Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The hypothetical surface of the earth that coincides everywhere with mean sea level.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A surface of constant gravitational potential at zero elevation.

from The Century Dictionary and Cyclopedia

  • n. An imaginary surface which coincides with the mean sea-level over the ocean, and extends under the continents everywhere at that level at which the mean surface of the sea would stand if it were allowed to flow in through a small subterranean canal.
  • n. See geode.

Etymologies

German, from Greek geoeidēs, earthlike : , earth + -oeidēs, -oid.
(American Heritage® Dictionary of the English Language, Fourth Edition)

Examples

  • Let the term geoid apply to the natural irregular surface of the earth and the term spheroid to the ideal regular sur - face of the geodesist which coincides nearly with sealevel and is necessarily a level surface.

    Transactions - American Philosophical Society

  • That span can then, in theory, be subtracted from the distance between those satellites and a kind of theoretical sea level known as the geoid, which is what the sea level would be at each point on Earth if undisturbed by weather, tides and currents.

    Why Measure a Mountain? Because It's There

  • A new map shows the Earth's "geoid" - the map of its gravitational pull.

    BBC News | News Front Page | World Edition

  • Technically speaking, the model at the top of this page is what researchers refer to as a geoid.

    BBC News - Home

  • The geoid is the shape of an imaginary global ocean dictated by gravity in the absence of tides and currents.

    PhysOrg.com - latest science and technology news stories

  • The geoid is a model of global mean sea level that is used to measure precise surface elevations.

    OceanGuy

  • Goce data will be used to construct an idealised surface called a geoid

    BBC News | Technology | World Edition

  • This will result in a unique model of the geoid, which is the surface of equal gravitational potential defined by the gravity field.

    PhysOrg.com - latest science and technology news stories

  • This will result in a unique model of the geoid, which is the surface of equal gravitational potential defined by the gravity field - crucial for deriving accurate measurements of ocean circulation and sea-level change, both of which are affected by climate change.

    WebWire | Recent Headlines

  • The geoid is the equipotential surface of the earth’s gravitational field that approximates the mean sea surface.

    State of fear

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Comments

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  • "There have been many definitions of the "geoid" over 150 years or so. Here is the one currently adopted at the National Geodetic Survey:

    geoid: The equipotential surface of the Earth's gravity field which best fits, in a least squares sense, global mean sea level

    Even though we adopt a definition, that does not mean we are perfect in the realization of that definition. For example, altimetry is often used to define "mean sea level" in the oceans, but altimetry is not global (missing the near polar regions). As such, the fit between "global" mean sea level and the geoid is not entirely confirmable. Also, there may be non-periodic changes in sea level (like a persistent rise in sea level, for example). If so, then "mean sea level" changes in time, and therefore the geoid should also change in time. These are just a few examples of the difficulty in defining "the geoid"."

    --What is the geoid?

    March 31, 2011

  • See discussion on potato Earth.

    March 31, 2011