Instrument Champ Electrique Research Articles

Calibration of electric field data of DEMETER satellite

ABSTRACTIn this paper, based on the data measured by the space-borne ICE (Instrument Champ Electrique) electric field meters of the DEMETER (Detection of Electro-Magnetic Emission Transmitted from Earthquake Regions) satellite, the induced electric fields generated by the electric antennas of ICE when they cut the Earth’s geomagnetic lines during the satellite’s motion are computed, and the electrostatic field data in the range of ultra low frequency (ULF: f < 3 kHz) are calibrated. The numerical results indicate that the induced electric fields generated by the electric antennas of the space-borne electric field meters account for a considerable proportion among the data of electric fields measured by the DEMETER satellite. Besides, a more conspicuous regularity is presented as the magnitude of the modified electric fields varies with the Earth’s latitudes and longitudes.

Irregularities of the ionospheric plasma and the ULF electric components obtained from DEMETER satellite experiments above Chile earthquake (27 February 2010)

The detection of ionospheric disturbances associated with seismic activity is one of the main purposes of the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) micro-satellite. In this view, this study attempts to analyze the problem of detecting these disturbances before an earthquake occurrence and to discuss the Chile earthquake case study. Using ultralow frequency (ULF) measurements of Instrument Champ Electrique (ICE) experiments on board the DEMETER satellite, possible irregularities in this electric component have been investigated in the vicinity of Chile (27 February 2010) earthquake region. The data used in this paper cover the period from 10 to 26 February 2010. The anomalous variations in the calculated ULF electric component in the direction Z of satellite were clearly observed on the 17th, 11th, and 1st days preceding the earthquake. It is noted that the electric component obviously strongly decreased prior to the earthquake. These unusual variations have also been observed in the variation of several plasma parameters recorded by DEMETER directly above the epicenter during the whole period. Hence, the detected anomalies resulting from the ICE ULF waveforms in quiet geomagnetic conditions could be regarded as seismo-ionospheric precursors.

Earth Magnetic Field Effects on Particle Sensors on LEO Satellites

Kinetic simulation results are presented for the interaction of spacecraft with space environment in low Earth orbit. Case studies are considered for DEMETER, for which small but distinctive potential variations have been measured on Instrument Champ Electrique (ICE) sensors, as the satellite goes through regions where the magnetic field B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">→</sup> is nearly parallel to the satellite velocity v <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">→</sup> . Our results point to a small variation in the potential of ICE probes under these conditions, but owing to the smallness of the signal and inherent statistical noise in our simulations, it is not possible to unambiguously explain observations. An earlier study of magnetic field effects on the Swarm electric field instrument is extended by computing Langmuir probe characteristics with and without a magnetic field. The possibility of probe crosstalk is also examined by comparing collected currents when the two probes have same and opposite bias voltages. Accounting for a representative ionospheric magnetic field is found to lead to appreciable quantitative differences in the probe characteristics. No significant crosstalk or mutual coupling is predicted between the probes under normal operation.

Novelty detection in time series of ULF magnetic and electric components obtained from DEMETER satellite experiments above Samoa (29 September 2009) earthquake region

Abstract. Using ULF (ultra low frequency) measurements of magnetometer and ICE (Instrument Champ Electrique) experiments on board the DEMETER satellite, possible irregularities in ULF magnetic and electric components have been surveyed in the vicinity of Samoa (29 September 2009) earthquake region. The data used in this paper cover the period from 1 August 2009 to 11 October 2009. The anomalous variations in magnetic components (Bx, By and Bz) were clearly observed on 1 and 3 days before the event. It is seen that the periodic patterns of the magnetic components obviously changed prior to the earthquake. These unusual variations have been also observed in the variations of polarization index obtained from the magnetic components during the whole period at ~10:30 and ~22:30 LT. It is concluded that the polarization exhibits an apparent increase on 1 and 3 days preceding the earthquake. These observed unusual disturbances in ULF magnetic components were acknowledged using the detected perturbations in ULF electric components (Ex, Ey and Ez) in the geomagnetic coordinate system. Finally, the results reported in this paper were compared with previous results for this Samoa earthquake. Hence, the detected anomalies resulting from the magnetometer and ICE ULF waveforms in quiet geomagnetic conditions could be regarded as seismo-ionospheric precursors.

Very‐low‐frequency saucers observed on DEMETER

Observations of very‐low‐frequency saucers by the electric field instrument (Instrument Champ Electrique, ICE) aboard the DEMETER spacecraft have added new evidence about the nature of the highly localized source of this radiation. DEMETER orbited sun‐synchronously at altitudes around 660 km, significantly below those at which earlier spacecraft detected saucers. Also, DEMETER data establish the existence of saucer sources in the dayside ionosphere. Frequency‐time slopes of saucers in DEMETER spectrograms have been analyzed with two‐dimensional ray tracing. To produce such slopes requires long vertical separations between the source and the spacecraft, in some cases much greater than the height of the spacecraft above ground. It is concluded that the sources lie above the satellite and radiate downward. Bidirectional radiation patterns and the broadband quasielectrostatic whistler mode energy spectrum are consistent with the published results of simulations of nonlinear two‐stream instabilities.

Effects of solar and geomagnetic activities on the sub-ionospheric very low frequency transmitter signals received by the DEMETER micro-satellite

In the framework of seismic precursor electromagnetic investigations, we analyzed the very low frequency (VLF) amplitude signals recorded by the Instrument Champ Electrique (ICE) experiment on board the DEMETER micro-satellite. The sun-synchronous orbits of the micro-satellite allowed us to cover an invariant latitude of between -65° and +65° in a time interval of about 40 min. We considered four transmitter signals emitted by stations in Europe (France, FTU, 18.3 kHz; Germany, DFY, 16.58 kHz),Asia (Japan, JP, 17.8 kHz) and Australia (Australia, NWC, 19.8 kHz). We studied the variations of these VLF signals, taking into consideration: the signal-to-noise ratio, sunspots, and the geomagnetic activity. We show that the degree of correlation in periods of high geomagnetic and solar activities is, on average, about 40%. Such effects can be fully neglected in the period of weak activity. We also find that the solar activity can have a more important effect on the VLF transmitter signal than the geomagnetic activity. Our data are combined with models where the coupling between the lithosphere, atmosphere and ionosphere is essential to explain how ionospheric disturbances scatter the VLF transmitter signal.

Features of the Electric Field HF Wave of the Sunsynchronous Orbit in the Solar Minimum Year

AbstractUsing the electric field High Frequency (HF) waves recorded by the Instrument Champ Electrique (ICE) onboard the DEMETER spacecraft in a solar low year, the spatial features of the waves from 10 kHz to 3.33 MHz are studied. During the quiet time of the geomagnetics, the higher the HF wave, the bigger the power spectrum intensity when the frequency lies between 2.08 MHz and 3.33 MHz. At the same time, the power spectrum intensity is almost uniform at different longitudes and latitudes. The difference of the power spectrum intensity between different longitudes and latitudes on the dayside is less than that on the nightside. The seasonal changes of the HF power spectrum intensity show that there are peaks at the dayside low latitudes in the frequency bands of 1.25 MHz and 1.66 MHz. During the quiet time, the discrepancy of the power spectrum intensities between different longitudes and latitudes obviously occurs at the frequency bands of 0.42 MHz and 1.66 MHz especially at high latitudea of the northern hemisphere on the dayside. During the geomagnetic activity, the HF response mainly appears at the low frequency band especially in high‐latitude areas. In the equator and regions close to the low latitudes (latitude is between ±40°), the geomagnetic response of the HF is weak while that on the nightside in the magnetotail direction becomes strong especially during storms. Both at the northern and southern high latitudes during the storms on the nightside, the biggest power spectrum intensity is ten times that during the quiet. The biggest power spectrum intensity on the dayside at high latitudes of the southern hemisphere during the substorm and the period of the high latitude magnetic perturbation are ten times that during the quiet time. Considering that the perturbation coming from the space has an effect on high‐latitude areas during the substorm and the periods of the high‐latitude magnetic perturbation, the enhancement of the HF power spectrum intensity may origin from the spatial process. In view of that the data used in this study were collected in the solar minimum year and most of the storms were very weak with the strongest storm belonging to the moderate storm, the enhancements of the HF power spectrum intensity during the strong, severe even the great storms may be more obvious. If there is anomalous accretion in local areas during the quiet time especially when there is no storm, the abnormal phenomena are likely the ionospheric seismic‐response to the dynamic processes of the internal earth such as earthquake preparation.

Investigation of TEC and VLF space measurements associated to L'Aquila (Italy) earthquakes

Abstract. In this study, we report on Total Electron Content (TEC) and Very Low Frequency (VLF) space measurements derived from Global Positioning System (GPS) and DEMETER satellites, respectively. These measurements are associated with the earthquake (EQ) of a magnitude of 6.3, which occurred on 6 April 2009, in L'Aquila (Italy). Anomaly features are derived from the analysis of TEC and VLF observations recorded two weeks before and after the seismic event occurrence. A TEC map with an interpolated regional pixel resolution of 1° × 1° × 15 min in latitude, longitude and time was generated, allowing for the checking of a possible presence of disturbances over the L'Aquila region. This analysis is combined with the study of the time profile associated to the VLF flux density variations recorded by the Instrument Champ Electrique (ICE) experiment on-board DEMETER satellite. We discuss, on the one hand, the combination efficiency of the electronic density and the VLF electromagnetic measurements and, on the other hand, the difficulty to distinguish between global effects and regional ones related to the earthquake.

Decrease of VLF transmitter signal and Chorus-whistler waves before l'Aquila earthquake occurrence

Abstract. We investigate the VLF emissions observed by the Instrument Champ Electrique (ICE) experiment onboard the DEMETER micro-satellite. We analyze intensity level variation 10 days before and after the occurrence of l'Aquila earthquake (EQ). We found a clear decrease of the VLF received signal related to ionospheric whistler mode (mainly Chorus emission) and to signal transmitted by the DFY VLF station in Germany, few days (more than one week) before the earthquake. The VLF power spectral density decreases of more than two orders of magnitude until the EQ, and it recovers to normal levels just after the EQ occurrence. The geomagnetic activity is principally weak four days before EQ and increases again one day before l'Aquila seismic event. Our results are discussed in the frame of short- and long-terms earthquakes prediction focusing on the crucial role of the magnetic field of the Earth.

Investigation of VLF and HF waves showing seismo-ionospheric anomalies induced by the 29 September 2009 Samoa earthquake (&amp;lt;i&amp;gt;M&amp;lt;/i&amp;gt;&amp;lt;sub&amp;gt;w&amp;lt;/sub&amp;gt;=8.1)

Abstract. In Samoa Islands, a powerful earthquake took place at 17:48:10.99 UTC (06:48:10.99 LT) on 29 September 2009 with a magnitude Mw=8.1. Using ICE (Instrument Champ Electrique) and IMSC (Instrument Magnetic Search Coil) experiments onboard the DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite we have surveyed possible variations in electromagnetic signals transmitted by the ground-based VLF transmitter NPM in Hawaii and in HF plasma waves close to the Samoa earthquake during the seismic activity. The indices Dst and Kp were used to distinguish pre-earthquake anomalies from the other anomalies related to the geomagnetic activities. In a previous study we have shown that anomalies in IAP (plasma analyzer) and ISL (Langmuir probe) experiments onboard the DEMETER and also TEC (Total Electron Content) data appear 1 to 5 days before the Samoa earthquake. In this paper we show that the anomalies in the VLF transmitter signal and in the HF range appear with the same time scale. The lack of significant geomagnetic activities indicates that these anomalous behaviors could be regarded as seismo-ionospheric precursors. It is also shown that comparative analysis is more effective in seismo-ionospheric studies.

Similar behaviors of natural ELF/VLF ionospheric emissions and transmitter signals over seismic Adriatic regions

Abstract. We report on the analysis of ELF/VLF emissions observed by the Instrument Champ Electrique (ICE) experiment onboard the DEMETER micro-satellite. We consider principally selected seismic events reported by Molchanov et al. (2006). These authors studied the VLF signals radiated by ground transmitters and received on board the DEMETER micro-satellite. They revealed a drop of the signals (scattering spot) connected with the occurrence of large earthquakes. In our investigations, we proceed to a spectral analysis of ICE observations with the aim to find if the natural ionospheric VLF/ELF emissions show, or not, a similar ''drop'' in the intensity as it is the case of the VLF transmitter signal. We combine our results with those of Molchanov et al. (2006), and we discuss the origin of such interesting ionospheric features in the frame of the investigation of the pre-seismic electromagnetic emissions. We show that the geomagnetic activity is a key parameter which could disturb the natural VLF ionospheric emissions, and also the transmitter signal. We find that it is not possible to conclude the presence, or not, of a preseismic effect when the Kp-index is higher than one.

Inter-Calibration Between Plasma Instruments Onboard DEMETER

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 analyser IAP (Instrument 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 electromagnetic waves in the ionosphere and on the ionospheric plasma. The satellite was placed on June 29, 2004, in a circular and quasi helio-synchronous orbit at ∼710 km altitude. The experiments function primarily at mid-latitudes (from +60° to −60°). The IAP data were analysed to deduce the ion population (densities of the dominant ions, i.e. generally O+, H+ and He+) therefore the total ion density. The use of data IAP thus requires some precaution to make sure that the electric equilibrium conditions of the satellite, such as the satellite potential (øsat), are obtained during 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 their proportion 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 impossible to measure H+ ions. This is likely to involve a significant error on the composition and the density of the plasma. Therefore we carried out a calibration to estimate the missing density. The ISL experiment (Langmuir probe) provided the collected current/polarized tension characteristics of a cylindrical probe from which both electron density Ne and temperature Te were obtained. In some situations it is necessary to examine the accuracy of the electron density using another technique, for instance the high frequency (HF) spectrogram, provided by ICE (instrument champ electrique) instrument. This technique could give precise information about the accuracy of the data provided by the plasma analyser and the Langmuir probes. The observed satellite surface potential was found to be remarkable and subject of question. It displayed negative values at daytime and positive at night.

ICE, the electric field experiment on DEMETER

The objective of the ICE (Instrument Champ Electrique) experiment on board DEMETER is to provide a nearly continuous survey of the electromagnetic and/or electrostatic waves that may arise from the coupling of seismic activity with the upper atmosphere and ionosphere. To this aim it makes use of 4 spherical electrodes with embedded preamplifiers that are deployed by stacer booms at approximately 4 m from the satellite. Measurements are made over a wide frequency range from DC to 3.175 MHz, subdivided in the signal processing unit in four frequency channels DC/ULF, ELF, VLF and HF. Three axis measurements are available in the DC/ULF range for all modes of operation of DEMETER and in the ELF range in the DEMETER Burst modes. In the VLF and HF ranges and in ELF during DEMETER Survey modes only one axis of measurement is available that can be selected by telecommand. We present in this paper a general description of the instrument and its modes of operation and in-flight performances. The sensitivity is ∼0.1–0.2 μV/m Hz 1/2 from ∼100 Hz through the HF range and the dynamical range is >80 dB in ELF and VLF and about 42 dB in HF. In order to illustrate the instrument capabilities, we briefly describe a number of observations from the first months of operation in various regions along the orbit from the equator to high latitudes.