TERRAIN 3D - TERmographic Reconstruction At INner 3D Interfaces

主动热成像技术由于其非接触和成本效益的应用，现在是一种非常成熟的无损检测和测量方法。有两种方法几乎完全用于此目的。具有类似闪光的能量输入的脉冲热成像和具有正弦调制的能量输入的锁相热成像都被归类为近表面测试方法，并且到目前为止仅能够测试薄部件。由于测试是在给定区域内进行的，因此可以快速直接地以图像的形式获得结果。定量重建的深度分辨表示的试样内部的测量结果是非常耗时的，到目前为止，只实施了非常简单的几何形状在实验室规模。在计划中的项目，两种方法来三维成像的试样内部将追求，以优雅地克服数学上复杂的正则化所需的解决不适定的逆重建问题。将使用一个灵活的红外系统为测试提供额外的信息。灵活的红外系统首次使使用空间和时间灵活的高强度红外辐射源进行主动热成像成为可能。从投影仪式红外系统的每个像素（超过一百万个像素）开始，可以发射以任意顺序编码的热波。在第一种方法中，热波以这样一种方式建模，即在整个组件上建立1D热通量，并且光热学的已知方法现在适用于二维测试中的复杂结构。在这种情况下，重建被简化为1D问题。在第二种方法中，我们利用热波的线性行为，并考虑每个像素的红外系统同时作为一个单独的编码热波。在解码之后，可以根据针对径向方向上的每个图像点获得的飞行时间信息来应用超声测试的已知重建方法。在这两种情况下，直接从测量结果输出内部界面的3D成像表示。将测试方法转化为测量方法，如果成功，该项目将有助于将主动热成像转化为直接的3D成像定量测量方法，提高缺陷检测率。

Active thermography is now a very well established non-destructive testing and measuring method due to its non-contact and cost-effective application. Two methods are used almost exclusively for this purpose. Both impulse thermography with flash-like energy input and lockin thermography with sinusoidally modulated energy input are categorized as near-surface testing methods and have so far only been able to test thin components. Since the test is carried out over a given area, the results are available quickly and directly in the form of an image. A quantitative reconstruction of the measurement results for a depth-resolved representation of the specimen interior is extremely time-consuming and has so far only been implemented for very simple geometries on a laboratory scale.In the planned project, two approaches to 3D imaging of the specimen interior will be pursued in order to elegantly overcome the mathematically complex regularization required to solve the ill-posed inverse reconstruction problem. A flexible infrared system will be used to provide additional information for the testing.The flexible infrared system makes it for the first time possible to use a spatially and temporally flexible IR radiation source of high intensity for active thermography. Starting from each pixel of the projector-like infrared system (more than one million pixels), a thermal wave encoded in arbitrary order can be emitted. In the first approach, the thermal waves are modeled in such a way that a 1D heat flux is established over the complete component and the known approaches of photothermics now hold for complex structures in a two-dimensional test. In this case, the reconstruction is simplified to a 1D problem. In the second approach, we take advantage of the linear behavior of thermal waves and consider each pixel of the infrared system simultaneously as an individually coded thermal wave. After decoding, known reconstruction methods of ultrasonic testing can be applied from the time-of-flight information obtained for each image point in the radial direction. In both cases, 3D imaging representations of the inner interfaces are output directly from the measurements. The test method is converted into a measurement method.If successful, the project will help to transform active thermography into a direct 3D imaging quantitative measurement method and increase the defect detection rate.