Figure 1. Example of Memory Effect in Landsat 5 Thematic Mapper (TM) Band 3.
Memory Effect (ME) is an artifact that has existed since the early days of optical systems and has been called "Bright Target Recovery" and "Detector Blindness". It manifests as alternating light and dark bands that are most visible near sharp boundaries between bright and dark terrain. Clouds, shorelines, and ice or snow are common terrain features that cause ME. The calibration lamps also cause ME, creating a banding pattern that has no apparent source in the imagery. The pattern slowly disappears as the detectors recover and return to normal operation. Thus, unlike banding and Scan Correlated Shift (SCS), ME changes in magnitude across a scan.
ME is characterized by magnitude and time constant, which is a measure of the length of the artifact. If both of these values are known, ME is correctable. Most modern processing systems correct ME by default; thus, it usually appears only in Level-0 data or in data processed by older systems.
Landsat 4 and 5 TMs have ME in several bands, with a time constant of approximately 1,100 pixels. ME has never been detected in reflective band Landsat 7 (L7) Enhanced Thematic Mapper Plus (ETM+) data, but insignificant amounts may exist in the ETM+ thermal band. It exists in most Multispectral Scanner (MSS) data.