A design of low-light-level night vision system is described,which can image objects selectively in the specific space. The system can selectively image some objects in specific distances,meanwhile ignore those shelte...A design of low-light-level night vision system is described,which can image objects selectively in the specific space. The system can selectively image some objects in specific distances,meanwhile ignore those shelters on the way of observation by combining an intensifying charge coupled device(ICCD) with a near infrared laser assisted in vision,whose operation wavelength matches with the photocathode of the image tube,and adopting the gated mode and adjustable time-delay. A semiconductor laser diode of 100 W in peak power is chosen for illumination. The laser and the image tube operate in 150 ns pulse width and 2 kHz repeat frequency. Some images of different objects at the different distances within 100 m can be obtained clearly,and even behind a grove by using a sampling circuit and a delay control device at 100 W in peak power of semiconductor laser diode,150 ns in pulse width of laser and image tube,2 kHz in repeat frequency.展开更多
Due to infrequent rainfall, high temperatures, and degraded land, the Sahel region often suffers from droughts. The Sahel region is considered as one of the world’s driest and extreme environmental conditions. In ord...Due to infrequent rainfall, high temperatures, and degraded land, the Sahel region often suffers from droughts. The Sahel region is considered as one of the world’s driest and extreme environmental conditions. In order to assess spatiotemporal vulnerability of potential drought impacts, we used remote sensing and ground station data to evaluate drought conditions in the Sahel region from 1985 to 2015. The standard precipitation index(SPI), standard precipitation evapotranspiration index(SPEI), vegetation condition index(VCI) anomaly, along with socioeconomic indicators were performed. In addition, Pearson correlation coefficient(PCC) was computed between drought indices and three main crops(sorghum, millet, and maize) in the region to estimate the effects. The analysis showed that temperature increased by 0.78°C from 1985 to 2015, which had a significant impact on crop yield for sorghum, maize, and millet with a statistical significance value of P > 0.05. In the decade spanning 1994 to 2005 alone, the temperature increased by 0.57°C, which resulted in extreme drought in Algeria, Sudan, Chad, Nigeria, and Mauritania. For the effect of drought on crop production, high significance was noted on the SPI and SPEI-3 timescale: sorghum with SPI-3(r = 0.71) and SPEI-3(r = 0.65), millet with SPI-3(r = 0.61) and SPEI-3(r = 0.72), and maize with SPI-3(r =0.81) and SPEI-3(r = 0.65) during the study period. In the growing season, VCI anomaly had strong correlations with sorghum and millet(r = 0.67 and 0.75, respectively). A significant agreement was also noticed between the combined drought index(CDI) and vulnerability index(VI) in Burkina Faso(r =-0.676;P < 0.00), Mali(r =-0.768;P < 0.00), Mauritania(r = 0.843;P < 0.001), Niger(r =-0.625;P < 0.001), and Nigeria(r =-0.75;P < 0.005). The results show that the above indices are effective in assessing agricultural drought and its impact on crop production in the Sahel, and in identifying areas most affected by drought.展开更多
文摘A design of low-light-level night vision system is described,which can image objects selectively in the specific space. The system can selectively image some objects in specific distances,meanwhile ignore those shelters on the way of observation by combining an intensifying charge coupled device(ICCD) with a near infrared laser assisted in vision,whose operation wavelength matches with the photocathode of the image tube,and adopting the gated mode and adjustable time-delay. A semiconductor laser diode of 100 W in peak power is chosen for illumination. The laser and the image tube operate in 150 ns pulse width and 2 kHz repeat frequency. Some images of different objects at the different distances within 100 m can be obtained clearly,and even behind a grove by using a sampling circuit and a delay control device at 100 W in peak power of semiconductor laser diode,150 ns in pulse width of laser and image tube,2 kHz in repeat frequency.
基金Supported by the National Key Research and Development Program of China(2019YFC1510203 and 2018YFC1506502)Fundamental Research Funds for Central Non-profit Scientific Institution(1610132020014)Open Fund of State Key Laboratory of Remote Sensing Science(OFSLRSS201910)。
文摘Due to infrequent rainfall, high temperatures, and degraded land, the Sahel region often suffers from droughts. The Sahel region is considered as one of the world’s driest and extreme environmental conditions. In order to assess spatiotemporal vulnerability of potential drought impacts, we used remote sensing and ground station data to evaluate drought conditions in the Sahel region from 1985 to 2015. The standard precipitation index(SPI), standard precipitation evapotranspiration index(SPEI), vegetation condition index(VCI) anomaly, along with socioeconomic indicators were performed. In addition, Pearson correlation coefficient(PCC) was computed between drought indices and three main crops(sorghum, millet, and maize) in the region to estimate the effects. The analysis showed that temperature increased by 0.78°C from 1985 to 2015, which had a significant impact on crop yield for sorghum, maize, and millet with a statistical significance value of P > 0.05. In the decade spanning 1994 to 2005 alone, the temperature increased by 0.57°C, which resulted in extreme drought in Algeria, Sudan, Chad, Nigeria, and Mauritania. For the effect of drought on crop production, high significance was noted on the SPI and SPEI-3 timescale: sorghum with SPI-3(r = 0.71) and SPEI-3(r = 0.65), millet with SPI-3(r = 0.61) and SPEI-3(r = 0.72), and maize with SPI-3(r =0.81) and SPEI-3(r = 0.65) during the study period. In the growing season, VCI anomaly had strong correlations with sorghum and millet(r = 0.67 and 0.75, respectively). A significant agreement was also noticed between the combined drought index(CDI) and vulnerability index(VI) in Burkina Faso(r =-0.676;P < 0.00), Mali(r =-0.768;P < 0.00), Mauritania(r = 0.843;P < 0.001), Niger(r =-0.625;P < 0.001), and Nigeria(r =-0.75;P < 0.005). The results show that the above indices are effective in assessing agricultural drought and its impact on crop production in the Sahel, and in identifying areas most affected by drought.
