光偏折层析重建流场中的两阶段降噪技术

光学层析技术中,包含在投影信息中的噪声会严重影响重建精度。针对偏折层析的关键环节,提出分两阶段对噪声进行抑制的方法。其一是在数据提取阶段使用小波分析技术对偏移量进行降噪,其二是重建时使用偏折角平均修正算法抑制噪声对迭代计算的影响。模拟实验中使用莫尔层析重建技术对三峰温度场进行了重建,结果显示降噪处理能够明显改善噪声对重建造成的不良影响,对误差曲线的分析表明,该处理使得100次迭代后误差的降幅高达45%。结合8邻域求导算法和降噪处理技术,对小型防风喷焰进行实际测量,证实了莫尔偏折层析技术在流场测量领域的实用价值。

Two-Stage Denoise Technique for Deflectometric Tomographic Reconstruction of Flow Field

Projection data obtained through optical techniques for tomographic measurement are often with noise. The reconstruction accuracy is deteriorated by the Gauss-or Poisson-distributed noise. Corresponding to the major steps of tomographic technique, a two-stage denoise technique has been developed. The deflectometric data are denoised by wavelet-based procedure after projection data reduction. Deflection-angle averaging revision algorithm is applied to suppress the noise in iteration. The Moire tomographic reconstruction technique with eight-neighbor derivative algorithm and denoise method is tested using numerically generated data from a known temperature distribution and noise source. The results show that the denoise processing is able to improve the reconstruction accuracy significantly, which reduces the reconstruction errors of 45%. The temperature field of butane flame is then measured by the Moire tomographic technique and the experimental reconstruction is compared with the thermocouple temperature measurement.