Since the launch of its first satellite in 1972,the Landsat program has operated continuously for more than forty years.A large data archive collected by the Landsat program significantly benefits both the academic community and society.Thermal imagery from Landsat sensors,provided with relatively high spatial resolution,is suitable for monitoring urban thermal environment.Growing use of Landsat data in monitoring urban thermal environment is demonstrated by increasing publications on this subject,especially over the last decade.Urban thermal environment is usually delineated by land surface temperature (LST).However,the quantitative and accurate estimation of LST from Landsat data is still a challenge,especially for urban areas.This paper will discuss the main challenges for urban LST retrieval,including urban surface emissivity,atmospheric correction,radiometric calibration,and validation.In addition,we will discuss general challenges confronting the continuity of quantitative applications of Landsat observations.These challenges arise mainly from the scan line corrector failure of the Landsat 7 ETM+ and channel differences among sensors.Based on these investigations,the concs are to:(1) show general users the limitation and possible uncertainty of the retrieved urban LST from the single thermal channel of Landsat sensors;(2) emphasize efforts which should be done for the quantitative applications of Landsat data;and (3) understand the potential challenges for the continuity of Landsat observation (i.e.,thermal infrared) for global change monitoring,while several climate data record programs being in progress.