Charactering Daytime Seeing Profiles And Wind Speed Profiles Based On The Wide Field Shack-Hartmann Wavefront Sensor

For the demand of high resolution observation of solar active region,solar multiconjugate adaptive optics(MACO)that has become one of the most interesting researches on adaptive optics,uses the vertical altitude distribution of atmospheric turbulence(atmospheric turbulence profiles)and controls a number of DMs conjugated into different altitude to widen the compensated field of view by correcting the phase distortions?Therefore,the basis and crucial knowledge of realizing the solar MCAO is how to characterize the daytime atmospheric profiles,namely how to obtain the characteristic parameters of atmospheric turbulence related to the corrected bandwidth of the solar MCAO system.,including the atmospheric isoplanatic angle,atmospheric coherence time,Greenwood frequency and Tyler frequency.Further,these characteristic parameters are closely related to the vertical height distribution of the seeing and the vertical height distribution of the atmospheric wind speed.For the demand of the specific application needs of the solar MCAO technology,this Ph D dissertation is aimed to the research on the characterization of daytime seeing profiles and daytime wind speed profiles,based on the 1-m new vacuum solar telescope(NVST)at the Fuxian Lake Solar Observatory(FSO)and the 37-unit wide-field Shark-Hartman wavefront sensor(SHWFS).More attention is paid to the algorithm improvement,simulation and experimental analysis.Firstly,the characteristics of atmospheric turbulence is introduced,as well as the technique of characterization of atmospheric turbulence profiles.Kolmogorov turbulence statistical theory is dominant in the study of turbulence theory,and its statistical characteristics of refractive index fluctuation and phase disturbance are introduced.Then,the mainstream techniques of charactering atmospheric turbulence profiles in the case of Kolmogorov turbulence statistical theory are studied,including scintillation detection and ranging(SCIDAR),slope detection and ranging(SLODAR)and solar differential image motion monitor plus(S-DIMM+).As the guide stars for characterizing daytime atmospheric turbulence profiles are two-dimensional extended structures,S-DIMM+ technique will be used to study the characterization of daytime seeing profiles.As the difficulty that the S-DIMM+ can't estimate the wind speed and the convenience that obtaining the slope data of guide star,SLODAR technique will be used to study the characterization of daytime wind speed profiles.Next,based on the 1-m new vacuum solar telescope(NVST)at the Fuxian Lake Solar Observatory(FSO)and the 37-unit wide field Shark-Hartman wavefront sensor(SHWFS),more attention is paid to research on wide-field SHWFS data preprocessing and the calculation of wavefront slope of guide stars.Pupil rotation is a problem that large aperture alt-azimuth telescope must face,which leads to rotation of open-loop solar image collected by wavefront sensor,and further leads to uncertainty of wavefront slope extraction and the characterization of atmospheric turbulence profiles,so the pupil rotation compensation is a necessary step for the wide-field SHWFS data preprocessing.According to the optical system design of NVST which is alt-azimuth solar telescope,the pupil rotation compensation method based on rotating platform is proposed.In addition,as the solar target images recorded by the SHWFS are two-dimensional extended structures,such as sunspots or solar granulation;and the telescope spider structure will cause the significant differences of contrast between the SHWFS subapertures,therefore,the cross-correlation algorithm will be used to calculate the wavefront slope of guide stars.Furthermore,we propose a modified S-DIMM+ method to measure daytime seeing profiles.S-DIMM+ is a technique to measure vertical seeing profiles.However,the number of height grids will be limited by the lenslet array of the wide-field Shack–Hartmann wavefront sensor(SHWFS).A small number of subaperture lenslet arrays will lead to a coarse height grid over the atmosphere,which can result in difficulty in finding the location of strong-turbulence layers and overestimates of the turbulence strength for the measured layers.To address this problem,we propose a modified SDIMM+ method to measure seeing profiles iteratively with decreasing altitude range for a given number of height grids;finally they will be combined as a new seeing profile,with a denser and more uniform distribution of height grids.This method is tested with simulations and recovers the input height and contribution perfectly.Furthermore,this method is applied to thedata-sequences recorded from the 1-m New Vacuum Solar Telescope at Fuxian Solar Observatory.A 7x7 lenslet array of SHWFS is used to generate a 16-layer height grid to 15 km,each with 1 km height separation.The experimental results show that the turbulence has three origins in the lower(0–2 km)layers,the higher(3–6 km)layers and the uppermost(?7 km)layers.At last,we propose a modified SLODAR to measure daytime wind speed profiles.An extension of SLODAR(slope detection and ranging)can be used for wind profiling by tracking the time-delayed cross-correlation peaks obtained from the slope of the Shack–Hartmann wavefront sensor.This wind-profiling method works well in situations where the cross-correlation peaks can be individualized,but in many cases the isolated crosscorrelation peaks for each turbulent layer are difficult to find in the 2D cross-correlation maps,which can result in difficulties when estimating the wind profiles.To address this problem,we propose a method to measure the wind speed and direction of each layer.The method distinguishes isolated peaks more easily and is valid for multiple peaks,even for a weak response.Instead of tracking peaks in 2D cross-correlation maps,the proposed method traces a series of cross-correlation peaks in the curves of 1D slices through the maps from different directions,and finally determines the wind speed and direction according to the frozen-flow hypothesis.This method is verified with simulations,in which the input wind profiles are recovered accurately.Furthermore,this method is applied to 47 data sequences from the 1-m New Vacuum Solar Telescope at Fuxian Solar Observatory.The wind profiles are estimated from the ground up to 12 km,and the experimental results show that all layers move with a relatively low speed.This Ph D dissertation is aimed to study the characterization of daytime seeing profiles and daytime wind speed profiles,for the demand of the specific application needs of the solar MCAO technology.This dissertation is pioneering work in domestic and overseas,which is very valuable for promoting the development of characterization technology of atmospheric turbulence profiles in China and adaptive optics technology.