The user of the HIA data needs to be cautious.
The DSDS parameters from the HIA experiment are moments of the distribution functions, that result from summing counting rates. Thus they do not convey information on the detailed structure of the 3D distributions.
Counting statistics are essential for reliable results. Besides instrument sensitivity and calibration, the accuracy of computed moments is mainly affected by the finite energy and angle resolution, and by the finite energy range.
HIA at Perigee :
Background due to penetrating particles, from the radiation belts.>> High background on HIA around the perigee pass (in the radiation belts)
Similar HIA high background, due to penetrating particles, also during some SPE (solar particle events).
Furthermore, in the inner radiation belts, HIA operates with a substantially reduced HV on the detector.
HIA calibrations :
The HIA calibration values are regularly updated to take into account the detector efficiency evolution. However, as the evaluation of the detector efficiency requires some «time history», necessary for a statistical analysis, there is an hysterisis between the detector efficiency drift and the calibration updates.>> Only reprocessed HIA data are based on the updated calibrations; for the near-real-time data the calibrations are preliminary
Telemetry noise :
In several cases the received HIA telemetry is very noisy. These cases are easy to identify visually in the HIA spectrogram plots.
Spacecraft potential effects :
Spacecraft charging to a positive floating potential repels low-energy ions, which in these cases cannot be detected by HIA. The operation of the ASPOC ion emitter provides a helpful contribution in the detection of low-energy ions by HIA (particularly in low-density regions), by reducing the spacecraft potential.>> Spacecraft potential effects have to be taken into account for low-energy ions.
Decreased detector efficient for anodes n°2 and 7 (out of 8 toatal anodes).
DSDS data quality :>> The DSDS data quality is not for publication, and the users should contact the PI.