Morphology-based landslide monitoring with an unmanned aerial vehicle

PhD ThesisLandslides represent major natural phenomena with often disastrous consequences. Monitoring landslides with time-series surface observations can help mitigate such hazards. Unmanned aerial vehicles (UAVs) employing compact digital cameras, and in conjunction with Structure-from-Motion (SfM) and modern Multi-View Stereo (MVS) image matching approaches, have become commonplace in the geoscience research community. These methods offer a relatively low-cost and flexible solution for many geomorphological applications. The SfM-MVS pipeline has expedited the generation of digital elevation models at high spatio-temporal resolution. Conventionally ground control points (GCPs) are required for co-registration. This task is often expensive and impracticable considering hazardous terrain. This research has developed a strategy for processing UAV visible wavelength imagery that can provide multi-temporal surface morphological information for landslide monitoring, in an attempt to overcome the reliance on GCPs. This morphological-based strategy applies the attribute of curvature in combination with the scale-invariant feature transform algorithm, to generate pseudo GCPs. Openness is applied to extract relatively stable regions whereby pseudo GCPs are selected. Image cross-correlation functions integrated with openness and slope are employed to track landslide motion with subsequent elevation differences and planimetric surface displacements produced. Accuracy assessment evaluates unresolved biases with the aid of benchmark datasets. This approach was tested in the UK, in two sites, first in Sandford with artificial surface change and then in an active landslide at Hollin Hill. In Sandford, the strategy detected a ±0.120 m 3D surface change from three-epoch SfM-MVS products derived from a consumer-grade UAV. For the Hollin Hill landslide six-epoch datasets spanning an eighteen-month duration period were used, providing a ± 0.221 m minimum change. Annual displacement rates of dm-level were estimated with optimal results over winter periods. Levels of accuracy and spatial resolution comparable to previous studies demonstrated the potential of the morphology-based strategy for a time-efficient and cost-effective monitoring at inaccessible areas

Deriving Planetary Surface Characteristics from Orbiting Laser Altimeter Pulse-Widths on: Mars, the Moon, and Earth

A set of equations linking the time-spread of a laser altimeter echo-profile, commonly known as the pulse-width, to the variance of topography within the pulse-footprint are tested by comparing pulse-width data to surface characteristics measured from high-resolution Digital Terrain Models. The research is motivated by the advent of high-resolution Digital Terrain Models over Mars, which enables the calibration of Mars Orbiter Laser Altimeter pulse-widths, and evolves to include lunar and terrestrial data in an attempt to validate the theory and develop new methods. Analysis of Mars Orbiter Laser Altimeter pulse-width data reveals mixed results. Over homo- geneously rough terrain, at kilometre-scales, these pulse-widths show some correlation to surface characteristics, once poor pulse data has been removed. However, where roughness is highly vari- able over short baselines, little correlation is observed, which is attributed to a mix of georeferencing errors and instrument methods. In a similar study, Lunar Orbiter Laser Altimeter pulse-widths are shown to produce only poor correlations with surface characteristics over local study sites. Instead, the observed correlations differ from orbit to orbit, with the majority of those used appearing to contain poor quality pulse- width data - attributed to the instrument methods - and only 14 % revealing correlations similar, or better, than observed over Mars. Finally, an examination of the relationship between footprint-scale surface characteristics and pulse-width estimates derived from smoothed Ice, Cloud, and land Elevation Satellite echo-profiles enables different pulse-width thresholds to be tested. Here, pulse-widths measured using a 10 % Peak Energy threshold are shown to produce greater correlations than those observed using the Mars Orbiter Laser Altimeter and the Lunar Orbiter Laser Altimeter data, which use a Full Width Half Maximum threshold. To conclude, pulse-widths can show strong correlations to surface roughness and slope within the pulse-footprint. However the assumption that detrended surface roughness can be derived by applying a slope contribution effect is shown to be unfounded. The principal recommendation is for future instruments to use a full echo-profile in estimating pulse-width values at a 10 % Peak Energy threshold, providing both efficient noise removal and a better correlated dataset

Field-based measurement of hydrodynamics associated with engineered in-channel structures: the example of fish pass assessment

The construction of fish passes has been a longstanding measure to improve river ecosystem status by ensuring the passability of weirs, dams and other in- channel structures for migratory fish. Many fish passes have a low biological effectiveness because of unsuitable hydrodynamic conditions hindering fish to rapidly detect the pass entrance. There has been a need for techniques to quantify the hydrodynamics surrounding fish pass entrances in order to identify those passes that require enhancement and to improve the design of new passes. This PhD thesis presents the development of a methodology for the rapid, spatially continuous quantification of near-pass hydrodynamics in the field. The methodology involves moving-vessel Acoustic Doppler Current Profiler (ADCP) measurements in order to quantify the 3-dimensional water velocity distribution around fish pass entrances. The approach presented in this thesis is novel because it integrates a set of techniques to make ADCP data robust against errors associated with the environmental conditions near engineered in-channel structures. These techniques provide solutions to (i) ADCP compass errors from magnetic interference, (ii) bias in water velocity data caused by spatial flow heterogeneity, (iii) the accurate ADCP positioning in locales with constrained line of sight to navigation satellites, and (iv) the accurate and cost-effective sensor deployment following pre-defined sampling strategies. The effectiveness and transferability of the methodology were evaluated at three fish pass sites covering conditions of low, medium and high discharge. The methodology outputs enabled a detailed quantitative characterisation of the fish pass attraction flow and its interaction with other hydrodynamic features. The outputs are suitable to formulate novel indicators of hydrodynamic fish pass attractiveness and they revealed the need to refine traditional fish pass design guidelines

Across Space and Time. Papers from the 41st Conference on Computer Applications and Quantitative Methods in Archaeology, Perth, 25-28 March 2013

This volume presents a selection of the best papers presented at the forty-first annual Conference on Computer Applications and Quantitative Methods in Archaeology. The theme for the conference was "Across Space and Time", and the papers explore a multitude of topics related to that concept, including databases, the semantic Web, geographical information systems, data collection and management, and more