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Detector Failure

Landsat data are systematic, geometric, radiometric, and terrain corrected to provide the highest quality data to the user communities. Occasionally, anomalies occur and artifacts are discovered that require research and monitoring. 

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Detector Failure is a term used for different anomalies that arise in the individual detectors of an instrument. Some of these anomalies are transient, while others are permanent.

Transient Detector Failure

Transient detector failure, also known as a "flaky detector," occurs when a single detector undergoes a sudden and drastic change in bias. Usually, the detector slowly returns to nominal behavior over the course of several scans. The cause of this artifact is unknown, but it is most likely due to energetic particle strikes within the detector circuitry. Transient failure has been observed many times in Landsat 5 Thematic Mapper (TM) data and once in Landsat 7 Enhanced Thematic Mapper Plus (ETM+) data.

Landsat Known Issues - Detector Failure
Detector Failure anomalies found in Landsat 7 and Landsat 5 TM data. From top: Landsat 7 Band 6, transient failure in detector 6; Landsat 5 TM Band 4, transient failure in detector 14; Landsat 5 TM Band 4, transient failure in detector 14; Landsat 5 TM Band 5, transient failure in detector 15. 

Flat Detector

A Flat Detector is a permanent but partial detector failure. Either the detector's bias values, the detector's gain values, or both are affected, with a resulting reduction in dynamic range. The detector return values may only vary within a range of a few DN values, or they may register a single constant value. They may also exhibit larger than usual random noise. Flat detectors have been seen in Landsat 4 TM and Side B engineering data in Landsat 7 ETM+, but these anomalies should not appear in any normal imagery.

Dead Detector

Absolute, permanent detector failure is known as a Dead Detector. Dead Detectors do not return any signal; they have a constant value of 0 Digital Number (DN). There are no dead detectors in any instruments on Landsats 5 or 7. Previous Landsat instruments have exhibited Dead Detectors near the end of their operating lifetime.

Detector Failure is uncorrectable, although interpolation of data from adjacent detectors can mitigate its effects. All forms of Detector Failure are matters for serious concern and may indicate progressive problems onboard the instrument. They are expected to increase in occurrence and severity as an instrument ages.