Wide band frequency domain forward and inverse modelling code for GPR data

Ground penetrating radar (GPR) surveys have been carried out at Schirmacher Oasis and Dakshin Gangotri located at Queen Maud Land, East Antarctica, during the 22nd Indian Antarctic Summer Expedition, 2002-2003. The present study confirmed the ability of the high-resolution GPR for monitoring the glaciers. It gives information about the health of the glaciers before it collapses. GPR survey over three frozen lakes near the Maitri Station provided the lakes' top ice thickness and bedrock depth. Similarly, the internal layers of the glaciers have been mapped in-situ using GPR. The results can be correlated with the results obtained by ice-core drill wells to understand the different field parameters (i.e., thickness of each layer, dielectric constant, etc.).

In spite of the prevailing dry and windy climate conditions the mega dunes in the Badain Jaran Desert in northwestern China are relatively moist underneath a dry surface layer of less than 1 m. It is very common to find a salt lake directly at the foot of the leeward side of a mega dune. Using 50- and 100-MHz antennas we have conducted ground penetrating radar (GPR) surveys on both the windward and leeward sides of a couple of sand dunes in southeastern part of the Badain Jaran Desert. The GPR surveys clearly revealed the existence of numerous, quasi-evenly spaced bedding features on the windward side of the mega dunes, with a slope of orientation parallel to the slope of the leeward side of the dunes which closely coincides with the angle of repose of dry sands. The reason for the existing beddings is that on the leeward side sands on the dune surface can be cemented by moisture with periodic precipitation into layered beddings; and the caliches generated by these calcareous cement will be likely inducing more infiltrated water flow toward the leeward side and consequently channeling more local recharging water to the leeward side than to the windward side. The calcareous cement beddings performed as the `skeleton' of the dunes and increased the mechanic strength of the sands and consequently facilitated the build-up of the high elevation mega dunes. This trend may be one of the key factors that help the existence of the lakes in a very arid environment with high evaporation rate. The GPR profile also clearly registered the water table beneath the sand dunes that gradually elevated toward the crest, implies that the desert lakes are recharged at least partly by the groundwater from local source. Numerically simulated radar profiles precisely reconstructed the observed profiles. It is a strong support to the rationality of the proposed internal structure of the dunes.

Badain Jaran Desert in northwestern China has the world's highest stationary sand dunes, which are up to 500 m tall from bottom to top. Despite the prevailing dry and windy climate conditions the mega dunes were relatively moist underneath a dry surface layer of less than 1 m. It is very common to find a salt lake directly at the foot of the leeward side of a mega dune. Using 50- and 100-MHz antennas we have conducted ground penetrating radar (GPR) surveys on both the windward and leeward sides of the mega dunes in southeastern Badain Jaran Desert. The GPR surveys clearly revealed the existence of numerous, almost evenly spaced bedding features on the windward side of the mega dunes. The reason for the existing beddings is on the leeward side sand dune surface can be cemented by moisture with annual precipitation and the caliches generated by these calcareous cement will be likely inducing more infiltration flow toward the leeward side and consequently channeling more recharging water to the lake than to the windward side. This trend may be one of the key factors that kept the lake exist in a very arid environment with high evaporation rate. The GPR profile also clearly revealed the shape of the water table beneath the mega dunes, which is gradually elevated toward the peak area from both toes, implies that the desert lakes are possibly recharged at least partly by the groundwater from the precipitation. Numerical simulation reconstructed the proposed internal structure.

A study of the problem of deterioration of stone buildings of cultural importance, integrating different non destructive techniques (microclimatic and Ground Penetrating Radar) is proposed. It is well known in fact that this deterioration can be attributed to the presence of water and/or moisture in the porous material that occurs in water-damaged and humid buildings, due to poorly manufactured constructions and inadequate maintenance. The distribution of moisture within stone mainly depends on not suitable environmental condition and by the presence of wet buried structures in the ground. The Ground penetrating radar (GPR) survey was carried out inside the Crypt of the “Cattedrale di Otranto” (Lecce, South Italy). The careful analysis of the 0.4 m spaced GPR parallel profiles, acquired in the Crypt, using a Sir2 GSSI radar system with a 500 MGHz antenna, allow us to distinguish the wet and moisture zone. GPR data were displayed in time slices form to obtain both the amplitude and the moisture variations map. Moreover GPR data were displayed in the form of frequency slices to evidence absorption losses probably linked to higher moisture content. The GPR data were compared with microclimatic data, acquired in a precedent campaign of measures. Microclimatic and GPR data are in good agreement and suggest that an important channelling of moisture has origin in the subsoil.

Conventional ground penetrating radar (GPR) surveys detect subsurface inhomogeneities by the reflection of radio-waves. A short pulse of radio-frequency energy (several nanoseconds in duration) is transmitted into the ground and variations of the electromagnetic field are recorded. The GPR interpreter then attempts to identify echoes in this record which will provide an indication of the subsurface structure. It is commonly believed that the shape of the echo will be either an exact or inverted replica of the transmitted pulse. This will be true when the radio-waves are normally incident on plane, perfect (non-conducting) dielectric boundaries. However, geological materials are usually considerably conductive and when the transmit and receive antennas are separated, normally incident reflections are not recorded. Therefore, to interpret GPR data and to design optimum survey configurations, it is important to realise that the radar pulse shape can change on reflection and to understand how it changes .

Building simplified uncertainty models of object depth measurement by ground penetrating radar

<p>Research over the past several decades has shown that preferential flow is more the rule than the exception. However, our collective understanding of preferential flow processes has been limited by a lack of suitable methods to detect and visualize the initiation and evolution of non-uniform wetting at high spatial and temporal resolutions, particularly in real-world settings. In this study, we investigate water infiltration initiation by tree trunk and root systems. We carried out time-lapse ground penetrating radar (GPR) surveys in conjunction with a simulated stemflow event to provide evidence of root-induced preferential flow and generate a three-dimensional representation of the wetted zone.</p><p>We established a survey grid (3.5 m × 5 m, with a local slope of 10.3°), consisting of ten horizontal and thirteen vertical parallel survey lines with 0.5 m intervals between them. The horizontal lines were downslope-oriented. The grid was placed around a Quercus suber L. We collected a total of 46 (2 GPR surveys × 23 survey lines) radargrams using an IDS (Ingegneria Dei Sistemi S.p.A.) Ris Hi Mod v. 1.0 system with a 900-MHz antenna mounted on a GPR cart. Two grid GPR surveys were carried out before and after the artificial stemflow experiment. In the experiment, we applied 100 L of brilliant blue dye (E133) solution on the tree trunk. The stemflow volume of 100 L corresponded to 63.2 mm of incident precipitation, considering a crown projected area of 201 m<sup>2</sup> and a 1.3% conversion rate of rainfall to stemflow. Trench profiles were carefully excavated with hand tools to remove soil and detect both root location and size and areas of infiltration and preferential pathways on the soil profile.</p><p>The majority (84.4%) of artificially applied stemflow infiltrated into the soil, while the remaining 15.6% generated overland flow, which was collected by a small v-shaped plastic channel placed into a groove previously scraped on the downhill side of the tree. The 3D diagram clearly demarcated the dimension and shape of the wetted zone, thus providing evidence of root-induced preferential flow along coarse roots. The wetted zone extended downslope up to a horizontal distance of 3 m from the trunk and down to a depth of approximately 0.7 m. Put all together, this study shows the importance of accounting for plant and trees trunk and root systems when quantifying infiltration.</p>

The development of modern cities heavily relies on the availability and quality of underground utilities that provide drinking water, sewage, electric power, and telecommunication services to sustain its growing population. However, the information of localization and condition of subterranean infrastructures is generally not readily available, especially in areas with congested pipes, which impacts urban development, as poorly documented pipes may be hit during construction, affecting services and causing costly delays. Furthermore, aging components are prone to failure and may lead to resources waste or the interruption of services. Ground penetrating radar (GPR) is a promising remote sensing technique that has been recently used for mapping and assessment of underground infrastructure. However, current commercial GPR survey systems are designed with wheel-encoders or GPS for positioning. Wheel-encoder based GPR surveys are restrained to linear-route only, preventing the use of GPR for accurate localization of city wide underground infrastructure inspection. While GPS signal is degraded in urban canyons and unavailable in city tunnels. In this work, we present a new GPR system integration with augmented reality (AR) based positioning that can overcome the limitations of current GPR systems to enable arbitrary-route scanning with a high fidelity. It has the potential for automation of GPR survey and integration with AR smartphone applications that could be used for better planning in urban development.

Characterization of the porosity distribution in the upper part of the karst Biscayne aquifer using common offset ground penetrating radar, Everglades National Park, Florida

Three-dimensional ground penetrating radar (GPR) has gained widespread usage in shallow surface exploration due to its ease of acquisition and ability to capture diverse polarization information Meanwhile, the quantitative interpretation of 3D GPR data through Full Waveform Inversion (FWI), particularly when incorporating various polarization methods, holds substantial practical significance. Nonetheless, Challenges in 3D GPR FWI, including multiple solutions and high memory demands, limit its theoretical potential. In this study, we propose an efficient 3D frequency-domain FWI approach utilizing dual-parameter attributes applied to 3D GPR synthetic polarization data. First, we develop the algorithm, frequency weighting and gradient preconditioning strategies are adopted to reduce the nonlinearity and enhance deep illumination of inversion, and the random source strategy is used to improve the efficiency. Subsequently, we apply the algorithm to investigate different polarization data. Then, we use the algorithm to realize 3D multi-parameters quantitative imaging of GPR polarization data, and discuss the reconstruction characteristics of different polarization data, which makes 3D GPR FWI feasible. Our findings not only enhance the understanding of GPR data but also pave the way for more accurate and efficient subsurface exploration using GPR multi-polarization data.

In a probabilistic formulation, the solution to an inverse problem can be expressed an a posteriori probability density function (pdf) that combines the independent states of information provided by data and a priori information. Here, we define an a posteriori probability density function that defines the solution to a tomographic full waveform inverse problem, which provides a means of obtaining an uncertainty estimate. Unfortunately, no explicit formulation of the solution to this problem can be defined. Therefore, the a posteriori probability density function has to be sampled. The full waveform inverse problem is known to be computationally very hard and is, traditionally, considered out of reach for Monte Carlo sampling strategies. We show that by means of informative a priori information this problem become tractable for a sampling strategy anyways. We outline the theoretical framework for a full waveform inversion strategy that integrates the extended Metropolis algorithm with sequential Gibbs sampling, which allows for arbitrary complex a priori information to be incorporated. At the same time we show how temporally correlated data uncertainties can be taken into account during the inversion. The suggested inversion strategy is tested on synthetic tomographic crosshole ground penetrating radar full waveform data using multiplepoint based a priori information. This is, to our knowledge, the first example of obtaining a posteriori realizations of a full waveform inverse problem.

Full-waveform inversion (FWI) is considered one of the most promising interpretation tools for hydrogeological applications using ground-penetrating radar. However, FWI has had limited practical uptake for several reasons: large computational requirements, an inability to reconstruct loss mechanisms of soil, and the need for a good initial starting model. We aim to address these issues via a novel FWI subject to a fractally correlated distribution of water. Initially, the dispersive properties of the soil are expressed as a function of the water fraction using a semiempirical model. This approach means that the permittivity, conductivity, and relaxation mechanisms are all correlated, and therefore, sensitivity problems between the permittivity and loss mechanisms no longer affect the performance of FWI. Subsequently, the distribution of the water fraction is constrained to follow a fractal geometry. Fractal-correlated noise is then compressed using a principal component analysis (PCA) in order to further reduce the number of the system’s unknowns and accelerate FWI. PCA reduces the volume and dimensions of the optimization space, and thus, initialization is no longer necessary. Finally, a novel measurement configuration is suggested that uses superposition with all the individual measurements in order to reduce the number of forward models that need to be executed for every iteration of FWI. These enhancements substantially reduce the computational requirements of FWI and therefore eliminate the need for high-performance computers and time-consuming algorithms. The proposed scheme has been successfully tested with several numerical case-studies, which indicates the potential of this approach to become a commercially appealing interpretation tool for hydrogeology.

Ground Penetrating Radar (GPR) has widely been accepted in geoengineering, and recently, many successful applications are reported in archaeological survey. After the East Japan great earthquake and tsunami 2011 which killed more than 15,000 and many houses must be relocated from seashore to inland, and we have many demands of archaeological surveys. In order to solve this problem, we have developed an array GPR system “Yakumo” which is consists from 8 transmitter and 8 receivers, operating at 50MHz-1.5GHz. Using this new array GPR system, we could achieve very fast GPR data acquisition. By using multi-static radar signal processing, we could achieve high resolution imaging and CMP processing. However, GPR survey on an uneven ground surface, such as burial mound (Kofun) provides us only very poor quality GPR images. We have many places like this in this occasion. Then, we have established new GPR techniques combined with high-precision positioning measurement instrument which include iGPS and total station. Using these systems, we could demonstrate high quality GPR profiles in Sakitama-kofun, Dangoyama-Kofun and Kassenyama-kofun.

Farmers and land improvement contractors, especially in the Midwest U.S., need methods to not only locate buried agricultural drainage pipe, but also to determine if the pipes are functioning properly with respect to water delivery. Previous investigations have already demonstrated the feasibility of using ground penetrating radar (GPR) to find agricultural drainage pipes, so the primary focus of this research project was to determine if GPR can provide additional insight into the condition of subsurface drainage pipes. Ground penetrating radar surveys using 250 MHz transmitter/receiver antennas were conducted at a specially designed field test plot under drained, moderately wet soil conditions (water table below drain lines) and undrained, extremely wet soil conditions (water table above drain lines). The test plot contained four drain lines, one open to flow and comprised of clay tile along part of its length with the rest constructed of corrugated plastic tubing (CPT); one comprised of CPT with an isolated obstruction near the midpoint, preventing through‐flow of water; one comprised of CPT but filled with soil; and one comprised of CPT but severed near its midpoint, producing a partial obstruction to water flow. Subsequent GPR computer simulations were employed to assist with interpretation of GPR data obtained from the test plot. Results of the GPR field surveys indicate that given suitable shallow hydrologic conditions, GPR can determine the position along a drain line where there is an isolated obstruction that completely blocks the flow of water. However, an obstruction that only partially limits water flow through the drain line will be difficult to locate using GPR. Surprisingly, the soil‐filled drain line was clearly detectable under drained, moderately wet and undrained, extremely wet soil conditions. The GPR computer simulations indicate that soil had likely settled within the initially soil‐filled pipe, and that the GPR responses obtained at the test plot for the soil‐filled pipe were responses representative of a pipe that was in fact only partially filled with soil. Overall, these research results provide valuable information for those contemplating the use of GPR to locate agricultural drainage pipes and then determine their functionality.

Ground penetrating radar (GPR) is a crucial method for shallow geophysical exploration method. GPR full waveform inversion (FWI) utilizes all available information including dynamics and kinematics, and theoretically achieving the highest imaging accuracy. However, a significant challenge for FWI is its low computational efficiency, which fails to meet the real-time requirements in actual exploration. To address this issue, we propose a finite domain method (FDM) based on the attenuation characteristic of high frequency GPR electromagnetic waves. This approach limits the calculation to a finite domain, thereby mitigating the excessive computational burden. We determine the size of the finite domain from absorption attenuation, wavefront diffusion, and scattering loss. Numerical experiments demonstrate that compared with traditional FWI, FWI based on FDM reduces the calculation time by more than 5 times.