scholarly journals A Method for Correcting the Interference of Overlapping Absorption Lines Using Second Harmonic Spectral Reconstruction

2021 ◽  
Vol 12 (1) ◽  
pp. 73
Author(s):  
Yue Hou ◽  
Kejin Huang
Keyword(s):  
Measurement Accuracy ◽  
Second Harmonic ◽  
Absorption Lines ◽  
Trace Gas ◽  
Detection Accuracy ◽  
Gas Temperature ◽  
Signal Restoration ◽  
Spectral Reconstruction ◽  
Peak Fitting ◽  
Waveform Change

The measurement accuracy of trace gas detection based on infrared absorption spectroscopy is influenced by the overlap of absorption lines. A method for correcting the interference of overlapping absorption lines using second harmonic spectral reconstruction (2f-SR) is proposed to improve the measurement accuracy. 2f-SR includes three parts: measurement of gas temperature and use of the differences in temperature characteristics of absorption lines to correct the temperature error, 2f signal restoration based on laser characteristics to eliminate the influence of waveform change on overlapping absorption lines, and fast multi-peak fitting for the separation of interference from overlapping absorption lines. The CH4 measurement accuracy based on overlapping absorption lines is better than 0.8% using 2f-SR. 2f-SR has a lower minimum detection limit (MDL) and a higher detection accuracy than the separation of overlapping absorption lines based on the direct absorption method. The MDL is reduced by two to three orders of magnitude and reaches the part per million by volume level. 2f-SR has clear advantages for correcting the interference of overlapping absorption lines in terms of both MDL and measurement accuracy.

scholarly journals Absolute accuracy and sensitivity analysis of OP-FTIR retrievals of CO<sub>2</sub>, CH<sub>4</sub> and CO over concentrations representative of "clean air" and "polluted plumes"

2011 ◽  
Vol 4 (1) ◽  
pp. 97-116 ◽  
Author(s):  
T. E. L. Smith ◽  
M. J. Wooster ◽  
M. Tattaris ◽  
D. W. T. Griffith
Keyword(s):  
Least Squares ◽  
Gas Absorption ◽  
Absorption Lines ◽  
Trace Gas ◽  
Gas Temperature ◽  
Band Shape ◽  
Fitting Procedure ◽  
Order Of Magnitude ◽  
Transparent Cell ◽  
Using Data

Abstract. When compared to established point-sampling methods, Open-Path Fourier Transform Infrared (OP-FTIR) spectroscopy can provide path-integrated concentrations of multiple gases simultaneously, in situ and near-continuously. The trace gas pathlength amounts can be retrieved from the measured IR spectra using a forward model coupled to a non-linear least squares fitting procedure, without requiring "background" spectral measurements unaffected by the gases of interest. However, few studies have investigated the accuracy of such retrievals for CO2, CH4 and CO, particularly across broad concentration ranges covering those characteristic of ambient to highly polluted air (e.g. from biomass burning or industrial plumes). Here we perform such an assessment using data collected by a field-portable FTIR spectrometer. The FTIR was positioned to view a fixed IR source placed at the other end of an IR-transparent cell filled with the gases of interest, whose target concentrations were varied by more than two orders of magnitude. Retrievals made using the model are complicated by absorption line pressure broadening, the effects of temperature on absorption band shape, and by convolution of the gas absorption lines and the instrument line shape (ILS). Despite this, with careful model parameterisation (i.e. the optimum wavenumber range, ILS, and assumed gas temperature and pressure for the retrieval), concentrations for all target gases were able to be retrieved to within 5%. Sensitivity to the aforementioned model inputs was also investigated. CO retrievals were shown to be most sensitive to the ILS (a function of the assumed instrument field-of-view), which is due to the narrow nature of CO absorption lines and their consequent sensitivity to convolution with the ILS. Conversely, CO2 retrievals were most sensitive to assumed atmospheric parameters, particularly gas temperature. Our findings provide confidence that FTIR-derived trace gas retrievals of CO2, CH4 and CO based on modeling can yield results with high accuracies, even over very large (many order of magnitude) concentration ranges that can prove difficult to retrieve via standard classical least squares (CLS) techniques. With the methods employed here, we suggest that errors in the retrieved trace gas concentrations should remain well below 10%, even with the uncertainties in atmospheric pressure and temperature that might arise when studying plumes in more difficult field situations (e.g. at uncertain altitudes or temperatures).

scholarly journals Absolute accuracy and sensitivity analysis of OP-FTIR retrievals of CO<sub>2</sub>, CH<sub>4</sub> and CO over concentrations representative of ''clean air'' and ''polluted plumes''

2010 ◽  
Vol 3 (4) ◽  
pp. 3675-3723 ◽  
Author(s):  
T. E. L. Smith ◽  
M. J. Wooster ◽  
M. Tattaris ◽  
D. W. T. Griffith
Keyword(s):  
Least Squares ◽  
Gas Absorption ◽  
Forward Model ◽  
Absorption Lines ◽  
Trace Gas ◽  
Gas Temperature ◽  
Band Shape ◽  
Fitting Procedure ◽  
True Value ◽  
Using Data

Abstract. When compared to established point-sampling methods, Open-Path Fourier Transform Infrared (OP-FTIR) spectroscopy can provide path-integrated concentrations of multiple gases simultaneously, in situ and near-continuously. Concentrations can be retrieved from the measured IR spectra using a forward model coupled to a non-linear least squares fitting procedure, without requiring ''background'' spectral measurements unaffected by the gases of interest. However, few studies have investigated the accuracy of such retrievals for CO2, CH4 and CO, particularly across a broad concentration range covering ambient to highly polluted air (e.g. from biomass burning or industrial plumes). Here we perform such an assessment using data collected by a field-portable FTIR spectrometer. The FTIR was positioned to view a fixed IR source placed at the other end of an IR-transparent cell filled with the gases of interest, whose target concentrations were varied by up to two orders of magnitude. Retrievals made using the forward model are complicated by absorption line pressure broadening, the effects of temperature on absorption band shape and by convolution of the gas absorption lines and the instrument line shape (ILS). Despite this, with optimal forward model parameterisation (i.e. the wavenumber range used in the retrieval, gas temperature, pressure and ILS), concentration retrievals for all gases were able to be made to within 5% of the true value. Sensitivity to the aforementioned model inputs was also investigated. CO retrievals were shown to be most sensitive to the ILS (a function of the assumed instrument FOV), which is due to the narrow nature of CO absorption lines and their consequent sensitivity to convolution with the ILS. Conversely, CO2 retrievals were most sensitive to assumed atmospheric parameters, particularly temperature. The analysis suggests that trace gas concentration retrieval errors can remain well below 10%, even with the uncertainties in atmospheric pressure and temperature that might arise when studying plumes in field situations (e.g. at uncertain altitudes or temperatures). Our findings provide confidence that FTIR-derived trace gas retrievals of CO2, CH4 and CO based on forward modeling can yield accurate results, even over very large concentration ranges that can prove difficult to retrieve via standard classical least squares (CLS) techniques.

scholarly journals Recent improvements of long-path DOAS measurements: impact on accuracy and stability of short-term and automated long-term observations

2019 ◽  
Vol 12 (8) ◽  
pp. 4149-4169 ◽  
Author(s):  
Jan-Marcus Nasse ◽  
Philipp G. Eger ◽  
Denis Pöhler ◽  
Stefan Schmitt ◽  
Udo Frieß ◽  
...  
Keyword(s):  
Light Source ◽  
Optical Density ◽  
Measurement Accuracy ◽  
Trace Gases ◽  
Detection Limits ◽  
Trace Gas ◽  
Light Sources ◽  
Light Path ◽  
Mixing Ratios ◽  
Spectral Residual

Abstract. Over the last few decades, differential optical absorption spectroscopy (DOAS) has been used as a common technique to simultaneously measure abundances of a variety of atmospheric trace gases. Exploiting the unique differential absorption cross section of trace-gas molecules, mixing ratios can be derived by measuring the optical density along a defined light path and by applying the Beer–Lambert law. Active long-path (LP-DOAS) instruments can detect trace gases along a light path of a few hundred metres up to 20 km, with sensitivities for mixing ratios down to ppbv and pptv levels, depending on the trace-gas species. To achieve high measurement accuracy and low detection limits, it is crucial to reduce instrumental artefacts that lead to systematic structures in the residual spectra of the analysis. Spectral residual structures can be introduced by most components of a LP-DOAS measurement system, namely by the light source, in the transmission of the measurement signal between the system components or at the level of spectrometer and detector. This article focuses on recent improvements by the first application of a new type of light source and consequent changes to the optical setup to improve measurement accuracy. Most state-of-the-art LP-DOAS instruments are based on fibre optics and use xenon arc lamps or light-emitting diodes (LEDs) as light sources. Here we present the application of a laser-driven light source (LDLS), which significantly improves the measurement quality compared to conventional light sources. In addition, the lifetime of LDLS is about an order of magnitude higher than of typical Xe arc lamps. The small and very stable plasma discharge spot of the LDLS allows the application of a modified fibre configuration. This enables a better light coupling with higher light throughput, higher transmission homogeneity, and a better suppression of light from disturbing wavelength regions. Furthermore, the mode-mixing properties of the optical fibre are enhanced by an improved mechanical treatment. The combined effects lead to spectral residual structures in the range of 5-10×10-5 root mean square (rms; in units of optical density). This represents a reduction of detection limits of typical trace-gas species by a factor of 3–4 compared to previous setups. High temporal stability and reduced operational complexity of this new setup allow the operation of low-maintenance, automated LP-DOAS systems, as demonstrated here by more than 2 years of continuous observations in Antarctica.

Research on Screw Thread Form Based on Non-Contact Measurement

2011 ◽  
Vol 101-102 ◽  
pp. 593-596
Author(s):  
Shao Feng Shen ◽  
Xian Cheng Wang ◽  
Jun Hua Chen
Keyword(s):  
Measurement Accuracy ◽  
Optical Axis ◽  
Optical Field ◽  
New Method ◽  
Detection Accuracy ◽  
Screw Thread ◽  
Characteristic Parameters ◽  
The Real ◽  
Contact Measurement ◽  
High Skill

There is a problem with non-contact measurement and detection, which reduces its measurement accuracy. Methods developed for measuring and inspecting screw thread characteristic parameters usually using a camera, which is controlled to scan the projection of thread in the parallel optical field to obtain thread images. However, with the block of screw line on the projection of the real thread form, it is impossible to acquire the real thread form from images. The traditional way is adjusting the optical axis to a suitable angle with the thread axis to acquire the real thread form projection, which has some problems, such as time consuming, high skill of operator, high-precision equipment for adjustment, inaccuracy, and so on. Hence, a new method through digital image calibration is presented. The results of relevant simulation indicated the feasibility of this new method, which improves thread measurement and detection accuracy.

scholarly journals Preliminary Research on the Nonlinear Ultrasonic Detection of the Porosity of Porous Material Based on Dynamic Wavelet Fingerprint Technology

Sensors ◽  
2019 ◽  
Vol 19 (15) ◽  
pp. 3328
Author(s):  
Xianghong Wang ◽  
Chenglong He ◽  
Wei Xie ◽  
Hongwei Hu
Keyword(s):  
Porous Material ◽  
Second Harmonic ◽  
Harmonic Component ◽  
Small Diameter ◽  
Distribution Range ◽  
Detection Accuracy ◽  
Graphite Composite ◽  
Preliminary Research ◽  
Nonlinear Feature ◽  
Aperture Distribution

Porosity is an important characteristic of porous material, which affects mechanical and material properties. In order to solve the problem that the large distribution range of pore size of porous materials leads to the large detection errors of porosity, the non-linear ultrasonic testing technique is applied. A graphite composite was used as the experimental object in the study. As the accuracy of porosity is directly related with feature extraction, the dynamic wavelet fingerprint (DWFP) technology was utilized to extract the feature parameter of the ultrasonic signals. The effects of the wavelet function, scale factor, and white slice ratio on the extraction of the nonlinear feature are discussed. The SEM photos were conducted using gray value to identify the aperture. The relationship between pore diameter and detection accuracy was studied. Its results show that the DWFP technology could identify the second harmonic component well, and the extracted nonlinear feature could be used for the quantitative trait of porosity. The larger the proportion of the small diameter holes and the smaller the aperture distribution range was, the smaller the error was. This preliminary research aimed to improve the nondestructive testing accuracy of porosity and it is beneficial to the application of porous material in the manufacturing field.

scholarly journals A Trace C2H2 Sensor Based on an Absorption Spectrum Technique Using a Mid-Infrared Interband Cascade Laser

Micromachines ◽  
2018 ◽  
Vol 9 (10) ◽  
pp. 530 ◽  
Author(s):  
Ye Mu ◽  
Tianli Hu ◽  
He Gong ◽  
Ruiwen Ni ◽  
Shijun Li
Keyword(s):  
Absorption Spectroscopy ◽  
Second Harmonic ◽  
Harmonic Signal ◽  
Gas Absorption ◽  
Tunable Diode Laser ◽  
Integration Time ◽  
Detection Accuracy ◽  
Laser Absorption ◽  
Interband Cascade Laser ◽  
Diode Laser Absorption

In this study, tunable diode laser absorption spectroscopy (TDLAS) combined with wavelength modulation spectroscopy (WMS) was used to develop a trace C2H2 sensor based on the principle of gas absorption spectroscopy. The core of this sensor is an interband cascade laser that releases wavelength locks to the best absorption line of C2H2 at 3305 cm−1 (3026 nm) using a driving current and a working temperature control. As the detected result was influenced by 1/f noise caused by the laser or external environmental factors, the TDLAS-WMS technology was used to suppress the 1/f noise effectively, to obtain a better minimum detection limit (MDL) performance. The experimental results using C2H2 gas with five different concentrations show a good linear relationship between the peak value of the second harmonic signal and the gas concentration, with a linearity of 0.9987 and detection accuracy of 0.4%. In total, 1 ppmv of C2H2 gas sample was used for a 2 h observation experiment. The data show that the MDL is low as 1 ppbv at an integration time of 63 s. In addition, the sensor can be realized by changing the wavelength of the laser to detect a variety of gases, which shows the flexibility and practicability of the proposed sensor.

scholarly journals Measuring impurity content in pipelines by positron annihilation

2020 ◽  
pp. 002029402096859
Author(s):  
Yahan Yu ◽  
Min Zhao ◽  
Jun Xu ◽  
Min Yao ◽  
Ruipeng Guo ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Measurement Accuracy ◽  
Impurity Content ◽  
Detection Accuracy ◽  
Detection Scheme ◽  
Oil Pipelines ◽  
Good Consistency ◽  
Piping Systems ◽  
Test Result

γ photon pairs produced by positron annihilation can penetrate metals well; thus, they can be used for nondestructive detection of the inner state of metal pipelines. An experimental device is designed to simulate the working state of lube oil pipelines and inject nuclide into it. A symmetrical structure and a ratio algorithm are proposed considering the effects of various factors. Two sensors with good consistency are used to record the number of γ photon events in liquids with and without impurities. The ratio of the recorded events of reference and impurity sensors is taken as the test result of impurity content. The advantage of the method proposed in this paper is that it can eliminate the environmental error and inconsistency of the sensors by using ratio calculation and improve the measurement accuracy. Experimental results show that the proposed detection scheme and algorithm can well detect impurity content, including metal, in various pipelines. The detection accuracy of matched sensors can exceed 2%. Detected impurities are not limited to metal particles. Thus, the proposed method can be applied to in situ and online detection of impurities in oil piping systems equipped with engines.

scholarly journals THE DEVELOPMENT OF PORTABLE AIR QUALITY DETECTION

2020 ◽  
Vol 15 (Number 2) ◽  
pp. 12-19
Author(s):  
Siti Farah Hussin
Keyword(s):  
Air Quality ◽  
Low Cost ◽  
Good Condition ◽  
Ammonia Nitrogen ◽  
Detection Accuracy ◽  
Gas Temperature ◽  
Chemical Waste ◽  
Detection Range ◽  
Quality Detection ◽  
Temperature And Humidity

Air quality is very important to ensure the health of humans, plants, and even animals. The tragedy of chemical waste disposal in the Kim Kim river has resulted in air pollution in the surrounding area. Therefore, this innovation has been developed to produce a mobile device that has a low cost, detection of the gas in real-time, and overcome the problems faced due to chemical waste pollution such as shortness of breath, nausea, and vomiting. Portable air quality detection is an innovation used to detected and measured the connections between software and hardware that are required for analysis purposes. The outputs detected are carbon dioxide, benzene, alcohol, ammonia, nitrogen oxide, and smoke. Data analysis was done by making a comparison between the output values in LCD and Favoriot and Blynk. This project also can measure the value of temperature and humidity. The sensor used to detect gas readings is MQ135 gas sensor and for temperature and humidity sensor is DHT22 sensor. The value of gas, temperature, and humidity in the environment will be displayed on the website as well as on the phone applications. This innovation used two types of platforms to display the data, Favoriot in website platform and Blynk used on smartphones. In addition, this value will be recorded and stored on the website for future use by the users. The users will also be able to compare readings before and after to ensure that the air in the environment is in good condition. In addition, this project can warn users if the reading is at danger level. The buzzer will sound and users will be notified by email. For future recommendations, the A3OZ sensor can be used to achieve high precision values for O3 and NO2 readings with a detection range of 0-10 ppm and detection accuracy of 20 ppb

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