Physical geodesy

The physical geodesy encompasses those branches of higher geodesy, in which geometric aspects to physical recede into the background.

Its main tasks are the determination of the earth's shape and the measurement and modeling of the Earth's gravity field. The methodology can be two - or three-dimensional ( scalar or vector field of the acceleration due to gravity ).

In the area of ​​research the physical geodesy contributes to exploration of the Earth's interior at ( eg density of rock layers ), but also to the gravitational field and the interference of satellite orbits. Some themes overlap with those of geophysics.

The knowledge of the gravity field is for the practice of surveying important because almost all geodetic measurements are associated with the gravitational field. For example, the measurement instruments before the measurement along the true plumb line to be leveled, which is principally influenced by all masses in the area and therefore runs irregularly on closer inspection.

The differences between reality and a simple mathematical model to show, for example, in the deviation of the true plumb line from the ellipsoidal, called the deflection of the vertical ( ξ, η, English:. Vertical deflection ). In gravimetry turn the disturbances in the form of gravity anomalies are (? G, gravity anomalies ) specified.

Deflection of the vertical and gravity anomaly can in the mountains of the order of 10-50 " or achieve some. In a survey network in rough terrain, these effects of the gravity field and geoid undulations of the act of up to 20 cm per kilometer. Since about 1995 it seeks to achieve the centimeter geoid, because otherwise the growing GPS survey would not be combined with terrestrial altitude measurements.

The calculations of the measurement points must abstract from these irregularities - ie " reduce " the noise - by running on mathematically defined surfaces and objects such as plane, sphere or spheroid. The reduction can only be dispensed with if the survey area is less than a few hundred meters and not in the high mountains.

The physical geodesy at major technical projects (power plants, tunnels, or Routing a high- speed line ) Particular care is to take action.

• Geodesy