1、Designation: D6318 03 (Reapproved 2014)Standard Practice forCalibrating a Fathometer Using a Bar Check Method1This standard is issued under the fixed designation D6318; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides the user with procedures used inmanually calibrating the fathometer or electronic depthsounder. T
3、his narrative 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 c
4、ited in this narrative 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 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are m
5、athematicalconversions to SI units that are provided for information onlyand are not considered standard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and
6、 health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD5073 Practice for Depth Measurement of Surface Water3. Terminology3.1 DefinitionsRefer to Terminology D1129 for termsused in this g
7、uide.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 fathometer bysetting a sound or accoustic reflector (bar) below a survey
8、vessel 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 water by measuring the time required for thetransmission and reflection o
9、f 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 for translating electrical energyto acoustical energy and acoustical e
10、nergy 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 waterwith changes in temperature, salinity, and depth of water. Inaddition in
11、stability of the equipment can also result in signifi-cant errors. For additional information see Practice D5073.4.2 Calibration of echo sounding instruments is absolutelycritical in assuring the adequacy of depth measurements. Whenan echo sounder has been accurately calibrated, any observed(recorde
12、d) 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 toconstruct, and most economical mechanical method to deter-mine corrections for
13、 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 for use in specific fieldconditions.1This practice is under the jurisdic
14、tion of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,and Open-Channel Flow.Current edition approved Jan. 1, 2014. Published March 2014. Originallyapproved in 1998. Last previous edition approved in 2008 as D6318 03 (2008).DOI: 10.1520
15、/D6318-03R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Dr
16、ive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. 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
17、 be a bar made outof a section 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 th
18、e transducer, and thedepth range to be covered during the survey. Usually, thelength of the bar is equal to the beam or width for 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 typ
19、e ofcurrents experienced, typical project depths, and beam of thevessel. Typical weights range from 40 to 100 lb (20 to 50 kg).In 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 i
20、nland or pro-tected bodies of water, a lighter weight may be used providedthe bar can be maintained directly beneath the transducer.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 l
21、east 100 ft longwith either easily visible markings at every 10 ft starting at thetop of the bar or carried on a calibrated reel. The bar checksuspension lines must be periodically checked to ensure theaccuracy and stability of the graduated marks on the line6. Condition Requirements6.1 The preferre
22、d environmental conditions for bar-checking are calm water, wind velocity less than 5 mph, anddepths less than 100 ft. Reasonable 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 wi
23、ll exist in the soundings.6.2 Bar checks should always be made when and wherewater conditions are calmest; observations taken during roughwater conditions or when differential current causes the bar tobe displaced from a position vertically below the transducer aresubject to unacceptable magnitudes
24、of error.6.3 For best results where salinity and temperature of thewater are unknown, the fathometer should be calibrated beforethe 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
25、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 conditions should run to a protected area for the barcheck. Bar checks, however, should not be made in areas wheresalinity, temperatures, and suspended sediment concentrat
26、ionsvary significantly from those at the area to be surveyed.7. Bar-check Procedure7.1 Turn the fathometer on about 10 min before 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 man
27、ufacturers speci-fications.7.3 Two depths are chosen that correspond to the minimumand maximum calibration range, such as 10 ft and 50 ft.7.4 Lower the bar into the water to the 10 ft mark on thelowering line. (Warningmake sure feet are clear of thelowering lines to prevent entanglement. Make sure t
28、hat the barFIG. 1 Calibration Bar ApparatusD6318 03 (2014)2is centered directly underneath the transducer. Failure to do sowill result in false or erroneous readings.)7.5 Adjust the “draft” fathometer settings so that the depthtracing on the sounding scroll or digital reading matches the 10ft depth
29、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 settings so thatthe depth tracing on the sounding scroll or digital readingmatches the 50 ft depth.7.8 Raise the bar to the
30、10 ft position. If there is no changethe echosounder is calibrated. If there is a difference, readjustthe “draft” fathometer settings to match 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 calibrat
31、ion intermediate readingsshould be checked to compare fathometer readings with knownbar depths. For this example readings could be taken at 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 p
32、ossible toadjust the instrument so that it reads equal the bar check at eachdepth increment. In such cases, an alternative approach may bethat 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
33、the initialmanufacturers fathometer settings, but to record the error at 5or 10 ft incremental depths and apply corrections during thepost-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 meter
34、s usually consist of an underwaterprobe attached by cable to a hand held unit that directlymeasures the velocity of sound.8.3 Amajor advantage 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 inte
35、rvals in feet ormeters.8.5 Some models use a pressure sensor for depth determi-nation which minimizes cable slant errors.8.6 Output typically 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
36、meter persecond.8.8 Readings usually are entered into a table in processingsoftware measured velocity at incremental depths.8.9 Velocity profiler 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 velocit
37、y profiler must be initially and periodicallycalibrated with a bar check.9. Keywords9.1 bathymetric surveys; depth sounding; echo sounders;fathometers; hydrography; reservoir surveys; sediment sur-veys; velocity profilerBIBLIOGRAPHY(1) “The Admiralty Manual of Hydrographic Surveying,” Hydro-graphic
38、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). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D6318 03 (2014)4
