Broadband synthetic aperture borehole radar interferometry

Trials in mines have established that wideband VHF borehole radars (BHR), w orking in the 10-100-MHz band, can be used to probe the rockmass between bo reholes over ranges from < 5 in to as much as 150 m with submeter resolutio n. There is evidence that ore bodies reflect these radar signals both specu larly and diffusely, much as the ground/air interface does when overflown b y synthetic aperture radar (SAR). In both SAR and BHR, multiple flight line s, together with diffuse reflections admit the possibility of developing in terferometric 3D images of the object. This paper examines the possibility of imaging buried objects in three dimensions by interferometrically combin ing broadband VHF borehole radar profiles shot in adjacent pairs, of boreho les. Broadbanding in BHR has the advantage of releasing the image from 2n p i, phase ambiguities, but practically, interferometric borehole radar (InBH R) needs high signal-to-noise ratios (SNR) to avoid noise capture. This mea ns that 3D InBHR is limited to ranges in wavelengths which are less than th e rock's attenuation factor Q. Interferometric methods are developed which are capable of mapping ore bodies and other structures in three dimensions. Tangent plane migration methods axe developed here in order to reconstruct surfaces that lie in the near-field of sparse interferometric arrays. (C) 2001 Elsevier Science B.V. All lights reserved.