| Carbon dioxide and methane are important greenhouse gases in the atmosphere and the main drivers of climate change.Human activities and anthropogenic emissions are the main reasons for the increase in atmospheric greenhouse gas content.Although great progress has been made in the modeling and observation capabilities of greenhouse gases,the carbon cycle process between the atmosphere,land and oceans has not been fully understood,and there is considerable uncertainty in the prediction of climate change.In recent years,the instruments used to monitor the vertical profile distribution of atmospheric greenhouse gases are mainly high-resolution Fourier transform spectrometers,but they have complex systems,large volumes,high prices,and high maintenance costs,making them difficult to use universally.But the ground-based laser heterodyne spectrum radiometer(LHR)based on laser heterodyne technology has the advantages of small size,high spectral resolution,and easy integration.It has been used for remote sensing detection of various gases to meet the above requirements.This paper focuses on atmospheric greenhouse gas column concentration and vertical profile inversion algorithm and wavelength modulated laser heterodyne spectroscopy technology.The main work and achievements of this paper are as follows:(1)A set of inversion algorithms for the concentration and profile of greenhouse gas CO2 and CH4 columns based on high-resolution laser heterodyne spectroscopy were compiled,and an approximate evaluation method for system measurement error was established.Through 9 months of experimental observations,the standard deviation of XCH4 is measured as 3?17 ppb,the standard deviation of XCO2 is 0.7?2.2 ppm,and the corresponding relative measurement accuracy ranges are 0.15%?0.7%for XCH4 and 0.17%?0.5%for XCO2,the measurement result is compared with the GOSAT data in the same period,and the change trend of the two is consistent.(2)Researches on the wavelength modulated laser heterodyne spectroscopy and the frequency division multiplexed wavelength modulated laser heterodyne spectroscopy technology are carried out.Compared with traditional LHR,the signal-to-noise ratio of CH4(1.653 ?m)in the WM-LHR system is increased by 1.31 times.In order to further simplify the system,the frequency division multiplexing technology is applied to WM-LHR,using a single detection channel to achieve simultaneous detection of atmospheric CH4 and CO2.In addition,the effects of different modulation frequencies on external differential signals are studied.(3)A fully digital,all-fiber-based near-infrared calibration-free wavelength modulation laser heterodyne radiometer(CF-WM-LHR)was built to measure atmospheric CH4 column concentration.The system adopts software signal generator and software digital phase locked amplifier based on Lab VIEW design.The performance of the software digital lock-in amplifier was verified by comparing the demodulation results of the software digital lock-in with the demodulation results of the SR830 digital lock-in amplifier,and the software digital lock-in amplifier was used to demodulate to obtain 1f,2f,2f/1f of the WM-LHR signals,verify the feasibility of CF-WM-LHR system. |
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