All books

Professional

Apps About Coach Log in Start reading

Earth and Space Sciences · Glossary

What is Geoid; geoid height?

Also known as: geoid · geoid height

Definition 11.15 University Earth and Space Sciences — Year 1 · Chapter 11 — Isostasy and Gravity Anomalies

The geoid is the equipotential surface of the Earth’s gravity (gravitation plus the centrifugal effect of rotation) that coincides with the mean sea surface over the open oceans, at rest, and is continued beneath the continents. The geoid height NN at a point is the height of the geoid above the reference ellipsoid, counted negative where the geoid lies below it.

The geoid (blue), the reference ellipsoid (dashed) and the ground (schematic; departures enormously exaggerated). Over the ocean the geoid is the sea surface at rest; under the land it is continued as an equipotential. The height H on a map is measured from the geoid, the height h_e given by satellite positioning from the ellipsoid, and h_e = H + N. A plumb line is perpendicular to the geoid, not to the ellipsoid: the angle between them (exaggerated here) is the deflection of the vertical that troubled the surveyors of India.
The geoid (blue), the reference ellipsoid (dashed) and the ground (schematic; departures enormously exaggerated). Over the ocean the geoid is the sea surface at rest; under the land it is continued as an equipotential. The height HH on a map is measured from the geoid, the height heh_e given by satellite positioning from the ellipsoid, and he=H+Nh_e = H + N. A plumb line is perpendicular to the geoid, not to the ellipsoid: the angle between them (exaggerated here) is the deflection of the vertical that troubled the surveyors of India.
Read in context →