title: An improved algorithm to remove cosmic spikes in Raman spectra for online monitoring.
abstract: Raman spectral analysis integrated with multivariate calibration is a fast and effective solution to monitor chemical product properties. However, Raman instruments utilizing charge-coupled device (CCD) detectors suffer from occasional spikes caused by cosmic rays. Cosmic spikes can  disturb or even destroy the meaningful chemical information expressed by normal Raman spectra. In online monitoring, some cosmic spikes have intensity and bandwidth similar to normal Raman peaks of chemical components when a low resolution and cost-effective Raman instrument is used. Moreover,  the online Raman spectra always contain variations of strong Raman peaks and fluorescence. Current spike-removal methods seem to have difficulty detecting and recovering cosmic spikes in these online Raman spectra. Therefore, an improved algorithm is proposed. In this algorithm, a new scheme  composed of intensity identification and local moving window correlation analysis is introduced for cosmic spike detection; intensity identification based on derivative spectra and local linear fitting approximation are used for the recovery of cosmic spikes. The algorithm is proved to be  simple and effective and has been applied in an online Raman instrument installed at a continuous catalytic reforming unit in a refinery.
authors: State Key Lab of Industrial Control Technology, Zhejiang University, Hangzhou, China 310027.
authors: Sheng
authors: S
authors: Li
authors: Liankui
authors: L
authors: Dai