Applications of wavelet transform to quantum cascade laser spectrometer for atmospheric trace gas measurements

Abstract

The application of wavelet transform-based digital filter to quantum cascade laser spectroscopy was investigated by its application to simulated spectra and experimental results obtained with our novel and compact QCL spectrometer, which offers the potential for high sensitive and selective measurements of trace gas concentration at high temporal resolution (less than 1 s) for species of interest in the atmosphere. With the application of wavelet digital filtering in post-signal processing, better measurement precision and higher detection sensitivity have been achieved, without reducing the fast temporal response. Details of wavelet transform theory applied to the spectroscopic data are presented. For comparison, the results of other commonly used filter techniques (i.e. Kalman filter, Wiener filter and moving average) are also tested. Finally, the experimental results show that the wavelet-based filter seems to be the superior choice for noise reduction, both for spectral signal processing and trace gas concentration signal evaluation.