# Level area

Level surfaces in the earth's gravity field are orthogonal trajectories to all plumb lines. They bulge slightly over mountains due to the higher potential (V P ). The sketch is very exaggerated .

In the geosciences, an equipotential surface of the gravitational potential is referred to as a level surface . On earth , level surfaces are approximately parallel to sea ​​level and are the ∞¹-manifold family of surfaces that are everywhere perpendicular to the local plumb line .

The level area at the mean sea ​​level is called the geoid .

The potential theory defines the level surfaces as those surfaces of a conservative force field on which the potential energy is constant. When moving a body (fictitiously an infinitely small test mass ) along a level surface - apart from friction losses - no physical work has to be done.

The physics uses the term level area to other force fields , such. B. for magnetic fields or electric fields .

## Geodesy and Oceanography

The Geodesy defines the physical height term by the vertical distance between two equipotential surfaces. The height difference ΔH between two points is the potential difference ΔV of their level surfaces (see picture) divided by the amount of the local acceleration due to gravity g :

ΔH = H 2 - H 1 = (V 2 - V 1 ) / g,

where g from the earth's equator to the poles increases from about 9.7803 m / s² to 9.8322 m / s² due to the flattening of the gravity . For this reason, and because of the geological deviations from the vertical , the level surfaces are not completely parallel. Those in mean sea is geoid called and is the reference surface for use in technology and everyday geometric use heights (see also orthometric height ).

The Oceanography used them with zero height excellent level surface in order from the deviations between her and the true sea -resistant ocean currents to model and winds. The sea level and geoid determination in the oceans is largely carried out by satellite altimetry , currently among other things by the ESA probe GOCE .