1、Designation: D 6318 03Standard Practice forCalibrating a Fathometer Using a Bar Check Method1This standard is issued under the fixed designation D 6318; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n
2、umber in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice provides the user with procedures used inmanually calibrating the fathometer or electronic depthsounder. This narrative
3、describes calibration terminology, de-scribes acceptable environmental conditions for calibration,and describes the calibration procedures.1.2 The references cited contain useful information in theconstruction and the correct operation of the calibration equip-ment.1.3 Any references cited in this n
4、arrative to specific prod-ucts or brand names are made for information only, and isintended to be descriptive, but not restrictive, of products thatwill perform satisfactorily.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsib
5、ility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 1129 Definition of Terms Relating to WaterD 5073 Practice for Depth Measurement of Surface Wate
6、r3. Terminology3.1 Refer to Terminology D 1129 for terms used in thisguide.3.2 Definitions of Terms Specific to This Standard:3.2.1 bara section of metallic channel, I-beam, T-beam,pipe, plate, or ball that will reflect sound waves produced by afathometer.3.2.2 bar-checka method for calibrating a fa
7、thometer bysetting a sound or accoustic reflector (bar) below a surveyvessel to a known depth below a sounding transducer.3.2.3 draft (transducer draft)the vertical distance fromthe bottom of the transducer to the surface of the water.3.2.4 fathometerAn electronic device for registeringdepths of wat
8、er by measuring the time required for thetransmission and reflection of sound waves between a sonictransducer and the lake or river bottom.3.2.5 soundto determine the depth of water.3.2.6 sounding scrollthe chart record of an underwatercross section or profile of the bottom.3.2.7 transducera device
9、for translating electrical energyto acoustical energy and acoustical energy back to electricalenergy.4. Significance and Use4.1 The accuracy of depth measurements made by a fath-ometer or echo sounder requires a number of correctionsbecause of the variability of sound or acoustic velocity in waterwi
10、th changes in temperature, salinity, and depth of water. Inaddition instability of the equipment can also result in signifi-cant errors. For additional information see Practice D 5073.4.2 Calibration of echo sounding instruments is absolutelycritical in assuring the adequacy of depth measurements. W
11、henan echo sounder has been accurately calibrated, any observed(recorded) depth can be related to the true depth of water. Sincethe intended purpose of echo sounding is to measure the “true”depth, an independent “true” reference must be used.4.3 A bar-check is the most wide-spread, easiest to con-st
12、ruct, and most economical mechanical method to determinecorrections for instrument and velocity errors.4.4 This procedure explains the calibration of a fathometeror electronic depth sounder using a bar-check.4.5 Bar-checking techniques and equipment are general innature and may need to be modified f
13、or use in specific fieldconditions.5. Apparatus5.1 The device used for bar-checking must be a sound-reflecting surface that can be lowered to a known depth belowthe transducer of the survey vessel. See Fig. 1. These sounding-refecting surfaces (or sounding targets) can be a bar made outof a section
14、of metallic I-beam or T-beam, pipe, a rectangularsection of sheet metal, or a section of metal screen.5.2 Bars used in depths greater than 30 ft (10 m) should beat least 9 in. (23 cm) wide. The dimensions of the target dependon the type of survey vessel, location of the transducer, and the1This prac
15、tice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphologyand Open-Channel Flow.Current edition approved Aug. 10, 2003. Published October 2003. Originallyapproved in 1998. Last previous edition approved in 1998 as
16、D 6318 98.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.depth range to be covered during the survey. Usually, thelength of the bar is equal to the beam or width for
17、small surveyvessels. For larger vessels, a spherical metal ball or steel plateis lowered through a well in the hull.5.3 The weight of the bar will be dependent on the type ofcurrents experienced, typical project depths, and beam of thevessel. Typical weights range from 40 to 100 lb (20 to 50 kg).In
18、deep water areas with large currents, a heavy bar is essentialbecause subsurface currents will pull to light a bar from thetransducers vertical plane. On small, shallow inland or pro-tected bodies of water, a lighter weight may be used providedthe bar can be maintained directly beneath the transduce
19、r.5.4 The lines used for lowering the bar should be made offlexible steel wire or chain. They must be easy to handle andmust not stretch. In addition, they should be at least 100 ft longwith either easily visible markings at every 10 ft starting at thetop of the bar or carried on a calibrated reel.
20、The bar checksuspension lines must be periodically checked to ensure theaccuracy and stability of the graduated marks on the line6. Condition Requirements6.1 The preferred environmental conditions for bar-checking are calm water, wind velocity less than 5 mph, anddepths less than 100 ft. Reasonable
21、results, however, can beobtained during wind velocities between 5 and 15 mph. Butwhen wind velocities are greater than 15 mph and depthsgreater than 100 ft, some error will exist in the soundings.6.2 Bar checks should always be made when and wherewater conditions are calmest; observations taken duri
22、ng roughwater conditions or when differential current causes the bar tobe displaced from a position vertically below the transducer aresubject to unacceptable magnitudes of error.6.3 For best results where salinity and temperature of thewater are unknown, the fathometer should be calibrated beforeth
23、e start, at midday and at the end of each days work to checkthe accuracy of the soundings. However, if stable waterconditions are known to exist, it is possible to limit the numberof bar-checks to one per day before the start of the work.6.4 A survey vessel operating in exposed rough water orwindy c
24、onditions should run to a protected area for the barcheck. Bar checks, however, should not be made in areas wheresalinity, temperatures, and suspended sediment concentrationsvary significantly from those at the area to be surveyed.7. Bar-check Procedure7.1 Turn the fathometer on about 10 min before
25、beginningthe calibration process to allow the machine to warm up.7.2 Set initial fathometer settings (tide and draft, speed ofsound, etc.) according to the fathometer manufacturers speci-fications.7.3 Two depths are chosen that correspond to the minimumand maximum calibration range, such as 10 ft an
26、d 50 ft.7.4 Lower the bar into the water to the 10 ft mark on thelowering line. WARNING: MAKE SURE FEETARE CLEAROF THE LOWERING LINES TO PREVENT ENTANGLE-MENT. Make sure that the bar is centered directly underneaththe transducer. Failure to do so will result in false or erroneousreadings.7.5 Adjust
27、the “draft” fathometer settings so that the depthtracing on the sounding scroll or digital reading matches the 10ft depth reading.7.6 Lower the bar to the increment mark on the loweringline closest to the greatest anticipated sounding depth, such as50 ft.7.7 Adjust the “sound velocity” fathometer se
28、ttings so thatthe depth tracing on the sounding scroll or digital readingmatches the 50 ft depth.FIG. 1 Calibration Bar ApparatusD63180327.8 Raise the bar to the 10 ft position. If there is no changethe echosounder is calibrated. If there is a difference, readjustthe “draft” fathometer settings to m
29、atch 10 ft.7.9 Repeat steps 7.4-7.8 as necessary until the correctfathometer settings are obtained for both deep and shallowwater.7.10 Upon completion of calibration intermediate readingsshould be checked to compare fathometer readings with knownbar depths. For this example readings could be taken a
30、t ten-footincrements such as 20, 30, and 40 ft depths.7.11 If the velocity of sound is not relatively constantthroughout the working depth range, it will not be possible toadjust the instrument so that it reads equal the bar check at eachdepth increment. In such cases, an alternative approach may be
31、that after calibration, to record the error at 5 or 10 ftincremental depths and apply corrections during post-processing. An additional approach is to not adjust the initialmanufacturers fathometer settings, but to record the error at 5or 10 ft incremental depths and apply corrections during thepost
32、-processing process.8. Velocity Profiler8.1 As an alternative to bar checking, consideration can begiven to use of a velocity profiler.8.2 Velocity profiler meters usually consist of an underwaterprobe attached by cable to a hand held unit that directlymeasures the velocity of sound.8.3 Amajor advan
33、tage of a velocity profiler meter over a barcheck is the ability to perform rapid calibrations in rough waterand currents.8.4 Cable is numerically labeled at intervals in feet ormeters.8.5 Some models use a pressure sensor for depth determi-nation which minimizes cable slant errors.8.6 Output typica
34、lly is speed of sound as function of waterdepth.8.7 Sound velocity should be recorded at even increments infeet or meters taken to the nearest foot per second or meter persecond.8.8 Readings usually are entered into a table in processingsoftware measured velocity at incremental depths.8.9 Velocity p
35、rofiler data can be used to obtain an averagesound velocity over given range and be used to adjust afathometer as done with bar check calibration.8.10 The velocity profiler must be initially and periodicallycalibrated with a bar check.9. Keywords9.1 bathymetric surveys; depth sounding; echo sounders
36、;fathometers; hydrography; reservoir surveys; sediment sur-veys; velocity profilerBibliography(1) “The Admiralty Manual of Hydrographic Surveying,” Hydro-graphic Department, Ministry of Defence, 1965 et seq.(2) “Hydrographic Manual,” U. S. Department of Commerce, 4thEdition, National Oceanic and Atmospheric Administration, 1976.(3) Ingham, A. E., “Hydrography for the Surveyor and Engineer,” JohnWiley or through the ASTM website(www.astm.org).D6318033
