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The GRACE/GRACE-FO satellites have observed large scale mass changes, contributing to the mass budget calculation of the hydro-and cryosphere. The scale of the observable mass changes must be in the order of 300 km or bigger to be resolved. Smaller scale glaciers and hydrologic basins significantly contribute to the closure of the water mass balance, but are not detected with the present spatial resolution of the satellite. The challenge of future satellite gravity missions is to fill this gap, providing higher temporal and spatial resolution. We assess the impact of a geodetic satellite mission carrying on board a cold atom interferometric gradiometer (MOCASS: Mass Observation with Cold Atom Sensors in Space) on the resolution of simulated geophysical phenomena, considering mass changes in the hydrosphere and cryosphere. Moreover, we consider mass redistributions due to seamounts and tectonic movements, belonging to the solid earth processes. The MOCASS type satellite is able to recover 50% smaller deglaciation rates over a mountain range as the High Mountains of Asia compared to GRACE, and to detect the mass of 60% of the cumulative number of glaciers, an improvement respect to GRACE which detects less than 20% in the same area. For seamounts a significantly smaller mass eruption could be detected with respect to GRACE, reaching a level of mass detection of a submarine basalt eruption of 1.6 109 m3. This mass corresponds to the eruption of Mount Saint Helens. The simulations demonstrate that a MOCASS type mission would significantly improve the resolution of mass changes respect to existing geodetic satellite missions.

Both GRACE and GOCE have proven to be very successful missions, providing a wealth of data which are exploited for geophysical studies such as climate changes, hydrology, sea level changes, solid Earth phenomena, with benefits for society and the whole world population. It is indispensable to continue monitoring gravity and its changes from space, so much so that a GRACE follow-on mission has been launched in 2018. In this paper, a new satellite mission concept named MOCASS is presented, which can be considered as a GOCE follow-on, based on an innovative gradiometer exploiting ultra-cold atom technology and aimed at monitoring Earth mass distribution and its variations in time. The technical aspects regarding the payload will be described, illustrating the measurement principle and the technological characteristics of a cold atom interferometer that can measure gravity gradients. The results of numerical simulations will be presented for a one-arm and a two-arm gradiometer and for different orbit configurations, showing that an improvement with respect to GOCE could be obtained in the estimate of the static gravity field over all the harmonic spectrum (with an expected error of the order of 1 mGal at degree 300 for a 5-year mission) and that estimates are promising also for the time-variable gravity field (although GRACE is still performing better at very low degrees). Finally, the progress achievable by exploiting MOCASS observations for the detection and monitoring of geophysical phenomena will be discussed: the results of simulations of key geophysical themes (such as mass changes due to hydrology, glaciers and tectonic effects) with expected gravity change-rates, time constants and corresponding wavelengths, show that an improvement is attainable and that signals invisible to past satellites could be detected by exploiting the cold atom technology.

The global gravity field obtained from the observations of the satellite Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite offers new opportunities in defining density variations of earth’s crust and mantle, allowing new insights into the structure of specific geologic features. The Central African Rift is a key feature in understanding the dismemberment of Gondwana, and we contribute to defining the crustal density structure underlying the rift. The presence of a narrow and up to 12 km deep basin implies crustal stretching allowed the sediment to accumulate, but a key question is whether the stretching processes also affected the deeper layers of the crust or was limited to the upper crust. The study area includes a subbasin of the greater Chad sag basin, which extends over 1500 × 1500 km and occupies the center of North-Central Africa, shared between the countries of Chad, Sudan, Nigeria, Niger, Algeria, Libya, and Cameroon. We find that the rifting affected the lower crust of the West African Rift, and we evaluate evidence for a 1500 km long and several km thick magmatic crustal intrusion presumably associated with underplating and crustal thinning. We estimate that the stretching factor must be at least 1.5 and had affected the entire crust. To our knowledge, the identification of a continuous body of magmatic intrusions is new and has been only possible through the recent global gravity field. The magmatism has altered the thermal conditions from the time of emplacement on, and it is relevant for the maturation of hydrocarbons present in the sediments. The timing of the magmatism is presumably tied to two pulses of volcanism documented in the rift, associated with the first postrift phase from 96 to 88 Ma and the second postrift phase from 23 Ma up to the Quaternary.

The availability of global gravity fields and topography through calculation services like the International Centre for Global Earth Models, allows easy access to gravity data, greatly enlarging the spectrum of users. The applications extend much farther than the classic modeling through the gravity-specialist. We investigate the sensitivity of the joint analysis of topography and gravity data based on linear regression analysis and clustering of the response to particular characteristics of the lithosphere structure. The parameters of the regression analysis are predicted to have characteristic values, which allow to distinguish continental crust from oceanic crust, and signalize the presence of crustal inhomogeneity. Predictions are made through theoretical considerations and on synthetic models. We use the South Atlantic Ocean and the confining South American and African continents for illustration, where the regression parameters distinguish oceanic crust from the ridge up to the bathymetric inflection point, from the transitional crust and the continental crust, allowing to map these units. The general properties of the parameters are statistically relevant, since the errors on the parameters are less than 10% the amplitude of the parameters. We compare the regression parameters with those produced by a global crustal model (CRUST1.0), and find good correspondence between the observed and predicted fields. The analysis can be applied with machine learning algorithms, without the need of specific forward or inverse gravity modeling skills. It is therefore particularly useful in view of the enhanced access to the data through the calculation service, and could be implanted as an add-on tool, since it allows to efficiently distinguish isostatic contribution to the gravity field from crustal sources. Given the experience on the gravity field of the Earth, the analysis can be analogously extended to other planets. For illustration, we show that for Mars a coherent class of Martian crust can be identified.

Water supply from karst sources is a worldwide natural resource and the exploitation is tied to the knowledge of the positions of the hydrologic channels. We show that surface deformation induced by flood events in karst conduits is observable, and consists in uplift and outward movement from the hydraulic channel. Precipitation events produce the natural occurrence of subsurface hydraulic overpressure up to 1 MPa. Numerical modeling shows that the stresses are so strong to uplift and dislocate the surface by several mm and induce tilts in the order of microradians. The naturally induced deformation is compatible with a transient internal pressure loading of a channel. The results can be used to find new channels with dense GNSS networks. Sea water incursion and channels accessed for tourism could be monitored. Seismicity has been shown to have a seasonal variation in some areas, which could be explained by the subsurface stresses induced by the natural subsurface overpressure. The pressure induced deformation is expected to be observed in all karstic systems worldwide.