dutch standards for hydrographic surveys - 1st edition - july 2009_tcm174-302218

8/22/2019 Dutch Standards for Hydrographic Surveys - 1st Edition - July 2009_tcm174-302218

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DUTCH STANDARDS FOR HYDROGRAPHIC SURVEYS

1st edition, July 2009

based on

IHO STANDARDS FOR HYDROGRAPHIC SURVEYS (S-44)

5th edition, February 2008

RijkswaterstaatMinistry of Infrastructure and the

Environment

Royal Netherlands NavyNetherlands Hydrographic Service


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Dutch standards for hydrographic surveys Juli 2009iii

DUTCH STANDARDS FOR HYDROGRAPHIC SURVEYS

1st edition, July 2009

based on

IHO STANDARDS FOR HYDROGRAPHIC SURVEYS (S-44)

5th edition, February 2008


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Dutch standards for hydrographic surveys Juli 2009v

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Colofon

Published by:

In corporation with:

RijkswaterstaatData-ICT-Dienst

Royal Netherlands NavyNetherlands Hydrographic Service

Information:

Telephone:

E-mail:

Data-ICT-Dienst Netherlands HydrographicService

+31(0)15-2757700 +31(0)70-3162800

[email protected] [email protected]

Made by: Periplus Consultancy b.v.

Rijkswaterstaat, Data-ICT-Dienst

Layout: Rijkswaterstaat

Date: 3 July 2009

Status: Definite

Version number: 3.0


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Dutch standards for hydrographic surveys Juli 20091

CONTENTS

Preface .................................................................................................................................. 3

Introduction....................................................................................................................... 5

1 Classification of Hydrographic Surveys................................................ 91.1 Introduction.......................................................................................................... 91.2 NL Order A ............................................................................................................ 91.3 NL Order B ............................................................................................................ 91.4 IHO Special Order .............................................................................................. 9

1.5 IHO Order 1a ..................................................................................................... 101.6 IHO Order 1b ..................................................................................................... 10

1.7 IHO Order 2........................................................................................................ 10

1.8 Overview orders ............................................................................................... 11

2 Positioning.............................................................................................................. 132.1 Horizontal uncertainty .................................................................................... 13

3 Depths ...................................................................................................................... 153.1 Introduction........................................................................................................ 15

3.2 Vertical uncertainty ......................................................................................... 15

3.3 Reductions for Tides / Water-level Observations.................................. 16

3.4 Minimum depth ................................................................................................. 163.5 Feature detection ............................................................................................. 163.6 Sounding density / Line spacing ................................................................. 17

4 Other measurements...................................................................................... 194.1 Introduction........................................................................................................ 19

4.2 Seabed sampling ..............................................................................................19

4.3 Chart and land survey vertical datums connection .............................. 194.4 Tidal predictions ............................................................................................... 194.5 Tidal stream and current observations ..................................................... 19

5 Data attribution .................................................................................................. 215.1 Introduction........................................................................................................ 215.2 Metadata ............................................................................................................. 21

5.3 Point data attribution ...................................................................................... 215.4 Bathymetric model attribution..................................................................... 22

5.5 Report of survey ............................................................................................... 22

6 Elimination of doubtful data ...................................................................... 236.1 Introduction........................................................................................................ 23

6.2 Extent of Area to be Searched .................................................................... 236.3 Conducting the search.................................................................................... 23

6.4 Presentation of search results ..................................................................... 23

Abbreviations and glossary................................................................................... 25


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Preface

Out of various responsibilities the Netherlands Hydrographic Service and

Rijkswaterstaat carry out hydrographic surveys. It is therefore logical that ourdepartments work together. Our activities are harmonized as much as possible anddata is being exchanged between the two departments. In order to aid thiscooperation, the Dutch Hydrographic Institute has been active for years. It takesinitiatives such as the here-described Hydrographic standards.

In order to be able to work together effectively, a common reference frame, suchas the S-44-Standards of the International Hydrographic Organisation (IHO), isimportant. The 5th edition of these Standards was published in February 2008. TheDutch Hydrographic Standards build on this with some additional Standards for theDutch situation.

The Dutch Standards prescribe the minimum requirements regarding hydrographicsurveys. They have influence in almost every hydrographic work process and endproduct, such as planning and execution of hydrographic surveys, the purchasing,maintenance and operational use of hydrographic equipment and the education and

competences of the personnel involved.

Rijkswaterstaat has declared the Dutch standards for hydrographic surveysapplicable to all surveys performed by the Meet- and Information services and forsurveys performed by external parties commissioned by Rijkswaterstaat. Furthermore the standards are applicable on all surveys performed by the Netherlands

Hydrographic Service for their survey plan. For military-hydrographicreconnaissance and surveys these standards are applied if the operational taskpermits it

We hope, that by using these standards, our organisations can have information

with a clearly defined quality and that our cooperation will be strengthened by it.

De Chef der Hydrografie RijkswaterstaatWaterdienst

F.P.J. de Haan Dr. R. AllewijnKapitein ter zee. Directeur Water en Gebruik


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Introduction

This publication has been prepared in accordance with the 5th edition of the IHO

Special Publication S-44 Standards for Hydrographic Surveys. The layout and apart of the text are similar to it. The big difference is that this publication isdedicated to hydrographic work as performed by the Dutch government. Ittherefore contains some important additions and extensions. The purpose of thispublication is to establish a set of standards for conducting and processinghydrographic surveys. The standards apply to all hydrographic surveys conductedby or on behalf of Rijkswaterstaat or the Netherlands Hydrographic Service.

The S-44 standard is an international standard for hydrographic surveys for themaritime shipping. Nautical information gathered and published for the maritimeshipping needs, in accordance with the International Convention for the Safety of

Life at Sea (SOLAS), to follow these standards. In the Netherlands, theHydrographic Service of the Navy Command is responsible for these activities.

For hydrographic surveys in the rest of the control region and hydrographic surveys

for purposes other than vessel traffic, Rijkswaterstaat in the past had formulatedstandards to complement those established by the IHO S-44 standard. These, forthe Netherlands specific standards, are more strict due to the stringentrequirements that apply to coastal protection, morphological research, environmentand management and maintenance of inland waterways and because methods forinland and the coastal region may be more accurate.

The Dutch standards are prepared in accordance with IHO standards, so theymutually well comparable. The result is six standards for hydrographic surveys. Thestrictest standard, NL Order A, corresponds to what is reasonably achievable withexisting equipment and existing way of working in the relatively shallow Dutchwaters. The least stringent standard, IHO Order 2, applies at sea at depths

exceeding 100 meters. This standard does not apply for the Dutch continentalwaters, however so in the waters around the Netherlands Antilles and Aruba.Sections exceeding 200 meters need to comply with the GEBCO standards and areoutside the scope of this document. The four IHO standards in this document aretranslated from the final version of the IHO S-44 standard, fifth edition, February

2008. To them NL Order A and B are added.

The standards describe, among other things, to what conditions validated xyz datamust comply and which objects / obstacles that should be able to be detected. Itmust be stressed that if a survey must comply with a specific standard from thisdocument, it thus must comply demonstrably with all the requirements for thisstandard, from this document. One should also realize that this publication provides

only the minimum requirements that must be fulfilled. Local circumstances may forexample lead to the collection of data with more stringent conditions than describedin this document. In occurring cases, the awarding authority should describe thesemore stringent requirements in accordance with the standards in this document and

notify the contractor of the more stringent requirements.

It is also important to note that the degree to which a survey meets thesestandards is the result of the whole measuring system and the processes applied

thereto. The uncertainties listed in the following chapters therefore describe thetotal propagated uncertainty of all parts of the system. Using a certain tool that intheory is able to achieve the mentioned precision is not necessarily sufficient tomeet the requirements of this document. The way the instrument was setup, used

and the interaction with other parts of the whole measuring system should be takeninto account. An online apriori THU / TVU calculation and an aposteriori analysis areneeded to test the results against the required standards. Due to the great variety


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of equipment, surveymethodes, local seabed conditions, etc., it is impracticable tolay down standard procedures for each standard. These procedures and instructionsare the responsibility of the awarding authority and the contracting authorities.They must have such procedures and competent staff to be able to comply with therequirements of this standard.

All individual components of the measuring system and the measuring systemas a whole must be able to deliver data at the desired standard level. Theawarding authority and the contracting authority should convince herself of this for

example by carrying out appropriate tests with the system used and by convincingherself that the appropriate calibrations are performed prior to, during and, ifapplicable, after the survey.

The hydrographic surveyor is an essential part of the hydrographic surveyingprocess. This person must have sufficient proven knowledge and experience toperform hydrographic surveys in accordance with the standards required. IHOManual M-5, Standards of Competence for Hydrographic Surveyors and IHOSpecial Publication S-47, Training courses in hydrography and nautical

cartography offer the internationally accepted guidelines for this. The hydrographiccompetences of the staff involved, should be mentioned in the report of thehydrographic survey.

At those locations where the seabed is dynamic as a result of for example erosion,sedimentation and sediment transport, surveys performed according to a particularstandard will be a good representation of reality for a shorter period. Such areasmust be re-surveyed periodically to ensure that the seabed in that area is inongoing compliance with the managing requirements. The corresponding surveyfrequency is to be determined by the awarding authority that should be based on

local morphological and climatic conditions, on risk defining factors, such as forinstance traffic intensity and under keel clearance and on the desired maximum

uncertainty in the presented results.

Although the standards in this publication apply to hydrographic surveys conductedby or on behalf of the Dutch government, it should be stressed that they certainlydont have the exclusive right of use. On the contrary, the use of these standardsby other hydrographic agencies is strongly recommended. The hydrographic sectoras a whole benefits from a general application of these standards. They provideclarity in the execution but also in the procurement of contracts for both theawarding and the contracting authorities. However, authorities should at all times

check if the standards listed in this document are applicable to the concerningcontract.

To the 5th edition of S-44 two appendices are added. Annex A Guidelines for

Quality Control and Annex B Guidelines for Data Processing. These annexes arenot part of this publication. The IHO states that they are not an integral part of theS-44 standards and that they will be removed when the information contained inthem is fully included in IHO Publication M-13, Manual on hydrography.Rijkswaterstaat and the Netherlands Hydrographic Service have, based on theseguidelines, established coordinated data management and quality controlprocedures to fulfil these NL standards.

A glossary of terms used in this publication is added, after Chapter 6. Italicwords inthe text are included in the glossary. In the electronic version there are hypertextlinks between the italicizedwords and their definition in the glossary. During the

translation of the terms from the original English version there has been chosen to

use the terms of Aquo-lex as much as possible as far as they are consistent withthe meaning of the terms in the S-44. An important exception is the use of the


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term uncertainty. In the Aquo-lex it is stated by the term uncertainty that theuse of this term in relation to measurements is to be discouraged. Because ofambiguity in the original IHO version and the there used terms it was chosen tomaintain the term uncertainty. The following fundamental terms of the glossaryare considered essential for understanding the standards and are therefore listedhere.

Fundamental terms:Full sea floor search: A systematic method for examining the sea floor performed in

such a way that most of the features and objects as specified in the applicablestandard will be mapped. In practice it is impossible to achieve 100% coverage andthe use of the term 100% bathymetric coverage is therefore discouraged.

Object detection: The ability of a system to detect objects and / or obstacles of aspecific size. The standards in this document define the minimum size of objectsthat must be able to be detected during the survey.

Reduced z-value: Observed z-value plus any subsequent adjustments associated

with the survey and processing with the result that the value is reduced to theappropriate datum.

Total propagated uncertainty (TPU): The resultant propagation of the uncertaintieswhen all known uncertainties, both random and systematic are considered. The TPUis due to the uncertainty in the measurements and is a 3-dimensional variable.

Total horizontal uncertainty (THU): The component of the total propagateduncertainty (TPU) calculated in the horizontal plane. The THU is a 2-dimensionalvariable and listed as a single number. The assumption is that the horizontal

uncertainty is isotropic, in other words, there is a negligible correlation betweenerrors in x-and y-direction. Because of this a normal distribution becomes circularly

symmetric, so a single number can be used to describe the distribution of the errorsaround the true value.

Total vertical uncertainty (TVU): The component of the total propagated uncertainty(TPU) calculated in the vertical dimension. The TVU is a 1-dimensional variable.

Z-value: This term indicates both the value for the depth as for the bottom height.


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1 Classification of Hydrographic Surveys

1.1 Introduction

This chapter describes the standards for hydrographic surveys that apply to varioustypes of activities and various areas. As the requirements and possibilities vary

strongly with depth, objective of the measurement, bottom conditions and the needfor information in general, two extra standards (NL Order A, NL Order B) have beendefined in addition to the four existing IHO standards (special, 1a, 1b, 2). For thesix standards is documented individually for which type of survey and in what kindof area they are applicable. The specification of each standard is given in Table 1,which is provided with a detailed explanation of the different categories used in thetable that must be read to be able to interpret the standard correctly.

The awarding authority for a survey, will determine which standard applies in theregarding area based on the information given here. It should be noted that it is

possible that multiple standards may apply within a single area. In that case, theawarding authority has to divide the area into zones in such a way that it is clear

which standard is applicable in a given zone. The situation as encountered in thefield may differ considerably from what was expected. After analyzing the data itcan become known that a different standard should be used in the future, forexample because shallows are less critical of even more critical than originallyassumed. In those cases where it turns out that a stricter standard should havebeen chosen, for example with the occurrence of shoals, the awarding authoritymust assess the area again using this stricter standard.

1.2 NL Order A

This standard was initially prepared by Rijkswaterstaat with the aim to establishmore stringent standards than specified by the IHO Special Order. This standard is

intended for specific projects such as morphologic research, examination ofconstructions, in particular for construction, management and maintenance, anddredging operations. This requires another survey regime than what is necessaryfor maritime shipping. This makes additional requirements necessary. In particular,the requirements regarding position and z-value have been strengthened withrespect to the IHO Special Order. Besides this, a full sea floor search has to becarried out so that all objects and characteristics of the sea floor can be sufficientlycaptured.

1.3 NL Order B

This standard was initially prepared by Rijkswaterstaat with the aim to establish a

standard that applies to waterways outside the scope of NL Order A. It concernsmostly areas that are not part of navigation channels and harbours, and where noinspection of construction applies. A full sea floor search is not necessary in allcases, meaning that some objects shall not be detected, although the size of

possibly undetected objects may be limited by the maximum line spacing. Thisstandard is recommended only for those areas where under keel clearance issupposed to be not a problem. With this, this standard is an alternative for IHOOrder 1b for the continental waters.

1.4 IHO Special Order

This standard was specifically enacted with the aim to ensure the safe navigation in

those areas where under-keel clearance is critical. It is therefore the most stringentstandard in the S-44 standard and is only exceeded by the Netherlands-specific


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standard, NL Order A. Because under keel clearance is critical a full sea floor searchis required and the size of the features to be detected by this search is deliberatelysmall Kept. The nature of the bottom is also relevant. In rocky soil, this standard ismore likely required then in case of for example sludge. Since under-keel clearanceis critical it is considered unlikely that Special Order surveys will be conducted inwaters deeper than 40 meters. Examples of areas that may warrant Special Order

surveys are: berthing areas, harbours and critical areas of shipping channels.

1.5 IHO Order 1a

This order is intended for those areas where the sea is sufficiently shallow to allow

natural or man-made features on the seabed to be a concern to the type of surfaceshipping expected to transit the area but where the under-keel clearance is lesscritical than for Special Order aboveor NL Order A. Because man-made or naturalfeatures may exist that are of concern to surface shipping, a full sea floor search isrequired, however the size of the feature to be detected is larger than for SpecialOrder and the NL Order A.Under-keel clearance becomes less critical as depthincreases so the size of the feature to be detected by the full sea floor search is

increased in areas where the water depth is greater than 40 metres. Order 1asurveys may be limited to water shallower than 100 metres.

1.6 IHO Order 1b

This order is intended for areas shallower than 100 metres where a general

depiction of the seabed is considered adequate for the type of surface shippingexpected to transit the area. A full sea floor search is not required which means

some features may be missed although the maximum permissible line spacing willlimit the size of the features that are likely to remain undetected. This order ofsurvey is only recommended where under-keel clearance is not considered to be anissue. An example would be an area where the seabed characteristics are such thatthe likelihood of there being a man-made or natural feature on the sea floor thatwill endanger the type of surface vessel expected to navigate the area is low.

1.7 IHO Order 2

This is the least stringent order and is intended for those areas where the depth ofwater is such that a general depiction of the seabed is considered adequate. A full

sea floor search is not required. It is recommended that Order 2 surveys are limitedto areas deeper than 100 metres. Parts deeper than 200 meter must comply with

the GEBCO-orders and therefore dont have to comply to this document. Once thewater depth exceeds 100 metres the existence of man-made or natural features

that are large enough to impact on surface navigation and yet still remainundetected by an Order 2 survey is considered to be unlikely. This order is not tobe used in the Dutch inlandwaters or on the Dutch continental shelf. In the watersaround the Dutch Antilla and Aruba however it does have to be used.


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1.8 Overview orders

An overview of the above mentioned orders can be found in table 1. To be able tounderstand this table some items will be explained here.

Notes on table 1:1. The line spacing for IHO Orders 1b and 2 can be expanded if procedures forensuring an adequate sounding density are used.

2. These only apply where such measurements are required for the survey.

3. Recognising that there are both constant and depth dependent uncertaintiesthat affect the uncertaintyof the depths, the formula below is to be used tocompute, at the 95% confidence level, the maximum allowable TVU. Theparameters a and b for each Order, as given in the Table, together with thedepth d have to be introduced into the formula in order to calculate themaximum allowable TVU for a specific depth:

22 )( dba +

Where:a represents that portion of the uncertaintythat does not vary with depthb is a coefficient which represents that portion of the uncertaintythat

varies with depthd is the reduceddepth

b x d represents that portion of the uncertaintythat varies with depth

4. For safety of navigation purposes, the use of an accurately specified mechanicalsweep to guarantee a minimum safe clearance depth throughout an area may

be considered sufficient for Special Order and Order 1a surveys.

5. If for the Dutch Orders A and B full sea floor search is required, a maximum of5% of the survey area may be left uncovered with bathymetric data. Theseuncovered areas may, individually, not be bigger then 0.5% of the total area.Using neighbouring values, an estimate must be made of the risk there is acritical bottom depth within the uncovered area. The intention is always to havefull bottom coverage. Due to circumstances during the survey it is not alwayspossible to meet the requirements in table 1 for the entire area

6. A cubic feature means a regular cube each side of which has the same length. It

should be noted that the NL Order A, IHO Special Order and Order 1a feature

detection requirements, are minimum requirements. In certain circumstances itmay be deemed necessary by the hydrographic offices / organizations to detectsmaller features to minimise the risk of undetected hazards to surfacenavigation. For Order 1a the relaxing offeature detection criteria at 40 metresreflects the maximum expected draught of vessels.


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2 Positioning

2.1 Horizontal uncertainty

The uncertaintyof a position is the uncertaintyat the position of the sounding orfeature within the geodetic reference frame.

Positions should be referenced to a geocentric reference frame based on theInternational Terrestrial Reference System (ITRS) e.g. WGS84 or ETRS89.Preferebly, reference to ETRS89 is used. If, exceptionally, positions are referencedto the local horizontal datum, such as RD, this datum should be tied to a geocentricreference frame based on ITRF. For RD this is accompliced by referring to the latesttransformation procedure RDNAPTRANSTM.

The uncertaintyof a position is affected by many different parameters, e.g. errorsin the positioning system, errors in the various sensors, errors in the geometry of

the vessel, e.d. The contributions of all such parameters to the total horizontaluncertainty(THU) should be accounted for.

A statistical method, combining all uncertaintysources, for determining positioninguncertaintyshould be adopted. The position uncertaintyat the 95% confidencelevelshould be recorded together with the survey data (see also 5.2). Thecapability of the survey system should be demonstrated by the THU calculation.

The position of soundings, dangers, other significant submerged features, navaids(fixed and floating), features significant to navigation, the coastline andtopographical features should be determined such that the horizontal uncertainty

meets the requirements specified in Table1. This includes all uncertaintysourcesnot just those associated with positioning equipment.


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3 Depths

3.1 Introduction

The navigation of vessels requires accurate knowledge of the water depth in orderto exploit safely the maximum cargo carrying capacity, and the maximum available

water for safe navigation. Where under-keel clearances are an issue the depthuncertainties must be more tightly controlled and better understood. In a similarway, the sizes offeatures that the survey will have or, more importantly, may nothave detected, should also be defined and understood.A similar situation occursduring the inspection of objects and the monitoring of dredging activities.

The measured depths and drying heights shall be referenced to a vertical datumthat is compatible with the products to be made or updated from the survey e.g.

chart datum. Ideally this sounding datum should also be a well-defined verticaldatum such as, LAT, MSL/MV, a geocentric reference frame based on ITRS or a

geodetic reference level(NAP).

3.2 Vertical uncertainty

Vertical uncertaintyis to be understood as the uncertaintyof the reduced depths.In determining the vertical uncertaintythe sources of individual uncertainties needto be quantified, e.g. errors in the positioning system, errors in the various sensors,errors in the geometry of the vessel, errors caused by tidal- and draft corrections,e.d. All uncertainties should be combined statistically to obtain a total verticaluncertainty(TVU).

The maximum allowable vertical uncertaintyfor reduced depths as set out in Table1 specifies the uncertainties to be achieved to meet each order of survey.

Uncertaintyrelated to the 95% confidence levelrefers to the estimation oferror

from the combined contribution of random errors and residuals from the correctionof systematic errors. The capability of the survey system should be demonstratedby the TVU calculation.

Recognising that there are both depth independent and depth dependent errorsthat affect the uncertaintyof the depths, the formula below is to be used tocompute, at the 95% confidence level, the maximum allowable TVU. Theparameters a and b for each order, as given in Table 1, together with the depth

d have to be introduced into the formula in order to calculate the maximumallowable TVU for a specific depth:

22 )( dba +

Where:

a represents that portion of the uncertaintythat does not vary withdepth

b is a coefficient that represents that portion of the uncertaintythatvaries with depth

d is the depthb x d represents that portion of the uncertaintythat varies with depth

The vertical uncertaintyat the 95% confidence levelshould be recorded togetherwith the survey data (see also 5.3).


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3.3 Reductions for Tides / Water-level Observations

Observations sufficient to determine variations in the water level across the entiresurvey area must be taken for the duration of the survey for the reduction ofsoundings to the relevant sounding datum. These may be determined either bydirect measurement of the water level (i.e. by using a gauge) and if necessary

carried across the survey area by co-tidal corrections or by 3D positioningtechniques linked to the required sounding datum by a suitable separation model.

Tidal / water-level reductions need not be applied to depths greater than 200metres if TVU is not significantly impacted by this approximation.

3.4 Minimum depth

All anomalous features previously reported in the survey area and those detectedduring the survey should be examined in greater detail and, if confirmed, theirposition and least depth determined. If a previously reported anomalous feature isnot detected refer to Chapter 6 for disproving requirements. The agency

responsible for survey quality may define a depth limit beyond which a detailed seafloor investigation, and thus an examination of anomalous features, is not required.

For wrecks and obstructions which may have less than 40 metres clearance above

them and may be dangerous to normal surface navigation, their position and theleast depth over them should be determined by the best available method whilemeeting the depth uncertaintystandard of the appropriate order in Table 1.

Side scan sonar should not be used for depth measurement but to define areasrequiring more detailed and accurate investigation.

3.5 Feature detectionWhen a full sea floor search is required, the equipment used to conduct the surveymust be demonstrably capable of detecting features of the dimensions specified in

Table 1. Additionally, the equipment must be considered as part of a system(includes survey / processing equipment, procedures and personnel) that will

ensure there is a high probability that these features will be detected. It is theresponsibility of the hydrographic office / organisation that is gathering the data toassess the capability of any proposed system and so satisfy themselves that it isable to detect a sufficiently high proportion of any such features.

The NL Order A and the IHO Special Order and Order 1a feature detectionrequirements of 1 metre and 2 metre cubes respectively are minimum

requirements. Features may exist that are smaller than the size mandated for agiven order but which are a hazard to navigationor are for other reasons important

enough to be detected/mapped. It may therefore be deemed necessary by thehydrographic office / organization to detect smaller features in order to minimisethe risk of undetected hazards to surface navigation. This extra demand must bedefined explicitly in the survey instructions.

It should be noted that even when surveying with a suitable system 100%detection offeatures can never be guaranteed. Therefore a minimum coverage of95% is requested in NL Order A, supplemented by criteria for the 5% that is notcovered. In case of single beam surveys combined with side scan sonar not theentire area is covered with depth data, but the gaps regarding the object detection

are filled with side-scan sonar observations. These measurements do not generatedepths, but give an image of the sea floor and the presence of possible objects and

the dimensions thereof.


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If there is concern that features may exist within an area that may not be detectedby the Survey System being used, consideration should be given to the use of analternative system (e.g. a mechanical sweep) to increase the confidence in theminimum safe clearance depth across the area.

3.6 Sounding density / Line spacing

In planning the density of soundings, both the nature of the seabed in the area andthe requirements of safe surface navigation have to be taken into account to ensure

an adequate sea floor search.

For NL Order A, IHO Special Order and IHO Order 1a surveys no recommendedmaximum line spacing is given, as there is an overriding requirement for full seafloor search.

Full sea floor search is not required forNL Order B and IHO Orders 1b and 2. Table1 recommends maximum line spacing (IHO Orders 1b and 2) and bathymetricLIDAR spot density (IHO Order 1b). The nature of the seabed needs to be assessedas early as possible in a survey in order to decide whether the line spacing / LIDAR

spot density from Table 1 should be reduced or extended. For surveys where NLOrder B is needed, no maximum line spacing is given. In these cases the linespacing is to be defined depending on the specific project and must be explicitlymentioned in the survey instructions.


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4 Other measurements

4.1 Introduction

The following observations may not always be necessary but if specified in thesurvey requirement should meet the following standards.

Additional requirements for these measurements may be specified in regulationsissued by the awarding authority. If so, the awarding authority will refer to thesedocuments and the requirements in these documents become part of the standardto be achieved.

4.2 Seabed sampling

The nature of the seabed should be determined in potential anchorage areas, butmay also be relevant for for instance dredging activities. It may be determined byphysical sampling or inferred from other sensors (e.g. single beam echo sounders,side scan sonar, sub-bottom profiler, video, etc.). Physical samples should begathered at a spacing dependent on the seabed geology and as required to ground

truth any inference technique.

4.3 Chart and land survey vertical datums connection

IHO Technical Resolution A2.5, as set out in IHO Publication M-3, Resolutions ofthe International Hydrographic Organisation, requires that the datum used for tidalpredictions should be the same as that used for chart datum. In order for thebathymetric data to be fully exploited the vertical datum used for tidal observationsshould be connected to the general land survey datum(e.g. NAP) via prominentfixed marks in the vicinity of the tide gauge/station/observatory. Ellipsoidal heightdeterminations of the vertical reference marks used for tidal observations should bemade relative to a geocentric reference frame based on ITRS, preferably WGS84 or

ETRS89, or to an appropriate geodetic reference level.

4.4 Tidal predictions

Tidal data may be required for analysis for the future prediction of tidal heights andthe production of Tide Tables in which case observations should cover as long a

period of time as possible and preferably not less than 30 days.

4.5 Tidal stream and current observations

The speed and direction of tidal streams and currents which may exceed 0.5 knots

should be observed at the entrances to harbours and channels, at any change indirection of a channel, in anchorages and adjacent to wharf areas. It is also

desirable to measure coastal and offshore streams and currents when they are of

sufficient strength to affect surface navigation.

The tidal stream and current at each position should be measured at depthssufficient to meet the requirements of normal surface navigation in the survey area.In the case of tidal streams, simultaneous observations of tidal height and

meteorological conditions should be made and the period of observation shouldideally be 30 days with a measurement interval not bigger then 1 hour.


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The speed and direction of the tidal stream and current should be measured to 0.1

knots( 0.05 m/s) and the nearest 10 respectively, at 95% confidence level.

Where there is reason to believe that seasonal river discharge influences the tidalstreams and currents, measurements should be made to cover the entire period ofvariability.

For current measurements other then for navigational purposes, extra requirementsmay be defined.


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5 Data attribution

5.1 Introduction

To allow a comprehensive assessment of the quality of survey data it is necessaryto record or document certain information together with the survey data. Such

information is important to allow exploitation of survey data by a variety of userswith different requirements, especially as requirements may not be known whenthe survey data is collected.

5.2 Metadata

Metadata should be comprehensive but should comprise, as a minimum,information on:

- the survey in general e.g. purpose, date, area, equipment used, name ofsurvey platform;

- the geodetic reference system used, i.e. horizontal and vertical datum

including ties to a geodetic reference frame based on ITRS (e.g. WGS84) if alocal datum is used;

- calibration procedures and results;- sound speed correction method;- tidal datum and reduction;- uncertainties achieved and the respective confidence levels;- any special or exceptional circumstances;

- rules and mechanisms employed for data thinning.

Metadata should preferably be an integral part of the digital survey record andconform to the IHO S-100 Discovery Metadata Standard, when this is adopted.The metadata must also comply with the Dutch Metadata Standard for Geography

as prepared by Geonovum. This national standard is a further specification of theinternational ISO 19115 standard for metadata and also meets the EuropeanINSPIRE directive. To support the above requirements both Rijkswaterstaat and theNetherlands Hydrographic Service have, for their activities, prepared lists with the

required and optional metadata elements that every dataset must contain. Thecontracting authority must see to this as regular part of their hydrographic reports.

5.3 Point data attribution

All data should be attributed with its uncertaintyestimate at the 95% confidencelevelfor both position and, if relevant, depth. The computed or assumed scalefactor applied to the standard deviation in order to determine the uncertaintyat the

95% confidence level, and/or the assumed statistical distribution oferrors shouldbe recorded in the surveys metadata. (For example, assuming a Normal

distribution for a 1 Dimensional quantity, such as depth, the scale factor is 1.96 for95% confidence. A statement such as Uncertainties have been computed at 95%confidence assuming a standard deviation scale factor of 1.96 (1D) or 2.45 (2D),corresponding to the assumption of a Normal distribution oferrors, would beadequate in the metadata.) For soundings this should preferably be done for eachindividual sounding; however a single uncertaintyestimate may be recorded for anumber of soundings or even for an area, provided the difference between the

individual uncertaintyestimates and the collectively assigned uncertaintyestimateis negligible. The attribution should, as a minimum, be sufficient to demonstratethat the requirements of these Standards have been met.


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5.4 Bathymetric model attribution

If a Bathymetric Modelis required, metadata should include: the model resolution;the computation method; the underlying data density; uncertaintyestimate/uncertainty surface for the model; and a description of the underlyingdata.

5.5 Report of survey

The Report of Survey is the principal means by which the Surveyor in Chargeapproves the contents of all survey records. It must give a clear and comprehensive

account of how the survey was carried out, the results achieved, the difficultiesencountered and the shortcomings. Emphasis should be placed on the analysis of

achieved accuracies and whether the survey specifications have been met.


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6 Elimination of doubtful data

6.1 Introduction

To improve the safety of navigation it is desirable to eliminate doubtful data, i.e.data which are usually denoted on charts by PA (Position Approximate), PD

(Position Doubtful), ED (Existence Doubtful), SD (Sounding Doubtful) or as"reported danger". To confirm or disprove the existence of such data it is necessaryto carefully define the area to be searched and subsequently survey that areaaccording to the standards outlined in this publication.

6.2 Extent of Area to be Searched

No empirical formula for defining the search area can cover all situations. For thisreason, it is recommended that the search radius should be at least 3 times theestimated position uncertaintyof the reported hazard at the 95% confidence levelas determined by a thorough investigation of the report on the doubtful data by aqualified hydrographic surveyor.

If such report is incomplete or does not exist at all, the position uncertaintymustbe estimated by other means as, for example, a more general assessment ofpositioning and depth measurement uncertainties during the era when the data in

question was collected.

6.3 Conducting the search

The methodology for conducting the search should be based on the nature of thefeature, the area in which the doubtful data is reported and the estimated danger ofthe potential hazard to surface navigation. Once this has been established, thesearch procedure should be that of conducting a hydrographic survey of the extent

defined in 6.2, to the standards established in this publication.

6.4 Presentation of search results

Doubtful data shall be replaced with actual data collected during the search if thehazard has been detected. If not detected, the agency responsible for the survey

quality shall decide whether to retain the hazard as charted or to delete it.


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Abbreviations and glossary

Abbreviations:

1D 1-Dimensional2D 2-Dimensional3D 3-DimensionaldGPS Differential Global Positioning SystemED Existence DoubtfulETRS89 European Terrestrial Reference System 1989GEBCO General Bathymetric Chart of the OceansGNSS Global Navigation Satellite SystemIHO International Hydrographic OrganisationITRS International Terrestrial Reference SystemLAT Lowest Astronomical Tide

LIDAR Laser Imaging Detection And RangingMSL Mean Sea LevelMV MiddenstandsvlakNAP Normaal Amsterdams Peil

PA Position ApproximatePD Position DoubtfulRD RijksdriehoeksmetingREP Reported but not confirmedRTK Real Time KinematicSD Sounding Doubtful

SOLAS Safety Of Lives At SeaTHU Total Horizontal UncertaintyTPU Total Propagated UncertaintyTVU Total Vertical UncertaintyWGS84 World Geodetic System 1984

Glossary:

Note: The terms defined below, are the most relevant for this publication. A muchlarger selection of terms are defined in IHO Special Publication S-32 Hydrographic

Dictionary and in the by the Information Desk Standards Water (Aquo-lex)maintained dictionary. If a certain term is not included here, the here mentioned

publications should be consulted. If a term as shown below has a different definitionwith respect to the mentioned publications, then the definition given below, shouldbe used for this publication.

While making the Dutch version of this document it was chosen to use the glossary

of the Aquo-lex as much as possible whenever their meaning is consistent with thatof the glossary from the original S-44. The hydrographic glossary in the Aquo-lex,used the glossary of the Hydrographic Working Group of Rijkswaterstaat, edition2006, for input.

Accuracy: The degree to which a measured or calculated value corresponds to the

assumed or accepted value. (See: uncertainty, error).

Bathymetric model: A digital representation of the topography (bathymetry) of theseafloor with coordinates andz-values.

Blunder: Sole errors that occur through negligence or a mistake. These errors are

often large and, by definition, unpredictable. They are usually caused by suddenchanges in environmental conditions, system failures or user errors. Blunders areeasily detected by performing more measurements than strictly necessary.


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Confidence interval: A measure ofuncertainty.

Confidence Level: The probability that a given confidence intervalcontains anunknown. It should be noted that the confidence level (often set at 95%) dependson the assumed statistical distribution of the data and the calculation is different for

1-dimensional (1D) than for 2-dimensional (2D) quantities. In this publication,based on the normal distribution of the error, the 95% confidence level for 1Dquantities (z-value) are defined as 1.96 x standard deviation and the 95% level for

2D quantities (XY coordinates) as 2.45 x standard deviation.

Correction: The best estimate that can be made of the difference between theactual and the measured value of a parameter. The sign is such that the correction

added to the observation yields the measurement.

Datum: The vertical reference plane to which z-values during a survey aredetermined.

Error: The difference between an observed or computed value of a quantity and thetrue value of that quantity. (NB The true value can never be known, therefore thetrue error can never be known. It is legitimate to talk about error sources, but thevalues obtained from what has become known as an error budget, and from ananalysis of residuals, are uncertaintyestimates, not errors. See uncertainty)

Feature detection: The ability of a system to detect objects and / or obstacles of aspecific size. The standards in this document define the minimum size of objectsthat must be able to be detected during the survey.

Feature: under this standard, an object, artificial or not, which protrudes above thebottom and yields a potential danger to shipping or should be examined.

Full sea floor search: A systematic method for exploring the sea floor performed insuch a way that most of the features and objects as specified in the applicable

standard will be mapped. In practice it is impossible to achieve 100% coverage andthe use of the term 100% bathymetric coverage is therefore discouraged.

Integrity monitoring: This is the ability of a system to provide timely warnings to

users when the system should not be used.

Integrity monitor: equipment consisting of a GNSS receiver and radio transmitterset up over a known survey point that is used to monitor the quality of aDifferential GNSS (DGNSS) signal/system. Positional discrepancies are continuously

monitored and timely warnings are transmitted to users indicating when the systemshould not be used.

Line spacing: The distance between two adjacent survey lines.

Metadata: Data about data. Or the information on the characteristics of the data,such as the uncertaintyof the survey, the overall quality, data set title, source,uncertaintyof positioning and copyrights.

Reduced z-value: Observedz-value including all corrections related to the survey

and post processing and reduction to the used vertical datum.

Survey line: An imaginary line across water and/or land, set out for conductingsurveys, measurements, sampling, etc.


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Total horizontal uncertainty (THU): The component of the total propagateduncertainty(TPU) calculated in the horizontal plane. Although THU is quoted as asingle figure, THU is a 2-dimensional quantity. The assumption has been made thatthe horizontal uncertaintyis isotropic (i.e. there is a negligible correlation betweenerrors in x- and y-direction). This makes a Normal distribution circularly symmetricallowing a single number to describe the radial distribution of the errors about the

true value.Total propagated uncertainty (TPU): The resultant propagation of the uncertainties

when all known uncertainties, both random and systematic are considered. The TPUis due to the uncertaintyin the measurements and is a 3-dimensional variable.

Total vertical uncertainty (TVU): The component of the total propagated uncertainty(TPU) calculated in the vertical dimension. The TVU is a 1-dimensional variable.

Uncertainty: The distribution of a stochastic variable around the given value. Thecorresponding confidence leveland the assumed probability distribution should begiven thereto.

Uncertainty surface: a model, typically grid based, which describes the depthuncertaintyof the product of a survey over a contiguous area of the skin of theearth. The uncertainty surface should retain sufficient metadata to describeunambiguously the nature of the uncertaintybeing described.

Under-Keel Clearance: The distance between the lowest point of the hull of theship, usually a point on the keel, and the bottom

Z-value: This term indicates both the value for the depth as for the bottom height.The Royal Netherlands Navy uses only depth. At Rijkswaterstaat the determinationof the bottom height is also used.


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dutch standards for hydrographic surveys - 1st edition - july 2009_tcm174-302218

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