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arXiv 2003.12538physics.geo-phmath.APphysics.comp-ph
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源扩展的全波形反演:为什么它有效

Full Waveform Inversion by Source Extension: Why it works

William W. Symes

摘要:

一个非常简单的单道传输的例子显示了如何扩展源公式的全波形反演可以产生一个优化问题,没有虚假的局部最小值(“周期跳跃”)。数据由在距点源给定距离处记录的单个道组成。假定速度或慢度是均匀的,并且假定目标震源子波是准脉冲的或聚焦在零滞后时间。通过允许能量在时间上扩展来扩展源,并且通过将扩展的源小波的加权均方添加到数据失配来控制扩展,以产生扩展的反演目标。目标函数及其梯度可以显式计算,并且很容易看出,所有局部最小值必须在正确慢度的波长内。推导表明所有类似的扩展源算法的几个重要功能。例如,嵌套优化,在内部优化(变量投影法)中的源估计,是必不可少的。控制扩展源自由度的权重算子的选择是至关重要的:这里提出的选择是微分算子,并且该属性对于产生不受循环跳跃影响的目标是至关重要的。

英文摘要:

An extremely simple single-trace transmission example shows how an extended source formulation of full waveform inversion can produce an optimization problem without spurious local minima ("cycle skipping"). The data consist of a single trace recorded at a given distance from a point source. The velocity or slowness is presumed homogeneous, and the target source wavelet is presumed quasi-impulsive or focused at zero time lag. The source is extended by permitting energy to spread in time, and the spread is controlled by adding a weighted mean square of the extended source wavelet to the data misfit, to produce the extended inversion objective. The objective function and its gradient can be computed explicitly, and it is easily seen that all local minimizers must be within a wavelength of the correct slowness. The derivation shows several important features of all similar extended source algorithms. For example, nested optimization, with the source estimation in the inner optimization (variable projection method), is essential. The choice of the weight operator, controlling the extended source degrees of freedom, is critical: the choice presented here is a differential operator, and that property is crucial for production of an objective immune from cycle-skipping.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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