Study On Effects Of Spaceborne Hyperspectral Imager’s Optical Component Positional Error

Spaceborne hyperspectral imager shows great advantages in use comparing withtraditional remote sensors. But the multiple optical components it consists of and thehigh precision requirements to fulfill high spatial and spectral resolution make it a bigchallenge to manufacture, especially in the process of alignment. Studying effects ofoptical components’ positional error on imaging is an effective way to enhance theefficiency of alignment, as well as to improve positional error’s negative impacts onimage.With respect to the fore-optics of a dispersive hyperspectral imager, opticalelements were categorized into three types according to positional error’s aberrationcharacteristic: aberration sensitive elements’ positional error caused significantwavefront aberrations; plane optical elements and optical components caused littleaberration when position changed; pointing mirror’s scanning error caused imagedegradation on orbit. Researches on the three types element were made as follows:constructed model to compute wavefront aberration induced by aberration sensitiveelements’ positional error, and studied precise inversion method from laboratorialtested wavefront error to positional error; studied compensation relationship betweenthe second type element’s positional error, and made optimized error budgets on these errors; studied pointing mirror’s low frequency oscillation induced image distortionwhen on orbit, and their rectification.Based on COM communication between Matlab and Code V, numerical relationbetween wavefront error’s fringe Zernike polynomials expansion coefficients andelement’s misalignment value was obtained, and quadratic polynomial was used to fitthe relationship. Simulation showed that quadratic fitting accuracy was10times betterthan that of the sensitivity matrix method based on linear model. Factors that causedthe inaccuracy of misalignment value’s inversion in computer aided alignment werestudied. Fringe Zernike coefficients’ analytic transformation into subaperture wasadopted to resolve the non-uniqueness of coefficients among different subaperture ofidentical wavefront. Geometrical parameters’ inversion from fringe Zernikecoefficients of different subapertures was studied, verification was made by bothsimulation and experiment. Dynamic optics theory was used to built relation betweenpositional error and Gaussian image’s rotation and defocus. The applicability ofGaussian image theory on alignment was studied. Appropriate adjustments werecalculated to compensate image rotation and defocus caused by teleobjective axis’sangular offset. An optimized error budget was made towards optical modular’sassembly. Monte Carlo method verified that the budget was within current technologylevel and focusing ability, meanwhile achieved the goal of loosest whole tolerance.Low frequency oscillation of pointing mirror induced image distortion was modeledbased on space remote sensor image motion model. Image motion of feature pointwas used to correct image output. Simulation showed that with the accurate value oforbit parameter, satellite attitude parameter and pointing mirror’s angular positionerror, this kind of distortion could be rectified thoroughly by the proposed method.Rectification on real distorted image also produced a good result.