Monitoring LST at canyon scale for urban micro-climate applications: in-situ, simulation and airborne data comparisons.

In a context of more frequent heat waves, urban overheating is a major environmental and public health issue. The Land Surface Temperature (LST) is a key variable to study this phenomenon and its estimation at district or city scale can help to diagnose the thermal behaviour of existing or future infrastructures. This paper compares in-situ sensors, 3D physical models and remote sensing observations to investigate the potential and accuracy of each approach to monitor LST at canyon scale. This comparison is performed based on the datasets acquired during the CAMCATT-AI4GEO experiment led in Toulouse city in June 2021 and a side experiment evaluating iButtons data using KT19 measurements as reference. This work shows that iButtons provide LST within +/- 1.25°C (over white walls) if the sensor is protected from direct sun. They offer a good spatial coverage over a small scene, providing direct LST measurement, but they seem sensitive to dark colour walls and sun exposition. On-ground TIR cameras allow for fine scale monitoring of the spatial and temporal variation of the LST, which provides information on the thermal behaviour of the surfaces over limited portion of the scene. On the other hand, airborne cameras allow to retrieve LST over horizontal surfaces at flight overpass time, which give an instant picture of the LST spatial variability at district or city scale. In both cases, retrieving LST from the thermal infrared images can be challenging. Finally, micro-climat models allow to simulate LST at high spatial and temporal resolutions up to district scale, provided that meteorological data are available and that the scene parametrization is correct. Each approach has advantages and drawbacks in terms of accuracy, spatial and temporal coverage, but they can also benefits from a combined used.