THE MICRO-SATELLITE DEMETER
LPC2E/CNRS, 3A Avenue de la Recherche,
45071 Orléans Cedex 2, France.
objectives of DEMETER are related to the investigation of the ionospheric perturbations
due to the seismic activity, and to the global study of the Earth electromagnetic
environment. The scientific payload is composed of several sensors: - Three Electric
and three magnetic sensors (6 components of the electromagnetic field to investigate
from DC up to 3.5 MHz), - A Langmuir probe, - An ion spectrometer, and, - An energetic
particle analyzer. They are associated to two special equipments: a large onboard
memory (8Gbits) in order to record data all around the Earth, and a high bit rate
telemetry in X band (18 Mb/s). There are two modes of operation: (i) a survey
mode to record low bit rate data, and (ii) a burst mode to record high bit rate
data above seismic regions. In the survey mode the telemetry is of the order of
950 Mb/day, and in burst mode, it is larger than 1 Gb/orbit. The launch by CNES
(French National Space Agency) will be in 2003, and the duration of the mission
is 2 years. DEMETER is a micro-satellite (110 kg) with a low-altitude (< 710
km) and a nearly polar orbit.
all earthquake precursors, those related to the electromagnetic field are the
most puzzling, and the many possible sources of noise are cause of lively controversies.
A large number of laboratory experiments clearly suggest that micro-fracturing
is associated with the appearance of spontaneous charge production (electrification)
and transient Electric or ElectroMagnetic (EM) Emission. Many electric and magnetic
preseismic and co-seismic effects have been reported in the past as well as ionospheric
perturbations. Satellite data also show EM transients related to the seismic activity
but up to now, observations are not performed by experiments dedicated to this
study. The scientific objectives of DEMETER are related to the investigation of
the ionospheric perturbations due to the seismic activity, and also to the global
study of the Earth electromagnetic environment. The experiment onboard the DEMETER
micro-satellite is proposed by a group of scientists involved in external and
internal geophysics. The list is given in Table 1.
TABLE 1. List of DEMETER experimenters.
||D. Lagoutte, F. Lefeuvre, M. Parrot, B. Poirier, J.L. Pinçon
||J.-A. Sauvaud, A. Cros
||J.J. Berthelier, M. Menvielle
||J. Artru, P. Bernard, Y. Cohen, G. Hulot, J.F. Karcewzski, J.L. Le Mouël, P. Lognonné, J.P. Montagner
||E. Blanc, J.L. Plantet
|Univ. of Electro-Comm. (Japan)
||J. Blecki, J. Juchniewicz
They are working on the
scientific topics which are described in section 2. They will built the scientific
payload which is described in section 3 and they will define the operations (section
4). Section 5 will give a short overview of the data processing. The platform
of the micro-satellite will be built under the CNES (French National Space Agency)
2. Scientific Objectives
main scientific objectives of the DEMETER experiment are to study the disturbances
of the ionosphere due to the seismo?electromagnetic effects, and due to anthropogenic
activities (Power Line Harmonic Radiation, VLF transmitters, HF broadcasting stations).
The seismo?electromagnetic effects are the electric and magnetic perturbations
caused by natural geophysical activity such as earthquakes and volcanic eruptions.
It includes: electromagnetic emissions in a large frequency range, perturbations
of ionospheric layers, anomalies on the records of VLF transmitter signals, and
night airglow observations . Such phenomena are of great interest, because
they start a few hours before the shock and can be considered as short?term precursors.
Electromagnetic emissions in the ULF/ELF/VLF range that are related to seismic
or volcanic activity are known since a long time but their generation mechanism
are not well understood. Many papers have presented ground observations of wave
emissions during seismic events . Examples can be found in . Two types of
emissions can be considered. First, precursor emissions occur a few hours before
earthquakes, in a large frequency range from one hundredth Hertz up to several
MHz. Second emissions observed after the shock generally are attributed to the
propagation of acoustic?gravity waves . However, all hypotheses concerning
the generation mechanism of precursor emissions are also valid after the shock,
when the Earth's crust returns to an equilibrium state. The emissions can propagate
up to the ionosphere, and observations made with low?altitude satellites have
shown increases of ULF/ELF/VLF waves above seismic regions. In contrast to ground
experiments, satellite experiments cover most seismic zones of the Earth, and
statistical studies become meaningful because of the much larger number of recorded
Since the great Alaskan earthquake in 1964, many evidence of electron
density perturbations in the ionosphere after strong earthquakes have been reported.
Ionospheric perturbations have been observed a few days before above the seismic
zone. They are better detected during the night when the ionosphere is calm. Increases
as well as decreases of the critical frequencies are observed in different regions
of the ionosphere before earthquakes. Additional information provided by GPS measurement
such as TEC (Total Electron Content) data will be used.
Wave emissions and
electron density perturbations can be linked through various mechanisms in the
ionosphere and the same hypotheses of generation mechanism of precursor are valid
for the two perturbations. These hypotheses are mainly related to: wave production
by compression of rocks, diffusion of water in the epicentral area, and redistribution
of electric charges at the surface of the Earth and then in the Earth's atmospheric
Only a statistical study with many events will show the general behaviour
of such ionospheric perturbations and will help to define a signature of ionospheric
perturbations prior to earthquakes . This will be achieved with the data of
the wave experiment.
In the interaction between the solar wind and the Earth's
magnetic field, the ionosphere is the first protective layer around the Earth.
Therefore the study of its evolution and its perturbations are of great interest.
The second objective of the DEMETER experiment are related to perturbations coming
from the Earth's surface and due to man?waves (PLHR, VLF transmitters, HF broadcasting
The Power Line Harmonic Radiation (PLHR) is the ELF and VLF waves
radiated by electric power systems at the harmonic frequencies of 50 or 60 Hz.
Evidence of PLHR Propagation in the magnetosphere was first observed on ground.
However direct observations by satellites are rather rare  and shown in few
papers (indirect effects are more often reported). The observations show that
the lines drift in frequencies and that it is most probably due to a non?linear
interaction between electrons and the coherent waves. All the observations indicate
that PLHR influences the atmosphere?ionosphere?magnetosphere coupling. On one
hand, non linear interactions between electrons and PLHR can participate in the
precipitation of electrons from the slot region in the radiation belts, on the
other hand, main part of the PLHR energy dissipates in the lower ionosphere and
modifies the ionospheric currents. This problem now requires serious attention
because the electrical power consumption is always increasing in the world.
At VLF frequencies between 10 and 20 kHz, the ground-based transmitters are used
for radio-navigation and communications. Their ionospheric perturbations include:
the triggering of new waves, ionospheric heating, wave-electron interactions,
and particle precipitation. At HF frequencies, the broadcasting stations utilise
powerful transmitters which can heat the ionosphere and change the temperature
and the density. All these wave dissipations in the ionosphere could participate
to the global warming of the Earth because the change in global temperature increases
the number of natural lightning discharges in the atmosphere. Then the supplementary
lightning discharges produce more magnetospheric whistlers which could produce
heating and ionization in the lower ionosphere.
Furthermore, it is a feedback
mechanism because two different processes could be involved. First, lightning
is a source of NOx, and NOx affects the concentration of ozone in the atmosphere
which contributes to the greenhouse effect. Second, precipitation of energetic
electrons by man?made waves may trigger other lightning discharges. It explains
the importance of the study of such man-made waves . Ionospheric perturbations
by natural geophysical activities have been made evident by two methods: the study
of the electromagnetic waves, and the measurement of the electron density.
3. Scientific Payload
scientific payload of the DEMETER micro-satellite (see Figure 1) is composed of
- Four Electric sensors in order to measure the three components
of the electric field. The distance between each probe is of the order of 9 meters
tip to tip.
- A three axis search coil magnetometer to measure the three components
of the magnetic field. This magnetometer will be located at the end of a 1m boom.
- A Langmuir probe,
- An ion spectrometer, and,
- An energetic particle
They are associated to two special equipments: a large onboard memory
(8Gbits), and a high bit rate telemetry in X band (18 Mb/s) which are built under
CNES responsibility. The experiment capabilities are given in Table 2. The power
consumption of the scientific payload is of the order of 15 W.
4. Onboard Data Processing and Technical Issues
are two modes of operation: (i) a survey mode to record low bit rate data all
around the Earth, and (ii) a burst mode to record high bit rate data above seismic
regions (see Figure 2). In the survey
TABLE 2. Experiment capabilities
|Frequency range, B
||10 Hz - 17 kHz
|Frequency range, E
||DC - 3.5 MHz
|Sensibility B :
||2 10-5 nT Hz-1/2 at 1 kH
|Sensibility E :
||0.2 mg Hz-1/2 at 500 kHz
||30 keV - 10 MeV
||90 keV - 300 MeV
||5 102 - 5 106 ions/cm3
||1000 K - 5000 K
||H+, He+, O+, NO+
||102 - 5 106 cm-3
||500 K - 3000 K
the telemetry is of the order of 950 Mb/day, and in burst mode, it is larger than
1 Gb/orbit. For the wave experiment the following data will be recorded:
the Burst mode
- Waveforms of 3 electric components up to 15 Hz,
of the 6 components of the EM field up to 1 kHz,
- Waveforms of 2 components
(1B + 1E) up to 17 kHz,
- Spectrum of one electric component up to 3.5 MHz
- Waveform of one electric component up to 3.5 MHz (snapshots).
During the Survey mode
- Waveforms of 3 electric components up to 15 Hz,
- Spectra of 2 components (1B + 1E) up to 17 kHz,
- Spectrum of one electric
component up to 3.5 MHz,
- Results of a neurone network to detect whistlers
the other experiments, the difference between the Burst and the Survey modes only
concerns the time resolution of the data. The number of telecommands is estimated
to be of the order of 600 octets/3 days.
The orbit of DEMETER will be LEO,
polar, and with an altitude around 710 km. The launch is expected to be in 2004,
and the duration of the mission is 2 years.
Ground-based Data Processing
telemetry will be received in Toulouse. The data processing center will be located
in LPC2E, Orléans. We will perform correlation with seismic activity using
data from the GEOSCOPE network. Quick-Looks of the data will be available in free
access on a WEB site dedicated to the experiment. The data processing center will
be also in relation with ground-based experiments. It is expected to have close
collaboration with ground-based experiments performing measurements of DC fields,
electromagnetic noise in various frequency bands, ionospheric parameters, optical
parameters,.... The satellite data will give an overview of the ionospheric parameters
above the regions where these ground-based measurements are performed. Mutual
comparison of all parameters (ground-based and satellite recorded) will allow
to understand the generation mechanism of the EM perturbations registered during
A call for guest investigators will be emitted by CNES in
order to formalise the collaboration and the exchange of data between scientists
interested by the DEMETER mission.
Scientific Mission Center of DEMETER Microsatellite
micro-satellite DEMETER in launch configuration (CNES document). The dimensions
are 60 x 60 x 80 cm3 and the weight is around 110 kg. The solar panel in black
can be seen on the right. The scientific payload is located in the upper part.
On the left there is a boom supporting the three magnetic sensors and the Langmuir
probe. Three of the four spheres for the electric sensors can be seen in green.
of the Earth where locations of the Burst mode are indicated in grey (from Pascal
Cliquez sur l'image pour l'agrandir
Parrot, M., et al., "High-frequency seismo-electromagnetic effects",
Physics of the Earth and Planetary Interiors, Vol.77, pp.65-83, 1993.
Parrot, M., "Electromagnetic noise due to earthquakes" in Handbook of
Atmospheric Electrodynamics, v.II, Ed. by H. Volland, CRC Press, Boca Raton, pp.
 Serebryakova, O.N., et al., "Electromagnetic ELF radiation
from earthquake regions as observed by low?altitude satellites", Geophysical
Research Letters, Vol.19, pp.91-95, 1992.
 Pokhotelov , O.A., et al., "Response
of the ionosphere to natural and man made acoustic sources", Annales Geophysicae,
Vol.13, pp.1197?1210, 1995.
 Parrot, M., "Statistical study of ELF/VLF
emissions recorded by a low altitude satellite during seismic events", Journal
of Geophysical Research, Vol.99, pp.23,339?23,347, 1994.
 Parrot, M., "Observations
of PLHR by the low-altitude AUREOL-3 satellite", Journal of Geophysical Research,
Vol.99, pp.3961-3969, 1994.
 Parrot, M. and Zaslavski, Y., "Physical
mechanisms of man made influences on the magnetosphere", Surveys in Geophysics,
Vol.17, pp.67-100, 1996.