ULTRASOUND MULTIPATH BACKGROUND CLUTTER MITIGATION BASED ON SUBSPACE ANALYSIS AND PROJECTION

In this paper, we consider ultrasound imaging of flaws in a metallic alloy where the presence of strong bottom surface reflection and other interference signals constitutes a challenging problem. A subspace-based approach is developed for removing, or significant-ly reducing, bottom surface reflections to enhance ultrasound imag-ing. In constructing the surface reflection, or clutter, subspace, we account for rough surface scatterings which, due to various possi-ble propagation time delays between the transmitter and receiver, expand the subspace dimension beyond that corresponding to ideal propagation. We also estimate and compensate, using signal corre-lation methods, for changes in the same time delays due to imper-fect sensor displacements on the top surface of the alloy. Experi-mental results show that substantial clutter suppression can be achieved with negligible effects to the flaw signals. Index Terms — Ultrasound imaging, clutter suppression, subspac