remotely sensed dune celerity and sand flux measurements of the world s fastest barchans bodele chad quantifying sand flux with field measurements is an expensive and time consuming process we here present an alternative approach using the cosi corr software package for earth surface deformation detection using pairs of aster satellite images we detected dune migration in the bodele depression of northern chad over time intervals of one month to 6 5 years the displacement map can be used to automatically distinguish dunes from interdunes which is a crucial step towards calculating sand flux we interpolated a surface between the interdune areas and subtracted it from a digital elevation model thus obtaining dune heights and volumes multiplying height with celerity yields a pixel by pixel estimate of the sand flux we applied this method to large diatomite dunes in the bodele confirming that these are some of the world s fastest moving barchans plotting dune height against inverse celerity reveals sand flux at the dune crest of 200 m 3 m yr average dune sand flux values for the eastern and western bodele are 76 and 99 m3 m yr respectively the contribution of the dunes to the total area averaged sand flux is 24 29 m 3 m yr which is similar to 10 of the saltation flux determined by previously published field measurements citation vermeesch p and n drake 2008 remotely sensed dune celerity and sand flux measurements of the world s fastest barchans bodele chad geophys res lett 35 l24404 doi 10 1029 2008gl035921

field measurements of the flux and speed of wind blown sand a field experiment was conducted to measure the flux and speed of wind blown sand under known conditions in a natural setting the experiment run at pismo beach california involved a tract 100 m long parallel with the wind by 20 m wide the site was instrumented with four arrays of anemometers to obtain wind velocity profiles through the lower atmospheric boundary layer temperature probes to determine atmospheric stability and wind vanes to determine wind direction from these measurements wind friction speeds were derived for each experimental run in order to measure sand saltation flux a trench 3 m long by 10 m wide transverse to the wind direction by 0 5 m deep was placed at the downwind end of the tract and lined with 168 collector bins forming an egg box pattern the mass of particles collected in each bin was determined for four experimental runs in order to assess various sand trap systems used in previous experiments 12 leatherman traps one fryberger trap and one array of ames traps were deployed to collect particles concurrently with the trench collection particle velocities were determined from analysis of high speed 3000 and 5000 frames per second motion pictures and from a particle velocimeter sand samples were collected from the trench bins and the various sand traps and grain size distributions were determined fluxes for each run were calculated using various previously published expressions and then compared with the flux derived from the trench collection results show that bagnold s 1941 model and white s 1979 equation most closely agree with values derived from the trench comparison of the various collector systems shows that the leatherman and ames traps most closely agree with the flux derived from the trench although these systems tended to under collect particles particle speeds were measured from analysis of motion pictures for saltating particles in ascending and descending parts of their trajectories results show that particle velocities from the velocimeter are in the range 0 5 7 0 m s 1 compared to a wind friction velocity of 0 32 0 43 m s 1 and a wind velocity of 2 7 3 9 m s 1 at the height of the particle measurements descending particles tended to exceed the speeds of ascending particles by 0 5 m s 1

barchan dune mobility in mauritania related to dune and interdune sand fluxes 1 we present a 1 year study of 50 dunes in a small field of barchan dunes in mauritania we documented the morphological evolution of the dunes and their migration rates and measured at 10 min intervals the interdune sand transport the wind strength and its direction for the same interval of time the dune heights h 0 range between 2 and 5 m and their celerity c is found to be well approximated by the standard migration law c q 0 h 0 with q 0 50 m 3 m yr from both the interdune sand flux and the migration rate of the dunes we were able to estimate the spatially averaged sand flux at the dune crest as well as the bulk sand flux associated with the mass of sand transported by the dune we found that the sand flux at the crest was about 3 times greater than the interdune mass transport rate whereas the bulk sand flux was surprisingly of the same order as the interdune flux moreover we analyzed carefully the interdune sand transport data which can be well described by the sorensen law the cumulative mass of sand transported during moderate wind events within 1 year was much greater than that transported during strong wind events

wind sedimentation in the jafurah sand sea saudi arabia the jafurah sand sea of the eastern province of saudi arabia extends along the arabian gulf coastline from kuwait in the north to the rub al khali in the south a distance of about 800 km sand drifts southward to south eastward from regions of high wind energy in the north to low wind energy in the south the aeolian landscape is zoned with areas of deflation transport and deposition from north to south drift rates in the zone of transport near abqaiq range from 2 m3 m w 1 yr 1 on sabkhas to 29 m3 m w 1 yr 1 on the crests of dunes average drift rates of approximately 18 m3 m w 1 yr 1 observed during the study can cause about 1 m of accumulation per 5500 yr in a 100 km zone of deposition downwind not including the bulk transport represented by the forward advance of dunes dune advance ranged from 23 m 2 9 m high dune to 3 m 23 m high dune during april october 1980 the study area consists of dune interdune sand sheet and siliciclastic sabkha terrains each of which is characterized by differing drift rates and differing rates of erosion or deposition sedimentation occurs by lateral movement of dunes and interdunes and vertical accretion by sand sheets and sabkhas

dust raising in the dustiest place on earth the bodele in northern chad is the dustiest place on earth it is dusty because of the co location of strong near surface winds and a large exposure of low density friable diatomite data are reported from three kinds of observation on dust generation in the bodele a two automatic weather stations and pilot balloon tracking complemented with reanalysis data measuring and estimating wind velocities b sun photometers measuring atmospheric dust concentrations c a vacuum pump dust sampler and an array of mwac sediment samplers measuring in situ sediment transport with these data we develop four hypotheses about dust generation 1 the pulsing of dust output from the bodele depends primarily on the varying strength of a low level jet llj i e at this scale dust production is transport limited 2 the most prolific mechanism of dust production is the breakdown of saltating diatomite flakes as they collide with each other and with the surface 3 disturbance of flow around the large barchans particularly turbulence and convergence on their horns is a major contributor to dust production i e the dunes are dust mills 4 in consequence dust production is localised within the main exposure of diatomite to places where there are the most dunes as on the eastern and northern fringes of the exposure

spatial analysis of sand dunes with a new global topographic dataset new approaches and opportunities on june 29 2009 version 1 of the aster gdem advanced spaceborne thermal emission and reflection radiometer global digital elevation model was made available at no cost or restrictions to users worldwide via electronic download the aster gdem provides expanded spatial coverage and better resolution than other global digital elevation models dems in this paper we demonstrate how the aster gdem provides new opportunities for investigating large aeolian sand dunes in three dimensions two dune specific spatial analysis methods are presented to illustrate potential applications of these data for discriminating dune generations and quantifying spatial variations of sediment supply moreover we review how existing and emerging fields of dune pattern analysis and simulation modeling will be able to make significant advances through application of these data potentially leading to future progress in studies of dune morphodynamics environmental controls and paleoenvironmental reconstructions copyright 2010 john wiley sons ltd

a 45 year time series of dune mobility indicating constant windiness over the central sahara although evidence is mounting that links global warming to changes in atmospheric dynamics over the atlantic realm similar studies over the african continent are lacking and even if such models would exist it would be difficult to verify their validity due to the paucity of meteorological observations and anemometers in the central sahara a pragmatic way around this problem is to monitor barchan dune velocity as a proxy for the windiness of desert areas dune migration rates are a measure of the amount of work done by the wind which does not require field measurements but can be observed from space instead this paper presents a novel application of the remote sensing tool cosi corr for the construction of time series of dune mobility from sequences of optical satellite imagery the technique has been applied to the bodele depression in northern chad to demonstrate that dune migration rates in the central sahara have been remarkably constant for nearly half a century leading us to conclude that wind velocities have not changed more than 0 2 per year over that period it is therefore unlikely that the frequency and intensity of dust storms originating from this hot spot has significantly changed over the past decades either

links between topography wind deflation lakes and dust the case of the bodele depression chad the bodele depression chad is the planet s largest single source of dust deflation from the bodele could be seen as a simple coincidence of two key prerequisites strong surface winds and a large source of suitable sediment but here we hypothesise that long term links between topography winds deflation and dust ensure the maintenance of the dust source such that these two apparently coincidental key ingredients are connected by land atmosphere processes with topography acting as the overall controlling agent we use a variety of observational and numerical techniques including a regional climate model to show that 1 contemporary deflation from the bodele is delineated by topography and a surface wind stress maximum 2 the tibesti and ennedi mountains play a key role in the generation of the erosive winds in the form of the bodele low level jet llj 3 enhanced deflation from a stronger bodele llj during drier phases for example the last glacial maximum was probably sufficient to create the shallow lake in which diatoms lived during wetter phases such as the holocene pluvial winds may therefore have helped to create the depression in which erodible diatom material accumulated instead of a simple coincidence of nature dust from the world s largest source may result from the operation of long term processes on paleo timescales which have led to ideal conditions for dust generation in the world s largest dust source similar processes plausibly operate in other dust hotspots in topographic depressions

retrieving sand dune movements using sub pixel correlation of multi temporal optical remote sensing imagery northwest sinai peninsula egypt sand dune movements pose potential hazards against various land use activities in egypt to avoid or to minimize the hazards associated with sand dunes it is critical to determine their rates and patterns of migration at high accuracy and over wide spatial coverage this is however a real challenge using field work and traditional remote sensing approaches the co registration of optically sensed images and correlation cosi corr complements traditional approaches to provide accurate measurements at wide spatial coverage applying the cosi corr technique to two spot 4 panchromatic images acquired above north sinai we measured lateral migration of 6 0 to 19 4 m yr with an average of 7 7 m yr and 9 3 to 15 0 m yr with an average of 11 9 m yr for the whole barchans dune areas and a selected sample of barchan dunes respectively we also detected that the lateral movements along the crest lines of linear dunes ranged from 4 0 to 20 1 m yr with an average of 6 8 m yr for the whole area occupied by linear dunes for a selected linear dune within the study area the lateral migration of peaks and saddles along the crest lines ranged from 5 5 to 16 7 m yr with an average of 12 4 m yr the lateral migration of both barchans dunes and linear dunes showed high spatial variability validation of these results against the previously measured migration rates indicated high degree of accuracy of the technique in addition the displacement field produced from the correlation indicated that the direction of sand dune movements occurred towards the east and southeast which is well aligned with the previously determined sand dune drifting potentials

predictability of dune activity in real dune fields under unidirectional wind regimes we present an analysis of 10 dune fields to test a model derived hypothesis of dune field activity the hypothesis suggests that a quantifiable threshold exists for stabilization in unidirectional wind regimes active dunes have slipface deposition rates that exceed the vegetation deposition tolerance and stabilizing dunes have the opposite we quantified aeolian sand flux slipface geometry and vegetation deposition tolerance to directly test the hypothesis at four dune fields bigstick white sands stable white sands active and cape cod we indirectly tested the hypothesis at six additional dune fields with limited vegetation data hanford ano nuevo skagen odde salton sea oceano stable and oceano active inverse calculation sites we used digital topographic data and estimates of aeolian sand flux to approximate the slipface deposition rates prior to stabilization results revealed a distinct quantifiable and consistent pattern despite diverse environmental conditions the modal peak of prestabilization slipface deposition rates was 80 of the vegetation deposition tolerance at stabilized or stabilizing dune fields results from inverse calculation sites indicate deposition rates at stabilized sites were near a hypothesized maximum vegetation deposition tolerance 1 m a 1 and active sites had slipface deposition rates much higher overall these results confirm the hypothesis and provide evidence of a globally applicable simple and previously unidentified predictor for the dynamics of vegetation cover in dune fields under unidirectional wind regimes

the application of cosi corr to determine dune system dynamics in the southern namib desert using aster data the coregistration of optically sensed images and correlation cosi corr algorithm was used to estimate dune migration and sand flux rates from a series of remotely sensed optical image pairs several areas of barchan and transverse dunes transport sand along definite pathways feeding the southern part of the namib sand sea from beaches and deflationary basins in the sperrgebiet we give a detailed description of the pre and post processing routines used for our cosi corr analysis and we evaluate the sub pixel dune migration results at the dune and dune field scales the best set of parameters for the application of the algorithm was systematically derived resulting in methodological refinements of the cross correlation windows the advanced spaceborne thermal emission and reflection radiometer aster sensor aboard the terra satellite provided the remote sensing imagery few comparisons have been made between dune migration measurements using cosi corr and other types of change detection analysis and few dune fields have served as test cases for cosi corr we suggest that analysis and interpretation of cosi corr output from aster data is more valuable if combined with other image analysis techniques such as manual digitization of dunes in a geographic information system gis processing of write memory function insertion wmfi imagery and multispectral image msi analysis of composition the dune migrations estimated from cosi corr results were validated using gis and wmfi and later msi analysis added an important regional contextual framework of sand transport pathways the synthesis of these works lends more confidence to understanding the namib dune system s dynamics and provides a basis for future comparisons to other dune fields copyright 2013 john wiley sons ltd

insight into the neogene tectonic history of the northern bolivian orocline from new paleomagnetic and geochronologic data a paleomagnetic study of 36 sites 315 samples of neogene strata from the peruvian altiplano and adjacent sub andean belt pilcopata area combined with 40ar 39ar dating of 13 lava flows provide new constraints on the cenozoic deformation history of the northern bolivian orocline in the peruvian altiplano 40ar 39ar dating brackets the age of the strata sampled for paleomagnetism between 26 5 and 12 1 ma for the huaccochullo basin 18 6 and 12 1 ma for the descanso yauri basin and 16 8 and 15 5 ma for the ayaviri basin sub andean sediments are paleontologically constrained as miocene yet pre 9 ma prefolding magnetizations isolated in the huaccochullo descanso yauri and pilcopata localities indicate significant counterclockwise vertical axis block rotations of 11 3 5 4 31 0 10 2 and 7 8 4 8 respectively the pattern of rotations together with mapped structures suggest that deformation of the northern altiplano was partitioned into large regions experiencing relatively minor rotation versus smaller isolated basins exhibiting high amplitude counterclockwise rotations that lie in a major left lateral shear zone our new results imply significant transpressional deformation occurred throughout the peruvian altiplano since circa 12 ma and are integrated in a model detailing the tectonic evolution of the northern bolivian orocline since 25 ma

remote sensing and spatial analysis of aeolian sand dunes a review and outlook abstract for more than four decades remote sensing images have been used to document and understand the evolution of aeolian sand dunes early studies focused on mapping and classifying dunes recent advances in sensor technology and software have allowed investigators to move towards quantitative investigation of dune form evolution and pattern development these advances have taken place alongside progress in numerical models which are capable of simulating the multitude of dune patterns observed in nature the potential to integrate remote sensing rs spatial analysis sa and modeling to predict the future changes of real world dune systems is steadily becoming a reality here we present a comprehensive review of significant recent advances involving rs and sa our objective is to demonstrate the capacity of these technologies to provide new insight on three important research domains 1 dune activity 2 dune patterns and hierarchies and 3 extra terrestrial dunes we outline how several recent advances have capitalized on the improved spatial and spectral resolution of rs data the availability of topographic data and new sa methods and software we also discuss some of the key research challenges and opportunities in the application of rs and sa dune field including the integration of rs data with field based measurements of vegetation cover structure and aeolian transport rate in order to develop predictive models of dune field activity expanding the observational evidence of dune form evolution at temporal and spatial scales that can be used to validate and refine simulation models the development and application of objective and reproducible sa methods for characterizing dune field pattern and expanding efforts to quantify three dimensional topographic changes of dune fields in order to develop improved understanding of spatio temporal patterns of erosion and deposition overall our review indicates a progressive evolution in the way sand dunes are studied whereas traditional field studies of airflow and sand transport can clarify event based process form interactions investigators are realizing a synoptic perspective is required to address the response of dune systems to major forcings the integration and evolution of the technologies discussed in this review are likely to form a foundation for future advances in aeolian study

the implications for dust emission modeling of spatial and vertical variations in horizontal dust flux and particle size in the bodele depression northern chad the bodele depression has been confirmed as the single largest source of atmospheric mineral dust on earth it is a distinctive source because of its large exposure of diatomite and the presence of mega barchan dunes direct measurements of horizontal dust flux and particle size were made to investigate dust emission processes and for comparison with mechanisms of emission assumed in current dust models more than 50 masts with traps mounted on each were located across and downwind of three barchans in 56 km2 study area of the eastern bodele the size distribution of surface material is bi modal there are many fine dust modes and a mixed mineralogy with a particle density three times smaller than quartz horizontal fluxes up to 70 m above the playa of particles up to 1000 m in diameter are produced frequently from the accelerated flow over and around the barchans even in below threshold shear conditions on the diatomite playa our data on dust sizes do not conform to retrievals of dust size distributions from radiance measurements made in the same area dust emission models for the region may need to be revised to account for saltators in the bodele which are a mixture of quartz sand and diatomite flakes the great spatial and vertical variation in the abundance mass and density of dust and abraders and the patterns of surface erodibility all of these have important local effects on the vertical dust flux and its particle sizes

shorelines in the sahara geomorphological evidence for an enhanced monsoon from palaeolake megachad the sahara desert is the most extensive desert on earth but during the holocene it was home to some of the largest freshwater lakes on earth of these palaeolake megachad was the biggest landsat tm images and shuttle radar topography mission srtm digital topographic data reveal numerous shorelines around palaeolake megachad at its peak sometime before 7000 years ago the lake was over 173 m deep with an area of at least 400 000 km2 bigger than the caspian sea the biggest lake on earth today the morphology of the shorelines indicates two dominant winds one northeasterly that is consistent with the present day winds in the region the other originated from the southwest we attribute it to an enhanced monsoon caused by a precessionally driven increase in northern hemisphere insolation subsequent desiccation of the palaeolake is recorded by numerous regressive shorelines in the sahara desert

sensitivity analysis of sub pixel correlation technique for measuring coseismic displacements using a pair of aster images abstract coseismic displacements play a key role in understanding earthquake dynamics to derive displacement fields from optical and microwave remote sensing datasets various methods are available this study evaluated in detail the offset tracking technique on optical aster data for 2005 kashmir earthquake this technique required input parameters like resampling methods correlator types window sizes and step sizes for accurate displacement field calculation careful selection of these parameters is imperative which depends on the study area and dataset characteristics in the study we made relative comparisons of coseismic displacement fields calculated by using different combinations of input parameters the results were validated by field based displacement data of vertical separation validation was based on the hypothesis that horizontal displacement component may also have vertical component contribution depending upon local characteristics of the fault validation results showed that general trend of the measured displacements was in agreement with the field data field measurements were bounded within the uncertainty limits of the technique however at some locations significant deviations were also observed all the coseismic displacement results obtained by using different input parameter were within the uncertainty limit 1 10 of the pixel size except for window size 4 4 and 8 8 the measured component of the fault rupture for northwest of muzaffarabad is irregular it may be due to rugged topography as compared to southeast part the measured fault rupture also coincided to surface rupture mapped in the field analysis of the results showed that in comparison to standard parameter set defined in the literature sinc resampling method frequential correlator with window size 32 32 and step size 8 selection of resampling method and correlator type had no significant effect on the calculated displacement field however window size and step size were found to be the most important parameters of the technique this study showed that changing the window size does not affect the detection limit of the technique but induces bias in the calculations step size is used in relation to window size however relatively larger step size is found to provide better sensitivity and accuracy of the technique

monitoring migration rates of an active subarctic dune field using optical imagery we developed a novel method to quantify subtle rates of landscape evolution using two satellite imaging systems with different viewing angles and spectral sensitivities we selected the slowly migrating high latitude subarctic great kobuk sand dunes gksd kobuk valley national park alaska usa for our study the cosi corr technique was used for precise orthorectification co registration and subpixel correlation of satellite data aster visible near infrared vnir and spot panchromatic images with a 5 year temporal separation were correlated to measure the horizontal velocity of the gksd to reduce correlation noise aster vnir bands were linearly mixed to match the spot panchromatic band and raw correlation measurements were projected onto a local robust migration direction to estimate unbiased velocity magnitudes the results show that the most likely migration rate for the gksd ranges from 0 5 to 1 5 m year with peak velocities up to 3 8 m year and uncertainty of approximately 0 16 m year the unprecedented ability to measure slow migration rates including those that may occur over a relatively short time interval illustrates the value of this method to reliably detect and monitor subtle ground movements including dune migration glacier flow mass movements and other small scale processes

megaripple migration on mars aeolian megaripples with 5 to 50 m spacing are abundant on the surface of mars these features were repeatedly targeted by high resolution orbital images but they have never been observed to move thus aeolian megaripples especially the bright toned ones often referred as transverse aeolian ridges tars have been interpreted as relict features of a past climate in this report we show evidence for the migration of bright toned megaripples spaced 1 to 35 m 5 m on average in two equatorial areas on mars indicating that megaripples and small tars can be active today the moving megaripples display sand fluxes that are 2 orders of magnitudes lower than the surrounding dunes on average and unlike similar bedforms on earth can migrate obliquely and longitudinally in addition the active megaripples in the two study areas of syrtis major and mawrth vallis show very similar flux distributions echoing the similarities between dune crest fluxes in the two study areas and suggesting the existence of a relationship between dune and megaripple fluxes that can be explored elsewhere active megaripples together with high sand flux dunes represent a key indicator of strong winds at the surface of mars a past climate with a denser atmosphere is not necessary to explain their accumulation and migration

object based dune analysis automated dune mapping and pattern characterization for ganges chasma and gale crater mars abstract a method that enables the automated mapping and characterization of dune fields on mars is described using ctx image mosaics the introduced object based dune analysis obda technique produces an objective and reproducible mapping of dune morphologies over extensive areas the data set thus obtained integrates a large variety of data allowing a simple cross analysis of dune patterns spectral and morphometric information and mesoscale wind models two dune fields located in gale crater and ganges chasma were used to test and validate the methodology the segmentation of dune related morphologies is highly efficient reaching overall accuracies of 95 in addition we show that the automated segmentation of slipface traces is also possible with expected accuracies of 85 90 a qualitative and quantitative comparison of the final outputs with photointerpretations is performed and the precision of the directional characterization of the dune patterns is evaluated we demonstrate a good agreement between the obda outputs and the photointerpreted dune morphologies with local trend deviations below 45 for 80 95 of the mapped areas because the developed algorithm is tuned for the recognition of linear features from the imagery the slipfaces of small barchans can be preferentially overlooked owing to their small extent at the spatial resolution of the ctx mosaics dune types composed of longer linear morphologies are much better represented including correct mapping of secondary structures having proved the effectiveness and accuracy of the mapping procedure we discuss its future applications for the improvement of dune catalogs on mars

evaluation of saltation flux impact responders safires for measuring instantaneous aeolian sand transport intensity the measurement of aeolian sand transport rates on small scales is of interest to the development and testing of detailed models of sand movement by wind this paper reports on laboratory evaluations and preliminary field tests of a new design of a piezo electric impact responder called a safire capable of measuring saltation impacts at a frequency of 20 hz the advantages of the safire are 1 that it provides high frequency measurements 2 that it presents a minimal obstruction to the wind flow no scour observed in the field and 3 that it is of a relatively low cost laboratory calibrations were performed with a vertical gravity flume generating known sand grain fluxes using both mixed sand and specific size fractions initial tests investigated three fundamental characteristics correspondence between digital and analogue signals generated by the instrument directional response of the probe and linearity of instrument response to mass flux instrument calibration included determination of the momentum threshold required for the sensor to register a grain impact based on this lower limit and the known distribution of grain size and speed at different fall heights a prediction is made as to the sand grain flux the safire ought to measure which is then compared with the signal response the result of this comparison is an assessment of the instrument s efficiency in counting saltating grains these safires were also deployed in the field as part of a larger investigationof spatio temporal transport variability thisexperiment providedthe opportunity to compare the instrument s performancewithtraditional sandtraps andthispaperdevelopsmethodsandassumptionsrequiredtoconvertmeasurements from impact responders to traditional mass transport rates the evaluations indicate that improvements to the instrument production process are required to ensure a standard momentum threshold among individual instruments furthermore the sensor design needs to be reconsidered in order to eliminate the variation in response depending on azimuth direction so that the sensor is uniformly omni directional d 2003 elsevier b v all rights reserved

movement of a small slipfaceless dome dune in the namib sand sea namibia abstract the migration of a small slipfaceless dome dune close to the northern edge of the namib sand sea has been measured by topographic survey the dune dimensions are 45 m wide and 1 m high with a volume of 551 m3 that has been calculated as the difference between the dune s surface elevation and an interdune surface extrapolated from measurements around the edge of the dune the migration direction 64 and distance moved 90 m are measured against stakes set out in 1976 the dune has moved about 90 m between 1976 and 1999 this is an average linear migration rate of around 4 m year 1 and is equivalent to an annual sand transport rate of about 1 2 tonnes m 1 year 1 the calculated total potential sand flow in this part of the namib desert is 119 tonnes m 1 year 1 and the resultant potential sand flow is 63 tonnes m 1 year 1 the dune migration is therefore about 1 of the total potential sandflow and 2 of the resultant indicating that dune migration is only a small part of total potential sand transport the results suggest that small slipfaceless dome dunes are very inefficient at trapping sand and that winds blowing across the interdune in this area are undersaturated with sand

quantifying the spatio temporal patterns of dune migration near minqin oasis in northwestern china with time series of landsat 8 and sentinel 2 observations abstract investigation of the spatio temporal patterns of dune migration in a large scale area with optical remote sensing techniques can help us to better understand aeolian phenomena and mitigate sand dust disasters with the rapid growth in data volume extracting more accurate dune displacement time series and rates from optical observations has become possible however the method is not yet fully fledged to address this issue we propose an extended algorithm for the mature optical imagery cross correlation oicc technique based on landsat 8 l8 and sentinel 2 s2 acquisitions the main innovative points of this algorithm are 1 the proposed pairing strategy for the oicc processing 2 the modularized post processing procedures for noise removal and 3 the introduction of singular value decomposition svd time series inversion of the redundant optical observations to quantify the dune migration to test the effectiveness of this algorithm it was applied in the study of dune migration near minqin oasis in northwestern china using enriched l8 and s2 images collected between april 2013 and april 2018 compared with the original oicc results in stable areas the post processing and inversion of the proposed algorithm reduce the uncertainty by around 22 35 and 3 5 for l8 29 48 and 5 12 for s2 respectively the cross comparison between the l8 and s2 derived displacement time series shows high consistency and presents a lower uncertainty than the result of the traditional no inversion method furthermore the derived displacement rates show spatial patterns that are similar to those of the manually digitized results obtained with historical google earth ge images these comparisons show the advantage of the proposed algorithm in automatically and accurately quantifying dune migration taking into account these measurements the spatio temporal evolution patterns of dune migration in the study area were analyzed from the spatial perspective the sand dunes move along a northwest southeast axis with four detected transport pathways our research also shows that around 1087 7 km2 of dune fields present an active status the active sand dunes are currently encroaching on around 155 5 km2 and 4 4 km2 of land each year outside and inside the oasis respectively representing a problem of rapid desertification temporally the displacement time series along the dominant migration direction appears as seasonal variations that are seemly consistent with the changes in local atmospheric conditions the proposed algorithm provides a new perspective to investigate the spatio temporal evolution of dune migration with medium resolution l8 and s2 optical datasets

analyzing dune dynamics at the dune field scale based on multi temporal analysis of landsat tm images abstract studying dune dynamics at the dune field scale requires intensive fieldwork and a relatively huge dataset however this is not always possible with the high cost and the limited availability of data here we present a technique based on the analysis of multi temporal landsat tm images for studying the dynamics of different dune morphologies from five dune field sites around the world a pair of landsat tm images for each site has been used after performing several steps of image pre processing and enhancement i e image co registration radiometric calibration and histogram equalization rgb clustering is a commonly used algorithm for data compression and iso clustering in this study we implemented this technique as an unconventional change detection algorithm with 32 clustering partitions per band a bi temporal layerstack of the near infrared bands was the input for the rgb clustering process rgb clustering produced thematic maps that gave an immediate insight into the dune dynamics at the dune field scale given the availability of landsat images the technique gave the best results with dunes developed under uni directional wind pattern in addition it was also easier to detect migration of simple dunes than in compound or complex dunes these maps can be used as a bi temporal digital atlas of large dune systems and help in defining areas for detailed field measurements on dune dynamics and migration moreover it can be implemented in analyzing aeolian systems where field measurements are practically impossible i e large and extra terrestrial aeolian systems

aeolian slipface dynamics and grainflow morphologies on earth and mars abstract in 2015 an active dune field on mars was visited up close by the curiosity rover in gale crater providing the first high resolution ground images of fine scale windblown features not previously resolved from orbital based imagery for the first time these images allow for direct comparison with terrestrial aeolian dynamics and provide critical ground truth data to bridge the gap between model predictions and satellite observations the image data from the slipface on the namib dune within the bagnold dune field shows grainflow morphologies that are similar to dunes on earth quantitative estimates of flow thickness based on shadow length are presented for the grainflows on the namib dune slipface and compared to grainflow characteristics measured by terrestrial laser scans from the maspalomas dune field located in gran canaria spain using observations from maspalomas to support interpretations of martian slipface dynamics we discuss implications for the local wind regime style of grainflow seasonal activity and dune migration the presence of multiple large magnitude grainflows on the namib slipface suggests an active aeolian environment capable of delivering enough sediment to the slipface to initiate these flows and transport sediment to the bottom of the lee slope however the thinness of grainflows on the namib dune the formation of smaller grainflows directly below the dune brink and limited grainfall suggest a lower wind energy environment at least for the most recent slipface activity large actively migrating stoss ripples obliquely oriented to the dune crest regularly deposit sediment on to the upper slipface and may be a mechanism in which larger grainflow occur during seemingly low energy wind events this mechanism of sediment delivery may also explain the existence of a variety of slipface morphologies both young and old which are otherwise quickly erased on earth due to sediment redistribution and grainfall

planetary science martian sand blowing in the wind high resolution spacecraft images show surprisingly large rates of sand transport on mars this finding suggests that the planet s surface is a more active environment than previously thought see letter p 339 there is clear evidence for wind erosion and dune formation on the surface of mars but the extent of these movements and whether the processes are current have remained unclear analysing data from the high resolution imaging science experiment hirise on the mars reconnaissance orbiter bridges et al measure the migration of sand ripples across the nili patera dune field in the martian southern hemisphere they find that the dunes have surprisingly large sand fluxes equivalent to those seen in extreme desert conditions on earth one view of mars has been that conditions since the end of the hesperian period between 1 8 billion and 3 5 billion years ago have been fairly static with very low erosion rates but these findings suggest that in parts of mars at least there are strong gusts of sand and wind still making themselves felt

earth like sand fluxes on mars strong and sustained winds on mars have been considered rare on the basis of surface meteorology measurements and global circulation models raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process recent studies showed sand activity but could not determine whether entire dunes were moving implying large sand fluxes or whether more localized and surficial changes had occurred here we present measurements of the migration rate of sand ripples and dune lee fronts at the nili patera dune field we show that the dunes are near steady state with their entire volumes composed of mobile sand the dunes have unexpectedly high sand fluxes similar for example to those in victoria valley antarctica implying that rates of landscape modification on mars and earth are similar

major elements and mg of the moon results from chang e 1 interference imaging spectrometer iim data abstract major elements such as fe ti mg al ca and si play very important roles in understanding the origin and evolution of the moon up to now there are still no high resolution maps for all the six major elements and mg showing their abundances and distributions the objective of this paper is to introduce the techniques and results to create high resolution maps of the six major elements with chang e 1 interference imaging spectrometer iim data the elemental contents of returned soils and feldspathic lunar meteorites are used as ground truth and correlated with the reflectance of the landing sites and northern farside highlands extracted from chang e 1 iim data the relationships linking geochemical information and optical data are established with empirical methods the final maps of the abundances of the six major oxides are produced with the modified partial least squares regression plsr model at a spatial resolution of 200 m pixel at the equator finally some implications for example producing the high resolution map of mg identifying the crustal heterogeneity of lunar highlands helping to search for ha basalts assessing the average elemental abundances of each terrane and the whole moon of these new maps are shown

persistent aeolian activity at endeavour crater meridiani planum mars new observations from orbit and the surface abstract aeolian driven bedform activity is now known to occur in many regions of mars based on surface and orbital observation of contemporary martian ripple and dune mobility events many of these sites have only been monitored with sufficient resolution data for the last few mars years when the high resolution imaging science experiment hirise began acquiring images of mars one exception is the well monitored endeavour crater in meridiani planum which was one of the first known sites of unambiguous dune activity migration and deflation however those early detections used lower resolution images over longer temporal baselines versus the hirise data now available leaving some measurements poorly constrained new orbital and surface observations of endeavour show multiple spatial cm m km and temporal seasons mars year scales of aeolian driven surface change which confirms earlier reports dome dunes in the eastern portion of the crater persistently deflate disseminating dark sand across lighter toned regolith and or eroded bright dust and likely contribute to the crater interior s episodic decreases in orbital albedo measurements other dome dunes are detected with the highest migration rates 4 12 m per mars year and volumetric sand fluxes reported yet for mars estimated dune construction times or turnover times here and elsewhere on mars are significantly shorter than martian obliquity cycles implying that it is not necessary to invoke paleoclimate wind regimes to explain current dune morphologies located on the crater rim the opportunity rover detected evidence for near and far field aeolian driven activity with observations of spherules sand movement in the rover workspace bedform albedo alteration and dust lifting events observations of intracrater dunes show periodic shifting dark streaks that significantly constrain local wind regimes directionality and seasonality constraints on wind directions from surface and orbital images show that aeolian bedforms can be extremely active in bi and possibly tri modal wind regimes and during periods without major dust storms