Frequent oversights in on-orbit modulation transfer function estimation of optical imager onboard EO satellites

Abstract

Modulation transfer function (MTF) is one among the key image quality indicators that characterizes the spatial response of an imaging system. There are various techniques suggested in the literature for quantification of MTF, for instance, slit-based method, point target-based method, image-structure-and fractal characteristic-based methods, and the slant-edge method. For high-resolution satellites, slant-edge-based method for on-orbit MTF estimation is the standard and widely used method due to its simplicity of implementation and practical feasibility. However, the edge-based method relies on accurate estimation of certain parameters failing, but the results may be misleading. We present the frequently occurred oversights and inadvertent miscalculations in MTF estimation using the slant-edgebased technique for high-resolution satellite sensors. We mainly address the two most common oversights in on-orbit MTF estimation process: (1) optimal edge width estimation and (2) precise empirical modeling of the slant edge. A rigorous sensitivity analysis suggests that oversights in any of these two factors can severely under or over estimate the MTF numbers. We establish accurate slant-edge-based MTF estimation procedure that can potentially avoid the aforementioned oversights.