Normalhöhen

Normalhöhen, also known as normal heights, are a concept in geodesy and metrology used to define a standardized vertical datum. They are a theoretical or physical realization of a gravity equipotential surface that serves as the zero-level reference for height measurements. Unlike geometric heights, which are measured perpendicular to the ellipsoid, normal heights are defined relative to the geoid, which approximates mean sea level. This distinction is important because the geoid is irregular due to variations in the Earth's mass distribution.

The concept of normal height arises from the fact that the gravity vector is not everywhere perpendicular to the reference ellipsoid. Therefore, a plumb line, which follows the direction of gravity, does not necessarily intersect the ellipsoid at a right angle. This leads to a difference between orthometric heights (heights above the geoid along the plumb line) and normal heights. Normal heights are calculated using a simplified gravity model, which makes them easier to compute and apply in practice.

In many national and international geodetic reference systems, normal heights are used as the primary vertical reference. They are crucial for applications such as engineering, construction, hydrology, and navigation, where accurate vertical control is essential. The establishment of precise normal height networks involves complex surveying techniques and the use of sophisticated gravity models and instruments like gravimeters and GPS. The accuracy of normal heights directly impacts the reliability of various geodetic and engineering projects.