Proceedings PaperImage correction via lunar limb knife-edge OTFs
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The edge of the mono is used as a high contrast target to perform a visible 'knife-edge' MTF test on a digital imaging system in geostationary orbit. An image of the moon is taken in the camera's normal scanning mode, and traces across the sharpest edge are used to form an edge spread function (ESF). The ESF is then sued to produce an MTF estimate. In a second trial, the imaging system stares as the lunar edge drifts by, creating an edge spread function with a much higher effective spatial sampling rate. In each case, a technique of combining and resampling traces is employed to adapt the knife-edge MTF technique for use with sampled data. The resulting MTF curves track ground test frequencies to within five percent. The phase transfer function is also extracted, and the process is repeated in the north/south direction. The functions are combined to produce a 2D optical transfer function (OTF) which is used as an inverse filter to restore raw images via deconvolution. The approach thus offers a means of testing the MTF and OTF of orbiting image acquisition devices as well as enhancing satellite imagery.