| CEOS EO HANDBOOK – MEASUREMENT INSTRUMENTS
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Measurements > Gravity and Magnetic Fields >
Gravity, Magnetic and Geodynamic measurements >
Electron Energy and Pitch Angle Distribution
  | Measurement Definition*: Electrons spiral around magnetic field lines, and their motion is described by their velocity along the local magnetic field and perpendicular to it. The pitch angle is derived from the ratio of those two velocities and can predict which electrons will precipitate in the ionosphere to produce the aurora and which will be reflected back along the magnetic field line. |
| Instrument | Status/
Accuracy | Instrument Description | Measurement Technology | Timeline |
HEPD
High Energy Particle Detector | Operational
| Fluxes of electrons (3 - 100 MeV), protons (30 - 200 MeV) and light nuclei. Measurement of the increase of the electron and proton fluxes due to short-time perturbations of the radiation belts caused by solar, terrestrial and anthropic phenomena. | n/a |  |
SEI
Suprathermal Electron Imager | Operational
| The SEI measures the electron energy and pitch angle distribution over the energy range of 1 to 200 eV, with particular emphasis on photoelectrons in the 1 to 50 eV range. The instrument now operates in passive mode as the High Voltage source has failed. | n/a | |
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* Description adapted from WMO.
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