Scan Correlated Shift (SCS)
Figure 1. Example of Scan Correlated Shift in Landsat 5 (L5) Thematic Mapper (TM) Band 1.
Click to view larger image. - .gif (144 KB)
Scan Correlated Shift (SCS) is a change in bias that occurs in all detectors in a band simultaneously. The bias change is linked to the start of the scan of the primary mirror, and so the bias changes randomly into one of two or more states with every scan. SCS exists in the Landsat 1-5 Multispectral Scanner (MSS) instruments and in Landsat 4 and 5 TM instruments. It does not exist on Landsat 7.
A characteristic of SCS is that the bias can have only one of a limited number of values corresponding to the SCS state of the scan. Thus, taking the example of a two-state SCS, the bright scans are always biased by the same value with respect to the dark scans. This makes correction simple; one bias is chosen arbitrarily to be correct, and scans in other SCS states are biased to match. SCS correction is performed by default in L5 processed data, so this artifact is not visible in most Level-1 images.
SCS is one of the two principal causes of Banding, the other being Memory Effect. The two artifacts are sometimes difficult to separate from each other. Memory Effect fades across the scanline as it gets further from bright/dark transitions in the imagery or at the IC pulse. SCS can be diagnosed by its random nature, by its fixed magnitude states, and by its appearance in otherwise completely dark nighttime data.