Aerial image capture has become very common within the geosciences due to the increasing affordability of low-payload (<20 kg) unmanned aerial vehicles (UAVs) for consumer markets. Their application ...to surveying has subsequently led to many studies being undertaken using UAV imagery and derived products as primary data sources. However, image quality and the principles of image capture are seldom given rigorous discussion. In this contribution we firstly revisit the underpinning concepts behind image capture, from which the requirements for acquiring sharp, well-exposed and suitable image data are derived. Secondly, the platform, camera, lens and imaging settings relevant to image quality planning are discussed, with worked examples to guide users through the process of considering the factors required for capturing high-quality imagery for geoscience investigations.
Given a target feature size and ground sample distance based on mission objectives, the flight height and velocity should be calculated to ensure motion blur is kept to a minimum. We recommend using a camera with as large a sensor as is permissible for the aerial platform being used (to maximise sensor sensitivity), effective focal lengths of 24–35 mm (to minimise errors due to lens distortion) and optimising ISO (to ensure the shutter speed is fast enough to minimise motion blur). Finally, we give recommendations for the reporting of results by researchers in order to help improve the confidence in, and reusability of, surveys through providing open access imagery where possible, presenting example images and excerpts and detailing appropriate metadata to rigorously describe the image capture process.
This contribution reviews the use of modern 3D photo-based surface reconstruction techniques for high fidelity surveys of trenches, rock exposures and hand specimens to highlight their potential for ...paleoseismology and structural geology. We outline the general approach to data acquisition and processing using ground-based photographs acquired from standard DSLR cameras, and illustrate the use of similar processing approaches on imagery from Unmanned Aerial Vehicles (UAVs). It is shown that digital map and trench data can be acquired at ultra-high resolution and in much shorter time intervals than would be normally achievable through conventional grid mapping. The resulting point clouds and textured models are inherently multidimensional (x, y, z, point orientation, colour, texture), archival and easily transformed into orthorectified photomosaics or digital elevation models (DEMs). We provide some examples for the use of such techniques in structural geology and paleoseismology while pointing the interested reader to free and commercial software packages for data processing, visualization and 3D interpretation. Photogrammetric models serve to act as an ideal electronic repository for critical outcrops and observations, similar to the electronic lab book approach employed in the biosciences. This paper also highlights future possibilities for rapid semi-automatic to automatic interpretation of the data and advances in technology.
•We review the methods and applications of photo-based 3D reconstruction techniques.•Unconstrained photographs used for high-resolution surveying similar to LiDAR.•We provide example applications to studies in structural geology and paleoseismology.•Ability to automate analyses and extract structural data from reconstructions.•High-fidelity, photo-realistic 3D archive of specimens and field exposures.
In June 2011, an eruption of rhyolite magma began at the Puyehue–Cordón Caulle volcanic complex, southern Chile. By January 2012, explosive activity had declined from sustained pyroclastic (Plinian ...to sub-Plinian) fountaining to mixed gas and ash jetting punctuated by Vulcanian blasts. This explosive activity was accompanied by synchronous effusion of obsidian lava in a hybrid explosive–effusive eruption. Fortuitous climatic conditions permitted ground-based observation and video recording of transient vent dynamics as well as real-time collection of proximal juvenile ash as it sedimented from the active plume. The main eruptive vent complex and site of lava effusion were represented by two loci of Vulcanian blasts within a single tephra cone containing a pancake-shaped proto-lava dome. These blast loci each consisted of clusters of sub-vents that expressed correlated shifts in eruption intensity, indicating the presence of partially connected and/or branching zones of high permeability within the upper conduit. Pyroclast textures were examined by X-ray computed microtomography and their permeability was modelled by lattice Boltzmann simulations. The porosity (39 to 67%) and Darcian permeability (3.1×10−15m2 perpendicular to fabric to 3.8×10−11m2 parallel to fabric) of fine ash emitted during ash jetting indicate that the permeable zones comprised highly sheared, tube-like bubbly magma, and contrast with the low porosity (~17%) and nul permeability of bombs ejected to hundreds of metres from the vent in Vulcanian blasts. Residual H2O content of ash (0.14wt.%) and two bombs (0.2–0.25wt.%), determined by Karl–Fischer titration indicate degassing of this pyroclastic material to near-atmospheric pressures. Ash textures and simple degassing/vesiculation models indicate the onset of permeability by ductile processes of shear-enhanced bubble coalescence in the upper 1 to 1.5km of the conduit. Repeated ash jetting and Vulcanian blasts indicate that such ductile processes were not sufficiently effective to accommodate all degassing requirements, and additional brittle (e.g., fragmentation) events transiently assisted in maintaining an open-system degassing regime that permitted long-lived, hybrid explosive–effusive activity. The eruption at Cordón Caulle has provided an excellent opportunity to closely observe key processes of silicic volcanism.
•Direct observations of a rhyolite eruption•Observation of hybrid explosive–effusive activity•Pyroclast textures in 3-D linked directly to observed eruption dynamics•Both ductile and brittle processes of permeability development drive effusive silicic volcanism.
With the increasing role that unmanned aerial systems (UAS) are playing in data collection for environmental studies, two key challenges relate to harmonizing and providing standardized guidance for ...data collection, and also establishing protocols that are applicable across a broad range of environments and conditions. In this context, a network of scientists are cooperating within the framework of the Harmonious Project to develop and promote harmonized mapping strategies and disseminate operational guidance to ensure best practice for data collection and interpretation. The culmination of these efforts is summarized in the present manuscript. Through this synthesis study, we identify the many interdependencies of each step in the collection and processing chain, and outline approaches to formalize and ensure a successful workflow and product development. Given the number of environmental conditions, constraints, and variables that could possibly be explored from UAS platforms, it is impractical to provide protocols that can be applied universally under all scenarios. However, it is possible to collate and systematically order the fragmented knowledge on UAS collection and analysis to identify the best practices that can best ensure the streamlined and rigorous development of scientific products.
Supraglacial lake drainage events influence Greenland Ice Sheet dynamics on hourly to interannual timescales. However, direct observations are rare, and, to date, no in situ studies exist from ...fast-flowing sectors of the ice sheet. Here, we present observations of a rapid lake drainage event at Store Glacier, west Greenland, in 2018. The drainage event transported 4.8 × 10⁶ m³ of meltwater to the glacier bed in ∼5 h, reducing the lake to a third of its original volume. During drainage, the local ice surface rose by 0.55 m, and surface velocity increased from 2.0 m·d−1 to 5.3 m·d−1. Dynamic responses were greatest ∼4 km downstream from the lake, which we interpret as an area of transient water storage constrained by basal topography. Drainage initiated, without any precursory trigger, when the lake expanded and reactivated a preexisting fracture that had been responsible for a drainage event 1 y earlier. Since formation, this fracture had advected ∼500 m from the lake’s deepest point, meaning the lake did not fully drain. Partial drainage events have previously been assumed to occur slowly via lake overtopping, with a comparatively small dynamic influence. In contrast, our findings show that partial drainage events can be caused by hydrofracture, producing new hydrological connections that continue to concentrate the supply of surface meltwater to the bed of the ice sheet throughout the melt season. Our findings therefore indicate that the quantity and resultant dynamic influence of rapid lake drainages are likely being underestimated.
PDF
