1. A scene tracker system adapted for responding to sequentially applied fields of data each of which are definitive of a scene within a field of view, so as to provide global correlation coordinate signals which are indicative of the relative spatial displacement between scenes defined by different fields of data, said system comprising: reference date storage means for storing reference cell data from a preselected plurality of portions of one field of data; means for correlating the data for each reference cell against data for an associated search cell, with the data for each associated search cell being derived from a portion of a subsequent field of data which encompasses the relative position of the associated reference cell; and for providing local correlation coordinate signals indicative of the relative location within each search cell of the correlation match between each search cell and its respective reference cell; and processor means for processing said plurality of local correlation coordinate signals so as to produce as a function thereof global correlation coordinate signals which are indicative of the relative spatial displacement between the scenes defined by said one field of data and said subsequent field of data.