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Monitoring urban heat environment using MODIS data for main cities in East Asia

Shiro Ochi, Daisuke Uchihama,
Wataru Takeuchi, Yoshifumi Yasuoka

Institute of Industrial Science, University of Tokyo.
Email : [email protected], [email protected], [email protected]

Abstract
TERRA /MODIS has 3 different modes of spatial resolution – 250m, 500m and 1000m – with 36 spectral bands in total and it covers the whole region of the earth both in day-time and night-time every day. The combination of spatial, spectral and time resolutions is considered to be more effective to monitor the regional heat environment associated with the land cover than the data of NOAA/AVHRR. The MODIS ground station at University of Tokyo covers the east part of Asia and data have been archived from May, 2001. In this study, major cities in the East Asia such as Tokyo, Seoul, Pyongynag, Peking and Shanghai are picked up for analysis, and the urban heat environments of the cities were monitored using MODIS data. The land cover characterization and the “Heat Island Intensity” were analyzed by comparing the summer images versus the winter images as well as day time images versus night time images. A method to normalize the hear environment of urbanized areas among different cities with different climatic conditions are proposed. The study concluded that the hear flux is most significant in Tokyo and it is about 100 times larger than that of Pyongyan in the summer-day time and 70 times in the summer-night time.

Introduction
The “Heat Island” is expanding for many big cities in the world, and the phenomenon is analyzed in terms of local/regional energy balance, economic activities, climatic aspect and so on. It is discussed as the site-specific issue5), however it is occurring in many places in global scale with different intensity. It seems to be important to analyze the heat island phenomenon among cities in different geographic location to understand the mechanism of it and forecasting the progress of it, because different stages of the heat island are exist and they are developing in different development stages.

The Institute of Industrial Science, University of Tokyo has been receiving NASA’s satellite “TERRA/MODIS” data starting from May, 2001 in order to monitor the environment and disaster parameters around the East Asia6). A project was launched to analyze and assess the environment and disasters of main cities in Asia. In order to acquire TERRA data for expanded continental-scale change researches into the Southeast Asian sub-region, the IIS has provided Asian Center for Research on Remote Sensing, AIT one identical MODIS receiving facility. That station is managed by the Joint Management Committee composing of ACRoRS (AIT), Geo-Informatics and Space Technology Development Agency (Thailand).

In this study, the comparison of the heat island intensity for cities in East Asia, different stages of economic development in different geographic locations.

Data used
In this study, five cities are picked up for analyzing the heat environment so called heat island. The cities are: Tokyo (Japan), Seoul (South Korea), Pyongyang (North Korea), Beijing and Shanghai (China), those are within the coverage of the ground station of Univ. of Tokyo, Komaba, and Tokyo. Table-1 shows the list of data used in this study. In order to obtain cloud free data, the date for summer data and winter data, and the time for day-time data and night-time data are not unified. For example, the date of summer-night data for Tokyo is 2nd of June, which is rather early comparing the date for summer-day data, which is observed on 24th of July. In this study, the differences are modified by normalized methodology.

Table-1 List of Data used

City Summer/Winter Day/Night Date Local Time G M T
Tokyo Summer Day 2001/07/24 10:36 01:36
Night 2001/06/02 22:04 13:04
Winter Day 2001/11/23 11:08 02:08
Night 2001/11/23 22:11 13:11
Seoul Summer Day 2001/08/27 11:59 02:59
Night 2001/08/27 23:03 14:03
Winter Day 2001/11/19 11:32 02:32
Night 2001/11/19 22:35 13:35
Pyongyang Summer Day 2001/08/27 11:59 02:59
Night 2001/08/22 22:45 13:45
Winter Day 2001/11/19 11:32 02:32
Night 2001/11/19 22:35 13:35
Peking Summer Day 2001/08/21 11:33 03:33
Night 2001/08/20 21:57 13:57
Winter Day 2001/11/20 11:13 03:13
Night 2001/11/20 22:17 14:17
Shanghai Summer Day 2001/07/21 10:42 02:42
Night 2001/0917 22:19 14:19
Winter Day 2001/10/30 10:56 02:56
Night 2001/10/30 22:00 14:00

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.

Results
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

Tokyo Seoul Pyongyang Peking Shanghai
Summer/Day time 107 43 1 52 18
Summer/Night time 70 21 1 10 5
Winter/Day time 59 22 1 -1 12
Winter/Night time 1 -4 1 35 1

Conclusion
In this study, the land surface temperature was calculated using thermal band with 500m resolution TERRA MODIS data in combination with the visible band data of 250m resolution for 5 major cites in East Asia, and a methodology to indicate the heat flux of urban area to estimate of the heat island phenomenon from the satellite images under the different geographic, climatic conditions. The method enables the comparison of heat flux for the 5 cites using the MODIS data.

Continuous observation will be made for more quantative analysis in terms of heat flux as well as the vegetation function to reduce the heat island phenomenon, using long term satellite information which avoid the temporal error such as local climatic condition including the whether of the observation day and time, and sensor anomalies. Furthermore, some more cities from South East Asia such as Bangkok, Hanoi, Hochimin city, Jakarta, Kuala Lumpur, Singapore, covered by Bangkok broadcasting station will be added for the study.

References

  1. MODIS Characterization Support Team: MODIS Level 1B Product User’s Guide for Level 1B Version 2.3x Release 2, 2000 Internet WEB Page
  2. NASA EOS: EOS AM-1 brochure,2000 Internet WEB Page
  3. NASA Jet Propulsion Laboratory: ASTER Spectral Library,2000 Internet WEB Page
  4. MODIS UCSB ICESS: MODIS UCSB Emissivity Library, Internet WEB Page
  5. (Japanese) Ministry of Environment of Japan, HEAT ISLAND, Internet WEB Page
  6. Institute of Industrial Science, Univ. of Tokyo, MODIS DB Reception Facility at IIS, Internet WEB Page
  7. Japan Association of Remote Sensing, Remote Sensing Note, p14, 1996