Data Processing

Raw science telemetry data from the spacecraft must be processed using the standard set of FGM Data Processing Tools, otherwise know as the DP Software.  If you are interested in using the DP software, then the software is available for both Solaris and Linux platforms.  Some documentation and guides are available to aid with the processing of data. Please contact either the TC-1 FGM PI Chris Carr or TC-2 FGM PI Tielong Zhang, as appropriate, for more information on availability.

Additionally, to process data using the DP Software, calibration data will be needed.  This can be obtained from the Imperial College FGM Web Server for those with access.  Discussion on how calibration is undertaken is included in the calibration section of this web site.  Essentially, the calibration values correct offsets of the scalar values from the true zero, non-unity gains of the field values, and the non-orthoganalities of the Sensors Coordinate system.  The latter is essential to convert from non-orthogonal coordinate systems such as FGM Sensor (FS) to orthogonal ones such as Geocentric Solar Ecliptic (GSE) or Geocentric Solar Magnetic (GSM).

The DP software carries out a number of functions:

• To decode the compact internal data format that is used to transmit FGM Telemetry.

• To remove bad data (e.g. data collected during eclipses, in calibration modes, or which is simply corrupted due to a bad downlink from the satellite).

• To apply calibration parameters to the raw data values.

• To convert to a variety of difference coordinate systems, including (but not necessarily limited to):
  
  
  • FS FGM Sensor System (this is the only spinning system, the remainder of the coordinate systems are despun)
  • SR FGM Spin Reference
  • SCS Spacecraft - Sun Coordinate System
  • GSE Geocentric Solar Ecliptic
  • GSM Ge ocentric Solar Magnetic
  • SM Solar Magnetic
  • J2K Geocentric Equatorial Inertial Epoch 2000
     

• The selection and removal of data from specific time periods, sensors , ranges etc.

• The merging of raw data files into time ordered sets for processing.

• The addition of spacecraft position data into the FGM science data stream to produce merged data products.

• The averaging of data to less than the full resolution data, either over the spin, a number of seconds, or minutes, or a fractional number of seconds.

• The formatting of output data with a variety of different elements in addition to the basic magnetic field data, these can include:

  • Several different time formats.
  • Spacecraft Spin Phase (for high-resolution data).
  • Data Variance (for averaged data).
  • Normalised Variance of the Field Magnitude (for averaged data).
  • Raw Data Variance (for high-resolution data)
  • Data Acquisition Frequency
  • Spacecraft Position
  • Field Magnitude

The DP software is composed of a selection of pipeline stages, which can be combined in a number of different configurations, depending on the degree of complexity of processing that is required.  For example, the Averaging pipeline stage is only needed when data is averaged over some period, if the stage is omitted, the processing is just carried out at the maximum available time resolution.

The diagram below shows some of the pipeline stages, and the ways in which they can be configured. Raw science data starts at the far left of the diagram, various auxiliary data products are added (STEF Short Term Event File, SATT Spacecraft Attitude and Spin Rate, STOF Short Term Orbit File, and CAL Calibration), and the data is progressively processed until the final data product leaves off the right hand side of the diagram (after using one of the output stages, igmvec & fgmvec).