John Barlow

High spatial resolution satellite imagery, DEM derivatives, and image segmentation for the detection of mass wasting processes

An automated approach to identifying landslides using a combination of high-resolution satellite imagery and digital elevation derivatives is offered as an alternative to aerial photographic interpretation. Previous research has demonstrated that per pixel spectral response patterns are ineffective in discriminating mass movements. This technique utilizes image segmentation and digital elevation data in order to identify mass movements based not only on their reflectance but also on their shape properties and their geomorphic context. Dividing the classification by process into debris slides, debris flows, and rock slides makes the method far more useful than methods that group all mass movements together. A hierarchical classification scheme is utilized to eliminate areas that are not of interest and to identify areas where mass movements are probable. A supervised classification is then conducted using spectral, shape, and textural properties to identify failures that were greater than 1 ha in area. The resulting accuracy was 90 percent for debris slides, 60 percent for debris flows, and 80 percent for rock slides.

Mapping changing temperature patterns over a glacial moraine using oblique thermal imagery and lidar

Due to access difficulties in active alpine moraine environments, it can be challenging to accurately map and quantify debris cover and ice-core extent. To aid in identifying the presence and extent of ice-cored moraine, a non-invasive method of mapping spatial and temporal moraine temperature patterns using a light detection and ranging (lidar) digital elevation model (DEM) and sequences of oblique thermal imagery was evaluated. A procedure of lidar DEM-based orthorectification of thermal images collected through time from different locations enabled maps of temperature change to be generated and thermal signatures plotted. Although no exposed ice was visible on the moraine slope studied, the presence of shallow ice core beneath the debris-covered surface was inferred in areas of cooler temperatures during daylight solar heating and rapid thermal decay after sunset. It is presumed that this apparent increased heat loss in some areas of the moraine is being used to drive internal melt processes. It is believed that such temporal thermal imaging at high repetition frequency will aid in remotely mapping the presence of buried ice and, with the combination of energy balance data and further field validation, could enable the estimation of debris cover depth.

Kinematic analysis of sea cliff stability using UAV photogrammetry

ABSTRACT Erosion and slope instability poses a significant hazard to communities and infrastructure located in coastal areas. We use point cloud and spectral data derived from close-range digital photogrammetry to perform a kinematic analysis of chalk sea cliffs located at Telscombe, UK. Our data were captured from an unmanned aerial vehicle (UAV) and cover a cliff face that is about 750 m long and ranges from 20 to 49 m in height. The resulting point clouds had an average density of 354 points m−2. The models fitted our ground control network within a standard error of 0.03 m. Structural features such as joints, bedding planes, and faults were manually mapped and are consistent with results from other studies that have been conducted using direct measurement in the field. These data were then used to assess differing modes of failure at the site. Our results indicate that wedge failure is by far the most likely mode of slope instability. A large wedge failure occurred at the site during the period of study supporting our analysis. Volumetric analysis of this failure through a comparison of sequential models indicates a failure volume of about 160 m3. Our results show that data capture through UAV photogrammetry can provide a useful basis for slope stability analysis over long sections of coast. This technology offers significant benefits in equipment costs and field time over existing methods.

Evaluating debris slide occurrence using digital data: paraglacial activity in Chilliwack Valley, British Columbia

Debris sliding is one of the most important processes acting to transport sediment within mountainous regions. Detailed study of debris slide activity at the basin scale typically involves landslide inventories generated from aerial photographs. However, it has been shown that some types of rapid mass movement can be accurately identified using a combination of high-resolution satellite imagery and digital elevation data. This approach is beneficial as the digital products allow for a more accurate and efficient data throughput into various types of geomorphic analysis. Here, we demonstrate the use of an automated inventory in the geomorphometric evaluation of debris slide initiation for the Chilliwack Basin, British Columbia, Canada. Our results indicate that the occurrence of debris sliding is primarily determined by topographical controls. For basins that are in equilibrium with the existing climate, the frequency of debris sliding should demonstrate a strong relationship to bedrock geology as the production of unconsolidated materials available for failure is a function of weathering rates under these conditions. The lack of bedrock control within the Chilliwack Basin suggests a state of paraglacial relaxation, wherein glacial deposits dominate the sediment cascade within the area. Therefore, topographic parameters can be used to discriminate the location of metastable slopes where debris slide erosion will be active. The use of digital data in the characterization of debris slide occurrence would seem to be a viable alternative to the more traditional methods.

Mapping snow avalanche chutes in the Canadian Rockies using Landsat TM and DEM data

Snow avalanches are a common occurrence within the Canadian Rockies. Such features result in a distinctive biogeographic response that can be associated with characteristic land cover patterns. These patterns are most visible when avalanches penetrate through mature forest stands, leaving a narrow track of open ground aligned parallel to the fall line. The recurrence of avalanches in the same location perpetuates the disruption of the forest canopy, leaving more avalanche-resistant shrubs and herbs to colonize these areas. To date, no reliable method to map snow avalanche features using satellite sensor data has been reported. The use of image segmentation and digital elevation model (DEM) derivatives provides a solution to this shortcoming. Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) data covering areas in the Canadian Rockies are used in conjunction with specific geomorphometry and image segmentation to isolate image objects that conform to the geomorphic and spectral characteristics consistent with avalanche tracks. Accuracy assessment using a database derived from manual inspection of stereo aerial photographs indicates approximately 80% accuracy for both errors of omission and errors of commission.

Mapping Hazardous Slope Processes Using Digital Data

The use of satellite sensor data can be used to detect discrete slope processes and landforms with a high degree of accuracy. Whereas previous attempts to classify slope features using per pixel spectral response patterns have provided classification accuracies that are less than 60%, it is demonstrated that a combination of high resolution optical imagery, image segmentation and ancillary data derived from a digital elevation model can discriminate some types of mass wasting processes with accuracies of 80% or higher. The spatial resolution of the imagery is critical to the successful classification of such features both in terms of information derived from textural analysis and in the ability to successfully segment landslide features. Furthermore, the data generated in this manner can be used for geomorphic research in terms of characterizing the occurrence of mass wasting within the bounds of the image scene.

Morphological Controls on Submarine Slab Failures

An understanding of submarine mass movements is of great importance to the hydrocarbon industry due to the risk they pose to sea floor infrastructure. Technological developments in deepwater surveying methods have produced datasets of the sea floor that rival the best terrestrial ones; however, the study of submarine mass movements remains poorly-developed. Multivariate statistical analysis has a well-established track record for producing quantitative estimates of associated risk for terrestrial landslides and given the often homogenous nature of sea floor sediments, a morphological control on mass movements seems viable. In this study, we perform a statistical analysis on an inventory of shallow slab slides in the West Nile Delta to identify morphometric controls on failure. We find that slopes with planar plan curvature and slope angles <6° account for approximately 95 % of observed landslides and that, beyond this, increasing plan concavity stabilises submarine slopes. This presents a foundation to ultimately reconcile geomorphological observation with geotechnical modelling, and provide additional insight on the controls on submarine instability.

Marine control over negative power law scaling of mass wasting events in chalk sea cliffs with implications for future recession under the UKCP09 medium emission scenario: Marine control over negative power law scaling of cliff erosion

Coastal cliff erosion represents a significant geohazard for people and infrastructure. Forecasting future erosion rates is therefore of critical importance to ensuring the resiliency of coastal communities. We use high precision monitoring of chalk cliffs at Telscombe, UK to generate monthly mass movement inventories between August 2016 and July 2017. Frequency-magnitude analysis of our inventories demonstrate negative power law scaling over 7 orders of magnitude and, for the first time, we report statistically significant correlations between significant wave height (Hs) and power law scaling coefficients (r2 values of 0.497 and 0.590 for β and s respectively). Applying these relationships allows for a quantitative method to predict erosion at the site based on Hs probabilities and sea level forecasts derived from the UKCP09 medium emission climate model (A1B). Monte-Carlo simulations indicate a range of possible erosion scenarios over 70 years (2020-2090) and we assess the impact these may have on the A259 coastal road which runs proximal to the cliffs. Results indicate a small acceleration in erosion compared to those based on current conditions with the most likely scenario at the site being 21.7 m of cliff recession by 2090. However, low-probability events can result in recession an order of magnitude higher in some scenarios. In the absence of negative feedbacks, we estimate an ~11% chance that the A259 will be breached by coastal erosion by 2090.