Testing the utility of structure‐from‐motion photogrammetry reconstructions using small unmanned aerial vehicles and ground photography to estimate the extent of upland soil erosion   总被引：1，自引：0，他引：1       下载免费PDF全文

Miriam Glendell  Gareth McShane  Luke Farrow  Mike R. James  John Quinton  Karen Anderson  Martin Evans  Pia Benaud  Barry Rawlins  David Morgan  Lee Jones  Matthew Kirkham  Leon DeBell  Timothy A. Quine  Murray Lark  Jane Rickson  Richard E. Brazier 《地球表面变化过程与地形》2017,42(12):1860-1871

Quantifying the extent of soil erosion at a fine spatial resolution can be time consuming and costly; however, proximal remote sensing approaches to collect topographic data present an emerging alternative for quantifying soil volumes lost via erosion. Herein we compare terrestrial laser scanning (TLS), and both unmanned aerial vehicle (UAV) and ground photography (GP) structure‐from‐motion (SfM) derived topography. We compare the cost‐effectiveness and accuracy of both SfM techniques to TLS for erosion gully surveying in upland landscapes, treating TLS as a benchmark. Further, we quantify volumetric soil loss estimates from upland gullies using digital surface models derived by each technique and subtracted from an interpolated pre‐erosion surface. Soil loss estimates from UAV and GP SfM reconstructions were comparable to those from TLS, whereby the slopes of the relationship between all three techniques were not significantly different from 1:1 line. Only for the TLS to GP comparison was the intercept significantly different from zero, showing that GP is more capable of measuring the volumes of very small erosion features. In terms of cost‐effectiveness in data collection and processing time, both UAV and GP were comparable with the TLS on a per‐site basis (13.4 and 8.2 person‐hours versus 13.4 for TLS); however, GP was less suitable for surveying larger areas (127 person‐hours per ha^?1 versus 4.5 for UAV and 3.9 for TLS). Annual repeat surveys using GP were capable of detecting mean vertical erosion change on peaty soils. These first published estimates of whole gully erosion rates (0.077 m a^?1) suggest that combined erosion rates on gully floors and walls are around three times the value of previous estimates, which largely characterize wind and rainsplash erosion of gully walls. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Shock metamorphism in plagioclase and selective amorphization     

Lidia Pittarello  Luke Daly  Annemarie E. PickersgilL  Ludovic Ferrire  Martin R. Lee 《Meteoritics & planetary science》2020,55(5):1103-1115

Plagioclase feldspar is one of the most common rock‐forming minerals on the surfaces of the Earth and other terrestrial planetary bodies, where it has been exposed to the ubiquitous process of hypervelocity impact. However, the response of plagioclase to shock metamorphism remains poorly understood. In particular, constraining the initiation and progression of shock‐induced amorphization in plagioclase (i.e., conversion to diaplectic glass) would improve our knowledge of how shock progressively deforms plagioclase. In turn, this information would enable plagioclase to be used to evaluate the shock stage of meteorites and terrestrial impactites, whenever they lack traditionally used shock indicator minerals, such as olivine and quartz. Here, we report on an electron backscatter diffraction (EBSD) study of shocked plagioclase grains in a metagranite shatter cone from the central uplift of the Manicouagan impact structure, Canada. Our study suggests that, in plagioclase, shock amorphization is initially localized either within pre‐existing twins or along lamellae, with similar characteristics to planar deformation features (PDFs) but that resemble twins in their periodicity. These lamellae likely represent specific crystallographic planes that undergo preferential structural failure under shock conditions. The orientation of preexisting twin sets that are preferentially amorphized and that of amorphous lamellae is likely favorable with respect to scattering of the local shock wave and corresponds to the “weakest” orientation for a specific shock pressure value. This observation supports a universal formation mechanism for PDFs in silicate minerals.  相似文献   

Identification and classification of geographically isolated wetlands in North Alabama using geographic object based image analysis (GeOBIA)     

Tyler Jones  Luke Marzen  Chandana Mitra  Michael Barbour 《国际地球制图》2019,34(7):769-784

Due to recent Supreme Court rulings, there has been an increased interest in the isolated wetlands of the United States. These types of wetlands serve vital ecological roles such as water quality regulation and as a habitat of biological diversity. This study focuses specifically on mapping of geographically isolated wetlands, or those that are separated from traditional wetlands by a given spatial extent, using Geographic Object-Based Image Analysis (GeOBIA). GeOBIA is a type of remote sensing analysis that identifies objects and features in data-sets via automated methodologies. This type of analysis offers the opportunity to increase the efficiency of what has traditionally been a very labour intensive process of manual photo-interpretation. This analysis resulted in the delineation of 26,424 areas as geographically isolated wetlands. These results were assessed for accuracy through both manual inspection of aerial imagery and field verification which yielded accuracies of 83.7 and 87.7%, respectively.  相似文献   

Simulated response of an intermittent stream to rainfall frequency patterns     

Ali Azarnivand  Matteo Camporese  Sina Alaghmand  Edoardo Daly 《水文研究》2020,34(3):615-632

The response of intermittent catchments to rainfall is complex and difficult to model. This study uses the spatially distributed CATchment HYdrology (CATHY) model to explore how the frequency of daily rainfall (λ) can affect the hydrologic regime of intermittent catchments. After a multi-objective calibration and validation of CATHY against experimental measurements of streamflow and groundwater levels in a catchment used as a pasture, the role of λ in affecting streamflow characteristics was explored using different scenarios. With different values of λ for the dry and wet periods of the year, CATHY showed that a series of frequent rainfall events was often associated with incipient streamflow, independent of the season. Activation of streamflow during the wet season was related to multiple factors and was not often associated with the shallow groundwater levels near the outlet of the catchment. The interplay between rainfall depth and intensity acted as the most important factor for the generation of streamflow. Using the difference between accumulated rainfall and evapotranspiration as a measure of wetness, saturated subsurface flow mechanism generated streamflow in simulations with wetness at least three times larger than mean wetness of other simulations. Although groundwater uprise near the outlet did not effectively contribute to streamflow in the initial days of flow, it strongly correlated with the magnitude of the runoff coefficient. Values of λ close or equal to the maximum value in the wet season can sustain the connectivity between groundwater and streamflow in the riparian zone. This connectivity increases the catchment wetness, which consequently results in an increase of the generated streamflow. Our study showed that rainfall regimes characterized by different λ were able to identify distinct flow regimes typical of either intermittent, ephemeral, or nonflowing catchments. Decrease of λ in the wet season is likely associated with a reduction of streamflow, with a shift of flow regime from intermittent to ephemeral or no-flow.  相似文献   

Effects of differential hillslope‐scale water retention characteristics on rainfall–runoff response at the Landscape Evolution Observatory          下载免费PDF全文

Peter A. Troch  Martijn J. Booij  Guo‐Yue Niu  Till H.M. Volkmann  Luke A. Pangle 《水文研究》2018,32(13):2118-2127

Hillslopes turn precipitation into runoff and thus exert important controls on various Earth system processes. It remains difficult to collect reliable data necessary for understanding and modeling these Earth system processes in real catchments. To overcome this problem, controlled experiments are being conducted at the Landscape Evolution Observatory at Biosphere 2, The University of Arizona. Previous experiments have revealed differences in hydrological response between 2 landscapes within Landscape Evolution Observatory, even though both landscapes were designed to be identical. In an attempt to discover where the observed differences stem from, we use a fully 3‐dimensional hydrological model (CATchment HYdrology) to show the effect of soil water retention characteristics and saturated hydraulic conductivity on the hydrological response of these 2 hillslopes. We also show that soil water retention characteristics can be derived at hillslope scale from experimental observations of soil moisture and matric potential. It is found that differences in soil packing between the 2 landscapes may be responsible for the observed differences in hydrological response. This modeling study also suggests that soil water retention characteristics and saturated hydraulic conductivity have a profound effect on rainfall–runoff processes at hillslope scale and that parametrization of a single hillslope may be a promising step in modeling rainfall–runoff response in real catchments.  相似文献   

Conceptualising the Migration–Food Security Nexus: Lessons from Nepal and Vanuatu     

Luke K. Craven  Hom N. Gartaula 《The Australian geographer》2015,46(4):455-471

In the past decade, international development practitioners have increasingly argued that migration improves the food security of households at origin, by providing the capital necessary for agricultural intensification or food purchase. These debates have occurred largely in isolation from a discussion of the values that underpin food production and consumption in the communities that migrants call home. We question the assumption that a shift from an agricultural-based economy to an economy based on remittances increases the ability of communities to secure access to food in the face of rapid economic and cultural change. In this paper, we present two independently conducted studies from Nepal and Vanuatu that investigate the impact of out-migration on local perceptions of agricultural and residential land and the meaning given to food security. Our data reveal that the value changes associated with large-scale out-migration have the potential to make the agricultural sector at origin more vulnerable, unproductive, unsustainable or unattractive, leaving a longer-term impact on food security. We offer some reflections on the implications of these findings for the structure of the migration–food security nexus.  相似文献   

A stochastic model describing the impact of daily rainfall depth distribution on the soil water balance     

Parikshit Verma  James YeatesEdoardo Daly 《Advances in water resources》2011,34(8):1039-1048

Simplified, vertically-averaged soil moisture models have been widely used to describe and study eco-hydrological processes in water-limited ecosystems. The principal aim of these models is to understand how the main physical and biological processes linking soil, vegetation, and climate impact on the statistical properties of soil moisture. A key component of these models is the stochastic nature of daily rainfall, which is mathematically described as a compound Poisson process with daily rainfall amounts drawn from an exponential distribution. Since measurements show that the exponential distribution is often not the best candidate to fit daily rainfall, we compare the soil moisture probability density functions obtained from a soil water balance model with daily rainfall depths assumed to be distributed as exponential, mixed-exponential, and gamma. This model with different daily rainfall distributions is applied to a catchment in New South Wales, Australia, in order to show that the estimation of the seasonal statistics of soil moisture might be improved when using the distribution that better fits daily rainfall data. This study also shows that the choice of the daily rainfall distributions might considerably affect the estimation of vegetation water-stress, leakage and runoff occurrence, and the whole water balance.  相似文献   

Evidence for coelacanths in the Late Triassic (Rhaetian) of England     

Luke M. Hauser  David M. Martill 《Proceedings of the Geologists' Association. Geologists' Association》2013

The right gular plate of an indeterminate coelacanth from the Westbury Formation (Upper Triassic, Rhaetian) of Blue Anchor Point, Somerset, southwest England is reported. This occurrence represents the first convincing evidence of coelacanths from the Triassic of the United Kingdom. The new specimen suggests a fish of approximately 0.61 m length.  相似文献   

Near-infrared spectroscopy of (proto)-planetary nebulae: molecular hydrogen excitation as an evolutionary tracer     

Christopher J. Davis  Michael D. Smith  Luke Stern  Thomas H. Kerr  Jean E. Chiar 《Monthly notices of the Royal Astronomical Society》2003,344(1):262-282

We present an in-depth analysis of molecular excitation in 11 H₂-bright planetary and protoplanetary nebulae (PN and PPN). From newly acquired K -band observations, we extract a number of spectra at positions across each source. H₂ line intensities are plotted on 'column density ratio' diagrams so that we may examine the excitation in and across each region. To achieve this, we combine the shock models of Smith, Khanzadyan & Davis with the photodissociation region (PDR) models of Black & van Dishoeck to yield a shock-plus-fluorescence fit to each data set.
Although the combined shock + fluorescence model is needed to explain the low- and high-energy H₂ lines in most of the sources observed (fluorescence accounts for much of the emission from the higher-energy H₂ lines), the relative importance of shocks over fluorescence does seem to change with evolutionary status. We find that shock excitation may well be the dominant excitation mechanism in the least evolved PPN (CRL 2688 – in both the bipolar lobes and in the equatorial plane) and in the most evolved PN considered (NGC 7048). Fluorescence, on the other hand, becomes more important at intermediate evolutionary stages (i.e. in 'young' PN), particularly in the inner core regions and along the inner edges of the expanding post-asymptotic giant branch (AGB) envelope. Since H₂ line emission seems to be produced in almost all stages of post-AGB evolution, H₂ excitation may prove to be a useful probe of the evolutionary status of PPN and PN alike. Moreover, shocks may play an important role in the molecular gas excitation in (P)PN, in addition to the low- and/or high-density fluorescence usually attributed to the excitation in these sources.  相似文献   

Site response zones and short-period earthquake ground motion projections for the Las Vegas Basin     

Barbara Luke  Ying Liu 《Journal of Earth System Science》2008,117(2):757-772

A deterministic seismic hazard analysis was conducted to address the effect of local soil conditions on earthquake-induced strong ground motion in the Las Vegas Basin, Nevada (US). Using a large geological and geotechnical database, two response units were defined: a fine-grained unit, predominantly clay; and a coarse-grained unit, predominantly gravel. A moderate number of high-quality shallow shear wave velocity measurements were collected from which characteristic shear wave velocity profiles were developed for each response unit. An equivalent-linear one-dimensional site response model was used. The model was calibrated using a basin-wide, small-strain ground motion database. Calibration tests showed that ground motion projections become increasingly conservative with increasing ground-motion amplitude. Projections were overconservative for the coarse-grained response unit, likely due to the sparseness of the velocity database. For the earthquake response analyses, historical ground motions were used to model characteristic ‘bedrock’ motion for earthquakes on 10 faults judged to be critical. Response spectral envelopes were generated for each unit through Monte-Carlo simulations. For the fine-grained response unit, 95th percentile peak ground acceleration, peak spectral acceleration and predominant period were 310 cm/s², 1100 cm/s², and 0.29 s, respectively. With respect to codified design spectra, projections are lower at short periods and higher at long periods. Projections of peak spectral accelerations for the coarse-grained response unit, were more than double that of codified spectra; however, they are believed to be overconservative. Near-fault effects and basin-edge effects, though potentially important, were not considered in these analyses.  相似文献