representing uncertainty on charts: the “hydrographic crisis” uncertainty workshop chc 2004

Representing Uncertainty on Charts: Representing Uncertainty on Charts: The “Hydrographic Crisis”The “Hydrographic Crisis”

Uncertainty Workshop

CHC 2004

The Gordon ReidThe Gordon Reid

The Canadian Coast Guard Ship (CCGS) Gordon Reid ran aground on an uncharted rock in Estavan Sound, off the coast of British Columbia on 28 September 2003

CHS Chart 3724: 1923 lead-line and sextant survey with 400 metres between sounding lines

Research UndertakenResearch Undertaken

Topic of the UNB Uncertainty Paper, “Bathymetric Uncertainty Representation on Nautical Charts”

Research taken on by UNB & USM graduate students under the direction of Dr. Dave Wells

The Uncertainty SituationThe Uncertainty Situation

Many users of nautical charts have no idea how uncertain is the information shown on the charts they are using

This leads to inappropriate navigation decisions, groundings, and sometimes loss of life

Uncertainty in Hazard DetectionUncertainty in Hazard Detection

Bathymetric Uncertainties Positioning UncertaintiesIncomplete coverage between survey

lines (as was the fate of the Gordon Reid)

Navigation DecisionsNavigation Decisions

Mariners have excellent positioning tools due to high accuracy GPS and ENCs

This does not account for positioning uncertainty present at time of survey

For example, over half of the inshore NOAA nautical charts were acquired by lead-line and sextant surveying prior to 1940

3 Methods of Representing Uncertainty3 Methods of Representing Uncertainty

Two methods, a Source Diagram (SD), and a Reliability Diagram (RD) are graphical insets on a paper chart– Showing the geographical limits for each

survey– A table describing the attributes of each

survey area in the diagram

Zone of Confidence (ZOC) methods used on Electronic Navigational Charts (ENC)

Source Diagrams (SCD)Source Diagrams (SCD)

Hydrographic organizationDate of survey Scale of survey Direct line spacing information

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NOS SDNOS SD(A) 1990 to the present. Full bottom coverage. DGPS positioning used.

(B1) 1990 to the present. Partial bottom coverage from single

beam echo sounder. GPS or DGPS used.

(B2) 1970 to 1989. Partial bottom coverage from single beam echo sounder. Primarily electronic radio-positioning .

(B3) 1940 to 1969. Partial bottom coverage from single beam echo sounder. Visual positioning

(B4) 1900 to 1939. Partial bottom coverage from lead line. visual positioning.

(B5) Pre-1900. Partial bottom coverage from lead line. visual positioning.

NOAA ApproachNOAA Approach

CHS CHS

RAN RAN

Reliability DiagramsReliability Diagrams

Give an assessment of accuracy as well as advising on preferred areas for navigation

Examples of the attributes – Estimated accuracy of soundings– Distance between survey sounding lines– Classification of the survey (e.g.

reconnaissance or incomplete; controlled; sounded by lead line; sounded by echosounder; shoals have been examined; has been sonar swept)

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Zones of Confidence (ZOC)Zones of Confidence (ZOC)

ZOC values assigned to areas on an ENC A1/A2: Full bottom ensonification with

depths determined for all

significant features B: Uncharted hazards may exist C: Uncharted depth anomalies are

expected D: Large depth anomalies are expected

ZOC CategoriesZOC Categories

3 Active Directions3 Active Directions

Education for users

Worldwide HO Survey

Presentation on charts

Canadian Power & Sail SquadronsCanadian Power & Sail Squadrons

Teaches courses to recreational boaters nationwide

General, advanced, and specialty boating

Status of Uncertainty Representation EducationStatus of Uncertainty Representation Education

No education currently available in Canada

No education availablethrough the United StatesPower Squadrons (USPS)

Worldwide HO SurveyWorldwide HO Survey

HOs from around the world have been contacted

5 questions were asked about their uncertainty policies

Survey QuestionsSurvey Questions

Asked 5 questions about their uncertainty information– Both paper and electronic charts– Methods of communication to users– Satisfaction with current policy– Plans to change current policies, and barriers which

prevent doing so Very diverse responses Australia, Canada, Denmark, Finland, Greece, Hong Kong,

Iceland, Italy, Japan, Mexico, Netherlands, New Zealand, Norway, Poland, Portugal, Saudi Arabia, South Africa, Sweden, Turkey, UK, US NGA, US NOAA

1: How is uncertainty represented on 1: How is uncertainty represented on your paper charts? your paper charts?

Some agencies do not use SDs or RDs at all (one agency removed SDs from their charts, since they were not kept updated)

Some agencies use SDs only on large scale charts

Most agencies are in the process of adding SDs to their charts. One agency claimed 100% of their charts had SDs

2. Are ZOC values on your ENCs fully 2. Are ZOC values on your ENCs fully

attributed? attributed? 40% have full ZOC attribution on all ENCs

(over half of these use only ZOC values B and C, or in one case only B on all ENCs)

30% use only U attribution so far 30% are partway to full attribution Reasons for not having full ZOC

attribution were lack of resources, lack of metadata upon which to base the ZOC, and the liability implied by assigning a ZOC

3. How else do you communicate 3. How else do you communicate information on chart uncertainties to users? information on chart uncertainties to users?

60% use Notices to Mariners 25% used web pages, other nautical

publications, and presentations to user groups.

The Danish hydrographic office booklet “Behind the Nautical Chart” is free for downloading from its website. This booklet explains the uncertainty associated with hydrographic survey methods over the years (and is soon to be translated from Danish to English)

4. Are you satisfied with your current 4. Are you satisfied with your current policies and practices? policies and practices?

30% answered yes 60% answered with a qualified or

unqualified no 10% dodged the question (e.g. “we will

always try to improve”) The qualified no answers were based on a

desire for better methods than SDs, RDs or ZOCs, and on liability issues associated with RDs and ZOCs

5. Are you considering any changes to 5. Are you considering any changes to

these policies and practices? these policies and practices? 15% answered no 10% answered they would comply with

any new international standards that might emerge

40% intend to work towards completion of SDs on all paper charts, and / or full ZOC attribution on all ENCs

35% seek improvements to their entire hydrographic data management strategy, uncertainty information

Defining the end userDefining the end user

Commercial ShippingFishing and Natural resourcesRecreational usersMilitary/Coast Guard

Need based representationNeed based representation

Establish product enhancements based on input from user groups.

Common factor being improved situational awareness.

What enhancements will most improve the safety and decision making of the Navigator?

Why add the enhancement?Why add the enhancement?

How and under what circumstances will it be used?

Voyage planning.Weather maneuvering.Shipboard medical emergency.Result: Time critical decision making

requires clear depiction of reliability.

What to add to the Chart?What to add to the Chart? Source diagram – Voyage and approach planning.

What to add to the Chart?What to add to the Chart? Primary chart depiction - Best for time critical

decision making.

Rocks, soundings and depth contours printed in red (Gulf of Finland)

UNB RecommendationsUNB Recommendations

Survey details including:- Date of survey- Survey and positioning technology

used - Line spacing/amount of coverage

Given by either exact survey details, or by a classification scheme to maximize clarity and simplicity

UNB RecommendationsUNB Recommendations

Timeless, without the use of descriptive quality terms such as “modern standards” or “current technology”

Be accompanied by a form of education for chart users

Be part of a national standard, with the ultimate future goal of a global standard