remote sensing of desert dune forms by polarimetric synthetic aperture radar sar abstract this report describes remote sensing experiments using highly capable polarimetric synthetic aperture radar sar in preparation for the launch of the sir c x sar mission nasa s jpl airborne polarimetric sar airsar was deployed over many locations worldwide the report describes sar observations of desert dune fields in north america bolivia and australia acquired by airsar and in namibia acquired by sir c x sar the use of polarimetric and multiwavelength sar is reviewed and comments on the advantages of the various combinations are noted sar data are very useful in mapping dunes because of the ability to control illumination parameters such as look angle wavelength and polarization furthermore the unique responses of sar to surface roughness are found very useful in mapping dune forms for most sites the longer wavelengths p and l band at 68 cm and 24 cm are advantageous over the shorter c band at 5 6 cm providing better contrast overall copolarized channels hh and vv are found best for mapping the dunes and dune types when trying to discriminate active from inactive dunes cross polarized channels provide essential information on vegetation

turbulent structure in unsteady depth varying open channel flows turbulence measurements over a smooth wall in unsteady depth varying open channel flows were conducted by the simultaneous use of a two component laser doppler anemometer lda and a water wave gauge in the present study velocity measurements in the viscous sublayer of highly unsteady flow have been first conducted to evaluate the friction velocity independently of the log law the von karman constant was calculated using this friction velocity it was proven then that the value of was really a constant of 0 41 even in unsteady open channel flows next statistical structures of mean velocity and turbulence characteristics were investigated across the whole flow from the near wall region up to the free surface in particular turbulence measurements near the depth varying water surface zone of flood flow were conducted successfully for the first time with the lda such measurements have been impossible with conventional velocity instruments such as hot film anemometers mean velocity profiles and turbulence characteristics were revealed in both the rising and the falling stages of the flood period

decorrelation in interferometric radar echoes a radar interferometric technique for topographic mapping of surfaces implemented utilizing a single synthetic aperture radar sar system in a nearly repeating orbit is discussed the authors characterize the various sources contributing to the echo correlation statistics and isolate the term which most closely describes surficial change they then examine the application of this approach to topographic mapping of vegetated surfaces which may be expected to possess varying backscatter over time it is found that there is decorrelation increasing with time but that digital terrain model generation remains feasible the authors present such a map of a forested area in oregon which also includes some nearly unvegetated lava flows such a technique could provide a global digital terrain map

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

fluid generation and pathways beneath an active compressional orogen the new zealand southern alps inferred from magnetotelluric data 1 forty one wideband magnetotelluric mt soundings were collected in a 150 km long transect across the southern alps of the central south island of new zealand an active compressional orogen decomposed mt impedance tensors vertical magnetic field relations and reconnaissance soundings at two locations off line imply an approximately two dimensional geometry here with average regional geoelectric strike of n40 e similar to surface geologic trends two independent two dimensional inversion algorithms were applied to the mt data and both imply a concave upward u shaped middle to lower crustal conductive zone beneath the west central portion of the island the average conductivity of this zone in the strike direction appears to be much higher than that required across strike and may represent anisotropy or along strike conductive strands narrower than the transverse magnetic cross strike mode mt data can resolve the deep crustal conductor under the southern alps is interpreted to represent mainly a volume of fluids arising from prograde metamorphism within a thickening crust fluid interconnection and electrical conduction are promoted by shear deformation the conductor rises northwestward toward the trace of the alpine fault but attains a near vertical configuration at a depth of 10 km and reaches close to the surface 5 10 km inland of the fault trace itself the transition to vertical orientation at this depth is interpreted to occur as fluids ascend across the brittle ductile transition in uplifting schist and approach the surface through induced hydrofractures the high grade schist becomes resistive after depletion of fluids and continues to extrude toward the alpine fault shallow extensions of the deep high conductivity are coincident with modern hydrothermal veining and gold mineralization interpreted to be of deep crustal provenance to the southeast high conductivity also reaches the surface coincident with a major back thrust fault zone of the doubly vergent southern alps orogen which also exhibits evidence for expulsion of high temperature fluids the higher conductivity inferred along strike possible anisotropy could reflect more efficient fluid interconnection in this higher strain direction as well as possible contributions by sheared fluid deposited graphite conductivity of the uppermost mantle of the south island is low consistent with advection of cold mantle lithosphere into the underlying asthenosphere as suggested by p wave delay studies

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

a magnetotelluric transect in the oregon coast range as part of emslab broadband magnetotelluric data have been collected and analyzed at 11 sites along an east west transect in the oregon coast range using one and two dimensional modelling the coast range was found to consist of marine sediments about 4 km deep near the coast and volcanic rocks about 8 km deep farther inland willamette valley consists of surficial conductive sediments to a depth of 1 km which overlie an eastern extension of the rocks that compose the coast range an east dipping conductor at a depth of approximately 20 km is associated with the upper surface of the subducting juan de fuca plate possible mechanisms for the high conductance are water saturated fractured basalts forming the surface of the plate subducted sediments and or the dehydration of the subducting slab trapped by metamorphic layering within the lower crust this conductor correlates with an east dipping reflector 35 40 km below the eastern flank of the coast range defined by cocorp profiling and thought to represent the surface of the subducting juan de fuca plate

formation of parabolic dunes from barchan and transverse dunes along israel s mediterranean coast the mediterranean coastal dunes of israel underwent a land use change during the second half of the 20th century due to intense agricultural and pastoral activity the coastal dunes were stripped of natural vegetation until the end of the first half of the 20th century the barchan and transverse dunes were shaped by strong southwesterly winter winds a decrease in human activity during the second half of the 20th century brought about a renewal of natural vegetation on the dune crest the only area with neither erosion nor deposition the establishment of vegetation on the crest changes the dynamics of these barchan and transverse dunes so that not all of the sand eroded from the windward side is carried to the lee slip face some is trapped by plants consequently there is a change in the shape of the windward slope from convex to concave and the dune gradually becomes parabolic in this study we trace the morphodynamics of the dunes by analysing 12 sets of aerial photographs which were taken from 1944 to 1995 the average rate of advance of 15 dunes has decreased from 3 4 m a 1 to 1 9 m a 1 while the vegetation cover has increased from 4 3 to 17 per cent during this period copyright 2002 john wiley sons ltd

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

electrical structure of the central cascadia subduction zone the emslab lincoln line revisited abstract the emslab experiment was an ambitious onshore offshore magnetotelluric mt transect of the cascadia subduction zone when completed 1985 1988 it was the largest experiment of its kind modeling and inversion capabilities at the time were however not sufficiently sophisticated to handle a fully regularized inversion of the data including the seafloor data and bathymetric constraints with the main final model presented based on trial and error forward modeling of the responses moreover new data collected as part of the earthscope usarray program are of higher quality due to improvements in instrument technology and augment the original emslab data set presenting an opportunity to revisit the structure in this part of the subduction system we have integrated the original wide band mt data as well as several long period stations from the original emslab data set and invert these in conjunction with emslab seafloor responses and new earthscope data on land this new composite data set has been analyzed in several ways within a two dimensional geometry in which conductivity is assumed to be invariant along a strike direction roughly coincident with that of the subduction zone we have solved for fully smooth regularized models as well as solutions that allow discontinuities in conductivity along the top surface of the descending slab finally we have tested specific features in the emslab model notably a moderately shallow 30 km depth forearc conductor a feature similar to this shallow conductor is a consistent and required feature in our new inversion models but the new models highlight the connection between the slab and what is interpreted to be an accumulation of aqueous fluids in the deep crust the depth 40 km at which the conductor intersects the slab suggests that the fluids are released by the transition of hydrous basalt to eclogite at upper greenschist facies and higher metamorphic grade the nose of the mantle wedge has a conductivity consistent with a dry peridotite composition and thermal models of the system at a depth of around 80 km the mantle intersecting the slab shows a slight increase in conductivity this increase is not sufficient to require the presence of melt but a conductor indicative of melt can be inserted into the model at this depth without compromising the fit

the spatial and temporal variability of sand erosion across a stabilizing coastal dune field this study aimed at quantifying the temporal and spatial variability in sand erosion and deposition over a coastal dune field in israel these were measured monthly over 2 years using 315 erosion pins over four transects that were placed perpendicular to the coastline vegetation cover was estimated based on aerial photographs and landsat satellite images whereas the relative height was based on a digital elevation model these variables were calculated for the area upwind south west of the erosion pins at various lengths ranging from 15 to 400 m nine geomorphologic units were defined five related to active units and four to stabilized units in active units at least 65 of the temporal variance in the annual absolute changes in sand level was explained by the index of resultant drift potential with most of the sand movement occurring during winter storms local rainfall had no apparent impact on sand mobility due to the low coincidence of sand carrying winds and rainfall in israel during the passage of frontal cyclones as for the spatial variables only a weak correlation was found between sand mobility with the distance from the coastline r 2 18 rather sand erosion and deposition were influenced by vegetation cover and the relative height of an area of 100 200 m upwind the values of soil adjusted vegetation index were significantly negatively correlated with annual absolute changes r 2 40 whereas the relative height was significantly positively correlated r 2 36 applying a multiple regression model 68 of the spatial variability in sand mobility was explained the resulting map of sand activity clearly shows that at this stage of the stabilization process most of the dunes are now disconnected and movement of sand grains from the beach or between the dunes is very limited these methods can be applied into spatial and temporal models of sand mobility thus assessing the impact of different management practices on coastal dunes

velocity deformation model for unsteady open channel flows over smooth and rough beds abstracta one dimensional depth averaged velocity deformation model is developed to study the characteristics of the unsteady flows in open channels the vertical profile of the streamwise velocity is expressed in a power series and the coefficients of the velocity are evaluated by using the unsteady equation of motion a concise form of the friction velocity for unsteady nonuniform flow is then proposed by utilizing the coefficients of the power series the applicability of the model is validated with experimental data producing reasonably good agreement between the model results and the observed data finally the deformation of velocity at the surface is assured by comparing velocity distribution of numerical model with the computational results from a previous model

preliminary analysis of shuttle radar laboratory srl 1 data to study aeolian features and processes in april 1994 the shuttle radar laboratory srl 1 obtained quad polarization data in l band spl lambda 24 cm and c band spl lambda 5 6 cm and vv polarized data in x band spl lambda 3 cm preliminary analyses show that radar backscatter coefficients spl sigma sup 0 can be used to map the aerodynamic roughness parameter z sub 0 over large areas from orbit as demonstrated by comparisons with measurements of z sub 0 obtained in the field although all wavelengths and polarizations show fairly good correlations with z sub 0 r 0 78 l band hv shows the best relationship r 0 81 this result has potential use in regional studies of sand and dust transport modeling atmospheric circulation and general climate studies srl images of aeolian landforms were also studied including dunes sand sheets and wind streaks dunes in the stovepipe wells area of death valley were clearly visible on l band hv images but not detected on c band images in the same area l band penetrated a sand sheet to reveal a buried fault scarp l band images in namibia showed the classic linear dunes near gobabeb and also revealed previously undetected sets of cross dunes wind streaks were imaged in several areas including namibia where streaks are associated with the impact crater roter kamm these features enable mapping of near surface wind patterns

radar interferometry and its application to changes in the earth s surface geophysical applications of radar interferometry to measure changes in the earth s surface have exploded in the early 1990s this new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times the resulting interferogram is a contour map of the change in distance between the ground and the radar instrument these maps provide an unsurpassed spatial sampling density 100 pixels km 2 a competitive precision 1 cm and a useful observation cadence 1 pass month 1 they record movements in the crust perturbations in the atmosphere dielectric modifications in the soil and relief in the topography they are also sensitive to technical effects such as relative variations in the radar s trajectory or variations in its frequency standard we describe how all these phenomena contribute to an interferogram then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments including the four satellites currently in orbit ers 1 ers 2 jers 1 and radarsat the next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement respecting the limits of the technique assessing its uncertainty recognizing artifacts and discriminating different types of signal we then review the geophysical applications published to date most of which study deformation related to earthquakes volcanoes and glaciers using ers 1 data we also show examples of monitoring natural hazards and environmental alterations related to landslides subsidence and agriculture in addition we consider subtler geophysical signals such as postseismic relaxation tidal loading of coastal areas and interseismic strain accumulation we conclude with our perspectives on the future of radar interferometry the objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it

use of optical and radar remote sensing satellites for identifying and monitoring active inactive landforms in the driest desert in saudi arabia abstract observing earth from the space is key for monitoring land surface dynamics and probing near surface geomorphic and geological features including those obscured by sand sheets dunes and human activity the hyper arid area of the arabian peninsula was selected for detecting and extracting obscure paleohydrological systems and modeling the spatio temporal dynamics of sand dunes using synthetic aperture radar sar and optical high resolution remote sensing images interferometric synthetic aperture radar insar coherence change detection ccd using sentinel 1 imagery was performed revealing subtle changes in the surficial landforms of the study area these images also discriminated between active and inactive geomorphic features in addition low frequency l band advanced land observing satellite phased array type l band synthetic aperture radar alos palsar and shuttle radar topography mission srtm data revealed the details of paleochannels in the basins that drain into the arabian gulf these ephemeral rivers are the source of sand that was later reshaped into dunes by aeolian processes the results also revealed that the morphology and extension of dunes were clearly influenced by topography slope and wind velocity and direction rather than human activities knowledge gained by exploring desert features is essential for planning settlements and development and integrated approaches using a variety of remote sensing datasets are key for enhancing earth observation across a range of spatial and temporal scales

analysis of topographic decorrelation in sar interferometry using ratio coherence imagery topographic decorrelation due to the local surface slope has been an obstacle to interferometric synthetic aperture radar insar applications a modified spatial decorrelation function is derived as a function of the baseline and topography this function explains the origin of the total topographic decorrelation phenomenon on the slopes directly facing radar illumination and layover which may mislead insar coherence image interpretation the authors define critical terrain slope or critical incidence angle as the angle for which two sar signals completely decorrelate regardless of surface stability it is found that the width of the critical terrain slope increases with the increase of the component of the baseline perpendicular to the radar look direction a new analytical method the ratio coherence imagery is then introduced to highlight total topographic decorrelation against the temporal decorrelation features the applications of this methodology are demonstrated in selected locations in the sahara desert algeria and almer spl inodot spl acute a spain using ers 1 and ers 2 sar data

analysis of large aeolian wind blown bedforms using the shuttle radar topography mission srtm digital elevation data abstract dry land areas cover large parts of the land masses of earth of these a large portion is mantled by aeolian wind blown deposits and subjected to aeolian process i e the transport of sand or dust by wind one of the most prominent morphologies created by wind driven deposits are dunes and in their larger form draas or mega dunes these mega dunes tend to be widely spaced very large often forming a base on which smaller dunes form producing a compound dune pattern in february 2000 the shuttle radar topography mission onboard the space shuttle endeavour flew an interferometric radar system whose objective was to create a dem of nearly all earth land masses in this paper dem data from the c band 90 m data set and the x band 30 m data set were used to map and characterize the height and spacing of the large sand seas ergs on earth only the larger forms of dunes could be mapped reliably the dune spacing and heights extracted from the srtm dems tended to be in overall agreement with those reported in the literature in a comparison between the x band and the c band data it was found that the x band data are more sensitive to the smaller scale undulations on the compound dunes and better revealed the full height of the dunes

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

formation of the highest sand dunes on earth characterization of dune morphology has historically been based on relationships between dune forms and wind regimes with dune height shown to be sensitive to atmospheric boundary layer depth sand availability and sediment properties while these parameters have been used in numerical simulations to model the occurrences of some types of dunes they cannot alone explain the great diversity in form and size seen on earth and on other solar system bodies here we present results from our studies of dune formation in the badain jaran desert in western china where earth s tallest dunes occur we measured the variability of the dune morphology in this desert on the basis of landsat etm data and we detected the bedrock landforms beneath the aeolian sands by applying gravity methods wind records from stations at the periphery of the desert and srtm topographical data were examined also to augment the interpretation our studies demonstrate that in addition to average wind parameters dune height is highly sensitive to local geology subsurface characteristics and topography and interactions between changing climate conditions and aeolian and fluvial processes these additional factors need to be considered in the interpretation and simulation of dunes on earth we anticipate that analysis of anomalous dune heights like those seen in the badain jaran may also provide critical information on subsurface characteristics and environmental conditions on earth and on other planetary bodies

should the electric line be straight in magnetotelluric surveys the usual description of electric field measurements in terms of potential differences is not entirely adequate at high frequencies in general the telluric electric field is non conservative and voltage measurements depend on the contour described by the cable a simple error analysis helps to recognize those situations where systematic errors may be significant for present day standards

flow resistance in natural turbulent channel flows the need for a fluvial fluid mechanics in fluvial environments feedbacks among flow bed forms sediment and macrophytes result in a complex fluid dynamics the assumptions underpinning standard tools in hydraulics are commonly violated and alternative approaches must be formulated i argue that we should question the assumption that classical notions in fluid mechanics provide the foundations for the techniques of the future recent work on turbulent dissipation interscale modulation of the dynamics intermittency and the role of complex forcings is discussed an agenda for future work is proposed that involves improving our characterization of complex forcings and developing better understanding of the behavior of the velocity gradient tensor in complex fluvial environments this leads to the formulation of modeling tools relevant to fluvial fluid mechanics rather than a reliance on methods developed elsewhere one avenue by which such methods might be developed is suggested based on the stretched spiral vortex as a baseline topology this would result in a nonequilibrium model for turbulence that has greater potential to capture the dynamics in which we are interested although these ideas are raised in the context of a future fluvial fluid mechanics they are applicable to any situation where turbulent flows are forced in complicated ways

reynolds stress and bed shear in nonuniform unsteady open channel flow expressions for the reynolds stress and bed shear stress are developed for nonuniform unsteady flow in open channels with streamwise sloping beds assuming universal logarithmic velocity distribution law and using the reynolds and continuity equations of two dimensional open channel flow the computed reynolds stress distributions are in agreement with experimental data

synthetic aperture radar interferometry to measure earth s surface topography and its deformation synthetic aperture radar interferometry insar from earth orbiting spacecraft provides a new tool to map global topography and deformation of the earth s surface radar images taken from slightly different viewing directions allow the construction of digital elevation models of meter scale accuracy these data sets aid in the analysis and interpretation of tectonic and volcanic landscapes if the earth s surface deformed between two radar image acquisitions a map of the surface dis placement with tens of meters resolution and subcentimeter accuracy can be con structed this review gives a basic overview of insar for earth scientists and presents a selection of geologic applications that demonstrate the unique capabilities of insar for mapping the topography and deformation of the earth

radar scattering of linear dunes and mega yardangs application to titan the ku band 13 8 ghz 2 2 cm radar instrument onboard the cassini huygens spacecraft has revealed the richness of the surface of titan as numerous seas lakes rivers cryo volcanic flows and vast dune fields have been discovered linear dunes are a major geomorphological feature present on titan covering up to 17 of its surface mainly in equatorial regions however the resolution of the radar instrument is not good enough to allow a detailed study of the morphology of these features in addition other linear wind related landforms such as mega yardangs linear wind abraded ridges formed in cohesive rocks are likely to present a comparable radar signature that could be confused with the one of dunes we conducted a comparative study of the radar radiometry of both linear dunes and mega yardangs based on representative terrestrial analogues the linear dunes located in the great sand sea in western egypt and in the namib desert in namibia and the mega yardangs observed in the lut desert in eastern iran and in the borkou desert in northern chad we analysed the radar scattering of both terrestrial linear dunes and mega yardangs using high resolution radar images acquired by the x band 9 6 ghz 3 1 cm sensor of the terrasar x satellite variations seen in the radar response of dunes are the result of a contrast between the dune and interdune scattering while for mega yardangs these variations are the result of a contrast between ridges and erosion valleys we tested a simple surface scattering model with parameters derived from the local topography and surface roughness estimates to accurately reproduce the radar signal variations for both landforms it appears that we can discriminate between two types of dunes bare interdunes as in egypt and sand covered interdunes as in namibia and between two types of mega yardangs young yardangs as in iran and older ones as in chad we applied our understanding of the radar scattering to the analysis of cassini radar t8 acquisitions over the belet sand sea on titan and show that the linear dunes encountered there are likely to be of both egyptian and namibian type we also show that the radar bright linear features observed in cassini radar t64 and t83 acquisitions are very likely to be mega yardangs possible remnants of ancient lake basins at mid latitude formed when titan s climate was different

electromagnetic expression of axial magma chambers the electrical conductivity of sea floor materials is a strong function of porosity pore geometry fluid content temperature and percentage of partial melt these material properties are particularly volatile near the midocean ridge tracking electromagnetic eddy currents generated on the sea floor as they diffuse across the ridge can provide images of the subaxial electrical and through interpretation the geological structure we have computed numerically in 2d the response of a crustal magma chamber located beneath the east pacific rise to excitation in two fundamental orthogonal modes rise normal te and rise parallel tm electric field a finite element representation of the electromagnetic em diffusion equations is solved in the laplace domain and the results inverted into the time domain via the gaver stehfest algorithm a sequence of snapshots for each mode for the time range 0 1 to 15 s shows the complete progression of the eddy currents into through and around the magma chamber the te and tm signals at a receiver site above the conductive magma chamber are delayed and attenuated in comparison with those expected for normal layered oceanic crust

spaceborne and airborne imaging radar observations of sand dunes seasat and aircraft radar imagery of five areas of sand dunes in the southwestern united states and northwestern mexico have been studied and compared to landsat imagery and air photos radar imaging system parameters included two wavelengths 23 5 cm and 3 0 cm and incidence angles ranging from 0 through 70 horizontal polarization was used on both transmit and receive for all radar imagery resolution ranged from 12 m for the best aircraft imagery to about 40 m for seasat sand dunes studied behave as smooth surfaces for both 23 5 cm and 3 0 cm wavelength radars and the reflection of the radar energy from the dunes is specular measured surface irregularities of sand dunes are inadequate to cause either bragg or incoherent scattering of the incident radar beam in the 3 0 to 23 5 cm wavelength region this results in dunes that appear dark when imaged at incidence angles greater than the angle of repose because none of the dune faces are oriented properly normal to the incident radar beam to give a specular return to the antenna a scattering model based on specular return from randomly oriented flat dune faces was used and experimentally verified using aircraft data imaging radar resolution must be adequate to define the changing distribution of dune faces that characterize the dune morphology linear dune features with interdune spacing of less than 3 4 resolution elements are not recognizable distributed dune types such as barchans or stars must be more than about 10 resolution elements in each direction to be defined on the imagery illumination direction of the radar beam is important directional dune features must be oriented within about 60 of perpendicular to the radar illumination direction in order to be imaged if such features have considerable topographic relief the direction of radar illumination is less important because directional trends in unexplored regions cannot be predicted availability of radar imagery from two directions greatly facilitates interpretation of dune morphology and hence conclusions about causative wind regimes

arid land surface characterization with repeat pass sar interferometry repeat pass ers sar interferometry was used to map different surface types of the death valley salt pan at this arid site the surface roughness varies between extremely smooth salt lakes clay pan and very rough alluvial fans eroded salt formations the moisture varies from very dry alluvial fans to wet wet clay salt crust with water ponds with seasonal changes in certain areas while the surface geometry is stable for certain surface types alluvial fans thick salt crusts it changes for others as a result of the changing water level and erosion by wind and rain the changing surface roughness moisture and vegetation conditions cause large variations of the backscattering and coherence this information is used to distinguish different surface types furthermore interferometry was used to map the topographic height in a second part of the study the potential of the degree of coherence to retrieve information on the vegetation density and the surface erosion was evaluated

linear dunes on titan and earth initial remote sensing comparisons thousands of dunes found in cassini radar images of the equatorial regions of titan a moon around saturn are similar in size and morphology to linear dunes on earth we present remote sensing images of terrestrial analogues to the dunes on titan obtained by landsat and radar both at considerably higher resolution than are available at titan that provide information about dune landforms and processes dunes are generally dark to radar indicating smooth surfaces and signal absorbing materials but at certain incidence angles dune surfaces can reflect the radar signal and lead to a bright return linear dunes on titan and earth diverge around topographic obstacles creating teardrop patterns that indicate mean direction of wind flow and sand transport when sand supply or wind conditions change in linear dune fields such as behind an obstacle or near the margin of the dune field dunes disappear change size and spacing or change dune type these comparisons of features on titan and earth provide a better understanding of the global sand transporting wind directions sand properties and supply and the nature of the underlying substrate on titan

experimental study on the triggering mechanisms and kinematic properties of large debris flows in wenjia gully debris flows are typically caused by natural terrain landslides triggered by intense rainfalls if an incoming mountain torrent flows along sloping channels at high velocity huge amounts of sediment from landslide dams and eroded channel beds will be entrained into the flows to form debris flows it is likely that large debris flows are due to the failure of many landslide dams of different scales due to bank slides or collapses bed erosion and solid transport the catastrophic debris flows that occurred in wenjia gully wenchuan earthquake area china on august 13 2010 two years after the mega earthquake were caused by intense rainfall and the serious erosion of sloping channels in the wake of the incident experimental tests were conducted to better understand the process of sediment erosion and entrainment on the channel bed and the formation of debris flows the results show that the bed erosion bank collapses and channel widening caused by erosion accounted for the triggering and scale amplification of downstream debris flows in the wenjia gully event this study illustrates how the hazardous process of natural debris flows can begin several kilometers upstream and how such a complex cascade of geomorphic events failure of landslide dams and erosion of the sloping bed can lead to catastrophic discharges neglecting recognition of these hazardous geomorphic and hydrodynamic processes may result in high cost c 2014 elsevier b v all rights reserved

evidence for early proterozoic plate tectonics from seismic reflection profiles in the baltic shield plate tectonics provides the linking framework for all tectonic and magmatic activity seen today but it is not known when plate tectonics first developed on earth new deep seismic reflection and

discrimination of geophysical phenomena in satellite radar interferograms various geophysical phenomena are recorded in the interference patterns formed by differencing two synthetic aperture radar sar images the fringes generated by the topographic relief can be removed using a digital elevation model dem the remaining fringes map the change in satellite to ground range which occurred between the acquisition times of the two images by comparing different pairs of images spanning different intervals of time it is possible to discriminate between geophysical signal and interferometric artifact here we apply this pair wise logic to the area around the 1992 landers california earthquake using sar images acquired by the ers 1 satellite the range varies with time as a constant step impulsive or sloping function examples of each type include a dem error an aftershock two atmospheric perturbations and postseismic afterslip respectively their signatures are identified and separated using the pair wise logic

magnetotelluric transect of long valley caldera resistivity cross section structural implications and the limits of a 2 d analysis twenty four magnetotelluric mt soundings have been collected in an east west profile across the center of long valley caldera the average station spacing is approximately 1 km and appears adequate to sample the important features of the upper crustal and deeper resistivity structures additional control on the shallowest resistivity is provided by a continuous profile of time domain electromagnetic soundings coincident with the western portion of the mt line our mt data set reveals numerous resistivity structures which illuminate the evolution and present state of the long valley system many of these have been quantified through two dimensional 2 d finite element modeling emphasizing the transverse magnetic tm mode important structural components include low resistivity layers 0 5 1 5 km deep under the eastern half of the caldera beneath the axial graben of the resurgent dome and under the west caldera moat most of this layering appears to lie in post caldera early rhyolite tuffs and the upp

two dimensional topographic responses in magnetotellurics modeled using finite elements we simulate the magnetotelluric response to two dimensional earth topography using finite elements linear interpolation of the secondary field parallel to strike over triangular elements allows accurate modeling of inclined resistivity boundaries including topographic surfaces to avoid discontinuities in field derivatives or resistivity care must be taken that the nodal values of the field parallal to strike used to obtain the auxiliary secondary fields are kept within uniform earth media the nodal locations may be shifted but the derivatives still are evaluated at the field points of interest correct values may be returned at gentle breaks in slope as well as along straight surfaces the finite element program is verified by comparison with the analytic transverse magnetic response of a hemicylindrical depression and with rayleigh scattering and transmission surface results for transverse electric and transverse magnetic polarization agreement with the other methods generally is excellent with t

a sand budget for the alexandria coastal dunefield south africa the sand in the alexandria coastal dunefield is derived from the sandy beach which forms the seaward boundary of the dunefield sand is blown off the beach onto the dunefield by the high energy onshore directed dominant wind the dunefield has been forming over the past 6500 years sand transport rates calculated from dune movement rates and wind data range from 15 to 30 m3 m 1 yr 1 in an ene direction the sand transport rate decreases with increasing distance from the sea due to a reduction in wind speed resulting from the higher drag imposed upon the wind by the land surface aeolian sand movement rates of this order are typical of dunefields around the world the total volume of sand blown into the dunefield is 375 000 m3 yr 1 sand is being lost to the sea by wave erosion along the eastern third of the dunefield at a rate of 45 000 m3 yr 1 the dunefield thus gains 330 000 m3 of sand per year this results in dunefield growth by vertical accretion at about 1 5 mm yr 1 and landward movement at about 0 25 m yr 1 the dunefield is a significant sand sink in the coastal sand transport system the rate of deposition in coastal dunefields can be 10 times as high as rates of deposition in continental sand seas the higher rate of deposition may result from the abundant sand supply on sandy beaches and the higher energy of coastal winds wind transport is slow and steady compared to fluvial or longshore drift transport of sediment and catastrophic aeolian events do not seem to be significant in wind laid deposits

observations of motional electromagnetic fields during emslab the long period 1 day behavior of the seafloor electromagnetic fields during emslab is considered in detail with an emphasis on interpretation in terms of oceanic motions the study begins with a summary of the physics of motional electromagnetic induction in which the seawater conductivity weighted vertically integrated velocity measured by the horizontal electric field is emphasized using frequency domain methods it is shown that seafloor and terrestrial magnetic variations have similar spectral shapes indicating a common origin but the seafloor electric field is not consistent with either at periods longer than 4 days suggesting an oceanic source the magnetic field variations are highly coherent across the emslab array at periods shorter than 9 days but the similarity decreases at longer periods probably due to long term instrumental drift the seafloor horizontal electric field data exhibit the broadband coherence characteristic of ionospheric sources only at periods shorter than 1 2 days and are essentially incoherent between 4 days and a week except in association with certain propagating wave phenomena the distinction between the depth averaged velocity inferred from the horizontal electric field and its point measurement by the vertical electric field is demonstrated with data some specific properties of the seafloor electric fields are then considered in detail the first of these is a 4 day wave observed to propagate from north to south along the east flank of the juan de fuca ridge the wavelength propagation sense and association with the ridge are all consistent with topographically trapped rossby wave behavior at a zero in the group velocity a second north to south propagating wave is seen at periods of 8 12 days in the middle of the emslab area with a probable wavelength of order 1000 km unresolved low frequency structures in the electric field are also mentioned these observations clearly demonstrate the power of electromagnetic array methods for the study of long period oceanic behavior

unsteady bed shear stresses induced by navigation laboratory observations time dependent bed shear stresses induced by the passage of a barge tow have been measured with hot film shear stress sensors in a 1 25 scale model conditions typical of those observed for upper mississippi river navigation traffic were simulated in the experimental facility two sets of experiments were carried out the first set consisted of simultaneous shear stress measurements at different locations for a variety of flow depths and boat operating conditions providing space time distributions of ensemble averaged wall shear stresses the second set included a large number of realizations gathered for one particular flow condition at a single position allowing analysis of the time evolution of the turbulence characteristics i e standard deviation of the bed shear stresses the results of the first set of experiments show that for all the experimental conditions the basic patterns of the shear stress are similar with two regions of high shear stress associated with the passage of the bow and the

dam break outburst flood propagation and transient hydraulics a geosciences perspective summary dam break outburst floods are sudden short lived and high magnitude discharges of water and sediment propagating over an initially dry terrain both field observations by geoscientists and experimental measurements by engineers have produced understanding of outburst floods but neither approach has satisfactorily supplied data that is directly of use to hazard managers this study draws together those two literature groups and provides new experimental data to test hypotheses concerning the effect of a series of external controls on resultant longitudinal flow propagation and transitory hydraulics these external controls form experimental treatments and are i the height of the lock gate raise as a surrogate for dam breach evolution and initial hydrograph ii bed roughness and iii suspended sediment concentration these control both horizontal and vertical fluid motion the latter of which is a key property for controlling aeration bed shear stress and turbulence intensity the experimental treatments show that outburst floods on horizontal beds can be identified to possess three longitudinal flow regimes firstly there is a short acceleration due to the reservoir pressure level i e the depth of impounded water secondly channel flow quickly converges to an inertial regime the third flow regime is viscous and dominated by channel bed friction flow depth increases in the inertial regime then decreases in the viscous regime experiments herein show that the timing of the peaks at a point down channel of each hydraulic quantity varies most notably peak bed shear stress precedes flow velocity which precedes peak flow depth a point of inflexion occurs with distance down channel that is a manifestation of the transition from accelerating to decelerating flows these external controls and the effects of them on longitudinal and vertical motion are analysed statistically and quantitative relationships are derived to underpin the resultant conceptual model this conceptual model should serve as a platform for future probabilistic and process based modelling of outburst floods

magnetotelluric observations across the juan de fuca subduction system in the emslab project a magnetotelluric mt transect has been obtained near latitude 45 n from the active juan de fuca spreading center across the subduction zone and cascades volcanic arc and into the back arc deschutes basin region this paper presents the mt data set and describes its major characteristics as they pertain to the resistivity of the subduction system in addition we discuss the measurement and processing procedures employed as well as important concerns in data interpretation broadband audiomagnetotelluric amt mt soundings approx 0 01 500 s period were collected on land with considerable redundancy in site location and from which 39 sites were selected which constrain upper crustal heterogeneity but sense also into the upper mantle fifteen long period mt recordings about 50 10 000 s on land confirm the broadband responses in their common period range and extend the depths of exploration to hundreds of kilometers on the juan de fuca plate offshore 33 out of 39 sea floor instruments at 19 locations gave good results of these locations five magnetotelluric soundings plus two additional geomagnetic variation sites covering the period range 200 105 s approximately constitute the ocean bottom segment of our profile the feature of the land observations which probably relates most closely to the subduction process is a peak in the impedance phase of the transverse magnetic mode around 30 50 s period this phase anomaly with a corresponding inflection in the apparent resistivity is continuous eastward from the seacoast and ends abruptly at the high cascades it signifies an electrically conductive layer in otherwise resistive lower crust or upper mantle with the layer conductance decreasing eastward from the coast to a minimum under the coast range but increasing suddenly to the east of the central willamette basin the higher conductance to the east is corroborated by the vertical magnetic field transfer function whose real component shows negative values in the period range 100 1000 s over the same distance the transverse electric mode apparent resistivity and phase on the land display a variety of three dimensional effects which make their interpretation difficult conversely both modes of the ocean floor soundings exhibit a smooth progression laterally from the coastal area to the spreading ridge indicating that the measurements here are reflecting primarily the large scale tectonic structures of interest and are little disturbed by small near surface inhomogeneities the impedance data near the ridge are strongly suggestive of a low resistivity asthenosphere beneath resistive juan de fuca plate lithosphere approaching the coastline to the east both impedance and vertical magnetic field responses appear increasingly affected by a thick wedge of deposited and accreted sediments and by the thinning of the seawater

multifrequency and multipolarization radar scatterometry of sand dunes and comparison with spaceborne and airborne radar images understanding the unusual radar scattering characteristics of sand dunes is necessary in the analysis of radar images of aeolian landscapes of the earth and of other planets in this paper we report on airborne radar scatterometer data of sand dunes acquired at multiple frequencies and polarizations radar backscatter from sand dunes is very sensitive to the imaging geometry at small incidence angles the radar return is mainly due to quasi specular reflection from dune slopes favorably oriented toward the radar a peak return usually occurs at the incidence angle equal to the angle of respose for the dunes the peak angle is the same at all frequencies as computed from specular reflection theory at larger angles the return is significantly weaker the scatterometer measurements verified observations made with airborne and spaceborne radar images acquired over a number of dune fields in the united states central africa and the arabian peninsula the imaging geometry constraints indicate that possible dunes on other planets such as venus will probably not be detected in radar images unless the incidence angle is less than the angle of repose of such dunes and the radar look direction is approximately orthogonal to the dune trends

new airborne imaging radar observations of sand dunes kelso dunes california abstract high resolution multiple wavelength and polarization radar data of kelso dunes were acquired during the mojave field experiment they offer the opportunity to develop criteria for the selection of optimal wavelengths and polarizations for imaging of dune areas the backscatter from unvegetated dune surfaces at all wavelenghts c l and p band with direct hh vv polarization is largely controlled by dune topography and incidence angle these data especially p band provide the best images of dune topography the best discrimination between active and inactive dunes is obtained by cross polarized c band data cvh chv as a result of multiple scattering from vegetation and small scale topography e g shadow dunes

turbulence characteristics in supercritical open channel flows effects of froude number and aspect ratio abstractan experimental investigation of supercritical uniform and gradually varied open channel flows is presented for a wide range of froude numbers and flume width to flow depth aspect ratios the instantaneous streamwise and vertical flow velocities were measured in a laboratory flume over the entire width using a two dimensional laser doppler anemometry 2d lda system to determine turbulence intensities and bed and reynolds shear stresses the mean velocity patterns show undulation across the flume indicating the presence of counterrotating secondary current cells these currents redistribute turbulence intensities and bed and reynolds shear stresses across the flume for aspect ratios 4 5 i e narrow open channel flow the velocity dip phenomenon is identified both in the streamwise velocity and the reynolds shear stress distributions for high aspect ratios i e wide open channel flow the strength of secondary currents diminish toward the flume center resulting in a 2d flow farther away

electromagnetic wave surface velocimetry electromagnetic wave surface velocimeters esvs measure the doppler shift in electromagnetic waves reflected from the water surface they provide nonintrusive water surface velocity measurements from bridges and river banks comparisons with laboratory and field tests show very good agreement over a wide range of elevation and planview angles laboratory testing shows comparable results between esv and other measurement techniques when 0 4v1 6 m s and 15 45 field testing at three different locations shows that the optimal operation conditions are at an elevation angle 30 planview angle 13 and 0 30v2 00 m s the ratio of cross section averaged velocity to mean free surface velocity is approximately cfdav0 88 for high flow velocities during floods the standard deviation of the field measurement for these three streams was less than 15 of the mean value

sar monitoring of progressive and seasonal ground deformation using the permanent scatterers technique spaceborne differential radar interferometry has proven a remarkable potential for mapping ground deformation phenomena e g urban subsidence volcano dynamics coseismic and postseismic displacements along faults as well as slope instability however a full operational capability has not been achieved yet due to atmospheric disturbances and phase decorrelation phenomena these drawbacks can often be at least partially overcome by carrying out measurements on a subset of image pixels corresponding to natural or artificial stable reflectors permanent scatterers ps and exploiting long temporal series of interferometric data this approach allows one to push the measurement precision very close to its theoretical limit in the order of spl sim 1 mm for c band european remote sensing ers like sensors in this paper the detection of both time uniform and seasonal deformation phenomena is addressed and a first assessment of the precision achievable by means of the ps technique is discussed results highlighting deformation phenomena occurring in two test sites in california are reported fremont in the southern bay area and san jose in the santa clara valley

verification of five magnetotelluric systems in the mini emslab experiment given the degree of complexity of modern magnetotelluric mt instrumentation comparison of the total performance for two or more systems is an important verification test this paper compares the processed data from five mt systems which were designed and constructed separately and which employ different electrode types electrode separations magnetometers and methods of signal processing the comparison shows that there is a high degree of agreement among the data from the different systems the study also demonstrates the compatibility and reliability of the mt systems employed as part of emslab juan de fuca electromagnetic sounding of the lithosphere and asthenosphere beneath the juan de fuca plate this project proposed by a consortium of institutions involves not only magnetotellurics studies but also studies of magnetic variation on land and on the sea bottom the project calls for the real time mt systems to occupy stations along segments of a profile in oregon a composite profile will be created from the segments prior to commencing the main mt profiling phase one week was set aside in august 1984 for all groups to record and process mt data sequentially at six sites in diverse geologic terrains this experiment was called mini emslab