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Monitoring urban heat environment using MODIS data for main cities in East Asia
Methodology Fig-1 shows the data processing flow in this study. The first step of the study is to make the land cover classification. TERRA /MODIS has 3 different modes of spatial resolution - 250m, 500m and 1000m - with 36 spectral bands in total. 
Fig-1 Processing Flow In the study, the land cover characterization as made sing 250m resolution optical images with categories of build up, forest, grass, water body and bare soil. The classification result is used to provide the emissivities of the land cover categories7). Then emissivity is used to estimate the land surface temperature from the brightness temperature value in the thermal band image with 500m resolution data1,2,3,4). Finally the heat island impact was analyzed. However, the land surface temperature is influenced by the geographic condition such as the climate and whether at the time of the area, so that it is difficult to compare the temperature itself to indicate the heat island intensity. In order to compare the heat island impact among the cities, the normalized surface temperature images were prepared by equalizing the temperature values of forested region (veg-2 in the classification category in this study) in suburbs where the heat island effect is supposed to be unrelated. Fig-2 shows the method to calculate the normalized land surface temperature. In this study the temperature at vegetation-2 category in Seoul image was used as the parameter for normalizing the land surface temperature for other cities. 
Fig-3 shows the results of the analysis. The left column of the figure shows the images of 250m resolution data composed with red-band/red-plain, infrared-band/green - plain, and infrared-band/blue-plain, for 5 cities. The right column shows the land surface temperature images for the cities. After normalizing the surface temperature using the surface temperature on the vegetated region classified as "vegetation-2" at the land cover classification, the heat flux intensity was calculated. Table-2 shows the comparison of the accumulated heat flux intensity within the urban area delineated with same area for the 5 cities. In this table, the heat flux intensity of Pyongyans is set as "1" for summer-day, summer-night, winter-day, winter-night, and the intensities for 4 other cities with 4 different season and time are calculated respectively. From this table, the heat flux intensity from Tokyo is most significant among the 5 cites, except the winter-night time. The second significant city is Seoul, however the heat flux intensity of Peking is most significant in the winter-night time among the 5 cites, and second significant at the summer- day time. The analysis was made using the single image for the 4 different season/time series(Summer, Winter, Day and Night), therefore, there might exists some reasons excluding the heat island impact, such as geographic, climatic and local conditions influencing the local heat flux on the day observed by the satellite. 
Table-2 Comparison of heat flux intensity among 5 cities
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