Mass Variation Observing System Proposal for new ESA Earth Explorer Satellite Mission

Climate change is one of the biggest societal challenges today, and understanding the underlying processes, which are most frequently related to mass transport in the Earth system, are a key element of Earth observation. Observing the gravity field of the Earth from space is the only available tool to observe and monitor mass distribution and mass transport in the system Earth consistently and globally. Such observations enable the quantification of the global water cycle and closure of the global water budget, melting of ice sheets and glaciers, determination of ocean circulation, mass contributions to sea level change, and constraining the geophysical and earthquake modelling. The value of such observations was proven by the ESA’s GOCE mission and the joint NASA/DLR GRACE satellites during the last decade. The success of these missions triggered the realization of another a joint US/German mission (GRACE Follow-On) to be launched in April/May 2018, which is designed to continue the observation of mass transport with the same spatial and temporal resolutions.

Since many years the chair of Astronomical and Physical Geodesy is involved in these activities and specifically works on future mission concepts for observing mass transport in the system Earth, which can fulfil the ambition requirements of Earth science disciplines asking for mass transport observations with higher temporal and spatial resolutions as it can be achieved nowadays (Pail et al. 2015). In recent projects performed for the European Space Agency (ESA), by means of extensive numerical closed-loop mission simulations the achievable performance of so-called Bender constellations of two satellite pairs flying in different inclined orbits are analysed, and innovative methods of data exploitation are developed. An alternative concept of high-precision ranging between high- and low-flying satellites is currently investigated in the frame of projects funded by DFG. Since such a constellation observes mainly the radial component of gravity-induced orbit perturbations, the error structure is close to isotropic and significantly reduces artefacts of previous along-track ranging low-low formations (GRACE, GRACE-Follow-On) such as the typical striping patterns.

This high-low concept was proposed in March 2018 by a group of European scientists with the support of technological and industrial partners and under coordination of the Chair of Astronomical and Physical Geodesy (who acts as lead proposer) as Earth Explorer 10 mission to ESA, and is considered as precursor for a future sustained gravity-based mass variation observing system from space. The name of this mission is MOBILE (Mass variation OBservIng system by high-Low inter-satellitE links). Depending on the constellation mass transport can be observed with factor of 5 to 50 increased sensitivity with respect to nowadays knowledge. Short latencies will provide important contribution to operational, societally relevant service applications, such as water management, groundwater monitoring, and forecasting of droughts and floods.