Nummela Standard Baseline is a baseline used to

calibrate In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known ...

rangefinders A rangefinder (also rangefinding telemeter, depending on the context) is a device used to measure distances to remote objects. Originally optical devices used in surveying, they soon found applications in other fields, such as photography, t ...

, in

Finland Finland, officially the Republic of Finland, is a Nordic country in Northern Europe. It borders Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bothnia to the west and the Gulf of Finland to the south, ...

, located in the municipality of

Vihti Vihti (; ) is a municipality in Finland, located in the southern interior of the country. Vihti is situated in the Uusimaa region. The population of Vihti is approximately . It is the most populous Municipalities of Finland, municipality in Fin ...

, Nummelanharju (

esker An esker, eskar, eschar, or os, sometimes called an ''asar'', ''osar'', or ''serpent kame'', is a long, winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions of Europe and North Amer ...

) where it was built in 1932. Winding ridge of stratified gravel and sand was chosen as a location for measurements since temperature variations cause very little displacement on soil where benchmarks are located. Measurement devices such as

theodolite A theodolite () is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying, but it is also used extensively for building and ...

and mirrors are then placed on those pillars. Careful preliminary measurements such as levelling height differences of observation pillars reference points are required before actual measurements can begin. In 1947, a white light

interference Interference is the act of interfering, invading, or poaching. Interference may also refer to: Communications * Interference (communication), anything which alters, modifies, or disrupts a message * Adjacent-channel interference, caused by extra ...

based measurement system was taken to use. It was developed by

Yrjö Väisälä Yrjö Väisälä (; 6 September 1891 – 21 July 1971) was a Finnish astronomer and physicist. His main contributions were in the field of optics. He was also active in geodetics, astronomy and optical metrology. He had an affectionate ni ...

. Before that baseline was defined by

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

made measuring rod, which was used to calibrate 24-meter long invar-wire. Standard baselines length is invar-wire multiplied by 36, which is 864 meters.} Measured numerical value for the 2007 standard baseline is 864 122.86 millimetres ±0.002 mm to ±0.007 mm uncertainty. 864 122.86 mm ≈ 864 m. Previously used quartz rod had 0.1 mm deviation from 1 meter – intended length – and it was taken account in new measurements. Because of accuracy, curvature of earth had to take in account when building the baseline: the middlepoint 432 m is 14.6 mm lower than zero & 864 -points. (Fig 17 in ref "144" )

References

External links

Nummela Standard Baseline – The Finnish Geospatial Research Institute

MIKES and Finnish Geodetic Institute perform the most accurate geodetic baseline measurements in the world
Geography of Uusimaa Geodetic surveys {{geodesy-stub