geoidimalliin

A geoid is a conceptual model of the Earth's shape. It represents the mean sea level if that level were extended through the continents, unaffected by tides and currents. Imagine a perfectly smooth, gravity-defined surface that approximates the Earth's irregular shape. The geoid is not a simple geometric figure like a sphere or ellipsoid. Instead, it follows the gravitational pull of the Earth's mass distribution, meaning it bulges in areas of higher density and dips in areas of lower density.

The geoid is crucial for accurate surveying and mapping. It serves as the reference surface for determining elevations. Orthometric heights, which are the elevations commonly used in everyday life (e.g., for buildings), are measured vertically from the geoid. This is different from ellipsoidal heights, which are measured from a mathematical reference ellipsoid that approximates the Earth. The difference between the geoid and the reference ellipsoid is called the geoid undulation or geoid separation.

Determining the geoid is a complex process that involves measuring gravity on the Earth's surface and using satellite altimetry data. These measurements allow scientists to construct detailed geoid models. Different geoid models exist, each with varying levels of accuracy and coverage, reflecting ongoing improvements in measurement techniques and computational power. Understanding the geoid is fundamental for disciplines like geodesy, oceanography, and earth sciences, enabling precise positioning and a better understanding of the Earth's internal structure.