[A Comparative Study on the Calibration Accuracy of Landsat 8 Thermal Infrared Sensor Data].

The satellite thermal infrared image has been an important data source for the acquisition of the earth’s surface temperature. The thermal infrared sensor (TIRS) Landsat 8 satellite newly launched onboard has added valuable data for this mission. However, the calibration parameters for the two bands of the TIRS, i.e., TIRS Bands 10 and 11, had been modified several times since its launch. This finally led the United States Geological Survey (USGS) to reprocess all achieved Landsat 8 data starting from February 2014. In order to examine the calibration accuracy of the reprocessed TIRS data, this paper crossly compares Landsat 8 TIRS data with synchronized, well-calibrated Landsat 7 ETM+thermal infrared data. A total of three date-coincident image pairs of western United States, downloaded from USGS Earth Explorer website, were used for the cross comparison. Three test sites were selected respectively from the three image pairs for the comparison, which representing moderate vegetation-cover area (test site 1), low vegetation-cover area (test site 2), and bare soil area (test site 3). The thermal infrared data of the three image pairs of both sensors had been firstly converted to at-sensor temperature. A band-by-band comparison and a regression analysis were then carried out to investigate the relationship and difference between the two sensor thermal data. The results show a very high degree of agreement between the three compared Landsat 8 TIRS and Landsat 7 ETM+thermal infrared image pairs because the correlation coefficients between the retrieved at-sensor temperature of the two sensors are generally greater than 0.95. Nevertheless, the cross comparison also reveals differences between the thermal infrared data of the two sensors. Compared with retrieved at-sensor temperature of Landsat 7 ETM+Band 6, TIRS Band 10 shows an overestimation, which can be up to 1.37 K, whereas TIRS Band 11 underestimates the temperature, with a difference reaching to -3 K. This suggests that in spite of the reprocessing of Landsat 8 thermal infrared data, the calibration parameters for the satellite’s TIRS data are still unstable, especially for TIRS Band 11. It was found that the at-sensor temperature difference between ETM+Band 6 and TIRS Band 10 was enhanced with the decrease in vegetation coverage from test site 1 to test site 3. The at-sensor temperature difference of test site 1 is 0.07 K and increased to 1.37 K in test site 3, a net increase by 1.3 K. While the at-sensor temperature difference between ETM+Band 6 and TIRS Band 11 had an inverse performance. With the decrease in vegetation coverage from test site 1 to test site 3, the at-sensor temperature difference was reduced from ~-3.0 to -0.4 K. Therefore, in bare soil dominated test site 3, the temperature difference was 1.37 K for TIRS Band 10 and -0.4 K for TIRS Band 11. The RMSE of TIRS Band 11 is also much lower than that of TIRS Band 10. This suggests that TIRS Band 11 can perform batter in bare soil area than TIRS Band 10 though the latter shows an overall batter performance than TIRS Band 11. The study also found that in low vegetation cover areas like in test sites 2 and 3, taking an averaged at-sensor temperature of TIRS Bands 10 and 11, the difference between the two sensors’ at-sensor temperature can be reduced to less than -0.5 K.