© ISO 2016 Hydrometry — Position fixing equipment for hydrometric boats Hydrométrie — Système de positionnement pour embarcation hydrométriques INTERNATIONAL STANDARD ISO 6420 Second edition 2016 10 0[.]
INTERNATIONAL STANDARD ISO 6420 Second edition 2016-10-01 Hydrometry — Position fixing equipment for hydrometric boats Hydrométrie — Système de positionnement pour embarcation hydrométriques Reference number ISO 6420:2016(E) © ISO 2016 ISO 642 0: 01 6(E) COPYRIGHT PROTECTED DOCUMENT © ISO 2016, Published in Switzerland All rights reserved Unless otherwise specified, no part o f this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission Permission can be requested from either ISO at the address below or ISO’s member body in the country o f the requester ISO copyright o ffice Ch de Blandonnet • CP 401 CH-1214 Vernier, Geneva, Switzerland Tel +41 22 749 01 11 Fax +41 22 749 09 47 copyright@iso.org www.iso.org ii © ISO 2016 – All rights reserved ISO 6420:2016(E) Page Contents Foreword iv Introduction v 3 4 5 Scope Normative references Terms and definitions Requirements for position fixing Position fixing equipment for streamgauging and sediment sampling 5.1 5.2 5.4 5 5.6 6 Glo b al navigatio n s atellite sys tems H ydro metric ap p licatio n 3 Sys tem s p ecificatio ns E lectro nic s urvey ins truments Position fixing equipment for morphological surveys 6.1 6.2 6.3 6.4 General Tapes and tag lines 5.3.1 General Targets and electronic distance measuring equipment 5.4.1 General 5.4.2 Targets 5.4.3 Electronic distance measuring devices Theodolites 5.6.1 Theodolites and stadia 5.6.2 Angular technique General Theodolites and stadia rods Glo b al navigatio n s atellite sys tems E lectro nic s urveying ins truments Uncertainty f 7.2.1 General 7.2.2 Tag lines 7.2.4 Targets and distance measuring devices 7.2.6 Theodolites f f 7.3.1 General 7.3.4 Triangulation method using theodolites Annex A (informative) Evaluation o f uncertainty components 10 Bibliography 12 7.1 D efinitio n o f uncertainty 7.2 Uncertainty o f p o s itio n fixing 7.3 o r s treamgauging and s ediment s amp ling 7.2 Glo b al navigatio n s atellite sys tems 7.2 E lectro nic s urveying ins truments Uncertainty o p o s itio n fixing o r mo rp ho lo gical s urveys 7.3 Glo b al navigatio n s atellite sys tems 7.3 E lectro nic s urveying ins truments © ISO 2016 – All rights reserved iii ISO 6420:2016(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies) The work o f preparing International Standards is normally carried out through ISO technical committees Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters o f electrotechnical standardization The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part In particular the different approval criteria needed for the di fferent types o f ISO documents should be noted This document was dra fted in accordance with the editorial rules of the ISO/IEC Directives, Part (see www.iso.org/directives) Attention is drawn to the possibility that some o f the elements o f this document may be the subject o f patent rights ISO shall not be held responsible for identi fying any or all such patent rights Details o f any patent rights identified during the development o f the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents) Any trade name used in this document is in formation given for the convenience o f users and does not constitute an endorsement For an explanation on the meaning o f ISO specific terms and expressions related to formity assessment, as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html The committee responsible for this document is Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 5, Instruments, equipment and data management This second edition o f ISO 6420 cancels and replaces ISO 6420:1984, which has been technically revised The following major changes have been made: — in formation on the use o f global navigation satellite systems has been added; — the former Annexes A and B have been removed; — the treatment o f uncertainty has been expanded and aligned with ISO/TS 25377 iv © ISO 2016 – All rights reserved ISO 6420:2016(E) Introduction T he ne ce s s ity o f p o s ition i ng hyd rome tric b o ats ari s e s in s evera l typ e s o f me a s urements on op en cha n nel s or la ke s , re s er voi rs and e s tuarie s Fi rs t, it i s ne ce s s ar y to p o s ition a b o at on a me a s u ri ng s e c tion i n order to conduc t the appropri ate ob s er vation s o f velo city a nd dep th Po s ition fi xi ng a l s o i s re qu i re d for for ver tic a l s on a river c ro s s s e c tion Si m i larly, p o s ition i ng o f a b o at i s ne e de d and sediment sampling of lakes, reservoirs and estuaries T h i s c u ment provide s i n formation from a d i s ch arge me as u rement col le c ti ng s u s p ende d s e d i ment a nd b e d lo ad s ample s at appropri ate for for p o s ition i ng hyd rome tric b o ats with variou s me tho d s ngi ng s tandard s u r veyi ng e qu ipment to navigation s ys tem s employi ng s igna l s satellites © ISO 2016 – All rights reserved morpholo gic a l s ur veys from the s tel lation o f v INTERNATIONAL STANDARD ISO 6420:2016(E) Hydrometry — Position fixing equipment for hydrometric boats Scope T h i s c u ment s p e c i fie s me tho d s o f de term i n i ng the p o s ition o f hyd rome tric b o ats b a s e d on s atel l ite navigation s ys tem s and/or with re s p e c t to known p oi nts on the b an ks o f rivers , e s tuarie s or la ke s I t app l ie s to ele c tronic p o s ition i ng e qu ipment a nd conventiona l s u r veyi ng te ch n ique s Normative references T he fol lowi ng c u ments are re ferre d to i n the tex t i n s uch a way th at s ome or a l l o f thei r content s titute s re qu i rements o f th i s c u ment For date d re ference s , on ly the e d ition cite d appl ie s For u ndate d re ference s , the late s t e d ition o f the re ference d c ument (i nclud i ng a ny amend ments) appl ie s ISO 748, Hydrometry — Measurement of liquid flow in open channels using current-meters or floats 3 Terms and definitions For the pu r p o s e o f th i s c u ment, the term s a nd defi n ition s given i n I S O 7 apply ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at http://www.iso.org/obp — IEC Electropedia: available at http://www.electropedia.org/ 4 Requirements for position fixing T he ne ce s s ity o f u s i ng p o s ition fi xi ng e qu ipment a ri s e s i n two typ e s o f me a s u rements on op en cha n nel s or lakes, reservoirs and estuaries Fi rs t, it i s ne ce s s ar y to p o s ition a b o at on a me as u ri ng s e c tion i n order to conduc t the appropri ate ob s er vation s o f velo city a nd dep th acous tic D oppler c u rrent pro fi lers d i m i n i she d the ne e d for p o s ition for for a d i s charge me a s u rement (as s p e ci fie d i n I S O 74 8) T he u s e o f ma ki ng d i s charge me as u rements (s e e I S O/ T R 45 78) s la rgely fi xi ng e qu ipment for hyd rome tric b o ats when ma ki ng d i s charge me as u rements H owever, there are s ti l l s ome typ e s o f me as u rements when ver tic a l s on a c ro s s s e c tion have to be p o s itione d for velo c ity and dep th de term i nation s Po s ition fi xi ng collecting suspended sediment and bedload samples at appropriate verticals T he s e cond re s er voi rs typ e and o f me as u rements e s tua rie s Po s ition re qu i ri ng fi xi ng is p o s ition re qu i re d observations and bottom samples are obtained fi xi ng to are also morpholo gic a l de term i ne the is re qu i re d s u r veys p o s ition s at for o f la ke s , wh ich dep th 5 Position fixing equipment for streamgauging and sediment sampling 5.1 General T here are d i fferent typ e s o f p o s ition-fi xi ng e quipment T h i s clau s e de s c rib e s the fol lowi ng: me a s u ri ng tap e s , tag l i ne s , glob a l navigation s atel l ite s ys tem s (GNS S ) , a combi nation o f targe ts a nd ele c tron ic d i s tance me a s uri ng e qu ipment, ele c tronic s u r veyi ng e qu ipment, and the o dol ite s and s tad i a ro d s © ISO 2016 – All rights reserved ISO 642 0: 01 6(E) 5.2 Tapes and tag lines Tapes and tag lines are the most frequently used means for width measurements when measuring rivers by boat or wading Steel measuring tapes with markings at metres and 10 ths of metres (or 100 ths o f meters) are used in streams and rivers less than 50 m wide A typical tag line consists o f a marked corrosion-resistant steel cable that is mm to mm in diameter The diameter of the tag line depends on the width o f the channel, the velocity o f the water and whether or not the same tag line is used for holding the boat and for determining its position Larger diameter tag lines may be needed i f used for dual purposes Tag lines are typically marked at intervals o f m to 10 m with double markings at 50 m and 100 m Tag lines are commonly used on channels up to 300 m wide, however, the accuracy o f the distance measurements depends on cable tension Long tag lines are usually wound on a drum having a diameter of at least 0,3 m and equipped with a cranking and braking mechanism Caution should be used when tapes and tag lines are used to position hydrometric boats on navigable rivers An observer on the river bank should be available to alert the hydrographers o f approaching boats and also alert boat operators o f the tape or tag line Other operators may be required to temporarily remove the tape or tag line to allow boat passage through the measuring section 5.3 Global navigation satellite systems 5.3.1 General Navigation systems that use GNSS technology are used on larger rivers that are too wide for stringing a tagline These systems provide reliable location and time in formation, in all weather conditions and at all times, anywhere on or near the Earth when and where there is an unobstructed line o f sight to four or more satellites in the constellation of satellites There are two operational GNSS — The NAVSTAR Global Positioning System (GPS) was developed by the U S Department o f De fense; it is composed of 24 satellites — GLONASS was developed by the Soviet Union and is operated by the Russian Aerospace De fense Forces; it also is composed o f 24 satellites Other global or regional systems under development include Galileo being developed by the European Union, Compass being developed by China, and IRNSS, a regional system being developed by India There are two general operating methods by which satellite-derived positions can be obtained; either absolute point positioning or relative (differential) positioning a) With absolute point positioning, measurements of the distance to each individual satellite are made by analysing the time it takes for a signal to travel from a satellite to the antenna o f the navigation system Trilateration is then used to establish the receiver’s position The accuracy o f the position is about m or less [6] b) Differential positioning is the technique or method used to position one point relative to another Differential positioning requires a ground station within line of sight distance of 20 km or less Di fferential positioning can provide a relative accuracy o f a few centimetres .[5] Receivers with real-time kinematic (RTK) technology can provide a relative accuracy o f cm to cm RTK uses a similar set-up to di fferential positioning, but with two significant di fferences: the RTK signal is evaluated for timing error (not just the in formation contained within the signal), and the error correction is transmitted immediately to the GNSS units resulting in real time accuracy Some RTK-enabled receivers are able to use satellite-broadcasted corrections and provide very accurate positioning over much longer distances There is an added cost of using broadcasted corrections from private satellites GNSS technology uses the World Geodetic System 1984 (WGS84) as the de fault datum Other earth models or coordinate re ference systems may be desired for specialized applications, such as for highresolution mapping and navigation in specific regions o f the Earth [7] The use o f any pre ferred local © ISO 2016 – All rights reserved ISO 642 0: 01 6(E) co ord i nate re ference s ys tem s i n s uch appl ication s re qui re s a s u itable co ord i nate tran s formation WGS84 [7] from 5.3.2 Hydrometric application S atel l ite navigation s ys tem s a l low op erators to pre s ele c t tra n s e c ts and ver tic a l s for ma ki ng dep th a nd velo c ity de term i nation s T he s ys tem s s i s t o f a re ceiver, navigation s o ftwa re , a nd a d igita l d i s pl ay that s hows the p o s ition o f the b o at on the cro s s s e c tion Navigation s ys tem s o f dep th and velo c ity or the col le c tion o f s a mple s at ver tic a l s with faci l itate the me as u rement on ly a b o at op erator a nd one hyd ro grapher 5.3.3 System specifications T here a re a wide nge o f navigation s ys tem s that c a n b e u s e d for hyd rome tric appl ic ation s S ys tem s should have the following minimum capabilities for positioning boats on river cross sections: — abi l ity to re ceive s igna l s from more tha n one glob a l or regiona l s atel l ite navigation s ys tem a nd grou nd re ference s tation s; — s u ffic ient cha n nel s to re cei ve s igna l s — water pro o f or re s i s tant s o ele c tron ics wi l l no t b e damage d du ri ng rai n or s pray — a d igita l d i s play th at s hows the b o at p o s ition, c ro s s s e c tion a nd wayp oi nts (ver tic a l s) ; — a s u n l ight mo de s o the s ys tem c an b e op erate d i n d i re c t s u n l ight; — abi l ity to s tore 10 or more wayp oi nts (ver tic a l s) ; — for up to s atel l ite s; a n a l arm s ys tem to i nd ic ate when the b o at d ri fts from from wave s; the cro s s s e c tion or de s ignate d wayp oi nt (ver tic a l) ; — output function for transferring position information to a discharge measurement application 5.4 Targets and electronic distance measuring equipment 5.4.1 General Targe ts a re u s e d to a l ign the b o at on the c ro s s s e c tion, and range fi nders or o ther d i s ta nce me as u ri ng e quipment a re u s e d to p o s ition the b o at on the corre c t ver tic a l T h i s appro ach u s ua l ly re qui re s a b o at op erator to a l ign the b o at on the c ro s s s e c tion b e twe en the ta rge ts , a hyd ro grapher to ma ke the dep th and velo city me a s urements , a nd ano ther i nd ividua l on the river b an k or on the b o at to re ad and re cord the distance measuring equipment Communication between the shore personnel and the boat operator is done using hand signals or radios 5.4.2 Targets The target technique requires that two targets be positioned on each bank to give the line of the cross the line, the spacing between the targets on each bank should not be less than 10 % of the channel width sec tion T he s i ze and type o f the targets wi ll depend on the channel width To ens ure s u fficient accurac y o f 5.4.3 Electronic distance measuring devices Electronic distance measuring devices use visible or infrared electromagnetic waves Laser rangefi nders c an b e u s e d to me as u re hori z onta l d i s tance s rangi ng from m to 0 m T he op ti mu m s e tup s i s ts o f a s i ngle len s or bi no c u lar rangefi nder and a refle c tor or mu ltiple refle c tors T he rangefi nder c an b e u s e d on the b o at with refle c tors mounte d on the ne a r- s hore targe ts on e ach b a n k, or the rangefi nder c an b e u s e d on one b an k with a refle c tor mou nte d on the b o at T he acc u rac y o f © ISO 2016 – All rights reserved ISO 642 0: 01 6(E) rangefinders is a function o f beam divergence Units used for measuring distances greater than 500 m should have good optics with tightly collimated beams to hold focus Distance measuring instruments using radio waves operate on the principle that if a carrier is requency modulated, it will exhibit a phase shi ft that is proportional to the distance travelled and to the modulating frequency By using a number o f modulating frequencies and comparing the phase f shifts of a signal that has travelled between a master unit and a remote unit to a reference signal, it is possible to determine distance within mm to mm over a distance of 500 m For streamgauging applications, the master unit is set up on one streambank and the remote unit or prism reflector is mounted on the hydrometric boat The accuracy o f the distance measurement is a ffected by the angle o f the line-o f-sight from horizontal The master unit should be levelled, and the prism reflector should be mounted at the same height above an arbitrary datum as the master unit 5.5 Electronic survey instruments A total station is an electronic/optical instrument used in modern surveying The total station is an electronic theodolite (transit) integrated with an electronic distance meter (EDM) to read slope distances from the instrument to a particular point For hydrometric applications, the total station is positioned and levelled on the cross section on one bank o f the river and a prism reflector is mounted on the hydrometric boat A typical total station can measure distances with an accuracy o f about mm to mm + 1,5 ppm1) over a distance of up to 500 m [4] This method requires a boat operator, a hydrographer, and an instrument operator on the river bank The boat is maintained on the cross section at the appropriate vertical by radio communication or hand signals between the instrument operator and the boat operator 5.6 Theodolites 5.6.1 Theodolites and stadia A combination o f theodolite or transit and a stadia rod can be used for positioning hydrometric boats; however, this is the least accurate method The approach is similar to the total station method The theodolite or transit is positioned on the cross section on one bank of the river, and the distance from the instrument to the boat is determined by the intersection o f the stadia lines on a surveying rod This method requires at least three experienced personnel: an instrument operator, a boat operator, and a hydrographer An assistant on the boat may be required to set an anchor and adjust the line so the boat remains stable on the cross section while stadia readings are made 5.6.2 Angular technique Another use o f theodolites for positioning hydrometric boats is the angular technique A baseline is established on one bank perpendicular to the cross section being measured The length of the baseline, which should be approximately the width o f the measuring section, is measured with a surveying tape or stadia readings The theodolite is then positioned on the end of the baseline that is not on the cross section as shown in Figure The angle measured determines the position on the cross section from the initial measuring point by the following formula: L AB = tan β ⋅ L AC � (1) 1) ppm = parts per million © ISO 2016 – All rights reserved ISO 642 0: 01 6(E) Figure 1 — Position fixing on a cross section by angular techniques 6 Position fixing equipment for morphological surveys 6.1 General The same type o f position fixing equipment that is used for streamgauging applications can be used for morphological surveys, however, some o f them have limited applications For example, tag lines could only be used for narrow estuaries and reservoirs not greater than 300 m wide Also, targets and electronic distance measuring equipment probably would only be used i f pre-surveyed cross sections were established on the banks o f the lake, reservoir or estuary The three types o f equipment discussed in this clause are GNSS, electronic surveying instruments, and theodolites and stadia rods 6.2 Global navigation satellite systems Navigation systems using GNSS, as discussed in 5.3 , provide a cost-e ffective and e fficient method for positioning boats for morphological surveys Surveys and sampling can be accomplished with a boat operator and a hydrographer Modern navigation systems allow operators to preset a large number o f transects and verticals for making depth measurements and/or collecting water or bottom-material samples 6.3 Electronic surveying instruments A total station, as discussed in 5.5 , is an effective, but more costly method for positioning hydrometric boats for morphological surveys The method requires the establishment o f one or multiple baselines on the bank o f the body o f water being surveyed as shown in Figure The total station is set up on one end o f the baseline, and the position o f the boat is determined by the angle from the baseline and the distance from the total station to the boat Surveys can be accomplished with an instrument operator, boat operator and hydrographer © ISO 2016 – All rights reserved ISO 6420:2016(E) 6.4 Theodolites and stadia rods Positioning o f hydrometric boats for morphological surveys also can be accomplished by using a theodolite and stadia rod Using one theodolite and a stadia rod is the same process as described in 6.3 The angle from the baseline to the boat is determined with the theodolite, and the distance from one end o f the baseline to the boat is determined by reading the intersection o f the stadia lines on the surveying rod This method has limited application because o f the di fficulty in reading the markings on the surveying rod while the hydrometric boat is in the water Another limitation is the length o f the distance that can be measured The maximum distance that can be measured with a typical surveying rod is 400 m, but the di fficulty in reading the rod increases dramatically beyond 100 m Triangulating the position o f the hydrometric boat using two theodolites is the pre ferred and more accurate method The two theodolites are set up on each end of the baseline, and the angles (α and β; Figure 2) from the baseline to the boat are determined The intersection of the two lines determines the position Figure 2 — Position-fixing o f hydrometric boat for morphological surveys Uncertainty 7.1 Definition o f uncertainty All measurements o f a physical quantity are subject to uncertainties These may be due to systematic errors (biases) in the equipment used for measurement, or to random scatter caused by a lack o f sensitivity o f the equipment used for the measurement A measurement thus is only an estimate o f the true value o f the measured quantity and is complete only when accompanied by a statement o f its uncertainty The discrepancy between the true and measured values is the measurement error The measurement error is a combination o f component errors that arise during the per formance o f various elementary operations during the measurement process For measurements of composite quantities that depend on several component quantities, the total error of the measurement is a combination of the errors in all component quantities Determination o f measurement uncertainty involves identification and characterization o f all components o f error, quantification o f the corresponding uncertainties, and combination of the component uncertainties The uncertainties are combined using the statistical rules for combining standard deviations, giving proper consideration to correlations among all of the various © ISO 2016 – All rights reserved ISO 642 0: 01 6(E) sources o f measurement error in order to account for both systematic and random errors The resulting uncertainty values are termed standard uncertainties; they correspond to one standard deviation o f the probability distribution o f measurement errors For further in formation on the evaluation o f uncertainty, see Annex A 7.2 Uncertainty o f position fixing for streamgauging and sediment sampling 7.2.1 General The uncertainty o f the relative position o f a hydrometric boat on a river cross section includes errors caused by the accuracy o f the positioning equipment, the accuracy o f the distance or width measuring instruments, the accuracy o f angle measuring instruments i f the angular technique is used, the cross section not being perpendicular to the flow, and the dri ft o f the boat upstream and downstream or laterally along the cross section 7.2.2 Tag lines A tag line is an accurate method of positioning a boat on a cross section for streamgauging and sediment sampling The uncertainty associated with this method is interpreting the distance between markings on the tag line and the tag line not being perpendicular to the cross section This is expressed as: U (2) = u 2s + u i2 + uα2 where is the uncertainty in the distance from the le ft bank resulting from the sag in the tag line and the unknown tension on the tag line; us is the uncertainty in the distance from the le ft bank caused by interpolating the distance between beads on the tag line; ui u α 7.2.3 is the uncertainty in distance from the le ft bank resulting from the tag line not being perpendicular to the flow Global navigation satellite systems A navigation system that uses GNSS is the most accurate method for positioning hydrometric boats on rivers wider than 300 m The uncertainty is limited to three factors: the section not being perpendicular to the flow, the relative position on the cross section, and boat dri ft This is expressed as: U 2 2 = uα2 + u pos + u dr (3) where u α is the uncertainty in distance from the le ft bank resulting from the cross section not being perpendicular to the flow; pos is the uncertainty o f the position from the le ft bank or station based on GNSS signals; u dr is the uncertainty resulting from boat dri ft upstream, downstream or horizontally on the u section © ISO 2016 – All rights reserved ISO 642 0: 01 6(E) 7.2.4 Targets and distance measuring devices Ta rge ts and d i s tance me a s u ri ng device s are a relatively acc urate me tho d o f p o s ition i ng hyd rome tric boats The uncertainties associated with this method are the distance measured from the left bank or and boat drift This is expressed as: s tation by the d i s tance me a s u ri ng device, the targe t l i ne no t b ei ng p er p end ic u la r to the river b an ks , U (4) 2 = u d2 + uα2 + u dr where ud uα i s the u ncer ta i nty o f the d i s ta nce me as u ri ng device; i s the u ncer ta i nty i n d i s ta nce from the le ft b an k re s u lti ng from the targe t l i ne no t b ei ng p er p end ic u la r to the flow; udr 7.2.5 i s the u ncer ta i nty re s u lti ng section from b o at d ri ft up s tre am, down s tre am or hori z onta l ly on the Electronic surveying instruments E le c tron ic s u r veyi ng i n s tru ments hyd rome tric b o ats T he u ncer tai nty or to ta l fac tors measuring devices, and Formula (4) applies 7.2.6 s tation s are a ver y acc u rate me tho d of p o s ition i ng are the s ame a s the me tho d that u s e s ta rge ts and d i s tance Theodolites T he u s e o f the o dol ite s and s tad i a a re the le a s t acc u rate me tho d uncer ta i nty fac tors for p o s ition i ng hyd rome tric b o ats T he a re the s a me as the two previou s me tho d s (s e e applies The angular method (see Figure 7.2.4 and 7.2.5), and Formula (4) ) that a l s o u s e s a the o dol ite s s l ightly d i fferent uncer ta i nty fac tors T hey i nclude the u ncer tai nty o f the d i s ta nce me a s uri ng device to e s tabl i s h the b as el i ne, the u ncer tai nty o f the b a s el i ne no t b ei ng p a l lel to the flow, the u ncer tai nty o f the angle me a s ure d from the b as el i ne to the hyd rome tric b o at, a nd the d ri ft o f the b o at T he u ncer tai nty i s expre s s e d as: U (5) 2 = u d2 + uα2 + u 2β + u dr where ud i s the u ncer ta i nty o f the d i s ta nce me as u ri ng device; uα i s the u ncer ta i nty o f the b as el i ne no t b ei ng p a l lel to the flow; uβ i s the u ncer ta i nty o f the angle me a s u re d udr i s the u ncer ta i nty re s u lti ng section from from the b a s el i ne to the hyd rome tric b o at; b o at d ri ft up s tre am, down s tre am or hori z onta l ly on the 7.3 Uncertainty o f position fixing for morphological surveys 7.3.1 General T he u ncer tai nty o f p o s ition i ng a hyd rome tric b o at for a hyd rome tric s u r vey i s s i m i la r to that for p o s ition i ng a b o at on a river c ro s s s e c tion T he uncer ta i nty i nclude s errors c au s e d b y the acc urac y o f © ISO 2016 – All rights reserved ISO 642 0: 01 6(E) the p o s ition i ng e qu ipment, the acc u rac y o f the d i s ta nce me a s uri ng i n s tr uments , the acc u rac y o f a ngle me as u ri ng i n s tr uments , and the d ri ft o f the b o at du ri ng the s u r vey or s ampl i ng p erio d 7.3.2 Global navigation satellite systems Navigation s ys tem s th at u s e GNS S a re the mo s t acc u rate me tho d for for p o s ition i ng hyd rome tric b o ats morpholo gic a l s u r veys T he uncer ta i nty i s l i m ite d to ab s olute p o s ition i ng b a s e d on GNS S s igna l s and the d ri ft o f the hyd rome tric b o at du ri ng dep th me as u rements and b o ttom s ampl i ng Formu l a (3 ) applies where upos 7.3.3 T he i s the u ncer tai nty o f the ab s olute p o s ition b a s e d on GNS S s igna l s Electronic surveying instruments uncer ta i nty o f p o s itioni ng hyd rome tric b o ats u s i ng ele c tron ic s u r veyi ng i n s tr uments or to ta l s tation s i nclude s the u ncer tai nty o f the leng th o f the b a s el i ne, the u ncer tai nty o f the d i s tance one end o f the b as el i ne to the hyd rome tric b o at, the u ncer tai nty o f the angle from from the b as el i ne to the hyd rome tric b o at, and the d ri ft o f the b o at T h i s i s e xpre s s e d a s: U (6) 2 = u d2 + u d2 + u 2β + u dr where ud1 i s the u ncer ta i nty o f the leng th o f the b as el i ne; u d2 i s the u ncer ta i nty o f the d i s tance b e twe en one end o f the b a s el i ne a nd the hyd rome tric b o at; uβ i s the u ncer ta i nty o f the a ngle me a s ure d udr i s the u ncer ta i nty re s u lti ng 7.3.4 from from the b a s el i ne to the hyd rome tric b o at; b o at d ri ft Triangulation method using theodolites T he u ncer tai nty o f p o s ition i ng hyd rome tric b o ats u s i ng a b a s el i ne and two the o dol ite s i s a ffe c te d by the u ncer tai nty o f the leng th o f the b a s el i ne, the u ncer tai nty o f angle s , This is expressed as: U α and β, and the drift of the boat (7) 2 = u d2 + uα2 + u 2β + u dr where ud i s the u ncer ta i nty o f the leng th o f the b as el i ne; uα i s the u ncer ta i nty o f the a ngle, α; uβ i s the u ncer ta i nty o f the a ngle, β; udr i s the u ncer ta i nty re s u lti ng © ISO 2016 – All rights reserved from b o at d ri ft ISO 642 0: 01 6(E) Annex A (informative) Evaluation o f uncertainty components A.1 General T he uncer ta i nty comp onents de s c rib e d i n Clause are eva luate d b y a Typ e B eva luation o f u ncer tai nty, wh ich i s a me tho d o f eva luati ng u ncer tai nty b y me an s o ther than a s tati s tic a l a na lys i s o f a s erie s o f ob s er vation s (s e e I S O/ T S 5377 ) T he u ncer tai nty i s e s ti mate d by de term i n i ng the upp er and lower l i m its o f a me a s urement s uch as the leng th o f a c ro s s s e c tion, a nd then applyi ng a prob abi l ity d i s tribution Re c tangu lar a nd tria ngu la r prob abi l ity d i s tribution s are the natura l form s for hu man estimation of readings from devices such as tapes, rulers, and verniers The choice between using a rectangular or triangular distribution is based on what seems most probable to the user, but a rectangular distribution should be used if the choice is not obvious T he u ncer tai nty b as e d on a re c tangu lar d i s tribution i s defi ne d as: U ( d mean ) = ⋅ ( d max − d ) (A.1) T he u ncer tai nty b as e d on a tri angu la r d i s tribution i s defi ne d a s: U ( d mean ) = where dmax dmin ⋅ ( d max − d ) (A.2) i s the d i s cern ible upp er l i m it o f the me as u rement; is the discernible lower limit of the measurement A.2 Uncertainty about the length o f a tag line and interpolating the distance between markings Tag l i ne s are typic a l ly marke d with b e ad s at m or 10 m i nter va l s I f the d i s cern ible lower and upp er l i m its o f a p oi nt m idway b e twe en b e ad s at 0 m and m are 02 , a nd 02 ,7 m, re s p e c tively; applyi ng a re c ta ngu l ar d i s tribution yield s a n u ncer tai nty o f ,1 m or , % I f the d i s cern ible upp er and lower l i m its o f a p oi nt m idway b e twe en b e ad s at 10 m i nter va l s at 0 m prob ab ly a re 4,7 and , m, the u ncer tai nty wou ld b e ,17 m or , % 10 © ISO 2016 – All rights reserved ISO 6420:2016(E) A.3 Uncertainty resulting from cross section not being normal to the flow An experienced hydrographer and instrument operator should be able to align a cross section within ± degrees of normal The error in a 300 m wide cross section that is degrees from normal is Ed = 300 m cos ° (A.3) − 300 m = 146 m , Applying a rectangular distribution with a lower discernible limit o f 300 m and an upper discernible limit o f 301,146 m yields an uncertainty o f 0,331 m or 0,11 % A.4 Uncertainty o f GNSS positioning Positioning through triangulation with four or more GNSS signals is usually within m [3] The upper and lower discernible limits at 300 m would be 297 m and 303 m, respectively Applying a rectangular distribution yields an uncertainty o f 1,732 m or 0,58 % Positioning through triangulation with four or more GNSS signals and a line of sight reference station is accurate to within 15 cm [2] The upper and lower discernible limits at 300 m would be 299,85 m and 300,15 m, respectively Applying a rectangular distribution yields an uncertainty o f 0,087 m or 0,029 % A.5 Uncertainty of EDMs EDMs can measure distances very accurately, within 1,5 mm + 1,5 ppm at distances up to 500 m [4] At 300 m, the uncertainty would be 0,001 m or 0,000 % A.6 Uncertainty of position because of boat drift The hydrometric boat dri fting o ff the cross section probably is the greatest source o f uncertainty associated with positioning a boat for a depth and velocity measurement or a sediment sample The dri ft will vary with wind conditions and macro-turbulence associated with water velocity and discharge For measurements with low velocities and no wind, the boat may dri ft m or m At 300 m, the lower and upper limits o f the positioning would be 298,5 m and 301,5 m The uncertainty would be 0,867 m or 0,29 % During windy conditions and high sur face turbulence, the boat may dri ft o ff position by 10 m or more At 300 m, the lower and upper limits o f positioning would be 290 m and 310 m The uncertainty would be 5,8 m or 1,9 % © ISO 2016 – All rights reserved 11 ISO 642 0: 01 6(E) Bibliography [1] [2] [3] [4] [5] [6] [7] ISO 772, Hydrometry — Vocabulary and symbols ISO/TR 24578, Hydrometry — Acoustic Doppler profiler — Method and application for measurement of flow in open channels ISO/TS 25377, Hydrometric uncertainty guidance (HUG) LEICA VIVA TS11 Datasheet http://leica-geosystems.com/ N ational D i ff erential GPS S ystem (NDGPS) http://www.gps gov/systems/augmentations/ U.S D epartment of D e f ense 2008 Global positioning system, Standard positioning service, Performance standard Fourth edition, September 2008, 135 p U S NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY 2014: World geodetic system 1984 – its definition and relationships with local geodetic systems, Standard 0036, version 1.0.0, July 2014, 207 p., http://earth-info.nga.mil/GandG/publications/NGA_STND_0036_1_0_0_WGS84/NGA STND.0036_1.0.0_WGS84.pdf 12 © ISO 2016 – All rights reserved ISO 642 0: 01 6(E) I CS 7.1 0.2 Price based on 12 pages © ISO 2016 – All rights reserved