3-D Directional Borehole Radar Imaging Based on Echo Separation.

Directional borehole radar (DBR) is a powerful tool for constructing the 3-D morphology of subsurface geological bodies. Direction of arrival (DOA) estimation is a key step in 3-D imaging. However, the existing DOA methods are constrained by factors such as DBR aperture, and can only identify one signal source within a time window. Consequently, when faced with multiple targets, DBR encounters challenges in effectively distinguishing them, especially when their echoes nearly overlap. In addition, the presence of interference waves makes echo overlap more likely to occur. So we propose a 3-D imaging method based on echo separation to solve this problem. This method first separates echoes of different targets through echo separation methods such as correlation method, deconvolution method, τ- p transformation method, and moving window method. Subsequently, the azimuth is obtained through the multiple signal classification (MUSIC) algorithm, while the depth and radial distance are obtained through the inverse bi-static boundary scattering transform (IBBST), finally achieving the 3-D imaging of multiple geological targets. The effectiveness of the proposed method is demonstrated through synthetic data of both simple and complex fracture models, and its feasibility in practical applications is demonstrated through field data examination. This method improves the detection capability of DBR, opening up new possibilities for accurately mapping subsurface geological features.