The gradient preconditioning approach based on seismic wave energy can effectively avoid the huge memory consumption of the gradient preconditioning algorithms based on the Hessian matrix. However, the accuracy of thi...The gradient preconditioning approach based on seismic wave energy can effectively avoid the huge memory consumption of the gradient preconditioning algorithms based on the Hessian matrix. However, the accuracy of this approach is prone to be influ- enced by the energy of reflected waves. To tackle this problem, the paper proposes a new gradient preconditioning method based on the energy of transmitted waves. The approach scales the gradient through a precondition factor, which is calculated by the ‘ap- proximate transmission wavefield’ simulation based on the nonreflecting acoustic wave equation. The method requires no computing nor storing of the Hessian matrix and its inverse matrix. Furthermore, the proposed method can effectively eliminate the effects of geometric spreading and disproportionality in the gradient illumination. The results of model experiments show that the time-domain full waveform inversion (FWI) using the gradient preconditioning based on transmitted wave energy can achieve higher inversion accuracy for deep high-velocity bodies and their underlying strata in comparison with the one using the gradient preconditioning based on seismic wave energy. The field marine seismic data test shows that our proposed method is also highly applicable to the FWI of field marine seismic data.展开更多
针对发射波形正交性退化影响机载多输入多输出(multiple-input multiple-output,MIMO)雷达的杂波特性,基于信号空间和子阵空间的变换原理,建立了波形正交性退化下的机载MIMO雷达杂波通用模型和标准模型。基于带限信号的最优逼近特性,分...针对发射波形正交性退化影响机载多输入多输出(multiple-input multiple-output,MIMO)雷达的杂波特性,基于信号空间和子阵空间的变换原理,建立了波形正交性退化下的机载MIMO雷达杂波通用模型和标准模型。基于带限信号的最优逼近特性,分析了波形正交性退化下的空时等效阵列孔径变化规律,提出了杂波自由度(degree of freedom,DOF)的估计准则。最后,仿真验证了杂波模型及杂波自由度估计准则的有效性。展开更多
声波测井技术作为地层评价的重要手段已经逐步从电缆测井向随钻(logging while drilling,LWD)测井过渡,未来随钻声波测井在油气勘探开发中将发挥重要的作用。以随钻声波测井关键技术为主线,综述了近年来在随钻四极子发射换能器、隔声体...声波测井技术作为地层评价的重要手段已经逐步从电缆测井向随钻(logging while drilling,LWD)测井过渡,未来随钻声波测井在油气勘探开发中将发挥重要的作用。以随钻声波测井关键技术为主线,综述了近年来在随钻四极子发射换能器、隔声体设计、接收声系及波形反演方法等方面的研究进展。研究结果表明:耐高温高压的非充油型随钻四极子发射换能器具有机械安装简单、造价低等优点;钻铤变径隔声结构具有良好的隔声效果,可以减小泥浆对钻铤内壁凹槽的冲蚀影响,增加仪器的使用寿命;长条管状接收声系设计方案能够很好地降低钻铤波的干扰,易于安装和维修维保;数据反演方面重点是如何解决随钻地层各向异性评价难题。下一代的随钻声波远探测技术研究有望实现从近井壁探测拓展到远距离探测的跨越,为井旁地质构造探测、地质导向等提供帮助。展开更多
多机协同探测雷达系统利用目标在不同机载雷达间的径向速度差异实现目标的有效检测,该系统已成为当前机载雷达领域的研究热点。该文首先建立了不同发射波形条件下多机协同探测雷达系统的信号模型,并给出了基于广义似然比(Generalized Li...多机协同探测雷达系统利用目标在不同机载雷达间的径向速度差异实现目标的有效检测,该系统已成为当前机载雷达领域的研究热点。该文首先建立了不同发射波形条件下多机协同探测雷达系统的信号模型,并给出了基于广义似然比(Generalized Likelihood Ratio Test,GLRT)准则的自适应检测器及其渐进统计分布特性,最后通过计算机仿真分析了3种特定发射波形下的运动目标检测性能。仿真结果表明多机协同探测雷达系统中发射波形的变化会严重影响雷达系统的运动目标检测性能,且相同发射波形的雷达系统对不同运动速度的目标检测性能也存在区别。展开更多
基金support of the NSFCShandong Joint Fund for Marine Science Research Centers (No. U1606401)the National Natural Science Foundation of China (Nos. 41574105 and 41704114)+1 种基金the National Science and Technology Major Project of China (No.2016ZX05027-002)Taishan Scholar Project Funding (No. tspd20161007)
文摘The gradient preconditioning approach based on seismic wave energy can effectively avoid the huge memory consumption of the gradient preconditioning algorithms based on the Hessian matrix. However, the accuracy of this approach is prone to be influ- enced by the energy of reflected waves. To tackle this problem, the paper proposes a new gradient preconditioning method based on the energy of transmitted waves. The approach scales the gradient through a precondition factor, which is calculated by the ‘ap- proximate transmission wavefield’ simulation based on the nonreflecting acoustic wave equation. The method requires no computing nor storing of the Hessian matrix and its inverse matrix. Furthermore, the proposed method can effectively eliminate the effects of geometric spreading and disproportionality in the gradient illumination. The results of model experiments show that the time-domain full waveform inversion (FWI) using the gradient preconditioning based on transmitted wave energy can achieve higher inversion accuracy for deep high-velocity bodies and their underlying strata in comparison with the one using the gradient preconditioning based on seismic wave energy. The field marine seismic data test shows that our proposed method is also highly applicable to the FWI of field marine seismic data.
文摘针对发射波形正交性退化影响机载多输入多输出(multiple-input multiple-output,MIMO)雷达的杂波特性,基于信号空间和子阵空间的变换原理,建立了波形正交性退化下的机载MIMO雷达杂波通用模型和标准模型。基于带限信号的最优逼近特性,分析了波形正交性退化下的空时等效阵列孔径变化规律,提出了杂波自由度(degree of freedom,DOF)的估计准则。最后,仿真验证了杂波模型及杂波自由度估计准则的有效性。
文摘声波测井技术作为地层评价的重要手段已经逐步从电缆测井向随钻(logging while drilling,LWD)测井过渡,未来随钻声波测井在油气勘探开发中将发挥重要的作用。以随钻声波测井关键技术为主线,综述了近年来在随钻四极子发射换能器、隔声体设计、接收声系及波形反演方法等方面的研究进展。研究结果表明:耐高温高压的非充油型随钻四极子发射换能器具有机械安装简单、造价低等优点;钻铤变径隔声结构具有良好的隔声效果,可以减小泥浆对钻铤内壁凹槽的冲蚀影响,增加仪器的使用寿命;长条管状接收声系设计方案能够很好地降低钻铤波的干扰,易于安装和维修维保;数据反演方面重点是如何解决随钻地层各向异性评价难题。下一代的随钻声波远探测技术研究有望实现从近井壁探测拓展到远距离探测的跨越,为井旁地质构造探测、地质导向等提供帮助。
文摘多机协同探测雷达系统利用目标在不同机载雷达间的径向速度差异实现目标的有效检测,该系统已成为当前机载雷达领域的研究热点。该文首先建立了不同发射波形条件下多机协同探测雷达系统的信号模型,并给出了基于广义似然比(Generalized Likelihood Ratio Test,GLRT)准则的自适应检测器及其渐进统计分布特性,最后通过计算机仿真分析了3种特定发射波形下的运动目标检测性能。仿真结果表明多机协同探测雷达系统中发射波形的变化会严重影响雷达系统的运动目标检测性能,且相同发射波形的雷达系统对不同运动速度的目标检测性能也存在区别。
