Abstract: A method for calibrating an imaging instrument, possibly located on an aircraft or satellite, is described. According to the method, an image acquired by the instrument is ortho-rectified, and then co-registered and correlated with a reference image. In this way, ground disparities between the acquired image and the reference image are measured. Updated instrument pointing directions that correct for the disparities measured are then determined and adopted as corrective calibrations for the distortions of the instrument.