What is the North American Vertical Datum of 1988 (NAVD 88)?

The North American Vertical Datum of 1988 (NAVD 88) is the official vertical datum established for orthometric heights in the United States. It is based on the General Adjustment of the North American Datum of 1988 and serves as the primary reference system for measuring elevations across the country. Orthometric heights represent the height of a point above a reference surface that approximates mean sea level.

What vertical datum did NAVD 88 replace, and what was its previous name?

NAVD 88 superseded the National Geodetic Vertical Datum of 1929 (NGVD 29). NGVD 29 was previously known as the Sea Level Datum of 1929.

When is NAVD 88 scheduled to be replaced, and what will replace it?

NAVD 88, along with the North American Datum of 1983 (NAD 83), is slated for replacement in 2025. It will be succeeded by a new geometric reference frame and a new geopotential datum.

How was the NAVD 88 established?

NAVD 88 was established in 1991 through a process called a minimum-constraint adjustment. This involved analyzing geodetic leveling observations collected across Canada, the United States, and Mexico to create a unified vertical reference system.

What specific benchmark was used as the fixed origin point for NAVD 88, and what was its reference value?

The height of the primary tide gauge benchmark located in Rimouski, Quebec, Canada, was fixed to its International Great Lakes Datum of 1985 local mean sea level (MSL) height value. This fixed point served as the origin for the NAVD 88 datum.

Why were elevations from other tidal benchmarks not utilized in the establishment of NAVD 88?

Elevations from other tidal benchmarks were excluded because variations in sea surface topography were observed. This means that mean sea level (MSL) is not a consistent equipotential surface across all tidal benchmarks, making a single benchmark height more reliable for establishing a unified datum.

What geographical regions are covered by the NAVD 88 leveling network?

The NAVD 88 leveling network spans the North American continent, extending from Alaska, through Canada, and across the United States. It is affixed to a single origin point on the continent.

When was NAVD 88 officially adopted as part of the National Spatial Reference System (NSRS)?

NAVD 88 was affirmed as the official vertical datum within the National Spatial Reference System (NSRS) for the Conterminous United States and Alaska in 1993, as announced in the Federal Register.

Does a single, official document define the NAVD 88 datum?

No, despite numerous publications discussing NAVD 88, there isn't one single document that serves as its official defining document.

What type of orthometric height calculation does the definition of NAVD 88 employ?

The definition of NAVD 88 utilizes the Helmert orthometric height. This method involves calculating the position of the geoid, which approximates mean sea level, using modeled local gravity measurements.

Is the NAVD 88 geoid model based on the latest available data?

No, the NAVD 88 model is based on the geodetic measurements available at the time of its establishment. It remains fixed even though more recent and improved geoid models have since been developed.

How did the gravity model used for NGVD 29 differ from the approach used for NAVD 88?

The National Geodetic Vertical Datum of 1929 (NGVD 29) used a simplified gravity model based solely on latitude to calculate the geoid. In contrast, NAVD 88 employs the Helmert orthometric height, which incorporates modeled local gravity, allowing for a more accurate representation of the geoid by accounting for gravitational variations.

What are the identified inaccuracies or issues with the NAVD 88 datum?

It has been determined that NAVD 88 suffers from both a bias, estimated at about 0.5 meters (1 ft 8 in), and a tilt, measuring approximately 1 meter (3 ft 3 in) across the continent from coast to coast.

What is the primary motivation for replacing NAD 83 and NAVD 88?

The replacement is driven by the need to improve the National Spatial Reference System (NSRS). The new reference frames are designed to be more accessible and easier to maintain than the current NAD 83 and NAVD 88, which rely on physical survey marks that degrade over time.

What technologies will underpin the new datums replacing NAD 83 and NAVD 88?

The upcoming datums will primarily rely on Global Navigation Satellite Systems (GNSS), such as the Global Positioning System (GPS), and an advanced gravimetric geoid model. This model is being developed through NOAA's Gravity for the Redefinition of the American Vertical Datum (GRAV-D) Project.

What is the fundamental purpose of a vertical datum like NAVD 88?

A vertical datum, such as NAVD 88, provides a standardized reference surface for establishing orthometric heights. Essentially, it defines 'zero elevation' for a region, allowing for consistent measurement of heights above sea level.

What does the term 'orthometric height' signify in the context of NAVD 88?

Orthometric height refers to the elevation of a point measured along the direction of gravity from a reference surface, typically approximating mean sea level. NAVD 88 provides the framework for calculating these heights accurately within its defined region.

What is the significance of the International Great Lakes Datum of 1985 (IGLD 85) in relation to NAVD 88?

IGLD 85 is significant because the specific mean sea level height value of a benchmark tied to this datum in Rimouski, Quebec, was used as the fixed origin point for establishing the NAVD 88 datum.

How is mean sea level (MSL) understood in the context of vertical datums?

Mean sea level (MSL) represents the average height of the sea surface over time. While it serves as a conceptual basis for vertical datums, NAVD 88 acknowledges that MSL varies geographically (sea surface topography) and is not a perfect equipotential surface, influencing datum definition.

What is the role of the National Geodetic Survey (NGS) concerning NAVD 88?

The National Geodetic Survey (NGS), part of NOAA, is responsible for the development, maintenance, and future replacement of vertical datums like NAVD 88. They manage the National Spatial Reference System (NSRS) and are leading the transition to the new datums planned for 2025.

What does the 'General Adjustment of the North American Datum of 1988' refer to?

The 'General Adjustment of the North American Datum of 1988' was a comprehensive survey adjustment process that established the horizontal and vertical reference framework for North America in 1988. NAVD 88 is the vertical component derived from this adjustment.

What is the purpose of the Gravity for the Redefinition of the American Vertical Datum (GRAV-D) Project?

The GRAV-D Project aims to collect highly accurate gravity measurements across the United States. The data gathered is crucial for developing an improved geoid model, which is essential for defining the new geopotential datum that will replace NAVD 88.

What are Global Navigation Satellite Systems (GNSS), and why are they important for the new datums?

Global Navigation Satellite Systems (GNSS) are constellations of satellites that provide positioning, navigation, and timing services globally. Examples include GPS, GLONASS, Galileo, and BeiDou. They are important because the new datums replacing NAD 83 and NAVD 88 will rely heavily on GNSS data for greater accessibility and accuracy.

What is a geoid model in the field of geodesy?

A geoid model is a representation of the Earth's mean sea level surface, extended conceptually through the continents using gravity measurements. It serves as the reference surface for defining orthometric heights (elevations) and is fundamental to vertical datums.

What is the key difference in maintenance strategy between NAVD 88 and its upcoming successor?

NAVD 88 relies on physical survey marks (benchmarks) which are prone to deterioration and require ongoing maintenance. The successor datums will primarily utilize satellite-based systems (GNSS) and geoid models, which are expected to be more stable, accessible, and easier to maintain over time.

How is the image captioned 'Illustration of vertical datums in the United States' described?

The image caption indicates a visual aid that explains or demonstrates the concept and application of vertical datums within the geographical context of the United States.

What does the image captioned 'An unusual vertical datum marker at a shoreline street end in Seattle' depict?

This caption describes a unique marker signifying a vertical datum, located at a specific point in Seattle, Washington, where a street terminates at the shoreline.

What is the function of the 'See also' section within the article?

The 'See also' section provides a list of related topics and concepts, such as altitude, geodesy, and topography, that readers might find relevant for further exploration of the subject matter.

What information is provided in the sidebar related to 'Geodesy'?

The sidebar offers a structured overview of geodesy, covering its fundamental principles, key concepts like the geoid and reference ellipsoids, related technologies such as GNSS, and a historical list of significant geodetic datums and standards.

What are some of the core 'Concepts' listed under Geodesy in the sidebar?

The core concepts listed include Geographical distance, Geoid, Figure of the Earth (radius and circumference), Geodetic coordinates, Geodetic datum, Geodesic, Horizontal position representation, Latitude/Longitude, Map projection, Reference ellipsoid, Satellite geodesy, Spatial reference system, Spatial relations, and Vertical positions.

Which Global Navigation Satellite Systems (GNSS) are mentioned in the Geodesy sidebar?

The sidebar mentions several GNSS: Global Positioning System (GPS) from the United States, GLONASS from Russia, BeiDou (BDS) from China, Galileo from Europe, NAVIC (Indian Regional Navigation Satellite System) from India, and Quasi-Zenith Satellite System (QZSS) from Japan.

What historical geodetic datums are listed in the sidebar navigation?

The sidebar lists historical datums including NGVD 29 (Sea Level Datum 1929), OSGB36 (Ordnance Survey Great Britain 1936), SK-42 (Systema Koordinat 1942 goda), ED50 (European Datum 1950), SAD69 (South American Datum 1969), GRS 80 (Geodetic Reference System 1980), ISO 6709 (Geographic point coord. 1983), NAD 83 (North American Datum 1983), WGS 84 (World Geodetic System 1984), NAVD 88 (N. American Vertical Datum 1988), ETRS89 (European Terrestrial Ref. Sys. 1989), GCJ-02 (Chinese obfuscated datum 2002), and Geo URI (Internet link to a point 2010).

What is the relationship between NAVD 88 and NAD 83?

NAVD 88 is a vertical datum used for measuring elevations, while NAD 83 is a horizontal datum used for measuring positions (latitude and longitude). Both are fundamental components of the North American geodetic reference system and are scheduled to be replaced together in 2025.

Can you define what a 'vertical datum' is?

A vertical datum is a reference system used to define orthometric heights, which are elevations relative to a mean sea level surface. It provides a standardized basis for measuring heights across a specific region.

What is a 'geodetic datum'?

A geodetic datum is a reference system that defines the size and shape of the Earth (using a reference ellipsoid) and establishes the origin and orientation of coordinate systems used in surveying and mapping. It encompasses both horizontal and vertical components.

What is the International Terrestrial Reference System (ITRS)?

The International Terrestrial Reference System (ITRS) is an internationally recognized standard for defining a stable, consistent coordinate system for the Earth. It serves as a fundamental reference for various geodetic applications.

What is the purpose of the 'Orthometric Height Conversion tool' mentioned in the external links?

This tool, provided by the U.S. National Geodetic Survey, allows users to convert orthometric height values between different datums. This is useful for tasks like comparing elevations defined under NAVD 88 with those under older or newer systems.

What does the term 'geoid' represent in geodesy?

The geoid is a model representing the Earth's mean sea level surface, extended conceptually through the continents. It is an equipotential surface that approximates mean sea level and serves as the zero-height reference for orthometric heights.

How does NAVD 88 account for the fact that mean sea level (MSL) is not uniform globally?

NAVD 88 acknowledges that mean sea level varies geographically due to factors like ocean currents and gravitational anomalies (sea surface topography). To address this, it fixed the height of a single primary benchmark rather than relying on multiple tidal benchmarks, which might show inconsistent MSL values.

What is the significance of the Federal Register Notice (FRN) regarding NAVD 88?

The Federal Register Notice (FRN) published in 1993 officially announced and affirmed NAVD 88 as the standard vertical datum for surveying and mapping activities within the National Spatial Reference System (NSRS) for the Conterminous United States and Alaska.

How does the GRAV-D Project contribute to the upcoming datum replacement?

The GRAV-D Project is collecting extensive gravity measurements across the nation. This data is essential for creating a highly accurate geoid model, which will form the basis of the new geopotential datum intended to replace NAVD 88.

What are the drawbacks of relying on physical survey marks for datums like NAVD 88?

Physical survey marks, such as benchmarks, are susceptible to damage, erosion, and other forms of degradation over time. This makes them less reliable and requires continuous effort and expense for maintenance and recovery, unlike modern satellite-based systems.

What is the fundamental difference between a horizontal datum and a vertical datum?

A horizontal datum, like NAD 83, defines the coordinate system for latitude and longitude, specifying locations on the Earth's surface. A vertical datum, like NAVD 88, defines the coordinate system for elevation or height, referencing a surface like mean sea level.

What is the significance of the year 1988 in the name 'North American Vertical Datum of 1988'?

The year 1988 refers to the 'General Adjustment' of the North American Datum, which established the foundational geodetic framework upon which the NAVD 88 vertical datum is based.

What is the historical significance of the year 1929 in relation to NAVD 88?

The year 1929 is associated with the National Geodetic Vertical Datum (NGVD 29), the predecessor vertical datum that NAVD 88 was created to replace due to advancements in surveying technology and understanding of Earth's shape.

What is the approximate magnitude of the tilt found in the NAVD 88 datum across North America?

The NAVD 88 datum exhibits a tilt of approximately 1 meter (about 3 feet 3 inches) when measured from coast to coast across the North American continent.

What is the approximate bias identified in the NAVD 88 datum?

NAVD 88 has a known bias of approximately 0.5 meters (about 1 foot 8 inches).

In geodesy, what is the purpose of a 'reference ellipsoid'?

A reference ellipsoid is a mathematically defined surface, typically an oblate spheroid, that approximates the shape of the Earth. It serves as a fundamental basis for geodetic coordinate systems, enabling calculations of positions, distances, and areas.

What constitutes a 'geodetic coordinate'?

A geodetic coordinate specifies a location using latitude, longitude, and height within a defined geodetic datum and reference system. It provides a precise three-dimensional position on or relative to the Earth's surface.

What role do tide gauges play in the definition of vertical datums like NAVD 88?

Tide gauges measure sea level at coastal locations over time. Data from these gauges helps establish benchmarks related to mean sea level, which are critical reference points for defining vertical datums. However, NAVD 88 recognized the variability of MSL and relied on a single benchmark for its definition.

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Introduction to NAVD 88

Defining Vertical Reference

The North American Vertical Datum of 1988 (NAVD 88) serves as the definitive vertical datum for orthometric heights across the United States. Established through a comprehensive adjustment of geodetic leveling data, it provides a standardized framework for measuring elevations.

Superseding Previous Standards

NAVD 88 was implemented to replace the older National Geodetic Vertical Datum of 1929 (NGVD 29), which was previously known as the Sea Level Datum of 1929. This transition aimed to incorporate more accurate surveying techniques and a better understanding of Earth's gravitational field.

A Datum in Transition

While NAVD 88 has been the standard for decades, it is slated for replacement in 2025. This upcoming transition, known as the Datum of 2022, will introduce a new geometric reference frame and geopotential datum, leveraging advanced technologies like GPS and sophisticated geoid models.

Methodology and Definition

Continental Adjustment

NAVD 88 was established in 1991 through a rigorous, minimum-constraint adjustment of geodetic leveling observations spanning Canada, the United States, and Mexico. This process integrated data from across the continent into a single, unified vertical reference system.

Fixed Origin Point

The datum's definition was anchored by fixing the orthometric height of a primary tide gauge benchmark at Rimouski, Quebec, Canada. This benchmark's height was referenced to the International Great Lakes Datum of 1985 (IGLD 85) local mean sea level (MSL). Tidal benchmarks were not used due to observed variations in sea surface topography.

Geoid Modeling

The definition of NAVD 88 utilizes the Helmert orthometric height. This method calculates the geoid's position, which approximates mean sea level, using modeled local gravity. Importantly, the NAVD 88 model remains fixed, even though subsequent, more refined geoid models have become available.

The Datum of 2022

Upcoming Transition

Recognizing the limitations of NAVD 88, including inherent biases and tilt, the National Geodetic Survey (NGS) is preparing to replace it. The Datum of 2022, scheduled for implementation in 2025, will introduce a new geometric reference frame and a modernized geopotential datum.

Leveraging Modern Technology

The new reference frames will primarily rely on Global Navigation Satellite Systems (GNSS), such as GPS, and advanced gravimetric geoid models derived from projects like NOAA's GRAV-D Project. This shift moves away from traditional survey marks that degrade over time.

Enhanced Accessibility

The Datum of 2022 is designed to be more accessible and easier to maintain than its predecessors. By utilizing satellite-based positioning and improved gravity data, it aims to provide a more stable, accurate, and user-friendly vertical reference system for North America.

Related Concepts

Vertical Positioning

Understanding vertical datums is crucial for accurate elevation determination. This section explores key concepts related to vertical positioning in geodesy.

Altitude: The height of an object or point in relation to sea level or ground level.
Geodesy: The science of accurately measuring and understanding the Earth's geometric shape, orientation in space, and gravity field.
Geoid: An equipotential surface of the Earth's gravity field that approximates mean sea level.
Reference Ellipsoid: A mathematically defined surface that approximates the shape of the Earth, used as a basis for geodetic calculations.
Topographic Elevation: The height of the Earth's surface above a reference datum, often mean sea level.
Topography: The arrangement of the natural and artificial physical features over an area.
Sea Level Datum of 1929: The predecessor to NAVD 88, also known as NGVD 29.

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References

A full list of references for this article are available at the North American Vertical Datum of 1988 Wikipedia page

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This page was generated by an Artificial Intelligence and is intended for informational and educational purposes only. The content is based on a snapshot of publicly available data from Wikipedia and may not be entirely accurate, complete, or up-to-date.

This is not professional advice. The information provided on this website is not a substitute for professional geodetic consultation, surveying, or engineering advice. Always refer to official documentation from organizations like the National Geodetic Survey and consult with qualified professionals for specific project needs. Never disregard professional advice because of something you have read on this website.

The creators of this page are not responsible for any errors or omissions, or for any actions taken based on the information provided herein.

Navigating Heights

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Introduction to NAVD 88 📍

📏 Defining Vertical Reference

🔄 Superseding Previous Standards

⏳ A Datum in Transition

Methodology and Definition ⚙️

🌐 Continental Adjustment

⚓ Fixed Origin Point

🧠 Geoid Modeling

The Datum of 2022 🚀

➡️ Upcoming Transition

🛰️ Leveraging Modern Technology

💡 Enhanced Accessibility

Related Concepts 📚

⬆️ Vertical Positioning

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Dive in with Flashcard Learning!

Introduction to NAVD 88

Defining Vertical Reference

Superseding Previous Standards

A Datum in Transition

Methodology and Definition

Continental Adjustment

Fixed Origin Point

Geoid Modeling

The Datum of 2022

Upcoming Transition

Leveraging Modern Technology

Enhanced Accessibility

Related Concepts

Vertical Positioning

Teacher's Corner

True or False?

Test Your Knowledge!

Gamer's Corner

Discover other topics to study!

References

Feedback & Support

Disclaimer

Important Notice