Abstract: Existing positioning technologies used in conjunction with Ground Penetrating Radar (GPR) are generally too time-consuming or insufficiently accurate for high resolution, high frequency, 3-d structural investigations. The invention provides an optical positioning system for use in GPR surveys that uses a camera mounted on the GPR antenna that takes video of the surface beneath it and calculates the relative motion of the antenna based on the differences between successive frames of video. Positioning accuracy to within several millimeters is provided. The procedure is orders of magnitude faster than surveying a grid of data points or laying out parallel lines and surveying each line with an odometer wheel. The system and method of positioning is suitable for mapping the subsurface of structures such as building columns or floors using GPR. Time domain synthetic aperture radar algorithms can be used to reconstruct an image of the subsurface using this position data.