Urban surface is one of the most important land cover types in the land surface ecosystem. Investigations on thermal radiation features of urban surfaces are helpful for researches about energy balance in urban environments and urban heat islands (UHIs). Thermal anisotropy in urban areas is more significant than that of natural surfaces. However, related researches have been slowed down. In recent years, observations onboard air-crafts and ground platforms have revealed that thermal anisotropy in urban area is related to the geometric conditions of sun-ground targets-sensor, the configurations and physical features of urban areas. In addition, models for describing the radiative temperature patterns, geometric relationships and radiative transfer schemes in urban areas have been proposed by literatures. In this study, the progresses of researches about thermal anisotropy in urban areas have been reviewed from several aspects, including experiments, modeling and the relationships between thermal anisotropy and surface UHI. It is also pointed out that the issues remain further investigation.
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