VIKING - V4 : Electric and Magnetic Fields Measurements

Two components (Ey and Ez) of the electric fields were measured by means of two orthogonal 80-m-long wire booms perpendicular to the spin axis. One component Bx of the high frequency magnetic field fluctuations was measured by a magnetic loop antenna, while the three components of the DC magnetic field and its related low frequency fluctuation (up to ~ 30 Hz) were determined thanks to a fluxgate sensor. The wave V4 experiment on Viking was divided into two parts depending of the frequency :

The Low Frequency Part Experiment (V4-L)

It could process wave signals at frequencies below 15.6 kHz. V4-L could process simultaneously two wave signals that might come from any of the electric antennas, from the magnetic loop antenna measuring fluctuations in the direction of the spin axis. One of the two signals could be processed by an onboard DFT (digital Fourier transform) analyzer and a filter bank comprising three filters (FBL). The waveform (WF) of both of the signals could be sampled with a Nyquist frequency of 214 or 428 Hz. One or two of the spherical probes on the 80 m booms were frequently used as Langmuir probes having a fixed positive bias potential with potential sweeps performed typically every 5 minutes to obtain measurements of density and density fluctuations.

The High Frequency Part Experiment (V4-H)

It was capable of measuring the fine frequency structure of electric and magnetic noise with a 2.4 s time resolution. The electric and magnetic signals were analyzed by stepped frequency analyzers (SFA) which stepped from 10 kHz up to 512 kHz in 256 steps. One electric component Ey was measured by using one of the 80 m dipole antennae, located perpendicular to the spin axis, while one magnetic component Bx was measured by means of an air core loop antenna with its axis oriented along the satellite spin axis. In addition a much better time resolution of 37.5 ms was obtained from the two electric and magnetic filterbanks (FB), each consisting of eight separate filters with center frequencies fc spaced 1 octave from 4 kHz up to 512 kHz. The 3 dB bandwidth was approximately 0.3 fc. Two active modes of the instrument, Mutual Impedance (MI) and Relaxation Sounder (RS) were controlled by the synthesizer which also controled the SFA's. These modes were devoted to the measurement of the electron density from the artificial excitation of the plasma resonances.