1. A method for estimating the movement of an observation instrument on-board a vehicle flying over a celestial body, the observation instrument comprising at least two strips with different lines of sight, each strip realizing the acquisition of successive image lines making up a composite image, by scanning its line of sight over the celestial body, parts of the composite images representing substantially a same scene of the celestial body, wherein the estimated movement is determined by searching a movement hypothesis that optimizes a global function, the value of the global function, obtained for a given movement hypothesis, cumulating the respective values of an image similarity function and of an external similarity function calculated for said given movement hypothesis: the value of said image similarity function corresponds to a similarity between values of matched pixels of at least a pair of composite images, matched pixels being pixels that represent, theoretically, the same point of the observed scene, given said given movement hypothesis, and the value of said external similarity function corresponds to a similarity between said given movement hypothesis and measurements of the observation instrument's movements, made by one or several sensors different from the observation instrument's strips, the method comprising, for calculating the value of the image similarity function for each movement hypothesis considered during the optimization of the global function, the following steps: determining, for the at least one pair of composite images, at least one spatio-temporal transformation using the considered movement hypothesis and a geometric model of the observation instrument; and matching the pixels of the at least one pair of composite images using the at least one spatio-temporal transformation.