Modeling the modulation transfer function measurement system of large aperture space cameras

Abstract

Large aperture space cameras are widely used in high-resolution remote sensing, ultra-weak space targets detection, high-precision astronomical observation, etc. Modulation transfer function (MTF) can directly reflect the information transmission ability of a space camera. Usually, the image quality of a camera is evaluated by measuring its MTF. The MTF of a space camera needs to be measured during alignment of the optical system and electronic system, preset of the vacuum focus position, mechanical experiment, thermal experiment, etc. This paper suggests a method to model the imaging chain of large aperture space camera MTF measurement systems. The model comprehensively considers the factors of the aberration of the collimator, air turbulence, temperature variation, gravity, and environmental vibration. We calibrate the aberration of the collimator, air turbulence, temperature variation, and gravity induced error by measuring the corresponding wavefront error with a 4D laser interferometer. A star point target is placed in the focus position of the collimator to calibrate the environmental vibration through extracting the centroids of the point target images captured by the space camera. The impacts of the previous factors on the MTF measurement results of the space camera are obtained with the proposed model and the corresponding calibration data. The proposed method can evaluate the impacts of different factors on the MTF measurement results and can guide the measurement of large aperture space camera MTF.