Barchan Research Articles

Investigation of fluid flow and heat transfer in a narrow channel with micro barchan-dune-shaped humps

• A bionic heat sink with micro barchan-dune-shaped humps is proposed. • The micro dune can reinitialize the boundary layer by inducing a secondary flow. • The micro dune generally outperforms traditional fins in overall heat transfer performance. This paper proposes an innovative bionic heat sink with micro barchan-dune-shaped humps for improving the flow and heat transfer performance of the smooth narrow channel. The effects of the Reynolds number of the main flow ( Re ) and pitch distance of the dune array ( P ) on the thermal-hydraulic performance are investigated. In this work, the air is the working flow. The Reynolds number range is considered to cover the regimes of laminar, transitional, and turbulent, Re = 860–6,050, and the pitch distance ( P ) equals 8, 12, and 16 mm. The results show that the micro barchan-dune-shaped hump can induce a secondary flow downstream of the slip face and enhance the local heat transfer performance. For the multi-dune models, the case with P = 16 mm provides the highest overall thermal performance parameter ( η ). The η value decreases monotonically with decreasing P in the considered range. In addition, compared with other micro pin fin shapes (including the hexagonal cylinder, square cylinder, and triangular cylinder), the η of the barchan dune shape is almost identical to that of the hexagonal cylinder and exceeds the other two shapes by more than 20%.

Diachronic analysis to Detect and Monitor Barchan Dune Migration in Ain Salah (Algeria)

The aim of this work is to analyse barchan dunes migration patterns and their effect on urban and agricultural areas in Ain Salah region in southern Algeria. A supervised classification of Landsat images over a 13 years period (2005, 2009, 2013 and 2017) was applied to create land cover maps which were used for a spatiotemporal monitoring of barchan migration by dune feature changes. The results show that sand dunes covered area has increased between 2005 and 2017 with direction movements from northeast to southwest and represents the potential of using time series imagery for a better understanding of dune migration and sand encroachment.

Mineralogy of Sand Dune Fields around Hor Al-Dalmaj Between Wasit and Al-Qadesiyah Governorates - Central Iraq

Vast percentage of the Hor Al-Dalmaj area is covered with sand dunes fields due to desertification. Therefore, it is vital to research these dunes to limit their bad action on the natural environment by defining the mineralogical composition of these sand dunes deposited around Hor Al-Dalmaj lake between Wast and Al-Qasisiyah Governorates to determine the provenance or the source of these dunes. Barchan and Nabkha dunes represent the main types that are recognized. The dimensions of barchan dunes are recognizing by a height range of about 0.5 to 3m, with lateral extension ranging from 2 to 15m and longitudinal extinction ranging from 3 to 15m. While the dimensions of nabkha dunes range from 10 cm to 2m in length and 15cm to 2m high. According to the major wind direction, these dunes are extended from North West to south-east. The mineralogical investigation reveals that the light minerals of studied dunes consist mainly of quartz, feldspars and various rock fragments such as carbonate, chert, mudstone, evaporate, igneous, and metamorphic rocks. The most frequent heavy minerals are opaque, chlorite, pyroxenes, amphiboles, muscovite, biotite, zircon, epidotes, garnet, tourmaline, rutile, kyanite, and staurolite. The source of these sediments is recent sediment that has formed in river terraces, flood plain and Quaternary deposits in the Mesopotamian Plain, and the outcrops of the ancient sedimentary formations in the north northwestern, west, and southwestern Iraq.

Reproducing size distributions of swarms of barchan dunes on Mars and Earth using a mean-field model

We apply a mean-field model of interactions between migrating barchan dunes, the CAFE model, which includes spontaneous calving, aggregation, fragmentation, and mass-exchange, yielding a steady-state size distribution that can be resolved for different choices of interaction parameters. The CAFE model is applied to empirically measured distributions of dune sizes in two barchan swarms in the north circumpolar region of Mars, three swarms in Morocco, and one in Mauritania, each containing more than 1000 bedforms. When the sizes of bedforms are rescaled by the mean size in each zone two attractor states appear, with the Tarfaya zones all displaying a common distribution and the Martian and Mauritanian zones sharing a different distribution. Comparison of these attractor states with the outputs of the CAFE model reveals that the Tarfaya-type distribution results from a preference for aggregation and fragmentation interactions whereas the Mars–Mauritania distribution is more likely a result of exchange–dominated interactions. We observe that there appears to be a greater number of collisions happening in Tarfaya than in the other areas which is consistent with a greater rate of aggregation–fragmentation processes as suggested by our model. Our comparison with the CAFE model also predicts a universal rule for the outputs of the different types of interactions with exchange interactions favouring the production of two dunes roughly equal in size. Fragmentation interactions often result in three bedforms with volumes approximately in the ratio 1:1:2. Finally, we find that spontaneous calving of dunes does not play an important role in shaping the size distributions in barchan swarms.

Getting the right age? Testing luminescence dating of both quartz and feldspars against independent age controls

When luminescence dating was being developed much scientific effort was invested in showing it could achieve the correct ages, but this is now not routinely carried out for established protocols. This paper focussed on known age deposits from two case studies to explore whether correct ages were achieved. Case study 1 used the Storegga tsunami deposit dated to 8.2 ka sampled both horizontally and vertically and measured with OSL, IRSL and pIRIR. All results, for both quartz and feldspars, returned the correct age for the horizontal sample. Results from the vertical sample were more problematic with issues attributed to ongoing feldspar contamination of quartz and to beta heterogeneity. To agree with the independent age control single aliquot results required combination of >400 palaeodose replicates and in the case of IRSL the use of minimum age models. Measurements of feldspars at the single grain level using pIRIR measurements showed much improvement. Case study 2 used a barchan dune on the Tibet Plateau, China known to have been in position ∼10 years. Both quartz and feldspars returned young ages close to the true age, but the feldspar ages with brighter luminescence signal were more accurate once the luminescence signal to background ratio was optimised. On the basis of this study we advise against sampling vertically. We also recommend measuring feldspars with single grain pIRIR where possible, measuring >150 palaeodose replicates per sample and choosing feldspars rather than quartz for very young samples.

Sand fixation mechanism and effect evaluation of sand barriers in Mu Us sandy land, China

<p indent="0mm">Sand barriers are an engineering measure for sand fixation, and play an important role in promoting dune fixation and vegetation restoration. As the most widely used means of sand control, sand barriers have a variety of materials and configurations. In recent years, some new sand fixation materials have appeared, but their benefits of sand fixation have not been compared and evaluated. Moreover, there is an insufficient amount of research on the sand fixation mechanism of sand barriers. Therefore, an accurate understanding of the sand fixation mechanism of sand barriers and the optimization of its configuration mode is conducive to improving the techniques of wind prevention and sand fixation. In this paper, four barchan dunes developed in the Mu Us sandy land were selected as the research carrier. One of the dunes is a reference dune without sand barriers, and the remaining three dunes are covered with sand barriers of different materials and specifications. There are 9 types of sand barriers, which can be divided into 3 materials (Salix, straw rope and PLA) and 3 specifications (1 m<sc>×1 m,</sc> 2 m<sc>×2 m</sc> and 3 m<sc>×3 m).</sc> This study revealed the surface processes of dunes under each type of sand barrier and evaluated the benefits of each type of sand barrier on sand fixation and ecological restoration through topography measurements, sand drift observations, sediment sampling, vegetation investigations and laboratory analyses. The results show that the sand barriers have the functions of reducing the height of dunes, reshaping the surface micromorphology, decreasing near-surface wind speed, blocking the sand transport and promoting vegetation restoration, and the strength of the functions is controlled by the material of the sand barrier, the configuration mode of the sand barrier and the relative positions on the dune. Detailed analysis of the benefits in sand fixation and vegetation restoration of each type of sand barrier suggests that the Salix barrier is the best choice in this area, the straw rope barrier is the second best choice, and the PLA barrier is the worst. The best configuration mode of the Salix barrier and straw rope barrier is 1 m<sc>×1 m,</sc> while that of the PLA barrier is 2 m<sc>×2 m.</sc> Moreover, this study considered that the effect of sand barriers on wind prevention and sand fixation are decided by multiple factors, and it is not sufficient to take the near-surface wind speed or micromorphology as the measurement standards of these effects. The selection of sand barrier materials and configurations needs to comprehensively consider many issues, such as the efficiency of sand fixation, the ability to promote vegetation restoration, sustainable time, economic cost and secondary pollution. Thus, sand barrier projects should take the regional sand fixation demand and field environment into account and select the most suitable configuration forms according to the main objectives or demand.

Dynamics of three-dimensional vortical structures behind a barchan dune based on tomographic particle image velocimetry

In this study, tomographic particle image velocimetry (PIV) was used to measure three-dimensional (3D) flow structures behind a fixed-bed barchan dune model at a Reynolds number of 2528 in a circulation water tunnel. The topological evolution of the 3D instantaneous vortex structures and their dynamic characteristics in the dune wake were analyzed. 3D instantaneous arch-shaped vortex “chains” shedding from the barchan and typical quasi-streamwise vortex structures induced by the development of an internal boundary layer were found to be located both before and after the reattachment region, which differs a little from the results of previous studies. Nevertheless, both conditionally averaged and typical instantaneous 3D flow fields revealed that the arch-shaped vortex system dominates the barchan dune wake, and the inclination angle of these spanwise-oriented structures was found to change as it propagates downstream. Additionally, the dynamic characteristics of the dune wake were found to be similar to a flapping phenomenon such as oscillation of the recirculation in a backward-facing step flow. To provide complementary insight into this phenomenon, the separated and reattached shear flow were also examined using two-dimensional time-resolved planar PIV. It was found that the basic unsteady flapping motion, vortex roll-up, and complex vortex interactions can all be analyzed with ease in a Lagrangian framework.

Analysis of movement and relationships between morphometric components of sand dunes (barchans) in the south-eastern of Iran

Morphology of barchan dunes plays a key role in the rate of movement of barchan dunes and accordingly, the areas that are in the path of barchan dunes can be identified. In this study, morphological parameters of eight barchan dunes in west Lut and movement were investigated. For this purpose, 8 parameters of windward slope length, back-to-wind slope length, right arm length, left arm length, length, width, right width and left width were measured in each barchan dune and Pearson correlation was calculated by SPSS software. In order to better understand the shape of barchan dunes, satellite images were extracted separately from google earth. The results of morphometry showed that barchan dune 6 was in the first place in terms of all morphometric factors. The right arm length to the width had the highest correlation (0.993). The back-to-wind slope length to the right arm length had the lowest correlation (0.815). The right arm length to the width had the highest coefficient of determination (0.9845). The movement during 2005–2019 was extracted from satellite images. It was found that until 2015, the highest movement belonged to barchan dune 3 (225.55 m) and during 2017–2019, the lowest movement belonged to barchan dune 6 (137.49 and 184.66 m). The highest movement during 2017–2019 was 288.24 and 307.67 m for barchan dune 5, respectively.

An application of CNN to classify barchan dunes into asymmetry classes

• CNNs can be used to extract morphometric data from barchan dunes. • Convolutional Neural Networks (CNNs) can classify barchans based only on their outlines. • There is no clear pattern regarding the use of hyperparpameters to improve the performance of CNNs. • The asymmetry of a barchan can be described using geometric morphometrics. 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.

Rational Analysis of Drag Reduction Variation Induced by Surface Microstructures Inspired by the Middle Section of Barchan Dunes at High Flow Velocity

Aerodynamic drag reduction is a key element for the design of aircrafts, and it is also considered to be affected by the flow velocity. Herein, the influence of high flow velocity on the drag reduction induced by the surface microstructure inspired by a cross-section of barchan dune was investigated by the computational fluid dynamics method in this work. Overall, the drag reduction ratio was decreased while the pressure drag and viscous resistance enhanced simultaneously with the augmentation of flow velocity. Otherwise, drag analysis revealed that the total drag was a power function of flow velocity, which meant that the effect of flow velocity on drag was extremely fierce. Additionally, the microstructure improved the thickness of the boundary layer with a growth rate of 14.2%, and then reduced the viscosity resistance with limits during the development process of flow velocity. Furthermore, the micro-vortex caused by the surface microstructure provided the reverse wall shear stress, with the maximum value ranging from −4.77 Pa to −51.27 Pa, and then reduced the velocity gradient above the microstructure, thereby improving the drag reduction. However, both Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) calculations showed that the excessive velocity could lead to the dissipation of micro-vortex, which augmented the contact area between the fluid and the surface, resulting in the enlargement of viscous resistance. Finally, it was confirmed that the variation of surface microstructure height had a significant influence on drag reduction at high flow velocity. The underlying mechanism of drag reduction could also provide theoretical guidance for the design and optimization of drag reduction coatings in aeronautical applications.

Shaping effects of sand flow channels on aeolian geomorphology – a case study of the Badain Jaran, Tengger, and Ulan Buh Deserts, northern China

Based on the interactions between mountains, we identified three sand flow channels in the Badain Jaran, Tengger, and Ulan Buh Deserts, northern China. We found that the height difference of the terrain in these areas provided favorable conditions for the transportation of sand. Owing to the venturi effect of their geomorphologies, airflow was compressed in these channels, and their wind regimes were strong and unimodal. Compared with the interior of the desert, the sand transport potential was relatively large in these areas, and westerly and northwest winds prevailed. We found that the wind accelerated in the sand flow channels, resulting in faster-moving dunes. The dune types that developed in these channels were relatively simple owing to the unimodal wind regimes; they mainly comprised barchan and transverse dunes. We also identified a transition landscape from barchan dunes to transverse, or complex dunes. Based on their sediment characteristics and the prevailing wind directions, we found that the sand flow channels provided a direct sand supply between the three deserts. The sand flow channels connected these independent deserts to an entire desert system. Similar sand flow channels can also be found in other deserts globally. Collectively, these sand flow channels reflect interactions between deserts.

Quantitative Study on Morphological Characteristics of Barchan Dunes in Yamarak Desert, China

Although scholars have conducted many studies on barchan dunes in deserts and sandy areas around the world, few studies have been conducted on the morphological characteristics and changes in movement patterns of barchan dunes in the Yamarak Desert, China. To assess the changes in and movement patterns of these dunes, As well as the impact on the wind-sand hazards and geohazards around the study area, we selected several typical barchan dunes of different sizes in the Yamarak Desert and measured and calculated their morphologies using a combination of a 3-D laser scanner (RIEGL VZ-2000) and remote sensing image interpretation. The results show that the average coverage of the barchan dunes in the Yamarak Desert was 37.19%. Moreover, 62.81% of this area was covered by interdune sites. The movement velocity of the barchan dunes in this study area was 0–20 m/a, with an average movement velocity of 8.45 m/a. Of these dunes, 44.18% were fast-dominated dunes, 37.20% were particularly fast-dominated dunes, and 18.62% were moderately fast-dominated dunes. The barchan dunes moved in the 95–130° direction, which was basically consistent with the main wind direction of the area. The determination and function fitting of the barchan dune morphology shows that the correlation coefficients between all of the morphological parameters are greater than 0.8, except for the degree of spread and the symmetry of the two wings. We suggest adding the influences of other factors affecting barchan dunes and dune chains in the Yamarak Desert in future studies and paying attention to new wind-sand hazards and geohazards in the downwind corridor.

High-precision remote sensing mapping of aeolian sand landforms based on deep learning algorithms

Abstract It is significant to adopt deep learning algorithms and higher-resolution remote sensing images in mapping large-scale and high-precision of aeolian landform. In this study, the western part of Horqin Sandy Land was taken as the study area. Based on the data collected from 2,786 verification points located in sandy land and remote sensing images of high-spectral and spatial resolution Sentinel-1, Sentinel-2, and GDEM (V3), this article made a research on data of large-scale and high-precision mapping classification of this area between 2015 and 2020 by using convolutional neural network deep learning algorithm. The results showed that the types of aeolian sandy landform in the west of Horqin Sandy Land mainly include longitudinal dune, flat sandy land, mild undulating sand land, nest-shaped land, parabolic dune, barchan dune, and dune chain, with an area of 1735.62, 51.32, 251.38, 902.07, 49.57, and 101.63 km2. Among them, longitudinal dune, barchan dune, and dune chain have the largest area, while parabolic dunes and flat sand land are smaller. Between 2015 and 2020, the area of aeolian landforms was reduced by 89.27 km2 and transformed into an oasis from a desert. This study adopted remote sensing data by high-resolution Sentinel and GDEM (V3) and convolutional neural network deep learning algorithm to map the aeolian landforms effectively. The precision of aeolian landform classification and Kappa coefficient in the western part of Horqin Sandy Land is as high as 95.51% and 0.8961. Combined with Sentinel-1, Sentinel-2, and GDEM (V3), the deep learning algorithm based on the convolution neural network can timely and effectively monitor the changes of sand dunes, which can be used for large-scale aeolian landforms.

Multi-year measurements of ripple and dune migration on Mars: Implications for the wind regime and sand transport

Aeolian sand dunes are observed across the Martian surface. The arrival of the HiRISE camera on Mars Reconnaissance Orbiter at Mars in 2006 enabled detection of modern-day movement of dunes and ripples from orbit for the first time. Since 2006, HiRISE collected a long timeseries of repeat imagery at a few Martian dune fields. We analyze this timeseries of imagery at two of these dune fields, using COSI-Corr for image registration and correlation, to study the movement and dynamics of dunes and meter-scale ripples at the Nili Patera and Meroe Patera barchan dune fields. We present measurements of whole-dune translational sand fluxes extracted at both dune fields via manual tracking of dune crestlines and slipfaces in HiRISE images. We also present a multi-Mars year timeseries of ripple flux measurements. Ripple migration shows a consistent pattern of seasonal variation, with maxima in flux during northern-hemisphere autumn and winter at both dune fields. Ripple migration is also observed to decrease away from the upwind margins of dune fields. We compare our observations with predicted sand transport using winds output from the MarsWRF atmospheric circulation model and theories of sand motion. The model predicts half-hourly, mesoscale winds, from which we estimate the 1 Hz, local-scale winds by assuming a Weibull distribution of wind speed, with parameters chosen based on landed wind data. This approach uses remote sensing observations of bedform migration, and comparisons with model output, to place constraints on the wind regime. Our measurements of the seasonal pattern of sand flux variation agree, to first order, with predictions based on modeled wind speeds. Comparison of the magnitudes of predicted and observed sand fluxes is not feasible due to the high uncertainties in our calculated sand fluxes caused by uncertainties in input parameters, most importantly the assumed fluid threshold for sand transport. However, we note that model predictions fit our observed sand fluxes best when relatively low values of the fluid threshold shear velocity of ~0.6–0.8 m/s (or shear stresses of O(10−3) Pa) are assumed.

Assessment of Aeolian Activity in the Bodélé Depression, Chad: A Dense Spatiotemporal Time Series From Landsat-8 and Sentinel-2 Data

There are several hotspots of dust production in the central Sahara, the Bodélé Depression (BD) in northern Chad is considered the largest source of aerosol dust worldwide, with the fastest Barchan dunes that migrate southwesterly. Less is known about the complex patterns of dune movement in the BD, especially on a short time scale. Time-series inversion of optical image cross-correlation (TSI-OICC) proved to be a valuable method for monitoring historical movements with low uncertainties, high spatial coverage, and dense temporal coverage. We leveraged ∼8 years of Landsat-8 and ∼6 years of Sentinel-2 data to capture the dune migration patterns at BD. We used TSI-OICC, creating four independent networks of offset maps from Landsat-8 and Sentinel-2 images, and forming three networks by fusing data from the two sensors. We depended on the multi spatial coherence estimated from Sentinel-1 interferograms to automatically discriminate between the active and stagnant regions, which is important for the postprocessing steps. We combined the data from the two sensors in areas of overlap to assess the performance of the fusion between two sensors in increasing the temporal scale of the observations. Our results suggest that dune migration at BD is subject to seasonal and multiyear variations that differed spatially across the dune field. Seasonal variations were observed with migration slowing during the summer months. We estimated the median for velocities belonging to the same season and calculated the seasonal sliding coefficient (SSC) representing the ratio between seasonal velocities. The median SSC reached a maximum value of ∼2 for winter/summer, while the ratios were ∼1.10 and ∼1.35 for winter/spring and winter/autumn, respectively. The seasonal variability of the temporal patterns was strongly supported by the wind observations. Between (1984–1998 and 1998–2007) and (1998–2007 and 2013–2021), decelerations in dune velocities were observed with percentages of ∼4 and ∼28%, respectively, and these decelerations were supported by a deceleration in wind velocities. Inversion of time series provides dense spatiotemporal monitoring of the dune activity. The fusion between two sensors allows condensing the temporal sampling up to a weekly scale especially for locations exposed to contamination of high cloud cover or dust.

Drag Reduction Characteristics of Microstructure Inspired by the Cross Section of Barchan Dunes under High Speed Flow Condition

A new type of microstructure inspired by the cross section of barchan dunes was proposed to reduce windage, which was considered as a passive drag reduction technology in aerospace manufacturing field. Computational fluid dynamics method was carried out to discuss the effect of the microstructure on the skin friction reduction under high velocity flow condition. Different microstructure heights were employed to survey the reduction of drag. The results illustrated that the appearance of microstructure led to a generation of pressure drag in non-smooth model (with microstructures inspired by cross section of barchan dune) in contrast to smooth model. However, the microstructure significantly increased the thickness of the low-speed fluid by 11.4% in the near-wall flow field, causing the low-speed fluid to rise and decreasing the velocity gradient near the wall, thereby reducing viscous resistance. In addition, high-speed fluid flowed above the microstructure units instead of along the inner side of the units due to the influence of micro-vortex, resulting in a reduction of friction near the surface. Furthermore, micro-vortex was considered to be the significant internal factor to achieve turbulent drag reduction since it could not only reduce the viscous resistance by promoting the fluid flow above the microstructure but also provide a reverse thrust force. The understanding of the mechanism of drag reduction provides theoretical guidance for further fabrication of drag reduction coatings using renewable materials.

Paraná quartz andesite rings and arcs formed by distal imprint of dune design from the Botucatu paleoerg

Rings and arcs in a Paraná Volcanic Province quartz andesite were formed by distal imprint of design of the top of barchan and linear dunes. Hydrothermal jetting occurred in the Lower Cretaceous from the dunes onto the upper amygdaloidal crust of the lava flow in Fronteira Oeste of southernmost Brazil. In one occurrence, hot water overflowed the quartz andesite in a hot spring and deposited sinter quartz. This unique register of the process in the continents was investigated with varied techniques, including satellite images, geological field survey, field gammaspectrometry, petrography and whole-rock geochemistry. We characterized the rings and arcs in the upper crust of the Catalán quartz andesite, design defined by hydrothermal processes, no ring dikes observed. We interpret the evidence as hydrothermal injection of sand and alteration of the upper crust of the quartz andesite, including silicification and deposition of epithermal quartz. The reproduction of the design of the dune tops was generated by focused jetting of hot water and vapor (plus sand) through the top of the dunes. The vertical channel maintained the design of the dune tops distally in the quartz andesite. The quartz andesite crusts now display sand dune design above the massive core in the pampas as a result of a special process in geology.

Data in "The Effects of Seasonal Wind Regimes on the Evolution of Reversing Barchan Dunes"

Data in "The Effects of Seasonal Wind Regimes on the Evolution of Reversing Barchan Dunes"

Data "The Effects of Seasonal Wind Regimes on the Evolution of Reversing Barchan Dunes"

Data "The Effects of Seasonal Wind Regimes on the Evolution of Reversing Barchan Dunes"

The Moving Trajectory Fitting Based on Three-Dimensional Digital Model of Barchan Dunes in Taklimakan Desert

In the hinterlands of the Taklimakan Desert, we monitored Barchan dune evolution with the Huace X90 GNSS in RTK working mode to obtain 3D coordinates of a dune with millimeter precision. Using these coordinates, a 3D digital model of the dune was built and superimposed with CASS 9.0 and ArcGIS 10.0. Auto CAD 2010 was used to draw an arc with the three elements of starting point, end point and included angle and to fit the corresponding characteristic point trajectory curve of the eight selected typical dunes. Results of the fitting showed that the dunes rotated counterclockwise with ranges of 33°∼38°and 25.5°∼30° in the monitoring intervals between stages one and two and stages three and four, respectively. The moving trajectories were curves pointing from NE to SW and convex to NW, with long lengths. Between stages two and three, the dunes rotated clockwise with a range of 31°∼37°, and the trajectories was curves pointing from NE to SW and convex to SE or SW, with varying direction and a short length. When the northward or southward angle between effective sand-driving wind and the axial direction was larger than 30°, the dune rotated clockwise or counterclockwise, respectively. This indicates that the moving trajectory should be a curve rather than a straight line, which would result in a better fit with the actual movement of the dune. Accurately fitting the moving trajectory of Barchan dunes can assist in learning how to fit the movement of other mobile dunes as well as how to correct raw dune evolution data, such as moving distance and speed. It can also lay a foundation for the improvement of a formula for moving speed, which is important because many fields of research concern the moving speed and direction of mobile dunes.