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MOCASS (Mass Observation with Cold Atom Sensors in Space) is an on-going study project funded by the Italian Space Agency in the framework of preparatory activities for future missions and payloads of Earth Observation. The object of the proposal is an innovative satellite gravity mission based on advanced cold atom interferometry (CAI) accelerometers, with the aim of modelling the static and time-variable gravity field of the Earth with high accuracy and resolution and of monitoring mass variations that occur on and below the Earth surface. The basic idea is a GOCE mission follow-on, launching a unique spacecraft with an on-board instrument capable of measuring some functionals of the Earth gravitational potential. The improvement with respect to the GOCE mission concept can only be achieved by going beyond the technology of electrostatic gradiometers, taking advan- tage of a new generation of sensors, such as cold atom interferometers. In the framework of the MOCASS study, the instrument characteristics are defined in terms of long-term stability, accuracy, and spectral responses. Then simulations on gravity field recovery based on the space-wise approach already used for the GOCE data processing are implemented. Finally an analysis on the geophysical signals that can be detected given the simulated mission performance are performed, with particular attention to hydrologic and tectonic modelling of changing masses. First simulations have already been performed by considering the GOCE orbit parameters but assuming that a CAI gradiometer is on board the spacecraft. This allows direct comparisons between GOCE and MOCASS per- formances. Instrument error spectra have been defined depending on the orbit and CAI configurations, all of them characterized by a flat error spectrum in the low frequencies, differently from the one of the GOCE electrostatic accelerometers. Given the error spectrum and the interferometer integration spectral response, simulated obser- vations have been produced and processed by the space-wise approach, which basically consists in a sequential application of a Wiener filter, a local collocation gridding and a spherical harmonic analysis. From sample statis- tics, the accuracy of the recoverable gravity field model can then be evaluated and compared with the expected gravity signal from selected geophysical phenomena, e.g. orogen geodynamics and glacier melting. Although the study is at this time not complete, these preliminary investigations show promising results.

The Alpine and neighboring Dinarides and Appennine orogens are subject to uplift, as documented by the GNSS vertical movement rates. The uplift is caused by crustal compression and thickening and/or mantle inflow below an uplifting crust. The two end-members can be distinguished by the amount of gravity change rate, the thickening having a smaller gravity signal than the crustal uplift, because the mass surplus at the surface is compensated at the level of lower crust. We calculate the expected rates using the observed GNSS determined uplift rates as geometrical surface constraints, and defining the two end-member geodynamic models. We analyze the gravity change rates of GOCE and GRACE and compare them with the expected rates. Hydrology must be considered in this context, as it contributes to a competing gravity change rate signal that is superposed to the tectonic signal. We find that the predicted signal is measurable, and that lateral changes in the sign of the observed gravity rates over the Alpine range have no counterpart in the ongoing uplift. We analyze possible candidates for this latter signal.

The Karst environment is characterized by a peculiar water system circulation, governed by a network of conduits in which the water flows. The name Karst is derived from the Classic Karst region which is located across Italy, Slovenia and Croatia borders. This area gave name to the phenomenon because it was one of the first worldwide to be studied and it is still object of many researches and hosts an important monitoring network. In this area the water is supplied mainly by infiltration during the autumn-spring rainfall events but also from the Reka river that sinks in the Škocjan caves and then flows underground up to the Timavo Springs. The water path is very well known near the Škocjan cave where the water inflow from the Reka river and the rain fall are continuously monitored and also the karst conduits have been mapped directly by speleology inspection. Such data are indispensable in order to construct and constrain 2D hydraulic models that explain very well the water dynamics in the area. However in Skocjan the water circulation is superficial while in other parts of the Karst the water flows deeper underground: in the Grotta Gigante, a natural cave, the water flow is located over 200m below the surface. Its movement could be hardly monitored by direct observation and also modelling is limited due to the lack of a 3D model of the aquifer. Indirect geophysical methods, in particular gravimetry, could be exploited in order to obtain some constraints for the underground conduits and cavities and also to gain information about the water mass movements through time. In this contribution we present some preliminary synthetic models for assessing the gravity signals expected for the underground cavities typical for the karstic area. In addition we evaluate the time gravity field change during strong rainfall events where the water is expected to fill the conduits and cavities. In future we will take advantage of these models to place a continuous gravity meter that cuold be useful to constrain the water fluxes in area where a direct observation of the water is difficult.