Providing Uncertainty: Mariner ’ s Perspective

1. Providing Uncertainty:Mariner’s Perspective CAPT Lee Alexander, USNR (ret)

2. Three Aspects • 1. What does “Uncertainty” mean? • Hydrographer vs. Mariner • Awareness and understanding • 2. Use of • “Thinking like a Mariner” • 3. Portrayal • Some considerations • Some examples • A Recommendation…

3. Hydrographic Uncertainty • IHO S-44 - Specifies the minimum standards for hydrographic surveys • So that the data collected are sufficiently accurate • spatial uncertainty is adequately quantified to be safely used by mariners (as primary users of this information)

4. As Defined in IHO S-44 • Confidence level - The probability that an error will not exceed the specified minimum value. • Error - The difference between an observed or computed value of a quantity and the ideal or true value of that quantity • Spatial uncertainty - [not defined]

5. S-57 ENC Product Specification • Object - M_QUAL • Attribute - CATZOC • Attribute values - POSACC, SOUACC, & TECSOU • No specific mention of uncertainty. Instead, confidence in terms of so-called “Zone of Confidence” (CATZOC) • Not really a zone but an assigned category within a defined area. • CATZOC “values” assigned in terms of: • 1. Position accuracy • 2. Depth accuracy • 3. Seafloor coverage • 4. Seafloor characteristics

6. Mariner’s Basic Assumption • The charted information provided is sufficient for safe navigation.* • Sufficiently accurate (depth and position) • Adequately quantified • Errors are known • within defined confidence level • spatial uncertainty is accounted for • * If not, why not?

7. The Reality… • Mariners are: • Less knowledgeable about charts than hydrographers.* • Not really interested in the survey, itself • what type, when conducted, or by who • More concerned about depths • known/unknown, coverage, density, and accuracy • Keen to obtain information in which to make informed decisions • Decision support based on current situation/task-at-hand *CAPT Robert Ward (HI “Insiders View, Sept. 04) RADM Tim McGee (USHydro 05)

8. AIS Speed Manoeuvrability Height of eye Regulatory Sea State Tasks Load Conditions Weather Deep-sea Navigation Radar Bridge Layout Pilotage Uncertainty? Voyage plan Cargo Currents Ship Configuration Traffic Density VTS Coastal navigation Chart in use Ice MIOs Navigation Display Time-to-go Human Factors Draft Visibility

9. Perceptions & Misperceptions • The more soundings you see, the better the area was surveyed. • The number of soundings shown are less than what is known. • Soundings in deep water are less accurate than those in shallow water. • Soundings are fixed, while depths are dynamic.

10. Thinking Like a Mariner • Hydrographers collect and provide, while mariners “digest” and use. • what may be interesting to a Hydrographer, may not be particularly useful to Mariners. • more information is not necessarily better • Give a Mariner good information and he/she will figure out how to use it • they decide what is/is not important • Good information is that which contributes to informed decision-making. • interesting is not the same critical • too much is often worse than too little

11. Thinking Like a Mariner (cont.) • The main use is decision support (i.e., “what if” or “can I”). • route/voyage planning Civil/Commercial Government/Military • current situation/task-at-hand • The display of uncertainty/confidence is less important than how it can/should be used. • source diagrams • numerical values (e.g., CATZOC) • color-coded graphics

12. Uses for Uncertainty/Confidence • Dynamic seafloor areas • Assign “changeability coefficient” (value or color scheme)  • Superceded Data • Previous replaced with new/better • Old superceded by new • Higher confidence than before

13. Source: LT Shep Smith

14. Depth & Uncertainty Combined Depth Grid Companion Uncertainty Grid

15. Combined Depth and Uncertainty Advantages: - intuitive - psudo-3D perspective - supplements nautical and cartographic info

16. Uncertainty Modeling • Traditionally, the measurement error of a given sounding is the value reported as the uncertainty of the depth. In other words: How good was that measurement? • But, what mariners really want to know is: How well is the depth known at this location?

17. CHS Pacific EM3000 – Esquimalt - 1m Surface defocused using 5m horizontal uncertainty estimate Defocusing (Horizontal Error) Source: “Total Propagated Error, BASE Surfaces and CARIS HIPS 5.4”, Lamey, B. et al., Proc. 3rd Int. Conf. On High-Resolution Surveys in Shallow Water, Sydney, Australia, 2003.

19. Smoothsheet Density Shoal-Biased Selected Soundings Reson 8101 at Survey Density (NOAA Ship WHITING)

20. Soundings Extracted from the Navigation Surface

21. Smooth Sheet Soundings from a Navigation Surface

22. Soundings and Contours from Navigation Surface

23. S-57 Ed. 3.1 ENC from Navigation Surface

24. Tide-Aware ENC 7Cs Tide Demo

25. CATZOC • For most ENCs that have been produced, the assigned CATZOC value is “U” (Un-assessed) • Unknown • Unable • Unwilling • CATZOC not widely understood or used by Mariners

26. ENC Uncertainty • S-57 ENC objects could be attributed with an estimated error. But,for depths: • depths are defined by a variety of measurements • some areas were interpolated without measurement •  One approach: require that the bathymetric portions of an ENC have uniform reported error. If there are areas that exceed the reported error: • classified as or “poorly surveyed” • assign a lower CATZOC value

27. Provision and Portrayal Strategy • Recommendation: Focus on New, not Old • Rather than trying to give uncertainty or confidence information on what occurred in the past (old surveys  current charts), • Provide new/better information that resulted from modern surveys (new surveys  better charts.