Mapping and Modeling of Urban Surface Thermal Radiation

A study was carried out measuring the surface temperatures of buildings stretching for eight miles along the West Side of Manhattan in New York City. This was followed by modeling the surface thermal radiation of two blocks with different construction densities. The measurements were done using a long-wave hyperspectral imager with 128 spectral bands, providing a spatial resolution of one meter, temporal resolution of three minutes and sub-kelvin degree accuracy. This was achieved by the derivation of the emissivity, a factor which is a mixture of physical and geometrical characteristics of the surfaces. The atmospheric effects were corrected for and surface temperatures were compared with the modeled temperatures. For the modeling, we used the digital surface map of NYC, and considered a geometrically structured two-dimensional surface composed of joined polygons. Each polygon was characterized by an emissivity, surface thickness, and thermal conductivity. On the inside of the surface a local equilibrium temperature was assumed. The equilibrium temperatures on the outside surfaces were computed and determined by equating the internal and external net flux densities for each polygon. This calculation included sum of the incoming fluxes from the sky and those scattered from all other visible polygons, as well as the heat radiated by the surface. Results comparing the measured and the modeled temperatures will be presented.