Time delay-phase harmonic model of transmitted laser signal for gas concentration estimation

Abstract

The proposed time delay-phase harmonic model takes into account absorption, scattering, and reflectance effects and the relationship between the phase shift and the time delay and the absorption pulse signal quality. The Levenberg–Marquardt algorithm is applied to define optimal model parameters, enabling an efficient and effective of gas concentration estimation process. Experimental results demonstrate a strong correlation between the harmonic ratio feature and methane concentration under varying laser power conditions. Furthermore, the phase shift effect on the absorption signal is investigated, revealing its impact on waveform symmetry and peak distribution. The proposed method has been proven to require only a few signal cycles for gas concentration estimation.