Concerns on cross comparison of satellite land surface temperature retrievals, a case study between VIIRS and MODIS LST product

land surface temperature is a key parameter in the physics of land surface processes on regional and global scales, combining the results of all surface atmosphere interactions and energy fluxes between the atmosphere and the ground. The cross-comparison of LST products from different satellites or sensors is widely used to evaluate one LST product with reference to the other, particularly between heritage satellite products. This method is not a real validation but allows identifying weak points in a product. As the VIIRS LST is expected to replace MODIS LST in the future, the inter-comparison between VIIRS LST and MODIS LST will provide the evaluation of VIIRS LST performance with respect to difference characterization, i.e. spatial pattern, systematic error budget, which may reflect the algorithm difference, limitations or errors. Some researchers have evaluated the VIIRS LST product after Suomi NPP launch mostly based on the temperature based approach and the cross comparisons between MODIS and VIIRS is mostly around the ground sites over time series. Cautions need to be taken in the whole chain of cross-comparisons, i.e. data selection for comparison, data processing procedures and results analysis. This study will focus on cautions regarding temporal differences, composite process, and angular differences. Some comparison cases are discussed and a guideline is provided for each of them in the cross satellite LST comparison.