| Measurements of vertical concentration profiles of greenhouse gases in the atmosphere provide a better understanding of air pollution,ozone destruction and climate change,and provide a way to validate chemical models and satellite observations.Laser heterodyne radiometers（LHR）have significant advantages in high spectral resolution,high sensitivity,small size,and low cost.The mid-infrared（MIR）region has been widely concerned in recent years because of its unique absorption window for specific gases in the atmosphere.However,due to the lack of mature optical fibers and optical waveguide components,the development of miniaturization and integration of midinfrared（MIR）LHR has been slow.This paper mainly focuses on the MIR laser heterodyne spectrum detection technology and its application.The main work and innovation of this paper are as follows:（1）Independently developed a set of high-precision free-space trackers for MIR LHR.The servo control system was built with high-resolution stepper motor.Based on the research on the basic principle of the sun tracker,the program of rough tracking and fine tracking of the sun was designed.The sun spot was binarized and then filtered and denoised to improve the system’s centroid calculation accuracy and tracking accuracy.The final test calculation shows that the tracking accuracy is±7 arc seconds,which provides a stable light source for the mid-infrared laser heterodyne radiometer.（2）A set of MIR LHR for atmospheric N2O detection was developed.The device uses an ICL as a local oscillator,which greatly improves the compactness and stability of the measurement system.The continuous observation experiment of atmospheric N2O was carried out in Hefei,and the comparison with the simulated absorption spectrum of the reference forward model showed good consistency,and the vertical distribution profile of atmospheric N2O was obtained through Python program inversion calculation,with a standard deviation of 0.031-2.6ppb.（3）A MIR LHR based on the MEMS mirror was developed,and the system was miniaturized and integrated.By analyzing the principle of MEMS mirror and modulation frequency,the optimal modulation frequency of the system was selected.The contribution of the main noise sources in the laser heterodyne radiometer system is quantitatively analyzed.The developed system is used to measure the atmospheric laser heterodyne absorption spectrum in the 3.93 μm.The measured laser heterodyne spectrum and Fourier transform infrared spectrum consistent with the atmospheric transport model.The small size,light weight and low power consumption of MEMS mirror greatly improve the integration and stability of MIR LHR.（4）A dual-channel MIR LHR based on MEMS mirror was designed for simultaneous remote sensing of CH4,H2O and N2O in the atmosphere.The stability of the system is evaluated by the Allan variance of the data obtained from the laboratory test.The detected absorption spectrum is consistent with the atmospheric simulated absorption spectrum,and the air mixing ratios of CH4,H2O and N2O are obtained by inversion calculation. |
