Research Of Image Rotation Compensation Technology Based Bilateral Control In Aerial Camera

In the aerial camera scanning imaging process,the most widely used scanning method is to keep the optical system does not move,by rotating the 45 ° scanning mirror imaging,it has several other imaging methods unparalleled advantages.But in the process of rotating 45°scanning mirror,the image will rotate around the optical axis as the swaying indication angle changes,resulting in image blur,contrast decreased,affecting the image quality,serious information loss will occur.So it is necessary to take measures to compensate for the image rotation.Common methods for elimination of image rotation are optical de-rotation,electronic de-rotation,and mechanical de-rotation.Optical de-rotation method usually adopts the Dowell prism,K mirror system constitutes an optical compensation system,but the Dowell prism due to the critical angle,optical materials,resulting in limited field of view angle is small and can only be applied to the visible light to near infrared band,K mirror system will reduce the optical efficiency and increase the camera's size and weight.The electronic de-rotation method results in missing edge view information,and the precision of the view depends on the accuracy of the rotation algorithm and the interpolation algorithm.In contrast,mechanical de-rotation method with high-speed,real-time,easy to install and adjust the advantages of high-quality aerial camera is widely used.How to improve the accuracy of image rotation is the key to realize the high-quality imaging of aerial camera.Based on the principle of mechanical de-rotation,the paper studies the image rotation compensation technology of aerial camera based on bilateral control.The rotation principle of the four-channel bilateral control image rotation compensation system is analyzed,and it is proved that the internal-loop compensator is the key factor that influences the image rotation compensation performance.The method of improving the four-channel bilateral control image rotation compensation system based on the robust internal-loop compensator is proposed.By improveing the robustness of the system and the system interference suppression,image rotation compensation baesd on four-channel bilateral control will be improved.Max and root mean square of position compensation errors of dynamic scan command are 0.001712°,0.000465°,respectively.Compared with the traditional control system using disturbance observer,the compensation errors of dynamic scan command in proposed system are reduced by 45.86%,44.84%,respectively.So the accuracy of image rotation compensation has been improved in the four-channel bilateral control system.In order to evaluate the image quality accurately and objectively,the method of evaluating the compensation accuracy of bilateral control system of the aerial camera based on the dynamic MTF is proposed.Firstly,based on the polar coordinate system,the dynamic MTF of the imaging performance of the system is described by the spatial frequency in the normal direction and the tangential direction.Then,by analyzing the rotation motion,the effect of the image rotation compensation error on the image quality of the system is studied,and the general dynamic MTF conclusion is obtained.The measurement method based on the combination of the slanted-edge method and the blur path method is proposed.Finally,simulate aerial camera rotation by rotating the turntable.The measured values and the theoretical calculated values of the MTF of the sectorial target image are obtained by using the rotating dynamic MTF function,the slanted-edge method and the blur path method.The experiment verifies the correctness of dynamic MTF and the accuracy of blur path method by comparison of the measured values and the theoretical calculated values.So the paper establishes the direct relationship between the imaging quality of rotary motion system and other control indexes.The dynamic MTF of rotation can be used to predict and evaluate the image quality in image rotation,and it is of theoretical significance for the design of bilateral control image rotation compensation of aerial camera.