Super-resolution of coherent targets by a directional borehole radar

In this paper, an analytical method based on the multiple signal classification (MUSIC) algorithm is applied to three-dimensional (3-D) estimation of target positions using a directional borehole radar. A cylindrical conformal array on a conducting cylinder in a borehole was used for experimental measurements estimating the position of targets. It is also shown that the algorithm provides much better resolution than the Fourier-based algorithm in both a computer simulation and real tests. Soil at the experimental site is not necessarily uniform, and there can be many clutter sources such as small stones in the subsurface. For this situation, it is difficult for the super-resolution technique to work properly. Results of the experiments show that the super-resolution technique for locating targets, despite being seriously limited by both the space available for the array and the bandwidth, is promising for directional borehole radar. In the developed algorithm, it is assumed that the distribution of electromagnetic constants inside a borehole is known before estimation of target positions.