In-orbit performance calibration method of imaging satellites based on stars

摘要

Traditional in-orbit imaging performance calibration of optical imaging satellite is always based on the sun or ground artificial target. As imaging system performance advancing, the calibration procedure could base on fainter target such as stars instead. The practical step of star-based satellite performance calibration procedure is to select proper stars according to their magnitude and spectral character, center them in image by image processing, and transform the image to achieve imaging MTF. Nowadays space-based camera with large aperture could transfer photoelectrons continuously to obtain enough long exposure duration, so faint stars can also be detected. But the center of star would always tilt from the center of detector pixels which would be very hard to align. With Discrete Fourier Transformation (DFT) and Point Source Function (PSF) correlation, the align accuracy could be improved observably. Finally, as a complex imaging system, the final image MTF would also includes defocus effect and satellite platform jitter etc, which the defocus is of circular shape and temporal independent , but the jitter is of linear type in short exposure and the direction and length may be a function of time. So based on a time serial images and the iteration algorithm, the jitter characteristic may be separated. Simulation calibration procedure mentioned above indicates satisfying consequence. So those calibration outcomes could also be used to determine the defocus of the focal plane in camera and the high frequency jitter of the satellite platform during exposure duration while imaging.