Thermo-radiative modeling and energy balance of the urban canopy: relations between simulated and measured temperatures

When studying an urban fragment (~ 10^4 m2), the presence of horizontal (ground and vegetation), vertical (walls) and oblique (roofs) elements implies complex descriptions of the 3D model and of the associated temperatures. Parametrical relations must be established between the different “surface temperatures” (physical temperature, aero-dynamical temperature, radiative temperature), taking into account the geometrical features and the micro-meteorological conditions of the urban fragment. To construct these relationships, numerical simulations are carried out with micro-scale, thermo-radiative and aerothermodynamical transfer models.

The software SOLENE simulates the air-solid thermo-radiative transfers with fine meshes (metric facets) and the restitution of the visible and thermal infrared radiative fluxes towards the sky or a virtual sensor. Parameterizations of heat exchange through walls are also introduced, with several layers. The basic configurations of urban fragment simulations reproduce the configurations of the experimental data files, obtained during two intensive observation periods of UBL-Escompte, in Marseilles, and CAPITOUL, in Toulouse. After computation of the simulated physical surface temperatures, virtual TIR sensors are introduced to evaluate the radiant temperature of the observed walls, with various types of sensor configuration: airborne or satellite, in oblique or vertical sighting. Then, infrared measurements from these virtual sensors are compared with the different calculated energy flows.

The final aim is to evaluate the heat flux to the atmosphere, from the infrared very high resolution remote sensing, for the currently operational sensors, e.g., to correlate the sensible heat flux to the infra-red values measured from nadir-aiming satellites.