Study On Detector Response And Instrument Line Shape In Passive Telemetry System With Infrared Spectrum Of Contaminated Gas

The passive infrared telemetry system of polluted gas has the advantages of on-line monitoring,non-contact,wide spectrum and high signal-to-noise ratio.The system is often used to monitor the emission of polluting gases in industrial parks,respond to sudden dangerous gas leakage and detect the release of chemical warfare agents in war.The core component of the system is the infrared spectral radiometer.The accuracy of the recovered spectrum of the infrared spectroradiometer determines the accuracy of the identification and concentration measurement of the polluted gas.How to improve the accuracy of radiance and wave number is the key technology and research difficulty of infrared spectrum passive telemetry system for polluted gas when measuring high temperature target.A great deal of research has been done on the instrument structure design and spectral correction algorithm of infrared spectral radiometer abroad.Compared with foreign countries,China started late,and there are still many shortcomings in the study of spectral correction algorithm with high precision.In this paper,according to the above key technologies of domestic instruments,a high precision correction algorithm is proposed for the radiance and wave number of infrared spectroradiometer when observing high temperature targets.Aiming at the error of radiance measured by infrared spectral radiometer,this paper analyzes the main cause of error,which is the nonlinear response of detector.The effects of nonlinear response on spectral radiance under different conditions are analyzed.Based on previous studies and analysis of nonlinear response models,a nonlinear response correction method based on gradient descent is proposed.This method can simultaneously calculate the nonlinear response coefficients of different orders,and the calculation speed is faster and more accurate.Compared with the convolution correction method and the cross iteration correction method,the positive accuracy of this method is increased by 2.6 times.Finally,standard black-body experiments were observed by infrared spectroradiometer to compare the results of convolution method,cross iteration method and gradient descent method for correction of nonlinear response.The goodness of fit of convolution method,cross iteration method and gradient descent method improved by 0.15%,0.29%and 0.39%respectively.The method can improve the accuracy of spectral radiance measurement by infrared spectroradiometer.Aiming at the wavenumber drift of infrared spectral radiometer,the main factor that causes the wavenumber drift of the instrument is analyzed in this paper.Based on the analysis of the interference principle of the infrared spectroradiometer,the truncation effect,finite field of view effect,off-axis effect and defocus effect which affect the instrument line shape are analyzed,and the linear error data of the instrument is simulated by using the method of line-by-line integration.Based on the analysis of the simulation data and the previous research,the factor weight method is proposed to correct the linear function error of the instrument.This method has low cost and can correct the spectral drift caused by the linear error of the instrument without obtaining additional parameters of the instrument.The wave number error of the water vapor absorption peak measured by the infrared spectroradiometer is reduced from 0.226cm-1 to 0.012 cm-1 by the air background observation experiment.Finally,this paper verifies the accuracy of spectral radiance and wave number measured by the infrared spectral radiometer when the pollution gas is monitored and the high temperature target is observed through the simulated emission experiment of pollution gas,the remote measurement experiment of the tail flame of civil aviation engine and the remote measurement experiment of the tail flame of combat aircraft.The experimental results show that the error of measured spectral wavenumber decreases by 0.670 cm-1 after correction.In the civil aviation engine exhaust telemetry experiment,the goodness of fit of the black body measurement spectrum is increased from 0.99988 to 0.99997.In the telemetry experiment of fighter exhaust,the noise equivalent radiance of the instrument is reduced by 41.93%in the high-temperature radiometric calibration,which makes the measurement of spectral radiance more accurate.The results of this paper show that the gradient descent method and factor weight method can effectively improve the radiance and wave number accuracy of the infrared spectral radiometer.This study provides effective technical support for radiation calibration and wavelength calibration of infrared radiometer in telemetry of high-temperature target,which is of great significance to improve the application range of infrared radiometer at home and abroad.