Eskdalemuir Observatory

A site chosen for quiet

Magnetic instruments are sensitive to iron and electric currents. By the early twentieth century, the electric trams and underground trains of London had made the magnetic readings at Kew unusable, and a search found a site at Eskdalemuir in Dumfries and Galloway, far from any such disturbance. The observatory was built in 1904, and in 1908 the magnetic instruments moved from Kew; the National Physical Laboratory ran the site. The Meteorological Office took over in 1910 and ran the site until 1967.

Lewis Fry Richardson, who later set out the idea of numerical weather prediction, was superintendent of the observatory in the 1910s.

From magnetism to seismology

In 1964 the observatory joined the global standard seismographic network established to detect and distinguish distant underground nuclear tests. A seismic array was also built in the hills nearby. In 1967 responsibility passed to the Natural Environment Research Council, and the British Geological Survey has operated the site since.

In 1988 the seismic stations recorded the time of the impact of the Lockerbie air crash. During the magnetic storm of October 2003 the observatory's magnetometers recorded the declination swinging by up to 5 degrees in six minutes.

Protecting the silence

The seismic array at Eskdalemuir has a modern constraint of its own: because wind turbines produce ground vibration that could mask distant earthquakes and nuclear tests, planning rules limit the size and number of wind farms within about 50 kilometres of the array. Quiet is a resource that has to be defended in planning decisions as well as in the instruments.

Quiet as a public good

Eskdalemuir shows that quiet is something that can be protected only by a community decision. The seismic array's sensitivity is a national asset in the verification of the test-ban treaty, and the planning limits on wind farms in the surrounding area are a cost that local landowners and developers carry. The observatory's magnetic record, in turn, is used to calibrate national models of the Earth's field that help navigation. A site that serves two purposes has two sets of neighbours with two sets of concerns, and the observatory's history is partly a history of negotiation about what may be built around it.

Instruments and technologies

• Fluxgate magnetometer A magnetic core driven into saturation by an alternating current; the distortion of its output measures the field along an axis.
• Absolute magnetometer A theodolite-mounted fluxgate used to measure declination and inclination by hand, to calibrate the continuous instruments.
• Seismometer array Sensors laid out over several kilometres to separate signals by direction and speed.

The people

• Lewis Fry Richardson Meteorologist and mathematician; superintendent in the 1910s.
• John Stagg Meteorologist named in the BGS history of the site.

Timeline

• 1904 Observatory built at a site chosen to be free of electrical disturbance.
• 1908 Magnetic instruments arrive from Kew; the National Physical Laboratory runs the site.
• 1910 The Meteorological Office takes over (to 1967).
• 1964 Joins a global standard seismic network set up to detect distant underground nuclear tests.
• 1967 NERC becomes responsible; the British Geological Survey operates the site.
• 1988 Its seismic network records the time of impact of the Lockerbie air crash.
• 2003 During the October magnetic storm, declination swings by up to 5° in six minutes.

Key lessons for observation today

• Protect the instrument environment A site's quiet is part of the instrument and can be lost to a neighbour. Planning and agreements are infrastructure.
• Absolute reference and continuous record together Hand measurements calibrate the continuous sensors. Every long record needs a reference measurement beside it.
• One site, several networks The site serves magnetic, seismic and weather networks. Multi-purpose sites need clear metadata for each.

Sources

• BGS / NERC Planet Earth, One hundred years at Eskdalemuir (2004)
• Wikipedia, Eskdalemuir Observatory (secondary)
• British Geological Survey, geomagnetism