Electric Field Instruments (EFI)
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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