Earth gravity from space Reiner Rummel Institut für Astronomische und Physikalische Geodäsie Technische Universität München NVR mini‐symposium, Delft, April 23, 2014

gravity and geoid in geophysics and geodesy A)Geoid and gravity define horizontal and vertical “If the sea were at rest, its surface would coincide with the geopotential surface.“ (AE Gill, 1982) B)Geoid and gravity anomalies: “anomalies” referred to what? C) Temporal changes of geoid and gravity “After three decades….of advances, space geodesy is poised for prime time in observing the integrated mass transports that take place in the Earth system…” (BF Chao, 2003) earth gravity from space: about the „why?“

earth gravity from space: about the „how?“ Source: I. Newton “De mundi systemate“ Volume of his „Philosophiae naturalis Principia mathematica“

earth gravity from space: about the „how?“ three principles of satellite gravimetry: orbit as close to the earth as possible measurement or elimination of non‐gravitational forces measurement of relative motion of test masses in free fall

October 4, 1957 launch of Sputnik 1 satellite gravimetry: the beginning

October 4, 1957 launch of Sputnik 1 Earth oblateness geometric 1:297.7 dynamic King‐Hele DG, 1958, Nature Buchar E, 1958, Nature satellite gravimetry: the beginning

Cox & Chao, 2002, Science also: Dickey et al 2002, Science, Cazenave & Nerem, 2002, Science temporal changes of the earth‘s oblateness Greenland/ West Antarctica Sea level rise (eustatic) Sea level rise (regional variations) LAGEOS 1+2

with argument and frequencies: Wagner & Klosko, 1977, p.145 Kaula, 1966 satellite gravimetry: the beginning

Henriksen SW Introduction p.14 National Geodetic Satellite Program, Part I, NASA 1977 Geoid as derived from terrestrial gravity anomalies (Uotila, 1962) Geoid as derived from optical tracking of artificial satellites (Izsak, 1964) first models of the geoid

SSE1 d/o 15 Lundquist CA & G Veis (eds.), 1966 GEM9 d/o 30 Lerch FJ et al GRIM 5s d/o 99 Biancale R et al., 2000 step by step improvements Free air gravity anomalies of South America (mGal)

geoid altimetry level surface gravity anomalies from satellite altimetry ocean topography

Andersen OB, P Knudsen, P Berry & S Kenyon The DNSC08 ocean‐wide altimetry derived gravity anomaly field EGU, Vienna, 2008 Also: Sandwell D, WHF Smith, Global marine gravity from retracked Geosat and ERS‐1 altimetry: Ridge segmentation versus spreading rate, JGR, 2009 gravity anomalies from satellite altimetry

CHAMP 2000‐2010 GRACE 2002‐… GOCE 2009‐2013 the new era of satellite gravimetry

 location (GPS)  time (atomic clocks of GPS)  “no” air drag  no micro‐seismicity free fall of a single satellite as measured by GPS principle of CHAMP

free fall of two test masses GRACE: relative motion of two satellites (in free fall), following each other at a distance of 200 km

relative acceleration between several test masses inside one satellite measurement principle of GOCE gravity gradiometry

Messprinzip GOCE-PROJEKTBÜRO DEUTSCHLAND iapg Kombination aus SST und SGG SGG Zemlja anomalija GPS - satelliti SSTSST

upper electrode proof mass 4cm x 4cm x 1cm Platin‐Rhodium 320 g cage: ULE‐ceramics gold electrodes accelerometer (Onera) GOCE satellite mission: principles

single accelerometer one axis gradiometer three axis gradiometer consisting of 6 accelerometers GOCE satellite mission: principles

ion thrusters ion thruster control unit nitrogen tank xenon tank gravitational gradiometer star sensor GPS receiver magneto‐torquers power supply control unit source: ESA GOCE sensor system an orbiting gravitational laboratory high performance of all sensors very different from „typical“ remote sensing satellites

[m] GOCE and solid earth geoid (or potential) variations relative to a best fitting ellipsoid figure

short scale geoid anomalies (degree/order 21 ‐200) meters GOCE and solid earth

GGM03s d/o150 Tapley et al 2007 GOCE TIM4 Pail et al 2011 EGM2008 Pavlis et al, 2012 combined model a new quality of gravity anomaly maps

identification of regions with poor gravity information: a comparison of GOCE and EGM2008 Yi W, R Rummel, J of Geodynamics, km S. America China SO Asia Africa Antarctica Antarctic Circumpolar Current 500km 200km GOCE and solid earth

Delft – almost 30 years back NRC, april 19, page W8: article about the recent selection of M‐3 mission of ESA’s science programme: PLATO was selected LOFT* did not make it De satelliet die niet de ruimte in ging Na vier jaar zwoegen viel de geavanceerde röntgensatelliet van de UvA alsnog buiten de boot // Slechts een paar van de satellieten die bedacht worden, gaan echt de ruimte in *LOFT= Large Observatory For X‐ray Timing 1985: invitation to tender for Horizon 2000 and a naïve letter from TUD to SRON from 1986 to 1991 several studies on ARISTOTELES (Applications and Research Involving Space Techniques Observing The Earth’s fields from Low Earth‐orbit Spacecraft) 1991 to 1993: STEP (Satellite Test of Equivalence Principle) work on GOCE begins 1996 User Consultation Meeting: from 19 down to ESA’s Living Planet Programme 1999 User Consultation Meeting: GOCE chosen (together with ADM) 2009: launch of GOCE 2013: successful mission end

acknowledgement It was the work of a team: members of the GOCE High level Processing Facility and of ESA