VDATUM: the Vertical Datum Transformation Tool

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VDATUM the Vertical Datum Transformation Tool
Kurt Hess Office of Coast Survey

• A vertical datum is a reference surface for
  elevations
• NOAA Chart Datum for Depths Mean Lower Low Water
  (MLLW)
• NOAA Shoreline Mean High Water (MHW)

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RTK/PPK-GPS Hydrographic Surveys
Depths are measured on the fly relative to
ellipsoidal datum (e.g., WGS84). Depths need to
be converted to chart datum (MLLW).

• Eliminates need for
• -tide gauges during survey
• settlement squat
• corrections for survey vessel
• time-consuming post-survey
• processing

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Need to Integrate Land and Water Datasets with
Different Elevation Reference Systems
NOAA
USGS (Tidal Datums) (Intertidal)
(Orthometric Datums)
MLLW MHW Charted Charted Shoreline
Shoreline
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Tidal DatumsMHHWMHWMSLMLWMLLW
How to convert between these various datums?
Vdatum Conversion Software
Orthometric Datums NAVD 88 NGVD 29
Ellipsoidal Datums WGS 84 ITRFxxxx NAD 83
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DELAWARE BAY PPK-GPS SURVEY, June 2001
Tide Zones
VDatum gives a more realistic series of depths
values
VDatum vs Zoning

VDATUM conversion fields
Jump due to crossing tide zones
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Digital Elevation Models to StudySea Level Rise
in North Carolina
NC Land Elevation
Inundated areas due to a 30 cm sea level rise
NOAA Bathymetry
Integrated DEM
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Consistentlydefined Shoreline

• first true consistently-
• defined MHW shoreline
• can utilize topographic
• LIDAR data from many
• sources
• can also measure MLLW
• from bathymetric LIDAR
• true interface between
• bathymetry topography

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VDATUM TODAY
Areas where VDatum tool is complete and available
to the public
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In Summary, VDatum Supports

• Faster, cheaper, more accurate hydrographic
  survey data
• Merging NOAA bathymetric data for GIS and
  other uses
• Integrated bathymetric-topographic DEMs for
• Storm surge and flooding
• Port planning and Homeland Security
• Sea Level Rise studies
• LIDAR coastal elevation data for
• Consistently defined shoreline for NOAA, USGS
• NOS charting products
• maritime boundaries

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Issues

• We must educate users about the importance of
  understanding and using the various vertical
  datums and reference systems
• Establishing VDatum for entire US will require
  (1) setting priorities for geographic areas and
  (2) long-term hydro survey planning
• Tide and surveyed benchmark data are often
  lacking or are outdated. Also true for
  bathymetric data, which are needed for tide
  modeling
• There is a need for many more elevation
  measurements (e.g., LIDAR) in the inter-tidal zone