Airborne experimental measurements of the angular variations in surface temperature over urban areas: case study of Marseille (France)

The directional surface temperatures over urban areas are measured using an airborne TIR camera equipped with wide-angle lenses. The experimental design is described and the possible sources of errors related to the instruments and the atmosphere are analysed and corrections proposed. The data acquisition protocol is adapted to provide directional TIR measurements in a −60° to +60° range for zenith and 0 to 360° for azimuth view angles. Two parts of the city of Marseille, the densely built old city centre and a built/vegetated mixture of individual houses and gardens in a suburb, have been studied during summer 2001 in the framework of the UBL-ESCOMPTE project. The results obtained reveal important hot spot effects and differences of surface brightness temperatures varying between −5 and 7 K between nadir and off-nadir measurements, according to azimuth view angles. Acquisitions performed over the two areas also illustrate the impact of the surface structure and presence of vegetation on the hot spot. An example application for the correction of two temporal series of NOAA 14 and NOAA 16 data is given.