Observing Mass Distribution and Transport in the Earth System from an ESA Perspective Roger Haagmans, Pierluigi Silvestrin, Rune Floberghagen, Christian Siemes, Luca Massotti and Olivier Carraz European Space Agency 28/11/2014 Credits: A. Atzenhofer Credits: A. Pereira ESA UNCLASSIFIED – For Official Use

Old and new: amazing complement!!! Gravity field around Honolulu 1929 submarine and GOCE Vening Meinesz Sea gravimeter: 3 pendulums (3 mGal) Source GOCE iBook

User Community Activities and Involvement Workshop 2007 Noordwijk, NL IUGG resolution and letter to Space Agencies, 2012 User Community Workshop 2009 Graz, AT Global User Community Science Team (IUGG, IAG, GGOS) Coordinator R. Pail. User need document Round table Satellite Gravity Exploration China-Euro meeting, Beijing 2013 ESA-NASA Interagency Gravity Science Working Group

Review of status User Community Workshop 2007 Noordwijk, NL Main outcome: Short term: full exploitation of GRACE and GOCE, continue GRACE with GRACE-FO Medium term: Next-Generation Gravity Mission (NGGM) (constellations with low-low SST, i.e. GRACE-2 and NGGM) Long term: study alternative technologies, e.g. cold-atom interferometry, clocks Move forward from science demonstration concepts towards sustained observations of mass transport in the Earth system supporting relevant application areas (like hydrology at catchment level) User Community Workshop 2007 Noordwijk, NL User Community Workshop 2009 Graz, AT

Review of status User Community Workshop 2007 Noordwijk, NL Main outcome: Short term: full exploitation of GRACE and GOCE, continue GRACE with GRACE-FO Medium term: Next-Generation Gravity Mission (NGGM) (constellations with low-low SST, i.e. GRACE-2 and NGGM) Long term: study alternative technologies, e.g. cold-atom interferometry, clocks Move forward from science demonstration concepts towards sustained observations of mass transport in the Earth system supporting relevant application areas (like hydrology at catchment level) User Community Workshop 2007 Noordwijk, NL User Community Workshop 2009 Graz, AT

Long Term: Where are we heading? If atomic clocks reach relative accuracies of 10-18: Measure direct potential differences with clocks (Einstein) Replace spirit leveling by clocks with “cm accuracy” or better Today we are around 3 to 5 10-18 ! 10-18~1 cm in height Harrison 1 first sea chronometer

Relativistic Geodesy: unify geometry (GNSS) & gravitational positioning Geometry measured with GPS Gravitational potential measured with optical clocks & two-way links Satellite link geoid ellipsoid B’’ B’ B A C D E (x,y,z) (x,y,z) 50 m glasfiber link glasfiber link clock frequency Gravitational potential nB/nA = DTA/DTB = 1 + (VB - VA)/c2 Courtesy D. Svehla

Review of status User Community Workshop 2007 Noordwijk, NL Main outcome: Short term: full exploitation of GRACE and GOCE, continue GRACE with GRACE-FO Medium term: Next-Generation Gravity Mission (NGGM) (constellations with low-low SST, i.e. GRACE-2 and NGGM) Long term: study alternative technologies, e.g. cold-atom interferometry, clocks Move forward from science demonstration concepts towards sustained observations of mass transport in the Earth system supporting relevant application areas (like hydrology at catchment level) User Community Workshop 2007 Noordwijk, NL User Community Workshop 2009 Graz, AT

Long term: Cold Atom Interferometry Gravity Gradiometer Concept and Inertial Sensor Gravity gradiometer (V – Ω2), gyroscope (Ω), accelerometer (a) Theoretical performance: (V+Ω2)  4.7 mE / sqrt(Hz) Ω  35 prad/s / sqrt(Hz) a  2 pm/s2 / sqrt(Hz) Hybrid Atom-Electrostatic System for Satellite Geodesy

Review of status User Community Workshop 2007 Noordwijk, NL Main outcome: Short term: full exploitation of GRACE and GOCE, continue GRACE with GRACE-FO Medium term: Next-Generation Gravity Mission (NGGM) (constellations with low-low SST, i.e. GRACE-2 and NGGM) Long term: study alternative technologies, e.g. cold-atom interferometry, clocks Move forward from science demonstration concepts towards sustained observations of mass transport in the Earth system supporting relevant application areas (like hydrology at catchment level) User Community Workshop 2007 Noordwijk, NL User Community Workshop 2009 Graz, AT

Constellation: no of satellites, inclinations/altitudes Atom interferometer inertial sensor + gradiometer (Rummel & Flury, 2003)

Gravity potential, gravity or gravity gradient Topography [m] in the Indonesian Archipelago Gravity gradients Signal attenuates at satellite height Q rQ GOCE 0 R CHAMP GRACE Satellite orbit Observed Gravity data Gravity potential (shapes the Geoid) (Haagmans, Prijatna, Omang, 2003)

For sensitivity fly as low as possible but …. Credits: E. Doornbos

Two-satellites: falling objects including laser ranging LOW-LOW SST Constellations: minimum two in-line pairs (polar and inclined); laser ranging with “fixed” proof masses and drag reduction long observation period 14

Error Characteristics 1-pair vs 2 pairs One pair (polar) Two pairs (polar + I=63°) Credits: P. Visser

Constellation: optimising sampling in space and time 302 km 1 day

Constellation: optimising sampling in space and time 4 days 302 km 1 day

Constellation: optimising sampling in space and time 302 km 316 km 331 km 11 days 11 days 4 days 4 days 4 days

Two-satellites: falling objects including laser ranging LOW-LOW SST Constellations: Aspects of optimising processing: short term solutions at larges spatial scales to absorb aliasing effect due to daily and sub-daily processes instead of using de-aliasing models longer term 7, 14 days or 30 days “cleaned” solution a high resolution (compatible with user needs) provide comparable quality at longer term intervals Maybe almost GOCE resolution at GRACE time intervals possible but what is needed ? Test done by simulations using the new updated ESA mass transport model 19

Mass Transport Model to Test Ideas Tides Oceans Atmosphere Ice Hydrology Solid Earth Simulated “real” world

New ESA Mass Transport Model ESAESM and desciption available at GFZ New model for simulations of future missions accessible through http://www.gfz-potsdam.de/en/research/organizational-units/departments/department-1/earth-system-modelling/services/esaesm/

What can we learn from gravity field missions ?

What is needed in the near future? Future Concepts? User needs document from global community (IUGG initiative)

Past, present and “near” future ? Continuation of observations at lower resolution CHAMP GRACE GRACE FO GOCE 2000 2010 2020 2030 Start of sustained observations at high resolution Past, present and planned Future constellation

GRACE heritage: examples for future concepts Low-low SST concept Laser SST demonstration (FO) Processing chain Long time series lower resolution Future SST

GOCE heritage: examples for future concepts Atom interferometer gradiometry Earth/planets static/time variations Future gradiometry Drag free system and control Stable structure Accelerometer & Thermal control Future SST

In summary: the potential for the future Enormous potential for studying Earth with on-going gravity missions (and soon GRACE-FO) Current science and technology activities are driven by past high quality proposals to ESA (Licody, e-motion) Lot of potential for future concepts that provide essential and unique high resolution information on system Earth and for applications requested by the user communities User community is in the driver seat: provide a convincing user case, convince politicians who fund and/or decide on space agencies programmes