Research On Imaging Quality For Airborne Sweeping Hyperspectral Imager

Hyperspectral imaging technology is an organic combination of optical imaging technology and spectral analysis technology.It can obtain the spatial information and the spectral information of the target at the same time,so as to analyze and identify the geometric shape and spectral characteristics of the target.Hyperspectral imaging remote sensing,which originated from the development of remote sensing technology in the 1980 s,is the cutting-edge technology of remote sensing.It has the characteristics of high spectral resolution,large number of spectral bands and abundant information.It can be widely used in geological exploration,marine research,agricultural production and many other fields.As a practical application direction of hyperspectral remote sensing,the airborne sweeping hyperspectral imager has the advantages of large imaging field,low cost,convenient use,good maneuverability,etc.,which is of great significance for the popularization and application of hyperspectral remote sensing in the civil field.In this dissertation,the airborne sweeping hyperspectral imager is the research object.In order to improve the imaging performance of the imaging spectrometer,the imaging quality of the optical system under complex image motion is studied,focusing on three aspects: the design of the spectrometer,the calculation of the image shift caused by various errors of the instrument and the calculation of the modulation transfer function(MTF)for complex motion.The main research work of this paper is as follows:Firstly,the application requirements for airborne spectral imaging instruments are introduced,the design scheme of the instrument is determined.The design of optical system is completed,and the parameters of each part of the system are introduced in detail.The sweeping method is determined,and the mirror and aperture design of the three mirror reflector are introduced.The dynamic imaging process of the spectrometer is analyzed,and the ground track and pixel corresponding relationship are simulated.The influence of instrument error on the image mosaic is studied,and the image correction is completed.The advantages of the spectrometer design scheme are introduced,and the existing problems are summarized.This chapter lays the foundation for the later research.Secondly,based on the optical structure of the instrument,eight coordinate systems in the imaging processes are defined,and the imaging link model of aerial whisk-broom imaging is established by using the homogeneous coordinate transformation.The errors of the instrument are analyzed,and the influence of machining and assembling errors of three mirror reflector is studied.On this basis,the image displacement is calculated,and the influence of machining and assembling errors of three mirror reflectors on the displacement of the image point are analyzed.Then according to the index target of the system,the errors of imaging spectrometer are allocated reasonably,and the image displacement is simulated by Monte Carlo method.Finally,the validity of the imaging link model is verified by simulation method,which proves that the instrument design scheme proposed in this paper can meet the requirements of high imaging quality.Finally,the influence of complex image motion in complex motion on MTF of the imaging system is studied.A general method for calculating the MTF for image motion is proposed,and the influence of single image motion on MTF is analyzed.Then,the model is applied to complex image motion relevant to the mixing of multiple forms of motions,the summation of infinitely many terms involving Bessel function is used to simplify the MTF expression,obtains the analytical expression of MTF for complex motion.The truncation error obtained by the use of finite order sum approximations instead of infinite sums is investigated in detail,and the numerical solution of MTF is obtained.In order to verify the MTF calculation method,a simulation method to calculate the variation of MTF in an actual optical system caused by image motion is proposed.An experiment is performed and the experimental results are consistent with the MTF calculation model.Finally,the change of image quality is simulated considering the instrument error,the simulation results and calculation results are the same.This project has completed the research on the design of the spectrometer,the calculation of image displacement in airborne imaging,and the calculation of MTF for complex image motion to study the imaging quality of airborne sweeping hyperspectral imager.The research conclusions can provide theoretical basis and technical guidance for the development of airborne sweeping hyperspectral imager and image restoration,which has important practical engineering value for promoting the development and application of airborne imaging spectrometer.