Basal Reflector Research Articles

Ground-penetrating radar antenna orientation effects on temperate mountain glaciers

Ground-penetrating radar (GPR) surveys on glaciers are generally restricted to a single pair of bistatic dipole antennas orientated either parallel or perpendicular to the surveying direction. Extensive helicopter-borne and ground-based GPR investigations on the Glacier d’Otemma, Switzerland, demonstrated that the detectability of the ice-bedrock interface varies substantially with dipole orientation. We recorded several across and along profiles using two different commercial GPR systems operated with 15, 25, 50, and 70 MHz antennas. Dipole alignments parallel to the glacier flow generated considerably stronger and more coherent bedrock reflections compared with a perpendicular dipole setup. We observed the behavior for all the systems and antenna frequencies that we used. To help explain these findings, we performed 3D numerical modeling using the open source software gprMax. Simulations with 20 MHz transmitting and receiving dipoles indicated that the changes of the bedrock reflection amplitude are primarily governed by the bedrock topography. Scattering and intrinsic attenuation may also influence the amplitudes of the bedrock reflections, but these effects seem to be much less pronounced. Evidently, to increase the GPR bedrock reflection quality, dipole antennas should be orientated parallel to the glacier flow direction on a glacier confined to a valley. Because the directional dependence is a first-order effect, it is advisable to perform multicomponent surveys when the general shape of the bedrock topography is unknown. The multicomponent setup preferably consists of two sets of dipole antennas, each in broadside configuration and the sets being orthogonal to each other.

Basin morphology, sedimentology and seismic stratigraphy of an upland lake from Serra dos Carajás, southeastern Amazon, Brazil

To understand the sedimentary processes in a lake environment, it is essential to investigate the morphological, sedimentalogical and limnological features of the basin. The present study was developed at Violão Lake, Serra Sul de Carajás. The methodological approach comprises the collection of bathymetric and sedimentary data, and shallow seismic profiles. Lake Violão has a NE-SW elongated guitar-shaped form and ~0.3 km2 of surface area, with a perimeter of ~2.7 km. The lake presents washing basin morphology and it is marked by a steep margin carved in duricrust outcrops, while the bottom is flat and constituted mainly by muddy sediments. The water column is stratified only during the dry season and it is mixed in the rainy season. Three seismic stratigraphic successions were identified in the lake resting on prominent basal reflector (bedrock), which reaches a maximum depth of ~15 m. Small lobate masses are deposited in the bottom of the lake from underflows, while the central part of the lake is characterized by drape deposition, suggesting that organic-mud sedimentation is associated to pelagic deposition from dilute interflows or overflows. Therefore, the sedimentary processes are strongly regulated by basin morphology, drainage water inflow and thermal stratification of the water column.

Seismic volcanostratigraphy of the NE Greenland continental margin

Abstract The Early Eocene continental break-up between the NE Greenland and the mid-Norwegian–SW Barents Sea margins was associated with voluminous magmatism and led to the emplacement of massive volcanic complexes including wedges of seawards-dipping reflections (SDR). We study the distribution of these break-up-related volcanic rocks along the NE Greenland margin by revisiting existing seismic reflection data and comparing our observations to better-studied segments of the conjugate margin. Seismic facies types match between the conjugate margins and show strong lateral variations. Seaward-dipping wedges are mapped offshore East Greenland, the conjugate to the Vøring continental margin. The geophysical signature of the SDRs becomes less visible towards the north, as it does along the conjugate Lofoten–Vesterålen margin. We suggest that the Traill Ø volcanic ridge is a result of plume–ridge interactions formed between approximately 54 and 47 Ma. North of the East Greenland Ridge, strong basement reflections conjugate to the Vestbakken Volcanic Province are interpreted as lava flows or ‘spurious’ SDRs. We discuss our findings in conjunction with results from seismic wide-angle experiments, gravity and magnetic data. We focus on the spatial and temporal relationships of the break-up volcanic rocks, and their structural setting in a late rift and initial oceanic drift stage. Supplementary material: The figures show the original seismic data used as the base for the interpretations shown in this paper. The seismic profiles are marked on Figure 1 (in the paper) as numbers 1 to 10 and are available at https://doi.org/10.6084/m9.figshare.c.3593780

Potential Field Data Guided Seismic Forward Modelling of Basement Structures: a Case Study from Offshore Nile Delta Basin

The offshore Nile Delta region has huge exploration potential, keeping in view the existing commercial oil and gas fields in and around this basin. The majority of the offshore Nile Delta basin is underexplored. Sparsity of geophysical data coverage and ambiguity in the interpretation of existing geophysical data have held back the exploration for many decades. In order to assess and evaluate the exploration potential, it is important to estimate the depth to the basement, the nature of basement and its topography. Identifying the basement reflector based on the current seismic data is challenging, because of limitations of the resolution and record length of the seismic data. Moreover, an estimation of sedimentary column is paramount for further detailed geological and geophysical investigations. The objective of the research is to perform seismic forward modelling of the basement reflector, guided by gravity and magnetic field data, and minimize the ambiguity involved in a single geophysical method of interpretation. The geophysical properties and their contrasts derived from seismic, gravity and magnetic methods of exploration are various criteria used in the integration and modelling process. Seismic stacking velocity data and depth values interpreted from gravity and magnetic field data are used in the modelling process. The uncertainty in modelling the basement character is assessed based on the stacking velocities and seismo-geological cross-sections interpreted from 2D seismic data, instead of cross-sections obtained from unreliable seismically derived depth data. The analysis of errors observed in the seismic data due to younger layer-cake reflections interfering with the basement reflector are analysed and the observed errors in the velocity models are accordingly reconciled based on the potential field data. The potential field data interpretation guiding the seismic forward modelling facilitates the redesign process of seismic data acquisition and processing in the hugely unexplored offshore Nile Delta basin in Egypt.

Imaging the Internal Structure of an Alpine Glacier via L-Band Airborne SAR Tomography

In this paper, we report results from the analysis of 3-D L-band airborne synthetic aperture radar (SAR) acquisitions acquired in March 2014 over the Mittelbergferner glacier, Austrian Alps, during the European Space Agency (ESA) campaign AlpTomoSAR. The campaign included coincident in situ measurements of snow and ice properties and ground-penetrating radar (GPR) data acquired at 600 and 200 MHz over a total length of 18 km. Radar data were acquired by repeatedly flying an L-band SAR along an oval racetrack at an altitude of about 1300 m over the glacier, such that two data stacks from opposite views are obtained. Data from all passes were coherently combined to achieve 3-D resolution capabilities, resulting in the generation of 3-D tomographic SAR (TomoSAR) cubes, where each voxel represents L-band radar reflectivity from a particular location in the 3-D space at a spatial resolution on the order of meters. TomoSAR cubes were finally corrected to account for wave propagation velocity into the ice, which was a necessary step to associate the observed features with their geometrical location, hence enabling a direct comparison to GPR data. The TomoSAR cubes show the complexity of the glacier subsurface scattering. Most areas are characterized by surface scattering in proximity of the ice surface, plus a complex pattern of in-depth volumetric scattering beneath and scattering at the ice/bedrock interface. Various subsurface features observed in GPR transects at 200 MHz clearly showed up in TomoSAR sections as well, particularly firn bodies, crevasses, layer transitions, and bedrock reflection down to 50 m below the ice surface.

Large, buried glacial moraines revealed by TOPAS sub-bottom profiling, South Orkney Islands, South Atlantic Ocean

Subglacial and ice-marginal landforms produced during the Last Glacial Maximum and subsequent regional deglaciation become progressively more buried, especially when postglacial sedimentation rates are high. Sub-bottom profiling is usually used to examine the stratigraphy of submarine glacial deposits, but is only rarely exploited to visualize the topography beneath postglacial infill. By picking and gridding the basal reflector from a relatively dense network (spacing of <1.5 km) of TOPAS parametric sub-bottom profiles, we visualize both the modern seafloor of Orwell Trough, South Orkney (SO) Islands, and reconstruct the glacial landforms buried beneath up to c. 54 m of subsequent fine-grained sedimentation (Fig. 1). Based on accompanying sedimentological evidence and the shallow acoustic stratigraphy, the basal reflector is interpreted as the upper surface of either a subglacial till or coarse-grained ice-proximal debris (Fig. 1d). Fig. 1. ( a ) Perspective view of large, buried moraines, revealed through gridding of a sub-bottom reflector (basal reflector a′), interpreted as the upper surface of a subglacial or glacial proximal till. Pink and black arrows are locations of moraine crests marked in (d) and (e), respectively. Corresponding water depths for vertical scale are c. 240 and 480 m. Horizontal scale bars and north arrows on all 3D images provide approximate scale …

Helicopter-borne ground-penetrating radar investigations on temperate alpine glaciers: A comparison of different systems and their abilities for bedrock mapping

On the basis of a large data set, comprising approximately 1200 km of profile lines acquired with different helicopter-borne ground-penetrating radar (GPR) systems over temperate glaciers in the western Swiss Alps, we have analyzed the possibilities and limitations of using helicopter-borne GPR surveying to map the ice-bedrock interface. We have considered data from three different acquisition systems including (1) a low-frequency pulsed system hanging below the helicopter (BGR), (2) a stepped frequency system hanging below the helicopter (Radar Systemtechnik GmbH [RST]), and (3) a commercial system mounted directly on the helicopter skids (Geophysical Survey Systems Incorporated [GSSI]). The systems showed considerable differences in their performance. The best results were achieved with the BGR system. On average, the RST and GSSI systems yielded comparable results, but we observed significant site-specific differences. A comparison with ground-based GPR data found that the quality of helicopter-borne data is inferior, but the compelling advantages of airborne surveying still make helicopter-borne data acquisition an attractive option. Statistical analyses concerning the bedrock detectability revealed not only large differences between the different acquisition systems but also between different regions within our investigation area. The percentage of bedrock reflections identified (with respect to the overall profile length within a particular region) varied from 11.7% to 68.9%. Obvious factors for missing the bedrock reflections included large bedrock depths and steeply dipping bedrock interfaces, but we also observed that internal features within the ice body may obscure bedrock reflections. In particular, we identified a conspicuous “internal reflection band” in many profiles acquired with the GSSI system. We attribute this feature to abrupt changes of the water content within the ice, but more research is required for a better understanding of the nature of this internal reflection band.

Evolution of subsea permafrost landscapes in Arctic Siberia since the Late Pleistocene: a synoptic insight from acoustic data of the Laptev Sea

Using high-resolution seismic data, this study aims at investigating the evolution and morphological diversity of subsea permafrost features on the eastern Laptev Sea shelf, Arctic Siberia. Several seismic facies were recognized. These relate to the major environmental changes, which affected the Laptev Sea area before, during, and after the last global transgression. Because this shallow shelf was part of the Beringian landmass, we consider a prominent subsurface seismic basal reflector as the top of the former terrestrial permafrost table. Five zones differing in geometry, reflection patterns, depths, and continuity of the permafrost top are identified. Where visible, the upper 70 m of the sediments consists of epigenetically and syngenetically frozen ice-poor sandy deposits at the base, possibly of early last glacial age, marine isotope stages (MIS) 5 and 4. These are followed by late glacial, ice-rich facies interpreted to be MIS 3 to 2. The early Holocene (MIS 1) features well-stratified lagoonal and taberal deposits. As verified by radiocarbon-dated sediment cores, these deposits are overlain by middle to late Holocene sediments with an increasingly marine signature.

Seismic and core investigation off Panama city, Florida, reveals sand ridge influence on formation of the shoreface ravinement

A high-resolution seismic reflection and vibracore survey was conducted on the inner shelf offshore of Panama City, Florida in April, 2011, to provide seabed characterization for Office of Naval Research acoustic reverberation experiments. The seafloor in this region is part of the MAFLA sand sheet: marine sands up to 5.5m thick extending from Mississippi to the Florida panhandle. The survey area spanned a transition in sand ridge morphology: northwest of the St. Andrews Bay inlet channel, sand ridges are up to ~4m tall, but die off southeast of the inlet channel. Analysis of reflection and core data documents a basal reflector beneath the ridges interpreted to be the shoreface ravinement separating estuarine and Pleistocene sediments below from the marine sands above scavenged from the eroded sediments. In the northwest, this surface truncates buried river channels filled with estuarine sediment. In the middle of the survey area, where sand ridges are ~2m high, the basal reflector is stratigraphically above the channel tops, and the presence of woody fragments in the intervening sand implies that it is relict barrier/estuarine material that has not been reworked into marine sand. In the southeast, where no sand ridges are present, the basal reflector is not observed, but the shoreface ravinement is identified in cores just ~0.4m below the seafloor; unreworked barrier/estuarine sands are up to ~4m thick above the channel tops. The stratigraphic progression implies reduced depth of shoreface erosion to the southeast, correlating with the reduction in sand ridge height. It is hypothesized here that sand ridge migration provides an addition to wave erosion in the formation of the shoreface ravinement along the lower shoreface and inner shelf, eroding through net negative bedform climb, and transferring sand to the sand ridges comprising the modern sand sheet.

Blind deconvolution of multichannel recordings by linearized inversion in the spectral domain

In seismology, blind deconvolution aims to recover the source wavelet and the Green’s function, or parts of it (e.g., reflectivity series), from a recorded seismic trace. A multitude of algorithms exist that tackle this ill-posed problem by different approaches. Making assumptions on the phase spectra of the source wavelet and/or the statistical distribution of the reflectivity series is useful for single trace. The nature of closely spaced multichannel recordings enables a better estimation of a common source wavelet and thus increases the confidence of the results. This approach has been exploited in the past, although different types of assumptions are used for a variety of algorithms. We introduced a new method for simultaneous reconstruction of arbitrary source wavelets and local vertical reflectivity series from teleseismic earthquakes. Closely spaced receivers record vertically incident earthquake body waves and their surface-related multiples, which comprise the unknown reflectivity series. By assuming a common source wavelet for all receivers, the observation of several events resulted in a set of convolution equations relating the unknown source wavelets and unknown reflectivity series to the observed seismic trace. The overdetermined system of equations was linearized and solved by conventional inversion algorithms in the spectral domain. Synthetic tests indicated a better performance of the introduced method than conventional deconvolution in the presence of white noise, which is attributed to the constraint of a common model for all observations. Application to field data from a local deployment allowed imaging a basement reflector from teleseismic body waves, although the data were contaminated with strong coherent noise. From a practical point of view, the presented method is potentially well suited for local and regional large-scale imaging from multichannel passive seismic data.

Origin and significance of intra-basement seismic reflections offshore western Norway

We use 3D seismic data to image a series of enigmatic, SW-dipping reflection packets within pre-Mesozoic crystalline basement offshore western Norway. Based on their low-angle dip and complex reflection wave-train our preferred interpretation is that the reflection packets are the seismic expression of mylonitic zones generated by nappe emplacement during the Caledonian orogeny. Late Jurassic faults truncate and offset these reflection packets by several hundred metres, suggesting that these faults did not exploit pre-existing basement weaknesses. Our observations suggest that older basement fabrics may not always play a significant role in determining the geometry of later fault systems. Supplementary materials: Details of the time-depth relationships from wells that have been used to depth-convert interpretations (S1), a supplementary figure showing an uninterpreted version of the seismic profile presented in Fig. 2 (S2) and a throw v. distance plot for fault F1 at the structural levels of the basement reflection and intra-basement reflection 1 are available at www.geolsoc.org.uk/SUP18683 .

First glacier‐vibroseismic experiment ‐ results from cold firn of Colle Gnifetti

ABSTRACTIn the summer of 2010, a small shallow reflection seismic experiment was carried out on the firn covered cold glacier of Colle Gnifetti, Monte Rosa group, Swiss/Italian Alps. At this site, the physical properties of ice are comparable to polar conditions, which is why this site is often used for methodological tests. The experiment at 4500 m elevation was designed to explore the scope of shallow vibroseis for seismic targets within and below the glacier. A small ELVIS vibrator system was used to generate shear waves and compression waves for SH‐ and P‐wave receiver setups of two profiles. The resulting sections clearly show a boundary from ice to rock around 60 m and deeper structures below the glacier. The deepest features are estimated to be 150 m for the SH‐waves and 220 m for the P‐waves. Reflections could be detected also within the ice overburden, which are preliminarily interpreted as a change of density in the upper 30 m and possibly crystal orientation fabric in the ice column. Furthermore, elastic parameters could be derived from seismic velocities, due to clear basement reflections. The results of this unique experiment enable new insights into the internal structure of ice masses and open a promising new investigation method for sub‐ice structures and properties, such as basal sediments.

Mapping of Bedrock Using the High-Resolution Seismic Reflection Technique at Wadi Al Dawasir Region, Saudi Arabia

This paper critically evaluates the utility of seismic data to assist in the interpretation of bedrock. Four high-resolution seismic reflection profiles were carried out to provide estimates of the depth to the bedrock and to detect any geological faults present in the area, which may affect the hydro-geological system at Wadi Al Dawasir region, 690 km south of Riyadh city. The bedrock reflection is clearly present in all sites. The depth of the bedrock at site 1 was approximately 750 m, 800 m at site 2, 700 m at site 3, and 950 m at site 4. The bedrock depth obtained from the seismic agreed with the well information. We developed a clear understanding of the bedrock in the study area and mapped its depth as well as mapped some of the clear fault locations.

A new interpretation of the sedimentary cover in the western Siljan Ring area, central Sweden, based on seismic data

Two new reflection seismic profiles over the Paleozoic successions of the western part of the Siljan Ring impact structure show a contrasting seismic signature. The more southerly c. 10km long Mora profile reveals a highly disturbed structure, with only a few kilometers of relatively horizontally layered structures observed. However, interpretations of refracted arrivals in the data, that can be correlated to reflections, indicate the Silurian clastic rocks to be about 200m thick in the central part of the profile. Weak reflections from about 600m depth suggest a 400m thick Ordovician limestone sequence to be present. Cores from the area show a mainly shale lithology for the Silurian and only a thin sequence of Ordovician strata, suggesting a rapid thickening of the Ordovician towards the north. On the more northern c. 12km Orsa profile clear reflections from the Paleozoic successions are seen along the entire profile, except on the southernmost few kilometers. Based on interpretations of refracted arrivals, the Silurian succession appears to be considerably thinner here, and possibly absent at some locations. The Ordovician is also interpreted to be thinner in this area, with a maximum thickness of about 200–300m along most of the profile. A deeper reflection from about 2km within the crystalline basement may represent a dolerite sill. The lack of clear basement reflections on the Mora profile can be attributed to near-surface conditions and the acquisition geometry. The seismic data and recent coring in the area suggest the presence of a deeper paleo-basin towards the southwest with significantly more shales being deposited and the Paleozoic successions being severely disturbed. The shallow coring and seismic data will help form the basis for locating future boreholes for deeper drilling to study impact processes and the Paleozoic evolution of central Sweden.

Now you see it, now you don't: Chirp imaging of the intermittently shelly shoreface ravinement surface on the inner shelf of Panama City, Florida

Reconnaissance CHIRP data and vibracores were collected on the inner shelf off Panama City, Florida, in April, 2011, for the purpose of providing seabed characterization for an upcoming ONR acoustic reverberation experiment. The seafloor in this region is part of the MAFLA sand sheet: Holocene shelfal marine sands, 0–5 m thick, extending from Mississippi to the Florida panhandle. Coring often samples a thin shelly layer, associated with the shoreface ravinement, at the base of the sand sheet, followed by finer-grained estuarine sediments. Prior CHIRP data collected by Steve Schock off nearby Fort Walton Beach revealed a highly intermittent reflector that could be correlated to the base of the sand sheet; whether the reflector is caused by the estuarine sediments or the shells was uncertain. The new data also reveal an intermittent basal reflector. Estuarine layering can also be identified, and in parts of our survey area the basal and estuarine horizons are distinct. A core at one of these locations sampled a 0.5-m thick shell layer corresponding to the basal reflector with sand both above and beneath. Shells are therefore likely responsible for this intermittent reflector, and thus themselves likely very heterogeneous in concentration at the ravinement surface.

Mapping of bedrock using the high-resolution seismic reflection technique at Wadi Al Dawasir Region, Saudi Arabia

This paper critically evaluates the utility of seismic data to assist in the interpretation of bedrock. Four high-resolution seismic reflection profiles were carried out to provide estimates of the depth to the bedrock and to detect any geological faults present in the area, which may affect the hydro-geological system at Wadi Al Dawasir region, 690 km south of Riyadh city. The bedrock reflection is clearly present in all sites. The depth of the bedrock at site 1 was approximately 750 m, 800 m at site 2, 700 m at site 3, and 950 m at site 4. The bedrock depth obtained from the seismic agreed with the well information. We developed a clear understanding of the bedrock in the study area and mapped its depth as well as mapped some of the clear fault locations.

Crustal seismic reflection profile across the alpine fault and coastal plain at Whataroa, South Island

Crustal seismic reflection data recorded across the Alpine Fault and coastal plain at Whataroa in 1998 are used to derive shallow (4 seconds two-way time or s twt) and deep (14 s twt) seismic reflection images and a simple refraction model. A single 25 km long, 636 channel receiver array recorded energy from 50 kg shots fired at 1 km intervals with intervening shots of 2.5 kg at about 300 m intervals along the profile. Record quality varied from good to poor. Across the Alpine Fault, basement lies at about 300–500 m (0.2–0.5 s twt), and a weak basement reflection may be attributed the Alpine Fault. Basement deepens sharply at about 6 km to the northwest of the fault, and a 3 km section of probably Miocene and younger sediments is imaged to the northwest. The southern boundary of the coastal basin probably corresponds to the South Westland Fault. The deeper section images a distinct band of strong reflectivity at a depth of about 9–10 s twt, the base of which is inferred to be Moho. Depth conversion gives a horizontal Moho across the whole profile at a depth of about 27 km.

Imaging glacial sediment inclusions in 3‐D using ground‐penetrating radar at Kongsvegen, Svalbard

AbstractThe quiescent‐phase surge‐type glacier, Kongsvegen, flows confluent with the continuously fast‐flowing Kronebreen in northwestern Spitsbergen. The lower regions of Kongsvegen overlie glaciomarine sediments, which have been incorporated into the ice during multiple surge events. The resulting englacial structures are exposed at the surface and on a cliff section. These structures have variously been interpreted as thrusts, formed by compression, or sediment‐filled crevasses, formed by extension. We collected a grid of closely spaced ground‐penetrating radar profiles in the area adjacent to the cliff section. Several structures were imaged in 3‐D, including a strong subhorizontal basal reflector, which was underlain by a second, weaker subhorizontal reflector. The basal reflector was occasionally reverse faulted, suggesting compression. Clear englacial features extended upwards from it, dipping up‐glacier at angles of &lt;40° and steepening towards the glacier surface; they had complex geometries that changed rapidly cross‐glacier. The structures were orientated at ∼30° to ice flow, suggesting modification by lateral compression from Kronebreen. Some of these englacial structures clearly crossed the basal reflector. We conclude that the englacial features imaged are not likely to be derived from crevasse filling and were probably formed by thrusting. The results contribute to our understanding of surge initiation and termination processes, and interpretation of features in the palaeorecord. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Radar signatures beneath a surface topographic lineation near the outlet of Kamb Ice Stream and Engelhardt Ice Ridge, West Antarctica

AbstractVisible and infrared satellite images reveal numerous lineations on the Siple Coast region of West Antarctica. We used 5 MHz ice-penetrating radar to probe the interior and the bed of the ice sheet beneath a lineation at the boundary between Engelhardt Ice Ridge and flat-ice terrain to the south of the Kamb Ice Stream (KIS) outlet. Results show curved reflectors that emerge from the bed beneath 600 m thick ice. The tops of the reflectors extend about 100m into the ice above the bed, where they become almost horizontal. Apparent reflectivity of the horizontal section is about 20 dB less than that of the bed. We conclude that the likely cause of such strong reflection is sea water that was accreted into basal crevasses when the flat-ice terrain was floating. Internal layers are warped downward just downslope from the basal reflectors. It is thought that the downwarping was caused by localized basal melting in the past. The spatial pattern of downwarping suggests that localized basal melting was stronger on the north side than on the south side of KIS; apparently ice/ocean interactions on the two sides of KIS were different.

Determination of total ice volume and ice-thickness distribution of two glaciers in the Hohe Tauern region, Eastern Alps, from GPR data

AbstractGlobal warming is causing an apparent rapid retreat of many glaciers worldwide. In addition to mass-balance investigation, the determination and monitoring of total glacial ice volume and ice-thickness distribution are important parameters for understanding the interactions between climate and the complex glacier system. Because of spatially irregular and sparse datasets, scaling of volume and ice-thickness distribution is often a challenging problem. This study focuses on two small (&lt;2 km2) temperate glaciers in the Hohe Tauern (Eastern Alps) region of central Austria. The period 2003–04 saw the first use of ground-penetrating radar (GPR) to determine the total ice volume and ice-thickness distribution of the two glaciers. A centre frequency of 20 MHz was used in point measuring mode. Despite variable data quality, bedrock reflections up to depths of &gt;100m were identified in the data. The acquired GPR data are irregularly distributed and the spatial density is too low to calculate reasonable bedrock topography with standard interpolation approaches. Thus one main focus of this study was to develop an appropriate interpolation technique. Eventually, kriging technique and a glacial mechanically based interpolation parameter were used. Mean calculated ice thicknesses for the two investigated glaciers are 40–50 m, with a maximum of 150–165 m. No direct validation data are available, so different considerations support the computed bedrock topography.