Influences of urbanization on surface characteristics as derived from the Moderate-Resolution Imaging Spectroradiometer: A case study for the Beijing metropolitan area

Moderate-Resolution Imaging Spectroradiometer (MODIS) global land surface temperature/emissivity (LST), vegetation indices, BRDF/Albedo and land cover products collected for the period of March 2000 to March 2006 are combined with the surface heat fluxes retrieved from MODIS as well as meteorological data to investigate the influence of urbanization associated with the surface characteristics of the city of Beijing. The results show that the use of different rural areas in the urban heat island (UHI) calculation influences the value of UHI and its seasonal variation. Daytime UHI shows a distinct seasonal variation, the maximum during summer being larger than 10 degrees C, while conspicuous negative UHI occurs in winter and spring. Seasonal variation of nighttime UHI is much less. The contrast in thermal inertia between rural and urban areas, anthropogenic heat from the urban area and less latent heat flux over urban areas are the main factors influencing daytime UHI, whereas anthropogenic heat controls the nighttime UHI. Surface broadband emissivity derived from MODIS LST/emissivity for the urban area is nearly equal to the rural areas. Surface albedo over the urban area is 0.03-0.08 less than that of rural areas, but aerosols substantially reduce surface incoming solar radiation over the urban area, which results in the surface absorbed solar radiation being nearly equal for urban and rural areas during autumn. Diurnal variation of UHI demonstrates a distinctively seasonal variation. The accuracy of MODIS LST is investigated and it was found that the influence of satellite view angle on the calculated UHI is small enough to be ignored.