DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) is a French micro-satellite operated by CNES devoted to the investigation of the ionospheric disturbances due to seismic and volcanic activity.
It was launched on June 29, 2004 on a quasi Sun-synchronous circular orbit with an inclination of about 98.23° and an altitude of about 710 km. The altitude was changed to about 660 km in December, 2005.
Due to the specific orbit, DEMETER is always located either shortly before the local noon (10:30 local time) or local midnight (22:30 local time). The satellite performs 14 orbits per day and measures continuously between -65° and +65° of invariant latitude.
Scientific Objectives 
- to study the ionospheric disturbances in relation to the seismic activity and to examine the pre- and post-seismic effects
- to study the ionospheric disturbances in relation to the volcano activity
- to survey the ionospheric disturbances in relation to the anthropogenic activity
- to contribute to the understanding of the generation mechanism of these disturbances
- to give a global information on the Earth electromagnetic environment
Scientific Payload 
- IMSC: three magnetic sensors from a few Hz up to 18 kHz
- ICE: three electric sensors from DC up to 3.5 MHz
- IAP: an ion analyzer
- ISL: a Langmuir probe
- IDP: an energetic particle detector
Modes of Operation 
Due to the limited capacity of the telemetry, there are two different modes of operation:
- during the "Survey mode", averaged data are collected all around the Earth. The telemetry flow in this mode is reduced by the on-board data processing to 25 kbit/s.
- during the "Burst mode", high-precision data are collected above the specific areas of interest, corresponding mostly to the seismic regions.
The data bit rate in this mode is 1.7 Mbit/s.
- CNES project web page
- DEMETER data server providing a free access to the low-resolution "quicklook" data
- Lagoutte et al. "The DEMETER Science Mission Centre". Planetary and Space Science 54 (2006) 428-440.