Study of the urban heat island of Athens, Greece during daytime and night-time

This study focuses on mapping and analyzing the daytime and night-time surface urban heat islands (UHIs) of the Athens metropolitan area, in Greece. For the needs of the study, two satellite thermal images of the city of Athens were acquired; a night-time image from the advanced spaceborne thermal emission and reflection radiometer (ASTER) sensor onboard Terra and a daytime image from the thematic mapper (TM) sensor onboard Landsat 5 (L5) dated on 11 October 2003 and 12 October 2003, respectively. The images are selected for the following reasons: (a) the year 2003 is classified by the National Observatory of Athens as one of the 6 warmest years of Athens temperature record, with October of 2003 included among the 10 warmest October of the record and (b) both images correspond to cloud-free atmospheric conditions with the daytime image recorded 12 hours later than the night-time image. The spatial inter-urban surface temperature patterns of the city during the day and night produced from the satellite images are examined and analyzed in relation to the different types of urban land cover and use obtained from the Corine Land Cover 2000 (CLC00) database for Greece. Urban land covers producing the highest surface temperatures (hot spots) are identified and related to urban surface characteristics. In a GIS environment, statistics of mean surface temperatures (Ts) by day and night for 11 urban and 2 rural land covers are extracted. Based on these, daytime and night-time UHI magnitudes are estimated and analyzed. The results indicate the development of a "negative" UHI during daytime with a mean magnitude of 2degC and a strong night-time UHI magnitude with a mean value of 3.1degC and a maximum value of 6.5degC.