Lu Junfeng

Land use and land cover change and its driving forces in the source region of the Yangtze River during 1990–2005

Land use and cover change (LUCC) is an important field in studying the global change or global warming. The source region of the Yangtze River locates in the northeast of Qinghai-Tibetan Plateau. The ecosystem there is extremely vulnerable and sensitive to global climate change and human activities, which have brought in significant change of eco-environment in this region in recent years. Therefore it is essential to investigate the land use and land cover change, and to explore its driving forces in the source of the Yangtze River. In this study, we used Landsat images obtained in 1990 and 2005 to establish databases of land use and cover. Then we derived LUCC information by overlaying these layers using GIS software. To examine the processes responsible for LUCC, we discussed its driving forces including climatic change, human activities, animal and insect damage. During the past 15 years, the forest, grassland experienced the most significant decrease. The forest and grassland decreased by 2509 hm2, 41847.1 hm2, respectively. However, unused land and water area showed the opposite trend, increased by 33903.8 hm2, 10480.1 hm2 respectively. The farmland and build-up land changed no obvious in past 15 years. These results suggested that the degradation of the eco-environment is obvious, showing a decrease in the forest, grassland, and an increase in the area of unused land. The major factors responsible for LUCC include increasing temperature, decreasing precipitation in summer and autumn, variation in the frozen soil environment, human activity (seasonal overgrazing) and rodent damage.

Designing a diffractive optical element for controlling the beam profile in a three-dimensional space using the simulated annealing algorithm

We have designed a spatially quantized diffractive optical element (DOE) for controlling the beam profile in a three-dimensional space with the help of the simulated annealing (SA) algorithm. In this paper, we investigate the annealing schedule and the neighbourhood which are the deterministic parameters of the process that warrant the quality of the SA algorithm. The algorithm is employed to solve the discrete stochastic optimization problem of the design of a DOE. The objective function which constrains the optimization is also studied. The computed results demonstrate that the procedure of the algorithm converges stably to an optimal solution close to the global optimum with an acceptable computing time. The results meet the design requirement well and are applicable.

Land use and land cover change and its driving forces in Maqu County, China in the past 25 years

Maqu County is located in the northeast Qinghai-Tibetan Plateau, and it is the main watershed for the Yellow River. The ecosystem there is extremely vulnerable and sensitive to climate change and human activities, which have caused significant deterioration of the eco-environment in this region. In order to restore the ecological environment, a government project to restore the grazing areas to grassland was implemented in Maqu County in early 2004. This study evaluates the effects of that restoration project on land use and land cover change (LUCC), and explores the driving forces of LUCC in Maqu County. In the study we used Landsat images obtained in 1989, 2004, 2009, and 2014 to establish databases of land use and land cover. Then we derived LUCC information by overlaying these layers using GIS software. Finally, we analyzed the main forces responsible for LUCC. The results showed that forests, high-coverage grasslands, and marshes experienced the most significant decreases during 1989-2004, by 882.8 ha, 35, 250.4 ha, and 2, 753.4 ha, respectively. However, moderate-and low-coverage grasslands and sand lands showed the opposite trend, increasing by 12, 529.7 ha, 25, 491.0 ha, and 577.5 ha, respectively. LUCC in 2004-2009 showed that ecological degradation slowed compared with 1989-2004. During 2009-2014, high-and moderate-coverage grasslands increased obviously, but low-coverage grasslands, marshes, unused lands, sand lands, and water areas showed the opposite trend. These results suggested that the degradation of the eco-environment was obvious before 2009, showing a decrease in the forests, grasslands, and water areas, and an increase in unused lands. The ecological degradation was reversed after 2009, as was mainly evidenced by increases in high-and moderate-coverage grasslands, and the shrinkage rate of marshes decreased obviously. These results showed that the project of restoring grazing lands to grassland had a positive effect on the LUCC. Other major factors that influence the LUCC include increasing temperature, variation in the seasonal frozen soil environment, seasonal overgrazing, and pest and rodent damage.