Optimization of acquisition setup for cross‐hole: GPR full‐waveform inversion using checkerboard analysis

• Published in: Near surface geophysics (Online) 2013-04, Vol.11 (2), p.197-209
• Main Authors: Oberröhrmann, Max, Klotzsche, Anja, Vereecken, Harry, van der Krak, Jan
• Format: Article
• Language: English
• ISSN: 1569-4445; 1873-0604
• DOI: 10.3997/1873-0604.2012045

ABSTRACT Tomographic inversions of cross‐hole ground‐penetrating radar provide images of electromagnetic properties of the shallow subsurface and are used in a wide range of applications. Whereas the resolutions of ray‐based methods like first‐arrival traveltime and first‐cycle amplitude tomography are limited to the scale of the first Fresnel zone, full‐waveform inversions incorporate precise forward modelling using the full recorded signal for a solution of Maxwell’s equation, which results in sub‐wavelength resolutions. In practice, the method can be time‐consuming in data acquisition and expensive in computational costs. To overcome these expenses, a semi‐reciprocal acquisition setup with a reduced number of transmitters and an interchange of transmitter and receiver boreholes instead of a one‐sided equidistant setup in either borehole yielded promising results. Here, this optimized, semi‐reciprocal acquisition setup is compared to a dense, equidistant, one‐sided acquisition setup measured at the field site Krauthausen, Germany. The full‐waveform inversion results are evaluated using the checkerboard test as a capable resolution analysis tool to determine resolvabili‐ties. We introduced also a new method of time‐zero correction by a cross‐correlation of a zero‐offset profile with corresponding horizontal traces of each multi‐offset gather. The obtained experimental results from Krauthausen combined with the checkerboard analysis indicate the main three‐permittivity layers that correspond with different porosities. Also fine‐layered structures within these main layers were reliably imaged. We conclude that the use of the semi‐reciprocal setup is optimum for acquisition speed, inversion speed and obtained permittivity inversion results. Our results indicate that conductivity results are better for denser transmitter‐receiver setups.