Landsat Missions

Data Loss

When data are missing from a digital image, an artifact known as data loss occurs. The missing data will often be substituted with telemetry data on board the satellite and will thus have a random appearance. Alternately the missing data may be replaced by null values, or filled with a designated fill pattern by the ground processing systems.

Figure 1. Example of a “Christmas Tree” anomaly in Level 1 data. Landsat 5 TM Bands 3,2,1.
Click to view larger image. - .tif (1.83 MB)

Data loss is sometimes referred to as a “Christmas Tree” anomaly when the loss occurs in all bands. When the artifact is viewed in any 3-band RGB combination, the lost data appear as bright red, green, and blue artifacts, often next to or overlapping each other. This colorful artifact is usually caused by telemetry data erroneously being included in the imagery.

Sometimes the data over an entire scan line are lost. This is usually due to either a temporary problem in the main scan mirror or transmission problems between the satellite and the receiving ground station. A dropped scan is also sometimes known as a dropped major frame.

In Level 0 Landsat 7 ETM+ data, dropped scans are filled with horizontal stripes of values 255 and 0. These stripes are removed during processing to Level 1, where the lost data are filled with either a flat value or with interpolated data.

Because Landsat 7 data is downlinked and processed in two different data format streams, transmission-related data loss will usually only affect one format—either Bands 1-5 and Band 6 low gain, or Bands 7-8 and Band 6 high gain.

A known problem on Landsat 5 causes severe Data Loss in a repeatable and predictable cycle. The sun glint anomaly occurs when sunlight reflects off a part of the spacecraft in a way that interferes with the omnidirectional downlink antenna, causing data to be lost in transmission. For data downlinked to EDC, these losses occurred over paths 31 and 32, rows 29 to 31, from day 100 to day 228 of each year.

Changes in the ground station hardware in late 2006 mitigated the transmission problem. Data downlinked to EDC should no longer have sun glint anomalies, but other ground stations may experience these losses in other locations and other times of year. This data loss is unavoidable but easily identified in browse imagery.

In all forms, data loss is uncorrectable in the scene in which it appears, but some transmission and ground processing problems may be corrected with reprocessing.

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Page Last Modified: May 13, 2008