Geoid
The geoid is the equipotential surface of Earth's gravity.
The geoid is the shape that the ocean surface would take under the influence of Earth's gravity and rotation, absent winds and tides. It is a smooth but irregular surface, first described by Carl Friedrich Gauss as the 'mathematical figure of the Earth,' resulting from uneven mass distribution. The geoid is essential for geodesy and satellite-based global positioning systems, though it was not precisely defined until the mid-20th century with satellite geodesy.
- field
- Geodesy, Geophysics
- known_for
- Mathematical figure of the Earth, reference surface for vertical coordinates
- first_described_by
- Carl Friedrich Gauss
- first_high_fidelity_synthesis
- Gladys West
Lore & Background
The geoid is defined as an equipotential surface of the Earth's gravity field, meaning all points on it have the same geopotential. Gravity acts perpendicular to the geoid, so plumb lines point perpendicular and bubble levels are parallel to it. If the ocean were undisturbed, its surface would resemble the geoid, and canals through continents would nearly coincide with it.
Reader's Guide
The geoid is a foundational concept in geodesy and geophysics, serving as a reference surface for orthometric heights, geopotential heights, and dynamic heights. It is crucial for global positioning systems, as GPS receivers correct ellipsoidal heights using geoid models like EGM96. The geoid's determination relies on extensive gravitational measurements and calculations, including satellite data, terrestrial gravimetry, and Stokes' formula. Mathematician Gladys West was the first to synthesize a high-fidelity geoid from satellite data. Despite being known for nearly 200 years, its precise definition awaited satellite geodesy. The geoid's irregular shape reflects Earth's mass distribution, with denser regions causing higher geoidal heights. It remains essential for accurate height measurement and understanding Earth's gravity field.
Did You Know?
- Gladys West was the first person to synthesize a high-fidelity geoid from satellite data.
- All points on a geoid surface have the same geopotential, and gravity acts perpendicular to it.
- The geoid is one of the essential components of satellite-based global positioning systems.
Frequently Asked Questions
What exactly is the Geoid?
The Geoid is the equipotential surface of Earth's gravity, representing the shape the ocean would assume if only gravity and rotation acted on it, with no winds or tides. In practice it is a smooth but lumpy surface that reflects the planet's uneven internal mass distribution.
Who first described the Geoid and what did they call it?
Carl Friedrich Gauss introduced the concept, referring to it as the 'mathematical figure of the Earth.' His framing treated the planet's true gravitational shape as a calculable geometric surface rather than a simple sphere or ellipsoid.
Why is the Geoid critical for GPS and surveying?
It provides the reference surface against which all vertical coordinates are measured in geodesy, so satellite-based positioning systems depend on an accurate geoid model to turn raw distance data into meaningful elevations. Without it, 'height above sea level' would have no consistent global definition.
Who produced the first high-fidelity global synthesis of the Geoid?
Gladys West is credited with the first high-fidelity synthesis of the geoid, a milestone that predated the satellite-geodesy era of the mid-20th century when the surface was finally defined with global precision.
More in Physical & Ocean Floor Features 1-24
Elsewhere in the Physical & Ocean Floor Features universe
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record