adaptation of prestack migration to multi offset ground penetrating radar gpr data in adapting the prestack migration technique used in seismic imaging to the inversion of ground penetrating radar gpr from time to depth sections we show that the theoretical integral formulation of the inversion can be applied to electromagnetic problems albeit with three assumptions the first two assumptions concern the electromagnetic characteristics of the medium primarily that the medium must be perfectly resistive and non dispersive and the third concerns the antennae radiation pattern which is taken to be 2d the application of this adaptation of the inversion method is confirmed by migrating actual gpr measurements acquired on the test site of the laboratoire central des ponts et chaussees the results show good agreement with the geometry of the structures in the medium and confirm that the possible departure from the assumption of a purely resistive medium has no visible effect on the information concerning the geometry of scattering and reflecting structures the field experiments also show that prestack migration processing is sufficiently robust with regard to the assumption of a non dispersive medium the assumption of a 2d antennae radiation pattern however produces artefacts that could be significant for laterally heterogeneous media nevertheless where the medium is not highly laterally heterogeneous the migration gives a clear image of the scattering potential due to the geometry of structural contrasts in the medium the scatterers are well focused from diffraction hyperbolae and well localized spatial geometry has limited dimensional accuracy and positions are located with a maximum error equal to the minimum wavelength of the signal bandpass objects smaller than one wavelength can nevertheless be detected and well focused if their dielectric contrasts are sufficiently high as in the case of iron or water in gneiss gravels furthermore the suitability of multi offset protocols to estimate the electromagnetic propagating velocity and to decrease the non coherent noise level of measurements is confirmed our velocity estimation is based on the semblance calculation of multi offset migrated images and we confirmed the relevance of this quantification method using numerical data the signal to noise ratio is improved by summing multi offset results after the addition of random noise on measurements thus the adaptation of prestack migration to multi offset radar measurements significantly improves the resolution of the scattering potential of the medium limitations associated with the methods used here suggest that 3d algorithms should be applied to strongly laterally heterogeneous media and further studies concerning the waveform inversion are necessary to obtain information about the electric nature of the medium

the role of the sediment budget in understanding debris flow susceptibility this study proposes a sediment budget model to predict the temporal variation of debris volume stored in a debris flow prone watershed the sediment budget is dominated by shallow landslides and debris outflow the basin topography and the debris volume stored in the source area of the debris flow prone watershed help evaluating its debris flow susceptibility the susceptibility model is applied to the tungshih area of central western taiwan the importance of the debris volume in predicting debris flow susceptibility is reflected in the standardized coefficients of the proposed statistical discriminant model the high prediction rate 0 874 for the occurrence of debris flows justifies the capability of the proposed susceptibility models to predict the occurrence of debris flows this model is then used to evaluate the temporal evolution of the debris flow susceptibility index the analysis results show that the numbers of watershed which are classified as a debris flow group correspond well to storage of sediment at different time periods these numbers are 10 before the occurrence of chi chi earthquake 13 after the occurrence of chi chi earthquake 16 after the occurrence of landslides induced by typhoon mindulle typhoon m and 14 after the occurrence of debris flows induced by typhoon m it indicates that the occurrence of 7 6 chi chi earthquake had significant impact on the debris flow occurrence during subsequent typhoons copyright 2009 john wiley sons ltd

multi temporal analysis of the role of check dams in a debris flow channel linking structural and functional connectivity abstract check dams represent one of the most common hydraulic engineering solution to manage debris flow risk however the design of these structures only rarely considers their impact on sediment connectivity and sediment fluxes both at the channel reach and catchment scale in the last two decades high resolution topography hrt provided fundamental data to analyse the morphology evolution of landscapes through the realization of sequential dtms digital terrain models and dtms of difference dods in the context of mountain catchments hrt offers essential information on the evolution of erosion and deposition patterns and allows the application of multi temporal geomorphometric indexes that can enrich the dods analysis with important data as the assessment of sediment connectivity in this research multi temporal lidar derived dtms were used to derive dods and to perform a multi temporal analysis of an index of sediment connectivity ic in three reaches of a debris flow channel moscardo torrent eastern italian alps where several check dams have been built over time the research aims at outlining the effects of torrent control works on sediment dynamics in steep channels affected by frequent debris flows the integration of the difference of ic with dod maps allowed quantifying the impact of newly built check dams on changes in sediment pathways and related erosion processes highlighting a close relationship between structural and functional connectivity in areas where erosive processes prevailed there were increases in connectivity while deposition areas showed a decrease of ic the geomorphometric analyses show that the new check dams have affected the sediment transfer along the main channel but also the hillslope to channel connectivity by altering sediment pathways in the moscardo torrent however the strong impact of these structures on sediment transfer is not matched by long term effectiveness in debris flow control

high resolution hydrothermal structure of hansbreen spitsbergen mapped by ground penetrating radar detailed ground penetrating radar gpr surveys at 50 and 200 mhz on hansbreen a polythermal glacier in southern svalbard are presented and interpreted comparison of the variations in character of the radar reflections with borehole thermometry and water levels in moulins suggests that gpr can be used to study the hydrothermal properties of the glacier the high resolution of the gpr data shows that the hydrothermal structure of the glacier is highly variable both along the centre line and on transverse profiles water contents for many places and depths within the glacier were calculated by estimating radar wave velocities to point reflectors we find typical water contents of 1 2 for the temperate ice but wetter ice associated with surface crevassing and moulins typically 4 water content there is evidence that wet ice sometimes overlays drier ice the hydrothermal structure is thus shown to be very complex temperature gradients in the cold ice indicate freezing rates of temperate ice below cold ice of 0 1 0 5 m a while isolated point reflectors within the cold ice indicate large water filled bodies that are probably related to the regular drainage structure of the glacier

the intracloud lightning fraction in the contiguous united states abstractthis work addresses the long term relative occurrence of cloud to ground cg and intracloud ic no attachment to ground flashes for the contiguous united states conus it expands upon an earlier analysis by boccippio et al who employed 4 yr datasets provided by the u s national lightning detection network nldn and the optical transient detector otd today the duration of the nldn historical dataset has more than tripled and otd data can be supplemented with data from the lightning imaging sensor lis this work is timely given the launch of goes 16 which includes the world s first geostationary lightning mapper that will observe total lightning ic and cg over the americas and adjacent ocean regions findings support earlier results indicating factor of 10 variations in the ic cg ratio throughout conus with climatological ic fraction varying between 0 3 and greater than 0 9 the largest values are seen in the pacific northwest central california and where colorado borders kansa

very high spatial resolution imagery for channel bathymetry and topography from an unmanned mapping controlled platform the increasing availability of aerial photography and satellite imagery offers new possibilities for characterizing river morphology the precision of new very high resolution vhr images allows smaller scale objects within river corridors to be studied high survey frequencies provide increased opportunities for the monitoring of river restoration following this evolution in platform technology a small radio controlled motorized vehicle flying at low altitude was used to study both channel water depth and gravel bar geometry the vhr imagery provided by this equipment allowed both channel bathymetry and a high accuracy photogrammetric digital elevation model dem to be realized using case studies from the ain and the drome rivers in france the accuracy of the results is presented and the various challenges associated with the new platform are discussed one significant issue is that due to the low elevation of the survey the coverage of a target area is usually based on several photographs which leads to variations in illumination conditions that stem from atmospheric changes the images were processed to minimize this source of error but a number of issues have yet to be resolved bathymetric models with r2 values between 0 59 and 0 90 were created in spite of the lack of channel bed homogeneity at the various sites the gravel bar was also effectively mapped and the photogrammetrically predicted dem provided a 5 10 cm pixel resolution with a vertical precision between 2 and 40 cm according to the position within the image this paper shows that despite unstable image acquisition unmanned radio controlled platforms provide significant advantages for the study of river processes offering a flexible very high resolution data source for both channel bathymetry and gravel bar topography copyright 2007 john wiley sons ltd

continuous profiles of electromagnetic wave velocity and water content in glaciers an example from bench glacier alaska usa we conducted two dimensional continuous multi offset georadar surveys on bench glacier south central alaska usa to measure the distribution of englacial water we acquired data with a multichannel 25 mhz radar system using transmitter receiver offsets ranging from 5 to 150 m we towed the radar system at 5 10 km h 1 with a snow machine with transmitter receiver positions established by geodetic grade kinematic differentially corrected gps nominal 0 5 m trace spacing for radar velocity analyses we employed reflection tomography in the pre stack depth migrated domain to attain an estimated 2 velocity uncertainty when averaged over three to five wavelengths we estimated water content from the velocity structure using the complex refractive index method equation and use a three phase model ice water air that accounts for compression of air bubbles as a function of depth our analysis produced laterally continuous profiles of glacier water content over several kilometers these profiles show a laterally variable stratified velocity structure with a low water content 0 0 5 shallow layer 20 30 m underlain by high water content 1 2 5 ice

stereophotogrammetry of archive data and topographic approaches to debris flow torrent measurements calculation of channel sediment states and a partial sediment budget for manival torrent isere france this paper focuses on a topographic methodology to characterize the amount of sediment stored in channels and the use of historical photographs for aerial survey by stereophotogrammetry as part of wider research on debris flow magnitude prediction the topographic methodology uses equidistant four point cross sections along the long profile of the channel each cross section is representative of a 50 m reach of the channel to calculate the volume of each reach the difference is calculated between a reference level and the topographic surface the reference level is the lowest level where the debris flow can erode and in the current method this level is estimated from fixed points along the long profile of the channel the accuracy of the method has been estimated by comparing results of a detailed topographic survey with a standard deviation corresponding to about 6 per cent of the total calculated sediment volume this topographic methodology has been used on aerial photographs by photogrammetry this tool was applied to photographs taken on 12 past dates the scales of the archive photographs used range from 1 3000 to 1 30 000 but results are consistent and permit us to calculate sediment states of the channel for different past dates with an uncertainty of about 6 per cent of the total volume the application of the technique to the manival debris flow torrent has permitted us to propose some partial sediment budgets and erosion rate estimates copyright 2006 john wiley sons ltd

channel scour and fill by debris flows and bedload transport abstract in steep channels debris flows are known to dramatically increase in volume under the effect of channel erosion however the critical factors controlling channel erosion by debris flows are not well documented by field studies this is particularly true for the effect of slope on the depth at which erodible beds are scoured during debris flows and during bedload transport this topic has been addressed by intensive cross section resurveys 54 cross sections of debris flows n 5 and flow events n 9 that occurred in two torrents of the french prealps the manival and real torrents between 2009 and 2012 this study provided evidence that debris flow scouring increases with slope whereas this is not the case for bedload transport no slope effect detected during floods a functional relationship defined from a piecewise regression model is proposed as an empirical fit for the prediction of channel erosion by debris flows with a critical slope threshold at 0 19 95 confidence interval 0 17 0 21 this slope threshold is interpreted as the transition between the transport limited and supply limited regimes associated with the upstream decreasing erodible bed thickness the erodible bed was also characterized by quantifying erosion deposition and surface roughness with multidate terrestrial laser scans tlss in a short reach of high sensitivity of the manival torrent debris flow erosion occurred preferentially on smooth surfaces corresponding to the unconsolidated gravel deposits from bedload transport a 20 cm resolution roughness profile from an airborne laser scan als and a slope profile of the whole channel were used to detect the unconsolidated sediment deposits that can potentially feed future debris flows

debris flows some physical characteristics and behaviour field observations on 449 debris flows in the queen charlotte islands british columbia are summarized movement of debris is classified according to seven characteristic types designated for the purposes of the study data on the physical characteristics of the events are presented an analysis of the data is made with reference to event initiation yield and deposition using both mechanistic and morphological criteria for those events which initiate on an open slope the infinite slope model is used to establish a relationship between field drainage class and slope angle for assumed frictional and cohesive soil strength parameters the field drainage classes are directly related to the postulated location of the groundwater surface within the depth of the rupture plane deposition of channelized events is found to be influenced by the ratio of channel width to channel gradient with the onset of deposition expected when the ratio exceeds unity five classes of depositional area are proposed the mag

geomorphic effectiveness of check dams in a debris flow catchment using multi temporal topographic surveys abstract torrent control works such as grade control dams and sediment retention dams are structural measures for controlling debris flows and debris floods in spite of the widespread presence of such hydraulic structures in steep mountain streams worldwide there are still few studies monitoring the effects of check dams on sediment dynamics the use of repeated topographic surveys allows us to characterize debris flow activity at multiple temporal and spatial scales and its interaction with torrent control works structure from motion sfm technique paired with multi view stereo mvs algorithms represents a low cost opportunity to conduct such multi temporal surveys this enables us to better study the effects of individual debris flows track geomorphic changes and evaluate the effectiveness of torrent control works e g check dams the effect of check dams on sediment dynamics is investigated by means of multi temporal topographic surveys before and after debris flow events in the moscardo torrent eastern italian alps where two check dams have recently been built multi temporal sfm based on images taken from the ground in combination with imagery taken by an unmanned aerial vehicle uav is used to obtain dems and to study topographic changes through the comparison of repeat dems dem of difference i e dod the results show that the new check dams considerably modified sediment dynamics in the studied channel but their performance cannot be considered satisfactory the sediment flowed around the upstream check dam on the right wing while deep erosion observed downstream of the check dam threatened to undermine the foundation s stability moreover debris flow lobes deposited upstream of the check dams could act as sources of sediment further increasing downstream debris flow volume the analysis proposed in this work could help improve design strategies and permitting the identification of a proper site for check dam building

velocity of radio waves in glaciers as an indicator of their hydrothermal state structure and regime the results of measurements of radio wave velocities rwv by wide angle reflection war methods in the temperate abramov glacier in the alai mountain ridge and the two layered sub polar fridtjovbreen and hansbreen on svalbard using a low frequency 2 13 mhz radar are considered and discussed the experimental data obtained and the data from the literature show that the values of rwv could be a good indicator of the hydrothermal state of glaciers as such these data enable the identification of cold temperate and transitional two layered glaciers and can be used for estimation of the water content in glaciers and changes in the hydrothermal state

total flash density and the intracloud cloud to ground lightning ratio over the iberian peninsula 1 analysis of the total intracloud and cloud to ground lightning flash density and the intracloud ic to cloud to ground cg ratio z ic cg over the iberian peninsula ip has been performed using 5 years of combined data from the spanish lightning detection network and the nasa optical transient detector otd the spatial distributions of total flash density and cg flash density show significant differences especially on the northwest of the ip the southern island of the balearic islands and the southern southeastern mediterranean coastline the spatial average of the annual value of z is 3 48 a correlation was found between z and latitude correlation coefficient 0 9 a relationship between z and the total flash density was also observed z f0 5 correlation coefficient 0 48 the spatial pattern of z is reminiscent of that of the percentage of positive cg flashes and high z values seem to occur where the percentage of positive flashes is high

on the pullout resistance of geosynthetics pullout tests are reported on geosynthetic test specimens embedded in a relatively dense coarse sand sample the tests are displacement controlled and are performed at different vertical effective

cloud to ground lightning in a tornadic storm on 8 may 1986 abstract on 8 may 1986 the national severe storms laboratory nssl collected doppler radar and lightning ground strike data on a supercell storm that produced three tornadoes including an f3 tornado in edmond oklahoma approximately 40 km north of nssl the edmond storm formed 30 km ahead of a storm complex and produced its first and most damaging tornado just as the storm complex began to overtake it from the west in the mesocyclone that spawned the tornado low level cyclonic shear peaked as the first tornado dissipated and a second tornado began as low level cyclonic shear initially increased negative cloud to ground lightning flash rates also increased reaching a peak of 11 min 1 a few minutes after the peak in cyclonic shear during this period lightning strike locations tended to concentrate just north of the mesocyclone near and inside a 50 dbz reflectivity core as cyclonic shear decreased from its peak during and after the second tornado negative ground flash rates also decreased and s

applying reflection tomography in the postmigration domain to multifold ground penetrating radar data acquisition and processing of multifold ground penetrating radar gpr data enable detailed measurements of lateral velocity variability the velocities constrain interpretation of subsurface materials and lead to significant improvement in image accuracy when coupled with prestack depth migration psdm reflection tomography in the postmigration domain was introduced in the early 1990s for velocity estimation in seismic reflection this robust accurate method is directly applicable in multifold gpr imaging at a contaminated waste facility within the u s department of energy s hanford site in washington the method is used to identify significant lateral and vertical velocity heterogeneity associated with infilled waste pits using both the psdm images and velocity models in interpretation a paleochannel system that underlies the site and likely forms contaminant migration pathways is identified

the contribution of geomorphological mapping to sediment transfer evaluation in small alpine catchments the assessment of sediment transfer processes is necessary to understand the hydro geomorphological functioning of small alpine watersheds prone to channelised debris flows because their occurrence often depends on the amount of debris available in the gully systems therefore sediment budgets should be studied through the identification of erosion transport and deposition processes sediment transfer processes were investigated in a small catchment by field measurements and more specifically through the application of a process based geomorphological mapping method the proposed methodology is based on data directly derived from gis analysis using high resolution dem field measurements and aerial photograph interpretations it has been conceived to estimate sediment transfer dynamics taking into account the role of different sediment stores in the torrential system the proposed geomorphological mapping methodology is quite innovative in comparison with most legend systems that are not adequate for mapping comprehensively active and complex geomorphological systems such as debris flow catchments maps representing the various sediment storages and their relationships can be used for hydro geomorphological hazard mitigation

rates of surface processes on slopes slope retreat and denudation results taken from 270 publications on rates are summarized and collated with those from 149 publications reviewed previously young 1969 1974 the data are classified by major climatic zone normal or steep relief and consolidated or unconsolidated rocks representative rates and their ranges are given for soil creep solifluction surface wash solution chemical denudation rock weathering slope retreat cliff free face retreat marine cliff retreat and denudation the last being compared with representative rates of uplift solifluction is of the order of 10 times faster than soil creep but both cause only very slow ground loss solution is an important cause of ground loss for siliceous rocks on which it may be half as rapid as on limestones total denudation brought about mainly by surface wash reaches a maximum in the semi arid and probably also the tropical savanna zones acceleration of natural erosion rates by human activities ranges from 2 3 times with moderately intense land use to about 10 times with intensive land use and considerably higher still where there is recognized accelerated soil erosion where there is active uplift typical rates are of the order of 10 times faster than denudation although in some high steep mountain ranges these may approach equality

englacial water distribution in a temperate glacier from surface and borehole radar velocity analysis we have obtained common offset common midpoint cmp and borehole vertical vrp ground penetrating radar profiles close to the margin of falljokull a small steep temperate valley glacier situated in southeast iceland velocity analysis of cmp and vrp surveys provided a four layered velocity model this model was verified by comparison between the depths of englacial reflectors and water channels seen in borehole video and from the depths of boreholes drilled to the bed in the absence of sediment within the glacier ice radar velocity is inversely proportional to water content using mixture models developed by paren and looyenga the variation of water content with depth was determined from the radar velocity profile at the glacier surface the calculated water content is 0 23 0 34 velocity 0 166 m ns 1 which rises sharply to 3 0 4 1 velocity 0 149 m ns 1 at 28 m depth interpreted to be the level of the piezometric surface below the piezometric surface the water content drops slowly to 2 4 3 3 velocity 0 152 m ns 1 until 102 m depth where it falls to 0 09 0 14 velocity 0 167 m ns 1 the water content of the ice then remains low to the glacier bed at about 112 m these results suggest storage of a substantial volume of water within the glacier ice which has significant implications for glacier hydrology ice rheology and interpretations of both radar and seismic surveys