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UBC Theses and Dissertations

Apodization of absorption and magnitude mode fourier transform spectra and the effects on SNR and resolution Lee, Judy Pihsien


The problem of sidelobes surrounding a peak in a Fourier transform spectrum is alleviated by apodization. This is performed by multiplying the time-domain function by a window function. A systematic study of the effects of window functions on damped time-domain signals is made by examining the resulting lineshapes at specific dynamic ranges for both the absorption and magnitude modes. A symmetrical window is shown to be effective for the magnitude mode, and half of the symmetrical shape is better for the absorption mode. Selection of a recommended window is based on the required dynamic range. For an increasing dynamic range, the Noest-Kort and Norton-Beer F3, Filler E0.20, and Kaiser-Bessel are efficient for the absorption mode; and the Hamming, 3-term Blackman-Harris and Kaiser-Bessel work for the magnitude mode. Sidelobes are often eliminated at the expense of SNR and/or resolution, therefore these factors are also examined. All of the recommended windows show sufficient SNRs except for the Noest-Kort. The apodized absorption spectra are well resolved, with a 10% valley as the criterion for resolution. The magnitude spectra do not display a simple pattern, and also show a phase dependence; however these are explained by the absorption and dispersion components. These findings lend themselves to various applications.

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