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IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING, VOL. 9, NO. 1, JANUARY 2016 159

Internal Structure of Sand Dunes in the Badain JaranDesert Revealed by GPR

Rongyi Qian and Lanbo Liu

Abstract—In spite of the prevailing dry and windy climate con-ditions the mega dunes in the Badain Jaran Desert in northwesternChina are relatively moist underneath a dry surface layer of lessthan 1 m. It is very common to find a salt lake directly at thefoot of the leeward side of a mega dune. Using 50- and 100-MHzantennas we have conducted ground penetrating radar (GPR) sur-veys on both the windward and leeward sides of a couple of sanddunes in southeastern part of the Badain Jaran Desert. The GPRsurveys clearly revealed the existence of numerous, quasi-evenlyspaced bedding features on the windward side of the mega dunes,with a slope of orientation parallel to the slope of the leeward sideof the dunes which closely coincides with the angle of repose ofdry sands. The reason for the existing beddings is that on the lee-ward side sands on the dune surface can be cemented by moisturewith periodic precipitation into layered beddings; and the calichesgenerated by these calcareous cement will be likely inducing moreinfiltrated water flow toward the leeward side and consequentlychanneling more local recharging water to the leeward side thanto the windward side. The calcareous cement beddings performedas the ‘skeleton’ of the dunes and increased the mechanic strengthof the sands and consequently facilitated the build-up of the highelevation mega dunes. This trend may be one of the key factors thathelp the existence of the lakes in a very arid environment with highevaporation rate. The GPR profile also clearly registered the watertable beneath the sand dunes that gradually elevated toward thecrest, implies that the desert lakes are recharged at least partly bythe groundwater from local source. Numerically simulated radarprofiles precisely reconstructed the observed profiles. It is a strongsupport to the rationality of the proposed internal structure of thedunes.

Index Terms—Badain Jaran Desert, calcareous cement,infiltration, sand dune structure.

I. INTRODUCTION

T HE Badain Jaran Desert in Alxa Plateau in western InnerMongolia has the second largest dune field in China. It

also has the highest mega-dunes in China, located in the south-east part of the Badain Jaran Desert, with the maximum heightof up to about 500 meters [1], [2]. (While Cerro Blanco sanddune in Peru is the highest sand dune in the world, measuring astaggering 2,078 meters above sea level and 1,176 meters from

Manuscript received November 29, 2014; accepted April 15, 2015. Dateof publication May 14, 2015; date of current version January 28, 2016. Thiswork was supported partially supported by the Natural Science Foundation ofChina through Project #91125024 and by University of Connecticut ResearchFoundation. (Corresponding author: Lanbo Liu.)

R. Qian is with the School of Geophysics and Geoinformation Technology,China University of Geosciences, Beijing 100083, China.

L. Liu is with the Department of Civil and Environmental Engineering,University of Connecticut, Storrs, CT 06269-3037 USA (e-mail: [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JSTARS.2015.2426507

base to peak). Despite the prevailing dry and windy climate inmodern time the mega dunes were relatively moist underneatha dry surface layer of sands with a thickness of about less thanone meter. Between the giant mega-dunes it is common to finda beautiful inter-dune lake directly at the foot of the leewardside of a mega dune, probably existing for a long time since theonset of the last inter-glacial age (∼11, 000 BP) [3]. Directlyrelated to the question of life duration of the inter-dune lakes,the issue of recharge-evaporation budget balance is still underbroad debate and no decisive evidence and conclusion has beenreached in the scientific community.

The question of the geological time when the Badain Jarandesert was formed is also under broad debate [4]. The rangeof the formation of the deserts in Northwest China is as wideas 0.5–2 Ma BP (million years before present) [5]. However,most researchers agree that the formation of this desert isclosely associated with the climatic response to the uplift of theTibetan Plateau. Studies in the dune fields and luminescencechronology revealed that both the stability of dunes and theextension of dune fields have undergone distinct variations inthe Late Quaternary. Strongly cemented, laterite-colored duneswere observed on the eastern margin of the Badain Jaran andthey were dated to ca 57–51 ka by thermoluminescene dating[6]. Similar aeolian sands underlying sandy loess on the easternmargin of the Badain Jaran were dated to ca 121 ka, showingthat the extent of the dune fields were larger at those times thanat present [6], [7].

Major characteristics of sand dunes are their shape, internalstructure and migration speed and direction. These parametersclosely relate to the climatic and depositional environment thatcreate and preserve the dunes and are consequently importantindicators for classification of a dune system [8]. As we focuson the theme of the formation of the mega-dunes in the BadainJaran Desert, the current hypothesis attributes the formationhigh mega-dunes to two factors that were thought crucial tothe formation of mega-dunes: a) overlapping of dunes formedduring various periods associated with climate fluctuations; andb) underlying bedrock landforms [7].

In this paper we report the study of the internal structureof the sand dunes using ground penetrating radar (GPR) sur-veys at two sites in the Badain Jaran Desert. We also conductedand verification and validation through numerical simulation ofradar wave propagation in a model closely resemble a typicalsand dune using electromagnetic parameters inferred from fieldobservations. We start from a section to describe the fundamen-tal geomorphological observations of sand dunes in this area toput our GPR study into the context of a larger picture. Next, wedescribe the GPR surveys these two sites in the Badain Jaran

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160 IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING, VOL. 9, NO. 1, JANUARY 2016

Fig. 1. Satellite image of the southeast part of the Badain Jaran Desert. The twolocations of GPR surveys (Baddam Lakes and Sumin Lake) are identified. Thetwo red bars are the locations of the topographic elevation maps and profilesshown in Figs. 3 and 9.

Desert: the Baddam Lakes area and the Sumin North Lake area.We introduce this section by discuss the GPR velocity-depthprofile on the sand dune, followed by the presentation of theprocessed GPR profiles at these two sites. Following the sectionof the description of the field observation we present the numer-ical modeling results of the radar wave propagation in a typicalsand dune to verify the observed features. In the result discus-sion section we discuss the GPR results’ significance in termsof geomorphology and hydrogeology. Finally, we conclude thepaper with restate the major findings of our study.

Based on our GPR study of the Badain Jaran sand dunes,we think that beyond the factors have been recognized byprevious studies there might be another important factor thatcan be crucial for the build-up of the high mega-dunes: therole of the calcareous cement beddings inside the mega-dunes,which acts as the ‘skeleton’ of the dunes and increases theirmechanic strength to enable them grown to the size and heightwe currently see in the modern time.

II. SURFACE EXPRESSIONS OF SAND DUNE STRUCTURE

The field study area is located in the southeast part of theBadain Jaran Desert, as shown with the Google Earth image inFig. 1.

It is very common to encounter numerous clear calcareousbeddings on the eroded dune surface and in the shallow depthexpressed as quasi-equally spaced cemented thin layers on thesand dunes in the southeast part of the Badain Jaran Desert, asshown in the photos of Fig. 2.

The cemented layers are likely caused by the periodic wettingof sands and glue them together to form a more in-permeablebut electrically more conductive layered structures. The spacingor thickness between the two adjacent layers is an indication ofthe rate of sand deposition between two adjacent wetting peri-ods, possibly annually, depends on the climate in that period

Fig. 2. The calcareous layer structure inside the sand dune exposed on theeroded surface in the Badain Jaran Desert (a, photo credit Xusheng Wang);and expressed in the freshly excavated trench (b, adapted from Fig. 3 of [25]and the sketch to illustrate the formation and motion of a sand dune (c).

of geological time. It is observed that the Calcium carbonate isbetween 0.5% and 2.5% by weight in the dune sands themselvesand approximates 23% in the calcareous layers [9], [10].

The dip angle of these calcareous beddings is closely con-sistent with the angle of repose of dry sand with fine grains,suggesting they are formed at the leeward side of the dune,and gradually progressed to the front side by erosion and re-deposition of the sand flows and dune migration. MacKenzie[11] is one of the pioneers to recognize that the strong beddingis due to calcareous surface cementation when he studied theBermuda sandstones. He speculated that percolating rainwa-ter induces rapid surface cementation and provides stabilizationand preserves the dune structures [11], but without evidence indepth of the dunes.

With the assistance of modern electronic technology such asGPR, we are able to extend the features we observed on dunesurface and image the deep internal structure of sand dunes andconstruct a fascinating snapshot of the dune building and migra-tion characteristics and present geomorphologists a look back intime. The next section presents the field GPR measurements forestablishing the internal structure at a number of sand dunes inBadain Jaran Desert, with more discussions of its implicationsto environmental evolution and climate change in the sectionfollows.

III. FIELD GPR PROFILING

Ground-penetrating radar (GPR) has been used successfullyto image the internal structures for a variety of desert andcoastal sand dunes. e.g., [12]–[16]. GPR works well in dunesands due mainly to the low conductivity of sands (with the factof the main mineral of quartz) and usually contain large scalesedimentary structures that can be imaged by GPR [17]. In thisstudy Sensors & Software’s PulseEKKO 50-MHz radar systemwas sued to collect GPR data on the sand dune between theBaddam Lakes (Figs. 1 and 3). Meanwhile, PulseEKKO 50- and

QIAN AND LIU: INTERNAL STRUCTURE OF SAND DUNES IN THE BADAIN JARAN DESERT REVEALED BY GPR 161

Fig. 3. The locations of the four GPR profiles (G1-G4) shown on the topo-graphic elevation profile over the sand dune between the Baddam east and westLakes in the Badain Jaran Desert.

Fig. 4. GPR reflection profile data collection using the 50-MHz PulseEKKOsystem on the Leeward side (west side) of the sand dune west of the SuminNorth Lake.

100-MHz system and MALA’s RAMAC radar 50-MHz systemwere used on the west and east flanks of the dunes beside theSumin Lake in Badain Jaran Desert (Figs. 1 and 9) during threefield trips in 2012 and 2013.

Fig. 4 shows a scene of GPR reflection data acquisition con-ducted by the field crew using the PulseEKKO radar system atthe Sumin North Lake site.

A. Radar Wave Velocity Depth Profile Determined by CMP

As we know, the structural features in a radargram are createdby reflection of waves at material interfaces due to a changingradar velocity. The common mid-point (CMP) GPR survey con-ducted at the Baddam Lake site shows that the surface dry sandhas a velocity about 0.162 m/ns, the unsaturated sand have avelocity of 0.131 m/ns (Fig. 5). Based on the analysis of the

Fig. 5. Velocity semblance analysis (a) for the CMP data (b) of the 50-MHzGPR for the reflection on the west flank of the sand dune between the east andwest Baddam Lakes.

Fig. 6. Velocity semblance analysis (a) for the CMP data (b) of the 50-MHzGPR for the reflection from the water table on the foot of sand dune betweenthe east and west Baddam Lakes.

Fig. 7. Three-dimensional view (fence diagram) of the 50-MHz GPR profilesviewed from the prevailing windward side (east side) of the sand dune betweenthe east and west Baddam Lakes.

reflection from the water table, the saturated sand has a velocityabout 0.08 m/ns (Fig. 6). Given the fact of that the solid skele-ton of the sand dune as a porous medium is close to pure quartzwith a dielectric constant of 4.5, the inferred porosity is 24% fordry sands, and 23.7% for saturated sands with the application


Fig. 8. Three-dimensional view (fence diagram) of the 50-MHz GPR profilesviewed from the leeward side (west side) of the sand dune between the east andwest Baddam Lakes.

Fig. 9. Google Earth image of the Sumin North Lake area with the locationsof the GPR profiles superimposed. The topographic elevation variation at theSumin North Lake area may reach about 200 meters.

of the complex refraction index model (CRIM), which is quitesuitable for sandy soil [18]:

√εb = (1− φ)

√εg + φS

√εw + φ(1− S)

√εa)

In this CRIM model, εb is the bulk dielectric constant forthe porous sand mix, and εg , εw, and εa are the dielectric con-stants for the solid grain of sand (use quartz), water, and air,respectively. φ is the porosity, and S is the degree of saturation.Porosity should not be varying too much with respect to depth.If we assume the unsaturated sands also has a porosity of 24%,it is straightforward to get the estimated degree of saturation inthe unsaturated zone is 23.7%. Using the widely accepted rela-tionship among water content w, porosity f, specific gravity ofsolid grains Gs, and degree of saturation S [19]:

w =S

Gs

φ

1− φ

We can also estimate the corresponding water content to be2.9% by assuming the solid grain of sand possessing a specificgravity of 2.65. This is exactly the averaged water content valuefrom 8 sampling points on the slopes of the sand dunes up to 5meters in depth in the Badain Jaran Desert [20].

As a check with results against other GPR surveys in a sanddune environment, Vriend et al. [8] obtained the radar velocity

TABLE IGPR DATA ACQUISITION PARAMETERS AT BADDAM LAKE SITE

from a CMP survey on the leeward face of the Dumont dunesin California is about 0.18 m/ns at the surface of the dune anddown to 0.14 m/ns at a depth of 8 m. Rejiba et al. [21] got anaveraged velocity of 0.13 m/ns for the unsaturated zone in thesand dunes in a GPR study in the niayes ecoregion, i.e., thenarrow interdunal zone of peat deposits of Tanma, Senegal.

These comparisons provide some lines of evidence of rea-sonability of the derived radar wave velocities. It also impliesthat the dunes in Badain Jaran Desert may contain higher watermoisture so that the radar velocity is relatively lower than itscounterparts in California. The GPR-derived in situ porosityis at the lower end when compared with porosity obtained bydirect measurement for similar sand dunes in other part of theworld; for example, Dickinson and Ward [22] report a porosityof 34% for the dunes in the Namib Desert in Southern Africa.Part of the reason for the lower porosity possessed by the dunesin the Badain Jaran Desert can be attributed to the fine grainsize distribution fund in the Badain Jaran Desert, for which thedunes are composed mainly by fine sand (0.250–0.125 mm) andvery fine sand (0.125–0.063 mm) [23]. Moreover, the existenceof the calcareous cemented beddings should have lower furtherdown the effective porosity.

B. GPR Profiles on the Transverse Dune at Baddam Lakes

As shown in Fig. 3, four GPR reflection profiles were col-lected on the sand dune between the east and the west BaddamLakes: three parallel profiles (G1 to G3) were set transverse tothe long axis of the dune, and one profile (G4) was set alongthe axis on the dune ridge. The nominal frequency of the radarsource is 50 MHz, with the antenna separation of 2.0 m in adata acquisition fashion of reflection profiling.

The data acquisition parameters for these four profiles arelisted in Table I. In the field operation the three transverse pro-files were acquired separately on the east and the west sides,and then merged together into an integrated complete profile.Surface elevation and the locations of the starting and endingpoints were acquired using real-time kinematic (RTK) differen-tial GPS survey technique, with the largest elevation differenceof 25 m for these four profiles. The vertical precision of the ele-vation reading can reach a few centimeters. This is more thanadequate to our GPR data analysis.

In time domain, the sampling interval dt = 1.5 ns, with thenumber of data points per trace of 267 and a total time windowof 400.5 ns for Profiles G1-G3; and a sampling interval dt =1.6 ns, with the number of data points per trace of 250 and atotal time window of 400 ns for Profiles G4.

The fence-diagrams formed by radar profile cross-sectionsG1-G4 are shown in Figs. 7 and 8 below. The most pronouncedfeature in the radargrams is the features of the continuous,


surface-perpendicular linear textures shown on the east side ofthe dune; and meanwhile, the surface sub-parallel linear tex-tures on the west side of the dune. Furthermore, we can tracethe water table expressed as the continuous strong reflectorextended from the east and west lakes into the subsurface ofthe sand dune. From the positive dipping slope towards thedune ridge we can infer that the groundwater underneath thedunes should have an increasing hydraulic pressure and shouldbe recharging the east and west lakes by the pressure-inducedoutward groundwater flow.

It is noteworthy that the location of the Baddam Lakes isquite close to the southeast edge of the Badain Jaran Desert andnext to the Yabulai Mountains to the southeast which is a topo-graphic height in this region. It blocks the regional northwestwinds and reflects it back as the southeast wind. The prevail-ing wind direction in the local area consequently is southeast inthe area in front of the Yabulai Mountain range. At the BaddamLake site the east side of the sand dune thus becomes the winddirection and west side becomes the leeward side. It can be seenfrom Fig. 7 that the major bedding direction inside the dune isdipping to west.

From geomorphological features in the Baddam Lakes Yang[23] suggested that the east and west lakes were a single big lakein about 5000 years ago; the current water level is about only20% of the original lake water level back to Holocene time. Theintruded sand dune migrates in and cut the big lake into two asthe east and west lakes that we see in modern time.

Livingstone [24] suggested that large dunes do migrate later-ally. He demonstrated that the crests of a large (∼70 m) lineardune in the Namib Desert shifts back and forth by ∼15 mdue to long-term seasonal wind changes. Bristow et al. [16]showed that a net migration of ∼300m laterally occurred on alonger timescale (∼2500 years) and proposed that large migra-tions may be temporarily activated or deactivated by long-termclimatic changes in rainfall and vegetation. From the slope sub-parallel bedding features shown in the long profile G4 in Figs. 7and 8 we can reasonably speculate that the dune might havea lateral migration to the north while have accumulation andbuild-up by southeast wind.

C. GPR Profiles on the Transverse Dune at Sumin North Lake

North of the Baddam Lakes we have also collected GPR threeprofiles on the west and east slopes of the linear dunes that arebeside the Sumin North Lake (Fig. 9). GPR survey profile G2and G4 were collected using 100 MHz PulseEKKO GPR sys-tem during the field campaign in June 2013; while the profileMala was acquired with MALA RAMAC Radar with 50- MHzun-shield Rough Terrain Antenna (RTA) during the field workcampaign in October 2013.

Fig. 10 shows the two sub-parallel GPR profiles on the lee-ward side of the sand dune west of the Sumin North Lake.Profile G2 is about 150-m long with 45 m elevation difference;and the depth range shown is about 20 meters. Profile Mala isabout 500-m long with 200-m elevation difference. The imageddepth range is about 25 meters. The reflection from the watertable is clearly seen from both G2 and Mala. In the shallowsubsurface, the arch shaped reflectors might be associated with

Fig. 10. GPR Profiles G4 (100-MHz) and Mala (50-MHz) on the west slope ofthe Sumin North Lake.

Fig. 11. Profile G4: 100-MHz GPR survey line on the east slope of SuminNorth Lake. Section of transverse dune facies and complex facies are amplifiedto show the details as the insets.

the buried cemented layer structures during the Holocene timewhen the climate was wetter and possibly more precipitationswere available.

Profile G4 shown in Fig. 11 is the 100-MHz GPR data col-lected on the windward side of the sand dune east of the SuminNorth Lake. This 450-m long profile shows a typical cross-section of the transverse dune phase in the center part of thedune and complex dune facies on the top part of the dune, sim-ilar to what have been observed on other mega-dunes in thisdesert [25].

IV. VERIFICATION VIA NUMERICAL SIMULATION

For verifying the understanding of the GPR signature of theinternal features of a sand dune we have constructed an artifi-cial sand dune model to mimic the radar wave propagation in atypical sand dune. The electromagnetic parameters used in themodel (Table II) closely resemble the observed values of theaeolian sand dunes [16].

We have conducted finite difference time domain (FDTD)modeling [26] for radar wave propagation inside the sand dune(Fig. 12). The numerical model consists of 5000× 1000 gridswith a grid size of dx = dz = 0.02 m to cover the 100 m inhorizontal extent and 20 m in elevation. The total horizontal


TABLE IIELECTROMAGNETIC PARAMETERS FOR DUNE MATERIALS

Fig. 12. The dielectric constant for the sand dune model for the FDTDnumerical simulation.

length is 100 m and the elevation from bottom to top is 20 m.The windward side has a slope of 15.9 degrees and the leewardside has a slope of 33.7 degrees. The water table has a slopeof 15% of the dune surface slope. The oldest part of the duneis the triangular tip on the left end, with a dielectric constantof 6.25. The shallowest surface is covered by a dry sand layerwith the lowest dielectric constant of 4.0. The thickness of thislayer is varying linearly from low elevation to the crest of thedune, with maximum thickness of 1 m. The calcareous beds arespaced by 0.7 m with a same dipping angle towards the leewardside.

We have run 360 ns as the recording time window; it is longenough to record the reflections from the water table and thedatum (supposedly the desert floor). The snapshots for visual-izing the radar wave propagation inside the dune are shown asFig. 13. Clearly, the leeward side parallel cemented beddingscause strong diffraction and direct the radar wave to focus oncertain directions.

From the radar wave propagation snapshots in Fig. 13 itis clear that the beddings inside the sand dune redirect radarwave to focus more wave energy to the right (the leeward side).Taking this as the visualization tool and expend wave propaga-tion into flow and transport phenomenon it is likely the flow isalso prevailingly flow to the right side. The simulated radargramprofile is shown below as Fig. 14. The synthetic data set has asize of 6000 (time step)× 500 (number of traces), with thetime interval dt = 0.06 ns and trace interval dx = 0.2 m.

V. RESULT DISCUSSION: THE IMPLICATIONS OF DUNE

STRUCTURE TO GROUNDWATER AND LAKE HYDROLOGY

Yang et al. [3] estimated that the mean evaporation fromthe land surface in the area surrounding lakes in the BadainJaran is about 100 mm based on 40 years observation from1961 to 2001. According to their preliminary calculation, thetotal rainfall (P) approximates the total evaporation (E), i.e.,the annual precipitation is about 100 mm. Ma and Edmunds[27] estimated the annual precipitation is 89 mm, quite close

Fig. 13. The snapshots of the 100 MHz radar propagation in the dune modelshown in Fig. 12.

Fig. 14. The synthetic GPR profile obtained from FDTD modeling based onthe sand dune model in Fig. 12.

to the estimates by Yang et al. in [3]. Mean annual evapora-tion, calculated using the modified Penman Equation, suggestsa ∼5 mm mean annual groundwater recharge rate across thedune surfaces. Using a chloride mass balance model, Ma andEdmunds [27] suggested that the mean annual recharge ratewould be 0.95–1.33 mm, while Gates et al. [28] arrived at avalue of 1.4 mm.

A scanning electron microscope analysis shows that thecement between individual grains is calcite (CaCO3) anddolomite CaMg (CO3)2, mixed with clay-sized particles. Thecementation of the sand grains will result in decrease in poros-ity and radar wave velocity. The alkaline character of the lakewater samples, as shown by their pH, is caused in part bycalcium carbonates found in the aquifer and in the unsatu-rated zone [9], [10]. This can be served as one piece of theevidence of local recharge contributions from shallow ground-water resources. Rainfalls may supply the minerals necessaryfor cementation and calcium is an important component in theprecipitation in the desert (for example, calcium in rainfalls for


Mojave Desert, California, USA is about 8 mg/L in spring 2002,[29]). Another possible source for calcium supply is desert dust;and the calcium can be percolated into the dune by precipitationor seepage [30].

In terms of the hydrological implication of the calcareouscement beddings, our results advocate the possibility of localrecharge as one significant part in total recharge to the inter-dune lakes [9] than previously thought with two factors have notmentioned by previous studies: 1) steeply water table slope onthe leeward side which in turn generate higher seepage speed;2) anisotropic hydraulic conductivity due to lake-direction (lee-ward) dipping cementation beddings favors a faster flow to theinter-dune lake at the foot of the sand dunes.

Based on numerous field observations and theoretical infer-ence we can estimate that there are about 1–2% of the annualprecipitations may infiltrate to the sand dunes and becomingpart of the resource to recharge the lakes. However, it is esti-mated that the watershed area to feed one lake is at least 50 to100 times larger than the lake surface (see Fig. 1), so that thelocal precipitation becomes a significance source for feedingthe lakes. Furthermore, both field observations and numeri-cal simulation demonstrate that the internal structure of thesand dune is in favor of the infiltrated precipitation becominggroundwater and preferably flow to the leeward by the leewardtilting cross beddings of the dune structure.

VI. CONCLUSION

GPR surveys conducted at two sites on the sand dunes in theBadain Jaran Desert revealed detail internal structures of thedunes and provided rich information for the study of formationand evolution of desert morphology. The calcareous cementbeddings inside the dunes played a role as the ‘skeleton’ ofthe dunes and increased the mechanic strength of the sands andconsequently facilitated the build-up of the high elevation megadunes.

This orientation of the cemented layered beddings may playone of the key roles to help the existence of the lakes in avery arid environment with high evaporation rate. The GPRprofile also clearly registered the water table beneath the sanddunes that gradually elevated toward the crest, implies that thedesert lakes are recharged at least partly by the groundwaterfrom local source. Numerically simulated radar profiles pre-cisely reconstructed the observed profiles. It is a strong supportto the rationality of the proposed internal structure of the dunes.

The fact of that the desert lakes are always sitting inthe leeward side of the prevailing wind blow direction areclosely associated with the internal structure of the sand duneswhich preferably lead the infiltrated precipitation water into thesteeper leeward side rather the windward side, as shown by theregion satellite image as below.

Furthermore, the cement-layer generated anisotropic natureof the hydraulic conductivity will induce higher flow ratetoward the leeward low land to form the lakes there. Thesefeatures were not explicitly discussed in previous studiesin the Badain Jaran Desert, or sand dune studies in otherlocations.

ACKNOWLEDGMENT

The authors appreciate the hard work done by a group ofgraduate students and assistants in an adverse desert environ-ment for acquiring the data discussed in this paper.

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Rongyi Qian is an associate professor in ChinaUniversity of Geoscience–Beijing. He receivedBS and PhD degrees in Geophysics from ChinaUniversity of Geoscience–Beijing. His research inter-ests focus on the development and application ofnear-surface geophysical techniques in geotechnicalengineering, environmental protection, and naturalresource explorations.

Lanbo Liu is a Professor in the Departmentof Civil and Environmental Engineering at theUniversity of Connecticut. He received BS and MSdegrees in Geophysics from Peking University, andMS in Civil and Environmental Engineering andPhD in Geophysics from Stanford University. Hewas the Carnegie Fellow at Carnegie Institutionof Washington before joining the faculty of theUniversity of Connecticut. He has been the SummerFaculty Fellow at Schlumberger-Doll Research andat NASA’s Goddard Space Flight Center. He is also

an Expert for the US Army Corps of Engineers, and received the US ArmyR&D Achievement Award for his work on radio wave propagation in com-plex terrains. He was a Fulbright Scholar to Norway in 2009-2010. Dr. Liuhas more than 100 publications in peer-refereed journals, conference pro-ceedings, and technical reports. He had served as an Associate Editor forGeophysics and is serving as the Associate Editor for Journal of Environmentaland Engineering Geophysics and Journal of Applied Geophysics. His currentresearch focuses on numerical modeling and imaging with electromagnetic,acoustic, and seismic waves for exploration, geotechnical, environmental, andbiomedical engineering applications.

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