On-orbit MTF estimation for the KOMPSAT-3 satellite using star images

Abstract

The KOMPSAT-3 (Korean Multi-Purpose Satellite-3) spacecraft was successfully launched on 18 May 2012, with the mission to provide high-resolution imagery for civilian and defence users. Star observation was performed for the purpose of various tests and evaluations such as modulation transfer function (MTF) measurement. This paper describes the method used to estimate KOMPSAT-3 on-orbit MTF performance using star images and presents the results obtained during the commissioning phase. The point spread function (PSF) model was built by estimating the position of the star at the subpixel level and applying a two-dimensional Gaussian curve fitting method. The line spread function (LSF) was derived from the PSF model, and the MTF and the full width at half maximum (FWHM) were estimated as a function of an azimuthal angle and were averaged out for the quantitative estimation. In our study, the MTF in panchromatic band was estimated to be stable at around 16% at the Nyquist frequency, which is a higher value than reported in previous work, and the FWHM was stable at around 1.69. Finally, we concluded that the MTF was maintained stably during star observation period, without any noticeable degradation in the aspect of temporal variation.