Initial Publication Date: January 18, 2022

Geoid Height Calculator

Description

The Geoid Height Calculator returns the geoid height at the latitude and longitude specified by the user. Elevation can be defined on Earth in several different ways -- geoid height, reference ellipsoid height, and orthometric height. Using this interactive tool can help learners gain a better understanding of the difference between them and calculate discrepancies.

Context

The resource could be useful anytime learners need to better understand the different ways elevations on Earth may be calculated. Can be particularly useful for college-level geoscience, geography, or surveying students.

Teaching Notes

The geoid is one approximation of Earth's shape due to gravity, roughly coinciding with mean sea level. Because the inside of our planet is non-uniform, gravity is not constant at the surface. If Earth were completely covered in an ocean, the water would swell over gravity highs (where there is more mass below the surface) and depress in areas of gravity lows (where there is less mass below the surface). The geoid approximates this hypothetical ocean surface, representing a geopotential surface. To think of it another way, if we were able to walk on the geoid, we would experience a constant value of gravity.
Spending some time exploring differences in ellipsoid, geoid, and orthometric height can help learners better understand Earth's variable gravity field and the challenges in defining elevation.