The structure of the ground-level heat island in a central business district.

Ground level temperature variations in Johannesburg were estimated from airborne infrared scanner images. During predawn flights over the city center and vicinity, radiances were observed from a 1-km wide swath under clear skies with a strong nocturnal inversion. The image was rescanned with the aid of a densitometer and the data were clustered to a 20 X 76 matrix. In order to locate the heat island center, the distance correlation matrix (DISTCORMAT) method was used. The spatial structure of the ground heat island cores shows a steep thermal gradient approximately 600-700 m from the city center, which fits the screen-level temperature distribution obtained previously using a meteorological mobile unit. In addition to the fact that the heat island center does not coincide with the highest ground elevation, the findings support the empirical contribution of the centrality factor to the study of heat island magnitude and structure.-Author