Thermal infrared (TIR) sensors prov

Thermal infrared (TIR) sensors provide direct measurements of skin temperatures of land surfaces. Widely used LST products are derived from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard the Terra spacecraft, the Thematic Mapper (onboard Landsat), and from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard two satellites: Terra (with a morning overpass) and Aqua (with an afternoon overpass). Terra, Landsat, and Aqua share a common sun-synchronous orbit with different overpass times. Among the TIR imagers on these satellites, only MODIS provides daily measurements of LST. Numerical modeling studies based on the empirical relationship between the ground temperature and air temperature have taken advantage of the MODIS LST products (e.g., [27–29]) to derive static maps of the spatial distribution of permafrost. Recently,a numerical modeling study has combined the MODIS LST products with gridded air temperature data to derive time-series maps of permafrost extent [5]. These dynamic maps of changes in permafrost are important to assess the impact of a warming climate to the state of the permafrost. The approach proposed in this article is a contribution toward creating temporally and spatially dynamic maps of the quantified state of permafrost and seasonally frozen ground, complementary to the previousregional-scale studies.