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Dive into the research topics where Nicholas G. Midgley is active.

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Featured researches published by Nicholas G. Midgley.


Remote Sensing | 2016

Ground-Control Networks for Image Based Surface Reconstruction: An Investigation of Optimum Survey Designs Using UAV Derived Imagery and Structure-from-Motion Photogrammetry

Toby N. Tonkin; Nicholas G. Midgley

The use of small UAV (Unmanned Aerial Vehicle) and Structure-from-Motion (SfM) with Multi-View Stereopsis (MVS) for acquiring survey datasets is now commonplace, however, aspects of the SfM-MVS workflow require further validation. This work aims to provide guidance for scientists seeking to adopt this aerial survey method by investigating aerial survey data quality in relation to the application of ground control points (GCPs) at a site of undulating topography (Ennerdale, Lake District, UK). Sixteen digital surface models (DSMs) were produced from a UAV survey using a varying number of GCPs (3-101). These DSMs were compared to 530 dGPS spot heights to calculate vertical error. All DSMs produced reasonable surface reconstructions (vertical root-mean-square-error (RMSE) of <0.2 m), however, an improvement in DSM quality was found where four or more GCPs (up to 101 GCPs) were applied, with errors falling to within the suggested point quality range of the survey equipment used for GCP acquisition (e.g., vertical RMSE of <0.09 m). The influence of a poor GCP distribution was also investigated by producing a DSM using an evenly distributed network of GCPs, and comparing it to a DSM produced using a clustered network of GCPs. The results accord with existing findings, where vertical error was found to increase with distance from the GCP cluster. Specifically vertical error and distance to the nearest GCP followed a strong polynomial trend (R2 = 0.792). These findings contribute to our understanding of the sources of error when conducting a UAV-SfM survey and provide guidance on the collection of GCPs. Evidence-driven UAV-SfM survey designs are essential for practitioners seeking reproducible, high quality topographic datasets for detecting surface change.


Geological Society, London, Special Publications | 2000

Moraine-mound formation by englacial thrusting: the Younger Dryas moraines of Cwm Idwal, North Wales

David J. Graham; Nicholas G. Midgley

Abstract The Younger Dryas (c. 11-10 ka bp) moraine-mound complex (‘hummocky moraine’) in the historically important site of Cwm Idwal, North Wales, has previously been interpreted using periglacial, subglacial, ice-marginal and englacial models. In this paper the morphology and sedimentology of these landforms is described and the competing hypotheses tested against this evidence. It is demonstrated that an englacial thrusting model, developed for polythermal glaciers in Svalbard, best fits the available evidence. Thrusting probably resulted from longitudinal compression against a reverse bedrock slope, although a frozen snout, downglacier of sliding ice, may also have been a trigger. It is suggested that the role of ice-deformation, especially thrusting, in landform development has been underestimated, and that the englacial thrusting model may find application in the interpretation of other sites in the palaeo-landform record.


Journal of Glaciology | 2011

Origin and significance of dispersed facies basal ice: Svínafellsjökull, Iceland

Simon J. Cook; Darrel A. Swift; David J. Graham; Nicholas G. Midgley

Dispersed facies basal ice - massive (i.e. structureless) ice with dispersed debris aggregates - is present at the margins of many glaciers and, as a product of internal glacial processes, has the potential to provide important information about the mechanisms of glacier flow and the nature of the subglacial environment. The origin of dispersed facies is poorly understood, with several hypotheses having been advanced for its formation, and there is disagreement as to whether it is largely a sedimentary or a tectonic feature. We test these established hypotheses at the temperate glacier Svinafellsjokull, Iceland, and find that none fully account for dispersed facies characteristics at this location. Instead, dispersed facies physical, sedimentological and stable-isotope (d 18 O, dD) character- istics favour a predominantly tectonic origin that we suggest comprises the regelation and strain- induced metamorphism of debris-rich basal ice that has been entrained into an englacial position by tectonic processes operating at the base of an icefall. Further thickening of the resultant dispersed facies may also occur tectonically as a result of ice flow against the reverse bed slope of a terminal overdeepening. Lack of efficient subglacial drainage in the region of the overdeepening may limit basal melting and thus favour basal ice preservation, including the preservation of dispersed facies. Despite the relatively low sediment content of dispersed facies (� 1.6% by volume), its thickness (up to 25 m) and ubiquity at Svinafellsjokull results in a significant contribution to annual sediment discharge (1635-3270 m 3 a -1 ) that is � 6.5 times that contributed by debris-rich stratified facies basal ice.


Geomorphology | 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

Toby N. Tonkin; Nicholas G. Midgley; David J. Graham; Jillian C. Labadz


Boreas | 2007

'A test of the englacial thrusting hypothesis of "hummocky" moraine formation: case studies from the northwest Highlands, Scotland': Comments

David J. Graham; Matthew R. Bennett; Neil F. Glasser; Michael J. Hambrey; David Huddart; Nicholas G. Midgley


Geomorphology | 2016

Ice-cored moraine degradation mapped and quantified using an unmanned aerial vehicle: a case study from a polythermal glacier in Svalbard

Toby N. Tonkin; Nicholas G. Midgley; Simon J. Cook; David J. Graham


Geomorphology | 2013

Origin, evolution and dynamic context of a Neoglacial lateral-frontal moraine at Austre Lovenbreen, Svalbard

Nicholas G. Midgley; Simon J. Cook; David J. Graham; Toby N. Tonkin


Geomorphology | 2011

Sedimentary signatures of basal ice formation and their preservation in ice-marginal sediments

Simon J. Cook; David J. Graham; Darrel A. Swift; Nicholas G. Midgley; William G. Adam


Geomorphology | 2017

Reconstruction of former glacier surface topography from archive oblique aerial images

Nicholas G. Midgley; Toby N. Tonkin


Archive | 2009

Sedimentology, Structural Characteristics and Morphology of a Neoglacial High‐Arctic Moraine‐Mound Complex: Midre Lovénbreen, Svalbard

Nicholas G. Midgley; Neil F. Glasser; Michael J. Hambrey

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Toby N. Tonkin

Nottingham Trent University

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Simon J. Cook

Manchester Metropolitan University

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Jillian C. Labadz

Nottingham Trent University

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David Huddart

Liverpool John Moores University

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