Underground GPR measurements for spatial investigations in a salt dome
Ground penetrating radar (GPR) is an efficient non destructive tool for the exploration of underground salt deposits. The complex geological structures (bent, folded, sometimes faulted layering of salt, potassium, clay, and anhydrite) in low-conductive salt can be mapped if distance and direction of reflecting objects are known. In boreholes the information is given by direction sensitive borehole radar. In shafts rotation symmetry helps to detect the direction. In drifts direction finding antennae provide the reflection angle. Various antenna types help to enhance the resolution or the penetration depth. Measurements with different polarizations offer additional information about the reflecting structures. Within the last two decades unique results from a salt dome in Northern Germany with various GPR systems were achieved. With this information and some geological knowledge a three dimensional model of the structures has been created.
Use of Geophysical and Radar Interferometric Techniques to Monitor Land Deformation Associated with the Jazan Salt Diapir, Jazan city, Saudi Arabia
Using integrated Interferometric Synthetic Aperture Radar (InSAR) datasets (Envisat: 2003–2009; Sentinel-1: 2014–2018), local gravity surveys, and passive seismic data, we investigated the environmental hazards associated with the rise of the Miocene Jazan salt diapir (JZD; ~ 2 km 2 ) within Jazan city, Saudi Arabia, and identified areas at risk in its immediate surroundings. Our findings include (1) the JZD outcrop and its northern, southern and western bordering areas have been undergoing substantial uplift (up to 4.7 mm/yr), whereas the sabkhas to the east are witnessing subsidence (up to − 7.5 mm/yr); (2) a low Bouguer anomaly (7.5 mGal) was observed over the JZD relative to its surroundings (8.5–12 mGal) with the steepest gradient along its eastern side; (3) strong and clear horizontal/vertical (H/V) spectral ratio peak and high frequency (5–10 Hz) over the JZD outcrop and areas proximal to its western margin, but areas to the east have a weak H/V peak and low frequency (1.5-3 Hz); (4) drilling confirmed presence of a shallow (4 m) salt bedrock layer west of the JZD and the absence of this layer to its east (up to depths of 60 m); (5) uplift patterns along the diapir margins are indicative of near-vertical contact along the JZD eastern margin and less steep contacts along the remaining margins; and (6) additional near-surface diapirs could potentially be identified in the vicinity of the JZD using our integrated approach.
A Directional Borehole Radar System
In this paper we present the simulation and design of a directional borehole radar. In addition we discuss an imaging method for the radar system. The antenna system contains an electric dipole which is in one direction shielded by a cylindrical perfectly conducting reflector. The radiation pattern of the reflected wavefield is computed by first solving the integral equation. This equation combines the unknown electric surface current density on the reflector and the known incident field from the electric dipole. Once the electric surface current density is known, the radiation pattern of the system is computed using the integral representation over the reflector and the dipole. The radiation patterns for various configurations have been computed in order to find an optimal configuration. A prototype of the antenna system based on an optimal configuration has been built, and the directional radiation pattern has been measured in the plane perpendicular to the antenna system. The measurements were in good agreement with the computations. Subsequently a three dimensional imaging method for the borehole radar is presented. Here a deconvolution is carried out in the angular direction, making use of the computed radiation pattern. Some imaging results will be shown.