Evaluation and improvement of the MODIS land surface temperature/emissivity products using ground-based measurements at a semi-desert site on the western Tibetan Plateau

Current MODerate-resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST, surface skin temperature)/ emissivity products are evaluated and improvements are investigated. The ground-based measurements of LST at Gaize (32.30 degrees N, 84.06 degrees E, 4420 m) on the western Tibetan Plateau from January 2001 to December 2002 agree well (mean and standard deviation of differences of 0.27K and 0.84 K) with the 1-km Version 004 (V4) Terra MODIS LST product (MOD11A1) generated by the split-window algorithm. Spectral emissivities measured from surface soil samples collected at and around the Gaize site are in close agreement with the landcover-based emissivities in bands 31 and 32 used by the split-window algorithm. The LSTs in the V4 MODIS LST/ emissivity products (MYD11B1 for Aqua and MOD11B1 for Terra) from the day/ night LST algorithm are higher by 1-1.7K (standard deviation around 0.6 K) in comparisons to the 5-km grid aggregated values of the LSTs in the 1-km products, which is consistent with the results of a comparison of emissivities. On average, the emissivity in MYD11B1 (MOD11B1) is 0.0107 (0.0167) less than the ground-based measurements, which is equivalent to a 0.64K (1.25 K) overestimation of LST around the average value of 285 K. Knowledge obtained from the evaluation of MODIS LST/ emissivity retrievals provides useful information for the improvement of the MODIS LST day/night algorithm. Improved performance of the refined (V5) day/night algorithm was demonstrated with the Terra MODIS data in May-June 2004.