Study On Doppler Asymmetric Spatial Heterodyne Spectrometer In Wind Velocity Retrieval

The middle and upper atmosphere of the earth is a valuable space territory and a significant section to the space weather study and space environment study.Upper atmospheric wind detection,which is a key element of the behavior of the upper atmosphere activities,is an important method of the atmospheric physics study.The need for higher altitude atmospheric wind measurements on the earth is typically derived from the desire to understand the atmospheric dynamics and energetics with the ultimate goal to improve weather forecasts and to constrain global scale models.Doppler Asymmetric Spatial Heterodyne Spectrometer(DASH)is an advanced upper atmospheric wind measurement method which can detect and compute ultraspectrum of the atmospheric trace gas with a low and accurate computational complexity.In the algorithm of the Doppler Asymmetric Spatial Heterodyne Spectrometer,it is necessary to imply data pre-processing to the acquired interferogram to obtain the high-precision wind data.This thesis studied and researched some of the unsolved problems of the Doppler Asymmetric Spatial Heterodyne Spectrometer for measurement of the upper atmospheric wind,and the main research of this thesis are as follows: Introduction of the current research status and significance of the middle and upper atmospheric wind measurement and the existing wind measurement methods.Doppler Asymmetric Spatial Heterodyne Spectrometer is introduced and the advantages of DASH is presented.The current research status and development orientation of DASH for the upper atmospheric wind measurement is presented.The basic principle and system configuration of Doppler Asymmetric Spatial Heterodyne Spectrometer is studied and properties of the airglow which is the target of the atmospheric wind measurement is researched.The basic principle and observation mode of the DASH for the atmospheric wind measurement is studied and presented based on the Doppler effect of the airglow spectrum.The design of system parameters of the Doppler Asymmetric Spatial Heterodyne Interferometer is presented and the retrieval algorithm of the atmospheric wind data is studied.The simulation and verification of the algorithm is completed on the Matlab.The calculation method of signal to noise ratio of the Doppler Asymmetric Heterodyne interferogram and the noise propagation is analyzed and simulated.Based on the system parameters and the whole data-processing algorithm,the atmospheric wind is calculated and the standard deviation of retrieval wind speed is 0.31 m/s.Using the average peak spectral radiance of the 630 nm airglow as observation object,the SNR of DASH is simulated and computed as 80 based on the SNR calculation method.Baseline removal which is an important part of the atmospheric wind retrieval algorithm is introduced and studied.Several baseline removal algorithms are studied and used in two different situations,ideal interferogram without noise and the interferogram with the Gaussian white noise.The result can be drown that the difference method is the optimization method from the comparison of several baseline removal algorithms.It indicates that the retrieval wind speed of difference method is about 2.5 m/s more accurate than other method for the interferograms which SNR are from 20 to 180.Apodization which is a key step in the interferogram pre-processing algorithm is presented.The principle and properties of different kinds of apodization method is studied.The process that the interferogram is apodized in different apodization method and two different situations,ideal interferogram without noise and the interferogram with the Gaussian white noise,is analyzed and compared.The result can be drown that Hanning window apodization,Hamming window apodization and Triangular window apodization provides the best performance and most stabilized retrieval wind speed in the case that the interferogram is affected by the noise.Comparing retrieval wind speed of different apodization method,for the interferogram which SNR is 20,the standard deviation of the retrieval wind speed of the Hanning window apodization,Hamming window apodization and Triangular window apodization is about 0.2 m/s more accurate than other apodization.Isolation of the target spectral line algorithm is analyzed by the Monte-Carlo method to the interferogram with the Gaussian white noise,the retrieved wind velocities of interferogram with different SNR optimized by different window function with different FWHM are analyzed.The conclusion is that rectangular window function method with FWHM equaling 7 to 12 times spectral resolution provides the best performance and optimization.Comparing the retrieval wind speed of different isolation algorithms for the interferograms which SNR are from 20 to 180,it can indicate that the standard deviation of the wind speed of the rectangular window function method with FWHM equaling 7 to 12 times spectral resolution is about 1~2 m/s more accurate than other isolation algorithms.For the interferogram which SNR equaling 80,the standard deviation of the rectangular window function method with FWHM equaling 8 times spectral resolution is 7.6586 m/s,the phase information which contain the Doppler frequency shift and the atmospheric wind speed can be calculated and retrieved.