This study assesses surface urban heat island (UHI) and its associated surface physical characteristics using remote sensing approaches. TERRA/MODIS images acquired in 2005 in three different seasons were selected to ...This study assesses surface urban heat island (UHI) and its associated surface physical characteristics using remote sensing approaches. TERRA/MODIS images acquired in 2005 in three different seasons were selected to generate land surface tem-perature and surface characteristics for the Changsha-Zhuzhou-Xiangtan metropolitan area in China. The intensity of urban heat is-land effects and its seasonal variations were examined. The result showed that UHI effects were significant both in the summer and the spring. Land surface temperatures in the city were 8 ℃ to 10℃ warmer than those in surrounding rural areas in the spring and the summer seasons. Although UHI effects exist in winter, they are not significant. Land surface temperature in the city was 4℃ warmer than that in surrounding rural areas in winter. This study uses normalized difference vegetation index (NDVI) and normal-ized difference built-up index (NDBI) as indicators of surface physical characteristics and investigates the relationship among land surface temperature (LST), NDVI and NDBI. The results from this study indicate that, while the relationship between LST and NDVI changes in different seasons, there is a strong positive linear relationship between NDBI and LST for all seasons. The amount of slope and intercept of the linear relationship between NDBI and LST can indicate the magnitude of UHI for different seasons. This finding suggests that NDBI provides an alternative physical indicator for analyzing LST quantitatively over different seasons, and therefore providing a useful way to study UHI effects using remote sensing.展开更多
In this work, the terahertz （THz） electromotive force （EMF） of the surface plasmon （SP） electric field and field strength was investigated in its propagation direction. Based on the nanowires structure, we intro...In this work, the terahertz （THz） electromotive force （EMF） of the surface plasmon （SP） electric field and field strength was investigated in its propagation direction. Based on the nanowires structure, we introduced physical models which were light wave energy of surface plasmon polariton （SPP） pulse and the variation of EMF changes in the active condition. Results of theory and verification showed SPP generated EMF with 10-2-10 V among wire radii of 5-30 nm; the electric field was up to 10^5-1066V/cm in the radius of 5 nm; the electric field intensity induced localization at λ=850 nm, and at the same time light intensity amplified 40 times. The characteristics which are femtosecond SPP pulse response and force-field amplifier in this work are significant for nonlinear spectroscopy research.展开更多
基金Supported by the National Natural Science Foundation of China (No.40771198)the Hunan Provincial Natural Science Foundation of China (No.08JJ6023)
文摘This study assesses surface urban heat island (UHI) and its associated surface physical characteristics using remote sensing approaches. TERRA/MODIS images acquired in 2005 in three different seasons were selected to generate land surface tem-perature and surface characteristics for the Changsha-Zhuzhou-Xiangtan metropolitan area in China. The intensity of urban heat is-land effects and its seasonal variations were examined. The result showed that UHI effects were significant both in the summer and the spring. Land surface temperatures in the city were 8 ℃ to 10℃ warmer than those in surrounding rural areas in the spring and the summer seasons. Although UHI effects exist in winter, they are not significant. Land surface temperature in the city was 4℃ warmer than that in surrounding rural areas in winter. This study uses normalized difference vegetation index (NDVI) and normal-ized difference built-up index (NDBI) as indicators of surface physical characteristics and investigates the relationship among land surface temperature (LST), NDVI and NDBI. The results from this study indicate that, while the relationship between LST and NDVI changes in different seasons, there is a strong positive linear relationship between NDBI and LST for all seasons. The amount of slope and intercept of the linear relationship between NDBI and LST can indicate the magnitude of UHI for different seasons. This finding suggests that NDBI provides an alternative physical indicator for analyzing LST quantitatively over different seasons, and therefore providing a useful way to study UHI effects using remote sensing.
基金supported by the National Natural Science Foundation of China (Grant No. 60877047)the Natural Science Foundation of Hebei Province,China (Grant No. F20100002002)
文摘In this work, the terahertz （THz） electromotive force （EMF） of the surface plasmon （SP） electric field and field strength was investigated in its propagation direction. Based on the nanowires structure, we introduced physical models which were light wave energy of surface plasmon polariton （SPP） pulse and the variation of EMF changes in the active condition. Results of theory and verification showed SPP generated EMF with 10-2-10 V among wire radii of 5-30 nm; the electric field was up to 10^5-1066V/cm in the radius of 5 nm; the electric field intensity induced localization at λ=850 nm, and at the same time light intensity amplified 40 times. The characteristics which are femtosecond SPP pulse response and force-field amplifier in this work are significant for nonlinear spectroscopy research.
