Land surface temperature (LST) is an important variable for studying environmental changes and monitoring the Earth climate system. The SLSTR on board Sentinel-3A and 3B satellites is a key sensor that provides LST data on a global scale with daily revisit. The objectives of this paper are: (i) To check the on-board calibration of the SLSTR thermal-infrared bands calibration against ground-measured data for the first time. (ii) To validate the SLSTR LST product and an alternative emissivity-dependent split-window algorithm (SWA) for SLSTR data. To this end, we used the temperature based (t-based) and radiance based (r-based) methods. Ground LSTs measured from narrow-band, directional radiometer measurements from nine homogeneous sites were used for the calibration assessment and the t-based validation. The nine sites represent four different biomes. R-based validation was performed over the same t-based sites plus other five sites of varied biomes where ground LST measurements were not available. The analysis was performed for a dataset corresponding to the period 2020–2022. Results from the calibration assessment showed R-RMSDs (robust root mean square difference) between the simulated and satellite brightness temperatures of 0.7 K and 0.6 K for bands 8 and 9, respectively, for both sensors (3A and 3B), with small median differences. Such R-RMSDs were well within the uncertainty limits of the simulated brightness temperatures. The validation of the operational SLSTR product and the SWA yielded consistent results when comparing Sentinel-3A and 3B. For the t-based method, the SLSTR product showed an overall daytime (nighttime) R-RMSD of 1.5 K (1.7 K), with medians (satellite minus ground) varying between −2.0 K and 1.5 K and thus exceeding the recommended ±1.0 K threshold. For the SWA, R-RMSDs were 1.3 K both for daytime and the nighttime, and medians varied between −0.2 K and −0.9 K for daytime and nighttime. The r-based results confirmed the large medians in the SLSTR product, which ranged from −1.5 K to 1.7 K (from 0.1 K to 0.4 K for SWA). The SLSTR product showed R-RMSDs of 1.0 K (1.0 K) for the overall daytime (nighttime), while they were 0.6 K (0.3 K) for the SWA, which were lower than those for the t-based validation. The results presented here contributed to the global validation of LSTs derived from the SLSTR sensor onboard the Sentinel-3A and 3B satellites.
Puchades et al. (Thu,) studied this question.