Dr. Yukun Wang Profile

Dr. Yukun Wang

at Shanghai Jiao Tong Univ

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SPIE Journal Paper | 29 September 2022

Forward projection multilayer refraction model for underwater camera calibration

Yukun Wang, Fan Ye, Yanzhen Dong, Xiaobo Chen, Juntong Xi

OE, Vol. 61, Issue 09, 094104, (September 2022) https://doi.org/10.1117/12.10.1117/1.OE.61.9.094104

KEYWORDS: Refraction, Calibration, Cameras, Imaging systems, Refractive index, Underwater imaging, Interfaces, Water, Optical engineering, Geometrical optics

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Unlike imaging in air, underwater imaging is affected by two distinct properties of water: the absorption and scattering effect of water and the refraction effect of water, resulting in the conventional pinhole model no longer being suitable for underwater imaging. Therefore, without prior calibration in air to calculate the camera intrinsic parameters and distortions for subsequent underwater calibration, an underwater multilayer refraction model based on forward projection method is represented. Along the direction of light propagation, the multilayer refraction model presents a unified scale factor instead of focal length during the perspective projection transformation from the camera coordinate system to the image coordinate system. Simulations regarding the analysis of different medium thicknesses, different medium refractive indices, and different point pixels are performed to explore the influence of the above three parameters on the refraction model. Through the underwater parameter identification and verification, the proposed multilayer refraction model has high measurement accuracy, excellent solution efficiency, stable identification results, more identification parameters, and wide application fields, which are suitable for both single-time refraction and double-time refraction.

Proceedings Article | 26 July 2022 Paper

Bow and twist deformation measurement system of fuel assembly with underwater dual-line structured light

Yukun Wang, Xiaojin Xu, Fan Ye, Xiaobo Chen, Juntong Xi

Proceedings Volume 12279, 122790J (2022) https://doi.org/10.1117/12.2615612

KEYWORDS: Calibration, Cameras, Structured light, Underwater imaging, Precision measurement, Measurement devices

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To realize the non-contact on-line measurement of the crucial dimension for the fuel assembly and assist the nuclear power plant to carry out regular maintenance works in the core, we design an underwater fuel assembly deformation measurement system (UFADMS). Based on the principle of dual-optical line laser triangulation, the deformation measurement system integrates two sets of optical units. During the measurement, each optical unit projects two beams of laser to the surface and captures the relevant image for further process, respectively. According to the point clouds obtained by underwater calibration, three-dimensional (3D) reconstruction, and global calibration, we can calculate the relative relationship between the two optical units, and normalize the corresponding measurement data to calculate the bow and twist deformation of the fuel assembly. Benefitting from the novel waterproof design, the dual-optical line laser triangulation principle, and the underwater single-layer refractive geometry, the measurement system has strong environmental adaptability, high measurement accuracy, and short measurement time. Through the underwater field measurement and validation of standard blocks and fuel assembly, the bow deformation measurement accuracy is within 0.4 mm, and the twist deformation measurement accuracy is within 0.15°. What’s more, the proposed system allows transient measurement at a certain depth of water, which provides a guarantee for on-line measurement of fuel assembly underwater.

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