Seamless Combination of Bathymetry and Topography: Transforming Vertical Datums

1. Seamless Combination of Bathymetry and Topography:Transforming Vertical Datums Dennis Milbert, Ph.D. Bruce Parker, Ph.D. National Ocean Service, NOAA

2. Acknowledgements • Collaboration of USGS and NOAA • National Ocean Service • Coast Survey • Coastal Services Center • National Geodetic Survey • Local Partners (so far) • Florida Marine Research Institute • Tampa Bay National Estuary Program • Rookery Bay National Estuarine Research Reserve • Port Authorities • Future Partners • Federal Emergency Management Agency • U.S. Army Corp of Engineers

3. Introduction • What is a Datum? • When Datums Don’t Match • The Shoreline/Datum Problem • Categories of Datums • VDatum -- the Datum Transformation Tool • How VDatum Works • Examples • Outcomes and Future Work

4. What is a Datum? • Two related definitions of “datum” • Idealization • “A set of constants defining a coordinate system” • Realization • “The constants, the coordinate system, and all points and lines that have been consistently determined by measurement and computation”

5. Datums Arise From Relative Measurements, I 25 20 15 10 10.0 5.0 5 5.0 0.0 0 Datum A

6. Datums Arise From Relative Measurements, II 20 15 10.0 10 5.0 5 0.0 0.0 0 -5 -10 Datum B

7. Datums Arise From Relative Measurements, III 20 25 15 10.0 20 10 5.0 15 5 0.0 0.0 10 0 10.0 5.0 -5 5 5.0 0.0 -10 0 Datum A Datum B Note: Discontinuity between A & B

8. When Datums Match 25 20.0 20 15.0 15 10.0 10.0 10 10.0 5.0 5 5.0 0.0 0 Datum A (All elevations are now consistent)

9. Shoreline/Datum Problem, I MSL MLLW N N 15 3 meters meters Mean Lower Low Water (MLLW) Mean Sea Level (MSL)

10. Shoreline/Datum Problem, II • A shoreline has a vertical datum imbedded in it • If you change a shoreline vertical reference -- • It will cause translations in the shoreline • It will also change the shape of the shoreline • As with all geo-referenced data, only combine data in a common datum

11. Shoreline and Legal Issues

12. Vertical Datums - 3 Categories • Tidal Datums • Related to particular stages of ocean tide • Mean Lower Low Water (MLLW) • Mean Sea Level (MSL) • Orthometric Datums • Related to equipotential surface of the Earth • North American Vertical Datum 1988 (NAVD 88) • Ellipsoidal (3-D) Datums • Related to an ellipsoidal figure of the Earth • Heights directly from GPS • North American Datum 1983 (NAD 83)

13. Ellipsoidal (3-D) Datums NAD 83 Control Point WGS 84 ~2-meter shift Differences in origins cause differences in height above the ellipsoid

14. Orthometric Datums NGVD 29 -- 21 US (5 Canada) fixed tide gauges NAVD 88 -- 1 fixed tide gauge The adopted control points and constants defining the heights cause NGVD 29 and NAVD 88 to differ by up to 2.2 meters

15. Tide Datums • Tide datum references are extracted from tidal measurements Mean Low Water Mean Lower Low Water

16. Tides Vary Globally • Tide ranges in feet • Cape Town • Dakar • Le Havre • Southampton • Bremerhaven • Causes differences in the tidal datums

17. Approximate Lowest Astronomical Tide Approximate Mean Low Water Springs Approximate Mean Low Water Tide Approximate Mean Low Water Approximate Mean Sea Level Equinoctial Spring Low Water Highest Astronomical Tide Higher High Water Large Tide Highest Normal High Water Higher High Water Highest High Water High Water High Water Springs International Great Lakes Datum 1985 Indian Spring High Water Indian Spring Low Water Lowest Astronomical Tide Lower Low Water Large Tide Lowest Low Water Springs Lower Low Water Lowest Low Water Low Water Low Water Springs Mean Higher High Water Mean Higher Water Mean High Water Mean High Water Neaps Mean High Water Springs Mean Lower Low Water Springs Mean Lower Low Water Mean Low Water Mean Low Water Neaps Mean Low Water Springs Mean Sea Level Mean Tide Level Nearly Lowest Low Water Neap Tide Spring Tide Various Tidal/Sounding Datums

18. The Vertical Datum Problem • A sizable number of vertical datums • Several versions in each of 3 categories • Topographic data in NAVD 88 or NGVD 29 • Hydrographic data in MLW and MLLW • Newest technology referenced with GPS (NAD 83, WGS84, or ITRF) • Need a tool to transform between vertical datums

19. VDatum • Java application -- Windows-like graphics • Transform heights and soundings between vertical datums • 2 modes -- interactive and batch • Uses regional datum transformation grids • Supports 26 different vertical datums

20. VDatum -- Interactive Mode

21. VDatum -- Batch Mode

22. VDatum -- Batch Input Data • H07934,27.536908,-82.806664,63.0 • H07934,27.537256,-82.813550,66.9 • H07934,27.543464,-82.815983,64.9 • H07934,27.544878,-82.813717,64.0 • H07934,27.547394,-82.812214,64.0 • H07934,27.547675,-82.801350,61.0 • H07934,27.547728,-82.807472,62.0 • H07934,27.533836,-82.822453,69.9 • H07934,27.536425,-82.826103,68.9 • H07934,27.538631,-82.818847,65.9

23. VDatum -- Batch Output Data • H07934,27.536908,-82.806664,140.4907 • H07934,27.537256,-82.813550,144.3543 • H07934,27.543464,-82.815983,142.3430 • H07934,27.544878,-82.813717,141.4552 • H07934,27.547394,-82.812214,141.4638 • H07934,27.547675,-82.801350,138.5223 • H07934,27.547728,-82.807472,139.4894 • H07934,27.533836,-82.822453,147.3081 • H07934,27.536425,-82.826103,146.2900 • H07934,27.538631,-82.818847,143.3269

24. Tidal MHHW MHW DTL MTL LMSL MLW MLLW Orthometric NAVD 88 NGVD 29 Ellipsoidal NAD 83 (86) WGS 84 (G873) WGS 84 (G730) WGS 84 (original) WGS 72 ITRF97 ITRF96 ITRF94 ITRF93 and 8 more ... Vertical Datums in VDatum

25. The Datum Transformation Constellation MLLW WGS 84 (G873) ITRF88 LMSL ITRF96 NEOS 90 ITRF93 MTL ITRF91 ITRF97 WGS 84 (G730) NAVD 88 SIO/MIT 92 DTL MLW MHHW ITRF94 ITRF92 WGS 84 (orig.) PNEOS 90 ITRF89 NAD 83 (86) NGVD 29 ITRF90 MHW How many paths ???

26. The Datum Transformation Roadmap, I WGS 84 (G873) MHHW WGS 84 (G730) WGS 84 (orig.) ITRF97 MHW NGVD29 ITRF96 ITRF94 MTL ITRF93 NAVD 88 NAD 83 (86) LMSL ITRF92 ITRF91 DTL ITRF90 ITRF89 MLW ITRF88 SIO/MIT 92 NEOS 90 MLLW PNEOS 90 Each edge is a transformation.

27. WGS 84 (G873) -12.0000 feet NAD 83 (86) -6.9001 NAVD 88 73.1061 LMSL 72.5713 MLLW 73.6934 The Datum Transformation Roadmap, II WGS 84 (G873) MHHW WGS 84 (G730) WGS 84 (orig.) ITRF97 MHW NGVD29 ITRF96 ITRF94 MTL ITRF93 NAVD 88 NAD 83 (86) LMSL ITRF92 ITRF91 DTL ITRF90 ITRF89 MLW ITRF88 SIO/MIT 92 NEOS 90 MLLW PNEOS 90

28. Tidal Datum Maps Figure portrays MSL - MLLW (meters) Produced by a calibrated and verified hydrodynamic model of Tampa Bay Digital maps were made for 7 tidal datums

31. Tidal Benchmark Data Geodetic level ties to tidal benchmarks allow evaluation of tide models and calibration of local mean sea level variations.

32. USGS Topography Integrated Bathy/Topo Model  NOAA Bathymetry 

33. 3-DVisualization of Bathy/Topo DEM (Visualizations are useful, but the form in which the actual data are provided to the coastal marine user is also critical.)

36. Outcomes • Transformation tool for integration of diverse datasets • Portable implementation • Can be imbedded in GIS software systems • Validated against geodetic control • Leveled benchmarks • GPS control points • Tide gauges • Easy to use • User can focus on the data, not on the geodesy

37. Future Work and More Outcomes • Extend to cover entire US coastline • Accuracy maps for the transformations • Support decision process for data acquisition • legacy data -- perhaps less accurate • new GPS-based data -- through transformation • Intersect various vertical reference planes through a seamless 3-D bathy/topo surface • Potential to establish shorelines with new technology and with accuracy equivalent to that of photogrammetry

39. Backup Slides

46. Tampa BayBathy/Topo/ShorelineDemonstration Project Mapping the Land-Sea Interface A Collaborative Approach

47. Tampa Bay Demonstration Project • Bathy/Topo Digital Elevation Model (DEM) • NOAA bathymetric data (referenced to the ellipsoid) • USGS topographic data (referenced to the ellipsoid) • Datum Transformation Tool (26 ortho, 3-D, and tidal datums) • geographic distribution of tidal datums from hydrodynamic model • incorporation of recent hi-res 3rd-party data (datums, standards) • recent hi-res shorelines from airborne and satellite remote sensing • internally consistent shorelines (HW, MSL, MLLW) from a DEM with a high-resolution shoreline elevation zone • GIS compatibility (with retention of maximum resolution) • Website-accessible, with tutorials and standards • append other data sets (e.g., demographics, environmental, etc.) • first steps towards a “National Shoreline”

48. The problems that motivated this project • Inconsistency between NOAA and USGS shorelines • referenced to different tidal datums • differences in measurement instruments and procedures • CONFUSED MARINE USER COMMUNITY • (for many purposes, consistency is more important than accuracy) • (plus, need to minimize the duplication of effort between the two agencies) • (plus, need to find the most-cost effective way to map 95,000 miles of coastline in the U.S.) • Sparse and outdated bathymetric and topographic data • AND, no national framework to allow the inclusion of recent high-resolution data from other sources (state, county, academic) • (And thus) a geospatial reference frame for other coastal data sets that is less consistent and accurate than is needed • Limits our ability to accurately represent the coastal zone and predict impacts on communities and the environment • hurricane evacuation planning -- local, state, and national boundaries • habitat restoration -- electronic navigational chart systems • permitting

49. Where is the Shoreline? NOAA Shoreline USGS Topo Sheet Spin 2 satellite imagery

50. Just 3 of the 26 Datums handled by the Datum Transformation Tool Allows transformation to a common datum for the blending of different data sets.