Determination of horizontal motion through optical flow computations
Determination of Horizontal Motion through Optical Flow Computations

For intelligent / antonomous subsea vehicles, reliable short-range horizontal positioning is difficult to achieve, particularly over flat bottom topography.A potential solution proposed in this paper utilizes a passive optical sensing method to estimate the vehicle displacement using the bottom surface texture.The suggested optical flow method does not require any feature correspondeuces in images and it is robust in allowing brightness changes between image frames. Fundamentallyt this method is similar to correlation methods attempting to match images and compute the motion disparity. However, in correlation methods, searching a neighbor region blindly for best match is lengthy. Main contributions of this paper come from the analysis showing that optical flow computation based on the general model cannot avoid errors except for null motion although the sign of optical flow keeps correct, and from the development of an iterative shifting method based on the error characteristics to accurately determine motions. Advantages of the proposed method are verified by real image experiments.