E4 Search Coil Magnetometer

The Search Coil Magnetometer, experiment E4, was designed by scientist at the Technische Universität Braunschweig in complement with experiment E2, the Fluxgate Magnetometer. Its purpose was to observe high frequency components of magnetic field fluctuations (up to 2.2 kHz).  E4 measured and processed two datasets: (1) rapid variations of the magnetic field and (2) power spectral density & peak values. Unfortunately, only the some of spectral data remains (data loss is attributable to financial constraints and corrupted files).

Original Data Description

  • Technical information about magnetic field measurement collection
    • Measurements ranged from 4.7 Hz to 2200 Hz[1]
      • With 8 logarithmically-spaced frequency channels periods[1][4]
  • Filter outputs are squared and averaged by a digital “mean-value-computer” over successive time intervals of length tavg[1]
    • tavg~1.125s  (but depends on bit rate, i.e. ~20min for the lowest bit rate)[1]
    • In addition to the mean square value Mn , the peak value in the same time interval is obtained and transmitted[1]
  • Similar to experiment E2, E4 experienced thermal issues: “Behavior suggests ‘healthy’ conditions up to the end of 1977”[2]

Data Availability and Reanalysis

  • Only a very limited subset of E4 data is available[3]
    • Helios 1 data covers time span of Dec 10, 1974 – Sept 09, 1975
    • Helios 2 data covers time span of Jan 15, 1976 – March 10, 1976
    • The rest of the data has been lost forever, see Neubauer’s Presentation[2]
    • 2 data products available (mostly collected simultaneously)[4]
      • Maximum value within 8 sec
      • Mean value within 8 sec
    • Saved in ASCII format
  • Search coil magnetometer data was read from 9-track tapes to CD and a decommutation program was written to restore the data to ASCII files[1][4]
    • Only 35% of the data seemed uncorrupted[1]
  • Page 4 of Dudok de Wit’s E4 presentation visually summarizes the available data
  • The reanalysis of the E4 data was done in conjunction with the E2 4Hz data. This information is also compiled in the Action Item List.
  • There are still various issues with the dataset, which are still not understood:
    • The amplitude of E4 power spectra, especially when compared to the power spectra compiled from the E2 4Hz data
    • Search coil noise level