Dynamic monitoring of plant cover and soil erosion often uses remote sensing data, especially for estimating the plant cover rate (vegetation coverage) by vegetation index. However, the latter is influenced by atmosph...Dynamic monitoring of plant cover and soil erosion often uses remote sensing data, especially for estimating the plant cover rate (vegetation coverage) by vegetation index. However, the latter is influenced by atmospheric effects and methods for correcting them are still imperfect and disputed. This research supposed and practiced an indirect, fast, and operational method to conduct atmospheric correction of images for getting comparable vegetation index values in different times. It tries to find a variable free from atmospheric effects, e.g., the mean vegetation coverage value of the whole study area, as a basis to reduce atmospheric correction parameters by establishing mathematical models and conducting simulation calculations. Using these parameters, the images can be atmospherically corrected. And then, the vegetation index and corresponding vegetation coverage values for all pixels, the vegetation coverage maps and coverage grade maps for different years were calculated, i.e., the plant cover monitoring was realized. Using the vegetation coverage grade maps and the ground slope grade map from a DEM to generate soil erosion grade maps for different years, the soil erosion monitoring was also realized. The results show that in the study area the vegetation coverage was the lowest in 1976, much better in 1989, but a bit worse again in 2001. Towards the soil erosion, it had been mitigated continuously from 1976 to 1989 and then to 2001. It is interesting that a little decrease of vegetation coverage from 1989 to 2001 did not lead to increase of soil erosion. The reason is that the decrease of vegetation coverage was chiefly caused by urbanization and thus mainly occurred in very gentle terrains, where soil erosion was naturally slight. The results clearly indicate the details of plant cover and soil erosion change in 25 years and also offer a scientific foundation for plant and soil conservation.展开更多
Ti：PbC was synthesized for the first time by pressureless reaction synthesis using Ti/Pb/TiC as starting materials at a heating rate of 2 ℃/rain and holding at 1370 ℃ for 2 h in a tube furnace protected by Ar atmos...Ti：PbC was synthesized for the first time by pressureless reaction synthesis using Ti/Pb/TiC as starting materials at a heating rate of 2 ℃/rain and holding at 1370 ℃ for 2 h in a tube furnace protected by Ar atmosphere. The effects of starting powders, heating rates, and holding temperatures on the formation of Ti2PbC were investigated. It was found that elementary mixture of Ti/Pb/C or higher heating rates fail to form Ti2PbC. The decreased lattice parameters in the synthesized Ti2PbC indicated the existence of Pb vacancies in the compound. A reaction mechanism was proposed to explain the formation of Ti2PbC.展开更多
文摘Dynamic monitoring of plant cover and soil erosion often uses remote sensing data, especially for estimating the plant cover rate (vegetation coverage) by vegetation index. However, the latter is influenced by atmospheric effects and methods for correcting them are still imperfect and disputed. This research supposed and practiced an indirect, fast, and operational method to conduct atmospheric correction of images for getting comparable vegetation index values in different times. It tries to find a variable free from atmospheric effects, e.g., the mean vegetation coverage value of the whole study area, as a basis to reduce atmospheric correction parameters by establishing mathematical models and conducting simulation calculations. Using these parameters, the images can be atmospherically corrected. And then, the vegetation index and corresponding vegetation coverage values for all pixels, the vegetation coverage maps and coverage grade maps for different years were calculated, i.e., the plant cover monitoring was realized. Using the vegetation coverage grade maps and the ground slope grade map from a DEM to generate soil erosion grade maps for different years, the soil erosion monitoring was also realized. The results show that in the study area the vegetation coverage was the lowest in 1976, much better in 1989, but a bit worse again in 2001. Towards the soil erosion, it had been mitigated continuously from 1976 to 1989 and then to 2001. It is interesting that a little decrease of vegetation coverage from 1989 to 2001 did not lead to increase of soil erosion. The reason is that the decrease of vegetation coverage was chiefly caused by urbanization and thus mainly occurred in very gentle terrains, where soil erosion was naturally slight. The results clearly indicate the details of plant cover and soil erosion change in 25 years and also offer a scientific foundation for plant and soil conservation.
基金supported by the grants from National Natural Science Foundation(Nos.51731004,51501038,and 51671054)the Fundamental Research Funds for the Central Universities in China
文摘Ti：PbC was synthesized for the first time by pressureless reaction synthesis using Ti/Pb/TiC as starting materials at a heating rate of 2 ℃/rain and holding at 1370 ℃ for 2 h in a tube furnace protected by Ar atmosphere. The effects of starting powders, heating rates, and holding temperatures on the formation of Ti2PbC were investigated. It was found that elementary mixture of Ti/Pb/C or higher heating rates fail to form Ti2PbC. The decreased lattice parameters in the synthesized Ti2PbC indicated the existence of Pb vacancies in the compound. A reaction mechanism was proposed to explain the formation of Ti2PbC.
