Relating the Observed Brightness Temperature by Landsat to the Air Temperature Distributions and the Structure of Urban Canopy Layer in Hiroshima City, Japan
1995 Volume 104 Issue 2 Pages 225-238
Details
1995 Volume 104 Issue 2 Pages 225-238
Thermal infrared imageries of the LANDSAT Thematic Mapper (TM) band 6 are compared to the air temperature distributions and the geometry and materials of the urban area in Hiroshima City (132.5 °E, 34.4 °N), Japan, to extract the information on the urban heat island from the images. The results are summarized as follows :
(1) Surface heat island is recognized on the LANDSAT TM nighttime thermal image taken at 21 JST on May 17, 1991. The distribution of brightness temperature matches closely with the air temperature distribution at 21 JST on MAY 19, 1992 (thermal image at that time was not able to be taken because of clouds). The discrepancy between air temperature and brightness temperature, recognized in the southern part of the city, can be explained well by the advection caused by the land breeze.
(2) The daytime thermal images, which was taken at 10 JST on May 21, 1992, shows that brightness temperature at the central part of the urban area is low compared with the suburban area. The part of low temperature is also recognized in the air temperature distribution observed at the same time of the satellite overpass.
(3) The distribution maps of height, surface area, volume and lot size of buildings are produced to compare the brightness temperature with the structure of the urban area. Brightness temperature is high along the major roads in the nocturnal thermal image. These parts correspond to the area where the buildings with high roof level, large lot size, large volume and large surface area are distributed. In these areas, daytime storage of heat and release of it at evening is considered to be important.
(4) The interior of the blocks surrounding to the major roads shows relatively low brightness temperature. The area corresponds to the densely built-up area with low roof buildings or the open spaces such as school grounds and parks. Rapid radiative cooling in these areas is important to the formation of brightness temperature contrast in the blocks.
