113 research outputs found
Surface and Meteorological Data at Sand Creek, Great Sand Dunes National Park, Colorado, USA in March and April 2019
No full textWind, sediment transport and surface morphological data collected at Sand Creek during a month long field campaign in March and April 2019 to investigate protodune development under bimodal winds. Data is used in the accepted paper ‘Dune initiation in a bimodal wind regime’, Journal of Geophysical Research: Earth Surface, by Delorme, P., Wiggs, G.F.S., Baddock, M.C., Claudin, P., Nield, J.M. and Valdez, A. (accepted 18th September 2020, article reference number 2020JF005757R; https://repository.lboro.ac.uk/articles/Dune_initiation_in_a_bimodal_wind_regime/12973817) Surface morphological data: This is terrestrial laser scanned (TLS) data collected of the creek sand surface during multiple visits. The data is raw point cloud format in text columns of x, y and z coordinate data. It has been orientation in local format (the origin is located at 13UTM 443152, 4184478). *_full_lowres cover the whole creek surface and the banks on either side. * is the date that the data was collected in yymmdd format. All other data is high resolution section of the actual creek surface within the channel. Each data set uses the same coordinate system. Data can be viewed in any spatial software. Wind and sediment data were collected from a fixed point on the eastern edge of the creek channel. The data is in csv file format with column titles and can be viewed in any text or database software. See Delorme et al. (accepted) for more details.</span
Understanding dust sources through remote sensing: Making a case for CubeSats
No full textAbstract: Dust sources have been revealed through remote sensing, first regionally by ~1° resolution sensors (TOMS), then at sub-basin scale by moderate-resolution sensors (MODIS). Sensors with higher spatial resolution until recently were poorly temporally-resolved, precluding their use for systematic investigations of sources. Now, “CubeSat” constellations with high-temporal-and-spatial-resolution sensors such as PlanetScope offer ~3 m resolution and daily (to sub-daily) temporal resolution. We illustrate the spatio-temporal dust plume observation capabilities of CubeSat data through a dust event case study, Bolson de los Muertos playa, Chihuahuan Desert, Mexico. For the event, PlanetScope showed numerous discrete point sources, revealing variability of surface erodibility and emission over ~8% of a focus area at time of capture. The unprecedented detail of PlanetScope imagery revealed plume development where outer-playa sands and fluvial-deltaic inputs contact lacustrine silts/clays, consistent with field-studies. PlanetScope's high fidelity improves spatial quantification and temporal constraint of source activity, and we assess the spatio-temporal capabilities of CubeSat in context with other dust observation remote sensing systems. Compared to previous satellite technologies, CubeSats bring better potential to link remote sensing to field observations of emission. This leap forward in the remote sensing of dust sources calls for the systematic analysis of CubeSat imagery in source areas
Early-stage aeolian protodunes: bedform development and sand transport dynamics
No full textEarly-stage aeolian bedforms, or protodunes, are elemental in the continuum of dune development and act as essential precursors to mature dunes. Despite this, we know very little about the processes and feedback mechanisms that shape these nascent bedforms. Whilst theory and conceptual models have offered some explanation for protodune existence and development, until now, we have lacked the technical capability to measure such small bedforms in aeolian settings. Here, we employ terrestrial laser scanning to measure morphological change at the high frequency and spatial resolution required to gain new insights into protodune behaviour. On a 0.06 m high protodune, we observe vertical growth of the crest by 0.005 m in two hours. Our direct measurements of sand transport on the protodune account for such growth, with a reduction in time-averaged sediment flux of 18% observed over the crestal region. Detailed measurements of form also establish key points of morphological change on the protodune. The position on the stoss slope where erosion switches to deposition is found at a point 0.07 m upwind of the crest. This finding supports recent models that explain vertical dune growth through an upwind shift of this switching point. Observations also show characteristic changes in the asymmetric cross section of the protodune. Flow-form feedbacks result in a steepening of the lee slope and a decline in lower stoss slope steepness (by 3°), constituting a reshaping of protodune form towards more mature dune morphology. The approaches and findings applied here, a) demonstrate an ability to quantify processes at requisite spatial and temporal scales for monitoring early-stage dune evolution, b) highlight the crucial role of form-flow feedbacks in enabling early-stage bedform growth, alluding to a fluctuation in feedbacks that require better representation in dune models, and c) provide a new stimulus for advancing understanding of aeolian bedforms
Coupling leeside grainfall to avalanche characteristics in aeolian dune dynamics
No full textAvalanche (grainflow) processes are fundamental drivers of dune morphodynamics and are typically initiated by grainfall accumulations. In sedimentary systems, however, the dynamism between grainfall and grainflow remains unspecified because simple measurements are hampered by the inherent instability of lee slopes. Here, for the first time, terrestrial laser scanning is used to quantify key aspects of the grainfall process on the lee (slip face) of a barchan sand dune. We determine grainfall zone extent and flux and show their variability under differing wind speeds. The increase in the downwind distance from the brink of peak grainfall under stronger winds provides a mechanism that explains the competence of large avalanches to descend the entire lee slope. These findings highlight important interactions between wind speed, grainfall, and subsequent grainflow that influence dune migration rates and are important for correct interpretation of dune stratigraphy
Surface and Meteorological Data at Medano Creek, Great Sand Dunes National Park, Colorado, USA on 15th April 2019
No full textWind and surface morphological data collected at Medano Creek on the 15th April 2019 to investigate protodune initiation. Surface morphological data: This is terrestrial laser scanned (TLS) data collected of the creek sand surface using three different co-located Leica TLS (C10, P20 and P50). The data is raw point cloud format in text columns of x, y and z coordinate data. It has been orientation into the same local coordinate system. Each data set uses the same coordinate system. Data can be viewed in any spatial software. Data is labelled using C10, P20 or P50, followed by the scan number. Scan times are indicated in a separate file. Wind data were collected from a fixed point next to the TLS instruments using a Gill 3D sonic anemometer. The data is in csv file format with column titles and can be viewed in any text or database software.</span
Surface and Meteorological Data of Saltation and Ripple Dynamics at Huab Dune Field, Skeleton Coast National Park, Namibia 2014, 2016 and 2018
No full textThis dataset includes raw point cloud data from repeat terrestrial laser scans (TLS) of rippled surfaces on barchan and dome dunes within the Huab Dune Field, Skeleton Coast National Park, Namibia. This raw data can be used to extract saltation height dynamics as well as 3D ripple data including celerity. As well as the TLS data, additional measurements of the wind speed through a CSAT 3D sonic anemometer or cup anemometer and sediment transport using a Sensit and Wenglor gate sensor.</span
Surface and Meteorological Data at Huab River Valley, Skeleton Coast National Park, Namibia in September 2019
No full textWind, sediment transport and surface/saltation data collected at Huab River Valley during a field campaign in September 2019 to investigate saltation on gravel and sand surfaces. Surface/saltation data: This is terrestrial laser scanned (TLS) data collected over sand and gravel surfaces during multiple days when saltation was active, on a surface approximately 8 m from the TLS, perpendicular to the wind direction. The data is raw point cloud format in text columns of x, y and z coordinate data. Files are named *_^_scan&amp; where * is the date that the data was collected in yymmdd format, ^ is surface type (sand or gravel) and &amp; is the scan number. Each data set uses the same coordinate system. Data can be viewed in any spatial software. Wind and sediment data were collected from a fixed point on each surface, directly downwind of the TLS data. The data is in csv file format with column titles and can be viewed in any text or database software. Data include hot wire measurements at different heights, Wenglor counts, sensit counts and 3D sonic measurements on some days. Sonic data is at 10 Hz, hotwire data at 10 second intervals, transport data is given within both datasets.</span
Topographic perturbation of turbulent boundary layers by low-angle, early-stage aeolian dunes
No full textDecimeter-scale early-stage aeolian bedforms represent topographic features that differ notably from their mature dune counterparts, with nascent forms exhibiting more gently sloping lee sides and a reverse asymmetry in their flow-parallel bed profile compared to mature dunes. Flow associated with the development of these “protodunes,” wherein the crest gradually shifts downstream towards its mature state, was investigated by studying the perturbation of the turbulent boundary layer over a succession of representative bedforms. Rigid, three-dimensional models were studied in a refractive-index-matched experimental flume that enabled near-surface quantification of mean velocities and Reynolds stresses using particle-image velocimetry in wall-normal and wall-parallel measurement planes. Data indicate strong, topographically induced flow perturbations over the protodunes, to a similar relative degree to that found over mature dunes, despite their low-angled slopes. The shape of the crest is found to be an important factor in the development of flow perturbations, and only in the case with the flattest crest was maximal speed-up of flow, and reduction in turbulent stresses, found to occur upstream of the crest. Investigation of the log-linearity of the boundary layer profile over the stoss sides showed that, although the profile is strongly perturbed, a log-linear region exists, but is shifted vertically. A streamwise trend in friction velocity is thus present, showing a behavior similar to the trends in mean velocity. Analysis of the growth of the internal boundary layer on the dune stoss sides, beginning at the toe region, reveals a similar development for all dune shapes, despite clear differences in mean velocity and turbulent stress perturbations in their toe regions. The data presented herein provide the first documentation of flow over morphologies broadly characteristic of subtle, low-angle, aeolian protodunes, and indicate key areas where further study is required to yield a more complete quantitative understanding of flow–form–transport couplings that govern their morphodynamics.</p
Aerosol concentration and meteorological data at Etosha Pan, Namibia (July 2015 - June 2016)
No full textAerosol concentration and meteorological data collected at five meteorological stations situated around Etosha Pan in Namibia during the year July 2015 to June 2016. Data are logged every 10 minutes. LiDAR data measured at Okaukuejo on 8/9/10 July 2015. Data support the publication Wiggs et al. 2022, Quantifying mechanisms of aeolian dust emission: field measurements at Etosha Pan, Namibia. Journal of Geophysical Research: Earth Surface.
Met and Dust Data.xlsx = Excel file detailing 10 minute measurements of aerosol concentration and meteorological data (2015-2016).
MSG3-SEVI-MSG15-0100-NA-*-NA_dust_250.tif - SEVIRI false colour composite data related to LiDAR data 8-10 July 2015
Processed_Wind_Profile_81_YYYYMMDD_L2.nc - LiDAR horizontal wind speed 8-10 July 2015
Stare_81_YYYYMMDD_L2.nc - LiDAR aerosol backscatter 8-10 July 201
A two-dimensional model for the dynamics of sand patches
No full textInternational audienceSand patches are one of the early stages of aeolian bedforms. They form onnon-erodible surfaces in both desert and coastal environments. Their initiation is associated with thechange of saltation transport law on rigid and granular beds [1]. Here wepresent a two-dimensional model that couples these surface-dependenttransport laws with the feedback of the bed elevation on the wind flow.Analysing the spatio-temporal evolution of an initial very flat sandpatch, we emphasise the central role of the input flux as well as thelengthscale over which occurs the transition between the two transportlaws. We also show that, for adjusted parameters of the model, we are ableto reproduce the growth and the propagation of these small metre-scalebedforms over time, in quantitative comparison with field measurements. [1] P. Delorme, J.M. Nield, G.F.S. Wiggs, M.C. Baddock, N.R. Bristow, J.Best, K.T. Christensen and P. Claudin, Field evidence for the initiationof isolated aeolian sand patches, Geophys. Res. Lett. 50 , e2022GL101553(2023)
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