Wide Angle Reflection And Refraction Research Articles

Delamination characterization in thin asphalt pavement structure using dispersive GPR data

Detection of delamination in asphalt pavement by non-destructive ground penetrating radar (GPR) is useful for effective maintenance and repair. However, limitations of GPR survey resolution and multiple wave interferences have made thin delamination layer characterization a challenging task in conventional common offset profiling (COP) mode. In this paper, a new method is proposed for characterizing delamination layers in asphalt pavement using the GPR waveguide dispersion model in a wide-angle reflection and refraction (WARR) configuration. The approach was validated through synthetic experiments and laboratory experiments using an asphalt pavement model. The results show that the cutoff frequencies of all modes are sensitive to air-filled delamination, while water-filled delamination leads to a significant decrease in the phase velocity of GPR waves. By observing these trends, we are able to detect delamination layers with 1 cm thickness and identify delamination layers with different properties. This new method can aid in the detection and identification of delamination layers in asphalt pavement structures.

Cretaceous magmatic underplating and delamination beneath continental SE Brazil and their tectonic implications: Evidence from the PABBRISE wide-angle reflection and refraction seismic profile

Controlled-source seismology provides robust methods to obtain information on the velocity structure of the crust and uppermost mantle. We present the first systematic wide-angle reflection and refraction (WARR) seismic experiment for continental southeastern Brazil: the NW-SE-oriented and ca. 700 km-long PABBRISE (PAraná Basin, Brasília and RIbeira orogens Seismic Experiment) profile. Using ray tracing, we obtained a two-dimensional P-wave seismic velocity model of the crust and uppermost mantle. Our model shows that Moho depths vary between ca. 31 and 45 km, with crustal thinning towards the continental margin. The modeled velocity structure sheds new light on the present-day lithospheric morphology of the region, with the most striking features noted within the lower crust and uppermost mantle. We show that beneath the Paraná Basin, parts of the lower crust and uppermost mantle were pervasively intruded due to magmatic underplating. We modeled a ca. 200 km-long and 11 km-thick (maximum thickness), high-velocity (7.20–7.80 km/s) lower crustal (HVLC) body in this region. Outside the Paraná Basin, near the continental margin, comparatively thinner crust (∼31 km) with low mean P-wave velocity (6.20 km/s) and a low velocity (<7.90 km/s) uppermost mantle probably are the result of delamination. Magmatic underplating and delamination can be linked with the breakup of Pangea and the opening of the South Atlantic Ocean during the Cretaceous.

The SHIELD’21 deep seismic experiment

The wide-angle reflection and refraction (WARR) SHIELD’21 profile carried out in 2021 crosses from SW to NE the main tectonic of Ukraine. The SHIELD’21 targeted the structure of the Earth’s crust and upper mantle of the southwestern margin of the East European Craton with overlying Neogene Carpathian Foredeep and Vendian-Paleozoic Volyn-Podolian Monocline, Archaean and Paleoproterozoic segments of Ukrainian Shield and Late Paleozoic Dnieper-Donets Basin. The ~650 km long profile is an extension of realized in 2014 RomUkrSeis line in Romania and Ukraine from Apuseni Mountains to southwestern Ukrainian Shield. The field work performed in 2021, included the deployment of autonomous seismic stations and drilling-explosive works. A total of 264 seismic receivers were deployed (160 DATA-CUBE and 104 TEXAN stations) with the average spacing between the observation points about 2.65 km. The sampling interval for all stations was 0.01 s. Seismic energy was generated by 10 shot points with ~50 km of distance between them and total charge in all wells 5775 kg. The SHIELD’21 experiment using TEXAN and DATA-CUBE short-period seismic stations provided high-quality seismic records. The main recorded seismic waves are the refractions of P- and S-waves in sediments, basement, crust and upper-most mantle, and reflections from crustal boundaries, Moho interface and boundaries in the uppermost mantle. Correlation of travel time arrivals of seismic waves provides calculation of the velocity model for both P- and S-waves. The main objective of the SHIELD’21 project is to get new seismic data that increase our knowledge on the lithosphere structure as well as geodynamics of the oil-and-gas-bearing and ore regions of Ukraine.

Crustal structure along the Wanzai–Yongchun profile in the Cathaysia Block, Southeast China, constrained by a joint active- and passive-source seismic experiment

SUMMARY Since the Mesozoic, the South China Block (SCB) has experienced multiple episodes of tectonic magmatism accompanied by metallogenesis. To explore the seismic velocity structure of the crust and its connection with mineralization, we constructed a wide-angle reflection and refraction (WARR) profile by deploying 435 short-period seismometers across the Cathaysia Block in Southeast China. Receiver functions and the H–κ stacking method were applied using a reference 2-D velocity model obtained from the analysis of WARR data. Integration of active- and passive-source seismic data enabled us to obtain an image of the crust and the average Vp/Vs ratio value of the SCB and produce several results: (1) The crustal thickness varies west-to-east from 28 km below the Qinhang metallogenic belt to 32 km below the Wuyishan metallogenic belt, and the average value of the Vp/Vs ratio for the crust is 1.71. Both the thickness of the crust and the average Vp/Vs ratio are lower than the average global values for the continental crust. (2) The relatively low Vp/Vs ratio and thin crust along the profile could be generated by thinning of the lower crust in the SCB as a result of the backarc extension related to westward subduction of the Paleo-Pacific plate below East Asia. (3) The Moho depth estimated from H–κ stacking with the help of the background P-wave velocity model modified by the WARR model fits better than using a global seismic velocity model with its common conversion point image, which supports a potential seismic data analysis technique provided with a joint deployment of both active- and passive-source seismic observation system with a shorter period.

TTZ-SOUTH seismic experiment

The wide-angle reflection and refraction (WARR) TTZ-South transect carried out in 2018 crosses the SW region of Ukraine and the SE region of Poland. The TTZ-South profile targeted the structure of the Earth’s crust and upper mantle of the Trans-European Suture Zone, as well as the southwestern segment of the East European Craton (slope of the Ukrainian Shield). The ~550 km long profile (~230 km in Poland and ~320 km in western Ukraine) is an extension of previously realized projects in Poland, TTZ (1993) and CEL03 (2000). The deep seismic sounding study along the TTZ-South profile using TEXAN and DATA-CUBE seismic stations (320 units) made it possible to obtain high-quality seismic records from eleven shot points (six in Ukraine and five in Poland). This paper presents a smooth P wave velocity model based on first-arrival travel-time inversion using the FAST (First Arrival Seismic Tomography) code. The obtained image represents a preliminary velocity model which, according to the P wave velocities, consists of a sedimentary layer and the crystalline crust that could comprise upper, middle and lower crustal layers. The Moho interface, approximated by the 7.5 km/s isoline, is located at 45—47 km depth in the central part of the profile, shallowing to 40 and 37 km depth in the northern (Radom-Łysogуry Unit, Poland) and southern (Volyno-Podolian Monocline, Ukraine) segments of the profile, respectively. A peculiar feature of the velocity cross-section is a number of high-velocity bodies distinguished in the depth range of 10—35 km. Such high-velocity bodies were detected previously in the crust of the Radom-Łysogуry Unit. These bodies, inferred at depths of 10—35 km, could be allochthonous fragments of what was originally a single mafic body or separate mafic bodies intruded into the crust during the break-up of Rodinia in the Neoproterozoic, which was accompanied by considerable rifting. The manifestations of such magmatism are known in the NE part of the Volyno-Podolian Monocline, where the Vendian trap formation occurs at the surface.

Crustal velocity structure of Cathaysia Block from an active-source seismic profile between Wanzai and Hui'an in SE China

With the purpose of exploring the widely distributed Mesozoic granitoids in SE China and the related mineralization, we carried out a new 530-km-long seismic wide-angle reflection and refraction (WARR) profile along the transect Wanzai- Hui'an. Based on a previous exploration in 2012 and the analysis of this WARR profile, we have deduced a detailed P-wave velocity model of the crust and uppermost mantle. The main results are: (1) The crustal thickness is about 30 to 32 km beneath the Yangtze Block and West Cathaysia, and 29 to 30 km below the East Cathaysia, which represents a significant thinning with respect to the worldwide average thickness of shields and platforms. (2) The variation in seismic velocity between the upper crust and middle-lower crust in the Yangtze Block and the Cathaysia Blocks indicates that the Shaoxing-Jiangshan-Pingxiang Fault (SJPF) is the tectonic boundary between the Yangtze and Cathaysia and the Zhenghe-Dapu Fault (ZDF) is the tectonic boundary between the west and east Cathaysia. (3) The middle crust exhibits a low P-wave velocity layer of 6.2 km/s below the Wuyishan Metallogenic Belt (WMB). This low velocity layer can be attributed to the delamination during the Caledonian orogeny and the Yanshanian extension. (4) The middle-lower crust shows a clear lateral velocity variation from west to east in Cathaysia. The subduction of the Paleo-Pacific plate is believed to be the main reason for the extensional tectonic environment and magmatism during the Yanshanian (Jurassic-Cretaceous) period, leading to significant crustal and lithospheric thinning. Relatively high velocity in the middle-lower crust and widely disseminated Cretaceous volcanic rocks in East Cathaysia may be related to the slab rollback of the Paleo-Pacific plate in the late Yanshanian (Cretaceous) period.

Structure of a diffuse suture between Fennoscandia and Sarmatia in SE Poland based on interpretation of regional reflection seismic profiles supported by unsupervised clustering

The Paleoproterozoic suture between Sarmatia and Fennoscandia (SFS), two major components of the East European Craton, extends SW-ward from Russia through Belarus to SE Poland. The exact character of this suture remains speculative, despite the results of the wide-angle reflection and refraction (WARR) soundings. Here, we show results of newly reprocessed deep reflection seismic data of the PolandSPAN™ survey, portraying the whole crust and uppermost mantle in SE Poland. Their interpretation is supported by the unsupervised clustering of seismic reflectivity patterns. From the integration of PolandSPAN™ data with both magnetic and WARR data, we conclude that the SFS cannot be interpreted as a localised lithospheric discontinuity coincident with the Minsk Fault. Instead, we observe a so-called diffuse cryptic suture zone, c. 150 km wide, where materials from two colliding plates are mixed over large distances to form a unified continental crust. The suture-related reflections are interpreted as a thrust-wedge rooted at the lower-middle crust interface underneath the Ivanowo-Borisov zone. We support Bogdanova et al. (2015) view that the Okołowo-Holeszów Belt and Belarus-Podlasie Granulite Belt have affinities to the NW margin of Sarmatia. We interpret both units as belonging to the diffuse SFS.

GPR wave dispersion for material characterization

This paper studies the dispersion of GPR wave’s phase velocity at different wideband frequencies in plywood and concrete with varying moisture content. This study makes use of two GPR antennas with 2 GHz centre frequency operating in wide angle reflection and refraction (WARR) mode and with computation of spectral analysis of the surface wave (SASW). Computation of phase velocities is based on the acquisition of the cross-power spectrum and phase unwrap of two distorted ground waves at positions closer to and farther away from the transmitting antenna. The velocities of the ground waves are found to experience greater dispersion in low frequency regimes within the effective frequency bandwidths determined and thresholded by time–frequency analysis (TFA) and coherence plotting of the ground waves. This study validates not only the methodology, but also identifies the optimal distance between the first (Rx1) and second (Rx2) receivers as λ/2, which is based on a fixed transmitter (Tx) minus the first receiver (Rx1) distance. It serves as an indication of changeable separation distance when other lower frequency GPR is used because the distances of Tx-Rx1 and Rx1-Rx2 are wavelength dependent and thus also frequency dependent. Effects of moisture contents and chloride contamination in concrete were also characterized according to the dispersion plots that wave traelling in lower frequencies in GPR wave is much decelerated than that in higher frequencies. This research also contributes to the building of the “GPR-WARR machine” suggested in Annan and Jackson (2017) [1], within which the effects of wave dispersion on phase velocity can be inversely modelled to characterize variations in the material properties of infrastructure as a means of detecting surface damage.

RomUkrSeis: Seismic model of the crust and upper mantle across the Eastern Carpathians – From the Apuseni Mountains to the Ukrainian Shield

RomUkrSeis is a controlled source wide-angle reflection and refraction (WARR) profile acquired in August 2014. It is 675 km long, running roughly SW-NE from the Apuseni Mountains in Romania and the Transylvanian Basin, crossing the arc of the Eastern Carpathian orogen and terminating in the East European Craton (EEC) in SW Ukraine. Well-constrained 2-D ray-tracing P- and partly S-wave velocity models have been constructed along the profile from 348 single-component seismic recorders and eleven shot points. The Eastern Carpathian arc formed in the Cenozoic and have obscured the pre-existing Teisseyre-Tornquist Zone (TTZ), which is a transition zone between the Precambrian EEC and continental terranes accreted to it from the southwest in the Palaeozoic. The TTZ is characterised by low-velocity through its entire crust (6.0–6.3 km/s) and a considerable width (~140 km). It is interpreted as EEC crust stretched during rifting and continental margin formation in the Neoproterozoic and early Palaeozoic. The crust of the TTZ has a “trough in trough” structure wherein an upper body of ~40 km width comprising Outer Carpathian (Vp 4.9 km/s) and Late Palaeozoic-Mesozoic (Vp 5.4 km/s) units to 15 km depth lies above a wider, deeper one of inferred Neoproterozoic-early Palaeozoic strata. The crust of the Transylvanian Basin and Apuseni Mountains is relatively thin (~32 km). A high-velocity body at 4–12 km depth in this area is interpreted as a rootless fragment of an ophiolite complex exposed at the surface in this area. The lower crust beneath the Transylvanian Basin displays higher velocities than adjacent segments. Moho topography is strongly differentiated along the profile, varying from 32 to 50 km. The Moho shape, especially in the area between the Inner and Outer Carpathians, suggests a NE dip and, hence, thrusting of the Tisza-Dacia lowermost crustal and upper mantle units under the TTZ domain which, in turn, could be thrust under the cratonic (EEC) block.

TTZ-South seismic experiment

The wide-angle reflection and refraction (WARR) TTZ-South transect carried out in 2018 crosses the SW region of Ukraine and the SE region of Poland. The TTZ-South profile targeted the structure of the Earth’s crust and upper mantle of the Trans-European Suture Zone, as well as the southwestern segment of the East European Craton (slope of the Ukrainian Shield). The ~550 km long profile (~230 km in Poland and ~320 km in western Ukraine) is an extension of previously realized projects in Poland, TTZ (1993) and CEL03 (2000). The deep seismic sounding study along the TTZ-South profile using TEXAN and DATA-CUBE seismic stations (320 units) made it possible to obtain high-quality seismic records from eleven shot points (six in Ukraine and five in Poland). This paper presents a smooth P-wave velocity model based on first-arrival travel-time inversion using the FAST (First Arrival Seismic Tomography) code. The obtained image represents a preliminary velocity model which, according to the P -wave velocities, consists of a sedimentary layer and the crystalline crust that could comprise upper, middle and lower crustal layers. The Moho interface, approximated by the 7.5 km/s isoline, is located at 45—47 km depth in the central part of the profile, shallowing to 40 and 37 km depth in the northern (Radom-Łysogory Unit, Poland) and southern (Volyno-Podolian Monocline, Ukraine) segments of the profile, respectively. A peculiar feature of the velocity cross-section is a number of high-velocity bodies distinguished in the depth range of 10—35 km. Such high-velocity bodies were detected previously in the crust of the Radom-Łysogory Unit. These bodies, inferred at depths of 10—35 km, could be allochthonous fragments of what was originally a single mafic body or separate mafic bodies intruded into the crust during the break-up of Rodinia in the Neoproterozoic, which was accompanied by considerable rifting. The manifestations of such magmatism are known in the NE part of the Volyno-Podolian Monocline, where the Vendian trap formation occurs at the surface.

Simultaneous multichannel multi‐offset ground‐penetrating radar measurements for soil characterization

AbstractFor vadose zone studies, it is essential to characterize the soil heterogeneity. However, manual soil coring is time consuming and lacks spatial coverage. Ground‐penetrating radar (GPR) has a high potential to map these parameters. However, with conventional common‐offset profile (COP) measurements, soil layer changes are only detected as a function of time, and no exact determination of velocities, and thus permittivity, is possible. For velocity estimation, time‐consuming point‐scale common midpoint (CMP) or wide‐angle reflection and refraction (WARR) measurements are necessary. Recently, a novel simultaneous multi‐offset multichannel (SiMoc) GPR system was released, enabling rapid profiling with virtually continuous acquisition of WARR gathers. For this system, we developed a new processing approach. First, time shifts caused by the different cables and receivers were eliminated by a novel calibration method. In the obtained CMP gathers, groundwave and (when present) reflection velocities were determined with an automated semblance approach. The obtained velocity can be converted to permittivity and soil water content. We tested SiMoc GPR with a synthetic study and time‐lapse field measurements. In the synthetic study, the accuracy of velocity and layer thickness were within 0.02 m ns−1 and 2 cm. The SiMoc field results (spatial sampling of 5 cm) are consistent with coarse sampled single‐channel data (spatial sampling of 10 m). Soil water content changes over the different measurement days were in agreement with nearby installed sensors (one per hectare). Overall, SiMoc GPR is a powerful tool for fast imaging of spatially highly resolved permittivity, and soil water content at a large scale.

Imaging the East European Craton margin in northern Poland using extended correlation processing of regional seismic reflection profiles

Abstract. In NE Poland, Eastern European Craton (EEC) crust of Fennoscandian affinity is concealed under a Phanerozoic platform cover and penetrated by sparse, deep research wells. Most of the inferences regarding its structure rely on geophysical data. Until recently, this area was covered only by the wide-angle reflection and refraction (WARR) profiles, which show a relatively simple crustal structure with a typical three-layer cratonic crust. ION Geophysical PolandSPAN™ regional seismic programme data, acquired over the marginal part of the EEC in Poland, offered a unique opportunity to derive a detailed image of the deeper crust. Here, we apply extended correlation processing to a subset (∼950 km) of the PolandSPAN™ dataset located in NE Poland, which enabled us to extend the nominal record length of the acquired data from 12 to 22 s (∼60 km of depth). Our new processing revealed reflectivity patterns, which we primarily associate with the Paleoproterozoic crust formed during the Svekofennian (Svekobaltic) orogeny, that are similar to those observed along the BABEL and FIRE profiles in the Baltic Sea and Finland, respectively. We propose a mid- to lower-crustal, orogeny-normal lateral flow model to explain the occurrence of two sets of structures that can be collectively interpreted as kilometre-scale S–C′ shear zones. The structures define a penetrative deformation fabric invoking ductile extension of hot orogenic crust in a convergent setting. Localized reactivation of these structures provided conduits for subsequent emplacement of gabbroic magma that produced a Mesoproterozoic anorthosite–mangerite–charnockite–granite (AMCG) suite in NE Poland. Delamination of thickened orogenic lithosphere may have accounted for magmatic underplating and fractionation into the AMCG plutons. We also found sub-Moho dipping mantle reflectivity, which we tentatively explain as a signature of the crustal accretion during the Svekofennian orogeny. Later tectonic phases (e.g. Ediacaran rifting, Caledonian orogeny) did not leave a clear signature in the deeper crust; however, some of the subhorizontal reflectors below the basement, observed in the vicinity of the AMCG Mazury complex, can be alternatively linked with lower Carboniferous magmatism.

The deep structure of the Dobrogea and Fore-Dobrogea trough as an indication of the development of the Trans-European suture zone

The tectonic structure of Dobrogea and Fore-Dobrogea trough are considered on the basis of geological and geophysical data. Dobrogea and Fore-Dobrogea trough are the key areas for understanding of Central Europe geodynamics, because they are located within the southeastern part of the Trans-European Suture Zone (TESZ), which is available here for direct field research. The current position of these units in the foreland of the Carpathians and on the north-eastern coast of the Black Sea makes them a link that connects the Pannonian-Carpathian region and Crimean-Black Sea region. The deep structure of the study area is described by the velocity models of wide-angle reflection and refraction (WARR) profiles VRANCEA-2001, DOBRE-4 and PANCAKE. Dobrogea is a system of northeastern vergence overthrusts, separated by a series of large faults. These faults, most important of which is Pecenega-Camena Fault, are part of the southern branch of the TESZ. The width of the Dobrogea thrust zone is about 60 km and close to the width of the thrust zone along PANCAKE profile. The modern fold and thrust structure of Dobrogea was formed on the place of the paleopaleozoic suture in Cimmerian tectonic stage (Upper Jurassic—Lower Cretaceous) and activated in the Early-Alpine stage (Upper Cretaceous—Paleogene), being later than the Jurassic, and earlier than the Alpine thrusting in the Pannonian-Carpathian region. Taking into consideration the geological and geophysical similarity of Rava-Ruska and North-Dobrogea elements of the East European platform, as well as similarity of the Inner zone of the Lviv Paleozoic trough and the Fore-Dobrogea trough, it can be suggested that within the study area, the northeast boundary of the TESZ passes close to the surface beneath the Fore-Dobrogea trough, while the southwest boundary coinside with the Peceneaga-Camena Fault and may even cross it at the boundary of the upper and middle crust. According to the data of the WARR profiles DOBRE-4 and PANCAKE, the TESZ is considered not to be vertical zone, but gently dipping system of overthrusts separated the East European platform from the Western European and Moesian platforms.

The WARR Machine: System Design, Implementation and Data

In this paper, we describe a ground penetrating radar (GPR) system called the wide angle reflection and refraction (WARR) machine, outline the design and discuss the implementation challenges. WARR and the closely related common-mid-point (CMP) GPR soundings have been standard survey methods to measure velocity since GPR first existed. Earliest efforts demonstrated the variation in ice sheet velocity versus depth. Although GPR multi-offset soundings are valuable survey methods, they have seen little adoption since many systems are not bistatic. In addition, surveys most often use a single transmitter with a single receiver deployed sequentially at varying antenna separations, making data acquisition slow. Modern instrumentation with recent advances in GPR timing and control technology has enabled deployment of systems with multiple concurrent sampling receivers. This development has resulted in the ability to continuously acquire multi-offset WARR data at the same rate as two dimensional (2D) common offset reflection surveys in the past. The concomitant issues of survey design plus organizing the WARR data storage, documentation and analysis present numerous challenges. The extraction of velocity information from the large volumes of GPR WARR/CMP data demands automated analysis techniques. We have explored the use of normal move out (NMO) stacking at creating enhanced zero offset section from multi-offset data. Furthermore, we investigated the use of semblance analysis at estimating move-out velocities in order to apply in the NMO stack. These traditional seismic processing steps have proven to be less effective with GPR. These conclusions point to the differences in data character between seismic and GPR. Results of in-field deployment are used to illustrate advances to date and point the way to further advancements.

Modeling and Simulation of Low Frequency Subsurface Radar Imaging in Permafrost

We describe simulated low frequency subsurface radar scans targeting the detection of a liquid water layer, or some other reflector such as conductive sulfides, under permafrost. A finite-difference time-domain (FDTD) and ray tracing simulation framework is used to model measurements and data analysis at depths from 350m to 800m. Operating characteristics such as pulse shape and noise levels of the measurement apparatus were obtained from an existing commercial radar scanning system. Results were used to test and optimize data analysis methods, predict maximum detection depth under realistic time constraints, and guide experimental design parameters such as the amount of replications required for denoising and length of the wide angle reflection and refraction (WARR) scan lines used for velocity estimation.

Balanced geological cross-section of the outer ukrainian carpathians along the pancake profile

The Outer Ukrainian Carpathians (OUC) are part of the Eastern Carpathians, which is a segment of the European Alpine belt. The OUC is crossed by recently acquired WARR (wideangle reflection and refraction) PANCAKE profile (Starostenko et al., 2013). To study the basin architecture of the OUC along the profile a balanced geological cross-section was onstructed. Reconstruction of the balanced geological cross-section has shown that the present day fold-and-thrust belt of the Outer (Flysch) Carpathians was formed in the Miocene from the deposits of the sedimentary basin∼460km in width. Evolution of the sedimentary basin to the present fold-and-thrust belt 70km in width occurred in two stages, characterized by accelerating the shortening rate of the basin from 11.5km/Ma between∼32 and 22 Ma to 22.5km/Ma between∼22 and 12 Ma. The detachment of the flysch complexes of the OUC occurred on the top of the basement located at a depth of 10−12km. The main phase of Miocene thrusting was followed by significant exhumation and erosion during the period of 12−2 Ma related to isostatic uplift in the OUC, which reached a maximum (up to 7km) in the central nappes (Krosno and Dukla-Chornohora). The collision regime, obviously, followed the subduction one; this could happen approximately at 22 Ma which is evident after changing the shortening rate of the basin.

Determination of electromagnetic wave velocity in horizontally layered sedimentary target: A ground-penetrating radar study from Silurian limestones, Estonia

Ground-penetrating radar (GPR) is a non-destructive geophysical technique to obtain information about shallow subsurface by transmitting electromagnetic waves into the ground and registering signals reflected from objects or layers with different dielectric properties. The present GPR study was conducted in Vohmuta limestone quarry in Estonia in order to describe the relationship between GRP responses to the variations in petrophysical properties. Sub-horizontally oriented cores for petrophysical measurements were drilled from the side wall of the quarry. The GPR profiles were run at the sloped trench floor and on the top of side wall in order to correlate traceable reflections with physical properties. Based on three techniques: (i) hyperbola fitting, (ii) wide angle reflection and refraction (WARR), and (iii) topographic, a mean electromagnetic wave velocity value of 9.25 cm ns−1 (corresponding to relative dielectric permittivity of 10.5) was found to describe the sequence and was used for time-to-depth conversion. Examination of radar images against petrophysical properties revealed that major reflections appear in levels where the changes in porosity occur.

Multimodal inversion of guided waves in georadar data

We analyze the dispersive characteristics of the electromagnetic guided waves (at georadar frequency) to infer the electrical properties of materials that constitute a layered wave guide. WARR (Wide Angle Reflection and Refraction) georadar acquisitions could be carried out in TE (Transverse Electric) configuration to collect the full wavefield at different offset from the source. The dispersive curves of TE modes are obtained by transforming the space-time acquisition into frequency-wavenumber domain (f-k spectrum); the relative maxima in the f-k spectrum for each frequency represent the different propagation modes. We adopt both global and local inversion algorithms for minimizing the misfit function between computed and theoretical curves in order to obtain a 1D model of the layered subsoil (thicknesses and electrical permittivity). We perform a multimodal and multilayer inversion of the dispersive events. The results of two field cases will be discussed; the first one refers to the propagation in a confined waveguide (layered subsoil) and the other in a leaky waveguide (snow cover on a glacier).

Application of ground‐penetrating radar in detecting water leakage from artificial sandy ground

ABSTRACTGround‐penetrating radar (GPR) surveys are frequently used to delineate the distribution of subsurface water. This paper demonstrates that GPR is suitable for detecting water leakage from underground construction areas because it produces detailed images of changes in water‐level that are related to water leaks. For this experiment, we used a test pit filled with river sand and a buried mortar wall that divides the pit into two sections. To simulate water leaks, we drilled holes through the mortar wall at a depth of 1.15 m and maintained constant water levels of 1.4 m and 0.4 m below the surface on each side of the wall. Water‐levels were controlled by pump‐extraction and injection using water‐control wells. Variations in water‐level under dynamic hydraulic conditions caused by water leakage through the holes were delineated by dense GPR single‐fold profiling measurements. Wide‐angle reflection and refraction (WARR) measurements were also performed to obtain velocity information and to support the interpretation of profiling data. To image minor changes in waterlevel accurately, we took minor topographic changes into account and applied finite‐difference method migration and time‐variant depth conversion to the GPR single‐fold profiling data. We were able to construct a three‐dimensional water‐level map using the water‐table depths extracted from migrated depth sections. Our results clearly demonstrate a rising trend in water‐level approaching the mortar wall, indicating water leakage from the drilled holes. In addition, the WARR data confirmed that the upward trend in water‐level continues to the mortar wall; it was not possible to image this trend on the single‐fold profiling section within 0.5–1 m of the mortar wall because of interference from measuring equipment buried close to the wall.

Análise do emprego do GPR para estimar o teor de umidade do solo a partir de um estudo na cidade de São Paulo

Este trabalho apresenta resultados de estudos visando a estimativa dos teores de umidade de solos superficiais com GPR em uma area teste na cidade de Sao Paulo/SP, Brasil, e a analise da acuracia dos processos envolvidos. Foram empregadas duas metodologias diferentes: i) ajuste linear dos tempos de chegada da onda direta no solo para diferentes afastamentos; ii) diferencas dos tempos de chegada da onda aerea e da onda direta no solo para um unico afastamento. Utilizamos o equipamento da RAMAC Mala Geosciences com antenas de 50 MHz, 100 MHz e 200 MHz. A aquisicao constituiu-se de diversos perfis multi-offset (multiplos afastamentos) com o emprego da geometria WARR (Wide Angle Reflection and Refraction ) ao longo de um perfil em tres periodos climaticos distintos (seco, intermediario e umido). Sendo o incremento entre os tracos dos perfis multi-offset 0,2 m para a antena de 50 MHz e 0,1 m para as antenas de 100 MHz e 200 MHz. Concomitantemente ao levantamento GPR foram coletadas amostras de solo a intervalos de 0,5 m desde a superficie do terreno ate a profundidade aproximada de 4,0 m para a determinacao de seus teores de umidade em laboratorio. Os resultados do GPR apresentaram boa correlacao com os dados obtidos atraves das analises de laboratorio, sendo que os obtidos com as antenas de frequencia central de 200 MHz propiciaram os melhores resultados. Os dois metodos empregados apresentaram diferentes acuracias. O metodo da diferenca dos tempos de chegada da onda aerea e da onda direta no solo foi o menos preciso devido a ocorrencia de um deslocamento de tempo da reta de ajuste dos tempos de chegada da onda direta no solo no afastamento zero. Esses resultados mostraram que, nesses casos, e importante aplicar um fator de correcao para melhorar a acuracia dos resultados finais.