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Introduction ASM VFM STR EFI GPSR LRR ACC

Electric Field Instruments (EFI)

Figure 6: Electric Field Instruments

Electric Field Instruments

The Electric Field Instrument determines the ion density, the ion drift velocity, and the electric field at the S/C front panel (in-flight). The instrument consists of two components: the Langmuir Probe (LP) and the Thermal Ion Imager (TII).

EFI Algorithm Overview

The detailed descriptions of the algorithms are formed in two documents:

A) The Langmuir Probe (LP) algorithms can be found in [AD-9],

B) The Thermal Ion Imager algorithms can be found in [AD-10].

The S/C ephemeris and magnetic field vector data needed by the EFI algorithms are taken from various sources:

  • The position is taken from Level 1b.Mag-L to co-locate plasma data with magnetic data (the ca. 7 m discrepancy between rEFI and rVFM is ignored). Interpolation in time is done using cubic Lagrange interpolation.
  • The velocity is taken from Level 1b.Eph. The transformation of this from the ITRF to the NEC frame is given by
    vNEC = RNEC←ITRF vITRF
    where the transformation matrix RNEC←ITRF is defined in Appendix ...
  • The transformation from the S/C frame to the NECVFM frame is given by qITRF←S/C ⊗ qNEC←ITRF, see also [AD-7] (the difference between the NECVFM and NECEFI frame is less than 1/3" and is ignored).
  • The magnetic field vector is taken from the Level 1b.Mag-H.BNEC.

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