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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) . RTK/PPK-GPS Hydrographic Surveys.

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Vdatum the vertical datum transformation tool
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)


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


Need to integrate land and water datasets with different elevation reference systems

‘MSL’

Mapped

Shoreline

Elevations

MHW

MLLW (MLW)

NAVD 88, NGVD 29

Depths

NAD 27

NAD 83

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


Tidal datums mhhw mhw msl mlw mllw

How to convert between these various datums? Vdatum Conversion Software

Tidal DatumsMHHWMHWMSLMLWMLLW

Orthometric Datums

NAVD 88

NGVD 29

Ellipsoidal Datums

WGS 84

ITRFxxxx

NAD 83


DELAWARE BAY PPK-GPS SURVEY, June 2001 Conversion Software

Tide Zones

VDatum gives a more realistic

series of depths values

VDatum vs Zoning

:

VDATUM

conversion

fields

‘Jump’ due to

crossing tide

zones


Digital elevation models to study sea level rise in north carolina
Digital Elevation Models to Study Conversion SoftwareSea Level Rise in North Carolina

NC Land

Elevation

Inundated areas due to a 30 cm sea level rise

NOAA

Bathymetry

Integrated DEM


LIDAR data transformed from ellipsiodal to the MHW datum using VDatum.

NOAA T-Sheet MHW shoreline (1977)

0 m contour is MHW shoreline (1996)

Consistently–defined 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


VDATUM TODAY using VDatum.

Areas where VDatum tool is complete and available to the public


In summary vdatum supports
In Summary, VDatum Supports: using VDatum.

  • 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


Issues using VDatum.

  • 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


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