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The in-situ measurements of the ionospheric plasma that we use come from twoinstruments of the scientific payload of the satellite DEMETER;the plasma analyser IAP(In-strument d’analyse du plasma)and the Langmuir probe ISL(Instrument Sonde de Langmuir).DEMETER is a micro-satellite realized by the CNES(Centre National d’Etudes Spatiales,France)with a principal objective to seek a possible influence of the seismic activity on the electromag-netic waves in the ionosphere and on the ionospheric plasma.The satellite was placed on June29,2004,in a circular and quasi helio-synchronous orbit at ～710 km altitude.The experimentsfunction primarily at mid-latitudes(from +60° to-60°).The IAP data were analysed to deducethe ion population(densities of the dominant ions,i.e.generally O~+,H~+ and He~+)thereforethe total ion density.The use of data IAP thus requires some precaution to make sure that theelectric equilibrium conditions of the satellite,such as the satellite potential(φ(sat)),are obtainedduring the treatment of routine,does not induce an error of measurement.When this potentialis negative,the minority light ions H+ and He+ can be measured in a reliable way when theirproportion is above 3% to 5% of that of O+.The critical limitation is:under certain conditions,the satellite potential becomes positive and reach a value about ～0.5 V so that it becomes impos-sible to measure H~+ ions.This is likely to involve a significant error on the composition and thedensity of the plasma.Therefore we carried out a calibration to estimate the missing density.TheISL experiment(Langmuir probe)provided the collected current/polarized tension characteristicsof a cylindrical probe from which both electron density N_e and temperature T_e were obtained.In some situations it is necessary to examine the accuracy of the electron density using anothertechnique,for instance the high frequency(HF)spectrogram,provided by ICE(instrument champelectrique)instrument.This technique could give precise information about the accuracy of thedata provided by the plasma analyser and the Langmuir probes.The observed satellite surfacepotential was found to be remarkable and subject of question.It displayed negative values atdaytime and positive at night.
The in-situ measurements of the ionospheric plasma that we use come from two instruments of the scientific payload of the satellite DEMETER; the plasma analyzer IAP (In-strument d’analyze du plasma) and the Langmuir probe ISL (Instrument Sonde de Langmuir). DEMETER is a micro-satellite realized by the CNES (Center National d’Etudes Spatiales, France) with a principal objective to seek a possible influence of the seismic activity on the electromag-netic waves in the ionosphere and on the ionospheric plasma. Satellite was placed on June 29, 2004, in a circular and quasi helio-synchronous orbit at ~ 710 km altitude. These experiments were at mid-latitudes (from +60 ° to -60 °). The IAP data were analyzed to deduce the ion population ( densities of the dominant ions, iegenerally O ~ +, H ~ + and He ~ +) therefore the total ion density. The use of data IAP requires only some precaution to make sure that the electric equilibrium condition of the satellite, such as the satellite potential (φ (sat)), are obta inedduring the treatment of routine, does not induce an error of measurement .When this potential is negative, the minority light ions H + and He + can be measured in a reliable way when theirproportion is above 3% to 5% of that of O +. critical number is: under certain conditions, the satellite potential becomes positive and reach a value about ~ 0.5 V so that it becomes impos-sible to measure H ~ + ions. This is likely to involve a significant error on the composition and the intensity of the plasma. Therefore we carried out a calibration to estimate the missing density. The experiments (Langmuir probe) provided the collected current / polarized tension characteristics of a cylindrical probe from which both electron density N_e and temperature T_e were obtained. accuracy of the electron density using an othertechnique, for instance the high frequency (HF) spectrogram, provided by ICE (instrument champelectrique) instrument.This technique could give preci se information about the accuracy of the data provided by the plasma analyzer and the Langmuir probes. The observed satellite surface potential was found to be remarkable and subject of question. It has been shown that negative values atdaytime and positive at night.