Ground Penetrating Radar Surveys Research Articles

The Aneto glacier's (Central Pyrenees) evolution from 1981 to 2022: ice loss observed from historic aerial image photogrammetry and remote sensing techniques

Abstract. The Aneto glacier, although it may be considered a very small glacier (<0.5 km2), is the largest glacier in the Pyrenees. Its surface and thickness loss have been continuous in recent decades, and there have been signs of accelerated melting in recent years. In this study, thickness and surface losses of the Aneto glacier from 1981 to 2022 are investigated using historical aerial imagery, airborne lidar point clouds and unoccupied aerial vehicle (UAV) imagery. A ground-penetrating radar (GPR) survey conducted in 2020, combined with data from photogrammetric analyses, allowed us to reconstruct the current ice thickness and also the existing ice distribution in 1981 and 2011. Over the last 41 years, the total glacierised area has decreased by 64.7 %, and the ice thickness has decreased, on average, by 30.5 m. The mean remaining ice thickness in autumn 2022 was 11.9 m, as against the mean thickness of 32.9, 19.2 and 15.0 m reconstructed for 1981 and 2011 and observed in 2020, respectively. The results demonstrate the critical situation of the glacier, with an imminent segmentation into two smaller ice bodies and no evidence of an accumulation zone. We also found that the occurrence of an extremely hot and dry year, as observed in the 2021–2022 season, leads to a drastic degradation of the glacier, posing a high risk to the persistence of the Aneto glacier, a situation that could extend to the rest of the Pyrenean glaciers in a relatively short time.

Ground penetrating radar applied to subsurface culverts

ABSTRACT The failures of culverts can result in water and soil loss in the surrounding subsurface, leading to collapses. In densely constructed urban areas, buried culverts are inaccessible and invisible, making Ground Penetrating Radar (GPR) inspection a widely adopted nondestructive and efficient method. Previous research has employed artificial intelligence to automate GPR interpretation by identifying special radargram textures, but the irregular GPR responses of degraded subsurface soils present a challenge. Therefore, this study proposes a method for preliminary diagnosing large-scale culverts based on GPR wave attributes. The method comprises three parts: (1) evaluating soil compactness by estimating the tortuosity of GPR responses at the culvert top; (2) investigating soil moisture using the attenuation rate of GPR responses; and (3) overlaying the results of the incompact and moist soils to pinpoint potential degradations. Two long-distance culverts were inspected and diagnosed using the proposed method, and three abnormal sections were identified and confirmed by excavation evaluation. The case studies indicate that the proposed method can quickly provide reference for further in-depth investigation, thereby improving GPR survey efficiency and reducing workload by narrowing the investigation scope. Consequently, this study can facilitate large-scale GPR culvert surveys and further safeguard the water system.

Late Quaternary Deformation of the Ambon fault, Indonesia: Preliminary Results

The Ambon fault in the northern Banda Arc has capability of generating Mw 6.9 earthquake. The Ambon fault poses a significant seismic hazard to Ambon Island because the fault is located near populous areas, the Ambon City. Recent seismicity in Ambon Island and surrounding areas indicates that this region is actively deforming. Ambon Island has experienced many damaging earthquakes since the 17th century. However, the potential seismic hazard on this island remains enigmatic due to the lack of detailed geological information, such as fault traces, slip rate, and paleoseismic history. This study reports the preliminary results of tectonic geomorphic investigations and ground-penetrating radar (GPR) surveys on the Ambon fault. Tectonic geomorphic features, such as fault scarps, warped surfaces, and sag ponds indicate the late Quaternary activity of the Ambon fault. The Ambon fault predominantly shows a normal sense of motion with a dip of ~60-70°. The Ambon fault is related to the extensional tectonics in the Banda Sea.

GPR survey on underwater archaeological site: A case study at Jenipapo stilt village in the eastern Amazon region, Brazil

In this work we present and discuss the results of a pioneering Ground Penetrating Radar (GPR) survey performed at the underwater archaeological stilt village called Jenipapo in the eastern Amazon region. Jenipapo stilt village is located on the Turiaçu River, Maranhão State, Northeast of Brazil. The region is known as the Maranhense wetland where settlements were built by indigenous populations that inhabited this region during the pre-colonial period (∼AD 1 – 1100). These settlements were built on the margin of rivers and lakes, being supported by wooden pillars, corresponding to prehistoric stilt houses. The objectives of this research are to refine the wooden pillars location at the Turiaçu River bottom and guide the search for underwater archaeological artifacts. A total of twelve GPR profiles were acquired with 270 MHz antennas using a rubber boat. The GPR results indicated clear signal reflection from the river bottom and several diffraction hyperbolas suspended over the river bottom related to the top of the wooden pillars. To support the interpretation of the results, a GPR numerical modeling was performed to simulate the diffraction hyperbolas suspended in the water related to the wooden pillars. The synthetic result presented a good agreement with real data. Finally, the location of several diffraction hyperbolas can guide the divers to find and collect archaeological artifacts around the underwater wooden pillars that are the best evidence of the stilt houses of indigenous settlements found in the eastern Amazon region. Several archaeological artifacts were found during previous work, including ceramic materials. The results of this research show the capability of the GPR method to map an underwater wooden pillar and increase the probability of finding archaeological artifacts on the river bottom, which contributes to improve the knowledge of the Amazonian archaeology in Brazil.

Late Tripolye Culture Settlement Spatial Pattering: Case study from the Gordineşti II-Stînca goală site, Northern Moldova

Abstract The Gordineşti II-Stînca goală is an archaeological site located in the northern part of the Moldavian Plateau in Edineț Region. Chronologically this settlement is linked to the later phase of the Tripolye Culture. Currently, in archaeological literature, the problems of human occupation, land management, and spatial arrangement of settlements in Moldova during the Eneolithic are highly understudied. In this paper, we present the results of recent archaeological works focusing on the spatial patterning of housing structures, Ground Penetrating Radar (GPR) survey, and desk-based Kernel Density Estimation (KDE) analysis, that has been undertaken to further the understanding of the spatial organisation of the Gordineşti II-Stînca goală settlement. The results indicate the high archaeological potential of this site, with the likely presence of multiple housing structures arranged in a planned and functional manner.

Investigating Wiradjuri marara (carved trees or dendroglyphs) and dhabuganha (burials) in the Central Tablelands, southeastern Australia

Marara (carved trees, dendroglyphs or tapholgyphs) are a distinct part of Wiradjuri Country in southeastern Australia. Each marara displays a unique muyalaang (tree carving) that a Wiradjuri person carved into the outer surface of a tree after removing bark. Marara mark the dhabuganha (burials) of Wiradjuri men of high standing, representing part of traditional cultural practices that extend into the deep past. Yet, the meaning of these sacred locations is not widely understood due to the lack of Wiradjuri teaching, knowledge and participation in previous studies. Here we present the first Wiradjuri-led archaeological study of marara, muyalaang and dhabuganha, completed in the Central Tablelands. We combine a review of previous studies with new information from interviews with Wiradjuri Elders and knowledge holders, Ground Penetrating Radar survey, and 3D modelling (photogrammetry) – guided by the Wiradjuri philosophy Yindyamarra (cultural respect). The results build new, culturally and scientifically informed understandings of practical and symbolic aspects of Wiradjuri culture, with marara and dhabuganha viewed not as individual objects or ‘sites’ but as connected parts of Wiradjuri Lore, beliefs, traditional cultural practices and Country. Consistent with Wiradjuri Elder requests, this paper is freely available and written in simple language for the Wiradjuri community and beyond.

Brief communication: How deep is the snow on Mount Everest?

Abstract. Exploring the snow depth on Mount Everest, one of the most inaccessible places on our planet, has long been a topic of interest. Previously reported snow depths have been inconsistent and have large uncertainties. Here, we report the ground-penetrating radar survey of snow depth along the north slope of Mount Everest in May 2022. Our radar measurements display a gradual increasing transition of snow depth along the north slope, and the mean depth estimates at the summit are 9.5±1.2 m. This updated snow depth on Mount Everest is much deeper than previously reported values (0.9–3.5 m).

Geologic and Geophysical Evidence of Repeated Normal Faulting on the Itozawa Fault—the Source of the Mw 6.6 Iwaki Earthquake Triggered by the Mw 9.0 Tohoku-Oki Megathrust Earthquake, Northeast Japan

ABSTRACT The 2011 Mw 9.0 Tohoku-Oki earthquake ruptured the 500 km long and 200 km wide convergent plate margin between the North American and Pacific plates, and changed the crustal stress field and triggered widespread seismic activity in northeast Japan. In particular, many crustal earthquakes struck the southern Fukushima area. The largest inland normal-faulting earthquake with Mw 6.6 occurred on the northwest-trending Yunodake fault and the north-northwest-trending Itozawa fault on 11 April 2011. The coseismic surface ruptures appeared along the previously identified active and presumed active faults. To investigate the near-surface structure of the Itozawa fault, we conducted ground-penetrating radar (GPR) profiling across the fault, and two drilling surveys on its hanging-wall and footwall blocks. The GPR survey line about 50 m long was located near the previous trenching site. The GPR two-way travel-time sections were collected by common-offset modes by 50 and 100 MHz GPR systems. We acquired common midpoint ensembles on both sides of the surface rupture for depth conversion of the time sections. The resulting GPR sections show detailed subsurface structures to a depth of about 7 m. We identified event horizons for the 2011, penultimate, antepenultimate, and preantepenultimate earthquakes, indicating that the Itozawa fault has ruptured repeatedly as a normal fault. The vertical displacements during these earthquake events, obtained from the GPR sections, were about 0.8, 0.3, 0.4, and 0.7 m, respectively. These observations suggest that the coseismic surface offset amount on the Itozawa fault varies greatly. The recurrence intervals of surface-rupturing earthquakes on the Itozawa fault, calculated from the previous research and this study, are much longer than those of giant interplate earthquakes along the Japan trench, such as the 2011 Tohoku-Oki earthquake. We conclude that not every giant earthquake along the Japan trench triggers a rupture of the Itozawa fault.

Geomorphic mapping and analysis of neotectonic structures in the piedmont alluvial zone of Haryana state, NW-India: a remote-sensing and GPR based approach

The Himalayan Frontal Thrust (HFT) and the surrounding piedmont alluvial region represent a zone of active deformation in the Indo-Gangetic plains. We investigated the Piedmont zone between the Ghaggar and Yamuna River basins in Haryana, India, for geomorphic signatures of active tectonics using remotely sensed data and validated by Geophysical Ground Penetrating Radar (GPR) surveys. The possible locations and the types of active tectonic features such as sub-surface fault, ridges, lineaments and warps were identified based on the presence of geomorphic signatures such as drainage gradient anomalies, abrupt change in flow direction, river offset, compressed meanders, paleochannels and topographic breaks. We used various optical satellite imageries to detect and map the temporal changes in the flow pattern of rivers in the study area. GPR investigations were done at selected test sites to locate and verify the continuity of subsurface fault. The GPR profiles were taken in the North-South direction using the common midpoint technique with 40 and 100 MHz antennae. Low frequency bi-static GPR scanning confirmed a number of dipping reflectors due to fault planes and warp surfaces in the study area. It is concluded that the piedmont zone of Haryana is actively deforming and could become a future seismic hazard zone.

Accuracy Assessment of GPR Data for Buried Objects with Different Pipes and Soil-Based Conditions

In terms of accuracy and speed, Ground Penetrating Radar (GPR) is the best approach for detecting and identifying underground utilities. This technology can precisely find a wide range of underground utilities, including both metallic and non-metallic materials. It analyses the ground by emitting a signal from an antenna at various frequencies of electromagnetic (EM) pulses. However, undesirable echoes caused by heterogeneous materials, such as the wide range of soil properties and utilities, are always present in these reflected signals. The site's soil composition has a direct influence on the accuracy of the GPR signal image. Thus, this study is carried out to evaluate the accuracy of GPR data for buried objects with different types of pipes between PVC and iron pipe in different soil characteristics: fine sand, topsoil and silt soil. The objective is to interpret the resolution of radargram images on different soil types due to different soil based characteristics and to evaluate the accuracy of depth values between GPR and conventional survey data sets for different pipes and soils using the RMSE formula. GPR Electronic TriVue with high frequency (1GHz) was employed, and the resolution of the resulting radargram image was post-processed in ReflexW software to yield promising depth results. Based on this research, the radargram obtained shows different textures that provides different presentations of each soil on the radargram image. Accuracy assessment from RMSE depth difference for Iron pipe depth for the three different soil types are: topsoil is 0.025 m, silt soil is 0.032 m, and fine sand is 0.087 m. While for PVC pipe topsoil is 0.035 m, silt soil is 0.038 m, and fine sand is 0.093 m. These differences show that iron pipe is more accurate compared with PVC in terms of tendency and fine sand is suitable soil in detection compared with topsoil and silt soil. In conclusion, the type of pipe play role in the choice of utility and soil properties (texture, moisture, and electrical conductivity) that impact the most on the accuracy assessment of GPR Data.

Practice of geo-radar research in the Republic of Kazakhstan

The article considers the issues of applying ground penetrating radar (GPR) technologies for engineering purposes concerning subsurface research. It describes the field of application of GPR research during road construction and operation and the advantages and disadvantages of this type of engineering survey. It presents comparative data on the accuracy (inaccuracy) of existing GPR control methods applied to determine the thickness of the monolithic pavement layers in Europe, CIS, and the USA. The main provisions of the GPR survey procedure are described, including four main stages: the analysis of initial materials of surveyed section and equipment preparation; GPR survey; geological verification; processing and interpreting of radargrams; and the preparation of a report. Geophysical works were performed using the geo-radar of the OKO series as part of the road measuring complex DVK-05 on the section of the Astana-Petropavlovsk A-1 highway with cement concrete pavement and on the section of the R-12 "Kokshetau - Atbasar" with asphalt pavement. The example of a radargram and the core sample of a cement concrete pavement taken during geological verification of the thickness of a monolithic layer is presented. Graphs of variation in the thickness of pavement layers by radargrams of longitudinal passages in the indicated road sections with the assumptions about the nature of the heterogeneity of the obtained values are given. The obtained results on the thickness of monolithic layers (cement concrete and asphalt concrete) were assessed on the criteria of quantitative deviation from the required standard value. Recommendations were provided to address positive deviations in the thickness of monolithic pavement layers at various stages of the road survey.

Combined electrical resistivity tomography and ground penetrating radar to map Eurasian badger (Meles Meles) burrows in clay-rich flood embankments (levees)

Globally, earth embankments are used to protect against flooding. Raised above the surrounding water table, these embankments make ideal habitats for many burrowing animals whose burrows can impact their structural integrity. Ground Penetrating Radar (GPR) is commonly used to identify and map animal burrows and other small cavities. However, the depth of investigation of a GPR survey can be severely limited in saline and clay-rich environments, soil properties commonly associated with flood embankments. In contrast, Electrical Resistivity Tomography (ERT) can image subsurface voids in conductive ground conditions but has been rarely used to image animal burrows. Here we aim to assess the efficacy of ERT and GPR to image two badger burrow networks, called ‘setts’, located in clay embankments on the River Ouse, Yorkshire, UK. The two setts were excavated to validate the geophysical results, and the soil was characterised through logging and geotechnical analysis to develop a ground model of the site. We find that ERT can accurately resolve tunnels down to 1.5 m depth, map the structure of a multi-entrance badger sett and successfully identify the end of the tunnels. This result compares favourably to the GPR surveys, which mapped all but the deepest tunnels, limited by its penetration depth due to clay soils. Our results show that ERT can be used as a primary survey tool for animal burrows in clay-rich environments and can be validated using co-located GPR surveys if penetration depth is sufficient. The implications of this study may allow embankment managers to map burrow networks, assess flood embankment stability, minimise repair costs, and reduce unexpected failures during flood events. Additionally, a better understanding of how, for example, local heterogeneities impact badgers' burrow geometry may be achievable using these geophysical methods, as they provide a non-destructive, repeatable method for imaging setts.

Clogging evaluation of porous asphalt pavement using ground-penetrating radar

Clogging reduces the porosity of porous asphalt (PA) pavement, which would jeopardize its permeability, noise absorption, and skid resistance. Existing evaluating methods use in-situ cores that damage the pavement with limited coverage. This study explored the feasibility of evaluating PA pavement clogging using ground-penetrating radar (GPR). Laboratory tests were performed on porous asphalt (PA) slabs under various clogging degrees. The effect of antenna type and moisture on clogging evaluation were investigated. The performances of two clogging indicators were examined, including the bulk dielectric constant obtained using the time-of-flight method and time–frequency spectrograms using the short-time Fourier transform (STFT). Effectiveness of GPR-based clogging evaluation was validated by permeability tests. Results show that both indicators could effectively evaluate clogging in PA pavement. The effectivenesses of proposed indicators were verified through permeability tests. GPR surveys are suggested 72 h after rainfall in sunny days using 2 GHz air-coupled antennas.

Evaluating subsurface flow connectivity in a pine-covered hillslope with stemflow infiltration and ground-penetrating radar surveys

The hydrological response of sloping catchments is strongly conditioned by the connectivity of subsurface preferential flows. The objective of this paper is to investigate the role played by stemflow infiltration in subsurface water flow dynamics, focusing on a forested hillslope located in an Aleppo pine Mediterranean forest (Pinus halepensis, Mill.) located at Sierra Calderona, Valencia province, Spain. We combined stemflow artificial experiments with the ground-penetrating radar (GPR) as a non-invasive technique to investigate stemflow-induced preferential flow paths activated by different trees and the related hydrological connectivity at the hillslope scale. Our observations allowed us to identify different dynamics associated with the initiation of stemflow and then lateral preferential flow, including the activation of connected preferential flow paths that received stemflow water from different trees. These observations provided empirical evidence of the role of stemflow in the formation of lateral preferential flow networks. Our measurements also provided estimations for flow velocities, which provided new insight on the magnitude of stem-induced lateral preferential flow paths. The applied protocol offers a simple, repeatable and non-invasive way to conceptualize hillslope responses to rainstorms.

Reconstructing the Geometry of the Yushu Fault in the Tibetan Plateau Using TLS, GPR and Trenching

Although geomorphic evidence and shallow geometry of active faults are significant for the understanding and assessing of fault activity and seismic hazards, it is challenging to acquire high-resolution topographic data and shallow geometry of the Yushu fault by conventional methods. Here, we present a case study to reconstruct the detailed surficial and subsurface geometry of the Yushu fault using terrestrial laser scanning (TLS), multi-frequency ground penetrating radar (GPR) and trenching. TLS was suitable for measuring the high-resolution three-dimensional (3D) topographic data of the fault. GPR surveys with different frequency antennas (25 MHz, 100 MHz, 250 MHz and 500 MHz) were conducted to image the shallow geometry of active faults at different depths and spatial resolutions. The typical groove landscape, parallel to surface traces of the fault, was clearly observed on the TLS-derived data. A ~40 m width narrow fault system and three faults were identified on the different frequency GPR profiles. Furthermore, faults F1 and F2 were supposed to be boundary faults but were sinistral-lateral strike-slip faults with a normal component, while fault F3 was inferred as the secondary fault. The western trench section, despite the limited investigation depth (~2 m), was well consistent with the 500 MHz GPR result, especially in the location of fault F2. Finally, a 3D surficial and subsurface model was established from the TLS-derived data and GPR data offering multi-sensor and multi-view spatial data to characterize and understand the fault’s kinematics and characteristics. In addition, the shallow geometry of the fault on the GPR results would be better interpreted with the help of the corresponding surficial data. The study results demonstrate that a combination of TLS, multi-frequency GPRs and trenching can be successfully used for reconstructing a detailed surficial and subsurface geometry of the Yushu fault. It will play an increasing role in comprehensive understanding and assessing fault behavior and seismic hazards, especially on the Tibetan Plateau and the adjacent area.

Reconstructing terrestrial ice sheet retreat dynamics from hummocky topography using multiscale evidence: An example from central Ireland

The research reported here combines high-resolution digital elevation models (DEMs) derived from airborne LiDAR with ground-penetrating radar (GPR) surveys and macro- and micro-scale sedimentological analyses to study the geomorphology and internal structure and composition of ridges and mounds within an area of hummocky topography in the Brosna basin, central Ireland. Our evidence indicates that much of the hummocky topography consists of fragmented mega-scale glacial lineations (MSGLs) indicating a phase of accelerated ice flow, overlain by groups of small ridges composed of subglacially derived till and sediment gravity flow deposits. Subtle differences in ridge morphology indicate they may be multi-genetic and formed both ice-marginally as moraines and subglacially as small ribbed moraine. We interpret MSGL-ridge associations as a subglacial bedform continuum reflecting the evolution from a deforming bed to brittle deformation, due to changing thermal and hydrological conditions at the ice-bed interface during ice sheet retreat. Adjacent glaciofluvial landforms indicate initial en- and supra-glacial meltwater drainage, possibly directly related to changing basal thermal/hydrological characteristics and subglacial ridge formation. Subsequently a subglacial conduit system evolved, and later retreat involved formation of ice-marginal ridges. The partially preserved landsystem reflects formation at a polythermal to active temperate ice marginal zone, rather than the stagnating temperate margin previously assumed for this area. Our work demonstrates the usefulness of hummocky topography in identifying changes in ice sheet bed thermal/hydrological characteristics during deglaciation and the importance of combining multiple evidence strands in reconstructing the processes involved in glacial landform construction.

Dike fields as drivers and witnesses of twentieth-century hydrosedimentary changes in a highly engineered river (Rhône River, France)

Hydraulic structures, such as groyne fields, were commonly used to channelize European and North American rivers, thus forming engineered margins on the edges of the active channel. On the Rhône River (France), which was corrected with dike fields (classical groyne fields and specific ones closed with a longitudinal submersible dike; i.e., closed fields) and equipped with numerous dams (mid-twentieth century), the engineered margins have mostly been filled with fine sediments and become terrestrial. On the 11 km bypassed studied reach (middle Rhône), 55.6 ha in 167 dike fields (i.e., 75 % of the cumulated surface) have been subject to terrestrialization (i.e., the transformation of aquatic areas into terrestrial ones). Our study aimed to understand the trajectory of dike fields that serve as both drivers (e.g., inducing in-dike fine sediment trapping) and witnesses (e.g., informing the diversion impact) of hydrosedimentary changes. We combined geohistorical analyses (aerial photographs, riverbed elevations, and water levels) and GIS modeling, as well as topographic and ground-penetrating radar surveys (GPR), to emphasize the terrestrialization patterns and hierarchize the drivers and processes involved. We obtained a classification of diachronic patterns (five types) that highlight local recurrences and specificities (inherited forms) in the terrestrialization trajectory. Topographic and GPR surveys complemented our data, shedding light on the main characteristics of sediment deposits (volumes, thicknesses) and structural units. We also determined that the contribution to terrestrialization of phase 1 (channelized state; 1900s–1970s) is lower than that of phase 2 (channelized and bypassed state; 1970s–2000s), at 42 % (23.4 ha) and 58 % (32.2 ha), respectively. In phase 1, fine sediment deposition leads to deposit construction, triggered by the dike field setting, which shapes spaces with reduced shear stresses. The riverbed incision (induced by channelization) is shallow on this reach, so its contribution (by lowering the water level) is considered negligible. In phase 2, terrestrialization is mainly provoked by the diversion-induced drop in water level that has caused the retraction of the active channel and promoted its abandoned edges as new terrestrial margins. Understanding the evolution of these ecotones made it possible to adjust our recommendations in terms of management and restoration. It also highlights the relevance of strategic dike field reconnections to support the river by recreating gradients of hydrological connectivity (which are favorable to habitat diversity).

The Spatial Analysis of Vegetation Cover and Permafrost Degradation for a Subarctic Palsa Mire Based on UAS Photogrammetry and GPR Data in the Kola Peninsula

Subarctic palsa mires undergo substantial transformation under climate impacts, and today a reliable marker of their degradation is the vegetation cover. We studied the correspondence between the surface traits of palsa degradation, as expressed in the vegetation composition, and the interior condition of permafrost within subarctic palsa mires in the central part of the Kola Peninsula. We have employed a set of methods to collect the data, including geobotanical relevés, unmanned aerial system (UAS) photogrammetry, and ground-penetrating radar (GPR) survey. Based on RGB orthophoto values and morphometric variables, we produced a land cover classification (LCC) consistent with the vegetation classes identified during field measurements. The outcome proves that the additional morphometric predictors improve the accuracy of classification algorithms. We identified three major patterns in GPR cross-sections defining (i) permafrost in palsas, (ii) water saturated peat, and (iii) the regular peat layer. As a result, our GPR data demonstrated a high correlation with land cover classes and pointed to some vegetation features controlled by the peat deposit inner structure. Under our results, palsas with thawing permafrost can be appraised using sequences of LCC. This is primarily the lichen hummock—tall shrub—carpet vegetation (LH–TSh–C) sequence from palsa top to foot. We have also detected an asymmetric configuration of permafrost in some palsas in the west-to-east direction and hypothesized that it can relate to the wind regime of the area and snow accumulation on the eastern slopes. Our results highlight that the combined application of the remote UAS photogrammetry and GPR survey enables a more precise delineation of the lateral degradation of palsas.

A Pixel-Scale Measurement Method of Soil Moisture Using Ground-Penetrating Radar

Ground validation of remote sensing soil moisture requires ground measurements corresponding to the pixel scale. To date, there is still a lack of simple, fast and reasonable methods for soil moisture measurement at pixel scale between point measurements and remote sensing observations. In this study, a measurement method of soil moisture using ground-penetrating radar (GPR) was proposed for pixel scale. We used a PulseEKKOTM PRO GPR system with 250 MHz antennas to measure soil moisture by Fixed Offset (FO) method in four 30 × 30 m2 plots chosen from the desert steppe. This study used a random combination method to analyze soil moisture measurements acquired by different numbers of GPR survey lines. The results showed that two survey lines of GPR would be sufficient under confidence level of 90% with the relative error of 7%, and four survey lines of GPR would be eligible under confidence level of 95% with the relative error of 5% for each plot. GPR measurement can reproduce the spatial distribution of soil moisture with higher resolution and smaller error, especially when two and four survey lines are designed in cross shape and grid shape, respectively. The method was applied to ground validation for the soil moisture from Landsat 8, showing the advantages of stable relative errors, less contingency and reliable evaluation when compared to point measurements. This method is fast and convenient and not limited to a certain pixel, and thus largely benefits the scale matching of remote sensing results and field measurements in ground validation.

Periglacial–Aeolian Polygonal Surface Structures in the Tibetan Plateau

Abstract—The surface pattern of permafrost area in the Tibetan Plateau, with 15–20 m polygons, resembles the patterned ground of the Arctic periglacial loess plains in northeastern Eurasia and North America. However, unlike the Arctic plains, it consists of semi-stabilized modern sand dunes, up to 2.5–3.0 m high, and U-shaped epigenetic ice wedge casts inherited from an ancient polygonal network on the surface of a 10–12-m terrace of the Yangtze River. The polygonal dunes and the U-shaped sand wedges were studied in the Yangtze head-waters in the vicinity of the high-altitude research station Bei-Lu-Xe. The polygons have desert pavement floors with ventifacts, composed of Late Pleistocene alluvial gravel and debris. The dunes and wedges consist of well sorted quartz-carbonate sand with an average grains size of 2.0–2.2 mm. Ground Penetrating Radar surveys in the area revealed the permafrost table at depths varying from 2 to 4 m below the dunes. The polygonal dunes may have formed by biogenic-aeolian deposition over an ancient system of ice wedges.