New refinements and validation of the collection-6 MODIS land-surface temperature/emissivity product

摘要

According to the radiance-based (R-based) validation of the collection-5 or version-5 (C5 or V5) Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) land-surface temperature (LST) level-2 products at 42 sites in a wide LST range in different seasons and years, the LST errors are within ±. 2. K (within ±. 1. K in most cases) for all the sites but six bare soil sites. The V5 LSTs are underestimated by more than 2. K and up to 4.5. K at the desert site near In-salah, Algeria. Three refinements were implemented in the V6.3.0 daily LST Product Generation Executive (PGE)16 code: 1) refine the original viewing angle dependent split-window algorithm by adding two sets of coefficients separately for retrieval of daytime and nighttime LSTs at bare soil pixels in the hot and warm bare soil zone (HAWBSZ) within latitude range from 38° to 49.5°, 2) adjust the emissivity difference in bands 31 and 32 for bare soil pixels in HAWBSZ, and 3) incorporate the new refined split-window algorithm into the dayight algorithm for retrieving surface emissivity and temperature values at 6. km grids in HAWBSZ. The V6.3.0 PGE16 code was tested with C6 Aqua and Terra MODIS input data over a period of one year or longer in selected tile regions. The resulting C6 level-2 LST products were evaluated at five bare soil sites in north Africa, where radiosonde observation data for atmospheric temperature and water vapor profiles are available, with 12 R-based validation data sets as follows: the mean LST error is within ±. 0.6. K in 10 validate data sets, 0.8. K in one data set (for daytime LSTs at SVU site) and 1.9. K in another set (for daytime LSTs at Farafra site). The standard deviation of the C6 LST validation errors is less than 0.5. K in all the 12 validation data sets but the data set for daytime LSTs at Farafra site at 0.7. K. Statistical and viewing angle dependence analyses of the retrieved surface emissivity values also indicate that the C6 level-3 LST products are much better than the previous C4.1 and C5 products.