Individual tree segmentation and biomass estimation based on UAV Digital aerial photograph

Digital aerial photograph(DAP)data is processed based on Structure from Motion(Sf M)algorithm and regional net adjustment method to generate digital surface discrete point clouds similar to Light Detection and Ranging(LiDAR)and digital orthophoto mosaic(DOM)similar to optical remote sensing image.In this study,we obtained highresolution images of mature forests of Chinese fir by unmanned aerial vehicle(UAV)flying through crossroute flight,and then reconstructed the threedimensional point clouds in the UAV aerial area by SfM technique.The point cloud segmentation(PCS)algorithm was used for the individual tree segmentation,and the F-score of the three sample plots were 0.91,0.94,and 0.94,respectively.Individual tree biomass modeling was conducted using 155 mature Chinese fir forests which were correctly segmented.The relative root mean squared error(rRMSE)values of random forest(RF),bagged tree(BT)and support vector regression(SVR)were 34.48%,35.74%and 40.93%,respectively.Our study demonstrated that DAP point clouds had great potential to extract forest vertical parameters and could be applied successfully in individual tree segmentation and individual tree biomass modeling.

Temporal and spatial variation characteristics of extreme precipitation on the Loess Plateau of China facing the precipitation process

The preceding and succeeding precipitation(PSP)often act together with extreme precipitation(EP),in turn,causing floods,which is an objective component that is often overlooked with regard to summer flood hazards in the arid region of Northwest China.In this study,event-based extreme precipitation(EEP)was defined as continuous precipitation that includes at least one day of EP.We analyzed the spatiotemporal variation characteristics of four EEP types(front EEP,late EEP,balanced EEP,and single day EEP)across the Loess Plateau(LP)based on data acquired from 87 meteorological stations from 1960 to 2019.Precipitation on the LP basically maintained a spatial pattern of"low in the northwest region and high in the southeast region",and EP over the last 10 a increased significantly.The cumulative precipitation percentage of single day EEP was 34%and was dominant for 60 a,while the cumulative precipitation percentage of front,late,and balanced EEP types associated with PSP accounted for 66%,which confirms to the connotation of EEP.The cumulative frequencies of front and late EEP types were 23%and 21%,respectively,while the cumulative frequency of balanced EEP had the lowest value at only 13%.Moreover,global warming could lead to more single day EEP across the LP,and continuous EEP could increase in the northwestern region and decrease in the eastern region in the future.The concept of process-oriented EP could facilitate further exploration of disaster-causing processes associated with different types of EP,and provide a theoretical basis for deriving precipitation disaster chains and construction of disaster cluster characteristics.

被动标量湍流的约束亚格子模型

本文采用约束大涡模拟(C-LES)模型来模拟湍流中的被动标量.通过施加一个基于被动标量大涡模拟(LES)中标量方差通量标度不变量的物理约束来计算动态混合非线性模型(MNLM)的系数.将约束亚格子(SGS)模型与不同的SGS模型在不可压各向同性湍流被动标量中进行比较.此外,C-LES模型减少了SGS标量方差通量在惯性-对流尺度以及较大的黏性-扩散尺度上的变化.先验测试表明,C-LES模型在预测SGS标量通量的方向和大小方面表现最好.此外,C-LES模型减少了SGS标量方差通量在惯性-对流范围内以及粘性-扩散范围内大尺度的变化.在后验测试中,与传统的动态Smagorinsky(DSM)和MNLM模型相比,C-LES模型在预测标量谱和内部间歇性的演变中表现明显更好.这些结果表明,在SGS模型中施加物理约束是在被动标量湍流大涡模拟中的一种有前途的方法.

Functional zoning in national parks under multifactor trade-off guidance:A case study of Qinghai Lake National Park in China

Functional zoning is an important mechanism for achieving national park planning and management objective.Better functional zoning is of great significance to the protection of ecosystem legitimacy and integrity,the appropriate utilization of resources,community integration,and feasible management.In the present study,the proposed Qinghai Lake National Park is the research object.Based on the critical goal of ecological protection,the importance of ecosystem service functions and the ecological sensitivities were evaluated.The results showed that the ecosystem service functions and the ecological sensitivity of the whole region are high.Among them,lake,river and wetland as the most strictly protected ecosystems account for the highest proportion.Then this study divided the proposed Qinghai Lake National Park into five functional areas through grid calculations,spatial analysis and multifactor trade-off.The results indicated that the goal of functional zoning for national park is to maximize the overall utility of park protection value and its comprehensive functions based on its spatial units with different functions,management and control requirements.The zoning scheme addresses the lack of sustainable development in Qinghai Lake National Park due to ecological environmental changes and single-resource zoning with resource protection as the primary goal.This study can serve as a reference for spatial functional zoning methods of national land parks,nature reserves and other natural protected areas.

The response of soil organic carbon to climate and soil texture in China

Soil organic carbon(SOC)plays an essential role in the carbon cycle and global warming mitigation,and it varies spatially in relation to other soil and environmental properties.But the national distributions and the impact mechanisms of SOC remain debated in China.Therefore,how soil texture and climate factors affect the SOC content and the regional differences in SOC content were explored by analyzing 7857 surface soil samples with different land-use.The results showed that the SOC content in China,with a mean value of 11.20 g·kg^(-1),increased gradually from north to south.The SOC content of arable land in each geographical area was lower than in grassland and forest-land.Although temperature also played a specific role in the SOC content,precipitation was the most critical climate factor.The SOC content was positively correlated with the silt and clay content.The lower the temperature,the greater the effect of environmental factors on SOC.In contrast,the higher the temperature,the more significant impact of soil texture on SOC.The regional difference in SOC highlights the importance of soil responses to climate change.Tempera-ture and soil texture should be explicitly considered when predicting potential future carbon cycle and sequestration.