earth science

U.S. National Geodetic Survey

U.S. National Geodetic Survey is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand U.S. National Geodetic Survey rather than just read about it. In short: The National Geodetic Survey (NGS) is a United States federal agency based in Washington, D.C. that defines and manages a national coordinate system, providing the foundation for transportation and communication, mapping and charting, and a large number of science and engineering applications. Since its founding in 1970, it has been part of the National Oceanic and Atmospheric Administration (NOAA), a division withi…

Key takeaways

U.S. National Geodetic Survey belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect U.S. National Geodetic Survey to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of U.S. National Geodetic Survey from memory before moving on to harder problems.

Reference excerpt

The National Geodetic Survey (NGS) is a United States federal agency based in Washington, D.C. that defines and manages a national coordinate system, providing the foundation for transportation and communication, mapping and charting, and a large number of science and engineering applications. Since its founding in 1970, it has been part of the National Oceanic and Atmospheric Administration (NOAA), a division within the Department of Commerce.

History

The National Geodetic Survey's history and heritage are intertwined with those of other NOAA offices. It traces its history to the Survey of the Coast, which was formed in 1807 as the first scientific agency of the U.S. federal government. It became the United States Coast Survey in 1836. In 1871, Congress officially expanded the Coast Survey's responsibilities to include geodetic surveys in the interior of the United States. The U.S. Coast Survey was renamed the United States Coast and Geodetic Survey in 1878 to reflect the increasing role of geodesy in its work. Upon the creation of NOAA in 1970, the Coast and Geodetic Survey was abolished and its responsibilities were split among various agencies and offices of NOAA. The Coast and Geodetic Survey's former geodetic responsibilities were placed under the new National Geodetic Survey in NOAA's National Ocean Survey (later renamed the National Ocean Service). In 2009, former NOAA Commissioned Officer Corps officer Juliana P. Blackwell was named NGS Director, becoming the first woman to head either NGS or any of its ancestor organizations.

Purpose and function The National Geodetic Survey is an office of NOAA's National Ocean Service. Its core function is to maintain the National Spatial Reference System (NSRS), "a consistent coordinate system that defines latitude, longitude, height, scale, gravity, and orientation throughout the United States". NGS is responsible for defining the NSRS and its relationship with the International Terrestrial Reference Frame (ITRF). The NSRS enables precise and accessible knowledge of where things are in the United States and its territories.

The NSRS may be divided into its geometric and physical components. The official geodetic datum of the United States, NAD83 defines the geometric relationship between points within the United States in three-dimensional space. The datum may be accessed via NGS's network of survey marks or through the Continuously Operating Reference Station (CORS) network of GPS reference antennas. NGS is responsible for computing the relationship between NAD83 and the ITRF. The physical components of the NSRS are reflected in its height system, defined by the vertical datum NAVD88. This datum is a network of orthometric heights obtained through spirit leveling. Because of the close relationship between height and Earth's gravity field, NGS also collects and curates terrestrial gravity measurements and develops regional models of the geoid (the level surface that best approximates sea level) and its slope, the deflection of the vertical. NGS is responsible for ensuring the accuracy of the NSRS over time, even as the North American plate rotates and deforms over time due to crustal strain, post-glacial rebound, subsidence, elastic deformation of the crust, and other geophysical phenomena. NGS will release new datums in 2022. The North American Terrestrial Reference Frame of 2022 (NATRF2022) will supersede NAD83 in defining the geometric relationship between the North American plate and the ITRF. United States territories on the Pacific, Caribbean, and Mariana plates will have their own respective geodetic datums. The North American-Pacific Geopotential Datum of 2022 (NAPGD2022) will separately define the height system of the United States and its territories, replacing NAVD88. It will use a geoid model accurate to 1 centimeter (0.39 in) to relate orthometric height to ellipsoidal height measured by GPS, eliminating the need for future leveling projects. This geoid model will be based on airborne and terrestrial gravity measurements collected by NGS's GRAV-D program as well as satellite-based gravity models derived from observations collected by GRACE, GOCE, and satellite altimetry missions. NGS provides a number of other public services. It maps changing shorelines in the United States and provides aerial imagery of regions affected by natural disasters, enabling rapid damage assessment by emergency managers and members of the public. The Online Positioning and User Service (OPUS) processes user-input GPS data and outputs position solutions within the NSRS. The agency offers other tools for conversion between datums.

See also Height Modernization Surveying Topography

References

External links Official website

Illustrations

Worked examples

Example 1 — a first encounter with U.S. National Geodetic Survey

Start with the simplest possible case. Write down what U.S. National Geodetic Survey claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to U.S. National Geodetic Survey before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about U.S. National Geodetic Survey ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of U.S. National Geodetic Survey

In research: U.S. National Geodetic Survey appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses U.S. National Geodetic Survey in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: U.S. National Geodetic Survey is common in secondary-school and first-year university syllabi. It links to neighbouring topics Exploration of North America, Geodesy organizations, Geographic data and information organizations in the United States, so understanding it makes those chapters shorter.
In everyday life: Look for U.S. National Geodetic Survey outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study U.S. National Geodetic Survey in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what U.S. National Geodetic Survey means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain U.S. National Geodetic Survey out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is U.S. National Geodetic Survey in simple terms?

Why does U.S. National Geodetic Survey matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study U.S. National Geodetic Survey?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on U.S. National Geodetic Survey.