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Istanbul-Kandilli Geomagnetic Observatory

There has been an observatory at Kandilli since 1911, when the Istanbul astronomical and meteorological observatory moved there from the centre of the city. The first magnetic measurement at Kandilli was made by the Director, Fatin Gökmen, on March 12, 1927, using a Chasselon-Brunner magnetic theodolite and a dip circle brought from France in 1926. Further measurements were made by Osman Sipahioglu between 1936 and 1947, but it was not until 1947 that systematic magnetic measurements were started. At a time when most of Europe was still suffering shortages and economies as a consequence of the second world war, the Turkish government found funds to establish a well-equipped magnetic in fine new buildings. Sipahioglu was its first Superintendent. Results were presented at the Oslo IUGG meeting in 1948 and the President (J.A. Fleming) subsequently wrote to say "It has been a pleasure to have such excellent works from a region where systematic observations are so much needed." Praise and encouragement were also given by Julius Bartels.

The Kandilli site is in wooded hills on the Asian shore of the Bosphorus with magnificent wievs both of the Bosphorus and the old city of Istanbul, about 15 km. distant. Many buildings related to a wide variety of geophysical and astronomical disciplines share the 36 hectare site, which since 1985 has been a postgraduate campus of Bogazici (Turkish for Bosphorus) University. The three main magnetic structures are a variometer building, absolute pavilion and magnetic offices.

The copper-roofed variometer building is 14m by 10m, plus lobby and staircase. The walls are of local stone and extend from 2m above ground to 5m below, increasing in thickness from 0.5m to 2m from top to bottom – a very solid structure! Inside are two wooden rooms entirely below ground level. Each measures 4.5m wide by 7m long by 3m high. They are separated by 1.5m surrounded by a 1m corridor and have 2m of space above and below. One room houses Askania, Eschenhagen system, photographic recorders and the other, until recently, housed a standby set of a La Cours. The offices are in two-story, recently renovated, Ottoman-style building 50m clear of the observing site. They include a paleomagnetic laboratory and workshop. Eleven meters north is the absolute pavilion, which is wooden, with a copper roof. It is 10m by 12m, with a 4m high ceiling. The absolute instruments have changed over the years, but still include a working Askania earth-inductor, BMZ63 and QHMs 169 and 171, as well as the currently used Elsec PVM for H and Z and the original Askania (Schmidt large size) declinometer for D, using the dome of a distant mosque as the azimuth mark.

In 1947 the population of Istanbul was about one million and Kandilli was out in the country. But the population is now about 12 million and rising, so the city has engulfed Kandilli. Fortunately, it is on a large, protected site, and the many residential houses and apartment blocks that come right up to the boundaries do not yet appear to have had a significant effect on the magnetic records. There are contingency plans to move to a new site near Iznik (formerly Nicea) about 100km to the south east, if interference becomes serious. This is a site of great geophysical interest because it lies on the very active North Anatolian fault in a seismic gap, so a major earthquake could occur there any time. The institute already maintains many field sites there, including 7 for the continuous monitoring of total magnetic field and 24 total-field repeat stations.

With a view to joining Intermagnet in our 50th year, we have recently replaced the La Cour variometers with two three-component EDA fluxgates (they may later be transferred to Iznik one at a time, to give an overlap) controlled by BGS "Flare" data loggers. These instruments are currently undergoing stability tests and their data are being compared with those from the Eschenhagen photographic records. Also to mark the 50th anniversary, the Istanbul-Kandilli magnetic hourly values will be deposited with the World Data Centres in computer-readable -form. They cover the interval 1949-1996, because the first two years were unreliable, and they include a gap from 1965 to 1969, for which interval the data are not yet prepared. After a gap since 1980, annual volumes are now being published, starting with that for 1992.

The Istanbul-Kandilli magnetic observatory is proud of its past 50 years of operation and looks forward to a yet more active future.

(published in IAGA News Feb.97,No.36)