An application of NOAA AVHRR thermal data to the study of urban heat islands

Brightness temperatures were derived from the Advanced Very High Resolution Radiometer (AVHRR) at channel 4 (10.5–11.5 μm) on the NOAA-9 and NOAA-10 satellites to examine the applicability of the AVHRR thermal data to the study of urban heat islands. Air and ground surface temperatures measured at meteorological stations in large cities (population over 300,000) in South Korea were compared with in situ brightness temperature data.

The correlation coefficient between air temperatures and brightness temperatures is 0.85 and the relationship may be expressed by the regression: AT=0.59 BT + 2.54. This equation explains 73% of variances at the 0.02% significance level. The best-fit line, however, underestimates air temperatures in such heat-processing industrial cities as Ulsan and Pohang, where smoke puffs up from the high stacks of industrial plants, and overestimates them in the Seoul metropolitan area. The regression equation of ground surface temperatures on brightness temperatures explains 72% of variances. Assuming that optimal meteorological conditions can be selected, the regression equation can be used as a tool to assess air temperature fields in cities.

Urban land-use, such as built-up, residential and industrial areas, was clearly identified from the AVHRR thermal data, while small-scale land-use, like parks, were not distinguishable. Brightness temperatures for the intensity of heat islands were related to the population size of cities. The areal magnitude of heat islands in the Seoul metropolitan area expanded considerably, reflecting the conurbation trend for the period 1986–1989. Urban temperatures in the area increased during the period, while temperature gradients declined.