Digital recording of vaiations in the earth's magnetic field in French observatories: description of equipment and results for the period 1972-86

Bitterly, J.; Cantin, J. M.; Burdin, J; Schlich, Roland; Folques, J.; Gilbert, D.

doi:10.4095/226583

Cited by 3 publications

(3 citation statements)

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“…They were used to measure the horizontal component of the transient ®eld (Mosnier and Yvetot, 1977) and had an automatic compensation to maintain the analog output in the range of 2 Volts, in addition to a sensitivity of 10 mV/nT, an accuracy superior to 0.02 nT, and a thermal stability of about 0.02 nT/°C. A vertical magnetic sensor designed by the EOPGS (Ecole et Institut de Physique du Globe, Strasbourg, France) and DT/INSU (Centre de Recherches GeÂ ophysiques, Garchy, France) teams was added for the IEEY experiment (Bitterly et al, 1988, Clerc, 1992. This sensor was a¯ux-gate magnetometer with a Thomson-Sintra short linear probe (L = 85 mm, é = 18.5 mm) and an analog output producing a direct current in the range of 2 Volts with a sensitivity of 10 mV/nT.…”

Section: The Electromagnetic Experimentsmentioning

confidence: 99%

A study of transient variations in the Earth's electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast)

Vassal¹,

Menvielle

Cohen³

et al. 1998

Annales Geophysicae

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Section: The Electromagnetic Experimentsmentioning

confidence: 99%

A study of transient variations in the Earth's electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast)

Vassal¹,

Menvielle

Cohen³

et al. 1998

Annales Geophysicae

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“…They were used to measure the horizontal component of the transient ®eld (Mosnier and Yvetot, 1977) and had an automatic compensation to maintain the analog output in the range of 2 Volts, in addition to a sensitivity of 10 mV/nT, an accuracy superior to 0.02 nT, and a thermal stability of about 0.02 nT/°C. A vertical magnetic sensor designed by the EOPGS (Ecole et Institut de Physique du Globe, Strasbourg, France) and DT/INSU (Centre de Recherches GeÂ ophysiques, Garchy, France) teams was added for the IEEY experiment (Bitterly et al, 1988, Clerc, 1992. This sensor was a¯ux-gate magnetometer with a ThomsonSintra short linear probe (L = 85 mm, é = 18.5 mm) and an analog output producing a direct current in the range of 2 Volts with a sensitivity of 10 mV/nT.…”

Section: The Electromagnetic Experimentsmentioning

confidence: 99%

A study of transient variations in the Earth's electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast)

Vassal

Menvielle

Cohen³

et al. 1998

Ann. Geophys.

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Abstract. In the framework of the French-Ivorian participation to the IEEY, a network of 10 electromagnetic stations were installed at African longitudes. The aim of this experiment was twofold: ®rstly, to study the magnetic signature of the equatorial electrojet on the one hand, and secondly, to characterize the induced electric ®eld variations on the other hand. The ®rst results of the magnetic ®eld investigations were presented by Doumouya and coworkers. Those of the electric ®eld experiment will be discussed in this study. The electromagnetic experiment will be described. The analysis of the electromagnetic transient variations was conducted in accordance with the classical distinction between quiet and disturbed magnetic situations. A morphological analysis of the recordings is given, taking into consideration successively quiet and disturbed magnetic situations, with the results interpreted in terms of the characterization of external and internal sources. Particular attention was paid to the e ects of the source characteristics on the induced ®eld of internal origin, and to the bias they may consequently cause to the results of electromagnetic probing of the Earth; the source e ect in electromagnetic induction studies. During quiet magnetic situations, our results demonstrated the existence of two di erent sources. One of these, the S R E source, was responsible for most of the magnetic diurnal variation and corresponded to the well-known magnetic signature of the equatorial electrojet. The other source (the S *E R source) was responsible for most of the electric diurnal variation, and was also likely to be an ionospheric source. Electric and magnetic diurnal variations are therefore related to di erent ionospheric sources, and interpreting the electric diurnal variation as induced by the magnetic ®eld diurnal variation is not relevant. Furthermore, the magnetotelluric probing of the upper mantle at dip equator latitudes with the electromagnetic diurnal variation is consequently impossible to perform. In the case of irregular variations, the source e ect related to the equatorial electrojet is also discussed. A Gaussian model of equatorial electrojet was considered, and apparent resistivities were computed for two models of strati®ed Earth corresponding to the average resistive structure of the two tectonic provinces crossed by the pro®le: a sedimentary basin and a cratonic shield. The apparent resistivity curves were found to depend signi®cantly on both the model used and the distance to the center of the electrojet. These numerical results con®rm the existence of a daytime source e ect related to the equatorial electrojet. Furthermore, we show that the results account for the observed di erences between daytime and night-time apparent resistivity curves. In particular, it was shown that electromagnetic probing of the Earth using the classical Cagniard-Tikhonov magnetotelluric method is impossible with daytime recordings made at dip latitude stations.

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“…They became the reference instruments only in 1986 (Bitterly et al, 1986). Typically they consist in a pair of magnetometers: a "variometer" made of fluxgates along three orthogonal axes and an absolute scalar instrument measuring the strength of the field.…”

Section: Observatory Setupmentioning

confidence: 99%

Estimating error statistics for Chambon-la-Forêt observatory definitive data

et al. 2017

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Abstract. We propose a new algorithm for calibrating definitive observatory data with the goal of providing users with estimates of the data error standard deviations (SDs). The algorithm has been implemented and tested using Chambonla-Forêt observatory (CLF) data. The calibration process uses all available data. It is set as a large, weakly non-linear, inverse problem that ultimately provides estimates of baseline values in three orthogonal directions, together with their expected standard deviations. For this inverse problem, absolute data error statistics are estimated from two series of absolute measurements made within a day. Similarly, variometer data error statistics are derived by comparing variometer data time series between different pairs of instruments over few years. The comparisons of these time series led us to use an autoregressive process of order 1 (AR1 process) as a prior for the baselines. Therefore the obtained baselines do not vary smoothly in time. They have relatively small SDs, well below 300 pT when absolute data are recorded twice a week -i.e. within the daily to weekly measures recommended by INTERMAGNET. The algorithm was tested against the process traditionally used to derive baselines at CLF observatory, suggesting that statistics are less favourable when this latter process is used. Finally, two sets of definitive data were calibrated using the new algorithm. Their comparison shows that the definitive data SDs are less than 400 pT and may be slightly overestimated by our process: an indication that more work is required to have proper estimates of absolute data error statistics. For magnetic field modelling, the results show that even on isolated sites like CLF observatory, there are very localised signals over a large span of temporal frequencies that can be as large as 1 nT. The SDs reported here encompass signals of a few hundred metres and less than a day wavelengths.

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Digital recording of vaiations in the earth's magnetic field in French observatories: description of equipment and results for the period 1972-86

Cited by 3 publications

References 0 publications

A study of transient variations in the Earth's electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast)

A study of transient variations in the Earth's electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast)

A study of transient variations in the Earth's electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast)

Estimating error statistics for Chambon-la-Forêt observatory definitive data

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