Past and Present of Polish Geomagnetic Observatories

Transcription

1 PUBLS. INST. GEOPHYS. POL. ACAD. SC., C-99 (398), 2007 Past and Present of Polish Geomagnetic Observatories Jerzy JANKOWSKI and Janusz MARIANIUK Institute of Geophysics, Polish Academy of Sciences ul. Księcia Janusza 64, Warszawa, Poland s: Abstract The paper outlines the history of Polish magnetic observatories, beginning from the oldest, presently inactive one, at Świder, to the three observatories operating at present: Belsk, Hel, and Hornsund. We describe changes in the equipment throughout the years, the present instrumentation and accuracies. While discussing the quality of data, of utmost importance is the lack of gaps in the recordings, and the high stability of bases. A specific trait of our observatories is the fact that the instruments they use are mostly of our own make. Key words: magnetic observatories, PSM variometer, proton magnetometer, recording system. History The first Polish geomagnetic observatory was put into operation in 1920 at Świder near Warsaw (see map in Fig. 1). Its founder and many-year director was Professor Stanisław Kalinowski. The observatory was equipped in modern measuring and recording instruments of that time. The absolute magnetic measurements of declination D and horizontal component H were performed with a magnetometer produced by Cambridge Scientific Instruments Co. and a large Sartorius magnetometer; the inclination angle I was measured by an earth inductor produced by Schultz company from Potsdam. The bases of the vertical component Z were calculated from measurements of H and I, in accordance with the generally accepted routine at that time. Three variometers, H, D and Z, and a recorder produced by the firm of Toepfer and Sohn from Potsdam, were installed for continuous magnetic recording. The Świder absolute measurement (wooden) and recording (brick) pavilions of modern design (Figs. 2 and 3) were erected following the example of the observatory at Potsdam.

2 Fig. 1. The location of Polish geomagnetic observatories Belsk, Hel, and Hornsund. Fig. 2. The Świder Observatory absolute measurement pavilion. The Świder observatory operated more-or-less normally (in spite of some errors made at the beginning of its activity) as long as the suburban railroad passing some 1.5 km from the Observatory had not been electrified. This DC powered railroad begun to produce strong artificial disturbances in the natural magnetic field, especially the Z component. A next segment of the railroad has been electrified in the post-war period, which further enhanced the artificial noise, as illustrated in Fig. 4.

3 Fig. 3. The Świder Observatory recording pavilion. Fig. 4. Artificial noise due to railroad at the Świder observatory (copies of three magnetograms). The second Polish geomagnetic observatory, established at Hel, begun its operation in Likewise Świder, it was equipped in modern instruments of the time. The absolute measurements of H and D were made with the use of a large Askania theodolite, and those of the magnetic inclination angle I by means of Edelman earth

4 inductor. Three quartz magnetometers QHM, Nos. 25, 26, and 27, were purchased in Denmark. The magnetic recording was first made by Mascard-system variographs, and since 1934 by a fast-run recorder of La Cour system. Unfortunately, the Hel observatory was destroyed in 1939 by German army. The pavilions with the instruments were demolished and all the archival data were lost. In 1929, in the region that then belonged to SW Poland (presently the Ukraine), a magnetic station was put into operation in Daszewo. Since 1932 the works of this station were continued in the newly founded magnetic observatory in Janów by Lwow (presently called Ivanofrankovsk). The observatory is still active, being affiliated to the Ukrainian Academy of Sciences. After the end of the Second World War, the only observatory that was not destroyed and was able to operate on the territory of Poland was Świder. Unfortunately, because of artificial railroad noise the data produced by this observatory were not very accurate. This was one of the reasons why at the beginning of the 1950s the decision was made to rebuild the Hel observatory and to move the geomagnetic observations from Świder to Belsk. Belsk is located some 45 km south of Warsaw (and some 50 km from Świder) in a typically rural region, with a low level of artificial noise. The decisions relating to the Belsk and Hel observatories fortunately coincided with the forthcoming III International Geophysical Year. The state authorities declared Poland s participation in this huge international undertaking. Special funds were granted for joining the Geophysical Year project. The Institute of Geophysics (at that time called Zakład Geofizyki ) was able to purchase a rich collection of various instruments for geomagnetic research. The instruments included three La Cour systems and one Mating Weisenberg system for observatory geomagnetic recordings, and three portable Askania GV3 systems (D, H and Z components) for field recordings. There were bought two large theodolites, Askania and Mating Weisenberg, for absolute measurements of D and H. There were bought two earth inductors for absolute measurements of magnetic inclination angle I, with the aim to equip the Belsk and Hel observatories. There were also bought a dozen or so quartz magnetometers QHM and a few BMZ magnetometers. Fig. 5. The Hel observatory recording pavilion.

5 Fig. 6. The Hel observatory absolute measurement pavilion. Fig. 7. The Belsk observatory recording pavilion. Fig. 8. The Belsk observatory absolute measurements pavilion. The newly purchased instruments provided a very modern, as for those times, instrumentation at the rebuilt Hel observatory and a new observatory at Belsk. In both observatories, the measurement and recording pavilions were constructed in a style that was classical for mid-twentieth century magnetic observatories. The photos are shown

6 in Figs. 5-8, while the main building of the Belsk observatory is shown in Fig. 9. The reconstructed Hel observatory begun its routine operation in 1958, while the Belsk observatory, whose construction took more time, in Fig. 9. The Belsk observatory main building. Fig. 10. Polish Polar Station Hornsund recording pavilion. Fig. 11. The Polish Polar Station Hornsund, Spitsbergen main building.

7 In 1989, there was activated a Polish geophysical station located far northerly, in Hornsund fiord, Spitsbergen, The station is in a sense a continuation of the Polish station operating o n Bear Island during the II International Geophysical Year. The Hornsund station is mostly focused on observations of events occurring in polar regions. It has two small magnetic pavilions, one being shown in Figs. 10; the main building of the station is shown in Fig. 11. Evolution of Observation Methods in Polish Magnetic Observatories The generous purchase of western measurement and recording instruments, associated with the III International Geophysical Year, gave grounds for modern instru- methods over the world forced us to make numerous changes to refine the instruments mentation of Belsk and Hel observatories. The fast development of new measurement and methodology of measurement (in spite of the fact that the system of real socialism in Poland was not favorable to any progress). The changes introduced are illustrated in Table 1. Table 1 Main instruments used at Polish geomagnetic observatories in the last 50 years The real break-through in the methodology of absolute measurements was the introduction of proton magnetometers (constructed in short series at the Institute of Geophysics). Previously, the observatory routine had been to calculate bases of the vertical component Z recordings using the horizontal component H measured in a

8 classical manner, and the magnetic inclination angle I measured with the Earth s inductor. In moderate geomagnetic latitudes, errors in the Z component determined in this manner were three times greater than those for the H component, so the method was not very accurate. The introduction of proton magnetometers made it possible to calculate Z from the measurements of F and angle I, which much improved the accuracy. A next important step in the measurement technique development was the designing and implementation of the so-called proton vector magnetometers. In these magnetometers, installed at Belsk and Hel, the measurement sensors were placed within the Braunbeck coils fixed at large non-magnetic theodolites. The use of these magnetometers in observatory practice much simplified the methodology of absolute measurements and the determination of base values of the recordings. The mean random errors of measurements made with this method were some 0.3 for magnetic declination, 1.2 nt for the horizontal component H, and 1 nt for the component Z. A considerable progress was also achieved in the mid-1990s by purchasing three Carl Zeiss Jena non-magnetic theodolites Theo 10B, on which flux-gate magnetometers were installed. Consequently, all three Polish geomagnetic observatories are able to make base determination from absolute measurements of D, I, and F. In the mid-1960s, continuous magnetic recording systems in Polish observatories were equipped with Bobrov s quartz variometers, of much more stable parameters. At the beginning, these variometers were used in a typical, classical manner for recording of a photo-paper. A next step was the development of the so-called Portable Magnetic Stations PSM. In these stations, the deflection of magnets sensitive to magnetic field changes are converted by the photoelectric converters into electric current changes in a system with a strong negative feed-back. The electric signals from the Fig. 12. Scheme of geomagnetic observations at Polish observatories in the framework of INTERMAGNET.

9 PSM station were first recorded by a three-channel analog pen recorders, and then by digital loggers, whose consecutive, refined models have been designed and constructed at the Belsk observatory. At present, the instrumentation at all the three Polish magnetic observatories, at Belsk, Hel, and Hornsund, can be regarded as quite up-to-date, satisfying all standard requirements of the INTERMAGNET network. In each of these observatories, the absolute magnetic measurements are made by means of DI-FLUX magnetometers and PMP magnetometers of Polish make. The recordings are carried out by means of PSM stations and 16-bit microprocessor-based digital loggers DR-03. To give an example, we present in Fig. 12 a simplified block diagram of geomagnetic observations at Belsk and Hel. In the Polar observatory at Hornsund, the scheme is similar, except that a small transduced magnetometer has been installed in the spare set 2. Fig. 13. The 2004 baselines from Belsk, Hel and Hornsund observatories.

10 Accuracy and Availability of Data The accuracy of the so-called long-term data produced by the geomagnetic observatories at Belsk and Hel is estimated at about ± 1nT. The estimates follow from an analysis of the accuracy of absolute base measurements, a comparison of recordings of the two sets, and an analysis of the differences ΔF = F X 2 + Y 2 + Z 2, where F stands for the proton magnetometer indications recorded in a continuous manner, and X, Y, and Z are the field component values calculated from recordings of set 1 or 2. The accuracies of basic instruments that are presently used in Polish magnetic observatories are listed in Table 2. Table 2 Accuracy of the main instruments that are presently used at Polish geomagnetic observatories The accuracy of Spitsbergen data is somewhat lower, mostly because of seasonal instability of the pier on which the PSM station variometers are installed at the recording pavilion. A good measure of the accuracy of observatory data is the stability of bases of the magnetic recordings. To give an example, we present in Fig. 13 the plots of bases at Belsk, Hel, and Hornsund in The absolute measurements of D, I, and F for base determination are performed 5 times a week at Belsk, few times a month at Hel, and 2-3 times a week at Hornsund. Of great importance is, in our opinion, the continuity of the collected data, i.e., the lack of gaps in recordings. Two recording sets work permanently at each of the observatories, and the probability of their simultaneous failure is very small. Infrequent gaps in the Belsk and Hel data throughout the last 40 years are listed in Table 3. At the polar observatory Hornsund, where the spare recording set II has not been in operation until the last few years, the gaps are somewhat more numerous, although in some recent years they have not occurred at all.

11 Table 3 Gaps in the data from the Belsk and Hel observatories in the years The results of geomagnetic observations from Polish observatories are published in a standard form of the so-called magnetic yearbooks (Publications of the Institute of Geophysics, Polish Academy of Sciences). For Belsk and Hel, the yearbooks have been published since 1966, and for Hornsund since Until 1999 the yearbooks had been presenting the monthly tables of hourly mean values, and since 2000 the tables have been replaced by the daily plots of X, Y, and Z, i.e., size-reduced magnetograms. The data from Polish observatories have been regularly sent to world data centers (WDC) in Boulder and Copenhagen. In the framework of INTERMAGNET, the one-minute values are everyday transmitted, in an automatic manner, to Paris and Edinburgh; this has been made for the Belsk data since 1984, Hel data since 1988, and Hornsund data since The archival and current data are also available from the Institute of Geophysics of the Polish Academy Sciences. Summary Throughout the last 40 years, we were able establish in Poland three fairly modern magnetic observatories, equipped in relatively up-to-date instruments, mostly of our own make at the Institute of Geophysics. The data produced by these observatories comply with the main accuracy standards, and the continuity of data can be regarded as very good.

12 At Belsk, the biggest of these three observatories, the routine geomagnetic observations there are accompanied with various works relating to the development of new instruments and measurement methods. The Belsk observatory is also a basis for numerous field surveys carried out by the Institute of Geophysics in Poland and abroad. Literature Yearbooks from Polish geomagnetic observatories: Results of Geomagnetic Observations, Belsk Geophysical Observatory, covering the period since 1966 up to the present, published in Publs. Inst. Geophys. Pol. Acad. Sc. Results of Geomagnetic Observations, Hel Geophysical Observatory, covering the period since 1966 up to the present, published in Publs. Inst. Geophys. Pol. Acad. Sc. Results of Geomagnetic Observations, Polish Polar Station Hornsund, Spitsbergen, covering the period since 1978, published in Publs. Inst. Geophys. Pol. Acad. Sc. Results of Geomagnetic Observations, Polish Antarctic Station Arctowski, covering the years 1978 to 1995, published in Publs. Inst. Geophys. Pol. Acad. Sc. Roczniki Magnetyczne (Annuaire magnetique), covering the years Prace Obserwatorium Geofizycznego im. S. Kalinowskiego w Świdrze. Other references: Czyszek, Z., and W. Czyszek, 1983, Geophysical Observatory at Hel , Acta Geophys. Pol. 31, 4, Jankowski, J., and B. Janke, 1963, O pomiarach za pomocą magnetometru protonowego w Obserwator ium na Helu, Acta Geophys. Pol. 11, 3, (in Polish). Jankowski, J., W. Kiełek and W. Romaniuk, 1965, Tranzystorowy magnetometer protonowy TMP-1, Acta Geophys. Pol. 13, 1, (in Polish). Jankowski, J., J. Marianiuk, A. Reda, C. Sucksdorff and M. Kivinen, 1984, Long-term stability of a torque balance variometer with photoelectronic converter in observatory practice, Geophys. Surveys 6, Marianiuk, J., 1977, Photoelectronic converter for recording the geomagnetic field elements, Publs. Inst. Geophys. Pol. Acad. Sc. C-4 (114), Ołpińska-Warzechowa K., 1985, Obserwatorium Geofizyczne im. St. Kalinowskiego w Świdrze, Prz. Geof. 30, 2, (in Polish). Accepted January 22, 2007