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We presented a ray-based iteratively traveltime tomography algorithm for crosshole radar direct-arrival data using the multistencils fast marching method (MSFM). The proposed scheme used MSFM to compute the traveltime solution at each grid point by solving the traveltime eikonal equation along several stencils and picked the solution that satisfies the upwind condition. Curved raypaths, which were...
Preferential flow due to fingering, funnelling or macropore flow results in small scale spatial variability in infiltration. On the plot scale (∼ 1 m × 1 m), a common method to characterize such infiftration patterns are sprinkling experiments using dye tracers. Typically, the resulting patterns are analyzed after excavation using digital photographs of selected vertical 2D slices. The observed preferential...
Holographic radar usually adopts antenna with wide beam pattern to form a big synthetic aperture and to obtain high spatial resolution. However, previous works have indicated that the antenna pattern is essentially a low-pass filter in wavenumber domain and it reduces the practical resolution. To eliminate the influence of the antenna pattern and improve the practical resolution, this paper presents...
A bi-static Ground Penetrating Radar (GPR) has been developed for the detection of cracks and buried pipes in urban grounds. It is made of two shielded Ultra Wide Band (UWB) bowtie-slot antennas operating in the frequency band [0.3;4] GHz. GPR signals contain not only responses of targets, but also unwanted effects from antenna coupling in air and in the soil, system ringing, and soil reflections...
This paper focuses on 3-dimensional (3D) image reconstruction by ground penetrating radar (GPR) data. Conventionally, we acquired a GPR gridded dataset with a fine interval, which satisfies the Nyquist spatial sampling criterion for an antenna. However, it takes long time for data acquisition. In this study, we tried two different approaches to reconstruct the image with sparse data that violated...
Single-hole, multi-offset borehole-radar reflection (SHMOR) is an effective technique for fracture detection. However, commercial radar system limitations hinder the acquisition of multi-offset reflection data in a single borehole. Transforming cross-hole transmission mode radar data to virtual single-hole, multi-offset reflection data using a wave interferometric virtual source (WIVS) approach has...
High contrast zones within aquifers like preferential flow paths or impermeable clay lenses can be related to low-velocity waveguides resulting in complicated electromagnetic wave propagation behavior in borehole GPR data. Recently, an amplitude analysis was introduced that was able to identify continuous low-velocity waveguides between boreholes already in the measured data. Here, we extend this...
Yichang-Wanzhou railway with total length of 377 km was constructed in the mountain region presenting the most complex karst geological conditions in the world. Several collapses happened in its artificially trenched sections since this railway opened in the December of 2010. We proposed GPR technique for accurate location of karst cavities and tubes beneath the railway basement for grouting reinforcement.
This article describes the Multi Channel GPR complex for Railway Roadbed monitoring and software for automated data processing. Llc “Geotech Research Institute” has significant experience in providing geological and geophysical survey on Russian railroads. At present we have examined more than 3000 km of Russian roads. We have always been using a geophysical methods complex that provides reliability...
The distribution of a backfill grouting layer behind concrete lining of a large diameter shield tunnel under construction is important for evaluation of its stability. In the paper, the numerical simulation is developed considering the three layered media of segment, backfill grouting and surrounding soil. In the simulation, the influences on the radargram from the steel bars in the segment are analyzed...
Successful GPR cases related to defects detection to concrete liners of tunnels can be found in the last ten years. Generally, it was very difficult to get high quality data due to the limited data acquisition condition in tunnel, which might decrease the reliability of interpretation results. It is a great challenge to highlight the deep reflection events from the background with strong noise. Attribute...
The Ground Penetrating Radar (GPR) is an effective method for shield tunnel grouting layer inspection. However, due to the large cross sections of highway shield tunnels, traditional manual inspections cannot meet the requirement. In accordance with the characteristics of the highway shield tunnel, a vehicle mounted integrated GPR inspection equipment is presented. Together with manual inspections,...
It is well-known that point scatterers appear as hyperbolas in ground-penetrating radar (GPR) B-scans and that the layer interfaces appear as horizontal lines. In this paper the shape and location of the hyperbolas, together with the location of the layer interfaces, are used to estimate the soil dielectric permittivity for a layered soil. For this, a procedure composed of following steps is used:...
A full-polarimetric radar system for non-contact, non-destructive high-resolution imaging and inspection of wooden buildings damaged by earthquakes is developed. The stepped frequency continuous wave system is based on a network analyzer and employs a multi-channel antenna array consisting of four linearly polarized Vivaldi antennas operating in an ultra-wideband ranging from 1 GHz to 20 GHz. The...
In order to assess the seasonal changes of the topography, the inner structure and the physical properties of a small glacier in the Eastern Alps, we performed a 4-D multi frequency GPR survey by repeating the same data acquisition in four different periods of the year 2013. The usual glacier mass balance estimation encompasses only topographic variations, but the real evolution is much more complex...
It has been observed that the corrosion of iron pipes in soil can produce variations in ground conductivity around the pipe, and that the visibility of such pipes to GPR can be greatly reduced. This new investigation and measurement of the permittivity and conductivity of soil contaminated by iron pipe corrosion products produces more accurate knowledge of permittivity and conductivity data and their...
Polarimetric decomposition techniques have been applied in remote sensing in the area of air-space-borne radar and have achieved much progress in recent years. However, very few apply these polarimetric decomposition techniques to the Ground Penetrating Radar (GPR).We currently apply GPR data sets to characterize and classify the subsurface targets using Pauli decomposition method. The Pauli decomposition...
In GPR data processing, it is an important task to find the reflections obscured by the noise. The ‘empirical mode decomposition’ (EMD) method, the key part of Hilbert - Huang transform (HHT), has been used widely to analyze nonlinear and non-stationary data. This paper uses the ensemble EMD (EEMD) combined instantaneous analysis to remove the noise from GPR data. Some obscured reflections are shown...
A fast method is proposed for the reconstructing of three-dimensional images of objects hidden under the non-planar surface of media on the basis of ultra-wideband (UWB) radar measurements of magnitude. It is assumed that the radar moves in the plane above the medium and produces UWB radar measurements with a fixed step. The solution of the inverse problem is made in the single scattering approximation...
Time and amplitude drift is a common problem for some time-domain radars. Some corrections have been suggested for far-field radar data, but due to the coupling effect, there is no equivalent for near-field radar data. In this paper we first quantified, considering the occurrence of the first reflection peak, the time drift of a 900 MHz center-frequency pulse radar system over a certain time period...
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