On-Orbit Radiometric Performance of the Landsat 8 Thermal Infrared Sensor

Abstract

The Thermal Infrared Sensor (TIRS) requirements for noise, stability, and uniformity were designed to ensure the radiometric integrity of the data products. Since the launch of Landsat 8 in February 2013, many of these evaluations have been based on routine measurements of the onboard calibration sources, which include a variable-temperature blackbody and a deep space view port. The noise equivalent change in temperature (NEdT) of TIRS data is approximately 0.05 K @ 300 K in both bands, exceeding requirements by about a factor of 8 and Landsat 7 ETM+ performance by a factor of 3. Coherent noise is not readily apparent in TIRS data. No apparent change in the detector linearization has been observed. The radiometric stability of the TIRS instrument over the period between radiometric calibrations (about 40 min) is less than one count of dark current and the variation in terms of radiance is less than 0.015 W/m 2 /sr/µm (or 0.13 K) at 300 K, easily meeting the short term stability requirements. Long term stability analysis has indicated a degradation of about 0.2% or less per year. The operational calibration is only updated using the biases taken every orbit, due to the fundamental stability of the instrument. By combining the data from two active detector rows per band, 100% detector operability is maintained for the instrument. No trends in the noise, operability, or short term radiometric stability are apparent over the mission life. The uniformity performance is more difficult to Remote Sens. 2014, 6 11754 evaluate as scene-varying banding artifacts have been observed in Earth imagery. Analyses have shown that stray light is affecting the recorded signal from the Earth and inducing the banding depending on the content of the surrounding Earth surface. As the stray light effects are stronger in the longer wavelength TIRS band11 (12.0 µm), the uniformity is better in the shorter wavelength band10 (10.9 µm). Both bands have exceptional noise and stability performance and band10 has generally adequate uniformity performance and should currently be used in preference to band11. The product uniformity will improve with the stray light corrections being developed.

Radiometric Calibration Methodology of the Landsat 8 Thermal Infrared Sensor

“…All indications from this dataset are that the TIRS instrument is thermally and electrically stable [2]. There have been, however, two anomalies that have been observed that require further investigation.…”

“…The image data from the OBC are used to monitor the stability of the radiometric response of the instrument. The OBC is normally fixed around 295 K, but can be set to temperatures from roughly 270 K to 320 K. The stability of the background and dark signals, as well as the response stability to the OBC are continuously monitored on-orbit [2].…”

“…Should this be the case, the change in counts from the dark band may be subtracted from the counts in the spectral bands to remove the fluctuation in the dark signal from the spectral bands. For analyses on the stability of the background and dark signals, refer to [2].…”

“…The band relative spectral response (see Section 3.2) is then multiplied per wavelength and integrated to arrive at the expected radiance for the band for the given source temperature. The appropriate values are inserted into Equation (2) and are expressed as,…”

“…An optical stray light issue has since been diagnosed that will require a correction to be applied to the calibration process in the future once a solution has been finalized [1]. The stray light affects certain aspects of the calibration, such as uniformity [2] and the absolute radiometric calibration [3].…”