In mountain regions such as Lake Sevan basin, landscape-ecological problems are manifested sharply. Lake Sevan basin lies in the east of the RA （Republic of Armenia） and is characterized by unique natural and econom...In mountain regions such as Lake Sevan basin, landscape-ecological problems are manifested sharply. Lake Sevan basin lies in the east of the RA （Republic of Armenia） and is characterized by unique natural and economic peculiarities. It covers an area of 4,891 km^2, or 16% of the entire territory of the country. The article considers the dynamics of the ecosystems of Lake Sevan basin through remote sensing data. To achieve the stated goal, multi-zonal satellite images Landsat ETM （Enhanced Thematic Mapper Plus）, Landsat TM （Thematic Mapper） and Landsat MSS （Multispectral Scanner） were applied. All satellite imagery data was geometrically and atmospherically corrected. Temporal changes were determined using both a supervised classification approach and NDVI （normalized difference vegetation index） in that time series. Supervised procedure, a hierarchical land cover classification system was used to detect the different land cover classes in the Lake Sevan basin, Armenia. According to this system, four land cover categories exist in this area： （1） water; （2） vegetation-bare; （3） man-altered land; （4） vegetated land, which indicate that for the last 40 years the study area has displayed expansion of man-made landscapes and vegetation-bare sites, ecosystems having lower biomass and reduction of woodlands. NDVI values and the area they covered indicate that between 1973 and 2011, the area of almost non-vegetated lands increased approximately by three times. The main cause of such changes is activation of erosion processes as a result of a climate warming.展开更多
直流偏置光正交频分复用(DC-biased optical orthogonal frequency division multiplexing,DCO-OFDM)可见光通信(visible light communication,VLC)系统具有较高的峰均功率比(peak-to-average power ratio,PAPR)。为解决此问题,提出一...直流偏置光正交频分复用(DC-biased optical orthogonal frequency division multiplexing,DCO-OFDM)可见光通信(visible light communication,VLC)系统具有较高的峰均功率比(peak-to-average power ratio,PAPR)。为解决此问题,提出一种联合限幅和归一化μ律压扩算法抑制DCO-OFDM系统的PAPR。首先,该联合算法利用限幅操作对时域信号中的大峰值信号进行削波来降低信号的幅值;其次,对限幅后的信号再进行压扩变换。通过这种联合算法,DCO-OFDM系统的PAPR可以显著降低。实验仿真结果表明,当采用16QAM调制方式,互补累计函数的值为10^(-3)时,相比较于联合限幅和传统μ律压扩算法,此联合算法的PAPR下降了约2.206 dB。展开更多
文摘In mountain regions such as Lake Sevan basin, landscape-ecological problems are manifested sharply. Lake Sevan basin lies in the east of the RA （Republic of Armenia） and is characterized by unique natural and economic peculiarities. It covers an area of 4,891 km^2, or 16% of the entire territory of the country. The article considers the dynamics of the ecosystems of Lake Sevan basin through remote sensing data. To achieve the stated goal, multi-zonal satellite images Landsat ETM （Enhanced Thematic Mapper Plus）, Landsat TM （Thematic Mapper） and Landsat MSS （Multispectral Scanner） were applied. All satellite imagery data was geometrically and atmospherically corrected. Temporal changes were determined using both a supervised classification approach and NDVI （normalized difference vegetation index） in that time series. Supervised procedure, a hierarchical land cover classification system was used to detect the different land cover classes in the Lake Sevan basin, Armenia. According to this system, four land cover categories exist in this area： （1） water; （2） vegetation-bare; （3） man-altered land; （4） vegetated land, which indicate that for the last 40 years the study area has displayed expansion of man-made landscapes and vegetation-bare sites, ecosystems having lower biomass and reduction of woodlands. NDVI values and the area they covered indicate that between 1973 and 2011, the area of almost non-vegetated lands increased approximately by three times. The main cause of such changes is activation of erosion processes as a result of a climate warming.
