Michael Smith Laboratories, The University of British Columbia, 2185 East Mall, Vancouver, British Columbia, Canada V6T 1Z4.
Appl Spectrosc. 2013 Apr;67(4):457-62. doi: 10.1366/12-06839.
Raman spectra often contain undesirable, randomly positioned, intense, narrow-bandwidth, positive, unidirectional spectral features generated when cosmic rays strike charge-coupled device cameras. These must be removed prior to analysis, but doing so manually is not feasible for large data sets. We developed a quick, simple, effective, semi-automated procedure to remove cosmic ray spikes from spectral data sets that contain large numbers of relatively homogenous spectra. Although some inhomogeneous spectral data sets can be accommodated--it requires replacing excessively modified spectra with the originals and removing their spikes with a median filter instead--caution is advised when processing such data sets. In addition, the technique is suitable for interpolating missing spectra or replacing aberrant spectra with good spectral estimates. The method is applied to baseline-flattened spectra and relies on fitting a third-order (or higher) polynomial through all the spectra at every wavenumber. Pixel intensities in excess of a threshold of 3× the noise standard deviation above the fit are reduced to the threshold level. Because only two parameters (with readily specified default values) might require further adjustment, the method is easily implemented for semi-automated processing of large spectral sets.
拉曼光谱中经常包含不需要的、随机定位的、强度高的、窄带宽的、正向的、单向光谱特征，这些特征是宇宙射线撞击电荷耦合器件相机时产生的。在进行分析之前，必须将这些特征去除，但对于大型数据集，手动去除是不可行的。我们开发了一种快速、简单、有效、半自动的程序，用于去除包含大量相对均匀光谱的光谱数据集中的宇宙射线尖峰。尽管可以处理一些不均匀的光谱数据集——它需要用原始数据替换过度修改的数据，并使用中位数滤波器去除它们的尖峰——但在处理此类数据集时需要谨慎。此外，该技术适用于插值缺失的光谱或用良好的光谱估计值替换异常的光谱。该方法应用于基线平滑的光谱，并依赖于在每个波数处通过所有光谱拟合三阶（或更高阶）多项式。超过拟合噪声标准偏差 3 倍的强度像素被降低到阈值水平。由于只有两个参数（具有易于指定的默认值）可能需要进一步调整，因此该方法易于实现大型光谱集的半自动处理。
