GEMMA (GOCE Exploitation for Moho Modeling and Applications)
New ESA missions dedicated to the observation of the Earth from space, like the gravity-gradiometry mission GOCE and the radar altimetry mission CRYOSAT 2, foster research, among other subjects, also on inverse gravimetric problems and on the description of the nature and the geographical location of gravimetric signals.
In this framework the GEMMA project (GOCE Exploitation for Moho Modeling and Applications), funded by the European Space Agency and Politecnico di Milano, aims at estimating the boundary between Earth's crust and mantle (the so called Mohorovicic discontinuity or Moho) from GOCE data in key regions of the world.
In the project a solution based on a simple two layer model in spherical approximation is proposed. This inversion problem based on the linearization of the Newton's gravitational law around an approximate mean Moho surface will be solved by exploiting Wiener-Kolmogorov theory in the frequency domain where the depth of the Moho discontinuity will be treated as a random signal with a zero mean and its own covariance function. The algorithm can be applied in a numerically efficient way by using the Fast Fourier Transform.
As for the gravity observations, we will consider grids of the anomalous gravitational potential and its second radial derivative at satellite altitude. In particular this will require first of all to elaborate GOCE data to obtain a local grid of the gravitational potential field and its second radial derivative and after that to separate the gravimetric signal due to the considered discontinuity from the gravitational effects of other geological structures present into the observations. The first problem can be solved by applying the so called space-wise approach to GOCE observations, while the second one can be achieved by considering a priori models and geophysical information by means of an appropriate Bayesan technique. Moreover other data such as ground gravity anomalies or seismic profiles can be combined, in an efficient way, to gridded satellite data in order to obtain better results. The research has to be firstly performed on case studies where existing data allow the calibration of the approach.
Among other things this project represents a careful study of the prior weighting of different information sources, including the rather qualitative geological information.