Radiative and derived thermal properties of urban surface materials using APEX imaging spectroscopy data

In the frame of the urban climate module of the HyperSwissNet-project, the city of Basel, Switzerland, was scanned with the imaging spectrometer APEX in June 2010. APEX measures reflected radiation in 313 spectral bands in the range 380 to 2500 nm. Data pre-processing includes radiometric calibration, atmospheric and geometric correction resulting in georectified spectral reflectance data covering an area of 3 x 5 km 2 . The Spectral Angle Mapper (SAM) classifier was used to separate surface materials. Broadband albedo was calculated from spectral reflectance data considering the ratio of direct to diffuse incoming radiation, the respective spectral weighting functions and the local horizon. The combination of surface material map and broadband albedo map with a high resolution (1x1 m 2 ) building model allows for a detailed analysis of the radiation properties of urban surfaces, including effects of inclined surfaces, street canyons and shadows. The thermal properties of surface material classes combined with surface brightness temperatures provide a new high resolution data base for the estimation of the heat storage term in the urban energy balance.