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November 3, 2015 - ​TIRS Scene Select Mirror Encoder Current Anomaly

By Landsat Missions

At approximately 4:00 PM Central Standard Time (22:00 GMT) Sunday November 1, 2015 the TIRS instrument experienced an anomalous condition related to the instrument's ability to accurately measure the location of the Scene Select Mirror (SSM).

The anomaly caused the upper bits of the encoder counts in the ancillary data to be corrupt, resulting in the TIRS bands becoming mis-registered by approximately 500 meters (18 pixels). The encoder was powered off during a morning EROS station pass on Monday November 2. The team is currently gathering and assessing available data and a TIRS Anomaly Review Board (ARB) will be convened within the next day or two to assess options for going forward.

The Operational Land Imager (OLI) is not affected, and TIRS imagery will continue to be collected along with OLI imagery. Until we have an opportunity to better characterize the conditions of and leading up to last night's anomaly, we are not able to process TIRS imagery within specifications. As a result, until further notice TIRS data will be zeroed out of Landsat 8 image products until the processing system is updated accordingly, and the data can be processed and made available to the public. At this point, the viability and accuracy of TIRS image data collected on the Encoder B-side electronics is unknown.