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The Navigation Surface

The Navigation Surface. A New Approach to Multiple Product Creation from Hydrographic Surveys. LT Shepard M. Smith, NOAA University of New Hampshire CCOM/JHC. What are we talking about?. Means and process to use a gridded data set for safety to navigation (nautical chart).

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The Navigation Surface

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  1. The Navigation Surface A New Approach to MultipleProduct Creation from Hydrographic Surveys LT Shepard M. Smith, NOAA University of New Hampshire CCOM/JHC

  2. What are we talking about? • Means and process to use a gridded data set for safety to navigation (nautical chart). • Priority placed on optimization for safety. • Highest resolution of survey preserved for other users and for different scales of navigation products. • Uncertainty management built into process. Shallow Survey 2001, Portsmouth, NH

  3. Overview • Motivation • The Navigation Surface-an example • Depth Surface • Uncertainty Surface • Application to Charting Shallow Survey 2001, Portsmouth, NH

  4. Motivations • High Data Volume • Other users of high-density bathymetry • Non-Traditional Sources of Bathymetry • Electronic Navigational Chart (ENC) • Prioritization of survey effort • Field quality control • CUBE-revolutionary method of modelling from raw data. Shallow Survey 2001, Portsmouth, NH

  5. High Data Volume • In Portsmouth: • Multibeam survey in +-15m water • IHO Order 1 survey required • 95% depth accuracy of 0.53m • Multibeam system has 0.3m error (95%) • It is important to stress that soundings are not binary good or bad • Processing procedures catch outliers >1m • Assume a normal distribution of error Shallow Survey 2001, Portsmouth, NH

  6. Normal Distribution of Error Shallow Survey 2001, Portsmouth, NH

  7. Traditional Processing --Shoal Biasing • Start with 45 Million “cleaned” soundings • Suppress Soundings (shoal-biased) to 1:10,000 scale • Result: 5200 “smooth sheet” soundings Shallow Survey 2001, Portsmouth, NH

  8. Statistical Implications of Shoal Biasing • If: one in 8,000 soundings are selected for the smooth sheet from a flat area • Then: Each smooth sheet sounding would be 0.55m shoaler than the “true” depth • Every sounding selected for the smooth sheet exceeds the IHO error limit for the survey. • Not only can we treat these data statistically, but we must in order to meet our standards. Shallow Survey 2001, Portsmouth, NH

  9. Other Users of Bathymetric Data • Other Customers • Coastal Zone Management • Marine Geology • Fisheries Habitat/Management • Hydrodynamic Modeling • Ocean Engineering • Current products are primarily focused on the charting process • The shoal-biasing and sounding suppression processes reduce the value of the data for other purposes Shallow Survey 2001, Portsmouth, NH

  10. Smooth Sheet Density Shallow Survey 2001, Portsmouth, NH

  11. High Resolution Grid Shallow Survey 2001, Portsmouth, NH

  12. Non-Traditional Sources of Bathymetric Data • Many federal, state, commercial, and academic institutions are collecting high quality bathymetric data • Usually not processed to hydrographic standards • Often best data available in the area • HO’s need a process to use the data for charting while accurately classifying its accuracy Shallow Survey 2001, Portsmouth, NH

  13. Electronic Navigational Chart • The transition to ENC makes it possible to deliver a more detailed vector product to mariners • USA must transition from feet to metric • Sub-meter contours necessary for some areas • With a surface model, contours and depth areas can be created at any intervals in any unit at any scale. Shallow Survey 2001, Portsmouth, NH

  14. Prioritization of Survey Effort • Surveys can be prioritized in areas with • Low underkeel clearances • High uncertainty of depth estimate • Older data in areas with a dynamic seabed • Known inconsistencies and large number of unresolved reported items Shallow Survey 2001, Portsmouth, NH

  15. Field Quality Control • Hydrographers can use the uncertainty surface • To assess the quality of the survey • To prioritize additional work • To meet a pre-defined standard Shallow Survey 2001, Portsmouth, NH

  16. CUBE • Dr. Brian Calder at University of New Hampshire CCOM-JHC • Revolutionary method to robustly create a model from raw data • Output of analysis is a gridded model and uncertainty model Shallow Survey 2001, Portsmouth, NH

  17. Current Process Survey Database Products Source Soundings Nautical Chart Shallow Survey 2001, Portsmouth, NH

  18. Proposed Process Survey Database Products Source Soundings Navigation Surface Other ENC Hydro Vector Database Nautical Charts Shallow Survey 2001, Portsmouth, NH

  19. Proposed Process Survey Database Products Source Soundings Navigation Surface Other ENC Hydro Vector Database Nautical Charts Shallow Survey 2001, Portsmouth, NH

  20. Populating the Navigation Surface Database • Smart Shoal Adjustment • Uncertainty Surface creation Shallow Survey 2001, Portsmouth, NH

  21. Advantages Preserves all shoal features exactly Disadvantages All system errors are preserved Small real features are lost in the noise Noisy contours and dtms Advantages Most probable surface created Clean surfaces and contours Bathymetric detail is preserved Easy to manipulate Disadvantages Shoal depths are not preserved Shoal-Biased Bin Mean Grid Shallow Survey 2001, Portsmouth, NH

  22. Advantages Preserves all shoal features exactly Disadvantages All system errors are preserved Small real features are lost in the noise Noisy contours and dtms Advantages Most probable surface created Clean surfaces and contours Bathymetric detail is preserved Easy to manipulate Disadvantages Shoal depths are not preserved Shoal-Biased Bin Mean Grid Navigation Surface Shallow Survey 2001, Portsmouth, NH

  23. Smart Shoal Adjustment • The value of the grid node is adjusted to the shoalest measurement when: • Point value is shoaler than any grid node within 5mm at survey scale (a similar methodology to sounding suppression) • Suppresses noise except in areas that are significant to navigation. • This step requires a cleaned sounding set. Shallow Survey 2001, Portsmouth, NH

  24. Smart Shoal Adjustment Shallow Survey 2001, Portsmouth, NH

  25. Depth + Uncertainty Surfaces=Navigation Surface • Two Cases • Case 1-Oversampled data (modern multibeam) • a mean surface • weighted by vertical accuracy • Shoal adjusted in critical places • Case 2-Undersampled data (historic single-beam and leadline) • Interpolated (IDW, TIN, etc) • Adjusted to match sparse data points. Shallow Survey 2001, Portsmouth, NH

  26. Uncertainty Surface-Overview • Model uncertainty • Not “How good is this measurement?” • But “How well do we know the depth at this location?” • When HOs put a depth curve or a depth area on a chart, we imply a model of the seafloor. • This is not new, we already construct a model of the seafloor. Shallow Survey 2001, Portsmouth, NH

  27. Uncertainty Surface-High Resolution Multibeam • For every depth grid node, there is an uncertainty estimate Two different methods: • Forward Error—Characteristics of Sonar/setup/conditions • off-nadir angle  greater uncertainty, etc. • Backward Error—95% variability in bin around node Shallow Survey 2001, Portsmouth, NH

  28. High backward error when: • There is a wide range in the measurements within a single bin for a given slope • System noise • Systematic error • The size of a point feature is smaller than the area of the sonar footprint. Shallow Survey 2001, Portsmouth, NH

  29. Backward Error Shallow Survey 2001, Portsmouth, NH

  30. Backward Error Draped Shallow Survey 2001, Portsmouth, NH

  31. Forward Node Error • Primarily shows density of coverage • More independent measurements of a node should reduce the uncertainty • Since the value of a single sounding depends on numerous measurements (not all of which are independent), there is a limit beyond which the forward node uncertainty can no longer be reduced. Shallow Survey 2001, Portsmouth, NH

  32. Forward Node Error Shallow Survey 2001, Portsmouth, NH

  33. Uncertainty Estimates-Sparse Data • Uncertainty increases: • as a function of distance from the nearest measurement • more rapidly on a rough seafloor Shallow Survey 2001, Portsmouth, NH

  34. Uncertainty Surface Shallow Survey 2001, Portsmouth, NH

  35. Uncertainty Estimates-Side Scan • When side scan sonar is towed and processed during a singlebeam survey (or a wide line spacing multibeam survey) • Uncertainty is limited to the sum of the largest “insignificant” contact and undetectable bathymetric changes • Set to 1m. Shallow Survey 2001, Portsmouth, NH

  36. Proposed Process-Chart Production Survey Database Products Source Soundings Navigation Surface Other ENC Hydro Vector Database Nautical Charts Shallow Survey 2001, Portsmouth, NH

  37. Supersede and Merge • Supersede • A more accurate node in the model supersedes a less accurate node OR • A more recent survey supersedes an older survey • Merge • When downsampling a model, a shoal biased approach is used Shallow Survey 2001, Portsmouth, NH

  38. Supersede and Merge Grids WHITING 8101 1950s Singlebeam RUDE 9003 Shallow Survey 2001, Portsmouth, NH

  39. Use of the Navigation Surface for Charting: Defocusing • Goal: To create a surface from the database that has: • Least depths on significant features • Constant shoal-side error (95% 0.3m) • Horizontal error reflected in the surface • Smooth surface for contour creation Shallow Survey 2001, Portsmouth, NH

  40. Defocusing Methodology Horizontal Error of Sounding Base Point Adjusted Point Shallow Survey 2001, Portsmouth, NH

  41. Error ellipse applied to surface Shallow Survey 2001, Portsmouth, NH

  42. Defocused Surface over Original Note Exact Match on Peak Shallow Survey 2001, Portsmouth, NH

  43. Defocusing Methodology-With excess error Horizontal Error of Sounding Excess Error Base Point Adjusted Point Shallow Survey 2001, Portsmouth, NH

  44. In areas of high uncertainty Shallow Survey 2001, Portsmouth, NH

  45. Contours from Defocused Surface Shallow Survey 2001, Portsmouth, NH

  46. Soundings Extracted from the Navigation Surface Shallow Survey 2001, Portsmouth, NH

  47. Soundings and Contours from Navigation Surface Shallow Survey 2001, Portsmouth, NH

  48. Review Charting From the Navigation Surface Navigation Surface Database Defocus for Uncertainty Extract Soundings, Contours Hydrographic Vector Database Charts-Raster And ENC Shallow Survey 2001, Portsmouth, NH

  49. Depth Areas as S-57 Objects Shallow Survey 2001, Portsmouth, NH

  50. Detail Shallow Survey 2001, Portsmouth, NH

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