Miocic, Johannes M.Sah, RituChawchai, SakonvanSurakiatchai, Peerasit...
18页
查看更多>>摘要：The development of coastal dunes is linked to environmental controls such as sea-level variability, climatic conditions, and coastal morphology. Understanding the spatial and temporal variations of dunes is crucial for predicting how coastal landscapes may react to future climate changes and sea-level rise. However, there are very few detailed studies on the longer time-scale evolution (centennial to millennial) of coastal dunes from subtropical and tropical regions. Here, we combine a high-resolution luminescence chronology with sedimentological analyses to study the depositional history of a transverse coastal dune located within the Bang Berd dune field, Western Gulf of Thailand. While luminescence dating of uniform aeolian deposits is normally straight forward, we observe strong variations in the natural dose rate which are likely explained by the enrichment of accessory minerals in some laminae. Deposition of the dune started at least around 3000 years ago and coincides with a regional sea level drop. Sedimentary structures indicate deposition occurring predominantly in relation to the northeasterly winter monsoon. As the sea-level rise and increased storm intensity in the future may lead to stronger erosion along the coast, this study is highlighting the importance of the Bang Berd dune system as natural protection against coastal inundation.
Smyth, A. G. ThomasWilson, RyanRooney, PaulYates, L. Katherine...
11页
查看更多>>摘要：Vegetation cover on coastal sand dunes has been increasing worldwide since at least the 1940s. Analysis of aerial and satellite imagery has been the principal source used to measure this change, however no studies have systematically evaluated the accuracy of remotely sensed estimates. Using established land cover classification methods and in-situ field measurements, we show that both the extent and accuracy of remotely sensed areas of bare sand and vegetation in dunes varies with image resolution and classification method. We found that supervised methods of classification (semi-automatic), whilst mapping a greater extent of bare sand and being more accurate than manual digitisation, had poor repeatability, exhibiting a relatively large range of bare sand and vegetation extent between classifications replicated under the same conditions. In contrast, areas of bare sand and vegetation classified by manual digitisation had high repeatability but a relatively low percentage of observed agreement with data collected in the field. For all classification methods, observed agreement with field data generally increased with image resolution. Our results demonstrate that users of land classification data in dunes should be cautious when interpreting trends of bare sand and vegetation cover due to substantial repeatability error in supervised classification methods, and relatively poor observed agreement with field data of manual classification. We recommend that analysis of bare sand and vegetation cover in dunes should be based on multiple replicates using supervised classification, employing the highest resolution imagery available and that all results presented should also include the range measured by multiple replicates.
查看更多>>摘要：The aim of this study was to describe the constructive details of a new collector called Mendezs Trap (MT) and to compare its performance with the Big Spring Number Eight (BSNE) and Modified Wilson and Cook (MWAC). A detailed description of the MT with dimensions, schemes, and photos is included in the paper. To evaluate the performance of the MT, eleven wind erosion events were measured with MT, BSNE, and MWAC installed at 22.5, 43, 63, 112, and 164 cm height on a loamy sand soil without cover and roughness. The material collected was weighed and divided by the inlet area to obtain the horizontal mass flux (HMF). Results showed that the HMF measured with MT is strongly correlated to the HMF measured with BSNE and MWAC. Relative efficiencies (slope of the regression curve between HMF of different samplers) showed that MT is 31.83% more efficient than BSNE and that MWAC is 81.37% more efficient than MT. Different relative efficiencies were measured at different heights, but no relationships between the relative efficiency and height were found. The average amounts of material collected were the highest at 22.5 cm height (1.74 g for MT) and the lowest at 164 cm height (0.03 for MWAC). At all heights, the amounts of sediments collected were ordered in the sequence MT > BSNE > MWAC. Percentages of samples weighing more than 0.1 g, 0.2 g, 0.3 g, 0.4 g, 0.5 g were ordered in the sequence MT > BSNE > MWA. Field evaluation showed that, the HMF measured with MT, BSNE, and MWAC can be compared, and MT can be used in wind erosion studies. MT collects more amounts of material than MWACs and BSNEs, which is especially important at greater heights where little amounts of material are normally collected. The results of this study must be confirmed in soils of other texture classes and the role of the particle size and wind speed in the efficiency of the MT must be measured in wind tunnel.
van der Merwe, BarendPillay, NelishiaCoetzee, Serena
16页
查看更多>>摘要：Barchan morphometric data have been used as proxies of meteorological and topographical data in environments where this data is lacking (such as other planetary bodies), gaining insights into barchan dune field dynamics such as barchan collision and sediment dynamics, and estimating migration speeds. However, manual extraction of this data is time-consuming which can impose limits on the spatial extent and temporal frequencies of observations. Combining remotely sensed big data with automated processing techniques such as convolutional neural networks (CNNs) can therefore increase the amount of data on barchan morphology. However, such techniques have not yet been applied to barchans and their efficacy remains unknown. This study addresses this issue by evaluating the classification performance (using the ACC, F 1 -score and MCC metrics) of CNNs on several different morphometric tasks: the side of horn elongation, the magnitude of elongation, the barchans a/c ratio, and a new metric, bilateral asymmetry, which takes a more holistic view of barchan asymmetry. Specifically, bilateral asymmetry offers a means by which the total points of variation on a barchan that is used in describing barchan morphology, can be expressed with a single measure. Twelve different CNN architectures, each with different hyperparameters, are trained and tested on a sample of 90 barchan dunes. Additionally, the potential of transfer learning is assessed using the VGG16 and ResNet50 architectures. The results show that the accuracy of the CNNs can exceed 80% in some cases and that "from scratch" CNNs can match the performance obtained using transfer learning approaches.
查看更多>>摘要：Snow drift which usually occurs in conjunction with snowfall can significantly alter the distribution pattern of snow cover around roads creating travel hazards for vehicles. To study the snow distribution around a road and evaluate the snow prevention efficiency of snow fence, based on the theories of two-phase flow and snowdrift erosion and deposition, a numerical model is developed. The model includes snowfall during snow drift, spatial distribution characteristics of wind speed and snow phase volume fraction, and dynamic changes of snow drift shape on the ground during drifting. We simulate the distribution characteristics of snowdrift around an embankment without and with the protection of a snow fence and under the conditions of no snowfall and snowfall. The results indicate that snow deposition is greatest on the leeward side of the embankment in comparison to the windward side of the embankment and takes a longer time to reach equilibrium. On the leeward side of the embankment, the snow accumulation rate under the condition of snow falling is higher than that under the condition of no snow falling. Nonetheless, the two conditions both suggest that installation of the snow fence intercepts a large amount of snow behind the snow fence, decreases the snow phase volume fraction near the ground, and reduces the snowdrift accumulation on the leeward side of the embankment within a certain period.
NSTL
Elsevier