SPIKE-CORRECTION OF WEAK SIGNALS FROM CHARGE-COUPLED-DEVICES AND ITS APPLICATION TO RAMAN-SPECTROSCOPY

The detection of weak signals by a charge-coupled device (CCD) can be restricted by charge spikes due to cosmic rays rather than by thermal background noise. Such spikes can be removed using missing point estimates calculated from neighboring data points. In this work, a multiple missing point fitting method is developed for the correction of heavily contaminated data as obtained after long-time integration of weak signals. Spikes or other outliers can be recursively identified on the basis of a comparison of the differences of measured and estimated values with their standard deviations. The standard deviations are calculated considering shot and read noise of the measurement as well as the variance of the estimates. This allows a reliable spike correction of up to four spikes within a nine-point interval. The performance of the spike correction is demonstrated for the determination of the thermal background signal of a nitrogen-cooled CCD and for low-signal-level Raman scattering of pyridine adsorbed at a "smooth" silver film.