All traditional photoconductors, such as the MIPS Ge:Ga unstressed and stressed detectors, show multiple time constant response. In addition, they can exhibit spontaneous spiking and non-monotonic response characteristics (the ''hook''). For much more discussion, see section 2.3.2. The result is a slow increase in detector response lasting tens of minutes (MIPS 160 µm detectors) to hours (MIPS 70 µm detectors). MIPS takes advantage of the fact that the fast generation-recombination response (fast response) of the detectors is inherently different than the longer term response by using the scan mirror to modulate (chop) the source signal on timescales of a few seconds, keeping measurements mostly confined to the fast response regime. Frequent use of on-board calibration sources (called stimulators, or stims) additionally allows tracking of the long-term drifts in response. However, some artifacts do remain (see Figure 7.19, for examples) and are discussed below along with possible mitigation methods.
Figure 7.19: Examples of several of the most common MIPS-70 artifacts; see next several sections for more discussion. Note that these data are pre-bias change data processed under S10. Techniques for improving these data are discussed in section 8.2.8 (These data are NGC 7331, from the SINGS Legacy team).