Dune Migration Rates Research Articles

Evolutionary stages of active to vegetated coastal transgressive dunefields in the San Matías Gulf coast, Argentina

The understanding of how active aeolian coastal dunes transform into fully vegetated forms, and the specific dune configurations that emerge, particularly within coastal dune systems, is limited. This study examines the changes in dune morphology associated with vegetation growth within transgressive dunefields in NE Patagonia, Argentina. The dunefields are located along the northern coast of the San Matías Gulf, ranging from relatively small to large, and dominantly active in the past ∼80 years. Satellite and aerial images were analyzed using GIS procedures to calculate vegetation cover changes and dune migration rates and identify different dune types and their evolutionary stages of fixation. Five stages were defined in relation to vegetation cover and dune shapes and patterns, from bare sand to fully vegetated dunes. Transverse or barchanoid ridges (sometimes with aklé [fish scale], or chaotic patterns) convert to partially vegetated sub-parabolic dunes and finish as parabolic dunes. In other cases, the dunes may convert to reticulate, aklé, or chaotic patterns, completely vegetated. Various stages span a continuous range from unvegetated to fully vegetated dunes across a wide array of timeframes. In some cases, it was possible to recognize changes from stage one to five in ∼20 years. Where the initial transverse dune is largely maintained during the stabilization process a distinctive pattern named “gusanos” (worms) was identified. The vegetated surface measured in some areas changed from 11 % to 51 % vegetation cover between 1961 and 2022, with migration rates decreasing from 9.53 m/year to zero between 1991 and 2020. The increase in vegetation growth also coincides with higher temperatures, weaker winds and decreasing grazing livestock within this Patagonia area. The recorded processes are similar to coastal dune and vegetation changes in some semiarid regions from the Southern Hemisphere between 30 and 60° S, especially in South Australia.

Dune behavior in the Source Area of the Yellow River under climate changes observed from various remote sensing datasets

Sand dunes are a landscape feature with a quick response time to climate change and human influences (e.g. grazing, greening projects, and fixation structures). Their migration rates and their development can help to gather information about changing environmental conditions over time. The Source Area of the Yellow River (SAYR), located upon the Tibetan Plateau, is highly complex with topographical, hydrological, and climatological influences on active dunes, making it a good study area for these interactions. Based on remote sensing datasets, spanning the last 54 years, 415 dunes were mapped for migration rate calculations. Further, climate data from ERA-5 reanalysis and a local climate station was used to assess their changes within a changing climate. Generally, dune migration rates are rather slow with an average of 3.62 m y-1. In accordance, the averaged resultant drift potential (RDP) values are lower than 10 m3/s−3(−|-). Further, we assessed the density development of the main active barchan dune field in direct premise of the Yellow River. Throughout the past 54 years, we observed the emergence of more than 5 new barchans per square kilometer. This increase is likely attributed to higher sand flux from the Yellow River, which has resulted from increased discharge due to declining snowfall and rising precipitation levels.

Quantifying dune migration patterns and influencing factors in the central Sahara Desert

Based on Landsat images and ERA5 climate data, here we analyzed geomorphic dune patterns and the spatial characteristics of dune migration in the central Sahara Desert region (SW Libya, SE Algeria), using the COSI-Corr technique. Our results revealed clear observable drift potential (DP) and resultant drift potential (RDP) gradients, these decreasing from a northerly to southerly direction. Moreover, the annual average RDP/DP in most areas was <0.3 (i.e., highly variable). The main dune types in the study area included complex transverse ridges (22.82 %), linear dunes (19.87 %), barchan and barchanoid chains (16.95 %), and star dunes (13.55 %). Of these, barchans and barchanoid chains, as well as complex transverse ridges, appeared in areas of relatively high DP, while complex longitudinal ridges and honeycomb dunes were found in those of low DP. Linear dunes had a simpler wind composition, being mainly distributed in areas with intermediate wind variability. Both the honeycomb dunes and complex longitudinal ridges had nearly always formed in complex multi-directional wind environments. Dune migration displacement in dune fields ranged widely, from 0.5 to 23.57 m (mean = 6.71 m), during the 30-year study period (1993–2022). Barchans and barchanoid chains migrated fastest, with a mean value > 10 m/yr; in contrast, complex longitudinal ridges and honeycomb dunes had the slowest migration rate, always at < 5 m/yr. Overall, the dune migration rate was mainly related to dune height and wind regime. Spatially, the dune migration trend was basically consistent with that of the resultant drift direction (RDD), mainly in a northwesterly direction (28.36 %). The accuracy testing results indicated that the COSI-Corr displacement measurement accuracy was generally higher than the dune migration direction accuracy. This study provides not only valuable reference data for regional aeolian activities, but also insight into the developmental environments and migration dynamics of differing dune types, which could be used for prospective regional aeolian geomorphology research in the Sahara Desert.

Dune movement under climatic changes on the north‐eastern Tibetan Plateau as recorded by long‐term satellite observation versus ERA‐5 reanalysis

AbstractThe movement of active dunes is tightly linked to climatic conditions (e.g., wind regime, temperature and precipitation) as well as human influence (e.g., grazing, dune fixation and greening). Dune migration rates can be studied to draw conclusions of changing wind conditions over time. The Gonghe Basin (GB), located on the north‐eastern Tibetan Plateau (TP), offers a good testing ground for these assumptions. The intramontane basin is highly influenced by two major wind regimes: the mid‐latitude Westerlies and the East Asian summer monsoon. To investigate environmental changes, this study combines optical remote sensing techniques with climatic datasets. High‐resolution satellite images of the last five decades, such as CORONA KH‐4B, are used to map dunes and calculate their respective migration rates. Further, height information was extracted as well. Climatic changes from the ERA‐5 reanalysis dataset and normalized difference vegetation index (NDVI) values were processed alongside. Relating the dunes' surface processes to climate model data shows an accordance between slowing migration, expanding vegetation and a decrease in sand drift potential. From 1968 to present time, an average dune migration rate of 7.3 m a−1 was extracted from the satellite images, with an overall reduction of −1.81 m a−1. The resultant drift potential (RDP) values for the GB are calculated to be below 10 m3 s−3 with a spatial decrease, following a direction from the NW to the SE, fitting well with a corresponding decrease in the migration rates. Our results indicate a good agreement between the development of aeolian landforms and the ERA‐5 climate reanalysis model data, even in a high‐altitude setting with complex topography, which is known to influence such datasets.

Sand sources and migration of the dune fields in the central European Sand Belt – A pattern analysis approach

Long-standing studies of the fixed late-glacial dune fields of the European Sand Belt (ESB) indicate that its development was driven by the degradation of permafrost and the widespread incision of rivers. Ice-marginal valleys, smaller valleys and limnic sediments are considered to be the main sand sources for dune fields within the ESB. However, the provenance of particular dune fields has not been independently assessed. Hence, discussion on the dynamics of the ESB dune fields has been limited to general statements about the distance and duration of aeolian transport. This problem was addressed through the geomorphological (pattern) analysis of 40 dune fields located within the central ESB. Using the calculated construction times and assumed migration rates, we identified the distances covered by the dune fields and their potential sand sources. The study confirmed that fluvial and fluvioglacial sediments were the main sand sources for the ESB dune fields. Most dune fields were found to have migrated over distances of 5–15 km during their development, confirming the short and local aeolian transport. At the same time, long-distance migration of dunes in areas located far from the Fennoscandinavian Ice Sheet was not ruled out. Results indicate dune migration rates as low as 0.5–3.5 m/yr. comparable to contemporary dune fields in cold regions. The methods used have the potential for use in studies in dune fields of other climatic zones, although the results need further verification based on geochemical studies.

In-situ characterisation of fluvial dune morphology and dynamics under limited sediment supply conditions, Seine River, France

Dune dynamics and associated sedimentary fluxes have been estimated over a period of a week in the river Seine characterised by limited sediment supply. Distributed into two corridors, typical medium and small dunes associated with fluvial environments have been characterised from multibeam data acquired on four dates, 23-29 March 2021, after a limited peak flood. Dune morphometric parameters have been quantified on cross-dune 1 m spacing of bed elevation profiles and dune migration rates have been calculated by analysing successive multibeam acquisitions. Evidence of limited sediment supply conditions have been recognised from areas uncovered by mobile sediment in the troughs between medium dunes. Under such conditions, bedload transport associated with dune migration has been estimated using three methods: differential bathymetry, dune tracking and the Van Rijn empirical formula using a correction factor accounting for limited sediment supply conditions. The three methods provide similar bedload fluxes (less than an order of magnitude difference), and the small differences are related to input data uncertainties and the capability of these methods to capture sediment transport processes, such as sediment bypassing dunes. Based on field observations, this paper brings new constrains to the relationships between dune morphological parameters, migration rates and sedimentary fluxes and environmental parameters (sediment grain size, flow velocity and water depth) under limited supply conditions in a real river.

Coastal dunes migration over the Itaúnas district - Espírito Santo, humid tropical coast of Southeast Brazil

The migration of transgressive coastal dunes over urban and farming areas is commonly observed in the semi-arid northern coast of the Brazilian northeast. However, it is unusual in the humid tropical coast of southeastern Brazil. This paper aims to investigate the aeolian dynamics and the drivers of the burial process over the Itaúnas District, Espírito Santo State landscape, by transgressive coastal dunes. Methodological procedures consist of remote sensing techniques, geoprocessing, wind regime simulations, and mathematical calculations of migration rate parameters. Satellite images were georeferenced using ArcGIS 10.3 software and wind regime information was simulated using HYSPLIT software using wind reanalysis data. The results suggest a sediment transport rate of 44.98 kg/m/s, wind drift potential of 123.96 v.u. and dune migration rate estimated at 4.0 m/yr. It was found that the northern and western sectors of the studied dunefield have the highest migration rates towards the main access road, water resources and urban area. The values obtained are considered significant because it is a coastal segment subjected to a humid tropical climate.

The morphodynamics of transverse dunes on the coast of South Africa

Transverse sand dunes located within the supratidal zones of beaches are a significant geomorphic feature along sand-dominated coasts worldwide and are generated by strong alongshore winds in areas of high sediment availability. Transverse dunes are present along the South African coast, and these are known to migrate dynamically in response to wind forcing. However, the detailed dynamics of individual dune systems along the same coastal stretch have not been compared to one another, and the relationship of transverse dunes to their hosting beach systems has also not been examined. This study examines the properties and dynamics of transverse supratidal dunes from three systems along the coast of South Africa, using remote sensing methods. Results show that, although the underlying beach system appears to be relatively stable over the time period of analysis, there is a dominant aeolian-driven migration of transverse dunes towards the northeast, following prevailing wind direction, countered by less dominant movement to the southwest. There are also considerable variations in calculated annual dune migration rates between adjacent systems, between summer and winter seasons, and between dunes within a single site. This highlights that, although beach and dune landforms can be conceptually considered as part of the same sediment system, there is not a clear relationship between phases of beach aggradation and phases of dune aggradation. Instead, a primary control appears to be beachface erosion by waves that reduces beach width and influences dune morphodynamics, independent of sediment supply.

A New Method for Automated Measurement of Sand Dune Migration Based on Multi-Temporal LiDAR-Derived Digital Elevation Models

While remote sensing methods have long been used for coastal and desert sand dune studies, few methods have been developed for the automated measurement of dune migration in large dune fields. To overcome a major limitation of an existing method named “pairs of source and target points (PSTP)”, this paper proposes a toe line tracking (TLT) method for the automated measurement of dune migration rate and direction using multi-temporal digital elevation models (DEM) derived from light detection and ranging (LiDAR) data. Based on a few simple parameters, the TLT method automatically extracts the base level of a dune field and toe lines of individual dunes. The toe line polygons derived from two DEMs are processed using logical operators and other spatial analysis methods implemented in the Python programming language in a geographic information system. By generating thousands of random sampling points along source toe lines, dune migration distances and directions are calculated and saved with the sampling point feature class. The application of the TLT method was demonstrated using multi-temporal LiDAR-derived DEMs for a 9 km by 2.4 km area in the White Sands Dune Field in New Mexico (USA). Dune migration distances and directions for three periods (24 January 2009–26 September 2009, 26 September 2009–6 June 2010, and 24 January 2009–6 January 2010) were calculated. Sensitivity analyses were carried out using different window sizes and toe heights. The results suggest that both PSTP and TLT produce similar sand dune migration rates and directions, but TLT is a more generic method that works for dunes with or without slipfaces that reach the angle of repose.

MIGRAÇÃO DE DUNAS E O PROCESSO DE SOTERRAMENTO NO LITORAL DE BARROQUINHA, CEARÁ, BRASIL

A migração dos corpos dunares no litoral cearense enuncia a intensa dinâmica eólica característica de litorais semiáridos nordestinos. Nesse sentido, este trabalho buscou analisar o processo de migração das dunas e sua relação com a questão dos soterramentos no litoral de Barroquinha. As taxas de migração das dunas foram definidas pela extensão Digital Shoreline Analysis System (DSAS), nas quatro áreas de interesse de Bitupitá e localidades de Venâncio e Curimã. A área de avanço das dunas foi obtida por meio do métodopolígono de mudanças. A migração das dunas no período de 2002 a 2014 evidenciou maior média das taxas de migração nas áreas 1 e 2, com 18,53 m/ano e 19,33 m/ano, e valores inferiores de 12,40 m/ano e 3,59 m/ano nas áreas 3 e 4. Ações de mobilização e sensibilização das comunidades são fundamentais para adequação da dinâmica socioespacial aos efeitos da migração dos corpos dunares.&#x0D; Palavras-chave: dunas, dinâmica eólica, soterramento.

Transverse Aeolian Ridge Growth Mechanisms and Pattern Evolution in Scandia Cavi, Mars

In Scandia Cavi on Mars, barchans migrating over a field of transverse aeolian ridges (TARs) leave behind distinctive trails (“wakes”) comprising both TARs undergoing exhumation and coarse-grained ripples being shed from the barchans. With distance upwind from the barchans, the combined pattern of these bedforms coarsens and defect density decreases, thus appearing to mature with exposure time. We present results of morphological analyses of the wake bedform crestlines using HiRISE images, seeking to determine how the wake pattern reflects TAR growth and pattern development. TARs interact with each other, exhibiting defect repulsions and possible lobe extensions, indicating that these bedforms have migrated in the past, despite the lack of identifiable change in overlapping images spanning 9.5 years. Mapping one wake in detail, we found that the TAR pattern is not affected by superposing ripples. However, the ripples undergo many interactions, first with one another, and later (with distance upwind) with the underlying TARs. Near the dune, many ripples laterally link, growing in length, and they preferentially form along TAR crests, resulting in small bedform repulsions and longer superposing ripples. Most of these ripples will be consumed by the TARs, an as-yet unreported growth dynamic for TARs that is consistent with the work of others, who have found a continuum between TARs and the meter-scale ripples that form on dunes. Constructing a DTM, orthorectifying HiRISE images, and measuring dune migration rates places the timescale of ripple absorption by TARs in a wake at several thousand years, with the first ∼1,000 years dominated by lateral linking of ripples. Assuming that TAR growth is accomplished entirely through dune burial and subsequent ripple consumption, we estimate a lower limit age of the TARs, and by extension, the dune field, to be ∼270 kyr.

Whole-island wind bifurcation and localized topographic steering: Impacts on aeolian dune dynamics

Topographic steering has been observed around Gran Canaria, a high-profile circular island located in the Canary Island Archipelago, Spain, culminating in a complex lee-side wind regime at the Maspalomas dunefield. Maspalomas has experienced rapid environmental changes since the 1960s, coincident with a boom in the tourism industry in the region and requires further examination on the linkages between meso-scale airflow patterns and aeolian processes modifying the landscape. The aim of this work is to simulate mean and turbulent airflow conditions at Maspalomas due to incremental changes in the regional wind direction and to compare these results to the predicted and observed aeolian dynamics taken from meteorological records, a global wind retro-analysis model, and remote sensing data. A Smagorinsky Large Eddy Simulation (S-LES) model was used to identify meso-scale airflow perturbations and turbulence at different locations around the island. Variability in meteorological data was also identified, with sites recording accelerated or retarded velocities and directional distributions ranging between unimodal to bimodal. Using a global retro-analysis model, relatively consistent up-wind conditions were predicted over a period coinciding with three aerial LiDAR surveys (i.e., 2006, 2008, and 2011) at the Maspalomas dunefield. Despite the consistent predicted airflow conditions, dune migration rates dropped from 7.26 m y−1 to 2.80 m y−1 and 28% of dunes experienced crest reversal towards the east, or opposite of the primary westerly migration direction during the second time period. Our results indicate that meso-scale airflow steering alters local wind conditions that can modify sediment transport gradients at Maspalomas. Given the rapidity of environmental changes and anthropogenic impacts at Maspalomas, these findings improve our understanding on the aeolian dynamics at Maspalomas and can be used to inform future management strategies. Lastly, the approach used in this study could be applied to other high-profile island settings or similarly complex aeolian environments.

Sand Dune Dynamics Exploiting a Fully Automatic Method Using Satellite SAR Data

This work presents an automatic procedure to quantify dune dynamics on isolated barchan dunes exploiting Synthetic Aperture RADAR satellite data. We use C-band datasets, allowing the multi-temporal analysis of dune dynamics in two study areas, one located between the Western Sahara and Mauritania and the second one located in the South Rayan dune field in Egypt. Our method uses an adaptive parametric thresholding algorithm and common geospatial operations. A quantitative dune dynamics analysis is also performed. We have measured dune migration rates of 2–6 m/year in the NNW-SSE direction and 11–20 m/year NNE-SSW for the South Rayan and West-Sahara dune fields, respectively. To validate our results, we have manually tracked several dunes per study area using Google Earth imagery. Results from both automatic and manual approaches are consistent. Finally, we discuss the advantages and limitations of the approach presented.

Semiautomated Identification and Characterization of Dunes at Hargraves Crater, Mars

AbstractThe Mars Global Digital Dune Database (MGD3) contains information on Martian dune fields and prepared manually from the Thermal Emission Imaging System (THEMIS; 100 m/pixel) images. Although the MGD3 outlines dune fields, it overlooks the recognition of smaller dune forms. This paper aims to identify individual dunes from a semiautomated object‐based image analysis technique and characterize dune materials at Hargraves crater, Mars. MGD3 would benefit to be updated for an improved understanding of the Martian surface and its atmospheric mechanisms at a local scale. An object‐based image analysis technique was applied here to the Context Camera (CTX; 6 m/pixel) data set to extract dune data in a more efficient, reliable, and accurate fashion. This study is a test case in validating a remote sensing method that has wide applicability to the entire Martian surface resulting in an update to the dune database at a higher spatial resolution—providing a better understanding of surface and atmospheric behavior of Mars at the local scale. We also explored the wind flow and dune stability—presenting an insight into the dune modification mechanism—within the crater. The prevailing wind inside the crater flows to the west‐northwest. The dunes are labeled as active (stability index of 2) and do not appear to have been influenced by subsurface water ice or volatiles. We emphasize that the technique used here has a wide prospect in temporal monitoring of dune sediment flux, dune migration or erosion rates, improving near‐surface airflow modeling, and dune stability analysis.

Improved optical image matching time series inversion approach for monitoring dune migration in North Sinai Sand Sea: Algorithm procedure, application, and validation

Sand dune migration poses a potential threat to desert infrastructure, vegetation, and atmospheric conditions. Capturing the patterns of long-term dune migration is useful for predicting probable desertification issues and wind conditions across vast desert areas. In this study, we employed optical image matching and a singular value decomposition approach to estimate the rates of dune migration in the North Sinai Sand Sea using the free Landsat 8 and Sentinel-2 archives. Our optical image matching time-series selection and inversion (OPTSI) algorithm limited the difference in the solar illumination of correlated pairs to decrease shadows and seasonal variability. We found that the maximum annual dune migration rates were 9.4 m/a and 15.9 m/a for Landsat 8 and Sentinel-2 data, respectively, and the results of time-series analysis revealed the existence of seasonal variations in dune migration controlled by wind regimes. The directions of sand movement extracted from the mean velocity solution agreed strongly with each other and with the drift directions estimated using wind data from meteorological stations. We assessed the uncertainty of each solution based on the variance of stable areas. Our results showed that the proposed inversion decreased uncertainty by up to 25% and increased the spatial coverage by up to 20%. This algorithm is also promising for the retrieval of historical time series on the ground displacements of glaciers and slow-moving landslides employing free archives that provide high-frequency images.

Observations of dune interactions from DEMs using through-water Structure from Motion

The role of three-dimensionality (3D) in modulating both flow and sediment transport remains poorly understood. 3D bed elevation measurements are difficult to obtain due to irregular dune shapes and submergence. Using photogrammetric tools for topographic reconstruction has become popular in surface studies, yet water refraction makes through-water image capturing of submerged dunes still challenging. We show that through-water images and Structure from Motion (SfM) tools can produce accurate Digital Elevation Models (DEMs) of a measured dune field, with a high level of detail. It is a low-cost and non-intrusive alternative for submerged bed elevation measurements. We provide a detailed SfM workflow, introduce and discuss the use of camera coordinates and underwater ground control points, and processing steps needed to obtain high accuracy DEMs. Our method results in DEMs with mm resolution in controlled laboratory conditions. New data for 23 dune field DEMs from 6 experiments were obtained and are presented.The dune field DEM time series provide insights on dune interaction processes. In our experiments, merging and defect creation were most common. Merging decreases the number of bedforms, and defect creation is responsible for more bedforms. Dunes continue to interact and jostle after achieving equilibrium. Simple crests are much more frequently observed than irregular, sinuous or double crests. Two-dimensional (2D) crest shapes were observed, although crest shapes were generally of 3D nature. Observed dune migration rates are not steady and vary in time and space. Bedform splitting speeds up dune migration, whilst neighbouring dunes tend to accelerate or decelerate. We identify a cascade of processes and show that 3D DEMs at high frequency are required to resolve observed rapid deformations and interaction of dunes. The identified dune interaction processes are inherent to sediment flux (variability), whereas the temporal component of the underlying sediment transport processes is still not well understood in relation to average transport.

Quantified Aeolian Dune Changes on Mars Derived From Repeat Context Camera Images

AbstractAeolian systems are active across much of the surface of Mars and quantifying the activity of bedforms is important for understanding the modern and recent Martian environment. Recently, the migration rates and sand fluxes of dunes and ripples have been precisely measured using repeat High Resolution Imaging Science Experiment (HiRISE) images. However, the limited areal extent of HiRISE coverage means that only a small area can be targeted for repeat coverage. Context Camera (CTX) images, although lower in spatial resolution, have wider spatial coverage, meaning that dune migration can potentially be monitored over larger areas. We used time series, coregistered CTX images and digital elevation models to measure dune migration rates and sand fluxes at six sites: Nili Patera, Meroe Patera, two sites at Herschel crater, McLaughlin crater, and Hellespontus Montes. We observed dune displacement in the CTX images over long‐term baselines (7.5–11 Earth years; 4–6 Mars years). Bedform activity has previously been measured at all these sites using HiRISE, which we used to validate our results. Our dune migration rates (0.2–1.1 m/EY) and sand fluxes (2.4–11.6 m3 m−1 EY−1) compare well to measurements made with HiRISE. The use of CTX in monitoring dune migration has advantages (wider spatial coverage, faster processing time) and disadvantages (ripples not resolved, digital elevation model dune heights may be underestimates); the future combined use of HiRISE and CTX is likely to be beneficial.

Characterisation of Sand Accumulations in Wadi Fatmah and Wadi Ash Shumaysi, KSA, Using Multi-Source Remote Sensing Imagery

The study area has three sand accumulations: Two in Wadi Fatmah and one in Wadi Ash Shumaysi, midwest of Saudi Arabia. The spatial extents of these sand accumulations have significantly increased over the last few decades. Multi-source satellite imagery, such as CORONA (1967, 1972), SPOT 5 (2013), LandSat TM (1986), and LandSat 8 OLI (2013), enabled monitoring and analysis of the interplay between the changes in the anthropogenic activities and spatial expansion of the areas of sand accumulation. The main driving force of the spatial expansion could be strongly linked to extensive changes in the anthropogenic regimes in the middle zone of Wadi Fatmah and its surrounding landforms and mountain masses. In this context, the once dominant agricultural lands of the middle zone of Wadi Fatmah have been transformed into abandoned agricultural areas. Extensive off-road driving has resulted in soil degradation. Excavation and mining activities for urban spatial expansion are widespread over the valley floor, the adjacent bajada, and the mountain blocks. These anthropogenic activities have remarkably induced strong wind erosion of the soil in severe arid conditions in the middle zone of Wadi Fatmah and Wadi Ash Shumaysi. Wind erosion has eventually produced a sufficient sand budget to be transported into the areas of sand accumulation. The primary consequence of the excess sand budget has been an increase in the spatial extents and dune migration rates of sand accumulations in the study area. However, this increase varies from one sand accumulation to another. In this study, we used multi-source remote sensing imagery and the state-of-the-art COSI-Corr technology to characterize sand accumulations in the study area and to determine the spatio-temporal changes in both the spatial extents and the dune migration rates. The mean annual migration rates of sand dunes in the three sand accumulations ranged from 5.5 and 7.2 to 8.6 m/yr. Analysis of the spatial extent and migration rates of sand accumulations indicates that the study area may have experienced desertification in response to changes in the anthropogenic regimes through the last few decades.

The Imprint of Vegetation on Desert Dune Dynamics

AbstractHere we demonstrate the qualitative and quantitative influence that vegetation has on stabilizing desert dunes. We use topographic data to isolate translation and deformation of dune patterns, upwind of and across a sharp gradient of vegetation, at White Sands dune field, New Mexico. Barchanoid dunes are unstable due to an aerodynamic surface wave instability. The dynamics of vegetated parabolic dunes are different; deformation becomes localized, and random, once plant density reaches a critical value associated with the barchanoid‐parabolic transition. Plants stabilize dunes not only by slowing them down but also by shutting off the fundamental mechanism that generates new sand waves and destabilizes dunes. Increasing plant density downwind increases vegetation‐induced form drag and results in decreasing dune migration rate. We suggest that similar biological modulation of pattern‐forming instabilities may also occur in other landscapes.

Measuring Sand Dune Migration Rates with COSI-Corr and Landsat: Opportunities and Challenges

It has been over a decade since COSI-Corr, the Co-Registration of Optically Sensed Images and Correlation, was first used to produce a raster map of sand dune movement, however, no studies have yet applied it to the full Landsat archive. The orthorectified and geolocated Landsat Level-1 Precision Terrain (L1TP) products offer the opportunity to simplify the COSI-Corr pre-processing steps, allowing an automated workflow to be devised. In the Bodélé Depression, Chad, this automated workflow has calculated average dune speeds of 15.83 m/year and an increase in dune movement of 2.56 m/year ±12.58 m/year from 1987 to 2009. However, this increase does not stem from a systematic increase in dune mobility. The fastest 25% of dunes from 1987 to 1998 reduced their speed by 18.16%. The overall increase stems from the acceleration of features previously moving under 13.30 m/year. While successfully applied to the Bodélé Depression, the automated workflow produces highly variable outputs when applied to the Grand Erg Oriental, Algeria. Variations within path/row scene pairings are caused by the use of mobile features, such as dune crests, as ground control points (GCPs). This has the potential to warp Landsat scenes during the L1TP processing, potentially obfuscating dune migration. Two factors appear to be crucial in determining whether a Landsat scene is suitable for COSI-Corr analysis. Firstly, dune mobility must exceed the misregistration criteria. Secondly, GPCs should be located on static features such as bedrock outcrops.