Geoscience Reference
In-Depth Information
Earth
Fig. 11
Scheme of GOCE: Six on-board 3-axis accelerometers, tracked by GNSS satellites
Gravity variations that GRACE is sensitive to include: changes due to surface
and deep currents in the ocean, runoff and ground water storage on land masses,
exchanges between polar ice sheets or glaciers and the oceans. For further information
3.1.3 GOCE: Satellite Gravity Gradiometry
Satellite gradiometry consists basically of the measurement of the acceleration dif-
ferences in three spatial orthogonal directions between the six test masses situated on
each end of the axes. This measurement quantity corresponds to the gradients of the
gravity acceleration, i.e. the second derivative of the gravitational potential (Fig.
11
).
GOCE (Gravity field and steady-state Ocean Circulation Explorer, (Rummel et al.
2000
)) was launched on 17 March 2009 and was the first mission of ESA's Living
Planet Program. It is the first satellite equipped with a gradiometer and thus helps to
better understand the static gravitational field of the Earth. The missions objectives
are to obtain gravity gradients from which new global and regional models can be
deduced at length scales down to 100km and the geoid with an accuracy of 1-2 cm.
To achieve this it is necessary to determine gravity field anomalies with an accuracy
of 1mGal. For further information see:
http://www.esa.int/goce
.
3.1.4 Future Missions
The
GRACE Follow-On
mission, a cooperation between GFZ and NASA, is focused
on maintaining data continuity from GRACE and is planned for launch in 2017
(Watkins et al.
2010
). To minimize the project schedule as well as the technical
and cost risk a high inheritance “replica” of GRACE is conceptualized, taking into
account the lessons learned from GRACE. Additionally to the microwave ranging
system a laser interferometer will be installed to demonstrate an improved ranging at
the nm/sec level, which also serves as a technical demonstration of this technology
for future missions with more satellites and different orbit constellations in the time
frame beyond 2020 (Gruber et al.
2011
).
