Analysis On Urban Heat Island And Air Quality

With the acceleration of urbanization, the phenomenon of temperature in urban cities which is higher than that in suburbs is called Urban Heat Island (UHI), which is put forward by Lake Howard[1] in 1833. This paper chose split window algorithm to retrieve land surface temperature after comparing with single window algorithm, split window algorithm and multi-band algorithm. And this paper improves the split window algorithm of AVHRR, so as to be suitable for MODIS image data. In this paper, land surface temperature is retrieved by split window algorithm based on MODIS images, and the temporal and spatial characteristics of Beijing urban heat island as well as its influencing factors are also analyzed. The result indicates that there is a clear urban heat island in summer, and it is quite close with vegetation index. Besides, the negative correlation relationship between land surface temperature and PM10 is also emphasizely analyzed.Land surface temperature (LST) plays an important role in energy balance of land surface and widely used in quite many fields. For example, soil moisture survey, forest fire monitoring, discrimination of geothermal locations, military camouflage applications and even deposit research, all these can not be separated from the land surface temperature. With the development of remote sensing applications, Single channel algorithm, split window algorithm and multi-band algorithm are the three algorithms of land surface temperature retrieval of existing thermal infrared remote sensed data. At first, this paper chooses split window algorithm after comparing the three algorithms and improves the split window algorithm of AVHRR, so as to be suitable for MODIS image data. This split window algorithm is based on the thermal radiation data which is observed by NOAA—AVHRR. With the basis of thermal radiation function, the brightness temperature can be translated from the two corresponding thermal channels (channel 4 and 5) of AVHRR, and that is to say: Choose MODIS 31(10. 780- 11. 280μm)and 32(11. 770- 12. 270μm)to take the place of the thermal channels (4,10.5-11.3μm and 5,11.5-12.5μm)of AVHRR. Secondly, this thesis discusses how to determine atmospheric transmittance and land surface emissivity, which are the two basic parameter of split window algorithm. Atmospheric transmittance can be retrieved by MODIS 2 and 19 with the relationship of the moisture of atmosphere and atmospheric transmittance. Thirdly, Land surface emissivity mainly depends on the structure of land surface substance, especially the vegetation index, and so land surface emissivity can be obtained by the land surface classification and vegetation index. Finally, land surface temperature can be retrieved through the land surface temperature model, and then the thesis analyses the retrieval precision and error causes.The result indicates that there is a clear urban heat island in summer and autumn, especially summer, with its maximum of not only the intensity but also the area. UHI seems does not exist in spring. In winter, urban cold island effect appears and takes the place of urban heat island. Another conclusion: the land cover types are sensitive to urban heat island effect, and there is a significant negative correlation between vegetation index and distribution of the urban heat island. That is to say: the higher land surface vegetation cover, the less urban heat island is. Therefore, land surface vegetation cover plays an important role on reducing urban heat island.Atmospheric aerosol refers to particles of small-scale range of 0.001-20μm size of liquid or solid caused by natural processes and human activities, which are suspended in the atmosphere. Aerosol plays an important role on weather and climate, while impacts the living environment of mankind. This paper takes Beijing area as an example ,the aerosol optic depth of Beijing has been tried to retrieve using DDV(Dark Dense Vegetation) method from MODIS 1B data. Firstly , the Look Up Table is built by 6S , the dark dense pixel is checked based on NDVI and the retrieved AOD(Aerosol Optical Depth) is validated by the comparation. The results show the DDV method can be used to monitor the urban aerosol very well during the summer in Beijing. analysis of geographic situation combined with Beijing and its surrounding area, the specific is as follows: AOD has higher value in densely populated areas, transportation, and areas of industrial and frequent commercial activities. High-resolution satellite remote sensing results has potential value in monitoring the distribution of emission sources,and can be characterized to the status of air quality in Beijing on a certain extent.Compared the land surface temperature to aerosol optical depth of Beijing on the horizontal scale in the space, this paper taking summer as an example, and find both land surface temperature and AOD have higher value in densely populated areas, transportation, and areas of industrial and frequent commercial activities, but urban heat island and air pollution of Beijing come mainly from the city itself, and temperature effects AOD is not great. the temperature can be characterized urban heat environment on a cetain extent. AOD after revising the vertical and humidity impact can be used to monitor the distribution of particulate matter pollutants in the ground as an effective means,and AOD can be the characterization of urban pollution. Respirable particulate matter is the most important air pollutant of Beijing at present. This paper combines the Municipal Environmental Protection Agency of Beijing air quality conditions and ground measurements, and analyses the relationship between temperature and respirable particulate matter from the microscopic, and finds that the temperature affectes the number of respirable particulate matter little. The number of particles can be decreased as the temperature increases,that is to say: The higher the temperature is, the lower the number of respirable particulate matter is.