Performance of the Thermal Infrared Sensor on-board Landsat 8 over the First Year On-Orbit

The Thermal Infrared Sensor (TIRS) has completed over one year in Earth orbit following its launch on-board Landsat 8 in February 2013. During that time, TIRS has undergone initial on-orbit checkout and commissioning and has transitioned to an operational Landsat payload obtaining 500+ Earth scenes a day. The instrument was radiometrically calibrated during pre-flight characterization testing in order to convert raw sensor signal into accurate at-aperture radiance. The pre-launch calibration was adjusted during the on-orbit checkout of the instrument to account for relative pixel-to-pixel artifacts such as striping. The accuracy of the relative and absolute radiometric calibration depends in part on the stability of the instrument response over time. To monitor stability, TIRS routinely views its onboard calibration sources, which include a variable temperature blackbody and a port that allows the instrument to view deep space. The onboard calibration is validated by in-situ measurements of large water bodies by instrumented buoys. In addition, the spacecraft is periodically slewed to image the moon across the field-of-view of TIRS. The moon provides a high contrast source which allows for studies of stray light and ghosting to be performed. These on-orbit methods provide the means to characterize the TIRS instrument performance post-launch. Analyses of these datasets over the first year on orbit indicate that, while the instrument itself is internally stable to within requirements, both bands were miscalibrated by at least 2 K (@300 K) and had higher than expected variability in the in-situ validation data. This has been traced to a stray light issue which is also causing banding in Earth scenes. An initial bias correction was made in February 2014 and various approaches are being explored to correct the ghosting issues associated with the stray light.