Ground Penetrating Radar Measurements Research Articles

Acceleration of Abramov Glacier (Pamir‐Alay) retreat since the Little Ice Age

The Koksu River valley is located in the Pamir‐Alay mountain range and contains 25 glaciers larger than 1 km2 and numerous smaller glaciers. The largest glacier in the catchment is Abramov Glacier with a current surface area of 22.55 km2 (in 2022), which was extensively monitored between 1965 and 1999, and resumed in 2011. The long and detailed mass balance time series provide, among other information, benchmark climate variables for the Pamir‐Alay range. We report 10 new cosmogenic 10Be exposure dates of glacial moraines directly deposited by Abramov Glacier to extend the glacial history of the valley. Six boulders indicate that the Local Last Glacial Maximum occurred at 17.1±1.0 ka. Four boulders suggest a Little Ice Age (LIA) glacial advance around AD 1750. Secular glacier mass balance reconstructions suggest a progressively negative mass balance since the LIA advance. The decrease in mass balance accelerated in the last quarter of the 20th century. Results from repeated ground penetrating radar (GPR) measurements suggest that Abramov Glacier lost about 403 million m3 of ice volume between 1986 and 2018. Based on the reconstruction of the glacier surface, the corresponding equilibrium line altitude, which is closely correlated with the mass balance, increased by about 70 to 80 m during this period. Our results also suggest that Abramov Glacier has become increasingly out of equilibrium with the climate over the last two decades. This is supported by repeated GPR measurements of the tongue area, which indicate a dramatic decrease in glacier area and ice volume over the period 1986–2018.

Characterization of a Contaminated Site Using Hydro-Geophysical Methods: From Large-Scale ERT Surface Investigations to Detailed ERT and GPR Cross-Hole Monitoring

This work presents the results of an advanced geophysical characterization of a contaminated site, where a correct understanding of the dynamics in the unsaturated zone is fundamental to evaluate the effective management of the remediation strategies. Large-scale surface electrical resistivity tomography (ERT) was used to perform a preliminary assessment of the structure in a thick unsaturated zone and to detect the presence of a thin layer of clay supporting an overlying thin perched aquifer. Discontinuities in this clay layer have an enormous impact on the infiltration processes of both water and solutes, including contaminants. In the case here presented, the technical strategy is to interrupt the continuity of the clay layer upstream of the investigated site in order to prevent most of the subsurface water flow from reaching the contaminated area. Therefore, a deep trench was dug upstream of the site and, in order to evaluate the effectiveness of this approach in facilitating water infiltration into the underlying aquifer, a forced infiltration experiment was carried out and monitored using ERT and ground-penetrating radar (GPR) measurements in a cross-hole time-lapse configuration. The results of the forced infiltration experiment are presented here, with a particular emphasis on the contribution of hydro-geophysical methods to the general understanding of the subsurface water dynamics at this complex site.

Validation of ALOS/PALSAR Subsurface Penetration Depth in Farafra Oasis as an Arid Region Based on Field Ground-Penetrating Radar Measurements

Validation of ALOS/PALSAR Subsurface Penetration Depth in Farafra Oasis as an Arid Region Based on Field Ground-Penetrating Radar Measurements

A convolutional neural network for creating near-surface 2D velocity images from GPR antenna measurements

Abstract In this research, our focus lies in exploring the effectiveness of a frequency-velocity convolutional neural network (CNN) in the efficient and non-intrusive acquisition of 2D wave velocity visuals of near-surface geological substances, accomplished through the analysis of data from ground-penetrating radar (GPR). To learn complex correlations between antenna readings and subsurface velocities, the proposed CNN model makes use of the spatial features present in the GPR data. By employing a network architecture capable of accurately detecting both local and global patterns within the data, it becomes feasible to efficiently extract valuable velocity information from GPR readings. The CNN model is trained and validated using a substantial dataset consisting of GPR readings along with corresponding ground truth velocity images. Diverse subsurface settings, encompassing different soil types and geological characteristics, are employed to gather the GPR measurements. In the supervised learning approach employed to train the CNN model, the GPR measurements serve as input, while the associated ground truth velocity images are utilized as target outputs. The model is trained using backpropagation and optimized using a suitable loss function to reduce the difference between the predicted velocity images and the actual images. The experimental results demonstrate the effectiveness of the proposed CNN method in accurately deriving 2D velocity images of near-surface materials from GPR antenna observations. Compared to traditional techniques, the CNN model exhibits superior velocity calculation precision and achieves high levels of accuracy. Moreover, when applied to unseen GPR data, the trained model exhibits promising generalization abilities, highlighting its potential for practical subsurface imaging applications.

Delineation of Nickel Laterite Deposits in “DCV” Block Southeast Sulawesi Based on Data Analysis of Ground Penetrating Radar (GPR) Method

The need for nickel is very intensive in the development of upstream to downstream industries so that domestic consumption of nickel ore will increase in the coming years, therefore domestic downstream is increasingly being improved. Overcoming the problem of the high demand for nickel in Indonesia can be done by conducting exploration and exploitation to support the downstream of nickel. Exploration of nickel laterite can be accomplished with geophysical methods that aim to obtain subsurface data from nickel laterite deposits. The Ground Penetrating Radar (GPR) geophysical method is one of the non-destructive methods that can be applied to determine the subsurface conditions of nickel laterite deposits based on physical properties in the form of dielectric constants and reflection patterns and amplitude contrasts produced on radargrams. The nickel laterite deposits can be separated into 4 layers based on Ground Penetrating Radar (GPR) data analysis: bedrock, saprolite, limonite, and topsoil. Based on GPR measurements, the average dielectric constant value of topsoil is 6.8 mS/m, the limonite layer is 10.87 mS/m, the saprolite layer is 12.37 mS/m, and bedrock is 7.87 mS/m. It can be seen that the saprolite layer has a high conductivity so that the dielectric constant value is also high, this is influenced by the very high nickel content in this layer. The depth of bedrock in the research area varies from 20 - 40 meters, the thickness of topsoil is dominated in the value range of 3.6 - 5 meters, while the thickness of the laterite layer which is the main target of nickel laterite mining includes saprolite and limonite layers which have varying values of 15 - 40 meters where the distribution of the thickness of this layer is in the eastern and central parts of the research area.

We Came for the Lake—Late Pleistocene Landscape Reconstruction in Lieth Moor, District Pinneberg, Germany

The Lieth Moor area, located in the district of Pinneberg, Schleswig-Holstein, Germany, is a hotspot of Late Palaeolithic settlement activity. The exceptional abundance of archaeological sites is commonly attributed to the presence of a large palaeolake. However, in the Weichselian Late glacial, there were numerous large lakes in Schleswig-Holstein. Thus, a well-founded explanation for the find concentration in Lieth Moor is still lacking, and forming a research desideratum until today. To improve our understanding of this Late Pleistocene landscape and its appeal to hunter–gatherer groups of that time, we conducted a large-scale archaeogeophysical study focusing on a possible ford of the potential palaeolake. We employed Ground-Penetrating Radar and Electromagnetic Induction measurements, supplemented by existing legacy drill-probing data, to identify and map limnic gyttja (organic lake mud) sediments and their spatial distribution within the area. The findings of our study indicate that during the Late Pleistocene to Early Holocene, the Lieth Moor area comprised a cluster of small ponds rather than a continuous lake. These ponds likely interconnected during periods of increased water levels. The presence of dry islands within the region corresponds with archaeological evidence, suggesting that Late Palaeolithic communities visited some of these islands. The absence of the previously postulated palaeolake places the known findings within a completely new palaeoenvironmental context: instead of the previously suspected ford, we assume that the proximity to the Elbe Palaeovalley played a decisive role in the repeated habitation of Lieth Moor. This area, rich in fresh water and fish, along with the dune chain situated to the west, serving as both a vantage point and windbreak, presented an ideal location for awaiting animals migrating along the river Elbe and/or as a resting place within the settlement system of mobile hunter–fisher–gatherer groups.

Glacier thickness and volume estimation in the Upper Indus Basin using modeling and ground penetrating radar measurements

Abstract In the Himalaya, ice thickness data are limited, and field measurements are even scarcer. In this study, we employed the GlabTop model to estimate ice reserves in the Jhelum (1.9 ± 0.6 km3) and Drass (2.9 ± 0.9 km3) sub-basins of the Upper Indus Basin. Glacier ice thickness in the Jhelum ranged up to 187 ± 56 m with a mean of ~24 ± 7 m, while the Drass showed ice thickness up to 202 ± 60 m, with a mean of ~17 ± 5 m. Model results were validated using Ground Penetrating Radar measurements across four profiles in the ablation zone of the Kolahoi glacier in the Jhelum and nine profiles across the Machoi glacier in the Drass sub-basin. Despite underestimating ice-thickness by ~10%, the GlabTop model effectively captured glacier ice-thickness and spatial patterns in most of the profile locations where GPR measurements were taken. The validation showed high correlation coefficient of 0.98 and 0.87, low relative bias of ~ −13% and ~ −3% and a high Nash–Sutcliffe coefficient of 0.94 and 0.93 for the Kolahoi and Machoi glaciers, respectively, demonstrating the model's effectiveness. These ice-thickness estimates improve our understanding of glacio-hydrological, and glacial hazard processes over the Upper Indus Basin.

Development of a method for identifying cracks in permafrost rocks based on differentiation of GPR data

Relevance. The presence of cracks significantly affects the physical and mechanical properties of rocks, which must be taken into account when planning mining operations and building mining structures. In the conditions of the distribution of permafrost rocks, characteristic of the North-East of Russia, the study of fracturing is possible using the ground penetrating radar method, which is used to assess the structure of rock masses of placer deposits. The criteria for identifying cracks based on the characteristics of GPR wave fields are currently known, and the main problem preventing the full use of the GPR method for studying cracks in subsurface layers of rocks is the significant complexity of processing and interpreting GPR measurement data. The purpose of the work is to develop a method for processing the results of ground penetrating radar measurements to identify cracks in frozen rocks. Methods. Physical and computer modeling of GPR measurements of a rock mass with a fracture, differential calculus methods for analyzing the GPR wave field structure model. Results and their scope. As a result of the research, based on an early developed model of the structure of the GPR wave field, the use of the differentiation operation for identifying cracks in permafrost rocks was justified. Special cases of rectilinear inclined and horizontal axes of in-phase of ground penetrating radar signals are considered and corresponding formulas are obtained for them. The theoretical results obtained were tested on computer and physical modeling data, as well as on field measurement data. An analysis of the features of the signals after differentiation was carried out, and the features of the original radargrams were noted, which may interfere with the reliable interpretation of the results obtained. Conclusions. In the practice of processing data from ground penetrating radar measurements, the results of the research will make it possible to more quickly identify zones of increased fracturing in rocks. In the future, it is planned to develop an algorithm and software that implements it for mapping rock fractures using ground penetrating radar data.

Linking horizontal crosshole GPR variability with root image information for maize crops

AbstractNon‐invasive imaging of processes within the soil–plant continuum, particularly root and soil water distributions, can help optimize agricultural practices such as irrigation and fertilization. In this study, in‐situ time‐lapse horizontal crosshole ground penetrating radar (GPR) measurements and root images were collected over three maize crop growing seasons at two minirhizotron facilities (Selhausen, Germany). Root development and GPR permittivity were monitored at six depths (0.1–1.2 m) for different treatments within two soil types. We processed these data in a new way that gave us the information of the “trend‐corrected spatial permittivity deviation of vegetated field,” allowing us to investigate whether the presence of roots increases the variability of GPR permittivity in the soil. This removed the main non‐root‐related influencing factors: static influences, such as soil heterogeneities and rhizotube deviations, and dynamic effects, such as seasonal moisture changes. This trend‐corrected spatial permittivity deviation showed a clear increase during the growing season, which could be linked with a similar increase in root volume fraction. Additionally, the corresponding probability density functions of the permittivity variability were derived and cross‐correlated with the root volume fraction, resulting in a coefficient of determination (R2) above 0.5 for 23 out of 46 correlation pairs. Although both facilities had different soil types and compaction levels, they had similar numbers of good correlations. A possible explanation for the observed correlation is that the presence of roots causes a redistribution of soil water, and therefore an increase in soil water variability.

Ground penetrating radar scanning and historical interpretation of the location of the destroyed Epiphany Cathedral in Kyiv Brotherhood Monastery (Ukraine)

Background The article presents results of a ground penetrating radar (GPR) scanning carried out in a site of the Epiphany Cathedral of Brotherhood Monastery in Kyiv, Ukraine, destroyed in 1936 by the Soviets. The Cathedral is known as a burial site of Hetman Petro Sahaidachnyi (1582–1622), a Ukrainian Cossack political and civic leader, guardian and patron of Kyiv Brotherhood Monastery. The collection of archival documents, blueprints, stock sources, photographs and cartographic materials of the 17th-19th centuries, as well as historical works of the 19th-21st centuries, were thoroughly analyzed and used as a basis for the interpretation of geophysical results. The set of historical data covers the period from 1615, that is, from the beginning of the construction of the wooden Epiphany Church, the predecessor of the cathedral, to the present day. Methods Summarized information about the construction, restoration after the fire, functioning and destruction of the Cathedral, as well as about the construction on its site in the 20th century, archaeological research in the 20th-21st centuries, was used to clarify possible location of hidden foundations and target GPR measurements. In this context, written testimonies of archaeologists who personally observed the foundations of the cathedral became especially valuable. The shielded GPR antennas, with a central frequency of 300 MHz and 700 MHz, is used for non-invasive investigation. Results GPR scanning specified the site and showed the best-preserved group of foundations of the western wall of the nave of the Epiphany Cathedral. Conclusions An integrated historical and geophysical study provided the basis to certify the foundation of the Epiphany Cathedral as a protected object of cultural heritage and facilitated its archaeological research.

PEMODELAN 2D DATA GROUND PENETRATING RADAR (GPR) PADA LAHAN GAMBUT DI DESA JATI MULYO

Research has been conducted using the ground penetrating radar (GPR) method which aims to determine subsurface lithology on peatlands in Jati Mulyo Village based on 2D modeling. The GPR method is one of the geophysical methods that applies electromagnetic wave propagation. GPR data measurements were carried out as many as 3 passes with each length of 200 meters. The result of the GPR measurement is a 2D model that describes subsurface lithology. The response of this 2D model is in the form of a distribution of color variations starting from yellow-red, green, light blue -dark blue. The yellow-orange color response indicates the presence of minerals found on peatlands. The green response describes the soil below the surface. While the blue response indicates a cavity filled with water. This is appropriate based on the geology of this peatland is a sedimentary deposit that has pores filled with water and the presence of mineral content contained in the peat soil.

Climatic controls on the dynamic lateral expansion of northern peatlands and its potential implication for the ‘anomalous’ atmospheric CH4 rise since the mid-Holocene

Understanding the dynamic changes in peatland area during the Holocene is essential for unraveling the connections between northern peatland development and global carbon budgets. However, studies investigating the centennial to millennial-scale process of peatland expansion and its climate and environmental drivers are still limited. In this study, we present a reconstruction of the peatland area and lateral peatland expansion rate of a peatland complex in northern Sweden since the mid-Holocene, based on Ground Penetrating Radar measurements of peat thickness supported by radiocarbon (14C) dates from four peat cores. Based on this analysis, lateral expansion of the peatland followed a northwest-southeast directionality, constrained by the undulating post-glacial topography. The areal extent of peat has increased non-linearly since the mid-Holocene, and the peatland lateral expansion rate has generally been on the rise, with intensified expansion occurring after around 3500 cal yr BP. Abrupt declines in lateral expansion rates were synchronized with the decreases in total solar irradiance superimposed on the millennial ice-rafted debris events in the northern high latitudes. Supported by the temporal evolution of peatland extent in four other Fennoscandian peatlands, it appears that the northern peatland areal extent during the early to middle Holocene was much smaller compared to previous empirical model reconstructions based on basal age compilations. Interestingly, our reconstruction shows the increments of peat area since the mid-Holocene coincide with the rise in atmospheric CH4 concentration, and that abrupt variations in atmospheric CH4 on decadal to centennial timescales could be synchronized with peatland lateral expansion rates. Based on our analysis we put forward the hypothesis that lateral expansion of northern peatlands is a significant driver of dynamics in the late Holocene atmospheric CH4 budget. We strongly urge for more empirical data to quantify lateral expansion rates and test such hypotheses.

Karangkates Railway Tunnel Risk Analysis Based on Ground Penetrating Radar Data

The Karangkates railway tunnel in Malang Regency is more than half a century old and has undergone land use changes into settlements and highways. This study aims to identify cavities between the ground surface and the roof of the Karangkates tunnel using Ground Penetrating Radar (GPR) data. Primary data were obtained through GPR measurements and interviews with residents. Qualitative methods are used to analyze GPR interpretation data readings and risk analysis. Risk analysis is carried out to determine the location and area of cavities and compile long-term risk management. From the results of the GPR analysis, 6 points were found with protruding cavities, with a cavity depth between 8 to 13.4 meters. The location of such cavities is in residential areas and highways. Risk management measures appropriate to the analysis and observation of the research site are carried out to reduce the impact of risk. The results showed that the risk value was low. By implication, appropriate corrective and maintenance actions must be taken to mitigate risks and maintain public safety.

A Ground Penetrating Radar (GPR) application for Depicting the Geoarchaeological pattern in Ancient Falasarna Harbour

In this work Ground Penetrating Radar (GPR) results achieved in the archaeological site of Ancient Falasarna Harbour in Western Crete (Greece), are presented. The survey has been performed in a site only slightly explored up to now and where has been covered by the tsunami deposits created by the AD 365 earthquake event with magnitude 8.3 located offshore of western Crete. This Ground Penetrating Radar (GPR) measurement campaign aimed to identify possible points where future localized excavation might and hopefully will be performed in the next few years. Based on the GPR findings, archaeological excavation works will be carried out in the region where the anthropogenic remains were estimated to be. This case study demonstrates and further corroborates the effectiveness and reliability of GPR for the non-invasive prospection of archaeological structures hidden in heterogeneous subsurface geoenvironment.

Assessment of Combustion Cavern Geometry in Underground Coal Gasification Process with the Use of Borehole Ground-Penetrating Radar

In this study, the shape and size of a combustion cavity with a fracture zone in the gasified coal seam was determined with the use of control boreholes and a ground-penetrating radar (BGPR) test. The underground coal gasification (UCG) field-scale experiment was performed in Carboniferous strata in coal seam 501 at a depth of approx. 460 m in the Wieczorek hard coal mine in the Upper Silesian Coal Basin, Poland. After the termination of the UCG reactor, five coring boreholes were drilled to identify the geometry of the resulting combustion cavity and the impact of the UCG process on the surrounding rock mass. Borehole ground-penetrating radar measurements were performed using a 100 MHz antenna in three boreholes with a length of about 40–50 m. This enabled the identification of the boundaries of the combustion cavity and the fracture zone in the coal seam. The fracture zones of rock layers and lithological borders near the control borehole were also depicted. As a result, the cavity was estimated to have a length of around 32 m, a width of around 7 m and a height of around 5 m. The analyses performed with the control boreholes and the BGPR provided sufficient information to determine the geometry of the combustion cavity and the fracture zone.

Field study of the dielectric constant of concrete: A parameter less sensitive to environmental variations than electrical resistivity

In this work, a field study was conducted to evaluate the curing effectiveness of concrete slabs cured by air and compound. Two non-destructive testing methods including ground penetrating radar (GPR) and electrical resistivity measurement were used. The dielectric constant value developments of air and compound cured concrete slabs were determined by GPR measurement. The compressive strength development was tested by concrete cylinders. The hydration degrees of air and compound cured slabs were determined by Ca(OH)2 (CH) content through thermogravimetric analysis (TGA) by a modified calculation method. The microstructure development of air and compound cured concrete slabs were characterized by mercury intrusion porosimetry measurement (MIP). It has found that the dielectric constant value of compound cured concrete slab was always higher than air cured concrete slab. The second reflected pulse peak amplitude of GPR waveform was less influenced by weather conditions, making it a reliable indicator of the dielectric constant value. On the other hand, the dielectric constant value determined by the first reflected pulse peak amplitude was greatly influenced by the weather conditions. The dielectric constant value determined by the two-way travel time method exhibited strong correlations with compressive strength, CH content and porosity. However, the electrical resistivity development of air and compound cured concrete slabs were not consistent with compressive strength, CH content and microstructure development. Our findings suggested that the GPR measurement can be practically used to evaluate the curing effectiveness of concrete and can be a good indicator of “hydration potential” from a development perspective.

Spreading of Localized Information across an Entire 3D Electrical Resistivity Volume via Constrained EMI Inversion Based on a Realistic Prior Distribution

Frequency-domain electromagnetic induction (EMI) methods are commonly used to map vast areas quickly and with minimum logistical efforts. Unfortunately, they are often characterized by a very limited number of frequencies and severe ill-posedness. On the other hand, electrical resistivity tomography (ERT) approaches are usually considered more reliable; for example, they do not require specific calibration procedures and can be easily inverted in 2D/3D. However, ERT surveys are, by far, more demanding and time consuming, allowing for the deployment of a few acquisition lines per day. Ideally, the optimal would be to have the advantages of both approaches: ease of acquisition while keeping robustness and reliability. The present work raises from the necessity to cope with this issue and from the importance of enforcing realistic constraints to the data inversion without being limited to (over)simplistic spatial constraints (for example, characterizing the smooth and/or sharp regularization). Accordingly, the present research demonstrates, by means of synthetic and field data, how the EMI inversion—based on realistic prior models—can be further enhanced by incorporating additional pre-existing pieces of information. While the proposed scheme is quite general, in the specific examples discussed here, these additional pieces of information are, respectively, a reference model along a line across the survey area, and an ERT section. The field EMI results were verified against extensive ground penetrating radar (GPR) measurements and boreholes.

An Integrated Geophysical and Unmanned Aerial Systems Surveys for Multi-Sensory, Multi-Scale and Multi-Resolution Cave Detection: The Gravaglione Site (Canale di Pirro Polje, Apulia)

Gravaglione represents one of the main swallow holes of the Canale di Pirro, low Murge, Apulia region, Italy. Here, after an intense rainstorm, a huge volume of rainwater accumulates at the surface. The drainage dynamics suggest that the Gravaglione could be part of a large, and potentially unknown, karst system. To verify this hypothesis and to acquire useful information on the possible karst environment features, an integrated aerial and geophysical multiscale and multimethod approach was applied. In particular, aerial photogrammetry, ground penetrating radar measurements and electrical resistivity tomography surveys were hence conducted and integrated to potentially detect the caves, define the subsurface volume possibly affected by karst systems and to verify the existence of links between the surficial morphology and the subsoil structure. The results provided interesting insights regarding the presence of a complex karst system extending up to 200 m b.g.l. and with a marked 3D nature. Overall, the Gravaglione case study demonstrates the geophysical approach validity and poses the basis for the development of an expeditive and low-cost high-resolution strategy for detecting and characterizing karst caves.

Non‐invasive surveys to assess animal burrows as potential causes of levee instability

AbstractAnimal activities threaten levee stability, especially during flood events, increasing levee failure risk. Indeed, while dens alter hydraulically‐induced failure mechanisms, it is difficult to locate them and to know in advance if critical conditions may be reached. This paper demonstrates that it is possible to perform nondestructive surveys to assess the risk of burrow animal activities in levee systems using a ground penetrating radar (GPR) for effective levee structure control, being GPR a nondestructive, expeditious, and cost‐effective geophysical technique. Here, a flood‐prone area in Sicily, where traditional hydraulic phenomena did not justify past levee failure events, is considered a case study. Through a visual inspection survey, several animal holes were recovered. GPR measurements allowed us to explore the levee interior and to detect the presence, distribution, and configuration of dens inside them. It was found that a complex burrow system crosses the entire embankment. Porcupine was recognized as a builder of such cavities. Although, previous studies established the porcupine presence in semi‐humid environments, for the first time, here we provide evidence of the development, articulation, and extension of porcupine burrows inside the levee system.

A method to estimate surface mass-balance in glacier accumulation areas based on digital elevation models and submergence velocities

AbstractMeasuring surface mass-balance in the accumulation areas of glaciers is challenging because of the high spatial variability of snow accumulation and the difficulty of conducting annual field glaciological measurements. Here, we propose a method that can solve both these problems for many locations. Ground-penetrating radar measurements and firn cores extracted from a site in the French Alps were first used to reconstruct the topography of a buried end-of-summer snow horizon from a past year. Using these data and surface elevation observations from LiDAR and Global Navigation Satellite System instruments, we calculated the submergence velocities over the period between the buried horizon and more recent surface elevation observations. The differences between the changes in surface elevation and the submergence velocities were then used to calculate the annual surface mass-balances with an accuracy of ±0.34 m w.e. Assuming that the submergence velocities remain stable over several years, the surface mass-balance can be reconstructed for subsequent years from the differences in surface elevation alone. As opposed to the glaciological method that requires substantial fieldwork year after year to provide only point observations, this method, once submergence velocities have been calculated, requires only remote-sensing data to provide spatially distributed annual mass-balances in accumulation areas.