Abstract: The invention relates to a method for determining the relative movement between a target tracking missile and a target being located at a target distance from said missile. The missile is equipped with an image processing seeker head provided with a seeker detecting said target. The seeker head observes the target in an observation direction. A target image is generated on the seeker. The size of the target image depends on the observation direction. The target moves with a target velocity relative to the missile. The method has the method steps of: defining a seeker head-fixed coordinate system; defining a maximum absolute size of said target; measuring further relevant quantities; and running a recursive algorithm in order to obtain estimated values of a three-dimensional vector of the target velocity in the seeker head-fixed coordinate system by using as inputs the defined maximum absolute size of the target and the image dimension appearing on the seeker as well as further relevant quantities.