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Earth gravity from space
Reiner RummelInstitut 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“ 1715
3. 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 0.0010856King‐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.14National Geodetic Satellite Program, Part I, NASA 1977
Geoid as derived fromterrestrial gravity anomalies (Uotila, 1962)
Geoid as derived from optical tracking of artificial satellites (Izsak, 1964)
first models of the geoid
SSE1d/o 15
Lundquist CA & G Veis (eds.), 1966
GEM9d/o 30
Lerch FJ et al. 1979
GRIM 5sd/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 KenyonThe 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
GRACE2002 …‐
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
iapgKombination aus SST und SGG
SGG
Zemlja
anomalija
GPS - satelliti
SST
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 tankxenon 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) variationsrelative to a best fitting ellipsoid figure
short scale geoid anomalies (degree/order 21 ‐200)
meters
GOCE and solid earth
GGM03s d/o150Tapley et al 2007
GOCE TIM4
Pail et al 2011
EGM2008Pavlis et al, 2012
combined model
a new quality of gravity anomaly maps
identification of regions with poor gravity
information: a comparison of GOCE and
EGM2008Yi W, R Rummel, J
of Geodynamics, 2013
100kmS. 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‐ missionof ESA’s science programme: PLATO was selectedLOFT* 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 4• 1998 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
