Sub-optimal wavelet denoising of coaveraged spectra employing statistics from individual scans.
This paper proposes a novel wavelet denoising method, which exploits the statistics of individual scans acquired in the course of a coaveraging process. The proposed method consists of shrinking the wavelet coefficients of the noisy signal by a factor that minimizes the expected square error with respect to the true signal. Since the true signal is not known, a sub-optimal estimate of the shrinking factor is calculated by using the sample statistics of the acquired scans. It is shown that such an estimate can be generated as the limit value of a recursive formulation. In a simulated example, the performance of the proposed method is seen to be equivalent to the best choice between hard and soft thresholding for different signal-to-noise ratios. Such a conclusion is also supported by an experimental investigation involving near-infrared (NIR) scans of a diesel sample. It is worth emphasizing that this experimental example concerns the removal of actual instrumental noise, in contrast to other case studies in the denoising literature, which usually present simulations with artificial noise. The simulated and experimental cases indicate that, in classic denoising based on wavelet coefficient thresholding, choosing between the hard and soft options is not straightforward and may lead to considerably different outcomes. By resorting to the proposed method, the analyst is not required to make such a critical decision in order to achieve appropriate results.
Galvão
Roberto Kawakami Harrop
RK
Universidade Federal da Paraíba, CCEN, Departamento de Química-Laboratório de Automação e Instrumentação em Química Analítica/Quimiometria (LAQA), Caixa Postal 5093, CEP 58051-970 João Pessoa, PB, Brazil.
Filho
Heronides Adonias Dantas
HA
Martins
Marcelo Nascimento
MN
Araújo
Mário César Ugulino
MC
Pasquini
Celio
C
D016477:Artifacts; D004560:Electricity / Q000009:adverse effects*; D019265:Spectroscopy, Near-Infrared / Q000379:methods / Q000592:standards* / Q000706:statistics & numerical data*