Hand-held radar with video positioning system for microwave imaging

Obtaining microwave images of subsurface objects with scanning radar systems requires positioning of the radar antenna within a fraction of the wavelength in the medium. At the frequencies of several gigahertz the positioning of the radar is achieved by a distance measuring wheel, which can be used only on smooth surfaces. In such a positioning system the data acquisition requires collecting data samples along parallel lines to get plan view images. In this paper a hand-held radar equipped with a video-based positioning system is considered. The video-based positioning system, which uses a web-camera and a contrast graphical marker (an AR-marker), enables positioning the radar in 3D with sufficient precision without any constraints on the sampling pattern. The radar position is calculated using correspondence between the physical coordinates of the marker corners and their projections on the web-camera image. Reconstruction of the microwave image is performed by a back projection method which uses 3D coordinates of each data sample. The result of data processing can be presented as a traditional microwave image, or as an overlay to the image of the scene (augmented reality). This way of data visualization removes the problem of radar data remapping from the computer screen to the probed scene. Several application areas of the developed technique are outlined. Among the considered problems are: obtaining radar images of concealed objects under clothing by a hand-held radar scanner and obtaining radar images over uneven surfaces (arched ceilings, columns, statues, natural soil etc.). The first of these applications is illustrated with experimentally obtained results.