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Oversaturation

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Known Issues

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. The Landsat Calibration and Validation (Cal/Val) team investigates and tracks anomalous data.

A number of known issues regarding Landsat data are listed on this page. Updates to this list are not only made when new anomalies and artifacts are discovered, but also when investigations require changes to already existing issues.

If you discover data artifacts that are not listed here, please contact us.

Known Issues Home, Banding, Coherent Noise, Coherent Noise Storm, Data Loss, Detector Failure, Detector Ringing, Detector Striping, Gimbaled X-band Antenna (GXA) Anomaly, IC Intrusion, Impulse Noise (IN), Lower Truncation Acquisitions, Memory Effect (ME), Optical Leak, Oversaturation, Scan Correlated Shift (SCS), Scan Mirror Pulse, Shutter Synchronization Anomalies, Single Event Upset (SEU), Thermal Infrared Sensor Select Mechanism Anomaly

Oversaturation

Figure 1

Figure 1. Example of Oversaturation, with crosstalk effect visible, over reflective targets on the ground (large greenhouses in England). Landsat 7 Enhanced Thematic Mapper Plus (ETM+) Band 1 data.
Click to view larger image. - .gif (165 KB)

When the detectors in a sensor view an object that is too bright, they record a flat value of 255 in the 8-bit data from the Landsat satellites (known as saturation). However, when the object viewed is much brighter than the sensor can handle, a semiconductor effect in the detectors causes an artifact known as Oversaturation. In general, Oversaturation causes the detector to cease operating correctly for a short time, returning null values (or occasionally, quick oscillations between 0 and 255). Sometimes, a crosstalk effect occurs, creating brief periods of noise in other non-saturated detectors in the affected band.

Oversaturation on the Landsat satellites is common over fires, some bright city lights, and more rarely over large reflective surfaces that are oriented to reflect the Sun toward the satellite. Depending on the cause, Oversaturation artifacts may affect all reflective bands, or they may affect some bands but not others–for example, Bands 5 and 7 are often affected, with no artifact in the visible bands. Band 6 is the only band in which Oversaturation has never been found.

 

Fire Saturation

Figure 2

Figure 2. Examples of Oversaturation over a wildfire in Landsat 5 Thematic Mapper (TM) data, visible in Bands 5 and 7 but not in Bands 3,2,1.
Click to view larger image. - .gif (409 KB)

Figure 3

Figure 3. Example of Oversaturation over a large wildfire. Landsat 7 ETM+, Band 7 data.
Click to view larger image. - .gif (291 KB)

Figure 4

Figure 4. Example of Oversaturation during an eruption at the Mt. Etna volcano in 1999. Landsat 7 ETM+, Band 7 data.
Click to view larger image. - .gif (181 KB)

Wildfires and active volcanoes are common causes of Oversaturation. They usually cause Oversaturation in the Short Wavelength Infrared (SWIR) bands (Bands 5 and 7), but the artifact has been seen in other bands. Because wildfires can cover a wide area, the Oversaturation artifacts associated with them can be large.

 

Extraneous Line Fill

Figure 5 & 6
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Figure 5 & 6
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Figure 5 & 6. Examples of extraneous line fill in Landsat 5 TM, Band 4 data.

Landsat 5 Thematic Mapper (TM) Band 4 is especially vulnerable to Oversaturation, and it commonly exhibits this artifact when viewing well-lit clouds. The name "extraneous line fill" has been used in the past to describe this form of Oversaturation.

Despite their dramatic appearance, Oversaturation artifacts are considered to be minor, and they cause no permanent harm to the Landsat sensors. They are uncorrectable.

About

Landsat represents the world's longest continuously acquired collection of space-based moderate-resolution land remote sensing data. Four decades of imagery provides a unique resource for those who work in agriculture, geology, forestry, regional planning, education, mapping, and global change research. Landsat images are also invaluable for emergency response and disaster relief.

 

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