Three-dimensional kinematic imaging of borehole radar data

Abstract

Broadband, 10-100 MHz, VHF borehole radar (BHR) can be used to map ore bodies, faults and marker horizons, and to identify hazards in advance of mining. Mine boreholes are often drilled in fans. BHR data acquired from these boreholes can be used to reconstruct targets in 3D. Significant progress has been made in using synthetic aperture radar interferometry (InSAR) to reconstruct 3D images from sparse arrays. However, automatic methods of projecting data into 3D image space, such as migration and InSAR, make stringent demands upon rock homogeneity, translucence, and the accuracy of borehole trajectories. These demands can be relaxed by kinematic mapping using geologically plausible 3D primitives such as cylinders, planes, and spheres. In this paper we show how interactive kinematic mapping can be applied in practice to BHR data acquired in a Western Australian mine. BHR data were shot from a fan of ~200 m long boreholes. The holes were drilled from a single station at relative angles of ~5°. Both cross-hole transmission and single-hole reflection surveys were performed. Reflection ranges of 50-60 m were achieved in the rocks hosting the deposit. Echo patterns correlated using kinematic primitives were used to infer the geometry of an interface that was interpreted to be approximately 20 m above the uppermost borehole in the array.