- SfM photogrammetry used to produce topographic data from archive aerial imagery and UAV derived aerial imagery.
- Datasets from 2003 and 2014 were compared to report on the de-icing of a lateral–frontal ice-cored moraine.
- The moraine appears to be de-icing predominantly via down-wastage affording the moraine a higher degree of stability.
- UAVs and SfM are shown to be useful tools for monitoring environmental change.
Abstract: Ice-cored lateral-frontal moraines are common at the margins of receding high-Arctic valley glaciers, but the preservation potential of these features within the landform record is unclear. Recent climatic amelioration provides an opportunity to study the morphological evolution of these landforms as they de-ice. This is important because high-Arctic glacial landsystems have been used as analogues for formerly glaciated areas in the mid-latitudes. This study uses SfM (Structure-from-Motion) photogrammetry and a combination of archive aerial and UAV (unmanned aerial vehicle) derived imagery to investigate the degradation of an ice-cored lateral-frontal moraine at Austre Lovénbreen, Svalbard. Across the study area as a whole, over an 11-year period, the average depth of surface lowering was -1.75 ± 0.89 m. The frontal sections of the moraine showed low or undetectable rates of change. Spatially variable rates of surface lowering are associated with differences in the quantity of buried-ice within the structure of the moraine. Morphological change was dominated by surface lowering, with limited field evidence of degradation via back-wastage. This is affording the moraine a greater degree of stability than observed at many other sites in Svalbard, although it is unclear whether the end point will be a fully stabilised ice-cored moraine, in equilibrium with its environment, or an ice-free lateral-frontal moraine complex. Controls on geomorphological change (e.g. topography and climate) and the preservation potential of the lateral-frontal moraine are discussed. The methods used by this research also demonstrate the potential value of SfM photogrammetry and unmanned aerial vehicles for monitoring environmental change and are likely to have wider applications in other geoscientific sub-disciplines.
Tonkin, T.N., Midgley, N.G., Cook, S.J. and Graham, D.G. (2015). Ice-cored moraine degradation mapped and quantified using an unmanned aerial vehicle: a case study from a polythermal glacier in Svalbard. Geomorphology, 258, pp. 1–10.
Publisher link: http://dx.doi.org/10.1016/j.geomorph.2015.12.019 (subscription required)
Preprint: https://dspace.lboro.ac.uk/2134/20069 (no subscription required; embargoed until 29 December 2016)
- An integrated sUAS and SfM approach is used to generate topographic data.
- The SfM dataset is compared with a total station ground survey.
- Causes of vertical difference between the two datasets are investigated.
- The integration of a combined sUAS and SfM approach is discussed.
Abstract: Novel topographic survey methods that integrate both structure-from-motion (SfM) photogrammetry and small unmanned aircraft systems (sUAS) are a rapidly evolving investigative technique. Due to the diverse range of survey configurations available and the infancy of these new methods, further research is required. Here, the accuracy, precision and potential applications of this approach are investigated. A total of 543 images of the Cwm Idwal moraine–mound complex were captured from a light (< 5 kg) semi-autonomous multi-rotor unmanned aircraft system using a consumer-grade 18 MP compact digital camera. The images were used to produce a DSM (digital surface model) of the moraines. The DSM is in good agreement with 7761 total station survey points providing a total vertical RMSE value of 0.517 m and vertical RMSE values as low as 0.200 m for less densely vegetated areas of the DSM. High-precision topographic data can be acquired rapidly using this technique with the resulting DSMs and orthorectified aerial imagery at sub-decimetre resolutions. Positional errors on the total station dataset, vegetation and steep terrain are identified as the causes of vertical disagreement. Whilst this aerial survey approach is advocated for use in a range of geomorphological settings, care must be taken to ensure that adequate ground control is applied to give a high degree of accuracy.
Tonkin, T.N., Midgley, N.G., Graham, D.G. and Labadz, J.C. (2014). The potential of small unmanned aircraft systems and structure-from-motion for topographic surveys: A test of emerging integrated approaches at Cwm Idwal, North Wales. Geomorphology, 226, pp. 35-43.
Publisher link: http://www.sciencedirect.com/science/article/pii/S0169555X14003857 (subscription required)
Preprint: https://dspace.lboro.ac.uk/2134/19115 (no subscription required)
Abstract: A passive seismology experiment was conducted across the main overdeepening of Storglaciären in the Tarfala valley, northern Sweden, to investigate the spatial and temporal distribution of basal microseismic waveforms in relation to known dynamics of this small polythermal sub-arctic glacier. The high ablation rate made it difficult to keep geophones buried and well coupled to the glacier during the experiment and reduced the number of days of good-quality data collection. The characterization of typical and atypical waveforms showed that the dominant waveforms were from near-surface events such as crevassing. Waveforms resembling basal microseismic signals were very rare, and seldom observed on more than two seismic stations simultaneously. The analysis of waveforms, amplitudes and particle motions suggested a near-field origin for most events. Even though basal sliding is known to occur in the overdeepening, no convincing examples of basal waveforms were detected, suggesting basal microseismic signals are rare or difficult to detect beneath polythermal glaciers like Storglaciären. We discuss the reasons for failing to locate basal signals, consider the origin of common waveforms and make recommendations for setting up passive seismology experiments on glaciers with high ablation rates.
Project supported by a British Society for Geomorphology Research Fund Award (to JAP) and an equipment loan from the UK Natural Environment Research Council (NERC) Geophysical Equipment Facility (GEF Loan 925)
Pomeroy, J., Brisbourne, A., Evans, J. and Graham, D.J. (2013). The search for seismic signatures of movement at the glacier bed in a polythermal valley glacier. Annals of Glaciology, 54(64), pp. 149 – 156.
Publisher link: http://dx.doi.org/10.3189/2013AoG64A203 (subscription required)
Preprint: https://dspace.lboro.ac.uk/2134/13100 (no subscription required; embargoed until March 2014)
- Ground-penetrating radar used to assess Austre Lovénbreen lateral–frontal moraine
- Buried ice forms a component of the lateral–frontal moraine
- Ice within the lateral–frontal moraine likely to be composed of basal glacier ice
- Post-formational deformation has thickened the basal ice sequence
- Evidence found on 1936 oblique aerial imagery of surge front
Abstract: Moraines marking the Neoglacial limits in Svalbard are commonly ice cored. Investigating the nature of this relict ice is important because it can aid our understanding of former glacier dynamics. This paper examines the composition of the lateral–frontal moraine associated with the Neoglacial limit at Austre Lovénbreen and assesses the likely geomorphological evolution. The moraine was investigated using ground-penetrating radar (GPR), with context being provided by structural mapping of the glacier based on an oblique aerial image from 1936 and vertical aerial imagery from 2003. Multiple up-glacier dipping reflectors and syncline structures are found in the GPR surveys. The reflectors are most clearly defined in lateral positions, where the moraine is substantially composed of ice. The frontal area of the moraine is dominantly composed of debris. The core of the lateral part of the moraine is likely to consist of stacked sequences of basal ice that have been deformed by strong longitudinal compression. The long term preservation potential of the ice-dominated lateral moraine is negligible, whereas the preservation of the debris-dominated frontal moraine is high. A glacier surface bulge, identified on the 1936 aerial imagery, provides evidence that Austre Lovénbreen has previously displayed surge activity, although it is highly unlikely to do so in the near future in its current state. This research shows the value of relict buried ice that is preserved in landforms to aiding our understanding of former glacier characteristics.
Midgley, N.G., Cook, S.J., Graham, D.J. and Tonkin, T.N. (2013). Origin, evolution and dynamic context of a Neoglacial lateral–frontal moraine at Austre Lovénbreen, Svalbard. Geomorphology, 198, pp. 96–106.
Publisher link: http://dx.doi.org/10.1016/j.geomorph.2013.05.017 (subscription required)
(no subscription required)
This new book chapter examines how imagery collected from the ground (as opposed to from aerial or satellite platforms) can be used as tools for research into river environments.
Bertoldi, W., Piégay, H., Buffin-Belanger, T., Graham, D.J. and Rice, S. (2012). Applications of Close-Range Imagery in River Research. In Carbonneau, P. and Piégay, H. (eds), Fluvial Remote Sensing for Science and Management. 341-366. Wiley-Blackwell, Chichester.
Publisher link: http://dx.doi.org/10.1002/9781119940791.ch15 (subscription required)
Abstract: Reconstruction of subglacial processes from sedimentological evidence is central to our understanding of glaciological conditions beneath former ice masses. At Svínafellsjökull, southeast Iceland, we assess the extent to which two different processes of basal ice formation (regelation and glaciohydraulic supercooling) can be identified from ice-marginal sediments. Our results indicate that the sedimentary characteristics of deposits produced by these two processes can be distinguished from one another and that it may be possible to recognise evidence of these processes in Quaternary sediments and to reconstruct their spatial pervasiveness. Sediments derived from the melting of regelation basal ice have (i) a massive structure; (ii) a sediment matrix (0 to 10Ф) dominated by coarse sand; and (iii) a higher proportion of angular clasts than supercool basal ice and associated sediments. Sediments derived from “supercool” basal ice (i) can be either massive or layered; (ii) tend to have a silt-dominated matrix; and (iii) contain a slightly higher proportion of rounded and well-rounded clasts than regelation basal ice and sediments. Previous studies indicate that the dominance of silt within supercool basal ice may be unique to this process, and hence, supercooling should leave a readily recognisable signature in the sedimentary record. Our results from Svínafellsjökull lend support to that idea, although we suggest that further work is required to assess whether silt dominance is a process signature diagnostic of supercooling, and in particular, the extent to which subglacial sediment supply determines the sedimentary character of basal ice facies and associated sediments.
Cook, S.J., Graham, D.J., Swift, D.A., Midgley, N.G. and Adam, W.G., 2011. Sedimentary signatures of basal ice formation and their preservation in ice-marginal sediments. Geomorphology, 25 (1), pp.122-131.
Publisher link: http://dx.doi.org/10.1016/j.geomorph.2010.08.018 (subscription required)
Preprint: http://hdl.handle.net/2134/7884 (no subscription required)