Derivation of Nighttime Urban Air Temperatures Using a Satellite Thermal Image

The aim of this study is to characterize the urban heat island (UHI) intensity in Hong Kong. The first objective is to explore the UHI intensity in Hong Kong by using the mobile transverse and remote sensing techniques. The second objective is to produce a satellite-derived air temperature image by integrating satellite remote sensing with a mobile survey, the methodology involved in making simultaneous ground measurements when the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite made an overpass. The average UHI intensity of Hong Kong was about 2 degrees-3.5 degrees C, although a very high value of 12 degrees C UHI was observed on a calm winter night by ASTER. The satellite-derived surface temperature was compared with the in situ measurements. The bias was found to be only about 1.1 degrees C. A good correlation was also found between the in situ surface and air temperature pair of readings at nighttime on 31 January 2007. The linear regression lines of temperatures in urban and suburban areas were then used to convert the satellite-derived surface temperatures into air temperatures. The satellite-derived air temperatures showed a good correlation with temperatures observed by 12 fixed stations. It is possible to derive the nighttime air temperature from the satellite surface temperature on calm and clear winter nights.