On the resolution limit of digital particle image velocimetry
On the resolution limit of digital particle image velocimetry
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DOI：
10.1007/s00348-012-1280-x
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发表时间：
2012-06-01
影响因子：
2.4
通讯作者：
Cierpka, Christian
中科院分区：
文献类型：
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作者：
Kaehler, Christian J.;Scharnowski, Sven;Cierpka, Christian
这项工作分析了空间分辨率，可以实现由数字粒子图像测速（DPIV）作为示踪粒子和成像和记录系统的功能。由于用于窗口相关性评估的平面内分辨率与询问窗口大小有关，因此过去假设单像素集合相关性将空间分辨率增加到像素极限。然而，它示出的决定因素限制的单像素集合相关的分辨率是颗粒图像的大小，这是依赖于颗粒的大小，放大倍率，成像系统的f数，和光学像差。此外，由于最小可检测颗粒图像尺寸由DPIV中摄像机传感器的像素尺寸确定，因此在本分析中也考虑了该量。结果表明，最佳的放大率，结果在尽可能最好的空间分辨率可以估计从颗粒大小，透镜的属性，和像素大小的相机。因此，本文提供的信息可以优化相机和物镜透镜的选择以及给定设置的工作距离。此外，还详细讨论了利用粒子跟踪测速技术（PTV）提高空间分辨率的可能性。结果表明，这种技术允许增加空间分辨率的子像素限制平均流场。此外，PTV评估方法不会显示基于相关性的方法通常存在的偏倚误差。因此，该技术最适合于速度剖面的估计。
This work analyzes the spatial resolution that can be achieved by digital particle image velocimetry (DPIV) as a function of the tracer particles and the imaging and recording system. As the in-plane resolution for window-correlation evaluation is related by the interrogation window size, it was assumed in the past that single-pixel ensemble-correlation increases the spatial resolution up to the pixel limit. However, it is shown that the determining factor limiting the resolution of single-pixel ensemble-correlation are the size of the particle images, which is dependent on the size of the particles, the magnification, the f-number of the imaging system, and the optical aberrations. Furthermore, since the minimum detectable particle image size is determined by the pixel size of the camera sensor in DPIV, this quantity is also considered in this analysis. It is shown that the optimal magnification that results in the best possible spatial resolution can be estimated from the particle size, the lens properties, and the pixel size of the camera. Thus, the information provided in this paper allows for the optimization of the camera and objective lens choices as well as the working distance for a given setup. Furthermore, the possibility of increasing the spatial resolution by means of particle tracking velocimetry (PTV) is discussed in detail. It is shown that this technique allows to increase the spatial resolution to the subpixel limit for averaged flow fields. In addition, PTV evaluation methods do not show bias errors that are typical for correlation-based approaches. Therefore, this technique is best suited for the estimation of velocity profiles.