Download New superconducting gravimeter - Finnish Geospatial Research

11.3.2014
The Most Precise Gravity Measurement Device in the World at the Finnish
Geodetic Institute
The world's most precise device for measuring changes in gravity has been taken into use at the Finnish
Geodetic Institute's Metsähovi research station. The device is called superconducting gravimeter. It can
measure changes in gravity that are a millionth of a millionth of normal gravity. The device will
replace the old superconducting gravimeter that has been in use since 1994 and is currently the oldest
continuosly operated superconducting gravimeter in the world.
How the gravimeter works
The great precision of the gravimeter is based on superconductivity. Superconductivity is a
phenomenon where the electrical resistivity of matter disappears completely. The two detectors in the
device have coils made out of the element niobium that have been cooled very close to absolute zero
temperature, -273,15°C. Electric field that circulates the coils without resistance creates a stable
magnetic field around the coils. Minute changes in gravity attempt to change the position of a niobium
sphere that is levitating in the magnetic field. By monitoring the sphere it is possible to determine the
change in gravity. The use of two detectors instead of one make the device more precise than earlier
models.
Earth's changing gravity field
Gravity is constantly changing. The most clearly observable effects of this are the ocean tides caused
be the gravitational pulls of the Moon and the Sun. The phenomena measured with the superconducting
gravimeter are a million times weaker. Some of the changes in gravity are caused by earthquake waves
or small height changes of the ground caused by changes in the atmospheric pressure. Some are caused
by local mass changes such as changes in groundwater height or thickness of snow cover. The
sensitivity of the device is high enough to measure the effect of the nearby scientist to the local gravity.
In addition to seismometers that measure the waves caused by earthquakes, the superconducting
gravimeter is the only device that can be used to study the inner structure of the Earth and phenomena
that take place there. Due to the high sensitivity and good long term measurement stability it can also
be used to study slow changes in gravity. Changes to the local gravity caused by mass changes in local
hydrology such as groundwater and snowcover as well as the height of the Baltic Sea are studied in
Metsähovi. The measurements done in Metsähovi have been combined to data measured by satellites
measuring global gravity changes in order to understand the contribution of various phenomena to the
overall change. This way it is possible to achieve better understanding about a variety of geophysical
phenomena such as melting of glaciers and sea level rise.
The superconducting gravimeter in Metsähovi is part of a global network comprising of 32 stations.
The data are gathered in an international databank where they are freely accessible by researchers.
Additional information:
senior research scientist Heikki Virtanen ([email protected], puh. 029 530 8089)
senior research scientist Jyri Näränen ([email protected], puh. 050 435 7258)
researcher Arttu Raja-Halli ([email protected], puh. 050 411 8882)