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Study on Influencing Factors of Pre-Stack Reverse Time Migration Imaging of Ground Penetrating Radar
MA Bowen, HUANG Qinghua
Acta Scientiarum Naturalium Universitatis Pekinensis    2023, 59 (3): 388-394.   DOI: 10.13209/j.0479-8023.2023.015
Abstract222)   HTML    PDF(pc) (6580KB)(96)       Save
To analyze the influence of various possible errors in the actual ground-penetrating radar data processing on the imaging effect of the reverse time migration algorithm, numerical simulation tests are used to analyze the effect of the velocity errors in model and noises in data. For velocity error, models with different velocities and abnormal body depths, and simplified velocity models are used to test the subsequent imaging effect. Results show that with the increase of the velocity error and the depth of the abnormal body, the deviation of the position of the abnormal body also increases. For the layered structure with slight differences in velocity between each layer, imaging using a simplified uniform half-space model can still effectively distinguish the anomalies. Imaging tests are also performed on data with different noise levels. The results show that the reverse time migration (RTM) algorithm is effective on noise suppression. Even if the signal-to-noise ratio of the valid signal in the received data is around ?15 dB, the RTM algorithm can still image the corresponding structure.
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Impact of Temporal and Spatial Resolution of CALMET on the Simulated Concentration Fields of CALPUFF
KANG Ling, ZHU Hao, HUANG Qianqian, LIU Xinjian, LIN Hongtao, CAI Xuhui, SONG Yu, ZHANG Hongsheng
Acta Scientiarum Naturalium Universitatis Pekinensis    2021, 57 (6): 1006-1018.   DOI: 10.13209/j.0479-8023.2021.081
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The hourly WRF forecast wind fields with a resolution of 1 km is used as the input of the CALMET diagnostic model to generate wind fields with different temporal and spatial resolutions, which drive CALPUFF to obtain concentration fields with a resolution of 50 m per minute. The impact of the temporal and spatial resolution of CALMET meteorological fields on the concentration fields and the calculation time of each scheme are analyzed. The results show that satisfactory wind field and concentration field can be obtained even with coarse temporal and spatial resolution at stable wind direction and high wind speed conditions. The temporal and spatial resolution has a significant impact on the wind and concentration fields when the wind direction changes and the wind speed is low. The difference between concentration fields driven by various meteorological schemes can be as high as 40%. During the transition of the wind field, the accuracy of the concentration field will worsen with finer meteorological grid if the modeling time step of CALMET is greater than 30 minutes. The longer the modeling time step is, the more significant the deviation of the concentration field is. Considering the calculation time and the accuracy of the concentration field simulation, CALMET meteorological scheme with a time step of 10 min and a grid resolution of 400 m is recommended in the emergency early warning of air pollution accidents.
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Distribution Pattern and Its Impact Factors of Thorny Shrubs in Mountains of the Beijing-Tianjin-Hebei Region
Qiuyi WANG, Weichao GUO, Tao WANG, Qian HAO, Chongyang XU, Xu LIU, Yue HAN, Shuang QIU, Hongyan LIU
Acta Scientiarum Naturalium Universitatis Pekinensis    2017, 53 (3): 545-554.   DOI: 10.13209/j.0479-8023.2017.061
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To analyze the distribution pattern of thorny shrubs and its impact factors, 460 sample sites were collected in mountains of the Beijing-Tianjin-Hebei region. Results showed that about 60% of sample sites had thorny shrubs, which were mainly the shrub community dominated by Vitex negundo var. heterophylla. In a small number of sample sites, thorny shrubs even became the dominant species. Twenty-four thorny shrub species were mainly from the families Rhamnaceae, Rosaceae and Leguminosae. The most common three species (Ziziphus jujuba, Rhamnus parvifolia and Caragana rosea) are mainly distributed on the gentle sunny and half-sunny slopes in the hilly area with elevation lower than 600 m a.s.l.. Quantitative analysis also showed that light condition and drought were limiting factors for growth of thorny shrubs (especially Ziziphus jujuba). Affected by climate, topography, and community factors together, thorny shrubs can be distributed under different habitats in mountains of the Beijing-Tianjin-Hebei region.

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Ecological Optimization of Land Spatial Pattern Based on the Reconstructions: Take the Reconstructions of Lushan, Sichuan for Example
CHAI Huixia, RAO Sheng, MOU Xuejie, HUANG Qi, WANG Ruibo
Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (6): 1068-1076.   DOI: 10.13209/j.0479-8023.2016.027
Abstract712)   HTML    PDF(pc) (1551KB)(1011)       Save

Based on status assessment of ecological environment and ecological system, this paper mainly analyzed significance and sensibility of ecological functions in Lushan earthquake-hit regions. An optimization program of land spatial pattern for the reconstructions of Lushan earthquake-hit regions was proposed to restore ecosystem function and optimize land spatial pattern. It could be divided into three sub-regions, ecological reserve, eco-agriculture development area, and eco-town development area. Main results are as follows. 1) The ecological protection area is extensive in Lushan earthquake-hit regions, accounting for 80.6% of the total area. In ecological protection area, the protection goal is to maintain ecological security by protect important ecological functions and carry out ecological restoration. 2) The eco-agriculture development area accounts for 13.4% of the total area. As an important agricultural production function zone, the dominant ecological function of this area is to provide safeguard for supply of agricultural products. It also needs providing guarantee of soil conservation function. 3) The eco-town development area only accounts for 6.0% of the total area. This area is the core region of regional urbanization and industrial development. On the premise of protecting ecological, the reconstructions direction is to construct the ecological city through optimization industrial structure and distribution.

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Changes of Ecosystem Structure in Qinghai-Tibet Plateau Ecological Barrier Area during Recent Ten Years
MOU Xuejie, ZHAO Xinyi, RAO Sheng, HUANG Qi, CHAI Huixia
Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (2): 279-286.   DOI: 10.13209/j.0479-8023.2015.108
Abstract1193)   HTML    PDF(pc) (3457KB)(1039)       Save

By using spatial dataset of ecosystem types, ecosystem transfer matrix and dynamic degree methods, the changes of ecosystem structure and spatial distribution in Qinghai-Tibet Plateau ecological barrier area were analyzed during recent ten years. The results show that: 1) The ecosystem structure of Qinghai-Tibet Plateau ecological barrier area is relatively stable, 69% of the total land area is grassland ecosystem. 2) There are increase or decrease both in ecological and un-ecological land use, the wetland increases 2660.9 km2, the grassland cuts 1377.5 km2, the urban expands 224.6 km2, the farmland reduces 163.4 km2, and the desert reduces 1388.5 km2. 3) The change rates of urban and farmland, which are significantly influenced by human activities, are distinctly higher than the wetland. For example, the urban area increases rapidly with an average annual growth rate of 2.88% and the farmland decreases 0.64% per year on average from 2000 to 2010, however the average annual growth rate of wetland is only 0.44%. 4) The overall transfer of ecosystem is small and only for 0.5% of entire study area. The areas of grassland shift to wetland and the desert shift to wetland are larger and contribute 69% to entire ecosystem transfer. 5) Both natural and human factors are the driving forces of ecosystem change, among which climate change is the main factor causing the increase of wetland area; the rapidly growth of population and GDP causes the urban expanding, but the development of industry and mining industry is the deep reason for the expansion; the increase of grazing capacity is the main cause of the grassland degradation , but the ecological protection projects play a rather positive role in grassland ecosystem recovery.

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3D Forward and Inversion Problems of Borehole-to-Surface Electrical Method
KE Ganpan,HUANG Qinghua
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract719)            Save
After simplifying the borehole-to-surface electrical problem as a model with a vertical line source, the authors achieved 3D resistivity forward modeling of a vertical line source of electrical current using finite element method (FEM). The authors also achieved 3D resistivity inversion on the basis of iterative nonlinear damped least square method. Some simplified models were adopted to test both the forward and the inversion algorithms. The authors used “synthetic data” obtained from the forward modeling to inverse the target resistivity in the model. The authors also investigated the possible effects of data surveying region and noises on the inversion quality of target resistivity. This study would provide some theoretical background for enhancing the quality of inversion problem of borehole-to-surface electrical method.
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Rainfall Infiltration Process and Its Effect on Apparent Resistivity
SONG Xiaolei,HUANG Qinghua
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract695)            Save
A simple one-dimension model considering fluid movement in unsaturated soils is proposed to simulate the rainfall infiltration process and explain its possible effect on apparent resistivity of the Earth. A convolution filtering method is adopted to analyze rainfall effect on apparent resistivity. As a case study, the result of the Changli Station is reported. The study may provide information for the quantitative analysis of geoelectric observation data.
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Numerical Simulation and Experimental Investigation on Vibration Control of A Rotating Flexible Beam
ZHU Farong,HUANG Qinghua,CHEN Decheng
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract487)            Save
Compared with the rigid-flexible coupling dynamic models that had been constructed in other published papers, comprehension about the equation of rotating flexible beam based on the method of small element is presented, and some fuzzy understanding are clarified.Numerical simulations on the vibration control of rotating flexible beam with positive position feedback are carried out. More over, using piezoelectric ceramic as sensors and actuators, several experiments are performed, their results are shown and discussed.
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