From Deutsche Seewarte Hamburg to Geoforschungszentrum Potsdam – Wingst Geomagnetic Observatory During Six Decades

From Deutsche Seewarte Hamburg to GeoForschungsZentrum Potsdam – Wingst Geomagnetic Observatory during six decades

G. Schulz Erdmagnetisches Observatorium Winst, Am Olymp13, D-21789 Wingst

A b s t r a c t: At the beginning of the year 2000, the operation of Wingst Observatory was transferred to GeoForschungsZentrum Potsdam. This is a good occasion for a brief retrospective look at the establishment of the observatory in 1938 and a few remarks on the development of its instrumentation. Special attention is given to the people who set the course at the very beginning as well as to those who influenced the observatory’s later development.

Keywords: observatories, history, instrumentation

1. History

Looking back at the late thirties, there existed two institutions in Germany which played a leading role in the establishment of Wingst observatory:

- the Marineobservatorium, Wihelmshaven, and

- the Deutsche Seewarte (German Naval Observatory), Hamburg.

The Marineobservatorium had carried out geomagnetic observations for several decades at that time, starting in 1878 with two-hourly readings. No data records had been kept between 1919 and 1930, and the measurements were definitively stopped 1936 (three years after the Second International Polar Year 1932/33) due to growing disturbances caused by electric streetcars and the expansion of the docks of the city of Wilhelmshaven. As a result, the entire geomagnetic department was transferred to Deutsche Seewarte. One of the first tasks was to find a new observatory site. The search was finally successful in the Lower Elbe area, on top of a terminal moraine of the Saale glacial period, in an area called ”Wingst”. After the Second World War, the two above-mentioned institutions were merged to form the Deutsches Hydrographisches Institut (German Hydrographic Institute), which was renamed Bundesamt für Seeschiffahrt und Hydrographie (Federal Maritime and Hydrographic Agency) in 1990. In the second half of the nineties, the Bundesamt decided to reduce the geomagnetic service in favour of other statutory obligations. Another interruption of the records appeared likely and - even worse – the observatory

Fig. 1 Photograph taken during the inauguration of Wingst Observatory in 1938. was threatened by a shutdown. Fortunately, GeoForschungsZentrum Potsdam signalized interest and took over, but its intention is to convert the observatory to a fully automated, remotely controlled station within a few years time. Let us look back on the thirties: Fig. 1 shows a photograph taken in front of the main building on April 30, 1938, when the observatory was inaugurated. The first observer in charge, O. Meier, is shown second from the left. Next to him, on his right side: F. Errulat, head of the new geomagnetism department in Hamburg and former director of the Geophysikalische Warte Groß Raum

2 (Errulat, 1974). J. Bartels can be seen in the second row (sixth from the right side). Just two years earlier, he had become director of the newly founded Geophysikalisches Institut Potsdam, which included the Adolf Schmidt- Observatory, Niemegk (Fanselau, 1965). H. Reich (Preußische Geologische Landesanstatlt) is shown first from the right. He provided geological advice concerning the new observatory’s location (Errulat, 1939). Next to him on the right side: F. Burmeister, who had been observer in München-Bogenhausen and Maisach before and was now observer in Fürstenfeldbruck, which came into operation at the same time as Wingst (Wienert, 1966). R. Bock (first row, third from the right) was observer at Niemegk in the early thirties. The expertise and experience of these men contributed essentially to the successful start of the new observatory. One of the founding members, however, is not shown in Fig. 1: P. Maier, who was the last observer at Marineobservatorium, had been instructed to transfer the instruments from Wilhelmshaven to Wingst and to install them at the new site. He died in 1937.

2. Instrumentation

A complete set of instruments had been specially purchased ten years earlier for the purpose of monitoring the geomagnetic field at the old site in Wilhelmshaven during the forthcoming Second International Polar Year. The set comprised a station theodolite (No 75), an Earth inductor (No 552) and a recording system, all made by SCHULZE, Potsdam. It is worth noting that the recording system is still in operation as an invaluable stand-by in case the modern digital equipment breaks down. The excellent stability of the system, which is in no way inferior to modern devices, has been achieved by two technical improvements:

1. Perfecting the temperature control (by installing contact thermometers, ±0.03°C) in 1956 (DHI, 1959), and

2. Replacing the Z variometer by a LA COURE type balance (sealed against humidity) in 1966 (DHI, 1968).

The first of the above improvements paid off particularly when the second- generation suspended double system of type DMI (FGE) was installed in 1993: The base-line fluctuations have been reduced to less than 2 nT per year (Schulz, 1998). The system is located on the northern pier of the variometer room (Fig. 2,

3 (Errulat, 1939)). It forms the backbone of the future concept of a remotely controlled observatory.

Fig. 2: Plan of the variometer house, 1938 (Errulat, 1939). An extension was constructed in 1963/64.

Since 1993: J and T: FGE double system; D: fluxgate for the W component (see text)

Digital recording had been introduced thirteen years earlier, when the first- generation fluxgate triple of type EDA (FM100C) was installed (Schulz, 1983). The reliability of the digitally acquired data has been enhanced considerably by two later improvements:

1 Rotation of the horizontal sensors by 45°, in 1984 (Schulz, 1S988) , and

2 Addition of a fourth fluxgate picking up the component W aligned parallel to the triple’s spatial diagonal, in 1993 (BSH, 1998).

4 Fig. 3: First PRM reading at Wingst Observatory on June 9, 1960.

These improvements are particularly useful during gaps in simultaneous F recordings. Let us once more look back on the thirties: To become an observatory with absolute control, the geomagnetic horizontal intensity level was derived from the Niemegk standard, i.e. it was transferred to Wingst by means of a travel theodolite. A remarkable development: Niemegk itself profited from this procedure a few years later, after having lost both of its standard magnets during The Second World War (Fanselau and Wiese, 1954). The level was successfully restored by re-transferring the standard from Wingst, which had not been affected by the war. The proton precession magnetometer was introduced at Wingst for the calculation of the Z base-line in 1960 (Fig. 3, see Schulz, 1988). Nelson’s method of measuring the vertical and horizontal components followed nine years later by means of a proton vector magnetometer of type ASKANIA/BRAUNBECK (Fig. 4), constructed by Voppel (1972). He was the second observer, in charge from 1954 to 1974. The instrument is still in operation. However, in the near future, it is intended to be used as a quasi- absolute recording device for permanent remote monitoring of the base-lines, in connection with an Overhauser magnetometer of type GEM (GSM19). The station theodolite was replaced by a DI-flux of type ZEISS (010B)/BARTINGTON (MAG 01H) in 1992. First experiments with this principle of measurement had already been carried out by MEIER and Voppel (1954) almost forty years earlier. However, the results were unsatisfactory insofar as the feedback current turned out to be unstable. This problem could not be solved until the eighties.

5 Fig. 4: The proton vector magnetometer of type ASKANIA/BRAUNBECK at Wingst Observatory. 3. Outlook

In this paper, a few of the activities have been described which had a direct impact on the operation of the observatory. It gives just a faint idea of the observatory’s full range of activities in observatory-related fields (research work in the field of seafloor spreading, investigation of the North German induction anomaly, development of transportable variographs, momentary value comparison between European stations since 1956, etc.). For additional historical information, the reader is referred to (Voppel, 1988).

6 Dehghani Spitta Nevanlinna Andersohn Schmucker Rudloff Auster Kring Lauridsen Simmons Schulz-Ohlberg Kämmerer Hegymegi Bahr Wonik Kataja Traeger Wildt Cosma Schulz Brodscholl Musmann Korschunow Barreto Green Voppel Theis Beblo Roeser

Fig. 5: Photograph taken during the 50th anniversary of Wingst Observatory.

At this point, a special event should be mentioned: The 50th anniversary of Wingst Observatory, which was celebrated in 1988. To mark the occasion, an international colloquium was held covering "Activities of Geomagnetic Observatories in the past and in the future". All papers presented during the colloquium were published in a thematic issue of Dt. hydrogr. Z. 41, 1988, H. 3- 6. Fig. 5 again shows a photograph in front of the main building, which was taken during the colloquium.

References

BSH, 1998: Geomagnetic results Wingst 1993. Annual Report No. 39, Hamburg and Rostock.

DHI, 1959: Ergebnisse der erdmagnetischen Beobachtungen im Observatorium Wingst in den Jahren 1955 und 1956. Jahrbuch Nr. 10, Hamburg.

7 DHI, 1968: Ergebnisse der erdmagnetischen Beobachtungen im Observatorium Wingst in den Jahren 1965 und 1966. Jahrbuch Nr. 15 Hamburg.

Errulat, F., 1939: Das erdmagnetische Observatorium Wingst der Deutschen Seewarte. Ann. Dt. Hydr. u. Mar. Meteor., 67, 355-360.

Errulat, F., 1974: Die geophysikalische Warte Gross Raum der Universität Königsberg/Pr. – Ein Rückblick. Zur Geschichte der Geophysik. Springer,Berlin, 131-138.

Fanselau, G. and Wiese, H., 1954: Ergebnisse und Beobachtungen am Adolf Schmidt- Observatorium für Erdmagnetismus in Niemegk im Jahre 1951. Berlin.

Fanselau, G., 1965: Nachruf auf Julius Bartels, Gerl. Beitr. Geoph. 74, 1-6.

Meier, O. and Voppel, D., 1954: Ein Theodolit zur Messung des erdmagnetischen Feldes mit der Förstersonde als Nullfeldindikator. Dt. hydrgr. Z. 7, 73-77.

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Schulz, G., 1998: Long-term experience with digital variometer systems of different generations at Wingst Observatory. Scientific Tech. Rep. 98,21, Potsdam, 27-39.

Schulz, G., 1988, The standard of Wingst Geomagnetic Observatory (Erdmagnetisches Observatorium Wingst) – its improvement and preservation, demonstrated by some examples. Dt. hydrogr. Z. 41, 119-129.

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Wienert, K., 1966, 125 Jahre erdmagnetische Beobachtungen in München, Maisach und Fürstenfeldbruck. Zum 125 jährigen Bestehen der Observatorien München – Maisach – Fürstenfeldbruck, München, 5-51