Ground Penetrating Radar Surveys Research Articles

Mapping water pipeline leakage by ground-penetrating radar diffraction imaging

Investigation of water pipeline leakage is a matter of great significance for water resources management. Among various approaches, ground-penetrating radar (GPR) attracts increasing attention as a fast and noninvasive technique. However, this method suffers from uncertainties in the stage of interpretation because diffractions from the leak region often are too weak to be identified. To address this problem, we have developed the use of diffraction imaging to enhance imaging and characterization of water leakage. Numerical seepage simulation allows us to establish an equivalent computational analog for a known leak condition. After the collection of parallel GPR survey lines, we apply diffraction separation and imaging techniques on 2D and 3D data. Although the actual situation is generally well reproduced by 2D and 3D results, 3D diffraction imaging provides improved mapping of leakage compared with its 2D counterpart. We then apply the method to field data collected at a training base for water pipeline leakage control in Shaoxing, China. The prediction from imaging results corresponds well with the true position and type of leakage. The laboratory and field experiments substantiate the viability of GPR diffraction imaging and illustrate the potential of using GPR to detect small water leaks.

A Time Series of Snow Density and Snow Water Equivalent Observations Derived From the Integration of GPR and UAV SfM Observations

Snow depth can be mapped from airborne platforms and measured in situ rapidly, but manual snow density and snow water equivalent (SWE) measurements are time consuming to obtain using traditional survey methods. As a result, the limited number of point observations are likely insufficient to capture the true spatial complexity of snow density and SWE in many settings, highlighting the value of distributed observations. Here, we combine measured two-way travel time from repeat ground-penetrating radar (GPR) surveys along a ∼150 m transect with snow depth estimates from UAV-based Structure from Motion Multi-View Stereo (SfM-MVS) surveys to estimate snow density and SWE. These estimates were successfully calculated on eleven dates between January and May during the NASA SnowEx21 campaign at Cameron Pass, CO. GPR measurements were made with a surface-coupled Sensors and Software PulseEkko Pro 1 GHz system, while UAV flights were completed using a DJI Mavic 2 Pro platform and consisted of two orthogonal flights at ∼60 m elevation above ground level. SfM-MVS derived dense point clouds (DPCs) were georeferenced using eight ground control points and evaluated using three checkpoints, which were distributed across the ∼3.5 ha study plot containing the GPR transect. The DPCs were classified to identify the snow surface and then rasterized to produce snow-on digital surface models (DSMs) at 1 m resolution. Snow depths on each survey date were calculated by differencing these snow-on DSMs from a nearly snow-off DSM collected near the end of the melt season. SfM-derived snow depths were evaluated with independent snow depth measurements from manual probing (mean r2 = 0.67, NMAD = 0.11 m and RMSE = 0.12 m). The GPR-SfM derived snow densities were compared to snow density measurements made in snowpits (r2 = 0.42, NMAD = 39 kg m−3 and RMSE = 68 kg m−3). The integration of SfM and GPR observations provides an accurate, efficient, and a relatively non-destructive approach for measuring snow density and SWE at intermediate spatial scales and over seasonal timescales. Ongoing developments in snow depth retrieval technologies could be leveraged in the future to extend the spatial extent of this method.

The Zonation of Mountain Frozen Ground under Aspect Adjustment Revealed by Ground-Penetrating Radar Survey—A Case Study of a Small Catchment in the Upper Reaches of the Yellow River, Northeastern Qinghai–Tibet Plateau

Permafrost distribution is of great significance for the study of climate, ecology, hydrology, and infrastructure construction in high-cold mountain regions with complex topography. Therefore, updated high-resolution permafrost distribution mapping is necessary and highly demanded in related fields. This case study conducted in a small catchment in the northeast of the Qinghai Tibet Plateau proposes a new method of using ground-penetrating radar (GPR) to detect the stratigraphic structure, interpret the characteristics of frozen ground, and extract the boundaries of permafrost patches in mountain areas. Thus, an empirical–statistical model of mountain frozen ground zonation, along with aspect (ASP) adjustment, is established based on the results of the GPR data interpretation. The spatial mapping of the frozen ground based on this model is compared with a field survey dataset and two existing permafrost distribution maps, and their consistencies are all higher than 80. In addition, the new map provides more details on the distribution of frozen ground. In this case, the influence of ASP on the distribution of permafrost in mountain areas is revealed: the adjustment of ASP on the lower limit of continuous and discontinuous permafrost is 180–200 m, the difference in the annual mean ground temperature between sunny and shady slopes is up to 1.4–1.6 °C, and the altitude-related temperature variation and uneven distribution of solar radiation in different ASPs comprehensively affect the zonation of mountain frozen ground. This work supplements the traditional theory of mountain permafrost zonation, the results of which are of value to relevant scientific studies and instructive to engineering construction in this region.

Nondestructive detection of cavities beneath concrete plates using ground penetrating radar and microphone

The objective of this study is to detect and estimate the size of a cavity beneath a concrete plate using ground penetrating radar (GPR) and microphone surveys in laboratory tests. A chamber in which a reinforced concrete plate is installed on one side, is filled with dry sand, and a cavity is placed between the concrete plate and sand. The GPR signals are measured at the surface of the concrete plate, and acoustic signals are acquired by impacting the concrete plate with an instrumented hammer and are measured by a microphone. Imaging methods are adopted for the GPR and acoustic signals, and the location and size of the cavity are evaluated using the images. The GPR survey results show that the evaluated location of the cavity may differ from the actual location, and the cavity size is underestimated because of the rebars. The microphone survey results show that the evaluated and actual locations match, and the estimated cavity size is slightly smaller than the actual size. This study demonstrates that microphones may be used efficiently for cavity identification and size estimation.

Reconstruction of relative sea-level changes based on a multiproxy study of isolated basins on the Onega Peninsula (the White Sea, northwestern Russia)

This study presents the results of lithological, diatom, geochemical analyses and radiocarbon chronology of the bottom lake sediments and peat bogs in the central part of the Onega Peninsula (the southern coast of the White Sea): Lake Maloye Murakanskoye (11.0 m a.s.l.), Lake Zhirovskoye (9.5 m a.s.l.), Lake Murakanskoye (7 m a.s.l.), and the Gorbovatiy Mokh bog (6.5 m a.s.l.). The bottom topography and sediments of Lake Murakanskoye were examined using sonar and ground penetration radar (GPR) survey, whereas in the other locations only the water depth was measured. Then, the digital models of the lake bottom topography were created. As an additional indicator of the relative sea-level (RSL) position, we used data on the altitude of the coastal terraces. Evidences of two transgressions in the White Sea (late glacial and Middle Holocene) are revealed. The transgressions were interrupted by two regressions (Early and Late Holocene). Our studies do not allow us to make a clear conclusion about the time and maximum level of the late glacial transgression. However, we may suggest that its level was above 11 m a.s.l. The regression of the Early Holocene started before 10.6–10.2 ka cal BP when the water level in the study area dropped below the altitude of 11m. At 9.4–9.1 ka cal BP the RSL was at an altitude of ca 7m. The Middle Holocene transgression (Tapes) started after 8.4 ka cal BP. The maximum level was reached before 7.4 ka cal BP and did not exceed an altitude of 9.5 m. The RSL stabilized at an altitude about 8.5–8 m during 7.4–6.0 ka cal BP. During 6.0–3.9 ka cal BP RSL very slowly decreased or fluctuated by the level of 8–7 m. RSL began to fall from the 7 m altitude about 4.0–3.9 ka cal BP and by 2.7–2.3 ka cal BP the sea-level reached 4.5 m. After that RSL dropped to its modern position. During the last 4.0 ka cal BP the rate of RSL fall was approximately 0.17–0.18 cm/year.

Subsurface Investigation of Voids using Ground Penetration Radar in Bismayah Site, Southern Baghdad, Central Iraq

Ground Penetration Radar investigation was used to survey the Bismayah pumping station site in Baghdad. The survey includes fifteen Ground Penetration Radar survey lines inside and outside the site, an antenna of 250 MHz was used. The total length of survey lines was about 706 m. The results of Ground Penetration Radar lines in outside station's radargrams exhibit reverberation events in the Ground Penetration Radar signal, it might be interpreted as the inverse of existing voids or noise near the surface. Grouted materials could be understood as the refractor. The results of the radargrams along the paths inside the pumping station revealed that the station collapsed in the north because the reflector of soil creep was visible in the north line path direction. After 4 m from the ground surface and right beneath the foundation base, there was a layer of loose dense river sand filled with water. It is expected that the process of soil creep caused the rush and drift of the pumping station structure towards the withdrawal of water from the well. The results show the efficiency of the Ground Penetration Radar technique in the near-surface investigation of the current study, due to the easy and time saving survey with reasonable results.

Ground Penetrating Radar (GPR) survey over a melting blue ice area (BIA) at the south of Schirmacher Oasis, Dronning Maud Land, East Antarctica

A blue ice area (BIA) is located in Dronning Maud Land, East Antarctica between Schiermacher Oasis (SO) and Ulthat mountain ranges. High-resolution ground-penetrating radar (GPR) survey has been carried out in the northern boundary of the BIA surrounded by Schirmacher Oasis (SO), Shivalinga and Veteheia nunataks to examine if the BIA in the area is wind-induced or melt-induced in nature. GPR study reveals that the glacier in this part of BIA is warm and showing prominent signatures of subsurface melting in the vicinity of the nunataks and other exposed rock masses. The signatures of bottom warming also have been detected in few profiles which are in agreement with the drilling results in nearby areas. Melting signatures vary over the area depending on the distances from the exposed rocks and proximity of subglacial bedrock topography. The results indicate the possible higher heat supply by the exposed rock mass to the BIA. Folding of the internal layers and the presence of two firn pockets also have been observed near the nunatak Veteheia. The present GPR study concludes that the survey area is predominantly melt-induced BIA. Further investigations are recommended to study the firn pockets and mass balance of the area.

Seasonal Impact on 3D GPR Performance for Surveying Yedoma Ice Complex Deposits

Ground-penetrating radar (GPR) is a popular geophysical method for imaging subsurface structures with a resolution at decimeter scale, which is based on the emission, propagation, and reflection of electromagnetic waves. GPR surveys for imaging the cryosphere benefit from the typically highly resistive conditions in frozen ground, resulting in low electromagnetic attenuation and, thus, an increased penetration depth. In permafrost environments, seasonal changes might affect not only GPR performance in terms of vertical resolution, attenuation, and penetration depth, but also regarding the general complexity of data (e.g., due to multiple reflections at thaw boundaries). The experimental setup of our study comparing seasonal differences of summertime thawed and winter- and springtime frozen active layer conditions above ice-rich permafrost allows for estimating advantages and disadvantages of both scenarios. Our results demonstrate major differences in the data and the final GPR image and, thus, will help in future studies to decide about particular survey seasons based on the GPR potential for non-invasive and high-resolution investigations of permafrost properties.

TO THE PROBLEM OF USING OF MODERN METHODS IN THE RESEARCH OF ARCHITECTURAL AND ARCHAEOLOGICAL URBAN COMPLEXES (ON THE EXAMPLE OF THE NATIONAL RESERVE "ANCIENT HALYCH" TERRITORY)

There are several dozen historical-architectural or historical-cultural reserves in Ukraine, which were created to preserve the valuable historical environment. As a rule, on the territory of such nature reserves, we have a combination of objects of architectural and archaeological heritage. In the past, these objects could be significant complexes with fortifications, and several auxiliary buildings, some of which were objects of wooden architecture. Today, a large part of such objects is lost. We can give a list of the most famous ones – the reserve "Sofia Kyivska", "Davnii Halych", "Knyazhy Belz", the historical and archaeological reserve "Plisnesko", the historical and architectural reserve in the city of Zhovkva or the reserve in the city of Lutsk, and many others. As a rule, the planning of research and restoration-conservation works in such nature reserves takes place by successive selection of individual objects and efforts to bring them to a proper state and museumization. With this method of planning, the most important scientific component is lost – the study and assessment of the entire complex with its preserved and unpreserved objects (including archaeological and landscape elements). The recording of all the wealth of movable and immovable heritage on the territory of the reserve is also relevant. Such a selective method is due to the weak instrumental base of reserves and limited opportunities to attract relevant specialists. We believe that scientific activity and conservation and restoration work in such nature reserves should be based on a primary survey of the entire territory. A thorough and complete inventory of all archaeological sites on the territory must be carried out. In the article, we reveal the possibilities of research and inventory of the territory of historical and cultural reserves using modern instrumental non-invasive methods. The most problematic are the tasks of detection, inventory, and identification of objects of archaeological heritage. This task can be solved with the use of modern equipment and appropriate methods – ground-penetrating radar surveys, thermal imaging, exploratory drilling, the use of micro video cameras, aerial photography of the territory using a quadcopter, laser 3D scanning, etc. We present specific recommendations and proposals for the formation of a scientific research program for the territory of the "Davnii Halych" national reserve.

Estimation of glacier ice storage in western China constrained by field ground-penetrating Radar surveys

Recent decades have witnessed the accelerated retreat of alpine glaciers, which likely portends a decline in the glacial ice melt on which large downstream populations rely for freshwater. Thus, estimating water storage in alpine glaciers is critical for predicting the trend of glacier melting. This study compiled a rich set of ice thickness observations for glaciers of varying sizes in western China. We here presented a first-order assessment of the various errors involved in interpreting ice thickness from ground-penetrating radar (GPR) observations. An empirical Bayesian kriging (EBK) method was used for ice thickness interpolation and volume estimation. We then established a new volume-scaling law specific to western China glaciers based on these 36 volume-area pairs. And together with the Second Chinese Glacier Inventory (SCGI), we obtain a regional volume estimate of 4451 ± 298 km3. By comparison, we believed that this result is the most reliable estimate of the total ice storage in western China and more reliably predicts gross glacier melting. However, our results show that the method of glacier division can strongly affect the total volume estimation, which previous studies ignored. This emphasizes the need for more surveyed glaciers data and more accurate glacier inventory to improve the evaluation of the climate impact on glacier melting water resources and to help ensure the future survival of these alpine glaciers.

Revised temporal and morphostratigraphic context for Clark Quarry: A late-Pleistocene, fluvially-reworked, Atlantic coast backbarrier deposit

Sediments along the Atlantic Coastal Plain (ACP) of North America have been the focus of numerous paleontological investigations and yielded a diverse array of vertebrate remains; yet the depositional environments associated with their preservation are poorly understood. In this study, we present a multidisciplinary analysis of the depositional environment at Clark Quarry, a late-Pleistocene, fossil-rich locality located within the ACP in Georgia, USA. Clark Quarry is currently positioned 15 km west of the Atlantic Ocean coast and lies within the Princess Anne Terrace, a 100–80 ka paleobarrier-island complex. Fossil-bearing sediments at Clark Quarry are interpreted to have been deposited as a low-energy, fluvial environment that subsequently reworked low-lying terrain of the Princess Anne Terrace backbarrier. Interpretations of digital elevation models (DEM) and infrared stimulated luminescence (IRSL) ages on K-rich feldspar sand grains indicate that this region was an estuarine zone backing (i.e., westward) the Princess Anne paleobarrier island that was subsequently reworked by fluvial activity 68–52 ka. These new interpretations, paired with additional radiocarbon ages from fossil carbonates and overlying soil horizons, indicate that radiocarbon samples may have been influenced by isotopic exchange and should be interpreted as minimum age estimates. Additionally, ground-penetrating radar (GPR) surveys in conjunction with DEM analysis may have captured the subsurface signature of a meandering fluvial system transitioning to a braided style, emphasizing the dynamic nature of this depositional environment. Non-preferential orientation of excavated long bones suggests multidirectional paleoflow, further suggesting a braided stream influence. When considered in conjunction, these data: 1) indicate that Clark Quarry represents a spatially and temporally resolved window into the late-Pleistocene ecosystem in southeastern North America, and 2) suggest that existing radiocarbon data from late-Pleistocene ACP localities should be considered with caution.

Automatic modelling of urban subsurface with ground-penetrating radar using multi-agent classification method

ABSTRACT The subsurface of urban cities is becoming increasingly congested. In-time records of subsurface structures are of vital importance for the maintenance and management of urban infrastructure beneath or above the ground. Ground-penetrating radar (GPR) is a nondestructive testing method that can survey and image the subsurface without excavation. However, the interpretation of GPR relies on the operator’s experience. An automatic workflow was proposed for recognizing and classifying subsurface structures with GPR using computer vision and machine learning techniques. The workflow comprises three stages: first, full-cover GPR measurements are processed to form the C-scans; second, the abnormal areas are extracted from the full-cover C-scans with coefficient of variation-active contour model (CV-ACM); finally, the extracted segments are recognized and classified from the corresponding B-scans with aggregate channel feature (ACF) to produce a semantic map. The selected computer vision methods were validated by a controlled test in the laboratory, and the entire workflow was evaluated with a real, on-site case study. The results of the controlled and on-site case were both promising. This study establishes the necessity of a full-cover 3D GPR survey, illustrating the feasibility of integrating advanced computer vision techniques to analyze a large amount of 3D GPR survey data, and paves the way for automating subsurface modeling with GPR.

Mapping of the Buried Paleochannels on the Terminal Fans in the Western Ganga Plain: A Geomorphological and Ground Penetrating Radar-based Approach

Abstract Paleochannels are valuable tools for delineating tectonics, climate, anthropogenic activities, reconstructing the paleo-geography, and studying the geomorphological evolution of the alluvial plains. Paleochannels on the terminal fans provide crucial information regarding their geomorphic evolution in space and time. Furthermore, paleochannels could be a good source for groundwater exploration. Exposed paleochannels in the recent alluvial plains are mappable by remote sensing and field evidence. However, mapping becomes difficult due to burial in relatively older alluvial surfaces, and anthropogenic disturbances complicate the case. This paper deals with an integrated method of mapping the buried paleochannels in the terminal fans from the western Ganga plain. Paleochannels have been mapped on three Holocene terminal fans, using remote sensing and Google Earth images, and Cartosat DEM. As continuity of the entire length of paleochannels could not be traced by the above tools due to burial and intense anthropogenic modifications, aligned surface water bodies were helpful at places to ascertain their continuity. The ground penetrating radar (GPR) survey by bistatic antennae (100 MHz frequency in distance mode) detected the subsurface existence of these buried paleochannels up to a maximum depth of about 35 m. Field evidence of some of these buried channels was confirmed at few excavations by the presence of channel sand. A previous study of these terminal fans through optical stimulated luminescence (OSL) dating suggests that channel abandonment occurred between 4.7 to 2.3 Ka, coinciding with the period of the dry climate and intense surface faulting episodes in the Ganga plain.

Climatically induced cyclicity recorded in the morphology of uplifting Tihu coastal ridgeplain, Hiiumaa Island, eastern Baltic Sea

Holocene relative sea level changes and palaeogeography of the uplifting Tihu ridge-swale beach system in the functionally tideless Baltic Sea were reconstructed using airborne LiDAR elevation data, ground-penetrating radar surveys, sedimentological proxies, recent models of Fennoscandian uplift due to glacial isostatic adjustment, and GIS-based terrain modelling. Considering that aeolian contribution to the ridge growth was relatively small and uniform along the studied profiles, it was possible to utilize an age estimation method based on terrain elevation and pre-determined RSL curves. The tested relative sea level curves converged around a linear trend during the past 7 ka, the rate of which (3.1–3.2 mm/a) is strongly correlated with relative-to-geoid uplift model output. We found that the Tihu system started to emerge from the sea ~5.4 ka ago. In its older part, it includes a complex of elevated barrier spits where both the isostatic uplift and gradual sediment aggradation due to longshore transport contributed to its nucleation and initial progradation. In its lower (younger) section, a forced progradation “staircase” of palaeocoastlines was formed in a regime of sediment deficit and low-energy hydrodynamic conditions. Analysis of near-cyclic occurrences of beach/foredune ridges and larger ridge sets within the Tihu ridgeplain revealed time intervals of enhanced storminess during 5.4–4.9, 4.8–4.5, 4.6–4.3, 4.1–3.8, 3.7–3.4, 3.2–2.9, 2.7–2.4, and 2.2–1.9 ka BP. Serving as a new independent proxy for past storminess and high sea level events in Estonia, these phases match well with some previous European Atlantic storminess reconstructions for Mid- to- Late Holocene.

Locating Graves in Different Soil Types and Burial Ages in Pulau Pinang using Ground Penetrating Radar

Ground-penetration radar (GPR) is a geophysical tool widely applied in archaeological and forensic research, such as identifying the exact position of graves. A detailed GPR survey was conducted on the cemeteries in Permatang Pasir and Titi Teras, Penang Island. Moving a 500MHz GPR antenna along parallel transects inside grids was used to collect data. The study’s aim was to present two case studies with varying soil types and burial ages. Analysis of reflection shape, reflection strength and signal polarity helped in the interpretation of burial anomalies. The results varied depending on the soil type; in the sandy field, the GPR investigations were clearer and less complicated than in the clayey sand field. When the conditions are ideal (low conductivity areas with little vegetation), GPR provides highly informative and precise results. Time-slices representations were used as a method to provide details about the subsurface reflection at a certain depth.

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

Ground Penetrating Radar (GPR) is often regarded a prospecting tool of underground targets rather than rigorous measurement tool where measurement uncertainty must be accompanied. This paper attempts to make use of GPR as a measurement tool by developing a simple model and evaluating the uncertainty of underground target’s depth estimation in two ways: (1) prior to GPR survey and (2) after GPR survey, for practical use by the partitioners. For (1), the expected uncertainty prior to GPR survey was modelled based on the estimation of the assumed host material’s dielectric permittivity and the assumed two-way travel time subject to required target depth. For (2), the expanded uncertainty of the estimated cover depth by GPR was propagated from the errors in the measured pairs of (xi,ti) of hyperbolas in the radargram. This effort attempts to simplify the complex computation in Xie et al. (2021a, 2021b) by assuming negligible uncertainties of buried target diameter and distance of GPR antenna separation. Experiments were carried out on various host materials to validate the model with a common offset antenna of nominal centre frequency at 400 MHz. The experimental results shows that (1) the expected uncertainty prior to survey was strongly dependent on the increase of the target depth. But in the evaluated uncertainty after the GPR survey, this strong dependency is replaced by the scattering noise in the reflection data (xi,ti). (2) The maximum percentage SD (i.e. error) is 11.5% of detected depth at 95% confidence level. This percentage is smaller than the the most stringent accuracy requirement in PAS 128 (15% of the detected depth) (ICE, 2014). This work contributes to the accuracy evaluation of the estimated depths of underground targets. The expected uncertainty of depth prior to GPR survey can provide a reference for the practitioners and clients during engineering, e.g. underground trenchless tunneling project). And the evaluated uncertainty after GPR survey turns a uncertain survey to a serious measurement reflecting the quality and reliability of the estimation results by GPR.

GPR mapping with mobile mapping sensing and tracking technologies

Ground Penetrating Radar (GPR) is commonly used for detecting and locating underground utilities, as well as identifying water leakages and other buried objects without the need for excavation. To precisely depict the subsurface by GPR, an accurate geo-referencing technique on each GPR scan is also essential. Traditional geo-referencing of GPR scans requires a survey wheel to walk along a predetermined grid, or relies on the Global Navigational Satellite Systems (GNSS) to work under open sky environments where enough satellites are available (Böniger and Tronicke, 2010; Chang, 2016). In this study, we attempt to use a mobile mapping system (MMS) backpack guided by SLAM as the geo-referencing device for synchronizing GPR scans in areas with bad or no GNSS, and is free of control points. The study develops a method to synchronise the SLAM positioning and GPR measurements and then validate the proposed method's precision and accuracy with a site case. It was proved that the integrationed time and labour required in the traditional gridding are minimized for improving the GPR survey efficiency, facilitating the large-scale survey in dense urban areas where good GNSS coverage is unavailable.

Reconnaissance GPR survey of the ice caps on islands of Wilhelm Archipelago and on Berthelot island (West Antarctica)

In this paper results of Antarctic ice caps investigations with GPR are represented. Local glaciological investigations of small glaciers on islands at the western coast of the AP are rare. Ice thickness is an important parameter for ice mass balance calculation. Investigation of the layering and in-situ sampling help to reveal information about past climate conditions and to understand glacio-geological history of the region. However, modern database Global Terrestrial Network for Glaciers contains neither the information about the thickness nor about interior structure of the ice caps discussed in this paper. The research is aimed at investigating the thickness and interior structure of the ice caps on Antarctic islands Plйneau, Petermann, Booth, Berthelot and Dannebrog. This territory was described only on the level of pioneering research in 19—20th centuries. The aim of the research is to obtain data about the general structure of the ice caps and ice thickness. Ground penetrating radar (GPR) VIY 3-300 (300 MHz) was applied to the surveying. Processed GPR profiles show up to 14 layers (Plйneau) inside the ice caps. There are interior crevasses, zones of moisture concentration and voids. Maps of the ice thickness were built for each island. The ice thickness on Dannebrog, Booth and part of Plйneau islands is more than 27 m, so it is recommended to use less frequency of the antennae than 300 MHz for a deeper and more detailed research of these ice caps. There are crevasses inside the ice near the surface, so for further investigations it is better to use special equipment to prevent any emergency situations (ropes, crampons, ice-hammerd, etc.). Landing sites on the islands with better access to the territories are mentioned in this paper.

Seyakha catastrophic blowout and explosion of gas from the permafrost in the Arctic, Yamal Peninsula

For the first time, in a channel of the Arctic river, on the Yamal Peninsula, a pingo-like feature (PLF) was revealed, where, as a result of powerful blowout, self-ignition and explosion of gas on the 28th of June 2017, the giant Seyakha Crater (C11) was formed. Expeditions in 2017, 2018 and 2019 on the C11 Crater and analysis of remote sensing data allowed to reconstruct geodynamical processes of rapid (approximately 3.5 years) growth of the PLF, caused by high gas pressure, and active thermoabrasive processes in summer seasons (speed up to 1.6 m per day), destroying the C11 Crater walls. It was discovered that before the explosion, a gas-filled thermokarst chamber (ice cavity) had existed in permafrost. Based on the use of the ground penetrating radar survey, a model of the crater and the structure of near-surface deposits was created. A previously unknown rise in the base of ground ice, probably connected with gas-dynamic process, was revealed. A scheme of distribution of frozen soil and ground ice fragments, ejected from the crater, was created and analyzed, their maximum distance from the explosion epicenter was defined as 380 m. Long-term gas emission from the crater was observed, which allowed to make a conclusion about volcanic mechanism of eruption. Large distances from deep wells to the location of the explosion (15 km and more) and determined microbial genesis of gas indicate high probability of natural origin of gas blowout and formation of the C11 Crater.

Ground Penetrating Radar Survey of the UNESCO Painted Churches in the Troodos Region (Cyprus)

In the framework of the IH-AT (Invisible Heritage Analysis and Technology) project, a cluster of churches ranging from the 11th to the 16th centuries, located in the Troodos Mountain range of Cyprus, designated by UNESCO as World Heritage monuments, were investigated using Non-Destructive-Techniques (NDT) (geophysical and topographic survey), 3D modelling and visualisation methods, contextualised and interpreted by art-historical and archaeological research. A geophysical survey, performed using a Ground Penetrating Radar (GPR), specifically aimed to confirm the presence or absence of buried features of archaeological interest at each of these sites, in particular, evidence of monastic complexes and buildings that used to surround preserved churches. This paper describes the preliminary results of this survey and some initial interpretations concerning what new information can be discerned about the now lost monastery complexes, in advance of future excavation.