Glitches are caused by such events as fast moving electrons and ions inside the earths magnetic field. Whatever causes a glitch, the effect of one is a sudden large increase of the output voltage which causes a large step (a ``glitch'') in the affected ramp. Derive-SPD attempts to remove glitches by ignoring the corrupted sample(s) and trying to construct two shorter slopes, one either side of the removed sample(s).
Note that glitches can have an effect that lasts for a long time (they have tails) and that a glitch in one detector can affect other detectors in that detector array.
Figure 5.1 shows an example of a glitch in the 24Hz ERD data . Note that the sets of two points with Bit values of around 2700-2800 are the result of the detector reset every second. The sample immediately after the two high points is also affected but appears okay due to the signal level.
Figure 5.2 shows two examples of a band 4 glitches in the SPD . In both cases the detector requires a long time to stabilise.
Figure 5.1: An example of a small glitch seen in the ERD
Figure 5.2: Two examples of glitches whose effects last for a long time. The data shown is SPD from a band 4 detector.
Another type of upset has been observed, called `scan jumps'. These appear to be similar to glitches, but they affect an entire detector block. The symptoms are that each detector in a block suffers a sudden rise in sensitivity, that slowly decays with time. They usually only affect one of an up-down scan pair, and the only solution is to throw a portion of the affected scan away.