An observatory is a site dedicated to the observation and careful quantification of natural phenomena. They must be maintained for long periods of time, at least for few decades, such that the intensity and direction of Earth’s magnetic field can be determined and its variations can be recorded over time. Magnetic observatories face a double challenge. The first is to preserve a magnetically clean environment. The second challenge relates to the impressive level of precision and dedication needed to understand Earth's magnetic field, since it involves the study phenomena of vastly different scales, ranging from a few seconds to tens of years. These two challenges are particularly difficult to overcome, for various reasons. First of all, geoscientists are practically powerless against the degradation of our magnetic environment, because of urban and industrial growth. Second, it is difficult to accurately compare the observations made with instruments that rely on specific and sometimes different technologies, not to mention the role played by outdated instruments and technological advancements.
Even though the first quantified observations of the terrestrial magnetic field were made in France as early as 1541, it wasn’t until 1883 that the first magnetic observatory was established. This first observatory, situated at Saint-Maur-des-Fossés, near the Marne River 10 km east of Paris, was initially used by France’s national weather service until being associated with the IPGP upon the creation of the institute in 1924. Several more magnetic observatories appeared in France at the beginning of the 20th century (Nantes, Puy de Dôme, Perpignan…), but these were later closed due to increasing urbanisation. The magnetic Observatory of Saint-Maur-des-Fossés itself had to be transferred 30 km east of Paris, in Val–Joyeux, at the beginning of the 20th century, because of the development of the tram. Shortly before the Second World War, the same reasons caused the Observatory at Val–Joyeux to be moved to the forest of Orléans, its current location. This new Observatory in Chambon-la-Forêt is now the only observatory in mainland France.
In 1985 Jean-Louis Le Mouël, then Director of the IPGP, decided to revitalise magnetic observations by starting the 'Planetary Magnetic Observatory' programme, a project entrusted to Xavier Lalanne. This very ambitious project, without precedent in the field, required new instruments to be created. This project was innovative, supporting data transmission by satellite for the first time. It took nearly 5 years to develop the vector magnetometer VM390 and to check its performance by comparison with data of the Chambon la Forêt Observatory. While instruments were being updated, scientists looked for areas lacking the most measurements of the magnetic field. However, finding observers was the greatest difficulty. In addition to being a site where instruments measure Earth’s magnetic field, a magnetic observatory is only considered as such if it benefits from regular human intervention (ideally, weekly) to regularly calibrate the instruments, a process called absolute measurements. It takes months, even sometimes years to become a good observer. It is a tiresome task, which requires absolute rigour. A good observer must adhere to a strict routine, systematically questioning his or her every action. Because the magnetic field is invisible and its influence on the environment is almost undetectable, measuring it is not at all intuitive, and the potential for error is very large.
Instead of constructing brand new observatories, the idea has been to update older observatories by replacing their analogue devices that, in many cases, were simple photographic recorders. Some of these observatories were no longer functional, due to difficulties in finding photographic paper with the right format. Other sites were still functional but their performances had become too low to contribute to scientific developments at the end of the 20th century. The general principle of this scientific collaboration was that the IPGP would provide and install equipment and train operators, while the partner would cover running costs and staff salary. Moreover, the IPGP is in charge of the processing, quality control, and publication of data.
The first observatory to benefit from these 70 years’ worth of technological advancements was Tamanrasset in the Algerian Sahara in 1992. Though it had been defunct for several years, it became the most modern observatory in Africa under the direction of Noureddine Akacem. Now, 22 years later, the closest magnetic observatory of this quality is over 2,000 km away. It was Xavier Lalanne who set up the observatory with Jean-Claude Delmond, who thus returned to the Tamanrasset Observatory where he had worked 30 years earlier, just after Algeria's independence. The instruments developed for this project, the vector magnetometer VM390 and the scalar magnetometer SM90, were used here for the first time. Data was transmitted in near real-time through the Meteosat satellite.
That same year, the M'bour Observatory, 60 km South East of Dakar (about 40 miles), was also updated. M'bour was an observatory operated by ORSTOM (the French Office of Scientific and Technical Research Overseas), which then became the IRD (the French Research Institute for Development). The observatory was equipped with innovative technology developed by Gilbert Juste. It was already able to produce digital data but the quality was insufficient and did not meet INTERMAGNET's new standards. The Observatory of M'bour was updated thanks in large part to Jacques Bitterly, head of the magnetic Observatories of the Ecole et Observatoire de Physique du globe de Strasbourg. It was set up by Gilbert Juste and Jacques Burdin. This observatory was operated by the IRD until 2013, and then jointly operated by the IPGP and the IRD. The observatory had to be closed in 2019, and the instruments moved to a nearby observation site, some 70 km away from M'bour, in the Sop village.
In 1994, the director of the Institute of Geophysics of Vietnam, Nguyen Thy Kim Thoa, visited the IPGP and suggested a collaboration. Vietnam operates four magnetic observatories using analogue magnetometers with photographic recorders. Within the framework of this collaboration, the IPGP takes responsibility for updating the Observatory of Phu Thuy, 25 km east of Hanoi, in 1995. The first installation was carried out by Xavier Lalanne and Jean-Claude Delmond. Since Vietnam was not in the Meteosat satellite coverage area, data could not be transmitted in real time. Two Vietnamese scientists, Ha Duyen Chau and Minh Le Huy, came to France to pursue PhDs in geomagnetism. Several operators spent time and studied at the Observatory of Chambon la Forêt.
The National Centre for Space Studies (CNES), another participant in this program, supported the installation of a magnetic observatory in Guyana, with the Ørsted satellite launch in mind. This satellite was intended to observe the Earth's magnetic field and its launch was initially planned for 1997. After an exploratory mission conducted in 1994, Xavier Lalanne and Jean Claude Delmond completed the basic installation of an observatory on the sounding rocket site of the Guyana Space Centre. This observatory was equipped with a VM391 vector magnetometer, a SM90 scalar magnetometer and a system for data collection and satellite transmission. For a long time it has been the only observatory producing digital data in South America.
In the fall of 1996, Laïke Afsaw, the Observatory of Geophysics director at the University of Addis Ababa in Ethiopia, visited the Observatory of Chambon la Forêt, asked the IPGP to update the magnetic Observatory of the University so it could once again be operated. This observatory had been created for the International Geophysical Year (1957-1958) but it had stopped operating during the Ethiopan Civil War (1974-1991). It was quickly decided to transfer the equipment to Addis Ababa, in order to continue observations started in 1958. Xavier Lalanne, who had visited this Observatory on several occasions between 1974 and 1975, completed this project, along with Jean-Claude Delmond. Data is being transmitted in near real time via the Meteosat satellite. The observatory had to be close in 2015 because of an increase of anthropogenic noise level.
In 1995, ORSTOM decided to put an end to its geophysics activities in Tahiti and to yield the land of the Observatory of Geophysics of Pamatai, opened in 1968, to a property developer. Because of the exceptional geographical location of this observatory in the Pacific Ocean, the IPGP volonteered to ensure its maintenance but lack the financial resources to purchase the land. An agreement was signed with the Commissariat à l'énergie atomique (French Atomic Energy Commission, CEA), which operates their Detection and Geophysics Laboratory (LDG) on the neighbouring land. This convention resulted in the installation of an observatory by Jean-Claude Delmond, in 1996. But because of the activities of the laboratory, the location was too noisy and the data of poor quality. After long negotiations, the CEA, which aims to push back the boundary line with its future neighbours, bought half of the ground of ORSTOM, which is where the buildings of the magnetic Observatory were located. The equipment was moved in 1997 and since then, the Pamataï Magnetic Observatory is jointly operated by the IPGP and the CEA.
In 1998, Alexandre Sursock, head of the French National Centre for Geophysical Research in Lebanon, contacted Jean-Louis le Mouel, who had supervised Sursock’s thesis before the Lebanese civil war interrupted his studies. When peace was restored, the National Centre for Geophysical Research planned to foster close collaboration with the IPGP in several fields, such as tectonics, seismology and magnetism. After an exploratory mission led by Xavier Lalanne, Qsaybeh, a site located 40 km east of Beirut and where the Centre for Geophysical Research had already considered an installation, was confirmed as the site for a new magnetic observatory. After massive excavation work, Xavier Lalanne, Christian Martino, and Jacques Bitterly installed the new observatory in 2000. Unfortunately, the new premises for the Centre for Geophysical Research in Qsaybeh were never built. In addition, this observatory was too far from the Centre for Geophysical Research and it was hard to comply with international standards, which require weekly calibration measurements. The complex political situation in Lebanon and the regional context did not help. After 10 years of chaotic operation, a Lebanese scientist declined to take up the post of director, and so the IPGP was obliged to close the observation in 2011.
In the early 80s, the IPGP collaborated closely with China in research areas such as tectonics and experimental seismology. Many Chinese delegations visited the IPGP, and were interested in the INTERMAGNET program. In the late 90s, a magnetic observatory project was officially announced after the annual meeting between the French National Institute for Earth Sciences and Astronomy (CNRS-INSU) and the China Earthquake Administration. After an exploratory mission conducted by Xavier Lalanne in Lanzhou in 1999, Jacques Bitterly and Christian Martino installed the first Chinese digital observatory in 2001. The data was not transmitted in real-time, but with a 24-hour delay. The observatory has been closed in 2019 due to a too lagre anthropogenic noise.
Whereas the Soviet Union at the time had a long tradition of observing Earth's magnetic field, its political collapse and subsequent economic crisis caused nearly all the Observatories to close. Xavier Lalanne conducted a preliminary exploratory mission in Sverdlovsk, which had adopted its former name, Yekaterinburg. Bureaucratic opposition to satellite data transmission hindered the planned update of the Observatory in Arti. Five years later, in collaboration with the Institute of Geophysics of Moscow and with the participation of Alexeis Ghishiany, the Observatory of Borok, 400 km north of Moscow, was selected to become the first digital Observatory in Russia. Jacques Bitterly and Christian Martino installed the observatory in 2004. As in China, data transmission is subject to a 24-hour delay.
In the early 2000s, the IPGP became the scientific institution with the highest number of magnetic observatories outside its national territory, and with the widest possible global coverage. NASA therefore asked the IPGP to install a brand new magnetic observatory on Easter Island, a Chilean territory in the Pacific Ocean. After Xavier Lalanne's preliminary exploratory mission, the installation of a magnetic observatory in the eastern part of the island was planned on the site of a former optical tracking station operated by NASA. Unfortunately, after more than 3 years of negotiations, the financial contribution required by the Chilean Center for Space Studies was so large that this project was abandoned. Denis Legrand, who stayed at the IRD in Santiago in Chile, allowed the IPGP to make contact with the Chilean Meteorological Office. The IPGP chose the Meteorology department, because of concerns about finding partners with the proper training in observation. After another exploratory mission conducted by Arnaud Chulliat and Xavier Lalanne, a site was selected at Mataveri airport on the edge of a runway. In 2008, Xavier Lalanne and Luis Gaya-Piquet started building the infrastructure, and Xavier Lalanne, Jean Savary and François Truong at last installed the equipment in 2009. The Easter Island magnetic observatory is still the farthest away from another observatory, the nearest being the IPGP-operated observatory in Tahiti, more than 4200 km away.
Since the update of Observatory in Phu Thuy, our Vietnamese colleagues have asked us to update another of their four observatories. The observatory of Dalat, about 1000 km from the South of Phu Thuy, and close to the equatorial Electrojet, was re-equipped in 2003 by Xavier Lalanne and Christian Martino. Entirely destroyed by the lightning a few years after it will be finally reinstalled by Xavier Lalanne, Jean Savary and Benoit Heumez in 2011 then again in 2016.
The most recent observatory opened by IPGP has been set in Edea (Cameroon), in collaboration with the IRGM, on a ground own by IRGM and where a station of the CTBTO is operated. The site has been selected in 2012 by Xavier Lalanne, but construction work started only in November 2017. Observatory setting has been finalised by Ted Luc in February 2018 and the first data produced. However, they reached the expected quality for scientific research only in early 2019.