3.2. Environment/Location

There are a number of factors that determine the quality of data recorded at an observatory and whether the recorded data conform to the INTERMAGNET standards for one-second data. Such factors include the types of instrument, the operating environment, the quality and frequency of absolute observations and the method used to apply baseline measurements to the vector magnetometer data.

The instrument’s operating environment varies greatly from observatory to observatory, but generally, vector magnetometers must be housed in a clean, dry, shelter with a stable pillar (preferably on bed rock), where there is low magnetic gradient and no man-made magnetic contamination. Since in general, vector magnetometers have a significant temperature coefficient, the vector magnetometer shelter should ideally maintain a constant temperature throughout the year as well as protecting the instrument from the elements. This may be achieved through thermal insulation and damping and may also include regulated heating or cooling.

Generally, scalar magnetometers, have an extremely small temperature coefficient and may be housed in non-temperature regulated housing, but they must still be protected from the elements. Instruments should be separated by a few meters to avoid cross-contamination.

The Manual on Magnetic Measurements and Observatory Practice (Jankowski and Sucksdorff, 1996) suggests establishing a magnetic observatory on a piece of land which is large enough not only to house the buildings, but also to limit the magnetic contamination from surrounding infrastructure or activity. In order to resolve the long period components of the natural magnetic field, care must be taken to select a site that is free from sources of man-made magnetic contamination over time-scales of many years. Contamination can come from nearby roads, buildings, power distribution infrastructure (transformers or cables), transmitters (radio or communication), local land use (e.g. housing, farm machinery, etc.) or from electric train lines. DC train lines can cause interference for tens of kilometers.

Other factors for consideration are:

  • The site should offer good visibility to distant target(s) to be used as an horizontal direction reference in absolute observations.

  • The observatory buildings should be located on a flat, well-drained, solid foundation. Buildings, lighting and heating systems should be made of non-magnetic materials. Electricity supplies to variometer and absolute buildings for lighting and heating should be AC.

  • There should be access to a reliable mains electricity supply to the site, preferably with some form of back-up power, so that power outages are kept to a minimum.

  • The site should offer good visibility to distance reference objects for absolute observations.

  • There should be access to local telephone or network communications for data transfer.

  • There should be an existing clean, dry environment nearby to house the data recording equipment.

  • The site should be easily accessible by observatory staff.