Imaging the Distribution of Hot Spots for Biogenic Gas in Peat From the Everglades Using Air‐Coupled Ground‐Penetrating Radar (GPR) at the Laboratory Scale

The spatial and temporal variability in production and release of greenhouse gases (such as methane) in peat soils remains uncertain, particularly for low‐latitude peatlands like the Everglades. Ground penetrating radar (GPR) is a hydrogeophysical tool that has been successfully used in the last decade to noninvasively investigate carbon dynamics in peat soils; however, application in subtropical systems is almost non‐existent. This study is based on four field sites in the Florida Everglades, where changes in gas content within the soil are monitored using time‐lapse GPR measurements and gas releases are monitored using gas traps. A weekly methane gas production rate is estimated using a mass balance approach, considering gas content estimated from GPR, gas release from gas traps and incorporating rates of diffusion, and methanotrophic consumption from previous studies. Resulting production rates range between 0.02 and 0.47 g CH4 m−2 d−1, falling within the range reported in literature. This study shows the potential of combining GPR with gas traps to monitor gas dynamics in peat soils of the Everglades and estimate methane gas production. We also show the enhanced ability of certain peat soils to store gas when compared to others, suggesting that physical properties control biogenic gas storage in the Everglades peat soils. Better understanding biogenic methane gas dynamics in peat soils has implications regarding the role of wetlands in the global carbon cycle, particularly under a climate change scenario.

Ground penetrating radar (GPR) measurements have been conducted to retrace the natural course of the Obra River and changes of spatial extent of Obrzanskie Lake (western Poland). The Obra River valley was subjected to intensive anthropogenic transformation. Three artificial canals were constructed here in the beginning of the nineteenth century. The GPR surveys were done using a georadar MALA ProEx equipped with 250 MHz antenna. The measurement was verified by coring and analyses of historical maps, aerial photographs, and satellite images. The research has shown that there are at least three elongated depressions preserved in the modern land surface near the village of Solec, situated in the middle course of the valley. Several structures suggesting functioning of a multi-channel pattern in the past have been detected inside and in the vicinity of the depressions. Filling the channels with silts and peats might have been the effect of flow deceleration caused by the construction of the Obra Canals. Moreover, situation of two of the retraced depressions suggests that the landforms might be the remains of a river bed disappearing in wetlands. Further studies including groundwater flux measurements in the area between the depressions are needed to confirm such hypothesis. Furthermore, the study allowed retracing the spatial extent of Obrzanskie Lake. The sediment structures detected by the GPR measurements and calibrated with coring were interpreted to be the traces of the lake shoreline. The interpretation was supported by the findings inferred from aerial and satellite images. It was shown that Obrzanskie Lake had had at least three islands and had been directly connected with a network of braided channels before the anthropogenic intervention. The spatial extent of the lake was significantly altered by the construction of the North Obra Canal. Disconnecting the lake from the Canal resulted in more than 50 % decrease of the lake surface.

Stratigraphic controls on pool formation in a domed bog inferred from ground penetrating radar (GPR)

Important research and technical issues are related to the prospection in urban area to locate subsurface cavities and/or archaeological remains and to produce hazard mapping. In many cases, cavities, voids and collapses represent disruptions to the geometry of an originally near-horizontal layered system. Geophysical techniques can be employed to identify the feature geometries by contrasts in the physical properties, but can be strongly conditioned by cultural features that interfere with instrument measurements (utilities, structures, surficial debris).The most promising non-destructive geophysical prospection method for use in urban area is GPR. GPR measurements are less affected by the presence of metallic structures compared to magnetometer prospection and they result in the largest amount of data of all commonly employed near-surface geophysical methods, providing detailed three-dimensional information about the subsurface [1], [4]. In thist paper the surveys made with GPR to investigate different sites in the area of S. Giovanni in Laterano and Santa Croce in Gerusalemme in Rome, as part of the ERC funded Rome Transformed project (2019-2024) are presented and discussed. The aim of the GPR survey is to identify Roman and high-medieval age remains which could enhance understanding of the ancient topography and the urban evolution of the study area.For the surveys a GPR SIR3000 (GSSI), equipped with a 400 MHz (GSSI) bistatic antenna with constant offset, a 70 MHz (Subecho Radar) monostatic antenna and a SIR4000 system equipped with dual frequency antenna with 300/800 MHz were employed.All the GPR profiles were processed with GPR-SLICE v7.0 Ground Penetrating Radar Imaging Software. The basic radargram signal processing steps included: (i) post processing pulse regaining; (ii) DC drift removal; (iii) data resampling; (iv) band pass filtering; (v) background filter and (vi) migration. With the aim of obtaining a planimetric vision of all possible anomalous bodies, the time-slice representation technique was applied using all processed profiles up to a depth of about 2.5 m, [2], [3]. Ground Penetrating Radar (GPR) survey at the selected areas has produced significant and fruitful results that will be discussed during the presentation. References1 - I. Trinks, P. Karlsson, A. Biwall and A. Hinterlaitner, Mapping the urban subsoil using ground penetrating radar – challenges and potentials for archaeological prospection, ArchaeoScience, revue d’archeometrié, 2009, suppl. 33,  pp. 237-240.2 - D. Goodman and S. Piro, GPR Remote sensing in Archaeology, 2013, Springer (Ed), ISBN 978-3-642-31856-6, ISBN 978-3-642-31857-3 (eBook), DOI 10.1007/978-3-642-31857-3. Springer, Berlin, (Germany).3 - S. Piro S. and D. Goodman, Integrated GPR data processing for archaeological surveys in urban area. The case of Forum (Roma, Italy), 2008, 12th International Conference on Ground Penetrating Radar, June 16-19, 2008, Birmingham, UK. Proceedings Extanded Abstract Volume.4 - Piro S., Zamuner D., 2016. Investigating the urban archaeological sites using Ground Penetrating Radar. The cases of Palatino Hill and St John Lateran Basilica (Roma, Italy). Acta IMEKO, Vol. 5, issue 2, pp 80-85. ISSN: 2221-870X. DOI: 10.21014/acta imeko/v5i2.234 . 

Identification of liquefaction and deformation features using ground penetrating radar in the New Madrid seismic zone, USA

Abstract. Estimating the ice volume contained in glaciers is a topic of increasing interest, because the cryosphere has rapidly evolved during the last decades of global warming. Many disciplines collaborate to study the global warming impacts on glaciers. From the perspective of a geophysical research team, we examine the advantages of integrating glaciological ice-thickness models into the workflow for geophysical data processing. In temperate glaciers, the widespread englacial water content often challenges the analysis of Ground Penetrating Radar (GPR) data, the most commonly used geophysical technique for measuring ice thickness. In fact, recognizing the ice-bedrock interface is hard where the englacial water content generate high levels of scattering in the GPR data. A past GPR survey estimated that the Rutor glacier (European Alps) stored about 150 million m3 of ice in 2008. However, this estimate proved unrealistic after analyzing the geodetic mass balance of the following decade. Therefore, we analyzed new GPR measurements on the same glacier, which highlight the difficulty in identifying the true bed reflection. On these data, we tested the idea that ice-thickness models can help the GPR data analyst to better recognize the ice-bedrock interface in the radargrams. We selected four models, OGGM, GlabTop2-Py, Original-GlabTop2 and GlaTE, that estimate bedrock topography starting from surface topography, following principles of ice flow theory, ice dynamics and mass conservation. Combined visualization of the GPR and model data in 2D and 3D helped the analyst to manually select the ice-bedrock interface. This proved useful especially where the GPR data was scattered and interpretation was uncertain. The GPR data were then used to constrain one of the models, GlaTE, to produce an ice-thickness map that is the result of both model estimates and GPR information. Without this modelling context, the GPR data could be misinterpreted, and the resulting GPR-derived ice-thickness estimates might then be used to constrain a subsequent model in a way that would introduce significant errors. According to this methodology, the Rutor glacier stored about 450 million m3 of ice in 2021, about three times the previous estimate. The workflow is openly available in the section “Code and data availability” and may improve future GPR surveys of temperate glaciers, especially when facing scattered data due to englacial water content or other sparse reflectors such as debris. More accurate ice-thickness estimates will improve local studies and provide better calibration data for regional studies.

Twelve kilometers of ground penetrating radar (GPR) data have been collected over the Brookswood aquifer in southwestern British Columbia. The data have been analyzed to assess how GPR can be used to characterize the distribution and connectivity of hydraulic units. We have used GPR to locate the aquifer/aquitard boundary at several locations in the study area. The electrical contrast between these two materials makes the aquifer/aquitard boundary an excellent target for GPR surveys. GPR was also used to reconstruct the paleo-environment of one area of the Brookswood aquifer. This was accomplished by using a modification of the concept of architectural element analysis. Radar elements were identified in the survey and were assigned sedimentary parameters using data from trenching and drilling in the area. These elements were used to develop an interpretation of the paleo-environment that provides information about the spatial distribution of hydraulic units. INTRODUCTION Hydrogeologists require quantitative data to produce a realistic model of the spatial variabilities in hydraulic properties of an aquifer. Such data can be difficult and expensive to obtain. A possible solution is to develop geophysical techniques as a means of aquifer characterization. Ground penetrating radar (GPR), a shallow geophysical technique, is well suited for this purpose as it can be used to image to a depth of up to 30m in sand and gravel environments. However, the image produced by a GPR survey does not supply hydrogeologic parameters directly. The focus of this paper is to investigate how GPR can be used for aquifer characterization. At an aquifer scale of lo’s to 100’s of meters, the most fundamental aspect of aquifer characterization is the determination of the aquifer’s hydraulic connectivity through mapping of aquifer/aquitard interfaces. GPR can be used for this purpose due to the large contrast in electrical conductivity between the sand and gravel material of an aquifer, and the clay rich material of an aquitard. The electrical conductivity of a material affects the penetration depth of radar waves, such that radar waves penetrate well through resistive material, but poorly through conductive material. Aquifers, composed of sands and gravels, are resistive, while aquitards, composed of clay rich materials, are electrically conductive. Therefore a radar survey will show good penetration in aquifer materials and very poor penetration in aquitards. By exploiting this difference in radar response, the aquifer boundaries can be mapped. At a smaller scale of centimeters to meters, the determination of the internal structure of an aquifer is also important for aquifer characterization. For example, anisotropy within the aquifer can cause significant differences in hydraulic properties and so must be identified where present. In addition, identification of sedimentary features aids in the determination of the paleo-environment that can provide important insight into the probable arcal extent and orientation of geological units. GPR can be used to image these features because of changes in their electrical properties. GPR and Sedimentology GPR has received considerable attention as a means of imaging sedimentary stratigraphy (Jo1 and Smith, 1992; Smith and Jol, 1992; Pratt and Miall, 1993; Greenhouse et al, 1987; Rea et al, 1991; Huggenberger et al, 1994). The key question that needs addressing is exactly which sedimentary aspects of the subsurface are imaged with GPR. A GPR survey, conducted by transmitting radar waves into the subsurface and recording the reflected energy, will image changes in the subsurface dielectric constant and conductivity. If these electrical properties correspond to changes in sedimentary parameters, then a GPR survey can be said to image sedimentary features. The dielectric constant and conductivity of earth materials are dependent upon composition and geometry of the solid and liquid components. Sedimentological classification is based upon five fundamental properties from which all others can be derived: grain composition, size, shapes, orientation and packing (Blatt et al, 1980). These five properties clearly are related to the composition and geometry of the solid component of a system. It is therefore reasonable to assume that a change in sedimentological properties at some boundary will cause a change in electrical properties. If the resulting change in electrical properties is large enough, then the sedimentary boundary will be imaged in a radar survey. The complicating issue is the liquid, usually water, component which does not play a role in sedimentary

Subsurface water flow in South Florida is largely controlled by the heterogeneous nature of the karst limestone in the Biscayne aquifer and its upper formation, the Miami Limestone. These heterogeneities are amplified by dissolution structures that induce changes in the aquifer's material and physical properties (i.e., porosity and dielectric permittivity) and create preferential flow paths. Understanding such patterns are critical for the development of realistic groundwater flow models, particularly in the Everglades, where restoration of hydrological conditions is intended. In this work, we used noninvasive ground penetrating radar (GPR) to estimate the spatial variability in porosity and the dielectric permittivity of the solid phase of the limestone at centimeter‐scale resolution to evaluate the potential for field‐based GPR studies. A laboratory setup that included high‐frequency GPR measurements under completely unsaturated and saturated conditions was used to estimate changes in electromagnetic wave velocity through Miami Limestone samples. The Complex Refractive Index Model was used to derive estimates of porosity and dielectric permittivity of the solid phase of the limestone. Porosity estimates of the samples ranged between 45.2 and 66.0% and showed good correspondence with estimates of porosity using analytical and digital image techniques. Solid dielectric permittivity values ranged between 7.0 and 13.0. This study shows the ability of GPR to image the spatial variability of porosity and dielectric permittivity in the Miami Limestone and shows potential for expanding these results to larger scales and other karst aquifers.

Research methods for evaluation of natural stone deposits are evaluated as a part of the project “Efficient use of natural stone in the Leningrad region and South-East Finland”. The most common methods in the beginning of the site investigation process of a new natural stone deposit are detailed mapping of fractures and ground penetrating radar (GPR) measurements carried out on an exposed mapping traverse. Small scale samples are also collected to evaluate the aesthetical appearance of the stone. After these diamond core drilling is carried out to get a three-dimensional view of the stone quality. Mapping, GPR measurements and diamond core drilling have each their strengths in evaluation and they also overlap in detection of some common features. Fracture mapping carried out on the surface and GPR measurements can be combined in conditions where GPR reflections are strong, usually in intersections of sub-horizontal and sub-vertical fractures. GPR and diamond core drilling can be combined to detect major sub-horizontal fractures and in some cases also fracture system of the surface layer if the fractures are open enough and contain water or moisture.

We tested a set of surface common mid‐point (CMP) ground penetrating radar (GPR) surveys combined with elevation rods (to monitor surface deformation) and gas flux measurements to investigate in‐situ biogenic gas dynamics and ebullition events in a northern peatland (raised bog). The main findings are: (1) changes in the two‐way travel time from the surface to prominent reflectors allow estimation of average gas contents and evolution of free‐phase gas (FPG); (2) peat surface deformation and gas flux measurements are strongly consistent with GPR estimated changes in FPG content over time; (3) rapid decreases in atmospheric pressure are associated with increased gas flux; and (4) single ebullition events can induce releases of methane much larger (up to 192 g/m2) than fluxes reported by others. These results indicate that GPR is a useful tool for assessing the spatial distribution, temporal variation, and volume of biogenic gas deposits in peatlands.

Application of GPR to normal faults in the Büyük Menderes Graben, western Turkey

Abstract. Observation of sea ice thickness is one of key issues to understand regional effect of global warming. One of approaches to monitor sea ice in large area is microwave remote sensing data analysis. However, ground truth must be necessary to discuss the effectivity of this kind of approach. The conventional method to acquire ground truth of ice thickness is drilling ice layer and directly measuring the thickness by a ruler. However, this method is destructive, time-consuming and limited spatial resolution. Although there are several methods to acquire ice thickness in non-destructive way, ground penetrating radar (GPR) can be effective solution because it can discriminate snow-ice and ice-sea water interface. In this paper, we carried out GPR measurement in Lake Saroma for relatively large area (200 m by 300 m, approximately) aiming to obtain grand truth for remote sensing data. GPR survey was conducted at 5 locations in the area. The direct measurement was also conducted simultaneously in order to calibrate GPR data for thickness estimation and to validate the result. Although GPR Bscan image obtained from 600MHz contains the reflection which may come from a structure under snow, the origin of the reflection is not obvious. Therefore, further analysis and interpretation of the GPR image, such as numerical simulation, additional signal processing and use of 200 MHz antenna, are required to move on thickness estimation.

Peat soils are a critical component of the global carbon cycle as natural producers of biogenic greenhouse gases (e.g., methane and carbon dioxide) that accumulate within the soil and are released to the atmosphere. Previous studies have showed the ability of ground‐based minimally‐invasive geophysical methods such as ground‐penetrating radar (GPR) to characterize carbon dynamics in peat soils. However, ground‐based GPR is limited by scale of measurement and soil disturbance potentially altering gas releases during deployment. Here, we explore the potential of drone‐based GPR for identification of hot spots and hot moments of gas accumulation and release in subtropical soils. We collected drone‐based GPR data sets across two grids (∼17,500 m 2 ) in the Everglades during January (dry season), September, and November (wet season) of 2023 to characterize peat thickness and seasonal variability of gas content. Results show that drone‐based GPR is effective and efficient for: (a) capturing the temporal variation of in situ biogenic gas content in peat soils with changes between 1% and 25 % volumetric gas content over repeatable grids; (b) inferring a total peat thickness between 0.8 and 1.2 m; and (c) estimating flux releases of 63 and 135 mg CH 4 m −2 day −1 for specific locations and periods that are strikingly consistent with our coincident gas trap measurements. This work also indicates that (a) spatial distribution of gas content in the Everglades is strongly controlled by landscape morphology such as ridges and sloughs and (b) the temporal variation of gas content is seasonal with increased gas production during the wet season.

Ground penetrating radar (GPR) is a proven method for detecting changes in the water table. In<br>this paper, we present data that suggest that GPR can also be used to monitor the percolation of rainfall<br>into the subsurface. Two series of bistatic 500 MHz GPR data were taken over a 4x4 foot grid in the<br>center of a polyethylene tank. For the first series of measurements, the tank was filled with gravel and<br>sand. The GPR measurements were taken both before and after two separate one-inch simulated<br>rainfalls were sprinkled on the top of the tank. For the second series of measurements, the tank was<br>filled with gravel, sand, and a sand-clay mixture. GPR measurements were taken both before and after a<br>single one-inch simulated rainfall.<br>For both experiments, multiple sets of GPR measurements were taken after the simulated<br>rainfalls over a number of hours. As time progressed we can see in both the 2-D sections and 3-D<br>blocks of our data how the water first infiltrates the tank, then accumulates in low permeability zones,<br>and finally migrates to the bottom of the tank. Although we are unable to image the wetting front, we<br>can see anomalies that arise as the water passes through the tank, and we can see water table rise as the<br>water accumulates at the bottom of the tank. The effect of the sand-clay mixture in the tank is to<br>attenuate the GPR signal.<br>We discuss the potential of using GPR measurements to estimate hydraulic parameters under the<br>proper field conditions. We conclude that GPR is sensitive to changes in water content in the vadose<br>zone. Not only is GPR sensitive enough to monitor changes in water table levels, but it is also sensitive<br>enough to monitor the infiltration of water into the subsurface.

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.).