Abstract
The Thermal Infrared Sensor (TIRS) has been collecting imagery of the Earth since its launch aboard Landsat 8 in early 2013. In many respects, TIRS has been exceeding its performance requirements on orbit, particularly in terms of noise and stability. However, several artifacts have been observed in the TIRS data which include banding and absolute calibration discrepancies that violate requirements in some scenes. Banding is undesired structure that appears within and between the focal plane array assemblies. In addition, in situ measurements have shown an error in the TIRS absolute radiometric calibration that appears to vary with season and location within the image. The source of these artifacts has been determined to be out-of-field radiance that scatters onto the detectors thereby adding a non-uniform signal across the field-of-view. The magnitude of this extra signal can be approximately 8% or higher (band 11) and is generally twice as large in band 11 as it is in band 10. A series of lunar scans were obtained to gather information on the source of this out-of-field radiance. Analyses of these scans have produced a preliminary map of stray light, or ghost, source locations in the TIRS out-of-field area. This dataset has been used to produce a synthetic TIRS scene that closely reproduces the banding effects seen in actual TIRS imagery. Now that the cause of the banding has been determined, a stray light optics model is in development that will pin-point the cause of the stray light source. Several methods are also being explored to correct for the banding and the absolute calibration error in TIRS imagery.
Highlights
The Thermal Infrared Sensor (TIRS) is the thermal instrument onboard the Landsat 8 observatory.The sensor was designed to continue broadband, long wave infrared measurements of the Earth for the Landsat program
After completing the initial on-orbit checkout and calibration activities, banding artifacts were noticed in Earth imagery that seemed to vary from scene to scene
TIRS has demonstrated internal stability over the first year of operation on-orbit, scene-dependent artifacts have been observed in Earth imagery that include banding and absolute calibration errors
Summary
The Thermal Infrared Sensor (TIRS) is the thermal instrument onboard the Landsat 8 observatory. TIRS has been operationally collecting Earth scene thermal infrared imagery since its activation in March 2013. After completing the initial on-orbit checkout and calibration activities, banding artifacts were noticed in Earth imagery that seemed to vary from scene to scene. All indications from the instrument telemetry showed that TIRS was thermally and electrically stable and that the radiometric response to the onboard calibration sources was stable [1]. The suspected cause of the banding artifacts was stray light, or radiance from outside the instrument field-of-view producing an additional non-uniform “ghost”. The stray light directly affects certain aspects of the instrument performance including the uniformity [1] and the absolute calibration [2]. This paper provides an overview of the investigation which led to the identification of the stray light issue and early attempts at developing a correction methodology
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