1. Dennis Milbert, Ph.D. Bruce Parker, Ph.D. National Ocean Service, NOAA
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, I25 20 15 10
10.0
5.0 5
5.0
0.0
Datum A

6. Datums Arise From Relative Measurements, II20 15
10.0 10
5.0 5
0.0
0.0 -5
-10
Datum B

7. Datums Arise From Relative Measurements, III20 25 15
10.0 20 10
5.0 15 5 10
10.0
0.0
0.0
5.0 5
5.0 -5
0.0
-10
Datum A
Datum B
Note: Discontinuity between A & B

8. When Datums Match Datum A (All elevations are now consistent) 25 20 15
20.0 20
15.0 15
10.0 10
10.0
10.0
5.0 5
5.0
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 (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 US (5 Canada) fixed tide gauges
NAVD 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. Various Tidal/Sounding Datums
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

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

23. VDatum -- Batch Output Data

24. Vertical Datums in VDatum
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 ...

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
NGVD 29
NAD 83 (86)
ITRF90
MHW
How many paths ???

26. The Datum Transformation Roadmap, I
WGS 84 (G873)
WGS 84 (G730)
MHHW
WGS 84 (orig.)
ITRF97
MHW
ITRF96
NGVD 29
ITRF94
MTL
ITRF93
NAD 83 (86)
NAVD 88
LMSL
ITRF92
ITRF91
DTL
ITRF90
ITRF89
MLW
ITRF88
SIO/MIT 92
NEOS 90
MLLW
PNEOS 90
Each edge is a transformation.

27. The Datum Transformation Roadmap, II
WGS 84 (G873)
WGS 84 (G730)
MHHW
WGS 84 (orig.)
ITRF97
MHW
ITRF96
NGVD 29
ITRF94
MTL
ITRF93
NAD 83 (86)
NAVD 88
LMSL
ITRF92
ITRF91
DTL
ITRF90
ITRF89
MLW
ITRF88
SIO/MIT 92
NAD 83 (86)
WGS 84 (G873) feet
NAVD
LMSL
MLLW
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. Integrated Bathy/Topo Model
USGS Topography 
NOAA Bathymetry 

33. 3-D Visualization 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 Bay Bathy/Topo/Shoreline Demonstration 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.

51. Except for around the navigation channels, the bathymetric data
is from the 1950s.
The original topographic data is also primarily from
the 1950s, with some 1960s and early 1970s data.
Need to be able
to take advantage
of other data sources.

52. Learning How to Obtain High-Resolution Up-to-Date
Shoreline from various Airborne and Satellite Techniques
In addition to the April 1999 airborne
photogrammetry and the SPIN2 satellite data,
shoreline data sets will be derived (and
inter-compared) from: airborne lidar data,
airborne hyperspectral data, IKONOS satellite
data, SAR data, and SHOALS (bathymetric
lidar) data.
How to cost-effectively map
95,000 miles of U.S. coastline?

53. The only way to accomplish all this is through A Collaborative Approach
USGS and NOAA working together to solve complex mapping issues on the front end
State and local needs, and participation
Working with Federal Emergency Management Agency (FEMA) and U.S. Army Corp of Engineers (USACE)
Local Partners include (so far):
Florida Marine Research Institute
Tampa Bay National Estuary Program
Rookery Bay National Estuarine Research Reserve
Ports

54. Dennis Milbert, Ph.D. Kurt Hess, Ph.D. National Ocean Service, NOAA
Combination of Topography and Bathymetry Through Application of Calibrated Vertical Datum Transformations in the Tampa Bay Region
Dennis Milbert, Ph.D.
Kurt Hess, Ph.D.
National Ocean Service, NOAA

55. Introduction What is a Datum? When Datums Don’t Match
The Shoreline/Datum Problem
Categories of Datums
VDatum -- the Datum Transformation Tool
Examples in Tampa Bay
Outcomes and Future Work