Method for extracting absorption characteristic peak in gas field monitoring

Abstract

The invention relates to a method for extracting an absorption characteristic peak in gas field monitoring. The method comprises the following steps: a smooth filtering step, a characteristic peak seeking step, a window linear fitting step and a characteristic peak background calculation and deduction step, wherein in the smooth filtering step, obtaining an original spectral array, then creating a smooth spectral array by adopting a moving average method and transferring to the absorption characteristic peak seeking step; in the characteristic peak seeking step, creating a first-order differential spectral array and a second-order differential spectral array and transferring left and right endpoints xL and xR of the absorption characteristic peak to the window linear fitting step; in the window linear fitting step, adopting a least square method to fit scattered data points in windows at the left and the right ends of the characteristic peak to obtain slopes and intercepts of fitting straight lines on the left side and the right side and transferring to the characteristic peak background calculation and deduction step; in the characteristic peak background calculation and deduction step, calculating a spectral background array within the range of the absorption characteristic peak through recursive interpolation for many times, and deducting a vector of a spectral intensity value stored in the smooth spectral array from a vector of a spectral intensity value stored in the spectral background array obtained by calculation to obtain a spectral array after background deduction and transferring to the smooth filtering step.

Description

technical field [0001] The invention relates to infrared laser spectrum analysis technology, which is a method for identifying and extracting characteristic absorption peaks of gas to be measured in on-site and on-line gas monitoring based on tunable semiconductor laser absorption spectrum. Background technique [0002] Tunable semiconductor laser absorption spectroscopy technology (TDLAS) utilizes the wavelength tunable and narrow-band characteristics of semiconductor lasers to make the output laser beam pass through the space area where the gas to be measured is located and receive the laser beam intensity to obtain the characteristic absorption spectrum of the gas. With the maturity of near-infrared tunable semiconductor laser technology and optical coupling and transmission technology, TDLAS technology has developed rapidly. Because TDLAS technology can realize fast and accurate non-invasive measurement of multiple parameters, and the system is compact, has good environm...

AI Technical Summary

Problems solved by technology

However, the on-site monitoring environment is changeable and it is difficult to maintain stability

This will make it difficult to maintain a consistent line shape of the baseline, which tends to vary randomly over time.

Therefore, it is difficult to fit the baseline with a fixed function line type

Moreover, when monitoring trace gases, the absorption peak is very small, and the randomly changing baseline background often overwhelms the part of the absorption peak close to the baseline. The above baseline fitting method is difficult to extract when the absorption peak is not obvious

Therefore, it is difficult for the baseline fitting method to identify the characteristic absorption peaks of trace gases, resulting in a high gas detection limit and a decrease in sensitivity

Although it is possible to introduce a reference optical path and eliminate the environmental influence of the laser through the ratio of the light intensity of the absorption optical path to the reference optical path, the environmental influence of other components in the TDLAS system cannot be eliminated. For example, the output current of the photodetector is easily affected by temperature. The reflectivity of the gas cell mirror is easily affected by humidity, etc.

Therefore, in the on-site detection of gases in a changing environment, it is difficult for the traditional baseline fitting method to effectively extract the characteristic absorption peaks of gas molecules, especially trace gases, and the baseline fitting method cannot even identify the characteristic absorption peaks.

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