Thermal and Shortwave Infrared Remote Sensing of Ecosystem Processes: Opportunities, Synergies, and Challenges

Land surface temperature (LST) is one of the preeminent state variables that affects the ecosystem functioning and it also gets modulated due to biotic and abiotic ecosystem processes. Understanding the factors controlling LST and the impacts of LST on the ecosystem water-carbon exchanges are very often hindered due to (1) the effects of LST retrieval uncertainty and angular variation on different processes, (2) the lack of authentic physically-based models that link LST with ecosystem physiological properties. Moreover, the synergy of LST and water-sensitive shortwave infrared (SWIR) bands in ecosystem modelling is absent until now, which could enhance the application of LST. The planned Indo-French polar-orbiting mission TRISHNA (Thermal infraRed Imaging Satellite for High-Resolution Natural resource Assessment) with its unprecedented spatial resolution and temporal revisit (57 m and 3 days noon-night observation capacity), 6 VSWIR and 4 TIR Bands in 8 – 12 m, will bring new insights to overcome these challenges. The optical-thermal observations will be used to attain LST, emissivity and surface reflectance with high accuracy and precision, underlying future scientific breakthroughs in understanding the energy-water-carbon exchange process. This paper briefly describes an overview of challenges in estimation of LST, role of thermal directionality and two of the most important ecosystem processes (evaporation and photosynthesis). The utility of SWIR reflectance in tandem with LST as a 'signal of opportunity' is also described.