Thermal Infrared Imaging of the Urban Landscape to Understand Urban Microclimate

Thermal remote sensor data have been widely used in urban climate and environmental research. The urban geometry, however, hinders a nadir-looking radiometer to observe all urban facets, which makes the observed urban radiometric surface temperature (Tr) different from the urban complete surface temperature (Tc). The T c of all urban facets conveys complete information on the response of the urban surface to radiometric and convective forcing. In this chapter, we firstly examined the limitations of three current most popular surface temperature retrieval methods for radiometric surface temperature retrieval. Then, we discussed a methodology using precisely designed numerical experiments through an urban micro-climate model to help understand thermal radiative transfer within the built-up space and the relationship between observed T r and T c. Specifically, T r is firstly retrieved from radiance observed at the top of atmosphere over urban areas by applying corrections for atmospheric and emissivity effects. Numerical experiments are designed to evaluate different combinations of urban geometry with the configuration of radiometric observations to construct the relationships between T r and T c. Finally, T c is estimated by using such relationships. T c can then be used for urban climate and environment research. We further present a case study to demonstrate the methodology discussed above, which was based on the estimation of T c from satellite TIR data under the condition that the urban areas have no vegetation or negligible vegetation. Lastly, we discussed some challenges that need to be addressed in the future for improving the applicability of thermal infrared remote sensing in urban areas.