Helioseismic Holography
Helioseismic Holography
复制标题
日震全息术
DOI：
10.1086/304445
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发表时间：
1997
期刊：
影响因子：
--
通讯作者：
D. Braun
中科院分区：
文献类型：
--
作者：
C. Lindsey;D. Braun
我们描述了“日震全息术”的基本原理，这是一种用于地下结构局部日震学的分析技术。该技术的目的是提供在声波中显示表面特征的地下结构的深度辨别。它是基于空间分辨日震观测的计算应用程序的表面的声学模型的太阳内部，不包含本地结构。观测到的表面振荡被应用于模型的时间反演，然后在其内部的不同深度对模型进行计算采样。这种技术利用了波在与地下结构相互作用后在光滑声学介质中保留的相干性，使我们能够以高精度将声场外推到结构所在的深度。然后通过聚焦-散焦诊断来完成深度辨别。我们从两个不同的角度，“光谱”和“空间”的技术描述计算方法。对于太阳内部的严格模型，光谱和空间方法的计算需求大致相同。对于相对浅的结构的诊断，模型的平面平行近似是有用的。在这种情况下，光谱方法基本上将计算全息简化为傅里叶变换，这可以用非常简单的硬件快速执行。我们说明了在这种情况下，使用人工数据表征波在一个理想化的平面平行介质位于不同深度的吸声体。目前，我们倾向于在全息术和建模之间保持安全的区别。虽然我们不讨论建模在本文中，我们认为这是重要的是开发一种方法来建模，利用全息重建。观测局部地下磁区和磁流的前景为日震学和一般的太阳和恒星物理学开辟了一个全新的领域。它可能使人们能够在太阳活动出现在地表之前很久就预测太阳活动。局部声学诊断可以彻底改变我们对太阳发电机和22年活动周期的理解。
We describe the basic principles of “helioseismic holography,” an analytic technique intended for local helioseismology of subsurface structure. The purpose of this technique is to provide depth discrimination of subsurface structure that manifests a surface signature in acoustic waves. It is based on the computational application of spatially resolved helioseismic observations to the surface of an acoustic model of the solar interior that contains no local structure. The observed surface oscillations are applied to the model in time reverse, and the model is then computationally sampled at various depths in its interior. This technique takes advantage of the coherence retained by waves in a smooth acoustic medium following an interaction with subsurface structure, allowing us to extrapolate the acoustic field with high accuracy to the depth where the structure lies. Depth discrimination is then accomplished by focus-defocus diagnostics. We describe computational approaches to the technique from two different perspectives, the “spectral” and the “spatial.” For rigorous models of the solar interior, the computational demands of the spectral and spatial approaches are approximately the same. For diagnostics of relatively shallow structure, the plane-parallel approximation of the model is useful. In this case the spectral approach reduces computational holography essentially to Fourier transforms, which can be performed rapidly with very modest hardware. We illustrate the technique in this case, using artificial data characterizing waves in an idealized plane-parallel medium with acoustic absorbers located at various depths. At present, we prefer to maintain a secure distinction between holography and modeling. While we do not discuss modeling in this paper, we think that it is important to develop an approach to modeling that takes advantage of holographic reconstruction. The prospect of viewing local subsurface magnetic regions and flows opens an entirely new dimension to helioseismology and to solar and stellar physics in general. It may make it possible to anticipate solar activity far in advance of its emergence to the surface. Local acoustic diagnostics could revolutionize our understanding of the solar dynamo and the 22 yr activity cycle.