How the Saint Santin incoherent scatter system paved the way for a French involvement in EISCAT Pierre Bauer, Alain Giraud, Wlodek Kofman, Michel Petit, Philippe Waldteufel To cite this version: Pierre Bauer, Alain Giraud, Wlodek Kofman, Michel Petit, Philippe Waldteufel. How the Saint Santin incoherent scatter system paved the way for a French involvement in EISCAT. History of Geo- and Space Sciences, Copernicus Publications, 2013, 4 (2), pp.97-103. 10.5194/hgss-4-97-2013. insu-01626392 HAL Id: insu-01626392 https://hal-insu.archives-ouvertes.fr/insu-01626392 Submitted on 30 Oct 2017 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. CMYK RGB Hist. Geo Space Sci., 4, 97–103, 2013 of www.hist-geo-space-sci.net/4/97/2013/ History Geo- and Space doi:10.5194/hgss-4-97-2013 © Author(s) 2013. CC Attribution 3.0 License. Open Access Open Sciences Advances in Science & Research Open Access Proceedings How the Saint Santin incoherent scatter systemDrinking paved Water Drinking Water the way for a French involvement in EISCATEngineering and Science Engineering and Science Open Access Access Open Discussions P. Bauer1, A. Giraud2, W. Kofman3, M. Petit4, and P. Waldteufel5 1Bureau des longitudes, 23 Quai de Conti, 75006 Paris, France Discussions 2Ecrivain scientifique, 5 rue de la clef, 75005 Paris, France Earth System Earth System 3Institut de Planétologie et d’Astrophysique de Grenoble CNRS/UJF, 38000 Grenoble, France 4Acdémie des sciences de Paris, 23 Quai de Conti, 75006 Paris, France Science Science 5Institut Pierre-Simon Laplace, Université de Versailles Saint-Quentin-en-Yvelines, 78520 Guyancourt, France Open Access Open Open Access Open Data Data Correspondence to: P. Bauer ([email protected]) Received: 29 May 2013 – Accepted: 20 August 2013 – Published: 13 September 2013 Discussions Abstract. This paper relates the development of a French incoherent scatter system which startedSocial its opera- Social tions in 1965. This development took place several years after the initial implementation of such systems in the Open Access Open Geography United States, in Peru and in the United Kingdom. The French system, owing to its bistatic configurationAccess Open Geography and the use of continuous waves, differed from the previous ones. These characteristics yielded signals of excellent spectral quality, unravelling the possibility of inferring physical parameters (Doppler shift, average ion mass) out of reach, at that time, of other systems. The possibility of making ion drift vector measurements led to extend the system into a quadristatic configuration. The multiple capabilities offered by the incoherent scatter technique, notably as concerns the thermodynamical properties of the ionosphere and of the thermosphere, led further the French community to a project of embarking an incoherent scatter radar on board a ship. Taking account of a project of a Scandinavian auroral zone radar and of the considerable interest of the study of auro- ral zone electrodynamics, the French community abandoned the idea of the ship and expressed an interest in joining the Scandinavian project in conjunction with Germany and the United Kingdom. 1 Introduction the “Gaullian era of big projects”, the Saint Santin bistatic continuous wave system which started its operations in 1965. The Saint Santin system turned later onto a quadristatic con- The scattering of electromagnetic waves by free electrons figuration, which paved the way for a French involvement in had been theoretically investigated at the beginning of the EISCAT (European Incoherent Scatter). 20th century, first by Thomson (1906) in the case of a single electron and later by Fabry (1928) for a cloud of electrons. However one had to wait until 1958 when Gor- 2 The French national centre for telecommunication don (1958) realized that powerful radars would be able to studies (CNET) and the study of the ionosphere detect the faint waves scattered by the free electrons of the ionosphere. Bowles (1958) was the first to detect such sig- During the early 1960s, CNET , for the sake of its appli- nals with an experimental set-up at the University of Illi- cations in the field of telecommunications, was deeply in- nois and, very rapidly, impressive radar systems were im- volved in fundamental studies of the propagation medium plemented by the United States in Peru (1962) at Jicamarca (atmosphere and ionosphere). As such, together with part- (300 m × 300 m array of dipoles), in Massachusetts (1963) ners such as CNES (National centre for space studies), CNRS at Millstone Hill (70 m parabolic antenna) and in Puerto (National centre for scientific research), INAG (National in- Rico (1964) at Arecibo (300 m spherical antenna, the largest stitute for astronomy and geophysics), DRME (military re- worldwide!). France, for its share, initiated in 1961, during search agency), CNET led major research endeavours such Published by Copernicus Publications. 98 P. Bauer et al.: Saint Santin incoherent scatter system Figure 1. Set up of the Saint Santin incoherent scatter system. The transmitter located in Saint Santin illuminated a vertical column. The Nançay Radio telescope, located 300 km north of Saint Santin,Figure scanned 1. the vertical column in order to collect power scattered by the ionosphere. as the development of FR1, a French satellite devoted to the 3 The Saint Santin incoherent scatter bistatic study of the ionosphere and the magnetosphere, and the set sounder up of ionospheric stations in Antarctica. In 1961,4. OwenThe non Storey,-linear a scientist regression well known analysis for his the- of theAs incoherent illustrated in scatter Fig. 1, thespectrum Saint Santin incoherent scatter oretical work on the whistlers (waves originating from light- bistatic sounder (du Castel et al., 1966) operated with one nings andA propagatingvery important along Earth’sresult of magnetic the Bowles field lines), experimtransmittingent in 1958 antenna (Bowles, located 1958) in Saint was Santin that 300while km south aware both of the pioneering incoherent scatter studies in of the Nançay radio telescope. The Saint Santin antenna the Unitedthe States return and power of the decimetricappeared radio to be telescope approximately un- illuminated of the aorder vertical of columnmagnitude with apredicted 140 kW continuous by der constructionGordon in(Gordon, Nançay, suggested1958), the that observed this radio bandwidth tele- wave was transmitter much tunednarrower at 935 than MHz. predicted. The vertical columnThis was scope shouldfinding be usedinitiated to collect considerable the electromagnetic theoretical waves workscanned on the by plasma the Nançay thermal radio telescope.fluctuation Thes mainand advantagethe scattered by a vertical ionospheric column illuminated by a of such a system was to avoid the convolution problems en- power transmitterrole of the properly ions located(see Bauer, several hundreds1975, for of kilo-a review).countered In turn, with it pulsedwas realized radar and thereforethat the toscattered yield signals of metres southsignals of the would radio telescope.provide Inmuch a matter more of few information days, excellent on the spectral ionospheric quality, unravellingmedium thethan possibility initially of infer- the computationsthought. by Quite a group elaborated from CNET, math led byematical François dudevelopmentsring physical were parameters to be made. (Doppler Following shift, average Owen ion mass) Castel, confirmed the soundness of the suggestion and gave out of reach, at that time, of other systems. rise to aStorey’s proposal swiftly suggestions, accepted byMichel CNET Petit and welcomed developed in his thesis work (Petit, 1968) an optimal by the radioscheme astronomy to extract community the physical which, under parameters the lead- and the statistical errors attached to them, using 4 The non-linear regression analysis of the ership ofthe Jean-François outstanding Denisse, purity had of previouslythe meas ouredffered spectrum to in CW conditions. provide up to 15 % of the radio telescope observing time for incoherent scatter spectrum geophysical research projects. The project, under the leader- ship of MichelHis first Petit step and throughwas to a closecompute cooperation the probability with the ofA verya particular important observed result of the signal Bowles throughout experiment ina 1958 radio astronomytime slot community,, taking into was ready account to operate the addition in 1965 at to the(Bowles, scattered 1958) signal was that of whilea much the larger return powerreceiver appeared to be approximately of the order of magnitude predicted by the time( ofGaussian completion) noise. of the radioThe telescope.second Itstep was inwa facts to use a Bayesian approach to determine the one of the first instruments to make use of the Nançay radio Gordon (1958), the observed bandwidth was much narrower telescope.physical Far from beingmedium a project parameters of the sole CNETwhich group, would thanmost predicted. likely Thisinduce finding the initiated actually considerable observed theoretical