array towed behind the ves￾sel at some depth to eliminate corrections for vessel heave, roll, and pitch. Typically, as many as 16 separate transducers are ar￾rayed, sweeping an arc of 90°. The area covered by these swath survey systems is thus a function of water depth. In shallow wa￾ter, track lines must be much closer together than in deep water. This is fine with hydrographers, because shallow waters need more closely spaced data to provide an accurate portrayal of the bottom on charts. The second type of multiple beam system uses an array of vertical beam transducers rigged out on poles abeam the survey vessel with transducers spaced to give overlapping coverage for the general water depth. This is an excellent config￾uration for very shallow water, providing very densely spaced soundings from which an accurate picture of the bottom can be made for harbor and small craft charts. The width of the swath of this system is fixed by the distance between the two outermost transducers and is not dependent on water depth. A recent development is Airborne Laser Hydrogra￾phy (ALH). An aircraft flies over the water, transmitting a laser beam. Part of the generated laser beam is reflected by the water’s surface, which is noted by detectors. The rest pen￾etrates to the sea bottom and is also partially reflected; this is also detected. Water depth can be computed from the differ￾ence in times of receipt of the two reflected pulses. Two different wavelength beams can also be used, one which re￾flects off the surface of the water, and one which penetrates and is reflected off the sea bottom. The obvious limitation of this system is water clarity. However, no other system can survey at 200 or so miles per hour while operating directly over shoals, rocks, reefs, and other hazards to boats. Both po￾lar and many tropical waters are suitable for ALH systems. Depth readings up to 40 meters have been made, and at cer￾tain times of the year, some 80% of the world’s coastal waters are estimated to be clear enough for ALH. HYDROGRAPHIC REPORTS 3006. Chart Accuracies The chart results from a hydrographic survey can be no more accurate than the survey; the survey’s accuracy, in turn, is limited by the positioning system used. For many older charts, the positioning system controlling data collection involved us￾ing two sextants to measure horizontal angles between signals established ashore. The accuracy of this method, and to a lesser extent the accuracy of modern, shore based electronic position￾ing methods, deteriorates rapidly with distance. This often determined the maximum scale which could be considered for the final chart. With the advent of the Global Positioning Sys￾tem (GPS) and the establishment of Differential GPS networks, the mariner can now navigate with greater accuracy than could the hydrographic surveyor who collected the chart source data. Therefore, exercise care not to take shoal areas or other hazards closer aboard than was past practice because they may not be exactly where charted. This is in addition to the caution the mariner must exercise to be sure that his navigation system and chart are on the same datum. The potential danger to the mari￾ner increases with digital charts because by zooming in, he can increase the chart scale beyond what can be supported by the source data. The constant and automatic update of the vessels position on the chart display can give the navigator a false sense of security, causing him to rely on the accuracy of a chart when the source data from which the chart was compiled cannot sup￾port the scale of the chart displayed. 3007. Navigational And Oceanographic Information Mariners at sea, because of their professional skills and location, represent a unique data collection capability unob￾tainable by any government agency. Provision of high quality navigational and oceanographic information by government agencies requires active participation by mariners in data col￾lection and reporting. Examples of the type of information required are reports of obstructions, shoals or hazards to navi￾gation, sea ice, soundings, currents, geophysical phenomena such as magnetic disturbances and subsurface volcanic erup￾tions, and marine pollution. In addition, detailed reports of harbor conditions and facilities in both busy and out-of-the￾way ports and harbors helps charting agencies keep their prod￾ucts current. The responsibility for collecting hydrographic data by U.S. Naval vessels is detailed in various directives and instructions. Civilian mariners, because they often travel to a wider range of ports, also have an opportunity to contribute substantial amounts of information. 3008. Responsibility For Information The Defense Mapping Agency, the U.S. Naval Ocean￾ographic Office (NAVOCEANO), the U.S. Coast Guard and the Coast and Geodetic Survey (C&GS) are the primary agencies which receive, process, and disseminate marine information in the U.S. DMA provides charts and chart update (Notice to Mari￾ners) and other nautical materials for the U.S. military services and for navigators in general in waters outside the U.S. NAVOCEANO conducts hydrographic and oceano￾graphic surveys of primarily foreign or international waters, and disseminates information to naval forces, gov￾ernment agencies, and civilians. The Coast and Geodetic Survey (C&GS) conducts hy￾drographic and oceanographic surveys and provides charts for marine and air navigation in the coastal zones of the United States and its territories. The U.S. Coast Guard is charged with protecting safety of life and property at sea, maintaining aids to navigation

416HYDROGRAPHYANDHYDROGRAPHICREPORTS1.IceMariners encountering ice,icebergs,bergyand improvingthequalityofthemarineenvironment.In theexecution oftheseduties,theCoast Guard collects,analyz-bits, or growlers in the North Atlantic should report toCommander,International IcePatrol,Groton,CTthroughaes, and disseminates navigational and oceanographicdata.U.S.Coast Guard Communications Station.DirectprintingModerntechnologyallows contemporary navigators toradioteletype(SITOR)isavailablethroughUSCGCom-contributeto the body of hydrographic and oceanographicmunications Stations Bostonor Portsmouth.information.Satellitetelephone calls may bemade to the Ice Pa-troloffice in Groton, Connecticut throughout the season atNavigational reports are divided intofour categories(203)441-2626(IcePatrolDutyOfficer).MessagescanalsobesentthroughCoastGuardOperationsCenter,Bos-1.SafetyReportstonat(617)223-85552. Sounding ReportsWhen sea ice is observed, the concentration, thickness,3. Marine Data Reportsand position of the leading edge should be reported.The size,4.Port InformationReportsposition,and,ifobserved,rateand directionofdrift,along withthe local weather and sea surface temperature, should be re-The seas and coastlines continually changethrough theportedwhen icebergs,bergybits,orgrowlersareencounteredactions ofman and nature.Improvementsrealized overtheIcesightings should alsobe included intheregular syn-years in the nautical products published by DMAHTCoptic ship weather report, using the five-figure groupNOS,andU.S.CoastGuardhavebeenmadepossiblelarge-following the indicator for ice.This will assure the widestly by thereports and constructivecriticism of seagoingdistribution to all interested ships and persons.In additionobservers,bothnavalandmerchantmarine.DMAHTCandsea surfacetemperature andweatherreports should beNOS continuetorely to a great extent on the personal ob-madetoCOMINTICEPATevery6hoursbyvesselswithinservations of those who have seen the changes and canlatitude 40°N and 52°N and longitude38W and 58°W,ifacompare charts and publications with actual conditions.Inroutine weather report is not madeto METEO Washington.addition,many oceanareas and a significantportion oftheworld's coastal waters have never been adequately sur-2. Floating Derelicts—All observed floating and driftingveyedfor the purpose of producingmodern nautical charts.dangerstonavigationthat could damagethehull orpropellersInformation fromall sources is evaluated and used in theof a vessel at sea should be immediately reported by radio.TheproductionandmaintenanceofDMAHTC,NOSandCoastreportshould includea briefdescriptionofthedanger,thedateGuard charts and publications. Information from surveys,time (GMT) and the location (latitude and longitude)while originally accurate, is subject to continual change.Asit is impossible for anyhydrographic office to conduct con-3.Wrecks/Man-Made ObstructionsInformation istinuous worldwide surveys,reports of changing conditionsneededto assure accurate charting ofwrecks,man-made ob-dependonthemariner.Suchreportsprovideasteadyflowofstructions,other objects dangerousto surface and submergedvaluableinformationfromall partsoftheglobenavigation,andrepeatablesonarcontactsthatmaybeofinAftercareful analysis ofareport and comparisonwithterestto theU.S.Navy.Man-made obstructions not in useorall other data concerning the same area or subject, the orga-abandoned are particularly hazardous if unmarked andnization receiving the informationtakes appropriate action.should bereported immediately.Examples include abanIf the report is of sufficienturgencytoaffectthe immediatedonedwellheadsand pipelines,submerged platforms andsafetyofnavigation,theinformationwillbebroadcastasapilings, and disused oil structures. Ship sinkings, strandings,SafetyNETorNAVTEXmessage.Eachreportiscompareddisposals.or salvagedata are also reportable,along with anywith others and contributes in the compilation, construc-large amounts of debris, particularly metallic.tion, or correction of charts and publications.It is onlyAccuracy,especiallyin position, is vital:therefore,thethrough the constant flowof new information that chartsdate and timeof theobservation of the obstruction as well asand publications canbekeptaccurateand up-to-datethemethodused in establishingtheposition,and anestimateAconvenientDataCollectionKitis availablefreefromof thefix accuracy should be included.Reports should alsoDMAHTC and NOS sales agents and from DMAHTC Rep-includethedepthofwater,preferablymeasuredbysoundresentatives.ThestocknumberisHYDRODATAKITings (in fathoms or meters).If known, the name, tonnage,cargo,and causeof casualtyshouldbeprovided3009.SafetyReportsDataconcerning wrecks,man-madeobstructions,othersunken objects,and any salvagework shouldbeascompleteaspossible.Additional substantiating information is encouragedSafety reports are those involving navigational safetywhichmustbereported and disseminated bymessage.Thetypes of dangers to navigation whichwill bediscussed in4. ShoalsWhen a vessel discovers an uncharted or erro-this section include ice,floating derelicts, wrecks, shoals,neouslychartedshoaloranareathatisdangeroustonavigationall essential details should be immediately reported tovolcanic activity,mines,and otherhazardstoshipping

416 HYDROGRAPHY AND HYDROGRAPHIC REPORTS and improving the quality of the marine environment. In the execution of these duties, the Coast Guard collects, analyz￾es, and disseminates navigational and oceanographic data. Modern technology allows contemporary navigators to contribute to the body of hydrographic and oceanographic information. Navigational reports are divided into four categories: 1. Safety Reports 2. Sounding Reports 3. Marine Data Reports 4. Port Information Reports The seas and coastlines continually change through the actions of man and nature. Improvements realized over the years in the nautical products published by DMAHTC, NOS, and U.S. Coast Guard have been made possible large￾ly by the reports and constructive criticism of seagoing observers, both naval and merchant marine. DMAHTC and NOS continue to rely to a great extent on the personal ob￾servations of those who have seen the changes and can compare charts and publications with actual conditions. In addition, many ocean areas and a significant portion of the world’s coastal waters have never been adequately sur￾veyed for the purpose of producing modern nautical charts. Information from all sources is evaluated and used in the production and maintenance of DMAHTC, NOS and Coast Guard charts and publications. Information from surveys, while originally accurate, is subject to continual change. As it is impossible for any hydrographic office to conduct con￾tinuous worldwide surveys, reports of changing conditions depend on the mariner. Such reports provide a steady flow of valuable information from all parts of the globe. After careful analysis of a report and comparison with all other data concerning the same area or subject, the orga￾nization receiving the information takes appropriate action. If the report is of sufficient urgency to affect the immediate safety of navigation, the information will be broadcast as a SafetyNET or NAVTEX message. Each report is compared with others and contributes in the compilation, construc￾tion, or correction of charts and publications. It is only through the constant flow of new information that charts and publications can be kept accurate and up-to-date. A convenient Data Collection Kit is available free from DMAHTC and NOS sales agents and from DMAHTC Rep￾resentatives. The stock number is HYDRODATAKIT. 3009. Safety Reports Safety reports are those involving navigational safety which must be reported and disseminated by message. The types of dangers to navigation which will be discussed in this section include ice, floating derelicts, wrecks, shoals, volcanic activity, mines, and other hazards to shipping. 1. Ice—Mariners encountering ice, icebergs, bergy bits, or growlers in the North Atlantic should report to Commander, International Ice Patrol, Groton, CT through a U.S. Coast Guard Communications Station. Direct printing radio teletype (SITOR) is available through USCG Com￾munications Stations Boston or Portsmouth. Satellite telephone calls may be made to the Ice Pa￾troloffice in Groton, Connecticut throughout the season at (203) 441-2626 (Ice Patrol Duty Officer). Messages can also be sent through Coast Guard Operations Center, Bos￾ton at (617) 223-8555. When sea ice is observed, the concentration, thickness, and position of the leading edge should be reported. The size, position, and, if observed, rate and direction of drift, along with the local weather and sea surface temperature, should be re￾ported when icebergs, bergy bits, or growlers are encountered. Ice sightings should also be included in the regular syn￾optic ship weather report, using the five-figure group following the indicator for ice. This will assure the widest distribution to all interested ships and persons. In addition, sea surface temperature and weather reports should be made to COMINTICEPAT every 6 hours by vessels within latitude 40°N and 52°N and longitude 38°W and 58°W, if a routine weather report is not made to METEO Washington. 2. Floating Derelicts—All observed floating and drifting dangers to navigation that could damage the hull or propellers of a vessel at sea should be immediately reported by radio. The report should include a brief description of the danger, the date, time (GMT) and the location (latitude and longitude). 3.Wrecks/Man-Made Obstructions—Information is needed to assure accurate charting of wrecks, man-made ob￾structions, other objects dangerous to surface and submerged navigation, and repeatable sonar contacts that may be of in￾terest to the U.S. Navy. Man-made obstructions not in use or abandoned are particularly hazardous if unmarked and should be reported immediately. Examples include aban￾doned wellheads and pipelines, submerged platforms and pilings, and disused oil structures. Ship sinkings, strandings, disposals. or salvage data are also reportable, along with any large amounts of debris, particularly metallic. Accuracy, especially in position, is vital: therefore, the date and time of the observation of the obstruction as well as the method used in establishing the position, and an estimate of the fix accuracy should be included. Reports should also include the depth of water, preferably measured by sound￾ings (in fathoms or meters). If known, the name, tonnage, cargo, and cause of casualty should be provided. Data concerning wrecks, man-made obstructions, other sunken objects, and any salvage work should be as complete as possible. Additional substantiating information is encouraged. 4. Shoals—When a vessel discovers an uncharted or erro￾neously charted shoal or an area that is dangerous to navigation, all essential details should be immediately reported to

417HYDROGRAPHYANDHYDROGRAPHICREPORTSDMAHTCWASHINGTONDCviaradio.Anuncharteddepthno stormwarninghasbeen received,isbound tocommuni-of300fathomsorless isconsideredan urgentdangertosubma-cate the informationby all means at his disposal to ships inrinenavigation.Immediatelyuponreceiptofmessagesreportingthevicinity.andalsotothecompetentauthoritiesatthefirstdangersto navigation,DMAHTC issues appropriateNAVARpoint on the coast with which he can communicate."EA warnings. The information must appear on published chartsThe report should be broadcast first on 2182 kHz pre-as“reported"until sufficient substantiating evidence (ie. clearfixed bythe safety signal"SECURITE."This should beand properly annotated echograms and navigation logs, and anyfollowed by transmission of themessageon a suitableother supporting information)is received.working frequency to the proper shore authorities.TheTherefore,originators of shoal reports are requested totransmissionofinformationregardingice,derelicts,tropi-verifyandforwardall substantiatingevidencetoDMAHTCcal storms. orany other direct danger to navigation isat the earliest opportunity.It cannot be overemphasized thatobligatory.Theform in which the information is sent isnotclear and properly annotated echograms and navigationobligatory.It maybe transmitted either inplain languagelogs areespeciallyimportant in shoal reports.(preferablyEnglish)orbyanymeansofInternationalCodeof Signals (wireless telegraphy section).It should be issued5.Volcanic Activity—Volcanic disturbances may beCQto all ships and should also be sent to thefirst stationobservedfromshipsinmanypartsoftheworldOnoccasion,with which communication can be made with the requestvolcaniceruptionsmayoccurbeneaththe surfaceofthewa-that it be transmitted to the appropriate authority.A vesselter.These submarine eruptions may occur more frequentlywill not be charged for radio messages to government au-and bemore widespread than has been suspected in the past.thorities reporting dangers to navigation.Sometimestheonlyevidenceofa submarineeruption is ano-Eachradio report ofa danger to navigation should an-ticeable discoloration of the water, a marked rise in seaswer briefly three questions:surface temperature, or floating pumice.Mariners witnessingsubmarine activity have reported steams with a foul sulfu-1.What?Adescriptionto oftheobject or phenomenonrous odor rising fromthe sea surface,and strange sounds2.Where?Latitudeand longitudeheard throughthehull, including shocksresemblinga sudden3.When?GreenwichMeanTime(GMT)anddategrounding.Asubseavolcaniceruptionmaybeaccompaniedbyrumbling andhissingashot lavameets thecold sea.Examples:In somecases,reports of discolored water atthe sea surface have been investigated and found to be the result ofnewlyIceformed volcanicconesonthesea floor.Thesecones cangrowrapidly (within a few years) to constitute a hazardous shoal.SECURITE.ICE:LARGE BERG SIGHTED DRIFT-Itisimperativethatamarinerreportevidenceofvolca-INGSWAT.5KT4605N,4410W,AT0800GMT,MAY15.nic activity immediately to DMAHTC by messageAdditional substantiating information is encouraged.Derelicts6.MinesAll mines orobjectsresemblingminesSECURITE.DERELICT:OBSERVEDWOODEN25should be considered armedand dangerous.An immediateMETER DERELICT ALMOST SUBMERGED ATradio reportto DMAHTC should include (ifpossible):4406N,1243WAT1530GMT,APRIL21.GreenwichMeanTimeanddateThe report should be addressed to one of the following2.Positionofmine,andhownearitwasapproachedshore authorities as appropriate:3.Size, shape, color, condition of paint, and presenceofmarinegrowth.1.U.S.Inland WatersCommanderoftheLocal4.Presenceor absence of horns or rings.Coast Guard District.5.Certainty of identification.2.OutsideU.S.Waters-DMAHTCWASHINGTONDC.3010. Instructions For Safety Report MessagesWhenever possible, messages should be transmittedThe International ConventionfortheSafetyof Lifeatvia the nearestgovermment radio station.If it is impracticalSea (1974),which is applicable to all U.S.flag ships,re-to usea governmentstation,a commercial stationmaybequires:"The master of every ship which meets withused.U.S.government navigational warning messagesdangerous ice, dangerous derelict, or any other direct dan-should invariably be sent through U.S.radio stations,gov-ger to navigation, or a tropical storm,or encountersernmentorcommercial,and neverthroughforeign stations.subfreezing airtemperatures associated with gale forceDetailed instructions for reporting via radio are con-winds causing severe ice accretion on superstructures,ortained inDMAHTCPub.II7,RadioNavigationAids.windsofforce10oraboveontheBeaufortscaleforwhich

HYDROGRAPHY AND HYDROGRAPHIC REPORTS 417 DMAHTC WASHINGTON DC via radio. An uncharted depth of 300 fathoms or less is considered an urgent danger to subma￾rine navigation. Immediately upon receipt of messages reporting dangers to navigation, DMAHTC issues appropriate NAVAR￾EA warnings. The information must appear on published charts as “reported” until sufficient substantiating evidence (i.e. clear and properly annotated echograms and navigation logs, and any other supporting information) is received. Therefore, originators of shoal reports are requested to verify and forward all substantiating evidence to DMAHTC at the earliest opportunity. It cannot be overemphasized that clear and properly annotated echograms and navigation logs are especially important in shoal reports. 5. Volcanic Activity—Volcanic disturbances may be observed from ships in many parts of the world. On occasion, volcanic eruptions may occur beneath the surface of the wa￾ter. These submarine eruptions may occur more frequently and be more widespread than has been suspected in the past. Sometimes the only evidence of a submarine eruption is a no￾ticeable discoloration of the water, a marked rise in sea surface temperature, or floating pumice. Mariners witnessing submarine activity have reported steams with a foul sulfu￾rous odor rising from the sea surface, and strange sounds heard through the hull, including shocks resembling a sudden grounding. A subsea volcanic eruption may be accompanied by rumbling and hissing as hot lava meets the cold sea. In some cases, reports of discolored water at the sea sur￾face have been investigated and found to be the result of newly formed volcanic cones on the sea floor. These cones can grow rapidly (within a few years) to constitute a hazardous shoal. It is imperative that a mariner report evidence of volca￾nic activity immediately to DMAHTC by message. Additional substantiating information is encouraged. 6. Mines—All mines or objects resembling mines should be considered armed and dangerous. An immediate radio report to DMAHTC should include (if possible): 1. Greenwich Mean Time and date. 2. Position of mine, and how near it was approached. 3. Size, shape, color, condition of paint, and presence of marine growth. 4. Presence or absence of horns or rings. 5. Certainty of identification. 3010. Instructions For Safety Report Messages The International Convention for the Safety of Life at Sea (1974), which is applicable to all U.S. flag ships, re￾quires: “The master of every ship which meets with dangerous ice, dangerous derelict, or any other direct dan￾ger to navigation, or a tropical storm, or encounters subfreezing air temperatures associated with gale force winds causing severe ice accretion on superstructures, or winds of force 10 or above on the Beaufort scale for which no storm warning has been received, is bound to communi￾cate the information by all means at his disposal to ships in the vicinity, and also to the competent authorities at the first point on the coast with which he can communicate.” The report should be broadcast first on 2182 kHz pre￾fixed by the safety signal “SECURITE.” This should be followed by transmission of the message on a suitable working frequency to the proper shore authorities. The transmission of information regarding ice, derelicts, tropi￾cal storms, or any other direct danger to navigation is obligatory. The form in which the information is sent is not obligatory. It may be transmitted either in plain language (preferably English) or by any means of International Code of Signals (wireless telegraphy section). It should be issued CQ to all ships and should also be sent to the first station with which communication can be made with the request that it be transmitted to the appropriate authority. A vessel will not be charged for radio messages to government au￾thorities reporting dangers to navigation. Each radio report of a danger to navigation should an￾swer briefly three questions: 1. What? A description to of the object or phenomenon. 2. Where? Latitude and longitude. 3. When? Greenwich Mean Time (GMT) and date. Examples: Ice SECURITE. ICE: LARGE BERG SIGHTED DRIFT￾ING SW AT .5 KT 4605N, 4410W, AT 0800 GMT, MAY 15. Derelicts SECURITE. DERELICT: OBSERVED WOODEN 25 METER DERELICT ALMOST SUBMERGED AT 4406N, 1243W AT 1530 GMT, APRIL 21. The report should be addressed to one of the following shore authorities as appropriate: 1. U.S. Inland Waters—Commander of the Local Coast Guard District. 2. Outside U.S. Waters—DMAHTC WASHINGTON, DC. Whenever possible, messages should be transmitted via the nearest government radio station. If it is impractical to use a government station, a commercial station may be used. U.S. government navigational warning messages should invariably be sent through U.S. radio stations, gov￾ernment or commercial, and never through foreign stations. Detailed instructions for reporting via radio are con￾tained in DMAHTC Pub. 117, Radio Navigation Aids

418HYDROGRAPHYANDHYDROGRAPHICREPORTSOCEANICSOUNDINGREPORTS3011.SoundingReportscharts are probably based on encounters with the DeepScattering Layer (DSL), ambient noise, or, on rare occa-Acquisitionofreliablesoundingdatafromalloceanar-sions,submarine earthquakes.Whileeachappearsrealeas of the world is a continuing effort of DMAHTCenoughatthetimeof itsoccurrence.aknowledgeoftheNAVOCEANO,and NOS.There are vast ocean areaseventsthatnormallyaccompanythese incidentsmaypre-vent erroneous data from becoming a charted feature.wherefewsoundingshave everbeen acquired.MuchoftheThe DSL is found in most parts of the world.It consistsbathymetricdata shown on chartshas been compiledfrominformationsubmittedbymariners.Continuedcooperationofaconcentrationofmarinelifewhichdescendsfromnearin observing and submitting sounding data is absolutelythe surface at sunrise to an approximate depth of200 fath-necessary to enablethe compilation of accurate charts.omsduringtheday.ItreturnsnearthesurfaceatsunsetCompliance with sounding data collectionprocedures byAlthough at times the DSL maybe so concentrated that itmerchant ships is voluntary,butforU.S.Naval vesselswill completelymask thebottom, usuallythebottom returncompliance is required under various fleetdirectives.can be identified at its normal depth at the same time theDSLisbeingrecorded3012.Areas Where Soundings Are NeededAmbientnoise or interferencefrom othersources cancause erroneous data.This interferencemay comefrom equip-Prior to a voyage, navigators can determine the impor-ment on board the ship,from anothertransducerbeingtance of recording sounding databychecking thecharts foroperatedcloseby,orfrom waterbornenoise.Mostofthesere-the route.Any ship crossing a densely sounded shippingturns can bereadily identifiedontheecho sounderrecords andlaneperpendicularor nearlyperpendicularto the lane canshouldcausenomajorproblems;however,onoccasiontheyobtainveryusefulsoundingdatadespitethedensity.Suchmaybesostrongandconsistentastoappearasthetruebottom.tracks providecrosschecks forverifying existing data. Oth-Finally,a volcanic disturbancebeneath the ship or inerindications that soundings maybe particularlyuseful arethe immediate vicinitymaygive erroneous indications of ashoal. The experience has at times been described as similarOld sources listed on source diagram or sourcenote1.to running aground or striking a submerged object.Regard-on chart.less of whether thefeature is an actual shoal or a submarine2.Absenceof soundings in largeareaseruption the positions, date/time,and other informationPresenceofsoundings,butonlyalong well-defined3.shouldbepromptlyreportedtoDMAHTC.lines indicating the track of the sounding vessel,withfewor no soundingbetweentracks.3015.Doubtful Hydrographic Data4.Legends such as"Unexplored area."Navigators are stronglyrequested to assist with the3013.FixAccuracyconfirmation and proper charting of actual shoals and theremoval fromthecharts ofdoubtfuldata which was errone-Arealisticgoalofopenocean positioningforsoundingously reported.reports is ±1 nautical mile withthe continuous use ofGPS.The classification or confidence level assigned toHowever,depthsof300fathomsorlessshouldalwaysbedoubtful hydrographic data is indicated by the followingreportedregardless ofthefixaccuracy.When suchdepthsstandard symbols:areunchartedorerroneouslycharted.thevshouldbereportAbbreviationMeaninged by message to DMAHTC WASHINGTON DC, givingthebestavailablepositioningaccuracy.Echogramsandother supporting information shouldthen beforwarded byRep (date)Reported (year)E.D.ExistenceDoubtfulmailtoDMAHTC.P.A.The accuracy goal noted above has been established toPositionApproximateP.D.Position Doubtfulenable DMAHTC to create a highquality data base whichwill support the compilation of accurate nautical charts.ItMany of these reported features are sufficiently deepisparticularly importantthatreportscontainthenavigator'sbest estimate of his fix accuracy and that the positioningthat if valid, a ship can safely navigate across the area. Con-aids being used (GPS, Loran C, etc.) be identified.firmation of the existenceofthe feature will result in propercharting.On theother hand,properlycollected and annotated3014.FalseShoalssounding reports of theareamayenableDMAHTCtoaccu-mulate sufficient evidence to justify the removal of theMany poorly identified shoals and banks shown onsounding from the chart

418 HYDROGRAPHY AND HYDROGRAPHIC REPORTS OCEANIC SOUNDING REPORTS 3011. Sounding Reports Acquisition of reliable sounding data from all ocean ar￾eas of the world is a continuing effort of DMAHTC, NAVOCEANO, and NOS. There are vast ocean areas where few soundings have ever been acquired. Much of the bathymetric data shown on charts has been compiled from information submitted by mariners. Continued cooperation in observing and submitting sounding data is absolutely necessary to enable the compilation of accurate charts. Compliance with sounding data collection procedures by merchant ships is voluntary, but for U.S. Naval vessels compliance is required under various fleet directives. 3012. Areas Where Soundings Are Needed Prior to a voyage, navigators can determine the impor￾tance of recording sounding data by checking the charts for the route. Any ship crossing a densely sounded shipping lane perpendicular or nearly perpendicular to the lane can obtain very useful sounding data despite the density. Such tracks provide cross checks for verifying existing data. Oth￾er indications that soundings may be particularly useful are: 1. Old sources listed on source diagram or source note on chart. 2. Absence of soundings in large areas. 3. Presence of soundings, but only along well-defined lines indicating the track of the sounding vessel, with few or no sounding between tracks. 4. Legends such as “Unexplored area.” 3013. Fix Accuracy A realistic goal of open ocean positioning for sounding reports is ±1 nautical mile with the continuous use of GPS. However, depths of 300 fathoms or less should always be reported regardless of the fix accuracy. When such depths are uncharted or erroneously charted, they should be report￾ed by message to DMAHTC WASHINGTON DC, giving the best available positioning accuracy. Echograms and other supporting information should then be forwarded by mail to DMAHTC. The accuracy goal noted above has been established to enable DMAHTC to create a high quality data base which will support the compilation of accurate nautical charts. It is particularly important that reports contain the navigator’s best estimate of his fix accuracy and that the positioning aids being used (GPS, Loran C, etc.) be identified. 3014. False Shoals Many poorly identified shoals and banks shown on charts are probably based on encounters with the Deep Scattering Layer (DSL), ambient noise, or, on rare occa￾sions, submarine earthquakes. While each appears real enough at the time of its occurrence, a knowledge of the events that normally accompany these incidents may pre￾vent erroneous data from becoming a charted feature. The DSL is found in most parts of the world. It consists of a concentration of marine life which descends from near the surface at sunrise to an approximate depth of 200 fath￾oms during the day. It returns near the surface at sunset. Although at times the DSL may be so concentrated that it will completely mask the bottom, usually the bottom return can be identified at its normal depth at the same time the DSL is being recorded. Ambient noise or interference from other sources can cause erroneous data. This interference may come from equip￾ment on board the ship, from another transducer being operated close by, or from waterborne noise. Most of these re￾turns can be readily identified on the echo sounder records and should cause no major problems; however, on occasion they may be so strong and consistent as to appear as the true bottom. Finally, a volcanic disturbance beneath the ship or in the immediate vicinity may give erroneous indications of a shoal. The experience has at times been described as similar to running aground or striking a submerged object. Regard￾less of whether the feature is an actual shoal or a submarine eruption the positions, date/time, and other information should be promptly reported to DMAHTC. 3015. Doubtful Hydrographic Data Navigators are strongly requested to assist with the confirmation and proper charting of actual shoals and the removal from the charts of doubtful data which was errone￾ously reported. The classification or confidence level assigned to doubtful hydrographic data is indicated by the following standard symbols: Many of these reported features are sufficiently deep that if valid, a ship can safely navigate across the area. Con￾firmation of the existence of the feature will result in proper charting. On the other hand, properly collected and annotated sounding reports of the area may enable DMAHTC to accu￾mulate sufficient evidence to justify the removal of the sounding from the chart. Abbreviation Meaning Rep (date) Reported (year) E.D. Existence Doubtful P.A. Position Approximate P.D. Position Doubtful

419HYDROGRAPHYANDHYDROGRAPHICREPORTS3016.Preparation Of Sounding Reportsclearly written on the echogram to ensure maximum use ofthe recorded depths:1. Ship's name—At the beginning and end of each rollThe proceduresfor preparing sounding reports haveofechogramorportion.been designedtominimizetheefforts of theshipboard ob-servers, yet provide the essential information needed by2.DateAnnotatedat1200hourseachdayandwhenDMAHTC.BlankOCEANICSOUNDING REPORTstarting and stopping the echo sounder, or at leastformsareavailablefromDMAHTCasastock itemoronce per roll.through DMA Representatives in Los Angeles/Long3.Time-Theechogramshouldbeannotated atthebe-Beach,New Orleans, and Washington,D.C.Submission ofginning of the sounding run, at least once each hourplottedsounding tracksisnotrequired.Annotatedthereafter, at every scale change, and at all breaks inechograms and navigation logs are preferred. The proce-the echogramrecord.Accuracy of thesetime marksdure for collecting sounding reports is for the shiptois critical for correlation with ship's position.operate a recording echo sounder while transiting an area4.TimeZone-GreenwichMeanTime (GMT)shouldwhere soundings are desired.Fixes and course changes arebe used if practicable.In theevent local zonetimesrecorded in the log,and theevent marker isused to noteare used, annotateechogram whenever clocks arere-these events on the echogram.Both thelog and echogramset and identify zonetime in use.It is most importantcan then be senttoDMAHTC whenever convenient.that the echogram and navigation log use the sameThe following annotations or information should betime basis.OfathomsofathomsofathonsSserus7INNiINLEL9019090EIOPOO.NAG"Cn,1264391025easENTI1boofatham2bo0ofathoms?6000fathams2Figure3016a.Properlyannotatedecho soundingrecordNAVIGATIONLOGREMARKS3NAY.LAT.LONG,FOURSESPEEDDATEF29r0240CEAEN09372.30/20231097"12.30340CHANGETOURSENEON29'40k12435709*12.30400TEAAW29'3525'220097*12.36728NARARUSREPACEENEB-MANUVERNGBOMTO08106.2TOANVDFIJMNETSAA234235860979RESUMNECOURSE AND SREED082612-3097*12.329'st's'se'r1011TARKWCHAUGECOURSE252312710212:416202230810272.52305102*10.7PEpucESPEEDFigure 3016b. Typical navigation log for hydrographic reporting

HYDROGRAPHY AND HYDROGRAPHIC REPORTS 419 3016. Preparation Of Sounding Reports The procedures for preparing sounding reports have been designed to minimize the efforts of the shipboard ob￾servers, yet provide the essential information needed by DMAHTC. Blank OCEANIC SOUNDING REPORT forms are available from DMAHTC as a stock item or through DMA Representatives in Los Angeles/Long Beach, New Orleans, and Washington, D.C. Submission of plotted sounding tracks is not required. Annotated echograms and navigation logs are preferred. The proce￾dure for collecting sounding reports is for the ship to operate a recording echo sounder while transiting an area where soundings are desired. Fixes and course changes are recorded in the log, and the event marker is used to note these events on the echogram. Both the log and echogram can then be sent to DMAHTC whenever convenient. The following annotations or information should be clearly written on the echogram to ensure maximum use of the recorded depths: 1. Ship’s name—At the beginning and end of each roll of echogram or portion. 2. Date—Annotated at 1200 hours each day and when starting and stopping the echo sounder, or at least once per roll. 3. Time—The echogram should be annotated at the be￾ginning of the sounding run, at least once each hour thereafter, at every scale change, and at all breaks in the echogram record. Accuracy of these time marks is critical for correlation with ship’s position. 4.Time Zone—Greenwich Mean Time (GMT) should be used if practicable. In the event local zone times are used, annotate echogram whenever clocks are re￾set and identify zone time in use. It is most important that the echogram and navigation log use the same time basis. Figure 3016a. Properly annotated echo sounding record. Figure 3016b. Typical navigation log for hydrographic reporting

420HYDROGRAPHYANDHYDROGRAPHICREPORTSfloor.This is helpful to our Naval forces and particularlyto5.Phase or scale changes-If echosounderdoes notindicate scale setting on echogram automatically,the submarine fleet, but is also useful to geologists, geo-clearly label all depthphase (or depth scale)changesphysicists, and other scientific disciplines.and the exact time they occur.Annotatethe upperAreport of oceanic soundings should contain theand lower limits of the echogram if necessary.following:1.Acompleted Oceanic SoundingReport,FormFigure3016a andFigure3016b illustrates thedatanec-DMAHTC8053/1.essaryto reconstructa soundingtrack.If ship operations2.Adetailed Navigation Logdictatethat only periodic single ping soundings can be ob-3.The echo sounding trace, properly annotated.tained, thedepthsmaybe recorded in the Remarks column.Each page of the report should be clearly marked withA properly annotated echogram is always strongly pre-the ship's name and date, so that it can be identified ifitbefered by DMAHTC over single ping soundings whenevercomes separated.Mail the report to:operationspermit.Thenavigation log is vital totherecon-struction of a sounding track.Without the positioninformation from thelog,theechogram is virtuallyuseless.The data received from these reports is digitized andDirectorbecomespart of the digital bathymetric data library ofDMAHydrographic/Topographic CenterDMAHTC.This library is used as the basis of new chartMC,D-40compilation. Even in areas where numerous soundings al-4600 Sangamore Rd.readyexist,soundingreports allowvaluablecross-checkingBethesda,MD,20816-5003to verify existingdata and more accurately portray the seaOTHERHYDROGRAPHICREPORTS3017.MarineInformationReportsobjects,thepositionmaybeexpressedasbearingsand ranges from them.Bearings should preferablyMarine Information Reports are reports of items ofbe reported as true and expressed indegrees.5.Alwaysreportthelimitingbearingsfromtheshipnavigational interest such as thefollowing:toward the light when describingthe sectors in1.Discrepanciesinpublished information.whicha light is either visible or obscured.Although2.Changes in aidsto navigation.thisisjustthereverseoftheformusedtolocateob-3.Electronicnavigationreports.jects, it is the standardmethod used on DMAHTC4.Satellitenavigationreports.nautical charts and in Light Lists.5.Radarnavigation reports.6.Areportpreparedbyonepersonshould,ifpossiblebe checked by another.6.MagneticdisturbancesReport any marineinformation whichyoubelieveInmostcasesmarineinformationcanbeadequatelyre-may be useful to charting authorities or other mariners.ported ononeofthevariousformsprinted byDMAHTCorDepending on thetype of report, certain items of infor-NOS.Itmaybemoreconvenienttoannotateinformationmation are absolutely critical for a correct evaluation.directly on the affected chart and mail it to DMAHTC. AsThefollowing general suggestions are offered to assist inan example, it may be useful to sketch uncharted or errone-ously charted shoals, buildings, or geological featuresreporting information that will beof maximum value:directly on the chart.Appropriate supporting information1.The geographical position included in the reportshould also be provided.DMAHTCforwards reports applicabletoNOS,NAV-maybe used to correct charts.Accordingly,itOCEANO,or CoastGuardproductstotheappropriateshouldbefixedbythemostexactmethodavailablemorethan one if possible.agency2.Reports by letter are just as acceptable as those pre-Ifgeographical coordinates areusedtoreportposi-tion, they should be as exact as circumstancespared on regular forms.A letter report will often allowpermit.Reference should bemadetothe chartbymore flexibility in reporting details, conclusions, or recom-number,edition number,and datemendationsconcerningtheobservation.Whenreportingon3.The report should state the method used to fix thetheregularforms,if necessary use additional sheetsto com-position and anestimateof fixaccuracyplete the details of an observation.When reporting a position within sight of charted4.Reportsarerequiredconcerninganyerrors ininformation

420 HYDROGRAPHY AND HYDROGRAPHIC REPORTS 5. Phase or scale changes—If echosounder does not indicate scale setting on echogram automatically, clearly label all depth phase (or depth scale) changes and the exact time they occur. Annotate the upper and lower limits of the echogram if necessary. Figure 3016a and Figure 3016b illustrates the data nec￾essary to reconstruct a sounding track. If ship operations dictate that only periodic single ping soundings can be ob￾tained, the depths may be recorded in the Remarks column. A properly annotated echogram is always strongly pre￾ferred by DMAHTC over single ping soundings whenever operations permit. The navigation log is vital to the recon￾struction of a sounding track. Without the position information from the log, the echogram is virtually useless. The data received from these reports is digitized and becomes part of the digital bathymetric data library of DMAHTC. This library is used as the basis of new chart compilation. Even in areas where numerous soundings al￾ready exist, sounding reports allow valuable cross-checking to verify existing data and more accurately portray the sea floor. This is helpful to our Naval forces and particularly to the submarine fleet, but is also useful to geologists, geo￾physicists, and other scientific disciplines. A report of oceanic soundings should contain the following: 1. A completed Oceanic Sounding Report, Form DMAHTC 8053/1. 2. A detailed Navigation Log. 3. The echo sounding trace, properly annotated. Each page of the report should be clearly marked with the ship’s name and date, so that it can be identified if it be￾comes separated. Mail the report to: Director DMA Hydrographic/Topographic Center MC, D-40 4600 Sangamore Rd. Bethesda, MD, 20816-5003 OTHER HYDROGRAPHIC REPORTS 3017. Marine Information Reports Marine Information Reports are reports of items of navigational interest such as the following: 1. Discrepancies in published information. 2. Changes in aids to navigation. 3. Electronic navigation reports. 4. Satellite navigation reports. 5. Radar navigation reports. 6. Magnetic disturbances. Report any marine information which you believe may be useful to charting authorities or other mariners. Depending on the type of report, certain items of infor￾mation are absolutely critical for a correct evaluation. The following general suggestions are offered to assist in reporting information that will be of maximum value: 1. The geographical position included in the report may be used to correct charts. Accordingly, it should be fixed by the most exact method available, more than one if possible. 2. If geographical coordinates are used to report posi￾tion, they should be as exact as circumstances permit. Reference should be made to the chart by number, edition number, and date. 3. The report should state the method used to fix the position and an estimate of fix accuracy. 4. When reporting a position within sight of charted objects, the position may be expressed as bearings and ranges from them. Bearings should preferably be reported as true and expressed in degrees. 5. Always report the limiting bearings from the ship toward the light when describing the sectors in which a light is either visible or obscured. Although this is just the reverse of the form used to locate ob￾jects, it is the standard method used on DMAHTC nautical charts and in Light Lists. 6. A report prepared by one person should, if possible, be checked by another. In most cases marine information can be adequately re￾ported on one of the various forms printed by DMAHTC or NOS. It may be more convenient to annotate information directly on the affected chart and mail it to DMAHTC. As an example, it may be useful to sketch uncharted or errone￾ously charted shoals, buildings, or geological features directly on the chart. Appropriate supporting information should also be provided. DMAHTC forwards reports applicable to NOS, NAV￾OCEANO, or Coast Guard products to the appropriate agency. Reports by letter are just as acceptable as those pre￾pared on regular forms. A letter report will often allow more flexibility in reporting details, conclusions, or recom￾mendations concerning the observation. When reporting on the regular forms, if necessary use additional sheets to com￾plete the details of an observation. Reports are required concerning any errors in information