Effect of antennas on velocity estimates obtained from crosshole GPR data

Geophysics ◽  
2005 ◽  
Vol 70 (5) ◽  
pp. K39-K42 ◽  
Author(s):  
James D. Irving ◽  
Rosemary J. Knight

To obtain tomographic images with the highest possible resolution from crosshole ground-penetrating radar (GPR) data, raypaths covering a wide range of angles between the boreholes are required. In practice, however, the inclusion of high-angle ray data in crosshole GPR inversions often leads to tomograms so dominated by inversion artifacts that they contain little reliable subsurface information. Here, we investigate the problems that arise from the standard assumption that all first-arriving energy travels directly between the centers of the antennas. Through numerical modeling, we show that this assumption is often incorrect at high transmitter-receiver angles and can lead to significant errors in tomographic velocity estimates when the antenna length is a significant fraction of the borehole spacing.

Geophysics ◽  
2007 ◽  
Vol 72 (4) ◽  
pp. J31-J41 ◽  
Author(s):  
James D. Irving ◽  
Michael D. Knoll ◽  
Rosemary J. Knight

To obtain the highest-resolution ray-based tomographic images from crosshole ground-penetrating radar (GPR) data, wide angular ray coverage of the region between the two boreholes is required. Unfortunately, at borehole spacings on the order of a few meters, high-angle traveltime data (i.e., traveltime data corresponding to transmitter-receiver angles greater than approximately 50° from the horizontal) are notoriously difficult to incorporate into crosshole GPR inversions. This is because (1) low signal-to-noise ratios make the accurate picking of first-arrival times at high angles extremely difficult, and (2) significant tomographic artifacts commonly appear when high- and low-angle ray data are inverted together. We address and overcome thesetwo issues for a crosshole GPR data example collected at the Boise Hydrogeophysical Research Site (BHRS). To estimate first-arrival times on noisy, high-angle gathers, we develop a robust and automatic picking strategy based on crosscorrelations, where reference waveforms are determined from the data through the stacking of common-ray-angle gathers. To overcome incompatibility issues between high- and low-angle data, we modify the standard tomographic inversion strategy to estimate, in addition to subsurface velocities, parameters that describe a traveltime ‘correction curve’ as a function of angle. Application of our modified inversion strategy, to both synthetic data and the BHRS data set, shows that it allows the successful incorporation of all available traveltime data to obtain significantly improved subsurface velocity images.


2020 ◽  
Author(s):  
Aleksandar Ristic ◽  
Lara Pajewski ◽  
Miro Govedarica ◽  
Milan Vrtunski

<p>Scientists and experts participating in COST Actions can benefit from a wide range of COST networking tools. Meetings, workshops, conferences and training schools can be organized. Short-term scientific missions (STSM) can be funded: these are exchange visits where an Action Member spends five days up to six months abroad, in a host institution; the aim of STSMs is to foster collaboration between institutions and sharing of new techniques that may not be available in a participant’s home institution. COST also funds dissemination and communication of Action’s outcomes within research communities and beyond. Finally, conference grants for early-career researchers from Inclusiveness Target Countries (ITC) aim at helping participants from ITC to attend international science and technology related conferences that are not organised by COST Actions.</p><p>In this presentation, we discuss the challenges and lessons learnt in COST Action TU1208 “Civil engineering applications of ground penetrating radar” [1] while using COST networking tools to fulfill the objectives of the Action, enhance its impact, and maximize the benefits of its Members. We consider one tool at a time focusing on the obstacles that we encountered and how we overcame them, as well as giving hints on how the Action and its Members made the most from the use of the tool. We describe how the use of the tools changed during the Action’s lifetime. </p><p>COST networking tools can of course be used in a customary way and they are all extremely frutiful. More creative solutions can be implemented too, to keep Members engaged or achieve particular goals. Therefore, this presentation continues with examples of less-common exploitations of the tools in TU1208. For instance, we used the “Meeting” tool for the organization of a series of science communication initiatives aimed at increasing public awareness about ground penetrating radar capabilities and applications and at establishing a dialogue with policymakers, stakeholders and end-users of our research (TU1208 GPR RoadShow [2]); the Roadshow included non-scientific workshops, practical demonstrations, and a series of educational activities with children and citizens. We repeatedly exploited the “Meeting” tool also for one week gatherings with a small number of Members, where we worked full-time together at bringing forward specific Action’s activities, one of the challenges of COST Actions being the lack of funds to finance research and the difficulty to “make Members work” for the Action when they are at their home institutions.</p><p>We hope that recently started Actions can build upon our experience.</p><p> </p><p>[1] L. Pajewski, A. Benedetto, X. Dérobert, A. Giannopoulos, A. Loizos, G. Manacorda, M. Marciniak, C. Plati, G. Schettini, I. Trinks, "Applications of Ground Penetrating Radar in Civil Engineering – COST Action TU1208," Proc. 7th IWAGPR, 2013, Nantes, France, pp. 1-6, doi.org/10.1109/IWAGPR.2013.6601528</p><p>[2] L. Pajewski, H. Tõnisson, K. Orviku, M. Govedarica, A. Ristić, V. Borecky, S. S. Artagan, S. Fontul, and K. Dimitriadis, “TU1208 GPR Roadshow: Educational and promotional activities carried out by Members of COST Action TU1208 to increase public awareness on the potential and capabilities of the GPR technique,” Ground Penetrating Radar, Volume 2(1), March 2019, pp. 67-109, doi.org/10.26376/GPR2019004</p>


2014 ◽  
Vol 19 (1) ◽  
pp. 110-119 ◽  
Author(s):  
Mercedes Solla ◽  
Belén Riveiro ◽  
Henrique Lorenzo ◽  
Julia Armesto

2016 ◽  
Vol 8 (2) ◽  
pp. 663-677 ◽  
Author(s):  
Johannes Petrone ◽  
Gustav Sohlenius ◽  
Emma Johansson ◽  
Tobias Lindborg ◽  
Jens-Ove Näslund ◽  
...  

Abstract. The geometries of a catchment constitute the basis for distributed physically based numerical modeling of different geoscientific disciplines. In this paper results from ground-penetrating radar (GPR) measurements, in terms of a 3-D model of total sediment thickness and active layer thickness in a periglacial catchment in western Greenland, are presented. Using the topography, the thickness and distribution of sediments are calculated. Vegetation classification and GPR measurements are used to scale active layer thickness from local measurements to catchment-scale models. Annual maximum active layer thickness varies from 0.3 m in wetlands to 2.0 m in barren areas and areas of exposed bedrock. Maximum sediment thickness is estimated to be 12.3 m in the major valleys of the catchment. A method to correlate surface vegetation with active layer thickness is also presented. By using relatively simple methods, such as probing and vegetation classification, it is possible to upscale local point measurements to catchment-scale models, in areas where the upper subsurface is relatively homogeneous. The resulting spatial model of active layer thickness can be used in combination with the sediment model as a geometrical input to further studies of subsurface mass transport and hydrological flow paths in the periglacial catchment through numerical modeling. The data set is available for all users via the PANGAEA database, doi:10.1594/PANGAEA.845258.


2012 ◽  
Vol 41 (1) ◽  
Author(s):  
Andrej Gosar

High frequency ground penetrating radar (GPR) is usually applied for cavities detection in a shallow subsurface of karst areas to prevent geotechnical hazards. For specific projects, such as tunnel construction, it is important to detect also larger voids at medium depth range. However, dimensions of classical rigid low frequency antennas seriously limit their applicability in a rough terrain with dense vegetation commonly encountered in a karst. In this study recently developed 50 MHz antennas designed in a tube form were tested to detect cave gallery at the depth between 12 m and 60 m. The Divaca cave was selected because of a wide range of depths under the surface, possibility of unknown galleries in the vicinity and a rough terrain surface typical for Slovenian karst. Seven GPR profiles were measured across the main gallery of the cave and additional four profiles NE of the cave entrance where no galleries are known. Different acquisition and processing parameters were analysed together with the data resolution issues. The main gallery of the cave was clearly imaged in the part where the roof of the gallery is located at the depth from 10 m to 30 m. The width of the open space is mainly around 10 m. Applied system was not able to detect the gallery in the part where it is located deeper than 40 m, but several shallower cavities were discovered which were unknown before. The most important result is that the profiles acquired NE of the cave entrance revealed very clearly the existence of an unknown gallery which is located at the depth between 15 m and 22 m and represents the continuation of the Divaca cave. Access to this gallery is blocked by the sediment fill in the entrance shaft of the cave. The results of the study are important also for future infrastructure projects which will involve construction of tunnels through karstified limestone and for speleological investigations to direct the research efforts.Keywords: ground penetrating radar, cavity detection, spatial resolution, limestone, Divača cave.


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