interpretation of slingram conductivity mapping in near surface geophysics using a single parameter fitting with 1d model1 electrical conductivity mapping is a prerequisite tool for hydrogeological or environmental studies its interpretation still remains qualitative but advantages can be expected from a quantitative approach however a full 3d interpretation is too laborious a task in comparison with the limited cost and time which are involved in the majority of such field studies it is then of value to define the situations where lateral variations are sufficiently smooth for a 1d model to describe correctly the underlying features for slingram conductivity measurements criteria allowing an approximate 1d inversion are defined these mainly consist of a limited rate of variation over three times the intercoil spacing in geological contexts where the weathering has generated a conductive intermediate layer between the underlying sound rock and the soil this processing can be applied to determine the thickness of the conductive layer from the apparent resistivity map when the other geoelectrical parameters are known the examples presented illustrate this application

layered and laterally constrained 2d inversion of resistivity data in a sedimentary environment quasi layered models often can represent the actual geology more accurately than smooth minimum structure models we present a 2d inversion scheme with lateral constraints and sharp boundaries lci for continuous resistivity data all data and models are inverted as one system producing layered solutions with laterally smooth transitions the models are regularized through lateral constraints that tie interface depths or thicknesses and resistivities of adjacent layers a priori information used to resolve ambiguities and to add for example geological information can be added at any point of the profile and migrates through the lateral constraints to parameters at adjacent sites similarly information from areas with well resolved parameters migrates through the constraints to help resolve areas with poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result a simple synthetic model proves the need for a quasilayered 2d inversion when compared with a traditional 2d minimum structure inversion a 2d minimum structure inversion produces models with spatially smooth resistivity transitions making identification of layer boundaries difficult a continuous vertical electrical sounding field example from sweden with a depression in the depth to bedrock supports the conclusions drawn from the synthetic example a till layer on top of the bedrock hidden in the traditional inversion result is identified using the 2d lci scheme furthermore the depth to the bedrock surface is easily identified for most of the profile with the 2d lci model which is not the case with the model from the traditional minimumstructure inversion

variability in categories of arctic sea ice in fram strait an attempt to quantify the temporal variability in the volume composition of arctic sea ice is presented categories of sea ice in the transpolar drift in fram strait are derived from monthly ice thickness distributions obtained by moored sonars 1990 2011 the inflection points on each side of the old ice modal peak are used to separate modal ice from ice which is thinner and thicker than ice in the modal range the volume composition is then quantified through the relative amount of ice belonging to each of the three categories thin modal and thick ice in the monthly ice thickness distributions the trend of thin ice was estimated to be negative at 8 8 per decade relative to the long term mean which was compensated for by increasing trends in modal and thick ice of 7 9 and 4 7 per decade respectively a 7 8 year cycle is apparent in the thin and thick ice records which may explain a loss of deformed ice since 2007 we also quantify how the categories contribute to the mean ice thickness over time thick predominantly deformed ice dominates the mean ice thickness constituting on average 66 of the total mean following the loss of deformed ice since 2007 the contribution of thick ice to the mean decreased from 75 to 52 at the end of the record thin deformed ice did not contribute to this reduction it was pressure ridges thicker than 5 m that were lost and hence caused the decrease in mean ice thickness

sea ice velocity in the fram strait monitored by moored instruments 1 the fram strait sea ice velocity was measured by means of a new method using moored doppler current meters in the period 1996 2000 almost 3 years of ice velocity observations near 79 n 5 w are analyzed the average southward ice velocity was 0 16 m s the correlation between the ice velocity and the cross strait sea level pressure slp difference was r 0 76 for daily means and r 0 79 for monthly means the same cross strait slp difference exhibits a positive trend since 1950 of 10 of the mean per decade by a simple linear model we compute mean sea ice area flux to 850 000 km2 year for the period 1950 2000 ice thickness monitored by means of upward looking sonars since 1990 is also discussed the combined data gave a monthly ice volume flux of 200 km3 during the last decade with no significant trend

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

can we extend local sea ice measurements to satellite scale an example from the n ice2015 expedition knowledge of arctic sea ice conditions is of great interest for arctic residents as well as for commercial usage and to study the effects of climate change information gained from analysis of satellite data contributes to this understanding in the course of using in situ data in combination with remotely sensed data the question of how representative local scale measurements are of a wider region may arise we compare in situ total sea ice thickness measurements from the norwegian young sea ice expedition in the area north of svalbard with airborne derived total sea ice thickness from electromagnetic soundings a segmented and classified synthetic aperture radar sar quad pol alos 2 palsar 2 satellite scene was grouped into three simplified ice classes the area fractions of the three classes are 11 2 thin 74 4 level and 14 4 deformed the area fractions of the simplified classes from ground and helicopter based measurements are comparable with those achieved from the sar data thus this study shows that there is potential for a stepwise upscaling from in situ to airborne to satellite data which allow us to assess whether in situ data collected are representative of a wider region as observed by satellites

the differential parameter method for multifrequency airborne resistivity mapping helicopter em resistivity mapping began to be accepted as a means of geologic mapping in the late 1970s the data were first displayed as plan maps and images some 10 years later sectional resistivity displays became available using the same pseudolayer half space resistivity algorithm developed by fraser and the new centroid depth algorithm developed by sengpiel known as sengpiel resistivity sections these resistivity depth images proved to be popular for the display of helicopter electromagnetic em data in conductive environments a limitation of the above resistivity and depth algorithms is that the resulting sengpiel section may imply that the depth of exploration of the em system is substantially less than is actually the case for example a target at depth may be expressed in the raw data but its appearance on the sengpiel section may be too shallow which is a problem with the depth algorithm or it may not even appear at all which is a problem with the resistivity algorithm an algorith

monitoring ice thickness in fram strait time series of ice thickness in fram strait are evaluated together with ice drift for estimation of the ice flux from the arctic ocean ice draft was measured from moored sonars every 4 min suggesting a nominal sampling interval of 30 m on the basis of these data the annual cycle of many statistics can be resolved the modal ice thickness shows a maximum of 3 15 m in may and a minimum in september of 2 43 m indicating an annual variation range of 0 72 m this compares with model results comprehensive drillings and most of the submarine observations during the last 2 3 decades indicating no significant long term ice thickness change this is also concurrent with the lack of significant temperature changes in the arctic ocean during the same period the mean ice thickness in the central core of the ice stream shows an annual amplitude of 1 m with a minimum in september of 2 25 m and a maximum in april may of 3 25 m the mean thickness of ice only open water excluded is 3 27 m and compares with 3 29 m which is the mean thickness of ice only from 17 submarine tracks in the arctic ocean 1960 1982 the mean annual ice export which is equal to the mean annual net production of ice in the arctic ocean is 2850 km 3 yr 1 for the period 1990 1996 this efflux shows significant variations from year to year with a minimum in 1990 1991 of 2050 km 3 yr 1 and a maximum in 1994 1995 of 4700 km 3 yr 1 this significant variation of nearly 130 is mainly caused by an increased atmospheric forcing and to a lesser degree by an increase in the annual mean ice thickness of 20 over the same period

the effect of structural porosity on the ablation of sea ice ridges 1 observations reveal that the decrease in ice thickness through melting in summer is much more rapid for ridges than for surrounding level ice a physical model that represents internal melting within ridge keels has been developed to explain this observed draft dependent ablation for first year pack ice in the beaufort sea the porous structure of a ridge keel permits percolation of a substantial fraction of the oncoming oceanic flow up to 20 for a feature with 30 porosity and 9 m draft the percolating flow delivers oceanic heat to a large surface area deep within the keel and increases melt rates relative to surrounding level ice by a factor of 5 when seawater temperatures are 0 18 degrees above freezing melt rates are sensitive to the internal geometry of ridges through keel porosity and block dimensions characteristics that vary widely between ridge features however the average rate of melting as a function of draft calculated for a realistic population of keels with average cross sectional shape and differing draft has the same draft dependence as the observations this concurrence suggests that the process of internal melting may be dominant in the ablation of ridged ice in addition internal melting during the summer may well hasten structural consolidation of surviving ridge keels through freezing during the following winter it appears that the evolution of the thickest ice within the arctic ice pack is dependent on the small scale structural characteristics of the ridged ice and its interaction with the upper layer of the ocean

decline in arctic sea ice thickness from submarine and icesat records 1958 2008 1 the decline of sea ice thickness in the arctic ocean from icesat 2003 2008 is placed in the context of estimates from 42 years of submarine records 1958 2000 described by rothrock et al 1999 2008 while the earlier 1999 work provides a longer historical record of the regional changes the latter offers a more refined analysis over a sizable portion of the arctic ocean supported by a much stronger and richer data set within the data release area dra of declassified submarine sonar measurements covering 38 of the arctic ocean the overall mean winter thickness of 3 64 m in 1980 can be compared to a 1 89 m mean during the last winter of the icesat record an astonishing decrease of 1 75 m in thickness between 1975 and 2000 the steepest rate of decrease is 0 08 m yr in 1990 compared to a slightly higher winter summer rate of 0 10 0 20 m yr in the five year icesat record 2003 2008 prior to 1997 ice extent in the dra was 90 during the summer minimum this can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to 55 during the record setting minimum in 2007 this combined analysis shows a long term trend of sea ice thinning over submarine and icesat records that span five decades

engineering properties of quartz mica schist quartz mica schist which is a highly anisotropic metamorphic rock usually presents a geotechnical challenge in construction projects to ensure a safe and economical design a comprehensive in situ and laboratory investigation scheme is necessary for projects to be built in quartz mica schist in this study such a comprehensive laboratory study of the engineering behavior of quartz mica schist has been carried out the p wave velocity tests tensile and uniaxial compressive strength tests and creep deformation tests conducted on specimens with differently oriented schistose planes all reveal the strong anisotropic characters of the rock the relevant crack initiation stress and crack damage stress analysis in uniaxial compression test which has not been previously applied to studying schistose rock has been performed in the present study when loading is parallel to schistose planes crack initiation stress and crack damage stress are lower than those in other loading directions as the compressive loading is applied parallel to schistose planes local tensile stresses are preferentially induced normal to the relatively weak schistose planes cracks are thus easier to develop than in any other loading directions since schistose plane orientation is one of the key factors to control the formation of macro cracks and hence failures of unloading test specimens these engineering geological characters should be taken into consideration in engineering design

riparian wetlands of the middle reach of the seine river france historical development investigation and present hydrologic functioning a case study along the middle reach of the seine river upstream from paris riparian wetlands that have been functioning for centuries first as a result of a succession of sedimentological hydrological processes and later of continuous management practices where the value of the wetlands has been acknowledged as well as their importance for the ecology here we present the results of a multidisciplinary research programme focused on this system with emphasis on its present hydrological functioning and on the tools used to understand and quantify it the major hydrological and geochemical processes that are active at present are reviewed but past processes are also described as well as the potential long term evolution of the system this study uses several innovative tools to investigate the wetlands and analyse them in space thermographic aerial survey and electromagnetic prospecting resulting in a map of clay layer thickness concerning the wetland hydrology water budgets established at different time scales several years one year a season illustrate the exchanges between the watershed the river and the wetland and water storage in the wetlands during flood events the results show how the upstream reservoirs built during the last 20 years presently control the preservation and functioning of downstream riparian wetlands monitoring and modelling of the hydrological functioning of one wetland site have made it possible to identify and quantify exchanges between the wetland especially in the unsaturated upper layer and its environment in situ measurements of denitrification rates in the wetland were used to make initial estimates of its nitrate elimination capacity

interpretation of shallow electromagnetic instruments resistivity and magnetic susceptibility measurements using rapid 1d 3d inversion we have developed an inversion process of electromagnetic induction emi data based on a two step approach with 1d inversion of the entire studied surface and a fast 3d inversion applied over limited areas this process is similar to that formerly used in resistivity prospection for the study of soil environmental engineering or archaeological explorations low frequency electromagnetic instruments referred to as slingram emi have highly useful specificities they are light are easy to move in the field and can simultaneously measure the ground s electric conductivity and magnetic susceptibility they have thus been used to map these properties over large surface areas within relatively short periods of time and at reasonable expense the possibility of combining several coil geometries has opened up the potential for multidepth techniques and systematic 1d inversion which are found to be sufficiently revealing to allow larger portions of surveyed areas to be analyzed in the targeted areas selected for 3d inversion the geometries of the 3d features and the resistivity and or susceptibility contrasts are determined this step is based on the method of moments where only 3d heterogeneities are meshed and only a small number of major characteristics such as contrast thickness width etc are sought we first applied this process to synthetic data then to data acquired at an experimental test site and finally to field cases the rapid 3d inversion complements the 1d inversion by solving a series of issues correction for the apparent anisotropy generated by the instrument configuration multiarched anomalies precise location of lateral changes and determination of the properties contrasts our inversion results highlighted the importance of the instrument geometry we also have determined that apparent magnetic susceptibility data can be more appropriate for the determination of the volume of man made features and can be highly complementary to conductivity data

joint inversion of em and magnetic data for near surface studies magnetic and electromagnetic measurements are influenced by magnetic susceptibility and thus are widely used in geophysical surveys for archeology or pedology to date the data inversion is performed separately a filtering process incorporating both types of data is presented here after testing the algorithm with synthetic data the algorithm is used in several case studies in archeological prospecting this approach presents two advantages establishing the presence of remanent magnetizations viscous or thermoremanent and achieving more refined depth analysis of the anomaly

thinning of arctic sea ice observed in fram strait 1990 2011 1 time series 1990 2011 of sea ice thickness observed by moored sonars in the transpolar drift in fram strait are examined contrasting the post 2007 years against the 1990s three remarkable changes in the monthly ice thickness distributions are highlighted 1 the thickness of old level ice modal thickness is reduced by 32 2 the old ice modal peak width is reduced by 25 and 3 the fraction of ridged ice thicker than 5 m is reduced by 50 the combined effect on the mean ice thickness is a reduction from an annual average of 3 0 m during the 1990s to 2 2 m during 2008 2011 most of the thinning took place after 2005 2006 while the old ice modal thickness and peak width show signs of recovery after 2008 the decreasing trend in fraction of ridged ice and mean ice thickness persists until the end of the record in 2011 the ice observed in fram strait carries an integrated signal of arctic change due to the advection of ice from many sites in the arctic based on concurrence in timing we conclude that much of the thinning quantified here is reflecting recent change in the age composition of the arctic ice cover toward younger ice the old level ice remains thin and as such the ice cover remains preconditioned for new summers of very low sea ice extent

time variability in the annual cycle of sea ice thickness in the transpolar drift the annual cycle of modal and mean sea ice thickness was derived from upward looking sonar ice thickness observations 1990 2011 in fram strait the average annual peak to trough amplitude of the mode of 0 54 m is superimposed on interannual variability with peak to trough amplitudes of 0 73 m on time scales of 6 8 years which again is superimposed on a long term trend of 0 55 m decade over the observation period the long term trend is stronger for april than for august the average months of maximum and minimum modal thickness as a result the annual peak to trough modal thickness amplitude was reduced by 30 between the 1990s and the 2000s the average annual peak to trough amplitude of the mean ice thickness of 1 20 m is also superimposed on interannual variability with as much as 0 97 m thickness change over only 3 years these two modes of variability are superimposed on a long term trend of 0 35 m decade through the entire data set in contrast to the modal thickness the long term trend is weaker for the average month of maximum mean thickness june than for the average month of minimum september therefore the annual peak to trough amplitude of the mean ice thickness increased by 14 between the 1990s and the 2000s

synoptic airborne thickness surveys reveal state of arctic sea ice cover 1 while summer arctic sea ice extent has decreased over the past three decades it is subject to large interannual and regional variations methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice thickness distribution to recent change limiting the ability to forecast sea ice change over the next decade we present results from a 2400 km long pan arctic airborne electromagnetic em ice thickness survey in april 2009 the first ever large scale em thickness dataset obtained by fixed wing aircraft over key regions of old ice in the arctic ocean between svalbard and alaska the data provide detailed insight into ice thickness distributions characteristic for the different regions comparison with previous em surveys shows that modal thicknesses of old ice had changed little since 2007 and remained within the expected range of natural variability

circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum september 2007 marked a record minimum in sea ice extent while there have been many studies published recently describing the minimum and its causes little is known about how the ice thickness has changed in the run up to and following the summer of 2007 using satellite radar altimetry data covering the arctic ocean up to 81 5 degrees north we show that the average winter sea ice thickness anomaly after the melt season of 2007 was 0 26 m below the 2002 2003 to 2007 2008 average more strikingly the western arctic anomaly was 0 49 m below the six year mean in the winter of 2007 2008 these results show no evidence of short term preconditioning through ice thinning between 2002 and 2007 but show that after the record minimum ice extent in 2007 the average ice thickness was reduced particularly in the western arctic citation giles k a s w laxon and a l ridout 2008 circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum geophys res lett 35 l22502 doi 10 1029 2008gl035710

a younger thinner arctic ice cover increased potential for rapid extensive sea ice loss 1 satellite derived estimates of sea ice age and thickness are combined to produce a proxy ice thickness record for 1982 to the present these data show that in addition to the well documented loss of perennial ice cover as a whole the amount of oldest and thickest ice within the remaining multiyear ice pack has declined significantly the oldest ice types have essentially disappeared and 58 of the multiyear ice now consists of relatively young 2 and 3 year old ice compared to 35 in the mid 1980s ice coverage in summer 2007 reached a record minimum with ice extent declining by 42 compared to conditions in the 1980s the much reduced extent of the oldest and thickest ice in combination with other factors such as ice transport that assist the ice albedo feedback by exposing more open water help explain this large and abrupt ice loss

the underside topography of sea ice over the continental shelf of the beaufort sea in the winter of 1990 a spatial section of draft across 348 km of sea ice was obtained by moored subsea sonars in the beaufort sea in the winter of 1990 the ice field was a mixture of first year and multiyear types with mean draft of the order of 3 m level ice of 0 to 4 m draft occupied approximately 50 of the section within this fraction draft values of 0 and 1 5 m were most common while at 2 to 3 m draft a noticeable contribution was made by rafted first year ice deformed ice was observed to a maximum draft of nearly 27 m keels within the section were identified using both the rayleigh criterion and a new criterion based on level ice both criteria defined exponentially distributed populations but with different e folding scales the observations revealed an ice cover whose statistical properties are consistent with other data from the periphery of the polar pack in the beaufort sea but which are much more severe than those of ice found in the seasonal ice zone only a few tens of kilometres to the south the cross sectional shape of individual keels was highly variable but on average the distribution of ice within a keel was an exponential function of draft the topography of both first year and old ice subsections of the data was fractal in character with a dimension of about 1 5 for both ice types the average mass of sea ice per unit area was estimated as 2540 2970 kg m 2 with 68 73 of this mass contributed by deformed ice the large uncertainties in these estimates arise because the porosity of keels and the burden of snow or melt water upon the ice are not known

the response of a three dimensional magnetic and conductive body in shallow depth electromagnetic prospecting summary the study of the abilities of an e m apparatus for shallow depth prospecting necessitates that we analyse the experimental data through theoretical modelling a 3 d model for a magnetic and a conductivity contrast is presented here applied to the slingram type sh3 case intercoil spacing equal to 1 5 m and frequency to 8 khz it shows that this apparatus is roughly equivalent to the classical wenner 1 m array and is more sensitive than magnetic prospection to susceptibility changes occurring in the soil above 60 cm depth the 3 d model will also be very valuable for the conception of improvements in the apparatus

fram strait sea ice outflow 1 we summarize 24 years 1978 2002 of ice export estimates and examine over a 9 year record the associated variability in the time varying upward looking sonar uls thickness distributions of the fram strait a more thorough assessment of the pmw passive microwave ice motion with 5 years of synthetic aperture radar sar observations shows the uncertainties to be consistent with that found by kwok and rothrock 1999 giving greater confidence to the record of ice flux calculations interesting details of the cross strait motion profiles and ice cover characteristics revealed by high resolution sar imagery are discussed the average annual ice area flux over the period is 866 000 km2 yr between the 1980s and 1990s the decadal difference in the net exported ice area is 400 000 km2 approximately half the annual average except for the years with extreme negative nao correlation of winter ice area export with the nao index remains high r2 0 62 with thickness estimates from uls moorings we estimate the average annual ice volume flux 8 years to be 2218 km3 yr 0 07 sv over the 9 year uls ice thickness data set there is an overall decrease of 0 45 m in the mean ice thickness over the entire time series and a decrease of 0 23 m over the winter months december through march correspondingly the mode of the my ice thickness exhibits an overall decrease of 0 55 m and a winter decrease of 0 42 m these are significant trends whether these trends are indicative of the thickness trends of the arctic ocean is examined as the time varying behavior of the monthly uls thickness distributions can be related not only to the seasonal cycle in the basal growth and melt but also to the magnitude and pattern of ice motion in the arctic ocean and the proximity of the uls moorings to the ice edge

thin sea ice thick snow and widespread negative freeboard observed during n ice2015 north of svalbard in recent years sea ice conditions in the arctic ocean changed substantially toward a younger and thinner sea ice cover to capture the scope of these changes and identify the differences between individual regions in situ observations from expeditions are a valuable data source we present a continuous time series of in situ measurements from the n ice2015 expedition from january to june 2015 in the arctic basin north of svalbard comprising snow buoy and ice mass balance buoy data and local and regional data gained from electromagnetic induction em surveys and snow probe measurements from four distinct drifts the observed mean snow depth of 0 53 m for april to early june is 73 above the average value of 0 30 m from historical and recent observations in this region covering the years 1955 2017 the modal total ice and snow thicknesses of 1 6 and 1 7 m measured with ground based em and airborne em measurements in april may and june 2015 respectively lie below the values ranging from 1 8 to 2 7 m reported in historical observations from the same region and time of year the thick snow cover slows thermodynamic growth of the underlying sea ice in combination with a thin sea ice cover this leads to an imbalance between snow and ice thickness which causes widespread negative freeboard with subsequent flooding and a potential for snow ice formation with certainty 29 of randomly located drill holes on level ice had negative freeboard