基于光场投影的有限角高时间分辨发射层析方法研究

Combustion process is a significant research for aviation, aerospace and energy engineering. Measuring the three-dimensional (3D) transient distribution in real time is quite valuable for combustion diagnosis. Emission Computed Tomography (ECT) provides non-contact, non-destructive and 3D full-field measurements for combustion diagnosis. However, the reconstruction of the combustion field is time-consuming due to the large amount of tomographic reconstruction data. Meanwhile, the performance of ECT degrades in non-free-space with limited observation angle. In this project, the theory of light field imaging is introduced to the ECT system with limited observation angle, acquiring multiple sub-aperture projections with directional high-resolution simultaneously. Furthermore, sub-aperture projection fits the parallel projection model approximately, which brings a sparse projection weight matrix and decreases the amount of tomographic reconstruction data. Therefore, it is possible for real time 3D full field reconstruction of combustion field. The research includes four aspects: optical design of multi-directional projection ECT system with limited observation angle based on light field projection; building up of the parallel projection model; reconstruction theory and algorithm light field projection based ECT; multi-directional sub-aperture projection calibration and 3D reconstruction of combustion flow field. The execution of this project will realize temporal high-resolution 3D reconstruction of combustion field in limited observation angle with ECT method, perfecting ECT in both spatial and temporal regions, and then prompt the wide application of optical computed tomography in more areas.

燃烧过程研究是航空、航天和能源工程中的核心内容，通过燃烧诊断测量燃烧场各参量，获得其三维瞬态分布对燃烧研究具有重要意义。发射计算层析方法(Emission Computed Tomography, ECT)可实现对燃烧场的非接触、无损三维测量，但现有ECT方法重建数据量大，且难以用于非自由空间观察角受限燃烧场诊断。本项目将光场成像理论引入多方向ECT投影采集方法研究，在有限的观察窗口获得高方向分辨率的子孔径投影信息。同时，子孔径投影逼近平行投影，保证投影权重矩阵的稀疏性，减小层析重建数据量，为实现高时间分辨率重建建立理论基础。项目主要从基于光场投影的有限角ECT多方向投影采集光路设计、平行投影模型建立、层析重建理论与算法、子孔径投影标定与燃烧场三维重建四个方面展开研究。本项目的开展将实现有限角燃烧场的高时间分辨重建，从空域和时域两方面完善ECT方法，促进光学计算层析方法在更多领域的应用。

燃烧过程研究是航空、航天和能源工程中的核心内容，通过燃烧诊断测量燃烧场各参量，获得其三维瞬态分布对燃烧研究具有重要意义。发射计算层析方法(Emission Computed Tomography, ECT)可实现对燃烧场的非接触、无损三维测量。本研究报告围绕非自由空间有限角、高时间分辨的多方向发射层析重建问题展开研究。首先，研究了基于微透镜阵列的有限角度光场投影多方向子孔径投影获取方法，建立了将光场投影用于逆Radon变换三维重建算法的模型；其次，建立了基于相机阵列的单窗口有限角度ECT重建装置，提出了基于透镜成像原理的相机阵列多投影标定算法，标定误差在0.25至0.75个像素之间；再次，基于提出的相机阵列标定方法，数值模拟三维重建确定了有限探测窗口相机阵列的排布方式；最后提出基于总变分稀疏正则化与卷积神经网络的有限角度火焰三维重建算法，用于对分离组分C2* 分布的重建，结果表明，这两种算法均可有效的去除ART重建场中的伪影，重建误差小，质量高。而且CNN算法重建速度快，重建时间只有传统ART算法的1%。该研究结果可进一步应用于实际中非自由空间角度受限燃烧场的快速三维重建与燃烧监控中。