a comparison of three methods of mass balance determination in the tuyuksu glacier region tien shan central asia a photogrammetric survey in 1998 formed the basis for compiling a map of the tuyuksu glacier region in the northern tien shan central asia comparison with a map from 1958 enables calculation of the change in glacier volume over 40 years the results are compared with direct annual measurements carried out continuously since 1956 central tuyuksu glacier shows a mass balance of 12 6 m w e for the geodetic method and 16 8 m for glaciological measurements in view of the high accuracy of the maps the discrepancy can be explained mainly by deficiencies in the glaciological measurements application of the precipitation runoff model hbv eth represents the hydrological method of mass balance determination and delivers specific mass balance losses almost twice those indicated by the geodetic observations this discrepancy is suspected to be caused by erroneous runoff measurements the volume balance derived by the geodetic method is used to calibrate both the glaciological and the hydrological method

effects of birefringence within ice sheets on obliquely propagating radio waves in this paper effects of birefringence on radio waves obliquely propagating though polar ice sheets are examined to facilitate interpretations of bistatic and side looking radar data a formalism applicable for arbitrary radar configurations is developed to predict the returned power from within and beneath the ice sheets that have arbitrary alignments of ice crystals ice fabrics we applied this formalism to a range of ice fabrics found in ice cores and assessed the effects of birefringence in terms of ray path configurations ice fabrics and radar frequency predicted frequency dependence of the bed return power replicates prominent features observed at greenland ngrip ice core site results show that birefringence in ice of 1 km or more thickness with strong weak fabric can reduce the power returned from the bed 2 db or more at frequencies higher than 200 mhz 20 mhz as compared to isotropic ice this suggests that quantitative interpretation of the power returned from the bed requires careful assessment of birefringence almost everywhere over the ice sheets application of this formalism also suggests a radar frequency range usable for attenuation measurements possible effects of fabric on synthetic aperture radar processing and a feasibility of remote sensing of ice fabric

complex dielectric permittivity measurements from ground penetrating radar data to estimate snow liquid water content in the pendular regime 1 monitoring the snow water equivalent swe is critical to effective management of water resources in many parts of the world that depend on the mountain snowpack for water storage there are currently no methods to remotely sense swe with accuracy over large lateral distances in the steep and often forested terrain of mountain basins previous studies have shown that measurements of ground penetrating radar gpr velocity can provide accurate estimates of swe in dry snow introduction of liquid water into the snowpack results in a three phase system that cannot be accurately characterized with gpr velocity alone we show that measuring the frequency dependent gpr signal attenuation and velocity provides a direct estimate of the complex dielectric permittivity because the imaginary component is a function only of liquid water content we can utilize both the real and imaginary components of the permittivity to estimate liquid water content snow density and swe using existing empirical relationships that are valid in the pendular regime we tested this new method at two field sites and found that the estimates were accurate to within 12 of gravimetric methods in both a moist and a dry snowpack gpr has the potential to provide swe estimates across large lateral distances over a broad range of snow conditions

can the mass balance of a glacier be estimated from its equilibrium line altitude the possibility of replacing or supplementing direct measurements of mass balance by estimates calculated from equilibrium line altitude ela measurements is investigated by statistical analyses of data from 31 glaciers a linear relationship between mass balance and ela in terms of two parameters the effective balance gradient and the balanced budget ela is tested it is concluded that existing mass balance series can be usefully extrapolated by using ela data for additional years however accurate mass balance cannot be calculated for glaciers where no such measurements have been made because of the difficulties in prescribing the two model parameters with sufficient accuracy for example the effective balance gradient is of the order of 5 mm water m so that errors of only a few decametres in the estimation of the balanced budget ela can have a great effect upon calculations of mass balance

georadar derived estimates of firn density in the percolation zone western greenland ice sheet 1 greater understanding of variations in firn densification is needed to distinguish between dynamic and melt driven elevation changes on the greenland ice sheet this is especially true in greenland s percolation zone where firn density profiles are poorly documented because few ice cores are extracted in regions with surface melt we used georadar to investigate firn density variations with depth along a 70 km transect through a portion of the accumulation area in western greenland that partially melts we estimated electromagnetic wave velocity by inverting reflection traveltimes picked from common midpoint gathers we followed a procedure designed to find the simplest velocity versus depth model that describes the data within estimated uncertainty on the basis of the velocities we estimated 13 depth density profiles of the upper 80 m using a petrophysical model based on the complex refractive index method equation at the highest elevation site our density profile is consistent with nearby core data acquired in the same year our profiles at the six highest elevation sites match an empirically based densification model for dry firn indicating relatively minor amounts of water infiltration and densification by melt and refreeze in this higher region of the percolation zone at the four lowest elevation sites our profiles reach ice densities at substantially shallower depths implying considerable meltwater infiltration and ice layer development in this lower region of the percolation zone the separation between these two regions is 8 km and spans 60 m of elevation which suggests that the balance between dry firn and melt induced densification processes is sensitive to minor changes in melt

six decades of glacier mass balance observations a review of the worldwide monitoring network glacier mass balance is the direct and undelayed response to atmospheric conditions and hence is among the essential variables required for climate system monitoring it has been recognized as the largest non steric contributor to the present rise in sea level six decades of annual mass balance data have been compiled and made easily available by the world glacier monitoring service and its predecessor organizations in total there have been 3480 annual mass balance measurements reported from 228 glaciers around the globe however the present dataset is strongly biased towards the northern hemisphere and europe and there are only 30 reference glaciers that have uninterrupted series going back to 1976 the available data from the six decades indicate a strong ice loss as early as the 1940s and 1950s followed by a moderate mass loss until the end of the 1970s and a subsequent acceleration that has lasted until now culminating in a mean overall ice loss of over 20 m w e for the period 1946 2006 in view of the discrepancy between the relevance of glacier mass balance data and the shortcomings of the available dataset it is strongly recommended to 1 continue the long term measurements 2 resume interrupted long term data series 3 replace vanishing glaciers by early starting replacement observations 4 extend the monitoring network to strategically important regions 5 validate calibrate and accordingly flag field measurements with geodetic methods and 6 make systematic use of remote sensing and geo informatics for assessment of the representativeness of the available data series for their entire mountain range and for the extrapolation to regions without in situ observations and 7 make all these data and related meta information available

high resolution water content estimation from surface based ground penetrating radar reflection data by impedance inversion 1 mapping hydrological parameter distributions in high resolution is essential to understand and simulate groundwater flow and contaminant transport of particular interest is surface based ground penetrating radar gpr reflection imaging in electrically resistive sediments because of the expected close link between the subsurface water content and the dielectric permittivity which controls gpr wave velocity and reflectivity conventional tools like common midpoint cmp velocity analysis provide physical parameter models of limited resolution only we present a novel reflection amplitude inversion workflow for surface based gpr data capable of resolving the subsurface dielectric permittivity and related water content distribution with markedly improved resolution our scheme is an adaptation of a seismic reflection impedance inversion scheme to surface based gpr data key is relative amplitude preserving data preconditioning including gpr deconvolution which results in traces with the source wavelet distortions and propagation effects largely removed the subsequent inversion for the underlying dielectric permittivity and water content structure is constrained by in situ dielectric permittivity data obtained by direct push logging after demonstrating the potential of our novel scheme on a realistic synthetic data set we apply it to two 2 d 100 mhz gpr profiles acquired over a shallow sedimentary aquifer resulting in water content images of the shallow 3 7 m depth saturated zone having decimeter resolution

mass balance parameters derived from a synthetic network of mass balance glaciers glacier mass balance parameters such as the equilibrium line altitude ela play an important role when working with large glacier samples while the number of observational mass balance series to derive such parameters is limited more and more modeled data are becoming available here we explore the possibilities of analyzing such synthetic mass balance data with respect to mass balance parameters a simplified energy balance model is driven by bias corrected regional climate model output to model mass balance distributions for 94 glaciers in the swiss alps over 15 years the modeling results in realistic interannual variability and mean cumulative mass balance subsequently model output is analyzed with respect to 18 topographic and mass balance parameters and a correlation analysis is performed well known correlations such as for ela and median elevation are confirmed from the synthetic data furthermore previously unreported parameter relationships are found such as a correlation of the balance rate at the tongue with the accumulation area ratio aar and of the glacier elevation range with the aar analyzing modeled data complements in situ observations and highlights their importance the small number of accurate mass balance observations available for validation is a major challenge for the presented approach

acoustic measurements in unconsolidated sands at low effective pressure and overpressure detection shallow water flows and over pressured zones are a major hazard in deepwater drilling projects their detection prior to drilling would save millions of dollars in lost drilling costs i have investigated the sensitivity of seismic methods for this purpose using p wave information alone can be ambiguous because a drop in p wave velocity vp can be caused both by overpressure and by presence of gas the ratio of p wave velocity to s wave velocity vp vs which increases with overpressure and decreases with gas saturation can help differentiate between the two cases since p wave velocity in a suspension is slightly below that of the suspending fluid and vs 0 vp vs and poisson s ratio must increase exponentially as a load bearing sediment approaches a state of suspension on the other hand presence of gas will also decrease vp but vs will remain unaffected and vp vs will decrease analyses of ultrasonic p and s wave velocities in sands show that the vp vs ratio especially at low effective pressures

a comparison of seismic and radar methods to establish the thickness and density of glacier snow cover we show that geophysical methods offer an effective means of quantifying snow thickness and density opportunistic efficient but non optimized seismic refraction and ground penetrating radar gpr

spatio temporal variability in elevation changes of two high arctic valley glaciers uncertainties in estimates of glacier and ice cap contribution to sea level rise exist in part due to poor quantification of mass balance errors particularly those resulting from extrapolation of sparse measurements centre line data are often assumed to be representative of the glacier as a whole with little attention paid to extrapolation errors or their effect on mass balance estimates here we present detailed digital elevation model dem measurements of glacier wide elevation changes over the last 40 years at two glaciers on svalbard norwegian arctic austre broggerbreen and midtre lovenbreen are shown to have lost 27 54 0 98 and 9 65 0 76 10 7 m 3 of ice respectively between 1966 and 2005 findings that we relate to trends in average summer air temperatures and winter accumulation these volume losses correspond to geodetic balances of 0 58 0 03 and 0 41 0 03 m w e a 1 respectively our analysis revealed high spatial complexity in patterns of elevation change varying between glaciers between measurement intervals and within and between elevation bins balances from extrapolated centre line geodetic data were the same within errors as those from full coverage dem differencing in the majority of comparisons yet significantly underestimated balance in three instances additionally field mass balance from centre line ablation stake data underestimated balances from full coverage geodetic measurements during three of six measurement periods these findings may support the hypothesis that field measurements under estimate svalbard glacier mass loss at least partly as a result of the failure of centre line measurements to account for glacier wide variations in ablation our results demonstrate the importance of deriving accurate interpolation functions and constraining extrapolation errors from sparse measurements

recent fluctuations in the extent of the firn area of austfonna svalbard inferred from gpr in spring during 2004 07 we conducted ground penetrating radar gpr measurements on the austfonna ice cap svalbard with the original aim of mapping the thickness and distribution of winter snow here we further exploit the information content of the data and derive a multi year sequence of glacier facies distribution that provides valuable spatial information about the total surface mass balance smb of the ice cap beyond the usually evaluated winter balance we find that following an initial decrease in the extent of the firn area 2003 04 the firn line lowered within two subsequent years by 40 100m elevation in the north and west and 150 230 m in the south and east of the ice cap corresponding to a lateral expansion of the firn area along the profiles by up to 7 3 and 13 3 km respectively the growth of the firn area is in line with stake measurements from etonbreen that indicate a trend towards less negative smb over the corresponding period

a re analysis of the 58 year mass balance record of storglaciaren sweden the use of glacier mass balance records to assess the effects of glacier volume change from climate change requires high quality data the methods for measuring glacier mass balance have been developed in tandem with the measurements themselves which implies that the quality of the data may change with time we have investigated such effects on the mass balance record of storglaciaren sweden by re analyzing the records using a better map base and applying successive maps over appropriate time periods our results show that errors 10 year oscillations the pseudo cyclic signal must thus be explained by factors other than cyclically occurring phenomena although the record may still be too short to establish significant signals we strongly recommend re analysis of long mass balance records in order to improve the mass balance records used for other analyses

mass balance of glaciers and ice caps consensus estimates for 1961 2004 1 working with comprehensive collections of directly measured data on the annual mass balance of glaciers other than the two ice sheets we combine independent analyses to show that there is broad agreement on the evolution of global mass balance since 1960 mass balance was slightly below zero around 1970 and has been growing more negative since then excluding peripheral ice bodies in greenland and antarctica global average specific balance for 1961 1990 was 219 112 kg m 2 a 1 representing 0 33 0 17 mm sle sea level equivalent a 1 for 2001 2004 the figures are 510 101 kg m 2 a 1 and 0 77 0 15 mm sle a 1 including the smaller greenland and antarctic glaciers global total balance becomes 0 38 0 19 mm sle a 1 for 1961 1990 and 0 98 0 19 mm sle a 1 for 2001 2004 for 1991 2004 the glacier contribution 0 77 0 26 mm sle a 1 is 20 30 of a recent estimate of 3 2 0 4 mm a 1 of total sea level rise for 1993 2005 while our error estimates are not rigorous we believe them to be liberal as far as they go but we also discuss several unquantified biases of which any may prove to be significant

mixing formulae and experimental results for the dielectric constant of snow on examine les proprietes dielectriques de la neige deduites de differents modeles et on les compare aux observations on suppose que la permittivite complexe de la neige humide est la somme des permittivites de la neige seche et de la permittivite due a l eau liquide cette derniere est particulierement examinee

depth characterization of shallow aquifers with seismic reflection part i the failure of nmo velocity analysis and quantitative error prediction as seismic reflection data become more prevalent as input for quantitative environmental and engineering studies there is a growing need to assess and improve the accuracy of reflection processing methodologies it is common for compressional wave velocities to increase by a factor of four or more where shallow unconsolidated sediments change from a dry or partially water saturated regime to full saturation while this degree of velocity contrast is rare in conventional seismology it is a common scenario in shallow environments and leads to significant problems when trying to record and interpret reflections within about the first 30 m below the water table the problem is compounded in shallow reflection studies where problems primarily associated with surface related noise limit the range of offsets we can use to record reflected energy for offset to depth ratios typically required to record reflections originating in this zone the assumptions of nmo velocity analysis are violated leading to very large errors in depth and layer thickness estimates if the dix equation is assumed valid for a broad range of velocity profiles saturated layer thickness will be overestimated by a minimum of 10 if the boundary of interest is 100 if the saturated layer is 10 m thick this degree of error has a significant and negative impact if quantitative interpretations of aquifer geometry are used in aquifer evaluation such as predictive groundwater flow modeling or total resource estimates

synaccretionary sedimentary and volcanic rocks in the ordovician tetagouche backarc basin new brunswick canada evidence for a transition from foredeep to forearc basin sedimentation

glacier mass balance determination by remote sensing and high resolution modelling an indirect methodology for determining the distribution of mass balance at high spatial resolution using remote sensing and ice flow modelling is presented the method based on the mass continuity equation requires two datasets collected over the desired monitoring interval i the spatial pattern of glacier surface elevation change and ii the mass flux divergence field at haut glacier d arolla valais switzerland the mass balance distribution between september 1992 and september 1993 is calculated at 20 m resolution from the difference between the pattern of surface elevation change derived from analytical photogrammetry and the mass flux divergence field determined from three dimensional numerical flow modelling constrained by surface velocity measurements the resultant pattern of mass balance is almost totally negative showing a strong dependence on elevation but with large localized departures the computed distribution of mass balance compares well r 2 0 91 with mass balance measurements made at stakes installed along the glacier centre line over the same period despite the highly optimized nature of the flow modelling effort employed in this study the good agreement indicates the potential this method has as a strategy for deriving high spatial and temporal resolution estimates of mass balance

calibrating a surface mass balance model for austfonna ice cap svalbard austfonna 8120 km 2 is by far the largest ice mass in the svalbard archipelago there is considerable uncertainty about its current state of balance and its possible response to climate change over the 2004 05 period we collected continuous meteorological data series from the ice cap performed mass balance measurements using a network of stakes distributed across the ice cap and mapped the distribution of snow accumulation using ground penetrating radar along several profile lines these data are used to drive and test a model of the surface mass balance the spatial accumulation pattern was derived from the snow depth profiles using regression techniques and ablation was calculated using a temperature index approach model parameters were calibrated using the available field data parameter calibration was complicated by the fact that different parameter combinations yield equally acceptable matches to the stake data while the resulting calculated net mass balance differs considerably testing model results against multiple criteria is an efficient method to cope with non uniqueness in doing so a range of different data and observations was compared to several different aspects of the model results we find a systematic underestimation of net balance for parameter combinations that predict observed ice ablation which suggests that refreezing processes play an important role to represent these effects in the model a simple pmax approach was included in its formulation used as a diagnostic tool the model suggests that the surface mass balance for the period 29 april 2004 to 23 april 2005 was negative 318 mm w e

a new framework for estimating englacial water content and pore geometry using combined radar and seismic wave velocities 1 ice mechanical properties and hence the response of glaciers to climate change depend strongly on the presence of liquid water at ice grain boundaries the propagation velocities of radar and seismic waves are also highly sensitive to this water mixing laws typically the looyenga and riznichenko formulae have traditionally been used to quantify liquid water content within glaciers from such velocity data however it has become apparent that these mixing laws are geometrically inconsistent we present an inclusion based effective medium approximation in which we model water inclusions within solid ice two types of inclusions are used spherical inclusions to represent water in the grain junction nodes and high aspect ratio spheroidal inclusions to represent water in the grain boundary veins we apply this model to radar and seismic data from a polythermal glacier in svalbard to quantify both inclusion geometry and the unfrozen water content within the warm ice

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

determining snow water equivalent by acoustic sounding the possibility of determining snow water equivalent swe by the use of an acoustic impulse was assessed at two field locations in saskatchewan and british columbia canada these sites represent cold windswept prairie and temperate deep mountain snowcovers a continuous frequency swept acoustic wave was sent into the snowpack and received signal processing was then subsequently used to estimate the depth and density of each snow layer by a recursive relationship involving frequency modulated continuous wave fmcw radar and seismological techniques from this method it is also shown that the tortuosity of snow can be estimated data collected by gravimetric sampling was used as comparison to the swe values determined by the use of acoustic sounding the results showed that for the saskatchewan sites the correlation between the measured and the modeled values of swe was 0 86 whereas at the british columbia sites the correlation was 0 78 the difference in the correlations was interpreted as being due to additional acoustic measurement error at the british columbia sites caused by higher liquid water contents and more layers in the snowpack the measured and the modeled swe for saskatchewan snowpacks with high liquid water contents were found to be weakly associated with correlations of 0 30 the acoustically determined values of tortuosity were close to unity 1 which is in agreement with the values characteristic of snow as a porous substance further research is necessary to determine whether this technique can be applied to snow in other environmental conditions copyright 2007 john wiley sons ltd

20th century climate change inferred from four long term point observations of seasonal mass balance four long term time series of seasonal mass balance observations all starting in 1914 have been compiled for two stakes on claridenfirn and one stake on grosser aletschgletscher and silvrettagletscher switzerland these data represent the longest records of mass balance worldwide a mass balance model based on the temperature index approach is used to correct field data for varying observation dates and data gaps and to separate accumulation and ablation the homogenized continuous 93 year time series cover most of the 20th century and enable us to investigate temporal regional and altitudinal variability in mass balance and changes in the climatic forcing on glaciers a high altitude site shows summer balance trends opposite to those at three stakes located near the equilibrium line since 1975 melt rates have increased by 10 10 a 1 periods of enhanced climatic forcing are detected 1943 53 and 1987 2007 the energy consumed for melt was higher in the 1940s despite lower air temperatures compared to the years since 1987 we find evidence for a change in the glacier surface heat budget which has important implications for the long term stability of degree day factors in empirical temperature index modelling

techniques for measuring high resolution firn density profiles case study from kongsvegen svalbard on an 11 m firn ice core from kongsvegen svalbard we have used dielectric profiling dep to measure electrical properties and digital photography to measure a core optical stratigraphy cos profile we also used a neutron scattering probe np to measure a density profile in the borehole from which the core was extracted the np and dep derived density profiles were similar showing large scale 30 cm variation in the gravimetric densities of each core section fine scale features 10 cm are well characterized by the cos record and are seen at a slightly lower resolution in both the dep and np records which show increasing smoothing a combination of the density accuracy of np and the spatial resolution of cos provides a useful method of evaluating the shallow density profile of a glacier improving paleoclimate interpretation mass balance measurement and interpretation of radar returns

seismic attenuation in glacial ice a proxy for englacial temperature 1 seismic attenuation or internal friction q 1 in glacial ice is highly sensitive to temperature particularly near the melting point here we detail a technique to estimate q and apply it to active source seismic data from jakobshavn isbrae greenland we compare our results to measured and modeled temperature profiles of the ice in the region we find an excellent match with differences between seismically estimated and modeled temperatures of less than 2 c mapping variations in seismic q through glacial ice thus is shown to allow detailed estimation of englacial temperature profiles which may be of special value in regions where in situ measurements are logistically difficult