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Determination of proton and electron fluxes using the SFD output currents

As described in Technical Note C section 5 the sfd program uses an input file (type .mdr) and produces 1 output file (type .iff), but if the option flag -d is set it produces also debugging output to standard out (which can be redirected to a file. It also uses a calibration file whose path has to be defined in the invironment variable edc_sfd_calfile and a "Spacecraft to Universal Time Conversion Data file" whose path is defined in the environment variable edc_scut_file.

The debug output (pure ASCII) contains :

  1. a copy of the calibration data (see Technical Note C appendix C.03 for an example)
  2. synchronisation information (see Technical Note C appendix C.03 for an example)
  3. the listing of the array of out strucures (one line per input telemetry format) (as example an extract is given in Technical Note C appendix C.04)
  4. the listing of the MEAS_POINT structures (as example an extract is given in Technical Note C appendix C.05)
  5. the detector current listing (as example an extract is given in Technical Note C appendix C.06)

When the program is run at the Equator Data Centre (EDC), the debug outputs are saved in files eq_sfd_YYYYMMDD.log which may be recovered. When the program is run on CD-ROM data files the debug output is saved too in files YYYYMMDD.d. Using the vi editor these files have been split in the segments 1 to 5 as defined above and were given names as follows:

1 : YYYYMMDD.def
1+2 : YYYYMMDD.sync
3 : YYYYMMDD.mux
4 : YYYYMMDD.cyc
5 : YYYYMMDD.idet

Each SFD measurement (also called "event" hereafter) is registered in .cyc files as a record of the Cordinated Universal Time (UTC), the time in number of seconds from middnight, the multiplexer/cycle position and the eight values of output voltages acquired every 64 seconds from the multiplexer.

These .cyc file can be used as input to programs that just apply the Boeder's formulae and reproduce files of the .idet type without having to read these huge CD-ROM files again, extract again the SFD data and try to find the synchronisation again. So the .cyc files are very useful intermediate data on which one can easily and rapidly use different algorithms or calibration files and compare the resulting detector currents.

By use of the .orb file (delivered by EDC) containing the satellite positions for each minute of Universal Time and the UTC of each measurement (from .cyc files) the (B,L) coordinates of the satellite are calculated for each event by interpolation. The final records used as input to flux calculation programs are made of the UTC, the actual (B,L) coordinates and the output currents of the NSF, SSF and SPINEL channels, derived from the output voltages (from .cyc files).

Among the records, only those for which were selected in our analysis. This trigger level, Ith was set taking into account the baseline current measured in regions with low radiation fluxes. The resulting number of events and their distribution versus L are shown in Figure 2.11 c. The SFD output currents and predicted proton and electron fluxes are displayed in Figure 2.12.


Figure 2.11: L coordinates analysis of the selected SFD events.

Figure 2.12: NSF output currents and predicted proton (AP-8) and electron (AE-8) fluxes.


Figure 2.13: SSF output currents and predicted proton (AP-8) and electron (AE-8) fluxes.

Figures 2.11 c., 2.12 and 2.13 show that the SFD trigger, i.e the NSF channel is set in space regions located around the separation line . This value of L was also found to separate two regions of space in which only one particle type (electron or proton) contributes to the SFD current. We must emphasize that without this preliminary discrimination, the equations are overdetermined. The only way to achieve particle discrimination without using L coordinates could be by increasing the number of channels: The number of channels must be at least equal to the number of parameters in the model of electron and proton spectra if particle discrimination is to be achieved with this kind of detector. Furthermore, the number of channels must exceed the number of parameters in the models in order to detect any occurrence of another type of particle: indeed, when new particle type contributes to the current, the function will abnormally increase.

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