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

2. September 26, 2001 Shallow Survey 2001, Portsmouth, NH2 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.

3. September 26, 2001 Shallow Survey 2001, Portsmouth, NH3 Overview  Motivation  The Navigation Surface-an example –Depth Surface –Uncertainty Surface  Application to Charting

4. September 26, 2001 Shallow Survey 2001, Portsmouth, NH4 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.

5. September 26, 2001 Shallow Survey 2001, Portsmouth, NH5 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

6. September 26, 2001 Shallow Survey 2001, Portsmouth, NH6 Normal Distribution of Error

7. September 26, 2001 Shallow Survey 2001, Portsmouth, NH7 Traditional Processing --Shoal Biasing  Start with 45 Million “cleaned” soundings  Suppress Soundings (shoal-biased) to 1:10,000 scale  Result: 5200 “smooth sheet” soundings

8. September 26, 2001 Shallow Survey 2001, Portsmouth, NH8 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.

9. September 26, 2001 Shallow Survey 2001, Portsmouth, NH9 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

10. September 26, 2001 Shallow Survey 2001, Portsmouth, NH10 Smooth Sheet Density

11. September 26, 2001 Shallow Survey 2001, Portsmouth, NH11 High Resolution Grid

12. September 26, 2001 Shallow Survey 2001, Portsmouth, NH12 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

13. September 26, 2001 Shallow Survey 2001, Portsmouth, NH13 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.

14. September 26, 2001 Shallow Survey 2001, Portsmouth, NH14 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

15. September 26, 2001 Shallow Survey 2001, Portsmouth, NH15 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

16. September 26, 2001 Shallow Survey 2001, Portsmouth, NH16 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

17. September 26, 2001 Shallow Survey 2001, Portsmouth, NH17 Current Process Source Soundings Nautical Chart Survey ProductsDatabase

18. September 26, 2001 Shallow Survey 2001, Portsmouth, NH18 Proposed Process Source Soundings Nautical Charts Survey ProductsDatabase Navigation Surface Hydro Vector Database ENC Other

19. September 26, 2001 Shallow Survey 2001, Portsmouth, NH19 Proposed Process Source Soundings Nautical Charts Survey ProductsDatabase Navigation Surface Hydro Vector Database ENC Other

20. September 26, 2001 Shallow Survey 2001, Portsmouth, NH20 Populating the Navigation Surface Database  Smart Shoal Adjustment  Uncertainty Surface creation

21. September 26, 2001 Shallow Survey 2001, Portsmouth, NH21  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

22. September 26, 2001 Shallow Survey 2001, Portsmouth, NH22  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

23. September 26, 2001 Shallow Survey 2001, Portsmouth, NH23 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.

24. September 26, 2001 Shallow Survey 2001, Portsmouth, NH24 Smart Shoal Adjustment

25. September 26, 2001 Shallow Survey 2001, Portsmouth, NH25 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.

26. September 26, 2001 Shallow Survey 2001, Portsmouth, NH26 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.

27. September 26, 2001 Shallow Survey 2001, Portsmouth, NH27 Uncertainty Surface-High Resolution Multibeam  For every depth grid node, there is an uncertainty estimate Two different methods: 1.Forward Error—Characteristics of Sonar/setup/conditions off-nadir angle  greater uncertainty, etc. 2.Backward Error—95% variability in bin around node

28. September 26, 2001 Shallow Survey 2001, Portsmouth, NH28 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.

29. September 26, 2001 Shallow Survey 2001, Portsmouth, NH29 Backward Error

30. September 26, 2001 Shallow Survey 2001, Portsmouth, NH30 Backward Error Draped

31. September 26, 2001 Shallow Survey 2001, Portsmouth, NH31 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.

32. September 26, 2001 Shallow Survey 2001, Portsmouth, NH32 Forward Node Error

33. September 26, 2001 Shallow Survey 2001, Portsmouth, NH33 Uncertainty Estimates-Sparse Data  Uncertainty increases: –as a function of distance from the nearest measurement –more rapidly on a rough seafloor

34. September 26, 2001 Shallow Survey 2001, Portsmouth, NH34 Uncertainty Surface

35. September 26, 2001 Shallow Survey 2001, Portsmouth, NH35 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.

36. September 26, 2001 Shallow Survey 2001, Portsmouth, NH36 Proposed Process-Chart Production Source Soundings Nautical Charts Survey ProductsDatabase Navigation Surface Hydro Vector Database ENC Other

37. September 26, 2001 Shallow Survey 2001, Portsmouth, NH37 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

38. September 26, 2001 Shallow Survey 2001, Portsmouth, NH38 Supersede and Merge Grids WHITING 8101 RUDE 9003 1950s Singlebeam

39. September 26, 2001 Shallow Survey 2001, Portsmouth, NH39 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

40. September 26, 2001 Shallow Survey 2001, Portsmouth, NH40 Defocusing Methodology Horizontal Error of Sounding Base Point Adjusted Point

41. September 26, 2001 Shallow Survey 2001, Portsmouth, NH41 Error ellipse applied to surface

42. September 26, 2001 Shallow Survey 2001, Portsmouth, NH42 Defocused Surface over Original Note Exact Match on Peak

43. September 26, 2001 Shallow Survey 2001, Portsmouth, NH43 Defocusing Methodology-With excess error Horizontal Error of Sounding Base Point Adjusted Point Excess Error

44. September 26, 2001 Shallow Survey 2001, Portsmouth, NH44 In areas of high uncertainty

45. September 26, 2001 Shallow Survey 2001, Portsmouth, NH45 Contours from Defocused Surface

46. September 26, 2001 Shallow Survey 2001, Portsmouth, NH46 Soundings Extracted from the Navigation Surface

47. September 26, 2001 Shallow Survey 2001, Portsmouth, NH47 Soundings and Contours from Navigation Surface

48. September 26, 2001 Shallow Survey 2001, Portsmouth, NH48 Review Charting From the Navigation Surface Navigation Surface Database Defocus for Uncertainty Extract Soundings, Contours Hydrographic Vector Database Charts-Raster And ENC

49. September 26, 2001 Shallow Survey 2001, Portsmouth, NH49 Depth Areas as S-57 Objects

50. September 26, 2001 Shallow Survey 2001, Portsmouth, NH50 Detail

51. September 26, 2001 Shallow Survey 2001, Portsmouth, NH51 Detail

52. September 26, 2001 Shallow Survey 2001, Portsmouth, NH52 Potential for New Navigation Products

53. September 26, 2001 Shallow Survey 2001, Portsmouth, NH53 Potential for New Navigation Products

54. September 26, 2001 Shallow Survey 2001, Portsmouth, NH54 Potential for New Navigation Products

55. September 26, 2001 Shallow Survey 2001, Portsmouth, NH55 Summary  Changes to Entire Charting Process –Survey product is a model and uncertainty at the horizontal resolution of the survey –Navigation products (ENC) extracted from database of multiple grids  Other products, other sources, quality control and efficiency