Gravity, Magnetic Field and Geodynamic
Instruments
Description
This category of instruments is used here to
describe a variety of sensors and supporting
systems used to derive information on
Earth’s gravity field, magnetic field or
geodynamic activity.
Gravity field measurements from space rely
on one of three techniques:
— Use of single or multiple accelerometers
on one or more satellites to derive gravity
or gravity-gradient information;
— Precise satellite orbit determination
(using satellite-to-ground navigation
systems such as GPS and satellite laser
ranging systems), and separation of
satellite motion, induced by Earth’s
gravitational force alone, from other forces
(such as solar radiation and aerodynamic
drag);
— Satellite-to-satellite tracking (e.g. by
GPS or microwave link) to measure relative
speed variations of two satellites induced
by gravitational forces.
Satellite-borne magnetometers provide
information on the strength and direction of
Earth’s internal and external magnetic field
and its time variations.
Applications
Gravity field measurements from space
provide the most promising advances for
improved measurement of the ‘geoid’ and its
time variations. The geoid (the surface of
equal gravitational potential at mean sea
level) reflects the irregularities in the
Earth’s gravity field at the surface due to
the inhomogeneous mass and density
distribution in the planet’s interior.
More accurate models of the static mean
geoid and its temporal variability are vital
for:
— A precise marine geoid, needed for the
quantitative determination, in combination
with satellite altimetry, of absolute ocean
currents, their transport of heat and other
properties;
— A unified global height reference system
for the study of topographic processes,
including the evolution of ice sheets and
land surface topography;
— New understanding of the physics of
Earth’s interior;
— Estimates of the thickness of the polar
ice sheets and their variations through a
combination of bedrock topography derived
from gravity measurements and ice sheet
surface topography from altimetry;
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Current & planned
instruments
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Gravity
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Precision orbit
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EFI
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ACC
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EGG
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DORIS-NG
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GRACE instrument
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DORIS-NG (SPOT)
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LRI
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EGG
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MWI
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GOLPE
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GPS (ESA)
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Magnetic field
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GPS Receiver (Swarm)
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Advanced GGAK-M
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GPSP
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ASM
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GRAS
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CSC FVM
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INES
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GGAK-E
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IST
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GGAK-M
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Laser Reflectors
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Magnetometer (NOAA)
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Laser Reflectors (ESA)
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MMP
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LCCRA
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Overhauser Magnetometer
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LRA
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SSJ/4
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LRA (LAGEOS)
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SSJ/5
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LRR
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SSM
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ROSA
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VFM
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RRA
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SI
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SSTI
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STR
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TDP
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— Estimates of the mass/volume redistribution
of fresh water in order to further understand
the hydrological cycle;
— Improved understanding of post-glacial
rebound processes on a global scale.
Magnetic field measurements are also valuable
in a range of applications, including
navigation systems, resource exploration
drilling, spacecraft attitude control systems,
assessments of the impact of ‘space weather’
caused by cosmic particles and earthquake
prediction studies.
The precision location capabilities of
satellite laser ranging and other systems
(such as DORIS and GPS), sometimes in
combination with interferometric SAR (INSAR),
are applied in support of studies of crustal
deformation, tectonic movements and Earth’s
spin rate.
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