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An Efficient MIMO Borehole Radar Imaging Method Based on High Degree of Freedom

In this paper, an efficient multiple-input-multiple-output (MIMO) borehole radar imaging method based on high degree of freedom is presented for subsurface sensing. The variable separations between different transmitter and receiver pairs in MIMO borehole radar are considered and introduced as imaging coefficients into the expanded unified MIMO sample set, which gives the MIMO sample set desired characteristics of high degree of freedom. By exploiting the high degree of freedom in the unified MIMO expanded sample set, the sample interpolation and energy migration of target reflections can be done in once efficient imaging processing for all transmitters of the MIMO radar system, and finally accurate target image with low sidelobe level can be delivered. The computational cost of the proposed method will barely increase with the number of transmitters in the MIMO radar survey, which enables the proposed method to handle MIMO borehole radar imaging in an accurate and efficient manner. The imaging properties of the proposed method are proven to be superior to the conventional imaging methods in sidelobe level and computational cost, which is suitable for large MIMO borehole imaging surveys in subsurface sensing applications.