Landsat 8 Operational Land Imager (OLI) Lower Truncation
The detectors of Landsat 8’s Operational Land Imager (OLI) can register data up to 14 bits. However, only the upper or lower 12 bits can be transmitted to the ground. In normal operations, the upper 12 bits are transmitted. When acquiring in the upper 12-bit mode, the lower 2 bits collapse (saturate) into the lowest data value. The lowest two bits are very noisy.
In 2013 and again in 2015, some Landsat 8 scenes were acquired in lower truncation - meaning data from the lower 12 bits were captured. During acquisitions in lower truncation, regions of high brightness within a scene exceed the lower 12-bit range of 4096, causing the count to begin again, using the 13th and 14th bits, which are beyond the lower 12 bits being reported. This causes the numeric values to "roll over" and start counting from zero again. Pixels affected by ‘roll over’ do not correctly reflect the brightness of the ground measured and will visually take on an apparently random value (See Figure 1).
These roll over values cannot be differentiated from valid values elsewhere in the image. Moreso, the cloud information in the Landsat 8 Quality Assessment Band will be unreliable. Users should be cautious when using these images for operational activities, although most cloud free data will not be affected.
The 2013 scenes were acquired during the on-orbit checkout period, prior to data becoming available to all users. The affected scenes are listed on this file.
The scenes acquired in 2015 are being used to investigate the value of the lower two bits and support the possibility of downloading all 14 bits of data for Landsat 9. Data to support two studies were acquired: 1) a night interval through the western United States over fires and urban areas, and 2) a day interval off the coast of eastern Australia over dark water. The artifacts are most noticeable over fires in the night data and over clouds in the day data. The locations and dates of the intervals are listed in the table below.