The Demeter mission’s primary objective was to:
- search for evidence of electrical and magnetic signals in the upper atmosphere, associated with seismic and/or volcanic events on Earth’s surface, and more specifically signals associated with the preliminary phase of seismic ruptures and/or volcanic eruptions;
- determine and characterise disruptions in the neutral atmosphere and the ionosphere associated with seismic activity, before and after events;
- search for particle precipitation occurrences linked to such events.
Its secondary objectives were to:
- determine the nature of signals mentioned above (directly linked to the primary objectives) as well as their spectral, spatial, and temporal characteristics;
- determine the conditions in which these signals occur at high altitude, as well as their variability depending on the trigger event’s geophysical characteristics on one hand, and the atmospheric, ionospheric, and magnetospheric conditions on the other. This last objective was an essential contribution to the effort undertaken by the geophysics community to understand how these signals appear and travel.
On 29th June 2004, the satellite was inserted into a near-sun-synchronous circular orbit (with an inclination of 98.23°) at an altitude of 715 km, with an ascending node at 10.15 pm. The orbit was then lowered to 660 km in December 2005, with almost no change to the ascending node.
The field measurement experiment involved magnetic and electrical sensors using wide frequency ranges and operating at high sampling rates to record the shape of electrical signals observed in the ionosphere and to determine their frequency distribution.
Demeter wasn’t the first mission to study Earth’s radio-electrical environment; however, it was the first detect and analyse very low frequency (VLF) transient electromagnetic events. To achieve this, the instrument included a neural network-based processing unit.
The mission’s payload operated in two main modes:
- Survey mode:
In addition to analogue control parameters, average and/or minimised scientific data would be generated, which was then processed by the onboard processing unit, in order to minimise the data flow in the mass storage to about 25 kbit/s.
- Burst mode
Scientific data was transmitted with little or no processing. This high-speed mode was mostly activated above seismic areas and could transmit up to 1.7 Mbit/s.
Specifications for different monitored parameters from Demeter experiments