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The quiet-day curves are an indication of the noise-level IRIS would be expected to measure on a day without any absorption, scintillation or interference. Quiet-day curves can be generated by theoretical or empirical means. The method we use is empirical and is explained below:
  1. For a given period (usually 14 days) arrange the data (per beam) into 10m intervals, based upon the sidereal time.
  2. Take the median of the 600 samples.
  3. For each interval sort the data.
  4. Discard the largest value as it may be corrupted by interference (e.g. lightning, solar radio emissions) or scintillation.
  5. Take the mean of the next two largest values.
  6. Repeat for each beam and each 10m interval in the sidereal day.
The basis of the algorithm is to find the largest value received (excluding interference) for any time in the sidereal day.

An alternative method sometimes is employed is based on the above, but with a sliding median of 1s resolution data. Thus 86164 blocks, per beam, per sidereal day, are considered.


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