The spatial autocorrelation(SPAC)(also known as the Aki’s spectral method)of ambient seismic noise has been widely adopted in surface wave phase velocity extraction.In two-dimensional cases,the surface wave velocity ...The spatial autocorrelation(SPAC)(also known as the Aki’s spectral method)of ambient seismic noise has been widely adopted in surface wave phase velocity extraction.In two-dimensional cases,the surface wave velocity can be calculated by fitting the SPAC coefficients with the zero-order Bessel function of the first kind or using the zeros of the Aki’s spectrum.This method has also been extended to active-source records.This study examined the application of the zeros of Aki’s spectra on active-source records using theoretical analysis and numerical simulation.We show that the zeros of the Aki’s spectrum should be associated with the zeros of the cosine function instead of the zeros of the zero-order Bessel function when extracting the phase velocity of the surface wave,considering the data acquisition and processing of the active-source records.The proposed method was then applied to the active-source data from methane explosion experiments collected using a dense array in Tongzhou,the subcenter of Beijing,for extracting the phase velocity of Rayleigh wave.The extracted dispersion curves were integrated with those obtained by beamforming the ambient noise to yield broadband dispersion curves at 0.3–6 Hz.This provides insightful results at high frequencies,at which less information can be obtained through the passive-source beamforming.The combing phase velocities from active-source with those obtained from ambient noise provide a better constrain on the shallow structure.Based on the combined fundamental mode dispersion curves at 28 excitation points,the S-wave velocity structure below the dense array is obtained by depth inversion.Due to the constraints imposed by the high-frequency information from active source,the estimated vS30 are more reliable and can be used to the site classification.展开更多
定量描述农田生态系统中土壤水分动态、碳氮循环过程和作物生长发育规律,对水氮资源高效利用、作物生产决策和环境保护具有十分重要的意义。该文在总结前人研究成果的基础上,引用了联合国粮食及农业组织的气象模块、荷兰的PS123作物模...定量描述农田生态系统中土壤水分动态、碳氮循环过程和作物生长发育规律,对水氮资源高效利用、作物生产决策和环境保护具有十分重要的意义。该文在总结前人研究成果的基础上,引用了联合国粮食及农业组织的气象模块、荷兰的PS123作物模型和丹麦的Daisy模型的碳氮循环模块;借鉴了RZWQM和Hydrus-1D的水分溶质运移模块的相关理论,并在其基础上进行了修改与完善,构建了土壤-作物-大气系统水热碳氮耦合模拟模型WHCNS（soil water heat carbon and nitrogen simulation）。该模型以天为步长,考虑了气象条件、作物生物学特性和田间管理驱动。土壤水分入渗和再分布过程分别采用Green-Ampt模型和Richards方程来描述。土壤氮素运移使用对流-弥散方程来描述,源汇项中考虑碳氮循环的各个过程（有机质矿化、生物固持、尿素水解、氨挥发、硝化、反硝化和作物吸收等）,在根系吸水吸氮源汇项中引入了补偿性吸收机制。有机质模块完全来自Daisy模型,将有机质库划分为3个快库和3个慢库。利用改进的荷兰PS123模型实现了作物生长发育进程、干物质生产、干物质分配及作物产量的模拟,通过水氮胁迫校准因子来实现水氮限制下作物产量的模拟。最后应用华北地区（山东泰安）冬小麦-夏玉米轮作体系2 a的田间观测数据对该模型进行了校验。结果表明,剖面土壤水分和硝态氮浓度、叶面积指数、作物产量与实测值均吻合良好,模拟误差均在合理范围之内,特别是对产量的模拟较好,均方根误差为206-319 kg/hm^2,相关系数为0.90,模型效率值均大于0.75,一致性指数值均大于0.9。WHCNS模型能够较好地模拟土壤水分动态、氮素运移及去向、作物生长发育等过程,表明该模型适用于中国华北地区高度集约化的农田生产系统。展开更多
基金supported by the National Natural Science Foundation of China(No.42474081)the Fundamental Research Funds from the Institute of Geophysics,China Earthquake Administration(No.DQJB 23K34)the Science and Technology Department of Henan Province of China(No.242102320039).
文摘The spatial autocorrelation(SPAC)(also known as the Aki’s spectral method)of ambient seismic noise has been widely adopted in surface wave phase velocity extraction.In two-dimensional cases,the surface wave velocity can be calculated by fitting the SPAC coefficients with the zero-order Bessel function of the first kind or using the zeros of the Aki’s spectrum.This method has also been extended to active-source records.This study examined the application of the zeros of Aki’s spectra on active-source records using theoretical analysis and numerical simulation.We show that the zeros of the Aki’s spectrum should be associated with the zeros of the cosine function instead of the zeros of the zero-order Bessel function when extracting the phase velocity of the surface wave,considering the data acquisition and processing of the active-source records.The proposed method was then applied to the active-source data from methane explosion experiments collected using a dense array in Tongzhou,the subcenter of Beijing,for extracting the phase velocity of Rayleigh wave.The extracted dispersion curves were integrated with those obtained by beamforming the ambient noise to yield broadband dispersion curves at 0.3–6 Hz.This provides insightful results at high frequencies,at which less information can be obtained through the passive-source beamforming.The combing phase velocities from active-source with those obtained from ambient noise provide a better constrain on the shallow structure.Based on the combined fundamental mode dispersion curves at 28 excitation points,the S-wave velocity structure below the dense array is obtained by depth inversion.Due to the constraints imposed by the high-frequency information from active source,the estimated vS30 are more reliable and can be used to the site classification.
文摘定量描述农田生态系统中土壤水分动态、碳氮循环过程和作物生长发育规律,对水氮资源高效利用、作物生产决策和环境保护具有十分重要的意义。该文在总结前人研究成果的基础上,引用了联合国粮食及农业组织的气象模块、荷兰的PS123作物模型和丹麦的Daisy模型的碳氮循环模块;借鉴了RZWQM和Hydrus-1D的水分溶质运移模块的相关理论,并在其基础上进行了修改与完善,构建了土壤-作物-大气系统水热碳氮耦合模拟模型WHCNS（soil water heat carbon and nitrogen simulation）。该模型以天为步长,考虑了气象条件、作物生物学特性和田间管理驱动。土壤水分入渗和再分布过程分别采用Green-Ampt模型和Richards方程来描述。土壤氮素运移使用对流-弥散方程来描述,源汇项中考虑碳氮循环的各个过程（有机质矿化、生物固持、尿素水解、氨挥发、硝化、反硝化和作物吸收等）,在根系吸水吸氮源汇项中引入了补偿性吸收机制。有机质模块完全来自Daisy模型,将有机质库划分为3个快库和3个慢库。利用改进的荷兰PS123模型实现了作物生长发育进程、干物质生产、干物质分配及作物产量的模拟,通过水氮胁迫校准因子来实现水氮限制下作物产量的模拟。最后应用华北地区（山东泰安）冬小麦-夏玉米轮作体系2 a的田间观测数据对该模型进行了校验。结果表明,剖面土壤水分和硝态氮浓度、叶面积指数、作物产量与实测值均吻合良好,模拟误差均在合理范围之内,特别是对产量的模拟较好,均方根误差为206-319 kg/hm^2,相关系数为0.90,模型效率值均大于0.75,一致性指数值均大于0.9。WHCNS模型能够较好地模拟土壤水分动态、氮素运移及去向、作物生长发育等过程,表明该模型适用于中国华北地区高度集约化的农田生产系统。
