Physical Geodesy

Since the geodetic boundary value problem in the Molodensky formulation does not allow a closed analytical solution due to the complexity of the boundary surface - the earth's surface - different approximations are introduced in the practical calculation of the quasigeoid. With the internationally renowned work at the chair the approximation errors caused by linearization, spherical and planar approximation could be investigated and numerically estimated. The results of this work are now taken into account in the calculations of highly accurate quasigeoid heights performed by various institutions.

A second focus was and still is the modelling of the effects of topographic masses and isostatic compensation masses on the Earth's gravitational field. Topographic and isostatic reductions have to be considered in connection with the highly accurate geoid and quasigeoid determination, which leads to a very high computational effort with traditional methods. The so-called tesseroid method, which was founded and further developed at the chair, was received with great interest internationally and is now used as a standard by many working groups.

The results of this work are incorporated into a practical calculation of the quasigeoid of Baden-Württemberg, which is carried out in cooperation with the LGL.

In recent work of the Physical Geodesy group an inverse tesseroid approach is used to derive global water circulation in the form of water column heights from the monthly solutions of the GRACE gravity field mission.

The unification of national elevation systems and the creation of a unified vertical elevation reference system has been the focus of the work of the IAG for several years. A unified, global, highly accurate height system is absolutely necessary, for example to be able to detect and quantify the movements of sea level caused by global change. This task methodically leads to an extension of the geodetic boundary value task.

A current focus, which will become more and more important, is the application of variance propagation to various functional relationships within the framework of physical geodesy.

On this picture you can see the geoid that was computed for Africa.
Height Reference Surface for Africa

For several years, an intensive cooperation with Prof. Hussein Abd-Elmotaal from Minia, Egypt and the working group Physical Geodesy of the GIK has existed. Scientific content of the cooperation is the determination of the height reference surface for the continent Africa.

This picture shows the geometry of a tesseroid.
Tesseroid Method

The so-called tesseroid method, founded and further developed at the chair, improves the computing times of topographic and isostatic reductions and is used internationally.

This picture shows Bouger anomalies for the Saarland in Germany.
Bouger anomalies for the German state of Saarland

The interpretation of Bouguer anomalies during prospection allows the localization of deposits of raw materials, which are prominent in the Bouguer anomalies due to their density contrast.

This picture shows the global Rock-Water-Ice gravity model.
Global Topographic-Isostatic Model

The so-called Rock-Water-Ice model (RWI model) is based on a three-layer decomposition of the topography with variable density values and a modified Airy-Heiskanen concept incorporating seismic Moho depths.

This picture shows a variance-covariance matrix of a gravity field model.
Quantification of Uncertainty in Gravity Field Modelling

Increased computing power and working memory availability make the quantification of uncertainties in gravity field modelling possible in the form of variance propagation.


Further Fields of Research

  • Ellipsoidal and topographical effects in the scalar free geodetic boundary value problem
  • Ellipsoidal effects in the inverse Stokes problem
  • Studies to determine vertical datums