On an $n-$Dimensional Travel Time Tomography Problem
关于一个$n$维走时层析成像问题
Michael V. Klibanov
AI总结 针对形式确定不完全输入数据的n维走时层析成像问题,提出半离散化方法并利用截断傅里叶级数展开,证明Lipschitz稳定性估计和唯一性。
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在他们的开创性工作中,Herglotz (1905) 和 Wiechert 与 Zoeppritz (1907) 解决了一维情况下的所谓走时层析成像问题(TTTP)。然而,对于具有形式确定不完全输入数据的 n 维(n≥2)TTTP,关于稳定性估计和唯一性定理的问题在一百多年后仍然基本未解决。“形式确定输入数据”意味着输入数据中自由变量的数量 p 等于未知的右端项(控制非线性程函偏微分方程)中自由变量的数量 n,即 p=n。先前的一些出版物表明,可以为形式确定输入数据的 TTTP 开发出性能良好的数值方法,这表明此类数据在实际应用中的重要性。这是第一篇解决上述问题的出版物。更精确地说,我们考虑一个半离散情况,其中由程函方程生成的偏微分方程关于 n-1 个变量用有限差分写出。此外,假设该半离散偏微分方程的解通过一个关于特殊正交函数基(仅依赖于点源位置)的截断傅里叶级数表示。在这些条件下,证明了 Lipschitz 稳定性估计,并且该估计蕴含唯一性。本文的一个重要工具是新的 Carleman 估计。引入了 Carleman 加权空间。此前,Carleman 估计未被应用于解决 TTTP 的稳定性估计和唯一性定理问题。
In their seminal works Herglotz (1905) and Wiechert and Zoeppritz (1907) have solved the so-called Travel Time Tomography Problem (TTTP) in the 1-D case. However, the question about stability estimates and uniqueness theorems for an n-D n>= 2 TTTP with formally determined incomplete input data still mostly stands open after more than one hundred years period. \textquotedblleft Formally determined input data" means that the number p of free variables in the input data equals the number $n$ of free variables in the unknown right hand side of the governing nonliniear eikonal PDE, p=n. Some previous publications demonstrate that it is possible to develop well performed numerical methods for the TTTP with formally determined input data, which indicates the importance of such data for practical applications. This is the first publication in which the above question is addressed. More precisely, we consider a semi-discrete case, in which a PDE generated by the eikonal equation is written in finite differences with respect to n-1 variables. In addition, it is assumed that the solution of that semi-discrete PDE is represented via a truncated Fourier-like series with respect to a special orthonormal basis of functions, which depend only on the position of the point source. Under these conditions, Lipschitz stability estimate is proven, and this estimate implies uniqueness. An important tool of this paper is a new Carleman estimate. Carleman Weighted Spaces are introduced. Carleman estimates were not applied previously to address questions about stability estimates and uniqueness theorems for the TTTP.