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The Navigation Surface A New Approach to Multiple Product Creation from Hydrographic Surveys LT Shepard M. Smith, NOAA University of New Hampshire CCOM/JHC Slide 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. Slide 3 September 26, 2001 Shallow Survey 2001, Portsmouth, NH3 Overview Motivation The Navigation Surface-an example Depth Surface Uncertainty Surface Application to Charting Slide 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. Slide 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 Slide 6 September 26, 2001 Shallow Survey 2001, Portsmouth, NH6 Normal Distribution of Error Slide 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 Slide 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. Slide 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 Slide 10 September 26, 2001 Shallow Survey 2001, Portsmouth, NH10 Smooth Sheet Density Slide 11 September 26, 2001 Shallow Survey 2001, Portsmouth, NH11 High Resolution Grid Slide 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 HOs need a process to use the data for charting while accurately classifying its accuracy Slide 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. Slide 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 Slide 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 Slide 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 Slide 17 September 26, 2001 Shallow Survey 2001, Portsmouth, NH17 Current Process Source Soundings Nautical Chart Survey ProductsDatabase Slide 18 September 26, 2001 Shallow Survey 2001, Portsmouth, NH18 Proposed Process Source Soundings Nautical Charts Survey ProductsDatabase Navigation Surface Hydro Vector Database ENC Other Slide 19 September 26, 2001 Shallow Survey 2001, Portsmouth, NH19 Proposed Process Source Soundings Nautical Charts Survey ProductsDatabase Navigation Surface Hydro Vector Database ENC Other Slide 20 September 26, 2001 Shallow Survey 2001, Portsmouth, NH20 Populating the Navigation Surface Database Smart Shoal Adjustment Uncertainty Surface creation Slide 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 Slide 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 Slide 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. Slide 24 September 26, 2001 Shallow Survey 2001, Portsmouth, NH24 Smart Shoal Adjustment Slide 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. Slide 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. Slide 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 ErrorCharacteristics of Sonar/setup/conditions off-nadir angle greater uncertainty, etc. 2.Backward Error95% variability in bin around node Slide 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. Slide 29 September 26, 2001 Shallow Survey 2001, Portsmouth, NH29 Backward Error Slide 30 September 26, 2001 Shallow Survey 2001, Portsmouth, NH30 Backward Error Draped Slide 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. Slide 32 September 26, 2001 Shallow Survey 2001, Portsmouth, NH32 Forward Node Error Slide 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 Slide 34 September 26, 2001 Shallow Survey 2001, Portsmouth, NH34 Uncertainty Surface Slide 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. Slide 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 Slide 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 Slide 38 September 26, 2001 Shallow Survey 2001, Portsmouth, NH38 Supersede and Merge Grids WHITING 8101 RUDE 9003 1950s Singlebeam Slide 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 Slide 40 September 26, 2001 Shallow Survey 2001, Portsmouth, NH40 Defocusing Methodology Horizontal Error of Sounding Base Point Adjusted Point Slide 41 September 26, 2001 Shallow Survey 2001, Portsmouth, NH41 Error ellipse applied to surface Slide 42 September 26, 2001 Shallow Survey 2001, Portsmouth, NH42 Defocused Surface over Original Note Exact Match on Peak Slide 43 September 26, 2001 Shallow Survey 2001, Portsmouth, NH43 Defocusing Methodology-With excess error Horizontal Error of Sounding Base Point Adjusted Point Excess Error Slide 44 September 26, 2001 Shallow Survey 2001, Portsmouth, NH44 In areas of high uncertainty Slide 45 September 26, 2001 Shallow Survey 2001, Portsmouth, NH45 Contours from Defocused Surface Slide 46 September 26, 2001 Shallow Survey 2001, Portsmouth, NH46 Soundings Extracted from the Navigation Surface Slide 47 September 26, 2001 Shallow Survey 2001, Portsmouth, NH47 Soundings and Contours from Navigation Surface Slide 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 Slide 49 September 26, 2001 Shallow Survey 2001, Portsmouth, NH49 Depth Areas as S-57 Objects Slide 50 September 26, 2001 Shallow Survey 2001, Portsmouth, NH50 Detail Slide 51 September 26, 2001 Shallow Survey 2001, Portsmouth, NH51 Detail Slide 52 September 26, 2001 Shallow Survey 2001, Portsmouth, NH52 Potential for New Navigation Products Slide 53 September 26, 2001 Shallow Survey 2001, Portsmouth, NH53 Potential for New Navigation Products Slide 54 September 26, 2001 Shallow Survey 2001, Portsmouth, NH54 Potential for New Navigation Products Slide 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