| Terrestrial Gravimetry
 Two realtive
gravity meters are available to the Institute for purposes of education
and research. The old LaCoste & Romber G688 gravimeter is shown on
the right. It is a "classical" relative gravity meter using a metal
spring and was procured about 20 years ago. No electronic components
are available and the measurements are not free of "subjective errors",
i.e. uncertainties related to the user that can introduce systematic
errors in the network adjustment.
 The new gravity
meter can be seen on the left of this page, a Scintrex CG-5 Autograv.
This device utilizes the same principle as the LaCoste & Romberg
meter, but Scintrex uses a Quartz spring instead of a metal spring. The
thermo-elasticity of such a device is approximately 10 times larger
than that of a metal spring, but drifts tend to be linear. The unit is
micro-computer controlled a offers a graphical and more or less
intuitive user interface. Readings are free of subjective errors. Data
are stored to non-volatile memory and can be easily transferred to the
PC afterwards.
The diagram below offers
a look on some performance characteristics of the new digital gravity
meter. The tidal signal dominates the blue curve and has been removed
using the device-internal (simplified) algorithm yielding the red
curve. After estimation and removal of the linear drift function, the
noise of the measurements tends to be around 4 µm/s².
Remaining systematic
(periodic) errors can be viewed in the diagram of the residuals shown
below. These peroidic function can be most likely explained by
uncertainties in the device-internal tidal correction algorithm which
is a rather simplified one and thus of limited accuracy.
For further information
on this topic please feel free to browse the research database
 GravAP - Gravimetric Adjustment Package
or contact the author by
e-mail.
Point of contact: Torben Schüler
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