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Above average warming in the Arctic is leading to increasing permafrost temperatures and a reduction in sea ice cover, which are expected to contribute to increasing rates of Arctic coastal erosion and sediment release. We studied a 1.5 km stretch of coastline off Richard’s Island, Northwest Territories, Canada, consisting of multiple retrogressive thaw slumps (RTSs) with varying degrees of activity over a one-year period. Multi-temporal 2D and 3D geomorphic analysis was based on unmanned aerial vehicle-Structure-from-Motion (UAV-SfM) data sets collected in 2018 and 2019. Over the observation period, −3.9 m and −1.1 m of planimetric cliff edge and toe retreat occurred, respectively, and corresponded to an average volumetric change of 8.1 m3 m−1. The accuracy of UAV-SfM-derived digital elevation models was tested using 12 data collection and processing scenarios, testing the influence of off-nadir camera angle, flight pattern, and georeferencing strategy. We found that oblique imaging and georeferencing strategy had a large influence on vertical accuracy and variability across the study site and has implications for studying volumetric changes in RTSs. This study furthers the geomorphological understanding of RTS processes by highlighting the complex relationship between planimetric and volumetric change along rapidly retreating Arctic coasts, and demonstrates advancements in measurement practices for UAV-SfM data sets.

The combined use of unmanned aerial vehicles (UAVs) and structure-from-motion (SfM) is rapidly growing as a cost-effective alternative to airborne laser scanning (lidar) for reconstructing glacier surfaces. Here we present a thorough analysis of the precision and accuracy of a photogrammetric point cloud (PPC) constructed through SfM from UAV-acquired imagery over the spring snow surface at Haig Glacier, Alberta, Canada, the first of its kind in a glaciological setting. An aerial lidar survey conducted concurrently with UAV surveys was used to examine spatial patterns in the PPC accuracy. We found a median error in the PPC of −0.046 ± 0.067 m, with a 95% quantile of 0.218 m. Mean precision of the PPC was 0.199 m, with large spatially clustered outliers. We found an association between high-error, low-precision, and high-surface roughness in the PPC, likely due to illumination characteristics of the snow surface. Glacier surface reconstructions are important for geodetic mass balance measurements, giving key insights into changing climate where in situ measurements are difficult to obtain. The PPC errors are small enough that they would have minimal effects on total mass balance, should the technique be applied across the glacier.

Models of glacier surface melt are commonly used in studies of glacier mass balance and runoff; however, with limited data available, most models are validated based on ablation stakes and data from automatic weather stations (AWSs). The technological advances of unmanned aerial vehicles (UAVs) and structure from motion (SfM) have made it possible to measure glacier surface melt in detail over larger portions of a glacier. In this study, we use melt measured using SfM processing of UAV imagery to assess the performance of an energy balance (EB) and enhanced temperature index (ETI) melt model in two dimensions. Imagery collected over a portion of the ablation zone of Fountain Glacier, Nunavut, on 21, 23, and 24 July 2016 was previously used to determine distributed surface melt. An AWS on the glacier provides some measured inputs for both models as well as an additional check on model performance. Modelled incoming solar radiation and albedo derived from UAV imagery are also used as inputs for both models, which were used to estimate melt from 21 to 24 July 2016. Both models estimate total melt at the AWS within 16 % of observations (4 % for ETI). Across the study area the median model error, calculated as the difference between modelled and measured melt (EB = −0.064 m, ETI = −0.050 m), is within the uncertainty of the measurements. The errors in both models were strongly correlated to the density of water flow features on the glacier surface. The relation between water flow and model error suggests that energy from surface water flow contributes significantly to surface melt on Fountain Glacier. Deep surface streams with highly asymmetrical banks are observed on Fountain Glacier, but the processes leading to their formation are missing in the model assessed here. The failure of the model to capture flow-induced melt would lead to significant underestimation of surface melt should the model be used to project future change.

In recent years, the analysis of firn in Greenland, Svalbard, and other high Arctic regions has contributed to the understanding of meltwater retention in firn and its importance to measurements of glacier mass balance. This has provided insight into firn densification processes and meltwater retention. Changes in these attributes can also provide insight into meteorological variability and climate trends. In spring 2018, two firn cores (21 m and 36 m in length) were extracted from the accumulation zone of Kaskawulsh Glacier, St. Elias Mountains, Yukon. The cores were analyzed for ice layer stratigraphy, density, and glaciochemical time series (oxygen isotopes and major ions). Meltwater percolation and refreezing events were evident in the cores. The quantity of ice layers, the presence of liquid water at 34.5 m depth, interpreted as a perennial firn aquifer (PFA), and the altered isotopic and glaciochemical signature all indicate this process. This melt resulted in an estimated surface lowering of 10 ± 0.8 cm/yr between 2005 and 2018. The information gleaned from Kaskawulsh Glacier supports the need for improved and field-validated density assumptions for geodetic mass balance methods.

Glacier surfaces are active microbial ecosystems which contribute to melt feedback cycles and biogeochemical processes. Despite this recognition, there is a lack of knowledge regarding the transport dynamics and residence time of microbes in this supraglacial habitat. Throughout the ablation season, meltwater is generated across a glacier’s surface and flows through the porous near-surface weathering crust before entering the channelised supraglacial network. Within the weathering crust, solar radiation provides a “photic zone” which, combined with nutrient availability, is conducive for microbial activity. The water flow through this porous near-surface layer provides a transport mechanism for these microbes. However, the nature of controls upon this phenomenon remain unexplored, despite the relevance for cellular export to downstream ecosystems, glacier surface albedo and biogeochemical cycling.To determine potential controls on microbial transport in the weathering crust, we present 913 measurements of microbial cell abundance in supraglacial meltwaters from 11 glaciers across the northern hemisphere. Each measurement is coupled with weathering crust hydraulic conductivity or stream discharge. These data reveal a mean microbial abundance of 2.2 × 104 cells mL-1 (with a range of 103 – 106) in supraglacial meltwaters within the weathering crust and stream channels. Modal microbe size was 1 – 2 μm (56 % of microbes), with 89 % of microbes smaller than 4 μm. No substantiated difference in size distributions between weathering crust and stream meltwaters were observed. No correlation between microbial abundance and near-surface hydraulic conductivity or stream discharge were observed, either across the entire dataset or when considered on a glacier-by-glacier basis. At three glaciers, water temperature and electrical conductivity (a proxy measure for ionic load) were also recorded; but we observe no correlation between these two variables and microbial abundance. Our data suggests weathering crust microbe abundance is consistent across differing glacial environments, and the concentrations entrained in the near-surface equal those seen in supraglacial streams. As such, despite the low transfer rate of meltwater, there appears to be limited evidence for substantial storage or accumulation of biomass in the near-surface weathering crust. Moreover, microbe entrainment does not appear to be driven by primary hydrological controls. Assuming that once liberated within the weathering crust entrained microbes reach channelised supraglacial networks, we estimate a delivery of 1.1 × 109 kg C a-1 to downstream environments globally (excluding Antarctica) to 2100, using existing discharge forecasts. This study represents a crucial first step in examining microbial abundance within, and transport across glacier surfaces and their potential role in biogeochemical process-feedbacks and the inoculation of downstream environments.

The hydrology of near‐surface glacier ice remains a neglected aspect of glacier hydrology despite its role in modulating meltwater delivery to downstream environments. To elucidate the hydrological characteristics of this near‐surface glacial weathering crust, we describe the design and operation of a capacitance‐based piezometer that enables rapid, economical deployment across multiple sites and provides an accurate, high‐resolution record of near‐surface water‐level fluctuations. Piezometers were employed at 10 northern hemisphere glaciers, and through the application of standard bail–recharge techniques, we derive hydraulic conductivity (K) values from 0.003 to 3.519 m day−1, with a mean of 0.185 ± 0.019 m day−1. These results are comparable to those obtained in other discrete studies of glacier near‐surface ice, and for firn, and indicate that the weathering crust represents a hydrologically inefficient aquifer. Hydraulic conductivity correlated positively with water table height but negatively with altitude and cumulative short‐wave radiation since the last synoptic period of either negative air temperatures or turbulent energy flux dominance. The large range of K observed suggests complex interactions between meteorological influences and differences arising from variability in ice structure and crystallography. Our data demonstrate a greater complexity of near‐surface ice hydrology than hitherto appreciated and support the notion that the weathering crust can regulate the supraglacial discharge response to melt production. The conductivities reported here, coupled with typical supraglacial channel spacing, suggest that meltwater can be retained within the weathering crust for at least several days. Not only does this have implications for the accuracy of predictive meltwater run‐off models, but we also argue for biogeochemical processes and transfers that are strongly conditioned by water residence time and the efficacy of the cascade of sediments, impurities, microbes, and nutrients to downstream ecosystems. Because continued atmospheric warming will incur rising snowline elevations and glacier thinning, the supraglacial hydrological system may assume greater importance in many mountainous regions, and consequently, detailing weathering crust hydraulics represents a research priority because the flow path it represents remains poorly constrained.

Enhanced temperature index (ETI) models of glacier surface melt are commonly used in studies of glacier mass balance and runoff. With limited data available most models are validated based on ablation stakes and data from automatic weather stations (AWS). With the technological advances of unmanned aerial vehicles (UAVs) and structure-from-motion (SfM), it is possible to measure glacier surface melt in detail over larger portions of a glacier. In this study, we use melt measured using SfM processing of UAV imagery to assess the performance of an ETI melt model in two-dimensions. Imagery collected over a portion of the ablation zone of Fountain Glacier, NU, on July 21 and 24, 2016 was previously used to determine distributed surface melt. Incoming solar radiation and temperature measured at the AWS, along with albedo derived from UAV imagery, are used as inputs for the model which was used to estimate melt from July 21–24, 2016. Modelled melt agrees with melt measured at the AWS within ±0.010 m. Across the study area the median model error (−0.044 m), calculated as the difference between measured and modelled melt, is within the uncertainty of the measurements. A strong link was found between the model error and glacier surface aspect with higher errors linked to south aspects. The highest errors were also linked to the density of water flow features on the glacier surface. The relation between water flow and model error suggests that energy from surface water flow is contributing significantly to surface melt on Fountain Glacier. Deep surface streams with highly asymmetrical banks are observed on Fountain Glacier, but the processes leading to their formation are missing in the model assessed here. The failure of the model to capture flow-induced melt and to under-estimate melt on south aspects would lead to significant underestimation of surface melt should the model be used to project future change.

Supraglacial streams are a significant part of the glacial hydrological system and important for understanding the connection between glacial hydrology and glacier dynamics. Here we determine the factors that influence the development of step-pool formation and pulsating flow in a supraglacial stream on Bylot Island, Nunavut. Results show that during the second week of a 2-week study, multiple successive rainfall events occurred, stream temperature increased and ablation decreased; which also caused stream discharge to decrease. In addition, the stream, which flowed over a 13 m high waterfall off the front of Fountain Glacier, rapidly formed 21 step-pools and began to pulsate. The pulsating phenomenon involved the complete stoppage of flow over the waterfall and the subsequent restart between 8 and 20 s later. Pulsating flow resulted from rapid changes in the streambed morphology. In particular, the formation of the step-pool sequence was caused by helical flow around meander bends and hydrologically induced slippage along transverse shear planes, evidenced by observations of high-pressure artesian flow from transverse fractures. Contrary to previous literature, this study shows that high discharge is not necessarily the cause of step-pool formation and pulsating flow within supraglacial streams.

Remotely sensed glaciological measurements can be expensive, often involving a trade-off between resolution, scale, and frequency. We report on a case study in which two low-cost techniques were used to generate digital elevation models and orthomosaics of an Arctic glacier in consecutive ablation seasons. In the first aerial survey we used an unmanned aerial vehicle and acquired images autonomously. The following year we took advantage of the helicopter used for site access, and were able to acquire images manually, for little additional helicopter time. We present a preliminary assessment of accuracy and apply these data to measure glacier thinning and motion.

Photogrammetric point clouds (PPCs) provide a source of three-dimensional (3-D) remote sensing data that is well-suited to use over small areas that are within the scope of observation by unmanned aerial vehicles (UAVs). We compared PPC-based structural metrics to traditional ground surveys conducted by field personnel in order to assess the capacity of PPC data to contribute to vegetation-reclamation surveys. We found good statistical agreement between key structural vegetation parameters, such as mean and maximum vegetation height, with PPC metrics successfully predicting most height and tree-diameter metrics using multivariate linear regression. However, PPC metrics were not as useful for estimating ground-measured vegetation cover. We believe that part of the issue lies in the mismatch between PPC- and ground-based measurement approaches, including subjective judgement on behalf of ground crews: a topic that requires more investigation. Our work highlights the emerging value of UAV-based PPCs to complement, and in some cases supplement, traditional ground-based sources of measured vegetation structure.

Small unmanned aircraft systems (UASs) are often suited to applications where the cost, resolution, and (or) operational inflexibility of conventional remote sensing platforms is limiting. Remote sensing with small UASs is still relatively new, and there is limited understanding of how the data are acquired and used for scientific purposes and decision making. This paper provides practical guidance about the opportunities and limitations of small UAS-based remote sensing by highlighting a small sample of scientific and commercial case studies. Case studies span four themes: (i) mapping, which includes case studies to measure aggregate stockpile volumes and map river habitat; (ii) feature detection, which includes case studies on grassland image classification and detection of agricultural crop infection; (iii) wildlife and animal enumeration, with case studies describing the detection of fish concentrations during a major salmon spawning event, and cattle enumeration at a concentrated animal feeding operation; (iv) landscape dynamics with a case study of arctic glacier change. Collectively, these case studies only represent a fraction of possible remote sensing applications using small UASs, but they provide insight into potential challenges and outcomes, and help clarify the opportunities and limitations that UAS technology offers for remote sensing of the environment.

Twin time-lapse cameras were set up to provide a convergent view of ten targets located on the surface of an Arctic glacier, near its terminus. Using photogrammetric analysis, daily target elevations were calculated over three winters and two ablation seasons. Results show that the glacier surface level dropped by approximately 2.9 and 2.5 m respectively over the 2009 and 2010 ablation seasons. GPS measurements suggest the associated average vertical errors were 0.105 m and 0.04 m respectively. Photogrammetric measurements indicated that thinning from melting exceeded surface gains due to ice inflow by a factor of ~ 5: 1 during 2009 and 2010. Horizontal flow rates of 6–12 mm d–1 were measured photogrammetrically during autumn 2008 and compared to interpolated winter rates established from GPS measurements, with differences ranging between 7.4% and 17.2%. The availability of a continuous series of data for the duration of the study allowed the start and end dates of each ablation season to be identified, making it possible to determine the length of each balance year. The results show the utility of time-series photogrammetry for observing surface elevation changes and dynamic processes in remote glacial environments.

Small unmanned aircraft systems (sUAS) are a relatively new type of aerial platform for acquiring high-resolution remote sensing measurements of Earth surface processes and landforms. However, despite growing application there has been little quantitative assessment of sUAS performance. Here we present results from a field experiment designed to evaluate the accuracy of a photogrammetrically-derived digital terrain model (DTM) developed from imagery acquired with a low-cost digital camera onboard an sUAS. We also show the utility of the high-resolution (0.1 m) sUAS imagery for resolving small-scale biogeomorphic features. The experiment was conducted in an area with active and stabilized aeolian landforms in the southern Canadian Prairies. Images were acquired with a Hawkeye RQ-84Z Areohawk fixed-wing sUAS. A total of 280 images were acquired along 14 flight lines, covering an area of 1.95 km2. The survey was completed in 4.5 h, including GPS surveying, sUAS setup and flight time. Standard image processing and photogrammetric techniques were used to produce a 1 m resolution DTM and a 0.1 m resolution orthorectified image mosaic. The latter revealed previously un-mapped bioturbation features. The vertical accuracy of the DTM was evaluated with 99 Real-Time Kinematic GPS points, while 20 of these points were used to quantify horizontal accuracy. The horizontal root mean squared error (RMSE) of the orthoimage was 0.18 m, while the vertical RMSE of the DTM was 0.29 m, which is equivalent to the RMSE of a bare earth LiDAR DTM for the same site. The combined error from both datasets was used to define a threshold of the minimum elevation difference that could be reliably attributed to erosion or deposition in the seven years separating the sUAS and LiDAR datasets. Overall, our results suggest that sUAS-acquired imagery may provide a low-cost, rapid, and flexible alternative to airborne LiDAR for geomorphological mapping.

Proglacial icings are one of the most common forms of extrusive ice found in the Canadian Arctic. However, the icing adjacent to Fountain Glacier, Bylot Island, is unique due to its annual cycle of growth and decay, and perennial existence without involving freezing point depression of water due to chemical characteristics. Its regeneration depends on the availability of subglacial water and on the balance between ice accretion and hydro-thermal erosion. The storage and conduction of the glacial meltwater involved in the accretion of the icing were analyzed by conducting topographic and ground penetrating radar surveys in addition to the modelling of the subglacial drainage network and the thermal characteristics of the glacier base. The reflection power analysis of the geophysical data shows that some areas of the lower ablation zone have a high accumulation of liquid water, particularly beneath the centre part of the glacier along the main supraglacial stream. A dielectric permittivity model of the glacier – sediment interface suggests that a considerable portion of the glacier is warm based; allowing water to flow through unfrozen subglacial sediments towards the proglacial outwash plain. All these glacier-related characteristics contribute to the annual regeneration of the proglacial icing and allow for portions of the icing to be perennial. Copyright © 2013 John Wiley & Sons, Ltd.

Interannual changes in seasonal ground freezing and near-surface heat flow beneath zones of bottom-fast ice (BFI) were examined over the winters of 2005‐06 and 2006‐07 within the near-shore zone of the Mackenzie Delta, Canada. Winter variability in ground thermal conditions was determined at three monitoring sites. Ground-penetrating radar surveys were conducted in late winter to determine spatial variability in landfast ice conditions and the extent of ice-bonded sediments. Shallow water sites ( 1m of water) experienced prolonged periods of floating ice, which limited the duration of ice contact with the sediment bed and the depth of seasonal frost, and resulted in warmer winter ground temperatures (between � 0.58 Ca nd� 2.68C). Under similar water depths, interannual changes in ice growth altered the timing of BFI and winter heat loss from the ground. When comparing conditions over the twowinters, 2005‐06 was characterised by a decrease in ice thickness that limited the extent of BFI and seasonal cooling of the ground. These changes in ice conditions had a greater effect on the thermal conditions at sites where water depths were close to the maximum ice thickness. The short ice contact times at these sites are important to the thermal state of permafrost, as only minimal heat exchange contributing to permafrost cooling occurs prior to freezeback of the active layer. Copyright # 2010 John Wiley & Sons, Ltd.

Topographic changes from erosion pins and on-site meteorological data document the spatial and temporal patterns of aeolian sediment transport at monthly to annual timescales across an active parabolic dune within a vegetation-stabilized inland, prairie dune field. Over two years, the sediment budget, calculated from digital elevation models, shows that the total volume of erosion (9890 m 3 ) is greater than the amount of deposition (6990 m 3 ), indicating a net loss of 2900 m 3 of sediment (or ∼ 29% of eroded sediment) from the dune. Sediment erosion occurred mainly on the stoss slope (3600 m 3 ; ∼ 36% of eroded sediment), but also on the south (2100 m 3 ; ∼ 21%) and north sides of the dune head (1700 m 3 ; ∼ 17%), the blowouts along the arms (1740 m 3 , ∼ 18%) and the crest (650 m 3 ; ∼ 7%). Erosion from the deflation basin is limited by surface roughness and armoring effects of a gravel lag deposit (100 m 3 ; ∼ 1%). Thus, the blowouts currently contribute to maintaining dune mobility because no other sediment input occurs from upwind. Sediment deposition onto the dune occurred primarily beyond the brink on the south and southeast lee slopes (5500 m 3 ; ∼ 80%), coinciding with the southeasterly resultant transport direction for November 2004–05. The net loss of about 2900 m 3 (∼ 29%) may be attributed to sediment carried in suspension over and beyond the dune. Correlation analysis between sediment transport and meteorological variables suggests that monthly to seasonal changes of surface conditions (e.g., vegetation cover, ground freezing, moisture) buffer the relative importance of temperature and precipitation on rates of sediment transport. Conversely, wind correlates well on a monthly to seasonal basis because it is a driver of transport under all types of surface conditions. Seasonal effects produce a complex interaction between wind, climate and surface conditions. This leads to a dynamic range of threshold velocities, which in turn causes spatial and temporal variations in transport-limiting and supply-limiting conditions. Collectively, these findings have implications for modeling parabolic dune morphodynamics and sediment transport in mid- to high-latitude inland settings.

This paper demonstrates the capabilities of ground penetrating radar (GPR) to map and resolve shallow subsurface features in the near-shore zone: (i) ice conditions (floating or bottom fast); (ii) water bathymetry; (iii) sedimentary structures; and (iv) interfaces between frozen and unfrozen sediment. These features were resolved in the near-shore zone of the Mackenzie Delta, N.W.T., Canada, using multi-frequency (50, 100 and 250 MHz) GPR data collected in winter (2005 and 2006). The capability of GPR to resolve subsurface features in the near-shore zone was strongly controlled by bottom-fast and floating ice conditions. The latter were discriminated using a novel approach involving the energy return from the base of ice and the presence of ice-bottom multiples. Beneath zones of bottom-fast ice, sedimentary structures and interfaces between frozen and unfrozen sediment were discriminated by reflection geometry and amplitude. Beneath floating ice, water depths were measured to depths greater than 5 m using a multi-layer depth calculation. Overall, this research demonstrates that baseline information for geotechnical investigations and climate change research in Arctic coastal zones can be greatly enhanced with GPR data.

Sand supply is a major controlling factor on parabolic dune form and stratigraphy in inland settings. In this study, aerial photographs, ground-penetrating radar (GPR), and stratigraphic analysis document the morphodynamics of an individual and compound parabolic dune in the Bigstick Sand Hills, southwestern Saskatchewan. Migration rates for the last 60 years are comparable, although the profile morphologies differ, with the individual dune having a more aerodynamic form. Stratigraphic facies are also similar in both dune types, but the overall internal architecture imaged by GPR differs considerably. Configurations of cross-strata parallel to the downwind axis represent dominant foreset development and lee-slope slipface advance of the individual dune, and impeded slipface development of the compound dune. Stratigraphy transverse to the downwind axis represents radial deposition and foreset development at the individual dune, and vertical accumulation at the compound dune. The overall difference in parabolic dune form and stratigraphy is attributed to variations in sand supply, which determine vegetation development and sedimentation processes along the crest and lee slope. Sand supplied from active blowouts upwind of the individual dune inhibits vegetation colonization on the dune, whereas an absence of sand supply upwind of the compound dune leads to high levels of vegetation cover on the dune. Once supply drops below a threshold level, vegetation cover increases, causing sediment deposition and vertical accretion, and ultimately changing dune form. Overall, this study demonstrates that local sand supply and feedback processes are critical to understanding dune development in vegetated, inland settings.

In this paper the development of a large-scale gravitational deformation involving the eastern lateral moraine of the Athabasca Glacier in Jasper National Park, Alberta, Canada, is described. Interpretation and analysis of sequential aerial photographs indicates that a 540-m-wide segment of the eastern lateral moraine began to deform in the early 1950s; however, significant movement only began in the late 1960s. Since then, the moraine has undergone progressive gravitational deformation leading to a network of fractures, bulging, and the development of a large gap in the moraine crest. Geographic information system analysis of topographic changes between 1967 and 2006 indicates that the displaced volume of the moraine is approximately 9.0×10 5 m 3 . In the last 39 years, the moraine crest has displaced 55 m (1.4 m yr -1 ) down towards the glacier. The development of slope instability is linked to a combination of debuttressing from recent glacier recession, deformation of the moraine, as well as the movement of a large, mobile, debris-mantled slope impinging the upslope margin of the lateral moraine. This case study illustrates the importance of glacial conditioning and local geomorphological factors in creating conditions for large-scale moraine instability in recently deglacierized alpine basins.

Geophysical techniques can be used to examine the spatial distribution of subsurface geophysical properties to delineate horizontally and vertically the active layer, permafrost and taliks. Spatial and temporal changes in subsurface geophysical properties due to permafrost cooling, warming, aggradation or degradation can also be assessed through geophysical monitoring. This paper reviews the geophysical methods most frequently applied in mountain and arctic/subarctic lowland permafrost investigations. Key results and recommendations based on the analysis of the applicability and reliability of different geophysical techniques for permafrost studies are summarised. Emphasis is put on the tomographic capabilities of geophysical methods. Recent advances in application and data interpretation are shown in relation to five case studies, and future perspectives are highlighted. Copyright # 2008 John Wiley & Sons, Ltd.

In this letter, we propose an interacting multiple-model (IMM)-based abrupt change detector for ground-penetrating radar (GPR) applications. Ground clutter varies with surface roughness, soil nature, as well as depth of the soil layer, necessitating a multiple-model approach. The IMM is first trained for a chosen number of models and then used to characterize the GPR data. The IMM predictor segments the entire GPR data into regions of identical models and then identifies targets by detecting abrupt changes in model parameters. The number of models is determined using the minimum prediction error criterion. The prediction performance of the IMM predictor is theoretically analyzed, and its detection performance is also evaluated through an receiver operating characteristics analysis to illustrate the improved performance of the proposed detector.

Sand–water flows were observed on the slopes of cold-climate eolian dunes in southwestern Saskatchewan, Canada, during episodes of intense thawing in the winters of 2004 and 2005. Meltwater produced flows with varying grain–water contents on slopes of active blowout hollows and parabolic dunes. The sand–water flows emplaced small, structureless, lobate- and tongue-shaped deposits and alluvial fans. The greatest concentration of deposits occurred on south-facing slopes, which frequently thaw in winter from intense insolation. Transport modes ranged from high-density, viscous slurry flows to lowdensity, hyperconcentrated flows. The triggering cause of these flows is high pore-water pressure that develops in thawed nearsurface sand due to impeded infiltration by frozen sand with pore ice at depth. These observations broaden the environmental context of sand–water flows on dunes and contribute to interpretations of these deposits in the eolian rock record and to recent alluvial features observed on Martian sand dunes.

In recent years, ground-penetrating radar (GPR) has been increasingly used for characterization of subglacial and englacial environments at polythermal glaciers. The geophysical method is able to exploit the dielectric difference between water, air, sediment and ice, allowing delineation of subsurface hydrological, thermal and structural conditions. More recent GPR research has endeavoured to examine temporal change in glaciers, in particular the distribution of the cold ice zone at polythermal glaciers. However, the exact nature of temporal change that can be identified using GPR has not been fully examined. This research presents the results of three GPR surveys conducted over the course of a summer ablation season at a polythermal glacier in the Canadian Arctic. A total of approximately 30 km of GPR profiles were collected in 2002 repeatedly covering the lower 2 km of Stagnation Glacier, Bylot Island (72°58′ N 78°22′ W). Comparison between profiles indicated changes in the radar signature, including increased noise, appearance and disappearance of englacial reflections, and signal attenuation in the latter survey. Further, an area of chaotic returns in up-glacier locations, which was interpreted to be a wet temperate ice zone, showed marked recession over the course of the ablation season. Combining all the temporal changes that were detected by GPR, results indicate that a polythermal glacier may exhibit strongly seasonal changes in hydrological and thermal characteristics throughout the ice body, including the drainage of 17 000 m 3 of temporarily stored intra-glacial meltwater. It is also proposed that the liquid water content in the temperate ice zone of polythermal glaciers can be described as a fraction of a specific retention capacity. Copyright © 2006 John Wiley & Sons, Ltd.

Monitoring the geological movements in areas of continuous permafrost requires that the surface movement due to the seasonal variation in the permafrost active layer be isolated from the underlying trend. Two potential ways of achieving this is to model the heave/settlement of the surface due to seasonal thaw/refreeze so that surface measurements can be utilised, or to place survey monuments that do not respond to the active layer and make point observations. This paper describes the requirements for monitoring natural trend and subsidence due to gas extraction in areas of the Mackenzie Delta/Beaufort Sea region of Canada, an area of continuous permafrost. Different solutions based on Differential Interferometric SAR and Differential Global Positioning are proposed to the monitoring problem based on the two methods of isolating the effects of permafrost movement described above. This paper reports on research undertaken to discover the long-term stability of survey monuments established in a test-bed in the area of the proposed gas extraction. Seven types of monument are present, with records of height variation available between 1987 and 1995. Two further epochs of measurement were made in 2003 and 2004, allowing analysis of a 17-year period to be made. Analysis of the data showed that only one type of monument displayed the required stability to model natural trend and subsequently to predict this trend in the analysis of subsidence caused by gas extraction.

Recent research has identified differences in processes contributing to suspended sediment concentration (SSC) dynamics in proglacial streams between High Arctic and alpine catchments, but does not examine processes explicitly linked to the periglacial environment. Three glacierized basins were studied: Austre Broggerbreen and Midre Lov´ enbreen, Svalbard (79 °N, 12 °E) and Glacier B28, unofficially named Stagnation Glacier, Bylot Island, Nunavut (73 °N, 78 °W). SSC variations were modelled from continuous turbidity, discharge and meteorological data throughout the summer months. Three statistical tools were utilized: principal component analysis, changepoint analysis and multivariate regression. These are shown to be effective in identifying subperiods of distinctive geocryological and glaciofluvial characteristics. Multivariate regression for the subseasons included autoregressive integrated moving-average modelling, and showed that SSC variations were related not only to discharge variability, but also to fluctuations in energy fluxes. The results are interpreted in terms of spatio-temporal changes in sediment mobilization and supply associated with changes in the relative importance of fluvial, glacial and periglacial processes. This evidence supports the notion of important linkages between glacial, fluvial and periglacial systems, but exemplifies distinct variability between High Arctic glaciers. Copyright  2005 John Wiley & Sons, Ltd.

Three important parameters that need to be quantified for many permafrost studies are the location of ice in the ground, the position of thermal interfaces, and spatial variations of the water content in the active layer. The data from over 100 investigations in permafrost regions demonstrate that ground-penetrating radar (GPR) offers an effective way to measure these parameters at a scale appropriate for many process and geotechnical studies. Horizontal to gently-dipping interfaces between unfrozen and frozen subsurface zones (such as at the base of the active layer or a suprapermafrost talik) were repeatedly detected by GPR and indicated by strong, laterally-coherent reflections. Coherent reflections are not generated by steeply dipping thermal interfaces (greater than 45°). However, the transition from frozen to unfrozen ground can frequently be located from the radar-stratigraphic signatures of the two units. The radar-stratigraphic signature of excess ice in the subsurface is determined by the size of the body. Ice lenses that are smaller than the resolution of the GPR system frequently can be detected and are represented by chaotic or hyperbolic reflections, while the size of larger ice units can be resolved and is defined by distinct laterally-coherent reflection patterns. This enables the delineation of the vertical and lateral extent of massive ice bodies, and their structural setting. By making precise measurements of the direct ground wave velocity, the water content in the near-surface can be determined for uniform soils. It is demonstrated that by collecting a grid of GPR data the lateral variations in active-layer water content can then be estimated. Copyright © 2003 John Wiley & Sons, Ltd.

Viruses preserved in ancient materials provide snapshots of past viral diversity and a means to trace viral evolution through time. Here, we use a metagenomics approach to identify filterable and nuclease-resistant nucleic acids preserved in 700-y-old caribou feces frozen in a permanent ice patch. We were able to recover and characterize two viruses in replicated experiments performed in two different laboratories: a small circular DNA viral genome (ancient caribou feces associated virus, or aCFV) and a partial RNA viral genome (Ancient Northwest Territories cripavirus, or aNCV). Phylogenetic analysis identifies aCFV as distantly related to the plant-infecting geminiviruses and the fungi-infecting Sclerotinia sclerotiorum hypovirulence-associated DNA virus 1 and aNCV as within the insect-infecting Cripavirus genus. We hypothesize that these viruses originate from plant material ingested by caribou or from flying insects and that their preservation can be attributed to protection within viral capsids maintained at cold temperatures. To investigate the tropism of aCFV, we used the geminiviral reverse genetic system and introduced a multimeric clone into the laboratory model plant Nicotiana benthamiana. Evidence for infectivity came from the detection of viral DNA in newly emerged leaves and the precise excision of the viral genome from the multimeric clones in inoculated leaves. Our findings indicate that viral genomes may in some circumstances be protected from degradation for centuries.

Hydrological systems near the terminus of a high Arctic glacier and a proglacial icing on Bylot Island, Canada, were investigated using ground-penetrating radar (GPR). The ice thickness and the location and depth of tunnels within the glacier and icing were imaged. Modelling of the GPR response was utilized to predict the data quality and to assist in its interpretation. The unique properties of the ice enabled velocity determinations from the diffraction patterns generated by point-source reflectors as well as traditional velocity surveys. The propagation velocity of the radar pulses through the ice depended on the air and water content in the ice. The identification of drainage tunnels was attained through pulse polarity analysis and interpolation between the profiles in gridded surveys. It was found that reflectivity analysis may enable GPR to be used for acquiring three-dimensional information on the thermal structure of glaciers. The much more complicated structure of the icing was imaged with higher frequency antennae and it was found that general ice types could be mapped using radar stratigraphical analysis. Both buried slush mounds and subsurface channel fills were identified within the icing. A portion of the icing near the centre of the valley floor, that has persisted perennially for over 50 years, was found to be sitting on a slightly higher area of the valley bottom and thus was not subjected to the same hydrothermal erosional forces as the edges of the icing, setting up a feed-back loop encouraging the preservation of the central core of ice and promoting the destruction and rebuilding of the edges every year.

Bathymetric mapping of lakes with sonar is essentially limited to the ice-free summer months. Recent developments in ground-penetrating radar technology have greatly increased its portability and capabilities for imaging through fresh water. The suitability of a backpack portable ground-penetrating radar (GPR) system for bathymetric mapping of ice-covered Arctic lakes was investigated by performing grid surveys on three lakes with water depths up to 19 m. It was demonstrated that GPR can now be used to quickly produce high quality bathymetric maps and sub-bottom profiles showing sediment type and lacustrine sediment thickness. While water depths were measured with a precision of ±3%, lacustrine sediment thickness measurements (up to 5 m) had an estimated precision of ±15%.

Remotely-sensed glaciological measurements can be expensive, and often involve a trade-off between resolution, scale, and frequency. In an attempt to overcome these issues we report on a case study in which two low-cost techniques were used to generate orthomosaic images and digital elevation models (DEMs) of an arctic glacier in two consecutive ablation seasons. In the first aerial survey we used an unmanned aerial vehicle (UAV) and acquired images autonomously, while in the second we used a piloted helicopter and acquired images manually. We present a preliminary assessment of accuracy and apply these data to measure glacier thinning and motion.

Continuous descriptions of the spatial variability of subsurface materials are desirable in many hydrogeological studies. However, traditional point-measurement techniques, such as soil coring and pit excavation, are destructive and provide an incomplete characterization of the subsurface. In this study, ground-penetrating radar (GPR) was used to continuously and nondestructively map shallow subsurface features along a small wetland catena in southeastern Newfoundland. Detailed profiles of soil dielectric constant and common midpoint velocity surveys were used to determine radar pulse velocities through subsurface features. Major reflectors identified in the study included: (i) organic soil-mineral soil contact, (ii) placic horizons (saturated mineral soil-unsaturated mineral soil contacts), (iii) water tables (unsaturated mineral soil-saturated mineral soil contact), and (iv) mineral soil-bedrock contact. Thicknesses of major soil features were estimated from radar profiles and compared with thicknesses determined from soil core-auger data. The relationship between estimated and observed thicknesses is strong (r = 0.99). Spatial relationships between placic horizons and wetland community types were also identified.

Permanent ice patches in the western Canadian Subarctic have been recently identified as sources of cryogenically preserved artifacts and biological specimens. The formation, composition, and constancy of these ice patches have yet to be studied. As part of the Northwest Territories (NWT) Ice Patch Study, ground-penetrating radar (GPR) and ice coring were used to examine the stratigraphy and internal structure of two ice patches. Results show the patches are composed of a core of distinct offset units, up to several metres thick, covered by a blanket of firn and snow. The interfaces between the units of ice are often demarcated by thin sections of frozen caribou dung and fine sediment. Radiocarbon dates of dung extracted from ice cores have revealed a long history for these perennial patches, up to 4400 years BP. Ice patch growth is discontinuous and occurs intermittently. Extensive time gaps exist between the units of ice, indicating that summers of catastrophic melt can interrupt extended periods of net accumulation. The results of this work not only display the character of ice patch development, but also indicate the significant role that ice patches can play in reconstructing the paleoenvironmental conditions of an area.

Alpine ice patches are unique repositories of cryogenically preserved archaeological artefacts and biological specimens. Recent melting of ice in the Selwyn Mountains, Northwest Territories, Canada, has exposed layers of dung accumulated during seasonal use of ice patches by mountain woodland caribou of the ancestral Redstone population over the past ca. 5250 years. Although attempts to isolate the DNA of known caribou parasites were unsuccessful, the dung has yielded numerous well-preserved and diverse plant remains and palynomorphs. Plant remains preserved in dung suggest that the ancestral Redstone caribou population foraged on a variety of lichens (30%), bryophytes and lycopods (26.7%), shrubs (21.6%), grasses (10.5%), sedges (7.8%), and forbs (3.4%) during summer use of alpine ice. Dung palynomorph assemblages depict a mosaic of plant communities growing in the caribou’s summer habitat, including downslope boreal components and upslope floristically diverse herbaceous communities. Pollen and spore content of dung is only broadly similar to late Holocene assemblages preserved in lake sediments and peat in the study region, and differences are likely due to the influence of local vegetation and animal forage behaviour. The 5000-year legacy of summer use of alpine ice patches by mountain woodland caribou suggests that these small, long-lived features may be important for the health of caribou populations in the Selwyn/Mackenzie Mountain range.

[1] The manner by which meltwater drains through a glacier is critical to ice dynamics, runoff characteristics, and water quality. However, much of the contemporary knowledge relating to glacier hydrology has been based upon, and conditioned by, understanding gleaned from temperate valley glaciers. Globally, a significant proportion of glaciers and ice sheets exhibit nontemperate thermal regimes. The recent, growing concern over the future response of polar glaciers and ice sheets to forecasts of a warming climate and lengthening summer melt season necessitates recognition of the hydrological processes in these nontemperate ice masses. It is therefore timely to present an accessible review of the scientific progress in glacial hydrology where nontemperate conditions are dominant. This review provides an appraisal of the glaciological literature from nontemperate glaciers, examining supraglacial, englacial, and subglacial environments in sequence and their role in hydrological processes within glacierized catchments. In particular, the variability and complexity in glacier thermal regimes are discussed, illustrating how a unified model of drainage architecture is likely to remain elusive due to structural controls on the presence of water. Cold ice near glacier surfaces may reduce meltwater flux into the glacier interior, but observations suggest that the transient thermal layer of near surface ice holds a hydrological role as a depth-limited aquifer. Englacial flowpaths may arise from the deep incision of supraglacial streams or the propagation of hydrofractures, forms which are readily able to handle varied meltwater discharge or act as locations for water storage, and result in spatially discrete delivery of water to the subglacial environment. The influence of such drainage routes on seasonal meltwater release is explored, with reference to summer season upwellings and winter icing formation. Moreover, clear analogies emerge between nontemperate valley glacier and ice sheet hydrology, the discussion of which indicates how persistent reassessment of our conceptualization of glacier drainage systems is required. There is a clear emphasis that continued, integrated endeavors focused on process glaciology at nontemperate glaciers are a scientific imperative to augmenting the existing body of research centered on ice mass hydrology.

Interferograms were generated from 10 TerraSAR-X image pairs, with the objective of obtaining estimates of winter surface motion for a slow-moving polythermal arctic glacier. Flow directions were computed using both ascending and descending-pass interferograms for each period, with the median value being adopted as the final direction. The weighted average flow was computed, with weighting based on the inverse of the difference between the ascending and descending-pass displacement estimates for each date. This study uses multiple interferograms with different imaging geometries to provide estimates of down-glacier flow. The methodology adopted minimizes the effects of glacier / satellite track alignment and those resulting from vertical motion of the glacier surface. Current velocities were compared with flow estimates derived from a 1992 ERS-1 image pair. The velocities were similar over most of the glacier, but current velocities were found to be 30% to 50% lower on the lower glacier.

TDL Irvine-Fynn, BJ Moorman. 2008. Arctic glaciers and ground-penetrating radar case study: Stagnation Glacier, Bylot Island, Canada. In: C Hauck and C Kneisel (Eds), Applied Geophysics in Periglacial Environments, Cambridge University Press, pp.179-190.

Proposed development of a gas pipeline southward from the Mackenzie Delta and the presence of known accumulations of gas and oil in the southern Beaufort Sea suggest that construction of pipelines and associated infrastructure in the nearshore are likely to be proposed in the future. Recent surveys undertaken by Natural Resources Canada and its partners have focused on the shallow, poorly mapped nearshore region of the Mackenzie Delta (