a sea ice lead detection algorithm for use with high resolution airborne visible imagery the detection of leads or cracks in sea ice is critical for the derivation of sea ice freeboard from altimetric measurements of sea ice elevation we present an approach for lead detection in sea ice using high resolution visible imagery from airborne platforms we develop a new algorithm i e the sea ice lead detection algorithm using minimal signal sildams that detects clouds extracts leads and classifies ice types within leads from airborne visible imagery cloud detection is based on an assessment of local variances of pixel brightness across image scenes and where available coincident altimetric measurements are used to confirm suspected cloudy scenes the lead extraction step computes affine time frequency distributions minimal signal for the red green and blue channels of each image the transformed outputs are combined to take advantage of three channels simultaneously finally lead pixel geolocations are extracted using a set of uniform thresholds for ice typing including open water thin ice and gray ice within leads along each flight line sildams was tested using data from the digital mapping system dms dms digital photographs represent the highest resolution 10 cm visible imagery available over sea ice and were collected during nasa operation icebridge sea ice flights in the antarctic and the arctic in 2009 and 2010 respectively we demonstrate that sildams has a high lead detection capability of 99

determination of residual strength parameters of jointed rock masses using the gsi system abstract the geological strength index gsi system proposed in 1995 is now widely used for the estimation of the rock mass strength and the rock mass deformation parameters the gsi system concentrates on the description of two factors rock structure and block surface conditions the guidelines given by the gsi system are for the estimation of the peak strength parameters of jointed rock masses there are no guidelines given by the gsi or by any other system for the estimation of the rock mass residual strength that yield consistent results in this paper a method is proposed to extend the gsi system for the estimation of a rock mass s residual strength it is proposed to adjust the peak gsi to the residual gsir value based on the two major controlling factors in the gsi system the residual block volume v b r and the residual joint condition factor j c r methods to estimate the residual block volume and joint condition factor are presented the proposed method for the estimation of rock mass s residual strength is validated using in situ block shear test data from three large scale cavern construction sites and data from a back analysis of rock slopes the estimated residual strengths calculated using the reduced residual gsir value are found to be in good agreement with field test or back analyzed data

sea surface height determination in the arctic ocean from ers altimetry 1 accurate sea surface height measurements have been extracted from ers altimeter data in sea ice covered regions for the first time the data have been used to construct a mean sea surface of the arctic ocean between the latitudes of 60 degreesn and 81 5 degreesn based on 4 years of ers 2 data an rms value for the crossover differences of mean sea surface profiles of 4 2 cm was observed in the ice covered canada basin compared with 3 8 cm in the ice free greenland iceland norwegian seas comparisons are made with an existing global mean sea surface osumss95 highlighting significant differences between the two surfaces in permanently ice covered seas in addition we present the first altimeter derived sea surface height variability map of the arctic ocean comparisons with a high resolution coupled ocean sea ice general circulation model reveal a good qualitative agreement in the spatial distribution of variability quantitatively we found that the observed variability was on average a factor of 3 4 greater than model predictions

sea ice thickness estimations from icesat altimetry over the bellingshausen and amundsen seas 2003 2009 1 sea ice thicknesses derived from nasa s ice cloud and land elevation satellite icesat altimetry data are examined using two different approaches buoyancy and empirical equations and at two spatial scales icesat footprint size 70 m diameter spot and advanced microwave scanning radiometer amsr e pixel size 12 5 km by 12 5 km for the bellingshausen and amundsen seas of west antarctica ice thickness from the empirical equation shows reasonable spatial and temporal distribution of ice thickness from 2003 to 2009 ice thickness from the buoyancy equation however additionally needing snow depth information derived from the amsr e shows an overestimation in terms of maximum mean 63 to 75 and standard deviation while underestimation in modal thickness 20 as compared with those from the empirical equation approach when icesat snow freeboard is used as the snow depth in the buoyancy equation i e the zero ice freeboard assumption the derived ice thicknesses match well with those from the empirical equation approach within 5 overall the amsr e therefore may underestimate snow depth and accounts for 95 of the ice thickness overestimation as compared with the buoyancy approach the empirical equation derived ice thickness shows a consistent asymmetrical distribution with a long tail to high values and seasonal median values ranging from 0 8 to 1 4 m over the 2003 2009 period that are always larger than the corresponding modal values 0 6 1 1 m and lower than the mean values 1 0 1 6 m with standard deviation of 0 6 1 0 m an overall increasing trend of 0 03 m year of mean ice thickness is found from 2003 to 2009 although statistically insignificant p 0 11 at the 95 confidence level starting from autumn a general picture of seasonal mean modal and median ice thickness increases progressively from autumn to spring and decreases from spring to the following autumn when new thin ice dominates the ice thickness distribution the asymmetric shape of the thickness distribution reflects the key role of ice deformation processes in the evolution of the thickness distribution the statistical properties of the thickness distribution interannually high range of mean thickness and standard deviation indicate the variability of deformation processes however spring ice volume the product of ice mean thickness and areal extent computed for the spring maximum shows variability year to year but is primarily dominated by ice extent variability with no increasing or decreasing trend over this record length the dependence of the volume on the ice extent primarily suggests that ice thickness changes have also not covaried with the ice extent losses seen over the satellite record in this region unlike the arctic these properties reflect the interactive processes of ice advection thermodynamic growth and ice deformation that all substantially influence ice mass balance in the bellingshausen amundsen seas region

antarctic sea ice altimetry scale and resolution effects on derived ice thickness distribution three ice type regimes at ice station belgica isb during the 2007 international polar year simba sea ice mass balance in antarctica expedition were characterized and assessed for elevation snow depth ice freeboard and thickness analyses of the probability distribution functions showed great potential for satellite based altimetry for estimating ice thickness in question is the required altimeter sampling density for reasonably accurate estimation of snow surface elevation given inherent spatial averaging this study assesses an effort to determine the number of laser altimeter hits of the isb floe as a representative antarctic floe of mixed first and multi year ice types for the purpose of statistically recreating the in situ determined ice thickness and snow depth distribution based on the fractional coverage of each ice type estimates of the fractional coverage and spatial distribution of the ice types referred to as ice towns for the 5 km 2 floe were assessed by in situ mapping and photo visual documentation simulated icesat altimeter tracks with spot size 70 m and spacing 170 m sampled the floe s towns generating a buoyancy derived ice thickness distribution 115 altimeter hits were required to statistically recreate the regional thickness mean and distribution for a three town assemblage of mixed first and multi year ice and 85 hits for a two town assemblage of first year ice only equivalent to 19 5 and 14 5 km respectively of continuous altimeter track over a floe region of similar structure results have significant implications toward model development of sea ice sampling performance of the icesat laser altimeter record as well as maximizing sampling characteristics of satellite airborne laser and radar altimetry missions for sea ice thickness

estimation of sea ice thickness distributions through the combination of snow depth and satellite laser altimetry data 1 combinations of sea ice freeboard and snow depth measurements from satellite data have the potential to provide a means to derive global sea ice thickness values however large differences in spatial coverage and resolution between the measurements lead to uncertainties when combining the data high resolution airborne laser altimeter retrievals of snow ice freeboard and passive microwave retrievals of snow depth taken in march 2006 provide insight into the spatial variability of these quantities as well as optimal methods for combining high resolution satellite altimeter measurements with low resolution snow depth data the aircraft measurements show a relationship between freeboard and snow depth for thin ice allowing the development of a method for estimating sea ice thickness from satellite laser altimetry data at their full spatial resolution this method is used to estimate snow and ice thicknesses for the arctic basin through the combination of freeboard data from icesat snow depth data over first year ice from amsr e and snow depth over multiyear ice from climatological data due to the nonlinear dependence of heat flux on ice thickness the impact on heat flux calculations when maintaining the full resolution of the icesat data for ice thickness estimates is explored for typical winter conditions calculations of the basin wide mean heat flux and ice growth rate using snow and ice thickness values at the 70 m spatial resolution of icesat are found to be approximately one third higher than those calculated from 25 km mean ice thickness values

winter snow cover on sea ice in the weddell sea measurements of snow thickness temperature salinity density and stratigraphy acquired during the 1992 winter weddell gyre study are presented results indicate that the winter snow cover on sea ice in the weddell sea is extremely variable extreme fluctuations in antarctic synoptic conditions air temperature precipitation humidity and wind speed occur during the austral winter they result in unique modifications and additions to the snow layer during the aging process and act to stabilize an otherwise easily wind redistributed shallow snow cover and develop well packed drift features the latter occur even over relatively undeformed areas of sea ice and have a significant localized effect on the snow thickness distribution significant variability in snow grain size mean 2 73 3 12 mm and density 0 32 0 09 g cm 3 is observed as a result of cyclical switches between high and low temperature gradient metamorphism multiple icy layers indicate multiple thaw freeze events one such event occurred during a 3 day station during which the air temperature rose by 22 c in 12 hours to approximately 0 c this paper also examines mechanisms for flooding of the snow ice interface including snow loading even where the latter is not a factor the layer of snow immediately above the snow ice interface is commonly damp and saline 10 limitations in the data set are discussed and comparisons are drawn with other experiments

effects of pre existing discontinuities on the residual strength of rock mass insight from a discrete element method simulation abstract when rock failure is unavoidable the designer of engineering structures must know and account for the residual strength of the rock mass this is particularly relevant in underground coal mine openings pre existing discontinuities play an important role in the mechanical behavior of rock masses and thus it is important to understand the effects of such pre existing discontinuities on the residual strength for this purpose the present study demonstrates a numerical analysis using a discrete element method simulation the numerical results indicate that fracture intensity has no significant influence on the residual strength of jointed rock masses independent of confining conditions as confining pressures increase both peak and residual strengths increase with residual strength increasing at a faster rate the finding was further demonstrated by analyzing documented laboratory compressive test data from a variety of rocks along with field data from coal pillars a comprehensive interpretation of the finding was conducted using a cohesion weakening friction strengthening cwfs model the effect of rock bolts on rock mass strength was also evaluated by using a discrete element method model which suggested that rock bolts can significantly increases residual strength but have limited effect on increasing the peak strength of rock masses

uncertainties in antarctic sea ice thickness retrieval from icesat a sensitivity study was carried out for the lowest level elevation method to retrieve total sea ice snow freeboard from ice cloud and land elevation satellite icesat elevation measurements in the weddell sea antarctica varying the percentage p of elevations used to approximate the instantaneous sea surface height can cause widespread changes of a few to 10 cm in the total freeboard obtained other input parameters have a smaller influence on the overall mean total freeboard but can cause large regional differences these results together with published icesat elevation precision and accuracy suggest that three times the mean per gridcell single laser shot error budget can be used as an estimate for freeboard uncertainty theoretical relative ice thickness uncertainty ranges between 20 and 80 for typical freeboard and snow properties ice thickness is computed from total freeboard using advanced microwave scanning radiometer for earth observing system amsr e snow depth data average ice thickness for the weddell sea is 1 73 0 38 m for icesat measurements from 2004 to 2006 in agreement with previous work the mean uncertainty is 0 72 0 09 m our comparison with data of an alternative approach which assumes that sea ice freeboard is zero and that total freeboard equals snow depth reveals an average sea ice thickness difference of 0 77 m

estimation of rev for fractured rock masses based on geological strength index abstract the representative elementary volume rev of fractured rock masses is a significant index to investigate the rock mass behaviors in the continuum mechanics in this research a new indicator to estimate the rev size of fractured rock masses based on the geological strength index gsi is proposed for this purpose a new method that combines the pfc based synthetic rock mass srm model with the hoek brown hb failure criterion is proposed to investigate the strength and deformation properties of fractured rock masses under biaxial stress conditions extensive numerical analyses are carried out to estimate variation of the uniaxial compression strength ucs deformation modulus e and gsi of the brunswick mine rock mass with increasing the size of the srm models up to a rev size results show that the gsi based indicator gives relatively larger rev size compared with the traditional ucs or deformation modulus e based indicators compared with the traditional indicators the proposed gsi based indicator has merits of not only reflecting the geometrical characteristics of rock structures but also containing both geometrical and mechanical properties of discontinuities

estimation of sea ice thickness and volume in the sea of okhotsk based on icesat data sea ice thickness in the sea of okhotsk is estimated for 2004 2008 from icesat derived freeboard under the assumption of hydrostatic balance total ice thickness including snow depth h t o t averaged over 2004 2008 is 95 cm the interannual variability of h t o t is large from 77 5 cm 2008 to 110 4 cm 2005 the mode of h t o t varies from 50 60 cm 2007 and 2008 to 70 80 cm 2005 ice thickness derived from icesat data is validated from a comparison with that observed by electromagnetic induction instrument em aboard the icebreaker soya near hokkaido japan annual maps of h t o t reveal that the spatial distribution of h t o t is similar every year ice volume of 6 3 10 11 m 3 is estimated from the icesat derived h t o t and amsr e derived ice concentration a comparison with ice area demonstrates that the ice volume cannot always be represented by the area solely despite the fact that the area has been used as a proxy of the volume in the sea of okhotsk the ice volume roughly corresponds to that of annual ice production in the major coastal polynyas estimated based on heat budget calculations this also supports the validity of the estimation of sea ice thickness and volume using icesat data

snow depth and ice thickness measurements from the beaufort and chukchi seas collected during the amsr ice03 campaign in march 2003 a field validation campaign was conducted on the sea ice near barrow ak the goal of this campaign was to produce an extensive dataset of sea ice thickness and snow properties depth and stratigraphy against which remote sensing products collected by aircraft and satellite could be compared chief among these were products from the polarimetric scanning radiometer psr flown aboard a nasa p 3b aircraft and the aqua advanced microwave scanning radiometer for the earth observing system amsr e the data were collected in four field areas three on the coastal sea ice near barrow ak and the fourth out on the open ice pack 175 km northeast of barrow the snow depth ranged from 9 4 20 8 cm in coastal areas n 9881 for three areas with the thinnest snow on ice that had formed late in the winter out in the main pack ice the snow was 20 6 cm deep n 1906 the ice in all four areas ranged from 138 219 cm thick n 1952 with the lower value again where the ice had formed late in the winter snow layer and grain characteristics observed in 118 snow pits indicated that 44 of observed snow layers were depth hoar 46 were wind slab snow and ice measurements were keyed to photomosaics produced from low altitude vertical aerial photographs using these and a distinctive three way relationship between ice roughness snow surface characteristics and snow depth strip maps of snow depth each about 2 km wide were produced bracketing the traverse lines these maps contain an unprecedented level of snow depth detail against which to compare remote sensing products the maps are used in other papers in this special issue to examine the retrieval of snow properties from the psr and amsr e sensors

sea ice thickness distribution of the bellingshausen sea from surface measurements and icesat altimetry abstract although sea ice extent in the bellingshausen amundsen ba seas sector of the antarctic has shown significant decline over several decades there is not enough data to draw any conclusion on sea ice thickness and its change for the ba sector or for the entire southern ocean this paper presents our results of snow and ice thickness distributions from the simba 2007 experiment in the bellingshausen sea using four different methods aspect ship observations downward looking camera imaging ship based electromagnetic induction em sounding and in situ measurements using ice drills a snow freeboard and ice thickness model generated from in situ measurements was then applied to contemporaneous icesat satellite laser altimetry measured freeboard to derive ice thickness at the icesat footprint scale errors from in situ measurements and from icesat freeboard estimations were incorporated into the model so a thorough evaluation of the model and uncertainty of the ice thickness estimation from icesat are possible our results indicate that icesat derived snow freeboard and ice thickness distributions asymmetrical unimodal tailing to right for first year ice 0 29 0 14 m for mean snow freeboard and 1 06 0 40 m for mean ice thickness multi year ice 0 48 0 26 and 1 59 0 75 m respectively and all ice together 0 42 0 24 and 1 38 0 70 m respectively for the study area seem reasonable compared with those values from the in situ measurements aspect observations and em measurements the em measurements can act as an appropriate supplement for aspect observations taken hourly from the ship s bridge and provide reasonable ice and snow distributions under homogeneous ice conditions our proposed approaches 1 of using empirical equations relating snow freeboard to ice thickness based on in situ measurements and 2 of using isostatic equations that replace snow depth with snow freeboard or empirical equations that convert freeboard to snow depth are efficient and important ways to derive ice thickness from icesat altimetry at the footprint scale for antarctic sea ice spatial and temporal snow and ice thickness from satellite altimetry for the ba sector and for the entire southern ocean is therefore possible

sea ice freeboard and thickness in the ross sea from airborne icebridge 2013 and satellite icesat 2003 2008 observations

triaxial strength and deformability of intact and increasingly jointed granite samples abstract triaxial strength tests were performed on artificially jointed standard size granite specimens with two sub vertical and three sub horizontal 2 3 joints a fully servo controlled press was used to load the samples and attain residual strength these tests add to an existing test database for intact and artificially jointed 1 2 joints samples of the same rock the main parameters from each test were used to analyse tendencies in particular changes in elasticity and peak and residual strength in line with increased jointing peak strength and apparent young s modulus decreased from the intact to the jointed specimens reflecting a tendency analogous to that deriving from the use of classification systems to characterize rock masses mohr coulomb and hoek brown failure criteria were fit to peak and residual strength tests results in the case of the hoek brown criterion it seems that an equivalent of the geological strength index gsi which reflects structure at the specimen scale could be of use in estimating the decrease in strength of increasingly jointed samples residual strength envelopes were practically the same for the intact and jointed specimens our results for granite would suggest that the so called rock mechanics scale effect at large i e the relevant change in material properties from rock samples at lab scale to that of the rock mass including the occurrence of natural discontinuities at the engineering work scale is more due to structure number orientation spacing and features of occurring joints than to sample scale effect i e the variation in properties when testing different size from a few mm to some decimetres unjointed intact rock samples at the laboratory

strength and dilation of jointed granite specimens in servo controlled triaxial tests abstract we investigated the complete stress strain response of artificially jointed granitic rock specimens with two joint sets a series of confined compressive tests on these jointed rock specimens were performed in a fully servo controlled press elastic strength and post failure parameters were calculated and analysed with special attention paid to the dilation angle the results were compared to those for corresponding intact specimens investigated in a previous study although the peak strength of the jointed cores was much lower than that for the intact cores the residual strength envelopes were practically equal the apparent elastic and drop moduli tended to be lower for jointed specimens than that for intact specimens at low confining stress levels the jointed rock tended to dilate less than the intact rock but at higher confinement dilation behaviour converged another finding with respect to post yield behaviour was that the dilation angle of the jointed specimens could adequately be represented by an existing plastic shear strain and confinement dependent model developed for intact specimens

numerical investigation into strength and deformability of veined rock mass abstract veined rock masses can be found in porphyry copper deposits like at the el teniente mine in chile rock masses with cemented joints or veins cannot be accurately represented using the methods commonly applied to predict the deformability and strength of jointed rock masses laboratory tests on veined rock andesite from the el teniente mine have shown that the veins control the fracturing process and strength in this work the behavior of veined rock was studied using a numerical model built in the finite element software abaqus in this analysis the rock mass was modeled as an assemblage of blocks bonded by layers representing the intact rock and veins respectively uniaxial compression tests on veined core size specimens were simulated and their results compared to experimental data the results show good agreement with the experiments in terms of strength stiffness and mode of failure after this a veined rock mass volume was modeled using the orientation of mapped and post processed discontinuities as input simulations of uniaxial and triaxial tests were performed on the modeled veined rock mass the observed failure mode confirms experimental results showing that at low confinement the failure is concentrated in the veins and the rupture of intact rock becomes significant at higher confinement the obtained strength envelope of the veined rock mass is non linear and its shape is independent of the strength of the intact rock however the hoek brown criterion did not fit the results the residual strength of the veined rock approximated the residual strength of the intact rock agreeing with previously reported observations in jointed rock

sea ice thickness in the coastal northeastern chukchi sea from moored ice profiling sonar time series ice draft data were obtained from moored ice profiling sonar ips in the coastal northeastern chukchi sea during 2009 10 time series data show seasonal growth of sea ice draft occasionally interrupted by coastal polynya the sea ice draft distribution indicates a slightly lower abundance of thick deformed ice compared with the eastern beaufort sea in january a rapid increase in the abundance of thick ice coincided with a period of minimal drift indicating compaction again the coast and dynamical thickening the overall mean draft and corresponding derived thickness are 1 27 and 1 38 m respectively the evolution of modal ice thickness observed can be explained mostly by thermodynamic growth the derived ice thicknesses are used to estimate heat losses based on era interim data heat losses from the raw 1 s ips data are 50 and 100 greater than those calculated using ips data averaged over spatial scales of 20 and 100 km respectively this finding demonstrates the importance of subgrid scale ice thickness distribution for heat loss calculation the heat loss estimate based on thin ice data derived from amsr e data corresponds well with that from the 1 s observed ice thickness data validating heat loss estimates from the amsr e thin ice thickness algorithm

satellite remote sensing of sea ice thickness and kinematics a review observations of sea ice thickness and kinematics are essential for understanding changes in sea ice mass balance interactions between the ice cover and the ocean and atmosphere and for improving projections of sea ice response in a warming climate these parameters are not directly observable with current sensor technology but are derived from satellite altimetry and imagery while there is progress in the retrievals of arctic sea ice thickness from satellite altimetry approaches to address southern ocean ice thickness require additional attention on the other hand procedures to derive sea ice motion from satellite imagery are more mature and better understood and have been employed to produce useful results for more than a decade adequate sampling of sub daily ice motion however remains a challenge generally satellite instruments provide large scale coverage but the frequency of temporal sampling is limited by orbit characteristics in this review i focus on the approaches uncertainties sampling limitations and validation issues associated with the estimation of sea ice thickness and motion i provide a summary of current and anticipated capabilities for monitoring sea ice thickness and kinematics from space the prospects for continuing these measurements into the next decade from a satellite remote sensing perspective are discussed

strength of jointed rock masses jointed rock masses comprise interlocking angular par ticles or blocks of hard brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials the strength of such rock masses depends on the strength of the intact pieces and on their freedom of movement which in turn depends on the number orientation spacing and shear strength of the discontinuities a complete understanding of this problem presents formidable theoretical and experi mental problems and hence simplifying assumptions are required in order to provide a reasonable basis for estimating the strength of jointed rock masses for engineering design purposes this paper summarizes some of the basic information upon which such simplifying assumptions can be made a simple empirical failure criterion is presented and its application in engineering design is illustrated by means of a number of practical examples des masses jointives de rochers comprennent des particules angulaires enchevetrees ou des

post failure behaviour of a rock mass under the influence of triaxial and true triaxial confinement in this paper results of triaxial and true triaxial testing conducted on physical models of a rock mass are used to describe its post failure behaviour the specimens comprised of three continuous joint sets and were prepared from blocks of sand lime model material the testing was performed using a true triaxial system tts developed by the authors the results show strain hardening strain softening and plastic behaviour in the simulated rock mass specimens depending upon joint geometry and stress state expressions are suggested to estimate post peak modulus in triaxial and true triaxial stress conditions finally a zonation table is proposed to assess the strain hardening softening and plasticity behaviour of a rock mass material with the help of joint geometry and confining stress conditions at site

influence of the sea ice thickness distribution on polar climate in ccsm3 abstract the sea ice simulation of the community climate system model version 3 ccsm3 t42 gx1 and t85 gx1 control simulations is presented and the influence of the parameterized sea ice thickness distribution itd on polar climate conditions is examined this includes an analysis of the change in mean climate conditions and simulated sea ice feedbacks when an itd is included it is found that including a representation of the subgrid scale itd results in larger ice growth rates and thicker sea ice these larger growth rates represent a higher heat loss from the ocean ice column to the atmosphere resulting in warmer surface conditions ocean circulation most notably in the southern hemisphere is also modified by the itd because of the influence of enhanced high latitude ice formation on the ocean buoyancy flux and resulting deep water formation changes in atmospheric circulation also result again most notably in the southern hemisphere there are indications that the itd also modifies simulated sea

thickness and density of snow covered sea ice and hydrostatic equilibrium assumption from in situ measurements in fram strait the barents sea and the svalbard coast modern satellite measurements of sea ice thickness are based on altimeter measurements of the difference in elevation between the snow or ice surface and the local sea surface for retrieval of sea ice thickness it is assumed that the ice is in hydrostatic equilibrium and that the snow load on the ice and the density of the sea ice and sea water are known this study presents data from in situ sea ice thickness drillings and snow and ice density measurements from fram strait the barents sea and the svalbard coast in the european arctic the error in the altimetry ice thickness products is assessed based on the spatial variability of snow and ice density and snow thickness data ice thickness uncertainty related to snow depth was found to be 40 cm radar altimeter and 90 cm laser altimeter while uncertainty related to ice density is 25 cm for both techniques the assumption of hydrostatic equilibrium at the scales of the measurements 10 100 m was found to hold better in the case of level landfast ice near svalbard than for fram strait drift ice which consists of mixed ice types where the deviation between the calculated and measured ice thicknesses was on average 0 5 m

spring snow conditions on arctic sea ice north of svalbard during the norwegian young sea ice n ice2015 expedition snow is crucial over sea ice due to its conflicting role in reflecting the incoming solar energy and reducing the heat transfer so that its temporal and spatial variability are important to estimate during the norwegian young sea ice n ice2015 campaign snow physical properties and variability were examined and results from april until mid june 2015 are presented here overall the snow thickness was about 20 cm higher than the climatology for second year ice with an average of 55 27 cm and 32 20 cm on first year ice the average density was 350 400 kg m 3 in spring with higher values in june due to melting due to flooding in march larger variability in snow water equivalent was observed however the snow structure was quite homogeneous in spring due to warmer weather and lower amount of storms passing over the field camp the snow was mostly consisted of wind slab faceted and depth hoar type crystals with occasional fresh snow these observations highlight the more dynamic character of evolution of snow properties over sea ice compared to previous observations due to more variable sea ice and weather conditions in this area the snowpack was isothermal as early as 10 june with the first onset of melt clearly identified in early june based on our observations we estimate than snow could be accurately represented by a three to four layers modeling approach in order to better consider the high variability of snow thickness and density together with the rapid metamorphose of the snow in springtime

a shear strength model for anisotropic blocky rock masses with persistent joints abstract the mohr coulomb mc shear strength parameters cohesion c and angle of friction are required in numerical models currently the geological strength index gsi system has been widely used for estimating shear strength of blocky rock masses in rock engineering however the gsi system does not include the effect of joint orientation on the mechanical properties of a rock mass which means that the shear strength model cannot reflect anisotropic rock mass strength behavior caused by joint orientation in this research udec based synthetic rock mass models which are calibrated by experimental data are adopted to study the effect of joint orientation on the shear strength of blocky rock masses with two perpendicular joint sets the values of cohesion c and angle of friction estimated from the numerical simulation are compared with those calculated from the empirical shear strength models based on the gsi system comparison of the results shows that the existing empirical model overestimates the shear strength of rock mass when 10

ice thickness in the arctic ocean the statistical reliability of experimental data the statistical reliability of ice thickness distributions derived from submarine sonar data sets of finite length is examined focusing on the standard error eh l in the mean ice draft h derived from a record of length l km this is important in assessing the significance or otherwise of quoted temporal or spatial differences in mean ice draft estimates for eh 50 are derived from four different submarine surveys each of which involved repeated sampling of apparently homogeneous ice fields values ranged from 7 18 to 15 29 of the mean for climate related comparisons of data sets from different years in the same location a value of 12 75 is recommended derived from data gathered at the north pole this value is used to reassess the significance of published data on ice draft variability quoted variability at the north pole over the 1977 1990 period is found to be not statistically significant but a difference in area averaged ice draft over the eurasian basin between 1976 and 1987 remains highly significant using hitherto unreported 1987 data from the north pole area the statistical variability of other parameters of the ice cover is examined the frequency of lead occurrence the width of leads the fractional cover of smooth ice and the frequency of keel occurrence all show standard errors of 22 24 in their mean values while mean keel draft has a 4 error all over a 50 km track length finally unreported 1987 data for an area extending from the pole to 72 n along the prime meridian and the east greenland shelf break are examined in 1 bins using eh l to assess the significance of variations in the mean a statistically significant decline in mean ice draft is observed starting at 86 n and continuing to 72 n a linear regression gives a thinning rate of 0 22 m deg the decline within the arctic basin itself is tentatively ascribed to a mixture of under ice melt and mixing of ice types since data on young ice occurrence show that divergence did not occur north of fram strait

validating icesat over thick sea ice in the northern canada basin only in the past eight years has the feasibility of using satellite borne altimeters to estimate sea ice freeboard and thickness been demonstrated and these estimates still have uncertainties primarily associated with limited knowledge of snow loading on sea ice because accurate estimates of arctic wide sea ice thickness and volume are fundamental inputs to global climate models validation of satellite derived thickness estimates using independent data is required a detailed assessment of freeboard retrieved by the geoscience laser altimeter system glas aboard the ice cloud and land elevation satellite has been carried out using high resolution laser altimetry from the national aeronautics and space administration s airborne topographic mapper atm the delay doppler radar altimeter and digital photography collected along a 300 km segment of sea ice in the canada basin exploiting the repeat coverage of the aircraft flight line a correction was applied to glas footprint geolocations to adjust for sea ice drift that occurred during the time between satellite and aircraft acquisitions comparisons of glas and atm measurements over sea ice show excellent agreement about a 0 00 m mean with no apparent bias between data sets freeboard estimates were examined using data from glas and atm independently employing measurements over refrozen leads to estimate local sea surface heights sshs the results demonstrate the sensitivity of freeboard and thickness calculations to an accurate estimation of local ssh snow depth derived by differencing laser and radar data was combined with the freeboard estimates to yield a mean sea ice thickness of 5 5 m over a 250 km subsection of the flight track

sea ice albedo climate feedback mechanism abstract the sea ice albedo feedback mechanism over the arctic ocean multiyear sea ice is investigated by conducting a series of experiments using several one dimensional models of the coupled sea ice atmosphere system in its simplest form ice albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature further decreasing the areal cover of snow and ice it is shown that the sea ice albedo feedback can operate even in multiyear pack ice without the disappearance of this ice associated with internal processes occurring within the multiyear ice pack e g duration of the snow cover ice thickness ice distribution lead fraction and melt pond characteristics the strength of the ice albedo feedback mechanism is compared for several different thermodynamic sea ice models a new model that includes ice thickness distribution the ebert and curry model the maykut and untersteiner model and the semtner level 3 an

albitization and quartz dissolution in paleoproterozoic metagranite central sweden implications for the disposal of spent nuclear fuel in a deep geological repository hydrothermal alteration resulting in albitization and quartz dissolution has been identified in paleoproterozoic metagranites down to 1000 m elevation at forsmark sweden the alteration features were discovered during investigations to locate a site for the disposal of spent nuclear fuel in a deep geological repository in general albitization occurs extensively but it is also observed locally adjacent to minor intrusive bodies of amphibolite the altered rocks show a marked decrease in k feldspar and an increase in quartz relative to the unaltered equivalents resulting in an epitonalitic composition plagioclase is metamorphic in character and generally richer in albite than in the unaltered rocks it is inferred that albitization was triggered by the input of basic or intermediate melts into the crust during igneous activity close to the peak of regional metamorphism at 1 87 1 86 ga the mineralogy of the epitonalites gives rise to an increased thermal conductivity and thereby a positive influence for the design and safety of a deep geological repository for spent nuclear fuel however the increased frequency of low conductive amphibolite in the albitized volumes consistent with the proposed mechanism for alteration gives a negative influence in sharp contrast to the albitization a majority of the occurrences of quartz dissolution which resulted in the formation of episyenite are located along fracture zones quartz dissolution took place between or after 1 8 1 7 ga when the bedrock was able to respond to deformation in a brittle manner most of the vugs left after the removal of quartz are to a variable extent refilled by hydrothermal assemblages including quartz albite k feldspar hematite chlorite and calcite the geometry and spatial distribution of episyenite argue against an extreme fluid rock ratio and it is inferred that the fluids had at least a moderate salinity with a temperature in excess of 300 degrees c the dissolution process was promoted by the generation of secondary permeability localized in columnar or pipe like volumes the close spatial connection to fracture zones provides a basis to avoid bedrock affected by this type of alteration and thereby reduce the negative mechanical and hydrogeological aspects for a deep geological repository c 2012 elsevier b v all rights reserved

sea ice topography of the arctic ocean in the region 70 degrees w to 25 degrees e in october 1976 a cooperative experiment was made to survey the sea ice topography in the european sector of the arctic ocean h m submarine sovereign acquired 4000 km of ice draft data by using an upward looking sonar while a canadian forces aircraft flew along the submarine s track and acquired 2200 km of ice elevation data by using a laser profilometer the two types of profile were processed in corresponding 100 km section lengths and the following statistical analyses and comparisons were made i probability density functions o f ice draft and elevation each distribution shows a peak for young ice and for undeformed multi year ice at large ice thicknesses the distributions take the analytical form of a negative exponential the mean drafts enable two distinct geographical ice regimes to be identified there is an offshore zone of very heavy pressure ridging extending up to 400 km from the coasts of ellesmere island and of north greenland with mean ice draft in the range 5 0 to 7 5 m while out in the central arctic ocean the mean ice draft is lower 3 9 5 1 m and the characteristics of the ice cover remain homogeneous over a length scale of 1000 km the transition between the two regimes is abrupt taking place in less than 25 km data from the same part of the central arctic taken in march 1971 showed a mean ice draft 0 3 m lower while data from the central beaufort sea showed a mean draft more than 0 8 m lower ii level ice distributions ice with a local gradient of less than 1 in 40 was defined as level ice and used as an indicator of the quantity and thickness distribution of undeformed i e thermodynamically grown ice in the arctic ocean the distribution has a mode at 3 0 3 1 m draft and level ice percentages are in the range 30 40 bottom side and 70 80 top side in the offshore zone and 45 55 bottom and 85 95 top in the central arctic thus about half of the arctic ice cover consists of deformed ice iii pressure ridge spacings the spacings of ridge keels fit a negative exponential distribution characteristic of randomness except at close spacings where there is a deficit of keels explained as a geometrical effect and at very large spacings where there is an excess due to the contribution of polynyas the distribution of sail spacings exhibits these two effects but also differs from a random distribution at moderate sail separations iv ridge elevations and drafts keel drafts fit a law of form p h d oc exp ah 2 d h except for an excess of keels at drafts beyond 20 m there is a positive correlation between mean keel draft and keel frequency there are 3 5 4 5 keels per kilometre with draft exceeding 9 m in the offshore zone and 2 3 in the central arctic sail elevations fit a law of form p h d h x exp a h d h with a positive correlation between mean sail elevation and sail frequency the sail elevation and ice elevation distributions can be related by assuming that all thick ice is contained in pressure ridges of triangular cross section v keel sail comparison for the 21 corresponding 100 km sections there are positive correlations between mean sail height and mean keel draft and between keel frequency and sail frequency from these it is possible to convert a sail distribution computed from a laser profile into a keel distribution enabling sea ice bulk characteristics to be derived from airborne surveys alone vi leads and polynyas a lead was defined as a continuous sequence of depth points greater than 5 m long and not exceeding 1 m draft the number density n d of leads per kilometre of width d m fits the power law n d 15 d 2 exceptionally wide leads were concentrated in the offshore zone and in the marginal ice zone close to the open water of the greenland sea

investigation of mechanical properties of jointed granite under compression using lattice spring based synthetic rock mass modeling approach abstract joint waviness is one of the important parameters of joint that need to be considered in civil and mining engineering design of structures built in or on jointed rock masses however this parameter is often overlooked by designers in this study the mechanical properties of laboratory scale jointed granite with both planar and non planar joints of different joint configurations are investigated using the lattice spring based synthetic rock mass ls srm modeling approach jointed granite models are calibrated using the laboratory test results and the calibrated lattice model parameters are used to perform both conventional triaxial and true triaxial compression tests in addition the influences of joint orientation intensity and persistence on the strength and deformability of jointed granite with both planar and non planar joints are investigated the simulation results show that the strength and deformation modulus of the jointed rock decrease with the increase of joint intensity and persistence the strength and deformation modulus of the jointed rock are higher for the ones with non planar joints under the true triaxial loading condition the strength and deformation modulus of the jointed granite depend strongly on the magnitude and orientation of the intermediate principal stress

metasomatic albitites and related biotite rich schists from a low pressure polymetamorphic terrane snake creek anticline mount isa inlier north eastern australia microstructures and p t d paths rocks of the snake creek anticline are mainly pelitic schists psammitic schists and quartzites that were metamorphosed during multiple high t low p events extending from d1 to d5 with the metamorphic peak occurring late to post d3 albitites are widespread but are concentrated in five areas they are typically fine to medium grained and consist of albite with or without combinations of quartz biotite staurolite cordierite garnet andalusite sillimanite kyanite gedrite and tourmaline from the presence or absence of albite inclusions in porphyroblasts the albitites are interpreted as forming early in the d3 event as a result of infiltration of external fluids psammitic schists and quartzites were preferentially altered but pelitic schists were also albitized in localities where the alteration was more extreme with the replacement of muscovite total and the replacement of quartz and biotite variable structural controls on albitization include fracturing and syn d3 shear zones in fold hinges biotite schists with abundant porphyroblasts combinations of staurolite garnet andalusite and cordierite occur adjacent to albitites and it is argued that they formed by the addition of fe and mg sourced from the albitites in several albitite rich areas cordierite grew early in d3 and was partly or entirely replaced during or after d3 by combinations of biotite andalusite tourmaline staurolite and sillimanite a postulated p t d path involved an increase in pressure with or without a decrease in temperature subsequent to early d3 albitization followed by an increase in temperature up to the metamorphic peak late d3 to early d4 the metamorphism was contemporary in part with the emplacement of the williams batholith c 1550 1500 ma which probably supplied the na rich fluids

comparison of coincident snow freeboard and sea ice thickness profiles derived from helicopter borne laser altimetry and electromagnetic induction sounding 1 sea ice thickness plays a critical role in global climate change but it cannot be measured directly from space alternatively sea ice freeboard is measured and converted to sea ice thickness with assumptions made for snow depth and snow ice densities this paper investigates the relationship between snow freeboard ice freeboard plus snow and total thickness ice thickness plus snow and addresses the uncertainties that arise from the unknown snow depth and snow ice densities a unique data set of coincident measurements of snow freeboard and total thickness was collected in the arctic and antarctic snow freeboard was determined by laser altimetry and total thickness was determined by electromagnetic induction with a helicopter borne instrument obtained total thickness snow freeboard ratios range from 2 to 12 in the arctic and from 2 to 8 in the antarctic the principal finding is that the ratios vary greatly within each region and a fixed ratio per profile should not be used as this can induce incorrect ice thicknesses the ratio uncertainties can induce a relative thickness error of 5 4 and 4 9 in the first year and multiyear ice mode additionally the coincident measurements allow the calculation of snow depth that can be used to densify existing in situ measurements to assess accuracy calculated snow depths were compared to in situ measurements and agree within 5 cm this increases if measurements and calculations differ spatially the method of deriving snow freeboard from laser altimetry is briefly described and the variability of the total thickness snow freeboard ratio is shown for one profile in the lincoln sea and one in the weddell sea

practical determination of mechanical design parameters of intact rock considering scale effect as a rule the change in mechanical properties of rock by specimen size is regarded as scale effect a rock mass basically consists of two components intact rock and discontinuities each of which has different scale effects in order to numerically analyze the behavior of discontinuous rock masses sufficient mechanical properties must be determined not only for discontinuities but also for intact rock taking into consideration the different scale effects this paper reviews the scale effect on strength and deformation characteristics of intact rock and also discusses the possibility of using standard specimens to estimate strength and deformation characteristics of actual scale rock finally we propose an adequate method for the practical determination of mechanical design parameters based on the above discussions

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

critical role of snow on sea ice growth in the atlantic sector of the arctic ocean during the norwegian young sea ice n ice2015 campaign in early 2015 a deep snow pack was observed almost double the climatology for the region north of svalbard there were significant amounts of snow ice in second year ice syi while much less in first year ice fyi here we use a 1 d snow ice thermodynamic model forced with reanalyses to show that snow ice contributes to thickness growth of syi in absence of any bottom growth due to the thick snow growth of fyi is tightly controlled by the timing of growth onset relative to precipitation events a later growth onset can be favorable for fyi growth due to less snow accumulation which limits snow ice formation we surmise these findings are related to a phenomenon in the atlantic sector of the arctic where frequent storm events bring heavy precipitation during autumn and winter in a region with a thinning ice cover

large scale surveys of snow depth on arctic sea ice from operation icebridge 1 we show the first results of a large scale survey of snow depth on arctic sea ice from nasa s operation icebridge snow radar system for the 2009 season and compare the data to climatological snow depth values established over the 1954 1991 time period for multiyear ice the mean radar derived snow depth is 33 1 cm and the corresponding mean climatological snow depth is 33 4 cm the small mean difference suggests consistency between contemporary estimates of snow depth with the historical climatology for the multiyear ice region of the arctic a 16 5 cm mean difference climatology minus radar is observed for first year ice areas suggesting that the increasingly seasonal sea ice cover of the arctic ocean has led to an overall loss of snow as the region has transitioned away from a dominantly multiyear ice cover

a method to automatically determine sea level for referencing snow freeboards and computing sea ice thicknesses from nasa icebridge airborne lidar abstract the nasa icebridge flights have obtained critical observations for earth s polar ice since icesat stopped collecting data in 2009 this study develops an automatic method in processing icebridge airborne topographic mapper atm altimeter l1b data one elevation per 3 4 m horizontally to derive a local sea level height for referencing snow freeboards and then computing sea ice thicknesses four 30 km l1b profiles a b c and d flown on october 21 2009 over the bellingshausen sea in antarctica are selected the local sea level reference is first obtained by visual examination of atm l1b heights over leads or thin ice identified on images simultaneously acquired from the digital mapping system camera called manual selection this sea level reference is then used as ground truth to validate sea level heights derived by automatic calculations using five thresholds of 2 1 0 5 0 2 and 0 1 of the lowest l1b data the l1b 0 2 method gives a similar sea level height as from the l1b manual selection by mean absolute difference of 0 01 0 06 m the sea level heights demonstrate a near linear gradient of 0 01 m km to 0 03 m km within each 30 km l1b profile along the flight track from section a to d the resulting mean snow freeboards are 0 59 m 0 67 m 0 53 m and 0 60 m on sections a b c and d respectively three empirical equations and the buoyancy equation with zero ice freeboard assumption all give similar statistics in ice thickness estimation with mean ice thicknesses of 1 91 m for section a 2 16 m for b 1 76 m for c and 1 94 m for d the sea level over leads cannot be accurately resolved from the atm l2 data 60 m x 80 m horizontal averaging however by using a sea level reference obtained from the l1b data the atm l2 data can achieve reasonable ice thickness estimates with mean absolute difference of only 0 10 m compared to thickness derived from the l1b data

considerations of the dilatancy angle in rocks and rock masses the present study responds to the poor treatment given to dilatancy in classical rock mechanics post failure problems such as tunnel or mine pillar design a comprehensive review of the literature and observations in regard to published test results would indicate that dilatancy is highly dependent both on the plasticity already experienced by the material and confining stress moreover it also appears that scale may play a non negligible role in our article we provide a detailed analysis of published test data with a view to proposing a sufficiently significant but conveniently simple formulation of the dilatancy angle that reflects these dependencies and that can be readily implemented in numerical codes the model is then tested demonstrating that it is capable of representing rock sample strain behaviour in compressive tests finally the model is applied to the resolution of ground reaction curves for tunnels in poor to average quality rock masses showing a good correlation with results obtained using practical rock engineering techniques r 2005 elsevier ltd all rights reserved

arctic ocean gravity geoid and sea ice freeboard heights from icesat and grace 1 icesat laser measurements provide a high resolution mapping of the sea ice surface of the arctic ocean which can be inverted to determine gravity anomalies and sea ice freeboard heights by a lowest level filtering scheme in this paper we use updated terrestrial gravity data from the arctic gravity project in combination with grace gravity field models to derive an improved arctic geoid model this model is then used to convert icesat measurements to sea ice freeboard heights with a coarse lowest level surface method the derived freeboard heights show a good qualitative agreement to the coverage of multi year sea ice however comparison to an airborne lidar underflight north of greenland shows that the lowest level filtering scheme may introduce a bias we finally use the icesat and grace results to derive new gravity anomalies by fourier inversion the satellite only gravity field shows all major tectonic features of the arctic ocean and has an accuracy of 6 mgal compared to recent airborne gravity data illustrating the usefulness of icesat data for gravity field determination

dilation in granite during servo controlled triaxial strength tests abstract we investigated the stress strain response of three different intact granitic rocks to do this a press with servo controlled loading was modified to control the confining pressure in triaxial tests and to measure the volume of hydraulic fluid displaced from hoek s triaxial cell so that this volume could be related to volumetric strain in the rock sample a series of unconfined and confined compressive tests were performed on the rock samples and results were plotted analysed and interpreted regarding the most relevant parameters including elastic strength and post failure parameters with special attention paid to the dilation angle our main conclusions refer to the capability to investigate consistent post failure rock properties by means of servo controlled loading set ups which we plan to improve in the future the dilation angle of granite was captured with all the tested granites showing similar behaviour trends that fit reasonably well with recently developed theories on plastic shear strain and confinement stress dependent dilation and that are analogous to those observed for other hard rocks

hydrothermal alteration of late to post tectonic lyon mountain granitic gneiss adirondack mountains new york origin of quartz sillimanite segregations quartz albite lithologies and associated kiruna type low ti fe oxide deposits quartz sillimanite segregations quartz albite lithologies ab95 98 and kiruna type low ti iron oxide deposits are associated with late to post tectonic c 1055 ma leucogranites of lyon mountain gneiss lmg in the adirondack mountains new york state most recent interpretations of these controversial features which are global in occurrence favour hydrothermal origins in agreement with results presented here field relations document that quartz sillimanite veins and nodules cut and therefore post date emplacement of host lmg leucogranites veins occur in oriented fracture networks and aligned trains of nodules are interpreted as disrupted early veins late dykes of leucogranite cut veins and nodules demonstrating formation prior to terminal magmatism veins and nodules consist of sillimanite surrounded by quartz that commonly embays wall rock feldspar indicating leaching of na and k from lmg feldspar by acidic hydrothermal fluids subsequent and repeated ductile flow disrupted earlier veins into nodular fragments but produced little grain shape fabric geochemical and petrographic studies of quartz albite rock indicate that it formed through metasomatic replacement albitization of lmg microperthite by sodic hydrothermal fluids that resulted in diagnostic checkerboard albite low ti iron oxide ores are commonly associated with the quartz albite sub unit and it is proposed that hydrothermal fluids related to albitization transported fe as well the regional extent of sodic alteration suggests large quantities of surface derived hydrothermal fluids fluid inclusion and oxygen isotope data are consistent with high temperature regionally extensive fluids consisting primarily of evolved surface derived brines enriched in na and cl quartz sillimanite veins and nodules which are significantly more localised phenomena and require acidic fluids were most likely formed from local magmatic fluids in the crystallizing carapaces of lmg plutons

vapor transport grain growth and depth hoar development in the subarctic snow measurements from the subarctic snowpack are used to explore the relationship between grain growth and vapor flow the fundamental processes of dry snow metamorphism due to extreme temperature gradients the subarctic pack undergoes extensive depth hoar metamorphism by the end of the winter a five layered structure with a pronounced weak layer near the base of the snow evolves grain size increases by a factor of 2 3 while the number of grains per unit mass decreases by a factor of 10 observed growth rates require significant net inter particle vapor fluxes stable isotope ratios show that there are also significant net layer to layer vapor fluxes soil moisture enters the base of the pack and mixes with the bottom 10 cm of snow while isotopically light water vapor fractionates from the basal layer and is deposited up to 50 cm higher in the pack end of winter density profiles for snow on the ground compared with snow on tables indicate the net layer to layer vapor flux averages 6 x 10 7 kg m 2 s 1 though detailed measurements show the net flux is episodic and varies with time and height in the pack with peak net fluxes ten times higher than average a model driven by observed temperature profiles reproduces the layer to layer flux pattern and predicts the observed weak layer at the base of the snow calculated layer to layer vapor fluxes are ten times higher than inter particle fluxes which implies that depth hoar grain growth is limited by factors other than the vapor supply this finding suggests that gain and loss of water molecules due to sublimation from grains takes place at a rate many times higher than the rate at which grains grow and it explains why grains can metamorphose into different forms so readily

energy evolution a new perspective on the failure mechanism of purplish red mudstones from the three gorges reservoir area china abstract purplish red mudstones from section four of the badong formation are broadly distributed in the three gorges reservoir area tgra and exhibit special characteristics distinct from the mudstones elsewhere this paper investigates the failure mechanism of such mudstones from a new perspective of energy evolution initially the complete failure process under three stress paths i e loading unloading and cyclic loading unloading is monitored and the related data are acquired methods to estimate the energy parameters i e total absorption energy tae cumulative dissipation energy cde and elastic strain energy ese under cyclic loading unloading conditions are presented two new parameters namely the proportion of cde pcde and proportion of elastic energy dissipation peed are introduced using the data the mechanical properties and energy properties are analyzed and the energy evolution is revealed the results show that the failure mechanism under the three stress paths is different from an energy evolution perspective the mechanical parameters deteriorate under unloading in comparison with those under loading the increase in the cde is similar to that in the tae and the ese strain relationship features a step shaped rise for cyclic loading unloading the tae and the pcde nearly linearly increase with cycle times this work provides a new perspective on the failure mechanism of the purplish red mudstones from the tgra

estimation of rock mass deformation modulus and strength of jointed hard rock masses using the gsi system abstract rock mass characterization is required for many applications in rock engineering practice including excavation design support design stope design amongst others for these purposes it is necessary to obtain design input parameters such as deformation moduli and strength parameters for numerical modeling although such parameters can ultimately be determined from in situ tests at the preliminary design stage where access to underground is limited the practical way to obtain these parameters is to apply a rock mass classification system to characterize the rock mass and estimate the rock mass properties over the years many classification systems such as rqd rock mass rating q and geological strength index gsi systems have been developed amongst them the q system is widely used for rock support system design and the gsi system is used for estimating design parameters the gsi system is the only rock mass classification system that is directly linked to engineering parameters such as mohr coulomb hoek brown strength parameters or rock mass modulus however the application of the existing gsi system is hindered by the facts that the use of the system is to some extent subjective and requires long term experience in the present study a quantitative approach to assist in the use of the gsi system is presented it employs the block volume and a joint condition factor as quantitative characterization factors the approach is built on the linkage between descriptive geological terms and measurable field parameters such as joint spacing and joint roughness the newly developed approach adds quantitative means to facilitate use of the system especially by inexperienced engineers the gsi system is applied to characterize the jointed rock masses at two underground powerhouse cavern sites in japan gsi values are obtained from block volume and joint condition factor which in turn are determined from site construction documents and field mapping data based on gsi values and intact rock strength properties equivalent mohr coulomb strength parameters and elastic modulus of the jointed rock mass are calculated and compared to in situ test results the point estimate method is implemented to approximate the mean and variance of the mechanical properties of the jointed rock masses it is seen that both the means and variances of strength and deformation parameters predicted from the gsi system are in good agreement with field test data

satellite based estimates of sea ice volume flux through fram strait sea ice volume fluxes through fram strait arctic ocean are estimated for the two icesat measurement periods in february march and october november 2003 by combining sea ice area fluxes determined from space borne microwave observations with estimates of the sea ice thickness distribution inferred from measurements of icesat s geoscience laser altimeter system glas instrument the thickness is derived from icesat data by converting its surface elevation measurements into an ice freeboard estimate combined with prior information about ice density and snow depth and density the freeboard is converted into ice thickness uncertainties in freeboard estimates due to geoid model errors are reduced through the use of the recent geoid from the arctic gravity project missing information about the ocean circulation and ocean tides is approximated locally by interpolating the sea surface height linearly between open leads meridional ice volume fluxes estimated for 798 n using ice drift observed by amsr e quikscat amount to 168 km 3 236 km 3 and 62 km 3 77 km 3 for 30 day periods in february march and october november 2003 respectively these values lie in the range of previous results from similar studies but are considerably smaller than the average ice flux during the 1990s most likely because of a smaller ice drift speed during 2003

icesat measurements of sea ice freeboard and estimates of sea ice thickness in the weddell sea 1 sea ice freeboard heights in the weddell sea of antarctica are derived from the ice cloud and land elevation satellite icesat laser altimeter measurements which have a unique range precision to flat surfaces of 2 cm within 70 m footprints spaced at 172 m along track although elevations of flat surfaces can be obtained to an accuracy of 10 cm 1s per footprint direct determination of freeboard heights is precluded by errors in knowledge of the geoid and temporal variability of the ocean surface therefore freeboards are determined relative to an ocean reference level detected over areas of open water and very thin ice within the sea ice pack using an along track filtering method the open water thin ice selections show good agreement in the combined analysis of icesat segments and envisat synthetic aperture radar sar imagery the average residual between the icesat measured ocean level and the egm96 geoid is 1 4 m estimates of snow depth on the sea ice from amsr e passive microwave data along with nominal densities of snow water and sea ice are used to estimate sea ice thickness four periods of icesat data in may june fall and october november late winter of 2004 and 2005 between longitudes 298e and 360e are analyzed in the fall the mean freeboards are 0 28 m in 2004 and 0 29 m in 2005 and the mean thicknesses are 1 33 m in 2004 and 1 52 m in 2005 in late winter the freeboards grew to 0 37 m in 2004 and 0 35 in 2005 and the thicknesses grew to 2 23 m in 2004 and 2 31 m in 2005 the interannual differences in freeboard are small and the larger interannual change in estimated thickness mainly represents differences in the snow depth estimates seasonal changes in the spatial patterns of freeboard and thickness over the 4 months correlate with the expected circulation of sea ice in the weddell sea as indicated by sea ice velocity fields

biotite and muscovite 40ar 39ar geochronological constraints on the post svecofennian tectonothermal evolution forsmark site central sweden in order to characterize the post svecofennian tectonothermal evolution of the fennoscandian shield 40ar 39ar biotite and some 40ar 39ar muscovite geochronological data are reported from a total of 30 surface outcrop and 1000 m long borehole samples at forsmark central sweden the thirteen surface samples were collected across three branches of a major wnw to nw trending system of deformation zones whereas the boreholes were drilled within a tectonic lens in between two of these zones the 40ar 39ar biotite ages indicate that the present erosion surface in central sweden cooled below 300 c at 1 73 1 66 ga and that the rocks could respond to stress by brittle deformation between 1 8 and 1 7 ga the variation in surface ages is suggested to be due to faulting along the large wnw to nw trending deformation zones following the establishment of a sub cambrian peneplain the minor variation of ages within a single crustal block may be due to disturbance along ene to nne trending fracture zones possible cooling paths derived from 40ar 39ar hornblende muscovite and biotite ages were calculated for the time interval from 1 80 to 1 66 ga when the area cooled from 500 c to 300 c between 1 70 and 1 64 ga uplift rates of c 22 m m y were calculated from borehole 40ar 39ar biotite data tectonothermal histories inferred from the combined cooling and uplift rates are related to simple slow cooling after the svecofennian orogeny to crustal movement in response to far field effects of c 1 7 ga orogenic activity further to the west or to a combination of these possibilities less

an assessment of state of the art mean sea surface and geoid models of the arctic ocean implications for sea ice freeboard retrieval state of the art arctic ocean mean sea surface mss models and global geoid models ggms are used to support sea ice freeboard estimation from satellite altimeters as well as in oceanographic studies such as mapping sea level anomalies and mean dynamic ocean topography however errors in a given model in the high frequency domain primarily due to unresolved gravity features can result in errors in the estimated along track freeboard these errors are exacerbated in areas with a sparse lead distribution in consolidated ice pack conditions additionally model errors can impact ocean geostrophic currents derived from satellite altimeter data while remaining biases in these models may impact longer term multi sensor oceanographic time series of sea level change in the arctic this study focuses on an assessment of five state of the art arctic mss models ucl13 04 dtu15 13 10 and a commonly used ggm egm2008 we describe errors due to unresolved gravity features inter satellite biases and remaining satellite orbit errors and their impact on the derivation of sea ice freeboard the latest mss models incorporating cryosat 2 sea surface height measurements show improved definition of gravity features such as the gakkel ridge the standard deviation between models ranges 0 03 0 25 m the impact of remaining mss ggm errors on freeboard retrieval can reach several decimeters in parts of the arctic while the maximum observed freeboard difference found in the central arctic was 0 59 m ucl13 mss minus egm2008 ggm the standard deviation in freeboard differences is 0 03 0 06 m

taking a look at both sides of the ice comparison of ice thickness and drift speed as observed from moored airborne and shore based instruments near barrow alaska data from the seasonal ice zone observing network sizonet acquired near barrow alaska during the 2009 10 ice season allow novel comparisons between measurements of ice thickness and velocity an airborne electromagnetic survey that passed over a moored ice profiling sonar ips provided coincident independent measurements of total ice and snow thickness and ice draft at a scale of 10 km once differences in sampling footprint size are accounted for we reconcile the respective probability distributions and estimate the thickness of level sea ice at 1 48 0 1 m with a snow depth of 0 12 0 07 m we also complete what we believe is the first independent validation of radar derived ice velocities by comparing measurements from a coastal radar with those from an under ice acoustic doppler current profiler adcp after applying a median filter to reduce high frequency scatter in the radar derived data we find good agreement with the adcp bottom tracked ice velocities with increasing regulatory and operational needs for sea ice data including the number and thickness of pressure ridges coordinated observing networks such as sizonet can provide the means of reducing uncertainties inherent in individual datasets

empirical estimation of rock mass modulus the deformation modulus of a rock mass is an important input parameter in any analysis of rock mass behaviour that includes deformations field tests to determine this parameter directly are time consuming expensive and the reliability of the results of these tests is sometimes questionable consequently several authors have proposed empirical relationships for estimating the value of rock mass deformation modulus on the basis of classification schemes these relationships are reviewed and their limitations are discussed based on data from a large number of in situ measurements from china and taiwan a new relationship based upon a sigmoid function is proposed the properties of the intact rock as well as the effects of disturbance due to blast damage and or stress relaxation are also included in this new relationship