Airborne video thermal radiometry as a tool for monitoring microscale structures of the urban heat island
Abstract. An advance thermal video radiometer (TVR) was mounted onboard a helicopter and used to collect data over Tel-Aviv, Israel, from an altitude of 7000 feet. The sensor, sensitive to the 3-12 mu m spectral region, consisted of an onboard calibration device and a 1.8 mRad instantaneous field of view (IFOV), which enabled direct assessment of surface radiometric temperature patterns in very high spatial and thermal resolutions. The TVR capability was examined by studying the microscale structures of the urban heat island (UHI) of Tel-Aviv, Israel, during a stable calm night on 28 February 1995. The TVR data were found to be of high quality in terms of signal to noise ratio, reproducibility, stability, thermal sensitivity and spatial resolution capabilities. The radiometric data were analysed against air temperature acquired during the flight time by four mobile traverses that crossed the city from north to south. A significant heat island was identified over the inner city areas, which was found to be 5 C warmer than the rural areas located 4 km to the south-east. Throughout the city, asphalt was found to be the major heat source whereas vegetation was found to be the most cooling element. A linear regression analysis between the air and radiometric temperatures showed that in general, good agreement exists between the two temperatures. Along the western routes (A and B) the correlation was relatively higher than that along the eastern routes (C and D) and was significantly different in the linear regression slope a . We assume that differences in atmospheric conditions, especially in the water vapour variation throughout the city, caused these inconsistencies. We concluded that the examined TVR is a very promising, low-cost remote sensing sensor, which can rapidly and quantitatively monitor the UHI in very high spatial and thermal resolutions from a high altitude. Based on these results we strongly recommend that the TVR be further examined in other remote sensing applications.