Detector Ringing
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 Ringing is an artifact that affects a few detectors on Landsat 7 Enhanced Thematic Mapper Plus (ETM+). This anomaly appears as alternating bright and dark pixels that appear suddenly and with no obvious cause. The intensity of the ringing gradually diminishes until the detector returns to normal operation. The initial magnitude of a ringing event may be 200 Digital Number (DN) or more. Because this value adds to any underlying imagery, this artifact almost always saturates the detector data at 0 or 255, or both.
A relationship was found between the Detector Ringing events and the appearance of anomalous coherent noise. While using the Side A electronics, only three detectors have exhibited ringing behavior: Band 1 detectors 9 and 11, and Band 8 detector 14. These detectors also have the largest magnitude anomalous coherent noise.
The current theory to explain this relationship is that charge buildup on the spacecraft leads to a dielectric breakdown event that allows noise current to enter the circuitry. The dielectric breakdown event creates a Detector Ringing artifact, and the noise current is the source of the anomalous coherent noise. This theory is supported by the observation that ringing artifacts are more frequently found at the beginning of subinterval collections. Moreover, the artifacts occur slightly more often in data over polar regions where the charged particle environment of the satellite is strongest. Ringing events have occurred less frequently since the failure of the Scan Line Corrector (SLC) in 2003, but they are still sometimes observed.
Detector Ringing artifacts are uncorrectable, but they are not expected to cause any lasting damage to the detectors involved. They have been rare on L7 ETM+. An examination of the Image Assessment System (IAS) trending database estimates that one percent of all Landsat imagery contains ringing artifacts.