USGS logoDec 8, 2015 • [Source: Landsat Update – Volume 9 Issue 7 2015] At approximately 4:00 PM Central Standard Time (22:00 GMT) on Sunday, November 1, 2015, the Thermal Infrared Sensor (TIRS) experienced an anomalous condition related to the instrument’s ability to accurately measure the location of the Scene Select Mechanism (SSM). The anomaly caused the upper bits of the encoder counts in the ancillary data to be corrupt, resulting in the TIRS bands becoming misregistered by approximately 500 meters (18 pixels). The encoder was powered off during a morning EROS station pass on Monday, November 2, 2015.

Landsat 8’s Operational Land Imager (OLI) data are not affected. TIRS data continue to be collected, but Level 1 products will be populated with zero-fill data until the geometric model parameters are finalized, and the algorithms and code in the Landsat Level-1 Product Generation System (LPGS) have been updated, tested, and verified. These activities are expected to be completed no sooner than February 2016. Following the implementation of a successful alternate TIRS processing capability, the Landsat 8 scenes containing zero-fill will be reprocessed and made available from the USGS archive.

Mission operations will continually assess potential opportunities for return to normal operations using the B-side encoder electronics. However, at this time, the schedule for return to normal operations is unknown.

Users are reminded that Landsat 8 scenes acquired after November 1, 2015, cannot yet be processed to Surface Reflectance at this time, due to the Thermal Infrared Sensor (TIRS) anomaly that started on November 1. The Landsat 8 OLI surface reflectance retrieval algorithm is dependent on TIRS data for cloud detection, and the algorithm is not currently configured to use the existing quality assessment (QA) band attribute for cloud contamination.

Nov. 17 Update:
The Landsat 8 flight operations team (FOT) continues to monitor current levels within the thermal infrared sensor (TIRS) Scene Select Mirror (SSM) encoder electronics. The FOT and Calibration Validation team are continuing to investigate the current anomaly and analyze instrument telemetry data in order to accurately measure the position of the SSM and to develop the necessary parameters for the processing TIRS data under an alternative operations concept.

TIRS data will continue to be routinely collected but will not be processed to Level-1 products until the geometric model parameters are finalized and the algorithms and code in the Landsat Level-1 Product Generation System (LPGS) have been updated, tested, and verified. These activities are expected to be completed no sooner than February 2016, at which time all products will be reprocessed to provide valid TIRS data.

Following the implementation of an alternate TIRS processing capability, the zero-fill Landsat 8 scenes will be reprocessed and made available from the USGS archive. Mission operations will continually assess potential opportunities for return to normal operations on the B-side encoder electronics. However, at this time, the probability of return to normal operations is unknown.

Nov. 3, 2015:
[Source: USGS Landsat] 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.

For the latest information visit the USGS Landsat website.