rheology of till beneath storglaciaren sweden in order to study in situ the rheology of a deforming subglacial till various instruments were emplaced in till beneath storglaciaren sweden boreholes were used to gain access to the till beneath about 100 m of ice tiltmeters provided an estimate of the shear strain rate in the till two other instruments yielded measures of till strength in addition water pressures were recorded in boreholes and in the till a computer controlled distance meter provided an effectively continuous record of the surface velocity and data from frequent surveys of a stake network were used to estimate the mean basal drag based on a force balance calculation tilt rates varied directly with effective pressure so decreases in water pressure apparently increased the coupling between the glacier and the bed surface speed was either out of phase with tilt or varied independently of tilt thus increases in speed were apparently a consequence either of longitudinal coupling or of reduced coupling between the glacier and the bed they were not a result of till deformation till strength varied directly with effective pressure which is consistent with it being a mohr coulomb or frictional material the devices measuring till strength are presumed to have been pulled through the till at a speed that varied in phase with the surface speed but till strength did not vary systematically with surface speed this implies that the residual strength of the till is insensitive to strain rate thus the appropriate constitutive equation for till rheology may be of the form e e k where k is a constant this is consistent with experimental data reported in the geotechnical literature

radiometric slope correction of synthetic aperture radar images the brightness in a sar image is affected by topographic height variations due to 1 the projection between ground and image coordinates and 2 variations in backscattering coefficient with the local scattering geometry this paper derives a new equation for 1 i e the radiometric slope correction based on a calibration equation which is invariant under a coordinate transformation an algorithm is described to obtain the slope correction from a sar interferogram which also enables retrieval of the full scattering geometry since the sar image and interferogram are derived from the same data set there is no need to match the image with the calibration data there is also no need for phase unwrapping since the algorithm only uses the fringe frequencies a maximum likelihood estimator for the fringe frequency is analyzed and the algorithm is illustrated by processing ers 1 sar data the example demonstrates that the spatial resolution and calibration error are adequate for most applications

influence of clay mineralogy on the stability of a landslide in plio pleistocene clay sediments near grassano southern italy abstract clayey silts involved in a landslide have been sampled to study the role of sediment composition in developing sliding surfaces five drillings enabled the collection of 46 samples and to define active slide surfaces and non active surfaces discontinuities active surfaces are enriched in 16 63 m fractions and depleted in 2 8 m fractions whereas discontinuities show grain size features similar to undisturbed sediments the organic carbon is low and the c org n ratio is bimodal but the c org and the c org n ratio are not related to sliding or discontinuities sheet silicates are more abundant than quartz carbonates and feldspars gypsum and hematite occur in some samples at trace levels in the clay fractions the kaolinite mixed layer ratio seems to be a sensitive parameter to the presence of sliding and discontinuities scanning electron microscopy demonstrated that active slide surfaces have an open texture clay minerals are impoverished and non oriented whereas secondary phases hematite and gypsum are enriched there is a relationship between geotechnical features and mineralogical composition

single and multipolarimetric sar tomography of forested areas a parametric approach in this paper a technique is described for the tomographic characterization of forested areas through multiple synthetic aperture radar sar observations based on either single or multipolarimetric acquisitions this technique is based on the idea of characterizing the fourier spectrum of the multibaseline data as being constituted by two effective scattering centers displaced along the vertical direction plus the associated decorrelation terms as a result sar tomography will be formulated as the problem of detecting the number of scattering centers within the resolution cell estimating the parameters that describe their spatial structure and evaluating the associated backscattered powers parameter estimation is carried out through the covariance matching estimation technique which provides an asymptotically optimal solution the results of an experiment performed on a real p band multibaseline fully polarimetric data set relative to the forested site of remningstorp sweden are reported

ground based array for tomographic imaging of the tropical forest in p band in this paper we discuss the design concepts and preliminary results relating to the european space agency s ground based campaign tropiscat whose main goal is to evaluate temporal coherence at p band in a tropical forest in quad polarization considering temporal lags ranging from hours to months and at different heights within the vegetation layer the experiment has been successfully set up and operated since october 2011 at the paracou field station french guiana where the equipment was installed on top of the 55 m high guyaflux tower to illuminate the forest below the system consists of a vector network analyzer connected to 20 antennas through a switchbox which allows the use of any of them either as a transmitter or as a receiver vertical imaging and fully polarimetric capabilities are achieved by operating the 20 antennas in a multistatic fashion resulting in an equivalent monostatic array consisting of 15 phase centers displaced along the vertical direction in each polarization such a design allows unambiguous imaging of the vegetation while yielding a minimum distance between nearby antennas on the order of 0 8 m so as to minimize coupling effects the equipment allows the gathering of signals with the tomographic array within a few minutes resulting in the possibility to produce a tomographic image of the forest with a temporal sampling of 15 min system calibration and validation was performed by employing a 2 m trihedral reflector and a rotating dihedral reflector this allowed the evaluation of the system pulse response in all polarizations and also assessment of the extent of tower motions as a result tomographic images have been generated from 500 p band to 900 mhz in all polarizations results from real data acquired in fall 2011 confirm the feasibility of carrying out reliable coherence measurements for the whole duration of the campaign

a three dimensional radar backscatter model of forest canopies three dimensional forest backscatter model which takes full account of spatial position of trees in a forest stand is described a forest stand was divided into cells according to arbitrary spatial resolution the cells may include crown trunk and gap components determined by the shape size and position of the trees the forest floor is represented by a layer of ground cells a ray tracing method was used to calculate backscattering components of 1 direct crown backscatter 2 direct backscattering from ground 3 direct backscattering from trunk 4 crown ground scattering and 5 trunk ground scattering both the attenuation and time delay of microwave signals within cells other than gap were also calculated from ray tracing the backscattering mueller matrices of these components within the same range intervals were incoherently added to yield the total backscattering of an image pixel by assuming a zero mean multiplicative gaussian noise for image speckle the high resolution images were aggregated to simulate a sar image with a given spatial resolution and number of independent samples looks a well characterized 150 m x 200 m forest stand in maine usa was used to parameterize the model the simulated radar backscatter coefficients were compared with actual jpl sar data the model gives reasonable prediction of backscattering coefficients averaged over the entire stand with agreement between model and data within 1 35 db for all channels the correlations between simulated images and sar data 10 by 15 pixels were positive and significant at the 0 001 level for all frequencies p l and c bands and polarizations hh hv and vv

compressive sensing for multibaseline polarimetric sar tomography of forested areas the structure of forests is an important indicator of ecosystem dynamics and enables the modeling and monitoring of ecological change synthetic aperture radar tomography tomosar provides scene reflectivity estimation of vegetation along elevation coordinates due to the advantages of superresolution imaging and a small number of measurements compressive sensing cs inversion techniques for sar tomography were successfully developed and applied this paper addresses the 3 d imaging of forested areas based on the framework of cs using fully polarimetric fp multibaseline sar interferometric mb insar tomography at p band a new cs based fp mb insar tomography method is proposed a sum of kronecker product skp decomposition based cs fp mb insar tomography method fp skpcs tomosar method the method based on an assumption that the reflectivity signal of a single scattering mechanism sm is more sparse than that of a composite of sms recovers the reflectivity profile of different sms by using the cs technique this method not only allows superresolution imaging with a low number of acquisitions but also can estimate the polarimetric sm of the vertical structure of forested areas the effectiveness of these novel techniques for polarimetric sar tomography is demonstrated using fp p band airborne data sets acquired by the onera sethi airborne system over a test site in paracou french guiana and the results of the vertical structure of forested areas derived by the method are verified by in situ test data

on the estimation of radar polarization orientation shifts induced by terrain slopes in recent studies d l schuler et al 2000 applied polarimetric imaging radar derived orientation angles to measure topography and j s lee et al 2000 used orientation angles for polarimetric sar data compensation to ensure accurate estimation of geophysical parameters in rugged terrain areas to support these applications it is important to accurately estimate shifts in orientation angles induced by the azimuth slope variations however in many cases inconsistency in the estimation of orientation angle shifts was encountered in several areas introducing noisy and erroneous results the present authors develop a unified analysis of estimation algorithms based on the circular polarization covariance matrix the concept of reflection symmetry is used to explain the soundness of the circular polarization method and to show problems associated with other algorithms l band polarimetric synthetic aperture radar sar images of camp roberts ca are used to substantiate this theory

retrieval of forest stem volume using vhf sar the ability to retrieve forest stem volume using carabas coherent all radio band sensing sar images 28 60 mhz has been investigated the test site is a deciduous mixed forest on the island of oland in southern sweden the images have been radiometrically calibrated using an array of horizontal dipoles the images exhibit a clear discrimination between the forest and open fields the results show that the dynamic range of the backscattering coefficient among the forest stands is higher than what has been found with conventional sar using microwave frequencies the backscatter increases with increasing radar frequency this work shows an advantage compared to higher frequencies for stem volume estimation in dense forests

the potential of alos palsar backscatter and insar coherence for forest growing stock volume estimation in central siberia abstract the full potential of alos palsar l band interferometric insar coherence data for the estimation of forest growing stock volume gsv in the boreal forest has rarely been investigated moreover alos palsar backscatter and insar coherence have yet to be used together to delineate gsv due to the observation strategy and the high acquisition success rate over eurasia a large amount of high quality alos palsar l band data is available over siberia consequently this paper investigates the capability of alos palsar backscatter and insar coherence for the estimation of gsv in central siberia russia the potential of backscatter and coherence are directly compared using the same inventory data altogether 87 palsar images are used and eleven forest inventory sites are investigated based on this large dataset it was observed that insar coherence acquired in frozen conditions offers the highest potential for gsv estimation the saturation level for single coherence images was on average 230 m 3 ha with an average r 2 between coherence and gsv of 0 58 palsar backscatter acquired in unfrozen conditions could also estimate gsv however the saturation levels 75 100 m 3 ha and the average r 2 0 42 0 48 were lower hv backscatter offered only a slightly greater potential than hh backscatter a simple inversion approach aiming at the delineation of forest gsv maps based on the multitemporal sar data was developed and applied to five forest inventory sites this approach combines hv backscatter data acquired in unfrozen conditions and insar coherence data acquired in frozen conditions in general the produced maps feature a corrected relative rmse corr of 2 between inventory data and sar data based maps varied between 0 54 and 0 83

simulation of time dependent movements in syncrude tailings dyke foundation foundation movements at the syncrude tailings dyke continued over several years in response to the construction of the dyke major movements have been observed in a relatively narrow layer of previ

dynamic centrifuge testing of slickensided shear surfaces movement along preexisting slickensided rupture surfaces in overconsolidated clay and clay shale slopes can represent a critical sliding mechanism during earthquakes the seismic behavior of preexisting slickensided surfaces in overconsolidated clay was examined by performing dynamic centrifuge model tests of two slickensided sliding block models constructed using rancho solano lean clay dynamic shear displacements were concentrated along the preformed slickensided surfaces the peak shear resistances mobilized along the slickensided surfaces during dynamic loading were 90 120 higher than the drained residual strength measured prior to shaking to accurately predict the displacements of the sliding blocks using newmark s method it was necessary to use dynamic strengths that were 37 64 larger than the drained residual strength of the soil dynamic loading caused a positive pore pressure response in the soil surrounding the slickensided planes the postshaking shear strengths were 17 31 higher than those measured prior to shaking

generalized terrain topography in radar scattering models modeling of terrain topography is crucial for vegetated areas given that even small slopes impact and alter the radar wave interactions between the ground and the overlying vegetation current missions either exclude pixels with large topographic slopes or disregard the terrain topography entirely potentially accumulating substantial modeling errors and therefore impacting the retrieval performance over such sloped pixels the underlying terrain topography needs to be considered and modeled to obtain a truly general and accurate radar scattering model in this paper a flexible and modular model is developed the vegetation is considered by a multilayered multispecies vegetation model capable of representing a wide range of vegetation cover types ranging from bare soil to dense forests the ground is incorporated with the stabilized extended boundary condition method allowing the representation of an n layered soil structure with rough interfaces terrain topography is characterized by a 2 d slope with two tilt angles alpha beta simulation results for an evergreen forest show the impact of a 2 d slope for a range of tilt angles a 10 circ tilt in the plane of incidence translates to a change of up to 15 db in hh 10 db in vv and 1 5 db in hv for the total radar backscatter terrain topography is shown to be crucial for accurate forward modeling especially over forested areas

analysis of a sample containing a shear surface from a recent landslip south cotswolds uk the paper reports analysis of a block sample taken from a trial pit hand dug across the shear surface of an active landslide in the south cotswolds the slide is located on the upper fuller s earth some 50m downslope of the overlying great oolite limestone the weathering of which has produced ooliths and gravel sized fragments which are incorporated within the slipped mass sampling at 5 mm intervals confirmed the inverse relationship between the natural moisture content and calcite content in order to assess the significance of changes in moisture content in the fine fraction the influence of the non sorptive calcite was removed and a normalized moisture content profile established examination of the lower shear surface using scanning electron microscopy confirmed the parallel orientation of the clay minerals for a thickness of some 1 m this thin veneer extended over areas of granular material highlighting the importance of obtaining representative samples when shear strength assessment is under

a case history of tunnel boring machine jamming in an inter layer shear zone at the yellow river diversion project in china this is a case study of a tunnel boring machine tbm jamming in a section of the connection works no 7 tunnel of the yellow river diversion project yrdp in china analysis of tunnel lithology rock convergence by shearing rock strength and ground stress indicates that a high rate of convergence within an inter layer shear zone in the lower part of an anticline was a dominant factor in the jamming in addition the shield encountered unfavorable tunnelling conditions in the form of wet clay groundwater inflow and cavities coincident with tensile stresses in the lower part of an adjacent syncline based on these diagnoses economical and quick measures were adopted including additional excavation outside of the shield leaving free space to release the tbm after 9 days of being jammed the tbm was totally released and resumed normal excavation this example highlights lessons learned from folding and inter layer shear zone in tbm tunnelling

radar modeling of a boreal forest the authors report on the use of microwave modeling ground truth and synthetic aperture radar sar data to investigate the characteristics of forest stands a mixed coniferous forest stand has been modeled at sar frequencies p l and c bands the extensive measurements of ground truth and canopy geometry parameters were performed in a 200 m square hemlock dominated plot inside a forest hemlock trees in the forest are modeled by characterizing tree trunks branches and needles leaves with randomly oriented lossy dielectric cylinders whose area and orientation distributions are prescribed the distorted born approximation is used to compute the backscatter at p l and c sar frequencies

down slope variation in geotechnical parameters and pore fluid control on a large scale alpine landslide abstract a geotechnical investigation has been carried out on a large volume landslide in the stambach valley on the slopes above the town of bad goisern austria undrained loading has been considered as a means of triggering a large volume debris flow the initiation of this landslide has been linked with the collapse of rock pillars from the rock face of zwerchwand onto the head of the flow the concept of pore tensions resulting from stress relief has been used to account for the time delays of up to 10 months between the loading and the reactivation of the debris flow

evaluation of common practice empirical procedures for residual friction angle of soils hawaiian amorphous material rich colluvial soil case study the residual strength of soils has received considerable attention after skempton suggested that the stability of reactivated landslides may be governed by residual strength in this respect numerous studies have been conducted to determine the factors affecting the residual strength of soils specifically research effort was focused on determining correlations between the residual friction angle of soils and soil indexes such as atterberg limits and clay fraction some of these researchers suggested that strong correlations exist with soil indexes other researchers claimed that there is no correlation between the soil index and the residual friction of soils thus there is a need to clarify whether there is a correlation between residual friction angle and soil index properties in this effort we describe general properties of landslides in hawaii with an emphasis on an active landslide followed by evaluating correlations between the residual strength and soil indexes the results of this study show that the existing empirical correlations for soil index properties and residual friction angle predict poorly the residual friction angle of colluvial soils that rich in amorphous materials however the results also show that a strong correlation between ll and pi and residual friction angle may exist depending on the soil mineral type

assessment of scattering mechanism of polarimetric sar signal from mountainous forest areas this study aims to understand the effects of the topographic slope variation on the vegetation backscattering characteristics of polarimetric imaging radar most of the previous studies in modeling microwave backscattering signatures of vegetated area have been carried out over relatively flat areas in order to model vegetation scattering mechanisms of mountainous forests this paper presents an improvement of the radiative transfer model that accounts for the tilted scattering surface beneath a forest canopy an l band polarimetric synthetic aperture radar sar data set acquired by the nasa jet propulsion laboratory airborne sar system was used to test and to assess the vegetation scattering model for a sloping forest area experimental result shows the proposed model to be adequate for evaluating slope induced changes in microwave scattering mechanisms

terrain influences on sar backscatter around mt taranaki new zealand an l band sar image from the japanese jers 1 satellite has been analyzed for the effects of local surface orientation relative to the radar illumination direction orthorectification of the sar imagery and determination of the local surface orientation is achieved with the aid of a high resolution digital terrain model an improved method of determining scatterer density for a surface in three dimensions is introduced and used to correct radiometrically the image for terrain variation residual radiometric effects due to surface orientation are shown to be dependent on the ground cover class backscatter from the indigenous forest was more isotropic than that from the farmland as accurate registration was required for this study a method for identifying control points in the rectified imagery is described which alleviated the difficulty of identifying them in the raw image

a ring shear device for the study of till deformation tests on tills with contrasting clay contents abstract deformation of subglacial sediment may have had a profound influence on the geomorphic effects and dynamics of pleistocene ice sheets but data that bear on the rheology of such sediment are few and contradictory a means of studying systematically the mechanical properties of glacial tills is provided by a ring shear device that shears a large annular specimen to high strains at variable rates special features of the device allow continuous observation of the distribution of shear strain measurement of local stresses normal to the direction of shear and isolation of wall effects thus far a linear viscous putty and two tills with different clay contents 4 and 32 by weight have been tested the experiments with till indicate as expected that the presence of dispersed clay minerals reduces markedly both the residual strength and hydraulic diffusivity of till clay also reduces spatial variations in normal stress associated with grain bridges the walls bounding the specimen support only 9 17 of the total resistance to shearing strain was localized in both tills but not in the linear viscous putty strain localization in the tills indicates that their theology departs significantly from linear and bingham viscous models

rate weakening friction characterizes both slow sliding and catastrophic failure of landslides abstract catastrophic landslides cause billions of dollars in damages and claim thousands of lives annually whereas slow moving landslides with negligible inertia dominate sediment transport on many weathered hillslopes surprisingly both failure modes are displayed by nearby landslides and individual landslides in different years subjected to almost identical environmental conditions such observations have motivated the search for mechanisms that can cause slow moving landslides to transition via runaway acceleration to catastrophic failure a similarly diverse range of sliding behavior including earthquakes and slow slip events occurs along tectonic faults our understanding of these phenomena has benefitted from mechanical treatments that rely upon key ingredients that are notably absent from previous landslide descriptions here we describe landslide motion using a rate and state dependent frictional model that incorporates a nonlocal stress balance to account for the elastic response to gradients in slip our idealized one dimensional model reproduces both the displacement patterns observed in slow moving landslides and the acceleration toward failure exhibited by catastrophic events catastrophic failure occurs only when the slip surface is characterized by rate weakening friction and its lateral dimensions exceed a critical nucleation length h h that is shorter for higher effective stresses however landslides that are extensive enough to fall within this regime can nevertheless slide slowly for months or years before catastrophic failure our results suggest that the diversity of slip behavior observed during landslides can be described with a single model adapted from standard fault mechanics treatments

modeling and observation of the radar polarization signature of forested areas to understand radar measurements of forested areas the authors have developed a model of l band 25 cm microwave scattering from a forest the forest floor is layer of nearly vertical dielectric cylinders representing tree trunks above this layer is a second layer consisting of randomly oriented cylinders which represent branches the authors identify several scattering mechanisms and calculate the corresponding stokes matrices which combine to give the total stokes matrix and resulting polarization signature it is found that this simple model permits accurate prediction of the polarization of the scattered waves and that additional mechanisms including the effects of leaves and twigs are not required for the 25 cm observation of the forests studied the authors present measurements of the polarization signature acquired over a forested area and show comparisons with model calculations

inverse long term stability analysis of a constrained landslide this paper deals with long term stability analysis of a constrained landslide the landslide has nowhere to go and its downhill movement is slowing in time which intuitively implies its long term stability however exactly because the landslide is slowing the shear strength on the sliding surface may decrease leading to increase in compressive stresses at the landslide foot and ultimately to a failure the proposed long term stability analysis of such a landslide is based on an inverse analysis which allows for the safety factor to be determined solely by curve fitting the observed displacement data for a safety factor lower than 1 the time of failure can be predicted using additional earth pressure measurements in the sliding layer the proposed procedure is illustrated using the observation data from the brattas st moritz landslide

retrieving root zone soil moisture profile from p band radar via hybrid global and local optimization we propose an inversion model for retrieving the root zone soil moisture profile using the p band radar observations and validate it using data collected during the airborne microwave observatory of subcanopy and subsurface airmoss mission the forward model utilized in this article uses an existing small perturbation method spm to calculate the electromagnetic wave scattered from multilayered rough surface dielectric structures to solve the inverse problem which is formulated as a least squares problem we utilize a novel global optimization technique that takes the advantage of the speed of a local optimization method while ensuring convergence to the global minimum we present the numerical results to demonstrate significant improvements in the inversion results and computational speed compared to the previously used airmoss baseline inversion algorithm the presented method is validated with in situ soil moisture measurements finally by utilizing a closed form analytical solution to richards equation we demonstrate improvements in the accuracy of our soil moisture retrieval results

the effect of topography on radar scattering from vegetated areas the ways in which radar scattering from vegetated areas is affected by the topography of the surface underneath the vegetation are discussed it is shown using a discrete scatterer model that the dominant scattering mechanism may change drastically when the ground surface is tilted relative to the horizontal for a horizontal ground surface for example the total scattering may be dominated by scattering off the tree trunks followed by a reflection off the ground surface for a relatively small tilt in the ground surface the ground trunk interaction term may be replaced by scattering from the branches alone as the dominant scattering mechanism the effect of the topography is more pronounced for scattering by longer wavelengths and the implications on algorithms designed to infer forest woody biomass and soil and vegetation moisture using polarimetric sar data are discussed the effect of the topography on the scattering behavior from forested areas is illustrated with images acquired by the nasa jpl three frequency polarimetric sar over the black forest in germany

underlying topography estimation over forest areas using single baseline insar data in this paper a method for digital elevation model dem extraction over forest areas from single baseline interferometric synthetic aperture radar insar data is proposed the main idea of this method is that some backscattering variations which are linked to the geometrical structures of forest occur during the radar acquisition the time frequency analysis is used to retrieve these variations by dividing the synthesized sar image into multiple sar images in the fourier domain called sublook images then by interferometry the sublook images characterized by the same doppler bandwidth and acquired from spatially separated locations at either end of a baseline are used to estimate the sublook coherences and the above backscattering variations are converted into the variations of sublook coherences as a result the number of insar observations can be increased the sublook coherences are then interpreted by the two layer vegetation scattering model and are assumed to follow a near linear relationship in the complex plane the ground phase can then be estimated by linear regression of the sublook coherences the performance of the proposed method was validated by e sar l and p band sar data acquired over coniferous and tropical forests for the coniferous scenario the underlying dem estimated by the proposed method has a root mean square error rmse of 4 39 m which is slightly less accurate than the dem with an rmse of 4 07 m derived by the polarimetric line fit lf method but represents a significant improvement in dem accuracy over the hh insar method for the tropical scenario the dems derived by the proposed method and the polarimetric lf method are closer to the ground surface than those derived by the hh insar method and their mean ground height difference is 0 62 m the two experiments confirm that it is feasible to extract a dem by the proposed method which has a comparable performance in dem inversion to the polarimetric lf method and only requires single polarization insar data

contraction driven shear failure in compacting uncemented sediments shear failure in sediments is universally linked with active boundary conditions such as those imposed by tectonic stresses under conditions of no lateral strain and in the absence of tectonic stress soil mechanics theories predict a simple one dimensional compaction in which sediment particles displace vertically without shear failure during pressure diffusion conflicting with this theory shear failure planes are often found in sediments that formed under near horizontal burial conditions we investigated the effect of particle scale volume contraction as a potential cause of shear failure in uncemented particulate materials and found that loss of particle volume under confined conditions no external loading resulted in pronounced lateral stress reduction often reaching coulomb frictional failure conditions shear strain localization was analytically predicted and modeled numerically due entirely to volume loss at the grain scale we define this mode of internally driven shear failure as contractile to distinguish it from that caused by external loading and show that it can explain many natural fracture systems without invoking regional tectonics

a new method for the correlation of residual shear strength of the soil with mineralogical composition mineralogical composition measured with x ray diffraction for soil specimens collected from more than 80 natural disaster areas show smectite kaolinite mica feldspar and quartz as major constituent minerals based on the results of more than 35 mixtures of smectite kaolinite and quartz in different proportions a new correlation method was proposed for estimation of the residual friction angle r with the proportion of the minerals the mineralogical compositions of the natural samples were used to estimate the r based on the proposed triangular model the estimation method resulted in values as close as 90 to the measured r and as close as 80 to the case of 53 samples tested by other researchers the paper incorporates the correlation of r with the liquid limit the plasticity index the clay fraction the specific surface area and the proportion of smectite various ranges are proposed according to the influence of the constituent clay minerals in addition the applicable range

microstructures in landslides in northwest china implications for creeping displacements abstract microstructures mineralogical composition and texture of selected landslide samples from three landslides in the southern part of the gansu province china were examined with optical microscopy transmission electron microscopy tem x ray diffraction xrd and synchrotron x ray diffraction measurements common sheet silicates are chlorite illite muscovite kaolinite pyrophyllite and dickite other minerals are quartz calcite dolomite and albite in one sample graphite and amorphous carbon were detected by tem edx analyses and tem high angle annular dark field images the occurrence of graphite and pyrophyllite with very low friction coefficients in the gouge material of the suoertou and xieliupo landslides is particularly significant for reducing the frictional strength of the landslides it is proposed that the landslides underwent comparable deformation processes as fault zones the low friction coefficients provide strong evidence that slow moving landsliding is controlled by the presence of weak minerals in addition tem observations document that grain size reduction in clayey slip zone material was produced mainly by mechanical abrasion for calcite and quartz grain size reduction was attributed to both pressure solution and cataclasis therefore besides landslide composition the occurrence of ultrafine grained slip zone material may also contribute to weakening processes of landslides tem images of slip zone samples show both locally aligned clay particles as well as kinked and folded sheet silicates which are widely disseminated in the whole matrix small newly formed clay particles have random orientations based on synchrotron x ray diffraction measurements the degree of preferred orientation of constituent sheet silicates in local shear zones of the suoertou and duang he ba landslide is strong this work is the first reported observation of well oriented clay fabrics in landslides

shear strength in preexisting landslides drained residual shear strength is used for the analysis of slopes containing preexisting shear surfaces some recent research suggests that preexisting shear surfaces in prior landslides can gain strength with time torsional ring and direct shear tests performed during this study show that the recovered shear strength measured in the laboratory is only noticeably greater than the drained residual strength at effective normal stress of 100 kpa or less the test results also show that the recovered strength even at effective normal stresses of 100 kpa or less is lost after a small shear displacement i e slope movement an effective normal stress of 100 kpa corresponds to a shallow depth so the observed strength gain has little if any impact on the analysis of deep landslides this paper describes the laboratory strength recovery testing and the results for soils with different plasticities at various rest periods and effective normal stresses

a radar backscatter model for discontinuous coniferous forests a radar backscattering model for low to medium density woodland in which each tree is treated as an individual backscatterer is described a forest stand viewed by radar is then an assemblage of scatterers standing on a background in a certain spatial pattern the backscattering components arising from the various intersections of radar beams with the forest stand are calculated separately and their stokes matrices are then added together to achieve the stokes matrix for total backscattering probabilities of radar beams intersecting tree crowns are introduced into the model

formation processes geomechanical characterisation and buttressing effects at the toe of deep seated rock slides in foliated metamorphic rock abstract in order to increase the understanding of deep seated rock slides in terms of formation processes kinematics and the impact of geometrical factors on slope stability and deformation behaviour a 300 m thick active rock slide located in austria was investigated results of geological and geodetic field surveys geophysical in situ investigations and numerical modelling are presented and analysed particular focus is given on the geomechanical characterisation of the rock slide mass progressive topographical slope changes due to initial rock slide formation processes internal rock mass deformation processes and back calculated strength properties of the basal shear zone back calculations considering the actual rock slide geometry yields a friction angle of the basal shear zone of about 24 rock slide volume balance analyses are performed in order to determine mass loss due to secondary slides and river erosion in relation to the pre failure topography the middle to upper part of the rock slide has lost zone of depletion and the foot of the slope has accumulated rock mass material zone of accumulation gis based estimations show an enormous volume imbalance between the depletion and accumulation zones given that the volume accumulation at the foot of the slope is nearly three times smaller than the volume depletion at higher elevations considerable erosion of the toe by the river has occurred the complex geological interaction of the rock slide with the alluvium at the toe of the slope was a key question of this study and thus the geomechanical impact of the alluvium on slope deformation and stability behaviour was studied by applying 2d discrete element modelling methods results show that the alluvium at the foot of the slope has a positive effect on the slope stability and the sensitivity of the stability behaviour

three dimensional coherent radar backscatter model and simulations of scattering phase center of forest canopies a 3 d coherent radar backscatter model for forest canopies was developed and used to improve the understanding of synthetic aperture radar sar interferometric data the model was based on a realistic 3 d spatial structure of a forest stand in which every scatterer has its deterministic location a backscattering signal from a scatterer was mapped into a pixel according to its range or signal time delay the range or the time delay also determines the phase of the scattered field all scattering matrices within a pixel were coherently added to yield the total backscattering field of the pixel the coherent radar backscatter model takes into account not only the scattering contribution from the scatterers in the forest canopy but also the direct backscattering of the ground surface forest stands with three different spatial structures were simulated using l system and field measurements the number and sizes of trees in these forest stands were identical but the 2 d arrangements of the trees were different the interferometric sar insar signals of these scenes were simulated using the 3 d coherent sar model and the heights of scattering phase centers were estimated from the simulated insar data the results reported in this paper show that the spatial structures of vegetation play an important role in the location of the scattering phase center the height of scattering phase center depends on canopy height attenuation of canopy and the gaps within the canopy this paper shows that the spatial structure needs to be considered when the insar data are used for the estimation of forest structural parameters

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl

shaft resistance and setup factors for piles jacked in clay abstractinstallation of a displacement pile often involves complex loading modes that cause substantial changes in the state of the soil surrounding the pile when a displacement pile is installed in saturated clay significant excess pore pressure develops as the excess pore pressure dissipates over time the effective stresses in the soil surrounding the pile and the pile capacity increase this paper investigates jacking of piles into clay using finite element analysis a two surface plasticity based constitutive model for clays was implemented in the finite element code solid nonlinear analysis code based on the numerical results equations are developed for quantifying the effects of undrained and residual shear strength on the shaft resistance of jacked piles in clay the gain in shaft resistance over time is assessed and setup factors are proposed that can be used to estimate the gain in shaft resistance as a function of time after installation of a jacked pile in clay good agreement was obtaine

model based compensation of topographic effects for improved stem volume retrieval from carabas ii vhf band sar images a limiting factor that has been identified for stem volume retrieval in coniferous forests using vhf synthetic aperture radar is that the backscatter varies depending on ground topography on sloping ground the backscatter from a forest is reduced since the dominant ground trunk double bounce scattering mechanism is changed this leads to underestimation of stem volume and the variations caused by topography can obscure real variations in stem volume by using multiple images acquired with different flight headings and combining the image information with ground topography data in a model based inversion method we are able to compensate for the ground topography influence on the backscatter the inversion method is based on image segmentation and the optimal estimation method using four or more images from the carabas ii system and a coarse digital elevation model with 50 m horizontal grid the stem volume can be retrieved with an average root mean square error rmse of less than 60 m3 ha 1 for stem volumes in range of 80 700 m3 ha 1 in terms of above ground biomass this is equivalent to an rmse of less than 40 ton ldr ha 1 over the range of 50 400 ton ldr ha 1 the retrieval accuracy is similar to that previously obtained for similar forests standing on flat and horizontal ground

particle size distribution of interlayer shear zone material and its implications in geological processes a case study in china abstract a case study was carried out at the gaobazhou dam site on the qingjiang river in hubei province central china to investigate the particle size distribution psd of interlayer shear zone material and its implications in the geological processes forty six disturbed samples were taken at various representative locations within the well characterized interlayer shear zones at the gaobazhou dam site the particle size distributions of these samples were analyzed and the mass based approach is used for fractal scaling of the particle size distribution curves it is shown that all curves on the log log scale can be approximated by two intersecting lines thus each curve can be quantified by 1 2 p s and r s which respectively correspond to the slopes of the two lines and the coordinates of the point of intersection 1 and 2 can be replaced by fractal dimensions d 1 and d 2 the statistical analysis results reveal that delta d 2 d 1 and p s are closely related to d 1 therefore only d 1 and r s are used to characterize each curve it is illustrated that 47 specimens are clustered into five groups with respect to r s and d 1 accordingly five categories of particle size distributions are identified it is found that the d 1 and r s values of a sample can reflect the geological processes of the interlayer shear zone the larger the value of d 1 the higher the degree of interlayer shear experienced the value of r s implies the degree of subsequent secondary geological processes but in a rather complex way due to the differences in intensity of interlayer shear undergone based on this the geological evolution processes of the interlayer shear zones are postulated and the current status can be defined through fractal scaling of the particle size distribution of disturbed samples

correlation of mineralogy and index properties with residual strength of iraklion marls abstract the marly formations of the city of iraklion in crete greece are described and classified according to their mineralogy and physical properties the residual angle of friction of these marls was determined using ring shear apparatus and the results were correlated with mineral composition and index properties such as atterberg limits and grain size distribution furthermore for better understanding of the determined interrelationships between the physical characteristics and the residual strength of these marls a number of marl bentonite mixtures were also tested thus the influence of the variation in clay mineral content on the residual strength was studied and correlations with clay sized fraction and plasticity index were attempted

low vhf band backscatter from coniferous forests on sloping terrain low frequency synthetic aperture radar sar is a promising technique for stem volume retrieval particularly for dense forests due to the good penetration of forest canopies however it is well known that the dominant scattering mechanism the trunk ground dihedral interaction decreases rapidly on sloping terrain in this paper we use low vhf band sar data collected with carabas over dense coniferous forests in sweden to examine the effect of topography using flight passes with different headings the effect of slope and aspect angle on backscatter is characterized for tall trees spl sim 30 m on the steepest slopes in the test site up to spl sim 12 spl deg differences of up to 8 db are observed between images acquired with different look directions relative to the slope a physical model is developed to investigate the different scattering mechanisms and their sensitivity to terrain slopes the model shows that the trunk ground scattering still dominates the response for large trees on moderate slopes and a semiempirical model for the effect of topography on backscatter is proposed the model shows good agreement with measurements indicating the possibility of using it to compensate for the effects of sloping terrain when retrieving stem volume in coniferous forest

unsupervised classification of scattering behavior using radar polarimetry data the use of an imaging radar polarimeter data for unsupervised classification of scattering behavior is described by comparing the polarization properties of each pixel in an image to that of simple classes of scattering such as even number of reflections odd number of reflections and diffuse scattering for example when this algorithm is applied to data acquired over the san francisco bay area in california it classifies scattering by the ocean as being similar to that predicted by the class of odd number of reflections scattering by the urban area as being similar to that predicted by the class of even number of reflections and scattering by the golden gate park as being similar to that predicted by the diffuse scattering class it also classifies the scattering by a lighthouse in the ocean and boats on the ocean surface as being similar to that predicted by the even number of reflections class making it easy to identify these objects against the background of the surrounding ocean

the experimental basis for interpreting particle and magnetic fabrics of sheared till particle fabrics of basal tills may allow testing of the bed deformation model of glacier flow which requires high bed shear strains 100 field studies however have not yielded a systematic relationship between shear strain magnitude and fabric development to isolate this relationship four basal tills and viscous putty were sheared in a ring shear device to strains as high as 714 fabric was characterized within a zone of shear deformation using the long axis orientations of fine gravel and sand particles and the anisotropy of magnetic susceptibility ams of small 5 8 cm3 intact samples results indicate that till particles rotate toward the plane of shearing with long axis orientations that become tightly clustered in the direction of shear 0 78 s1 0 94 for three dimensional data these strong steady state fabrics are attained at shear strains of 7 30 with no evidence of fabric weakening with further strain regardless of the specific till or particle size fraction under consideration these results do not support the jeffery model of particle rotation which correctly describes particle rotation in the viscous putty but not in the tills owing to fluid mechanical assumptions of the model that are violated in till the sensitivity of fabric development to shear strain magnitude indicates that for most till units where shear strain magnitude is poorly known attributing fabric variations to spatial differences in other variables such as till thickness or water content will be inherently speculative attributing fabric characteristics to particular basal till facies is uncertain because shear strain magnitude is unlikely to be closely correlated to till facies weak or spatially variable fabrics in the absence of post depositional disturbance or major deviations from unidirectional simple shear indicate that till has not been pervasively sheared to the high strains required by the bed deformation model strong flow parallel fabrics are a necessary but insufficient criterion for confirming the model copyright 2008 john wiley sons ltd

estimation of near surface soil moisture in a sloping terrain of a himalayan watershed using envisat asar multi incidence angle alternate polarisation data soil moisture is one of the important input variables in hydrological and water erosion models the extraction of information on near surface soil moisture from synthetic aperture radar sar is well established mostly for flat terrain and using low incidence angle single polarisation data the envisat advanced sar asar data available in multiple incidence angles and alternate polarisation modes were investigated in this study for soil moisture estimation in sloping terrain the test site was sitla rao watershed in the lesser himalayas of northern india empirical models were developed to estimate near surface soil moisture in bare agricultural fields using alternate polarisation asar data both soil moisture and surface roughness field measurements were performed during the satellite passes backscatter from medium incidence angle is 4 and vertical vertical vv polarisation signal is correlated better with volumetric soil moisture content compared to other incidence angles the model parameters were further improved and soil moisture estimation was refined by combining medium incidence angle is4 vertical horizontal polarisation response as another variable along with vv polarisation response the effect of slope on the radar backscatter was minimized by incorporating local incidence angles derived from an aster dem copyright 2012 john wiley sons ltd

full wave electromagnetic scattering from rough surfaces with buried inhomogeneities we develop a methodology for modeling coherent electromagnetic scattering from rough surfaces with buried inhomogeneities in three dimensions the inhomogeneities considered in this paper include random spherical media random cylindrical media and root like cylindrical clusters they are used to simulate rocks ice particles and vegetation roots buried beneath the ground surface that can be seen by the low frequency radars in earth remote sensing applications the approach we develop first calculates volumetric scattering from the media using coherent approaches including both the conventional recursive transition matrix t matrix method as well as a new generalized iterative extended boundary condition method we developed for tilted finite cylinders and then transforms the t matrix to the scattering matrix which is then used to form the full scattered field of layered structures with rough surface and subsurfaces we validate the methodology by comparing with other numerical solutions for special cases and show sensitivity results for scattering from rough surface with buried random spherical media and random cylindrical media of different densities we also construct a basic root model and calculate the scattering cross sections from single and multiple root clusters with or without a subsurface interface underneath with the approach developed in this paper we are able to study the sensitivity of radar signals to subsurface scatterers for example our simulations show that depending on their density and water content buried roots could enhance the backscatter from a single rough surface by as much as 5 db in co pol components and substantially more in cross pol components the results of this model are expected to enable more accurate geophysical retrievals of soil moisture as well as soil organic content

a microwave scattering model for layered vegetation a microwave scattering model was developed for layered vegetation based on an iterative solution of the radiative transfer equation up to the second order to account for multiple scattering within the canopy and between the ground and the canopy the model is designed to operate over a wide frequency range for both deciduous and coniferous forest and to account for the branch size distribution leaf orientation distribution and branch orientation distribution for each size the canopy is modeled as a two layered medium above a rough interface the upper layer is the crown containing leaves stems and branches the lower layer is the trunk region modeled as randomly positioned cylinders with a preferred orientation distribution above an irregular soil surface comparisons of results obtained using this model with measurements from deciduous and coniferous forests show good agreement at several frequencies for both like and cross polarizations

a multi method approach to study the stability of natural slopes and landslide susceptibility mapping abstract in this paper a multi method approach for the assessment of the stability of natural slopes and landslide hazard mapping applied to the dakar coastal region is presented this approach is based on the effective combination of geotechnical field and laboratory works of gis and of mechanical deterministic and numerical stability analysis by using this approach valuable results were gained regarding instability factors landslide kinematics simulation of slope failure and coastal erosion this led to a thorough assessment and strong reduction in the subjectivity of the slope stability and hazard assessment and to the development of an objective landslide danger map of the sw coast of dakar analysis of the results shows that the slides were influenced by the geotechnical properties of the soil the weathering the hydrogeological situation and the erosion by waves the landslide susceptibility assessment based on this methodological approach has allowed for an appropriate and adequate consideration of the multiple factors affecting the stability and the optimization of planning and investment for land development in the city

measurement of topography using polarimetric sar images a processing technique for polarimetric synthetic aperture radar sar data has been developed which produces profiles of terrain slopes and elevations in the azimuthal or along track direction this technique estimates the average shift in orientation angle of copolarization backscatter caused by azimuthal tilts of the scattering plane using p band data tests of this technique have been made for an area in the black forest near villingen schwenningen in baden wurttemberg germany the radar measured slope and derived elevation profiles have low rms errors and high correlation values when compared with a stereo photograph digital elevation map dem for the area this algorithm is capable of adaptively making transitions from the forested areas to nearby regions with open terrain subsequent tests of the algorithm have been conducted using polarimetric sar l band data for a mountainous nonforested region in the mojave desert ft irwin ca where an accurate dem also was available complete elevation and slope mapping of the terrain in two dimensions using this technique is possible when azimuthal elevation profiles are produced throughout the range extent of the sar image

slope stability analyses in stiff fissured clays results of torsional ring shear direct shear and triaxial compression tests on cohesive soils reveal that the fully softened shear strength is stress dependent and related to the type of clay mineral and quantity of clay size particles an empirical relationship for the fully softened friction angle is presented that is a function of liquid limit clay size fraction and effective normal stress studies of first time slides i e slopes that have not undergone previous sliding in stiff fissured clay with a liquid limit between 41 and 130 suggest that the mobilized shear strength along the failure surface can be lower than the fully softened shear strength recommendations are presented for estimating the mobilized shear strength in first time slides based on soil plasticity soils with a liquid limit greater than 30 exhibit a large difference between the fully softened and residual friction angles in these soils the presence or absence of a pre existing shear surface should be clarified

correction of sar imagery for variation in pixel scattering area caused by topography the radiometric correction of synthetic aperture radar sar imagery for topographically induced changes in the pixel scattering area is examined the relative significance of ground slope in the range and azimuth directions is compared and a widely used correction factor based on the sin of the local radar incidence angle is shown to be sufficiently accurate the importance of performing this correction in slant range rather than ground range is demonstrated

backscatter model for the unusual radar properties of the greenland ice sheet a number of planetary objects exhibit large radar reflectivity and polarization ratios and more recently a similar behavior has been observed over a vast portion of the earth s surface the percolation facies of the greenland ice sheet surface based ranging radar data and snow stratigraphy studies demonstrated that the radar properties of that portion of greenland are caused by enhanced scattering from massive large solid ice bodies buried in the top few meters of the dry cold clean snowy surface of the ice sheet and created by seasonal melting and refreezing events from author

fiber bundle model for multiscale modeling of hydromechanical triggering of shallow landslides 1 sudden and rapid mass movements associated with landslides and snow avalanches present a hazard to life and infrastructure yet their predictions and triggering mechanisms remain poorly understood statistical methods and correlative studies have been used to produce landslide or avalanche susceptibility maps often with limited physical basis mechanistic approaches based on factor of safety computation seldom represent the progressive transition from local failure events to a landslide and in general do not include heterogeneities associated with land cover or with subsurface material properties and hydrologic pathways focusing on rainfall induced shallow landslides we propose the use of the fiber bundle model fbm a generic yet powerful and adaptable model used in modeling fatigue and fracture of complex and disordered materials the primary strength of the fbm is its ability to represent the progressive failure of cracks and shear zones and the ruptures of highly heterogeneous bonding elements that are present in soils at all scales the model also provides a natural framework for interpretation of acoustic emission signatures from failing slopes which may form the basis of a monitoring and warning system

friction experiments on saturated sediments and their implications for the stress state of the nankai and barbados subduction thrusts the nankai and barbados forearcs have low stress subduction thrusts the sediments entering the subduction zone and namely the material in the decollement zones have been well characterized by numerous deep sea drilling legs and studies of the recovered cores nankai has high heat flow and significant amounts of illite while barbados is a smectite dominated system based on results from ring shear 2 mpa normal stress and direct shear 30 mpa tests on marine sediments and mineral standards this translates into a residual frictional resistance of r 0 25 and r 0 11 in clay horizons respectively such values agree with theoretical estimates from critical wedge theory nankai b 0 16 0 26 and barbados b 0 06 0 09 and fault spacing geometries from seismic profiles nankai b 0 12 0 23 and barbados b 0 11 0 19 maximum pore pressure ratios of 0 85 and 0 73 for nankai and barbados respectively allow us to estimate effective shear stresses as a function of friction coefficient and density of the sediment gouge to reach only 10 mpa or less in the frontal 50 km of the decollement zone respectively our data support the contention that fluid pressure transients and sediment composition contribute equally to the weakness along plate boundary faults down to the seismogenic zone with the first probably dominating the shallow decollement shear velocity stepping tests show that the clay dominated gouges strengthen velocity irrespective of the clay mineralogy and hence suggest that clay transformation does not affect the onset of seismogenesis

displacement field in contraction driven faults we investigate the distribution of strain and deformation in the host sediment that arises once a contraction driven shear fault has localized and propagated under a zero lateral strain condition numerical modeling of displacement distributions compares well with those measured using 3d seismic data the parameters that determine the displacement field for a single normal fault embedded in sediments are fault height overburden effective stress stiffness and residual friction angle or post peak strength proximity to the free boundary biases the displacement pattern which becomes asymmetric although the measured displacements and numerical predictions are similar the measured magnitude requires pronounced low stiffness of the sediment as well as low post peak shear strength this requirement suggests that sediments hosting contraction driven shear faults most likely have high porosity and high clay fraction and have undergone diagenetic reactions involving significant mineral dissolution the diagenetic evolution of the sediment and its current composition may explain the global scaling relationship between the measured displacement and fault height for polygonal fault systems

virgin compression of structured soils this paper describes a study of the virgin compression behaviour of both naturally and artificially structured soils under one dimensional compression or isotropic compression it is proposed that during virgin compression the additional voids ratio sustained by soil structure is inversely proportional to the current mean effective stress the proposed formula has been verified for 20 different naturally and artificially structured soils and it is seen that the proposal describes well the behaviour of all these soils finally a general discussion on soil structure and its features is presented and the proposed compression equation is extended to describe the compression of structured soil along a general stress path cet exposa est une etude du comportement d une consolidation vierge sur des sols structuras de mani gravere naturelle et artificielle avec une consolidation unidimensionnelle on isotrope nous avancons que pendant la consolidation vierge le taux de pore additionnel subi pa

a physical optics model for double bounce scattering from tree stems standing on an undulating ground surface in this paper a model for prediction of radar backscatter from coniferous forests in the vhf and uhf band is proposed the model includes the double bounce scattering originating from vertical stems standing on an undulating ground surface and is based on a physical optics approach the model can be used to assess the importance of ground topography in synthetic aperture radar sar imagery of forests and it is applicable to sar systems using horizontally transmit and receive polarization hh the model was validated against data from the airborne sar systems carabas ii and lora precision measurements of ground topography and forest characterization at a single tree level were used as model input to simulate sar images the simulated images were compared to radar data in the frequency bands 22 82 and 225 470 mhz and it was found that the model could predict much of the variation in backscatter observed in images r2 0 44 and 0 65 at best for the lower and higher frequency band respectively which should be compared to r2 0 1 if the same model but assuming a flat ground was used the results thus indicate that ground topography must be considered when predicting the variations in backscatter in the sar images studied the model did however fail to predict the absolute values of the backscattered intensity the reason for the discrepancy is believed to be the value chosen for stem dielectric constant and unmodeled effects due to wave attenuation tilting stems and small scale surface roughness

polarimetric radar measurements of a forested area near mt shasta the authors present the results of an experiment using the nasa jpl dc 8 airsar aircraft synthetic aperture radar over a coniferous forest near mt shasta california in 1989 calibration devices were deployed in clearings and under the forest canopy and passes at 20 degrees 40 degrees and 55 degrees incidence angles were made with the airsar a total of eight images at differing incidence angles have been processed and calibrated the multipolarization multifrequency data were examined and it was found that the c band cross section averaged over like and cross polarizations is the best parameter for distinguishing between two stands with differing forest biomass the average cross section at p and l bands is useful only for smaller incidence angles parameters describing the polarization behavior of the scattering were primarily useful in identifying the dominant scattering mechanisms for forest backscatter

a three component scattering model for polarimetric sar data an approach has been developed that involves the fit of a combination of three simple scattering mechanisms to polarimetric sar observations the mechanisms are canopy scatter from a cloud of randomly oriented dipoles evenor double bounce scatter from a pair of orthogonal surfaces with different dielectric constants and bragg scatter from a moderately rough surface this composite scattering model is used to describe the polarimetric backscatter from naturally occurring scatterers the model is shown to describe the behavior of polarimetric backscatter from tropical rain forests quite well by applying it to data from nasa jet propulsion laboratory s jpls airborne polarimetric synthetic aperture radar airsar system the model fit allows clear discrimination between flooded and nonflooded forest and between forested and deforested areas for example the model is also shown to be usable as a predictive tool to estimate the effects of forest inundation and disturbance on the fully polarimetric radar signature an advantage of this model fit approach is that the scattering contributions from the three basic scattering mechanisms can be estimated for clusters of pixels in polarimetric sar images furthermore it is shown that the contributions of the three scattering mechanisms to the hh hv and vv backscatter can be calculated from the model fit finally this model fit approach is justified as a simplification of more complicated scattering models which require many inputs to solve the forward scattering problem

residual strength of slip zones of large landslides in the three gorges area china abstract slip zones of the large landslides in the three gorges area are commonly composed of fine grained soils with substantial amount of coarse grained particles particularly gravel sized particles in this study residual strength of the soils from slip zones of these landslides were examined in relation to their index properties based on a survey of 170 landslides it was found that laboratory determined residual friction angle using gravel free fraction of the disturbed soils from the slip zones was closely related to clay content liquid limit and plasticity index on the other hand in situ residual friction angle of these soils i e including gravel fraction showed very weak correlations with clay content and atterberg limits but was largely dependent on gravel and fines clays silts contents increasing with gravels and decreasing with fines and displayed strong linear correlation with the ratio of gravel to fines contents these observations indicate that among the index properties clay content and atterberg limits can be used to estimate residual strength of the soils finer than 2 mm but they are not appropriate evaluate the residual strength of the soils containing considerable amount of gravel sized particles for the latter particle size distribution particularly the ratio of gravel to fines contents appears to be a useful index additionally it was found that there was no identifiable correlation between relative abundance of individual major clay minerals and residual friction angles of both gravel free fraction of disturbed and in situ soils suggesting that influence of clay minerals on residual strength of these soils can not be simply evaluated based on their abundance

quantification of rock control in geomorphology abstract rock control the influence of rock properties on landform development has for long been a relatively under researched topic but numerous techniques have been developed especially by geotechnical engineers and stone conservationists that are now being applied to geomorphological issues by geomorphologists these techniques range in scale from the quantification of major discontinuities through to analysis of micro pores rock control studies that have taken place over the last few decades have contributed important insights into our understanding of such diverse phenomena as 1 river terraces bedrock channel forms and gradients pot hole development drainage density and gully badland development 2 slope forms and failures especially with respect to rock mass strength 3 the form of glacial troughs and of subglacial erosional landforms 4 weathering controls on rock durability and the association of weathering with porosity 5 classic karst features including various types of karren 6 sandstone landforms 7 inselbergs and tors and 8 cliffs and shore platforms

a generalized radar backscattering model based on wave theory for multilayer multispecies vegetation a generalized radar scattering model based on wave theory is described the model predicts polarimetric radar backscattering coefficients for structurally complex vegetation comprised of multiple species and layers compared to conventional two layer crown trunk models modeling of actual forests has been improved substantially allowing better understanding of microwave interaction with vegetation the model generalizes an existing single species discrete scatterer model and by including scattering and propagation effects through judiciously defined vegetation layers enables its application to an arbitrary number of species types the scatterers within each layer are modeled as finite cylinders or disks having arbitrary size density and orientation as in the predecessor model the distorted born approximation is used to represent the propagation through each layer while scattering from each is modeled as a linear superposition of scattering from its respective random collection of scatterers interactions of waves within and between each layer and direct scattering from the ground are accounted for validation of the model is presented based on its application to 23 wooded savanna sites located in queensland australia and comparison with advanced land observing satellite alos phased arrayed l band synthetic aperture radar palsar and national aeronautics and space administration nasa jet propulsion laboratory jpl airborne synthetic aperture radar airsar data results indicate good agreement between simulated and actual backscattering coefficients particularly at hh and vv polarizations more discrepancies are found at hv polarizations and can be explained by uncertainties in the knowledge of input parameters such as inaccuracies in the surface model surface roughness parameterization and soil moisture

the effect of topography on sar calibration during normal synthetic aperture radar sar processing a flat earth is assumed when performing radiometric corrections such as antenna pattern and scattering area removal the authors examine the effects of topographic variations on these corrections local slopes will cause the actual scattering area to be different from that calculated using the flat earth assumption it is shown that this effect may easily cause calibration errors larger than a decibel ignoring the topography during antenna pattern removal may also introduce errors of several decibels in the case of airborne systems the effect of topography on antenna pattern removal is expected to be negligible for spaceborne sars the authors show how these effects can be taken into account if a digital elevation model is available for the imaged area the errors are quantified for two different types of terrain a moderate relief area near tombstone az and a high relief area near oetztal in the austrian alps the authors show errors for two well known radar systems the c band ers 1 spaceborne radar system and the three frequency nasa jpl airborne sar system airsar

retrieval of permafrost active layer properties using time series p band radar observations we propose a method to estimate the active layer properties including soil dielectric profiles and active layer thickness alt in permafrost regions using time series p band polarimetric synthetic aperture radar sar observations the active layer and underlying permafrost are modeled as a three layer dielectric structure with the layer dielectric constants representing the soil moisture and freeze thaw state of the layer to resolve the ambiguity of the retrieved layer thicknesses an approach of finding the largest possible depths lpds is combined with time series observations where the alt is assumed time invariant between the maximum thaw and before the upward freezing front rises significantly from the permafrost table the lpd assisted time series retrieval algorithm is applied to the radar data acquired by the airborne microwave observatory of subcanopy and subsurface airmoss p band sar in august and october 2014 and 2015 over the alaska north slope the results show that the retrieved alt values are generally underestimated for the sites where the in situ alt is larger than the p band sensing depth with a retrieval bias ranging from 0 05 to 0 24 m as validated against the in situ alt collected at circumpolar active layer monitoring calm sites for the sites where the in situ alt is smaller than 0 55 m the retrieval errors are generally less than 0 1 m the retrieval results also show that the active layer properties are strongly influenced by the land cover types at the regional scale and not as much by the north south temperature gradient across a 180 km long transect along the deadhorse flight line

measurements on individual trees using multiple vhf sar images multiple vhf band radar images from the airborne carabas ii system retrieved with varying look direction to the imaged area are coregistered and combined to improve spatial and radiometric resolution combined images over boreal forest in southern sweden are used to identify and make backscatter measurements of individual trees a coregistration scheme is proposed and backscatter is compared to ground measurements of individual stem volume it is found that the spatial resolution and radiometric precision could be significantly improved by combining the images coherently a nearly linear relation between backscattered amplitude and individual stem volume for trees with a stem volume over 0 2 m sup 3 was found which is in agreement with previous results at stand level

landslide hazard in the nebrodi mountains northeastern sicily abstract the eastern sector of the nebrodi mountains ne sicily a part of the apenninic maghrebian orogenic chain is characterized by an high landslide hazard the village of s domenica vittoria which lies in the area has been particularly affected by various landslide phenomena with resulting damage to buildings and infrastructure the rocks outcropping in the area belong to the cretaceous monte soro flysch they consist of an alternation of argillaceous and calcareous beds at the base and argillaceous and quartzarenitic beds at the top the lithotechnical characteristics of the formation and the steepness of the slopes in the area lead to an elevated instability as testified by the widespread occurrence of sub vertical arcuate cliffs landslide scarps and sub horizontal areas landslide terraces typical of a landslide controlled morphology from a kinematics point of view the observed phenomena can be referred to multiple rotational slides flows and complex landslides often with a retrogressive development and enlargement triggering causes lie principally in the intense rainfalls that determine the decay of the geomechanical properties of the terrain and supply discontinuos groundwater circulation that is evident in seasonal springs human activity such as the construction of roads and buildings on steep slopes and dispersal of water from supply systems and sewers has a significant impact as well due to the instability of the area expansion of the village which is already limited by the morphological conditions is made difficult by the high hazard level especially in the areas at higher elevations where the principal landslide scarps are located and even more on the rims of the scarps considering the high hazard level s domenica vittoria has been inserted by the national geological service among the sites in sicily to be monitored by means of a gps network the survey carried out along the entire slope hosting the village has furnished the base for geological and geomorphological knowledge needed for the planning of the network to identify the areas at landslide risk where parts of the village lie including the areas of expansion of the village the main roads and a portion of the favoscuro river bed

phenomenology of ground scattering in a tropical forest through polarimetric synthetic aperture radar tomography this paper aims at characterizing the scattering mechanisms occurring at the ground level in a tropical forest illuminated by a p band synthetic aperture radar sar the analysis is carried out based on the multibaseline fully polarimetric data set collected by onera over paracou french guyana in the frame of the european space agency campaign tropisar the favorable baseline distribution of this data set results in the possibility of removing most contributions from the vegetation layer by tomographic techniques thus allowing the generation of a new fully polarimetric single look complex sar image relative to scattering contributions from the ground level only such a ground layer image is then analyzed by considering the variation of its polarimetric signature with respect to terrain local slope and radar look angle two major conclusions are drawn 1 double bounce scattering from trunk ground interactions is observed to be the dominant scattering mechanism at the ground level on flat terrains whereas it rapidly tends to vanish as the topographic slope increases and 2 the characteristic parameter that rules trunk ground scattering is not the tree height but rather the available free path facing the tree as a result of the presence of nearby trees undulating topography or understory preventing double bounce scattering from taking place whenever the ground bounce occurs too far away from the considered tree the mean free path length resulting from the analysis of this data set is found to be l 7 m finally we discuss how the concept of free path length can be accounted for in simple terms by assuming an equivalent extinction model characterized by a variation along the horizontal dimension

spatial distribution of inter layer shear zones at gaobazhou dam site qingjiang river china abstract the spatial distribution of inter layer shear zones is studied based on the fully mapped inter layer shear zones at the gaobazhou dam site on the qingjiang river in hubei province china the field observations revealed that two types of inter layer shear zone under developed and well developed are distributed differently the former are associated with the incompetent rock layers and the latter are controlled by the inter bed folds and lithological properties of the strata to represent their lithological properties geomechanically data on strength by the schmidt hammer test and thickness of each field identified rock layer were collected to form strength sequences and thickness sequences the adjacent rock layers of similar strength are then grouped and two grouped sequences are combined into a single sequence whose individual term is the strength weighted by the exponential function value of the centralized thickness sct the rescaled range r s analysis results of sct sct r s taking into account the presence of inter bed folds are in good agreement with r s analysis results of the spacing sequence of the well developed inter layer shear zones thus the sct r s model has the potential to predict their spatial distributions