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Vertical DatumsVertical Datums

A vertical datum is used for measuring the elevations of points on the earth's surface.

– Geodetic Datums (NGVD29, NAVD88) – Hydrologic Datums (LWRP, IGLD)– Tidal Datums (MSL or LMSL, MLLW, MHW)– Local (Cario, Memphis Datum) – Ellipsoid (Space-based) Surfaces

Influenced by Gravity

Not Influenced by Gravity

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Orthometric HeightsComparison of Vertical Datum Elements

NGVD 29 NAVD 88

DATUM DEFINITION 26 TIDE GAUGES FATHER’S POINT/RIMOUSKI IN THE U.S. & CANADA QUEBEC, CANADA

BENCH MARKS 100,000 450,000

LEVELING (Km) 102,724 1,001,500

TIDAL EPOCH None 1960 - 1978

GEOID FITTING Distorted to Fit MSL Gauges Best Continental Model

Vertical DatumsVertical Datums

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The North American Vertical Datum of 1988 is referenced to 1 tide

gage on the St. Lawrence Seaway

1,000,000+ km

The Sea Level Datum of 1929 was

referenced to 26 tide gages in the US and

Canada~100,000 km

The Sea Level Datum of 1929’s name was

changed to the National Geodetic

Vertical Datum in 1973

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4 cm

125 cm

70 cm

85 cm 102 cm

NGVD 29Referenced to 26 Tide Gages

NAVD 88Referenced to 1 Tide Gage

(Father’s Point)

NAVD88 minus LMSL(1960-1978)

-23 cm

-23 cm

-11 cm

-11 cm

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• NOAA's National Geodetic Survey (NGS) defines and manages a national coordinate system.

• This network, the National Spatial Reference System (NSRS), provides the foundation for our spatial infrastructure

• NGS develops Federal standards for geodetic surveys and helps to coordinate surveying methods.

• NGS State Geodetic Advisors are stationed in several states to work with local communities to expand surveying capabilities.

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Changing Elevations in a Dynamic EnvironmentChanging Elevations in a Dynamic Environment

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Changing Elevations in a Dynamic EnvironmentChanging Elevations in a Dynamic Environment

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Additional Information Available at:

http://crunch.tec.army.mil/information/SM_CoP/ndsp

james.k.garster@usace.army.mil

mark.w.huber@usace.army.mil