Abstract
Abstract As changes in gravity are directly related to mass variability, satellite missions observing the Earth’s time varying gravity field are a unique tool for observing mass transport processes in the Earth system, such as the water cycle, rapid changes in the cryosphere, oceans, and solid Earth processes, on a global scale. The observation of Earth’s gravity field was successfully performed by the GRACE and GOCE satellite missions, and will be continued by the GRACE Follow-On mission. A comprehensive team of European scientists proposed the next-generation gravity field mission MOBILE in response to the European Space Agency (ESA) call for a Core Mission in the frame of Earth Explorer 10 (EE10). MOBILE is based on the innovative observational concept of a high-low tracking formation with micrometer ranging accuracy, complemented by new instrument concepts. Since a high-low tracking mission primarily observes the radial component of gravity-induced orbit perturbations, the error structure is close to isotropic. This geometry significantly reduces artefacts of previous along-track ranging low-low formations (GRACE, GRACE-Follow-On) such as the typical striping patterns. The minimum configuration consists of at least two medium-Earth orbiters (MEOs) at 10000 km altitude or higher, and one low-Earth orbiter (LEO) at 350-400 km. The main instrument is a laser-based distance or distance change measurement system, which is placed at the LEO. The MEOs are equipped either with passive reflectors or transponders. In a numerical closed-loop simulation, it was demonstrated that this minimum configuration is in agreement with the threshold science requirements of 5 mm equivalent water height (EWH) accuracy at 400 km wavelength, and 10 cm EWH at 200 km. MOBILE provides promising potential future perspectives by linking the concept to existing space infrastructure such as Galileo next-generation, as future element of the Copernicus/Sentinel programme, and holds the potential of miniaturization even up to swarm configurations. As such MOBILE can be considered as a precursor and role model for a sustained mass transport observing system from space.
Highlights
Climate change is one of the biggest societal challenges today
The dedicated gravity mission Gravity Recovery And Climate Experiment (GRACE) (Tapley et al 2014) provided the rst global determination of Earth’s mass transport by measuring spatial and temporal changes in the gravity eld caused by mass variations at all depths, while the static gravity eld retrieved from the Gravity eld and steady-state Ocean Circulation Explorer (GOCE) mission (Drinkwater et al 2013) has improved our knowledge of the long-term mass distribution and has provided the physical reference surface of the geoid with a resolution down to 70-80 km
In this paper we present an innovative observation concept of high-precision high-low inter-satellite ranging, which was proposed as the MOBILE mission in response to European Space Agency (ESA)’s Earth Explorer 10 call
Summary
Mass variation observing system by high low inter-satellite links (MOBILE) – a new concept for sustained observation of mass transport from space.
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