| Space-borne camera is one of the most important component and core load of satellite detection system,mainly divided into two types: ground observation camera(remote sensing mapping,environmental monitoring,military reconnaissance,etc.)observation and space objects observation camera(spacecraft,space debris,stars,etc.).However,due to assembly,transportation,launch impact and thermal state may gradually influence the imaging performance and spoil the sharpness of captured images.The modulation transfer function is an important parameter wildly used to evaluate the image quality of the optical system,and the modulation transfer function can not only evaluate the image quality of on-orbit space-borne camera,but also has great significance for later calibration and image restoration.Currently,the on-orbit MTF measurements for ground imaging remote sensing camera is tending to reach perfection.While space-borne camera used for space detection is limited by its specific imaging target and the risk of flipping itself to capture ground images.Therefore,the on-orbit MTF measurements for ground imaging satellite camera cannot directly used on the space detection satellite camera.In this paper,based on the specific orbit state and imaging target of space detection satellite camera and combined with the related theories of the photo-electric imaging system and the commonly used MTF measurements,two reasonable on-orbit MTF measurements named lunar-edge MTF measurement and star-point MTF measurement for space detection satellite camera are proposed.Afterwards,the two proposed measurements are simulated and validated by means of simulation and experiment respectively.The high-contrast ellipse edge image formed by lunar and deep-space background provides an ideal target for lunar-edge on-orbit MTF measurement.Also the star image in deep-space background provides a reasonable target for star-point on-orbit MTF measurement.First,in MATLAB simulation part,the principle of imaging chain in digital cameras is analyzed.A reasonable simulation target image generation method is proposed and its theoretical MTF curve is calculated,which can be used to quantitatively verify the precision of lunar-edge method and star-point method.We mainly study the key processing step of our lunar-edge MTF method and star-point MTF method,analyze and compare the precision and operation speed of various processing methods,thus two sets of improved test algorithm are obtain respectively.After that,the influence of various factors on the proposed methods is quantitatively analyzed.Second,in experiment part,a set of experimental verification system including optical lens,electronic circuit and image acquisition system was set up.The image of the designed round edge target and the star array target is captured by this optical system.Then MTF measurements are carried out to verify our proposed optimization algorithm flow and influence factors analyzed in simulation section.It shows that the experiment results are in good agreement with simulation results.In conclusion,our lunar-edge MTF method and star-point MTF method can provide theoretical reference and technical support for space-borne camera on-orbit MTF measurement. |
PDF Full Text Request