impact of spatial averaging on radar reflectivity at internal snowpack layer boundaries microwave radar amplitude within a snowpack can be strongly influenced by spatial variability of internal layer boundaries we quantify the impact of spatial averaging of snow stratigraphy and physical snowpack properties on surface scattering from near nadir frequency modulated continuous wave radar at 12 18 ghz relative permittivity density grain size and stratigraphic boundaries were measured in situ at high resolution along the length of a 9 m snow trench an optimal range of horizontal averaging 4 6 m was identified to attribute variations in surface scattering at layer boundaries to dielectric contrasts estimated from centimetre scale measurements of snowpack stratigraphy and bulk layer properties single vertical profiles of snowpack properties seldom captured the complex local variability influencing near nadir radar surface scattering we discuss implications of scaling in situ measurements for snow radiative transfer modelling and evaluation of airborne microwave remote sensing of snow

a 200 ka record of climatic change and dune activity in the thar desert india abstract an 18 4 m excavated dune section in the thar desert of india with a chronology based on 12 tl ages and a basal age of 190 ka has preserved 12 cycles of dune accretion soil formation calcrete development and subsequent erosion together with the presence of stone artefacts ranging in age from lower palaeolithic to mesolithic coeval with more humid climatic interludes phases of soil development and carbonate precipitation were relatively wet and phases of dune accretion relatively dry so that there were 12 significant moist intervals separated by 11 drier intervals during the past 190 ka the calculated time interval between successive phases of dune sand accumulation ranged from 22 2 ka to 15 8 ka with a mean of 19 0 ka these values are consistent with a precessional influence on dune activity and on the associated onset of early monsoonal activity in this region carbon isotopes measured on organic matter within the sand profiles show consistent values close to 21 6 1 pointing to deposition during a transitional climatic regime characterized by a change from open c3 grassland to c4 woodland or forest

comparison of traditional and optical grain size field measurements with snowpack simulations in a taiga snowpack knowledge of snow microstructure is relevant for modelling the physical properties of snow cover and for simulating the propagation of electromagnetic waves in remote sensing applications characterization of the microstructure in field conditions is however a challenging task due to the complex sintered and variable nature of natural snow cover a traditional measure applied as a proxy of snow microstructure which can also be determined in field conditions is the visually estimated snow grain size developing techniques also allow measurement for example of the specific surface area ssa of snow from which the optical equivalent grain size can be derived the physical snow model snowpack simulates evolution of snow parameters from meteorological forcing data in this study we compare an extensive experimental dataset of measurements of traditional grain size and ssa derived optical grain size with snowpack simulations of grain size parameters on average a scaling factor of 1 2 is required to match traditional grain size observations with the corresponding snowpack simulation a scaling factor of 2 1 was required for the optical equivalent grain size standard deviations of scaling factors for the winters of 2011 12 and 2012 13 were 0 36 and 0 42 respectively the largest scaling factor was needed in early winter and under melting conditions

in situ sampled snow particle sizes of the east antarctic ice sheet and their relation to physical and remotely sensed snow surface parameters knowledge of snow properties across antarctica is important in estimating how climate could potentially influence the mass balance of the antarctic ice sheet however measuring these variables has proven to be challenging because appropriate techniques have not yet been developed and extensive datasets of field estimates are lacking the goal of this study was to estimate the relationship between field observed snow particle size parameters from across the east antarctic ice sheet and a suite of spatial datasets i e topography remote sensing data using a principal component analysis pca five snow particle size parameters were correlated to spatial datasets of the following five groups 1 relief properties such as elevation and slope 2 remote sensing data from moderate resolution imaging spectroradiometer modis and synthetic aperture radar sar sensors 3 spatially interpolated data i e 10 m maps of temperature and approximate snow accumulation in kg m 2 a 1 4 field retrieved data on surface roughness and 5 in situ elevation and distance from the coast the results show that the relief parameter slope correlated best with the snow particle length and area r 0 76 r 0 80 further the pca indicated that the different remote sensing parameters correlated differently with the size parameters and that the most common parameter in visual analysis particle length grain diameter is not always the optimal parameter to characterize the snow particle size as for example area correlates better to slope and aspect than length

luminescence chronology of the inland sand dunes from se india abstract records of past climate changes have been preserved variously on the earth s surface sand dunes are one such prominent imprint and it is suggested that their presence is an indicator of periods of transition from arid to less arid phases we report inland sand dunes from andhra pradesh se india spread over an area of 500 km 2 75 km inland from the east coast the dune sands are examined to understand their provenance transportation timing of sand aggradation and their relationship to past climates the dune distribution grain morphology and the grain size studies on sands suggest an aeolian origin physiography of the study area heavy mineral assemblage and abundance of quartz in the parent rocks indicate that the dune sands are largely derived from first order streams emanating from hills in the region and from weathering of the nellore schist belt it appears that the geomorphology and wind direction pattern both facilitated and restricted the dune aggradation and preservation to a limited area osl dating of 47 dune samples ranged from the present to 50 ka thereby suggesting a long duration of sand dune aggradation and or reworking history

recording microscale variations in snowpack layering using near infrared photography deposition of snow from precipitation and wind events creates layering within seasonal snowpacks the thickness and horizontal continuity of layers within seasonal snowpacks can be highly variable due to snow blowing around topography and vegetation and this has important implications for hydrology remote sensing and avalanche forecasting in this paper we present practical field and post processing protocols for recording lateral variations in snow stratigraphy using near infrared nir photography a fuji s9100 digital camera modified to be sensitive to nir wavelengths was mounted on a rail system that allowed for rapid imaging of a 10 m long snow trench excavated on the north side of toolik lake alaska 68 3 n 149 36 w post processing of the images included removal of lens distortion and vignetting a tape measure running along the base of the trench provided known locations control points that permitted scaling and georeferencing snow layer heights estimated from the nir images compared well with manual stratigraphic measurements made at 0 2 m intervals along the trench n 357 r2 0 97 considerably greater stratigraphic detail was captured by the nir images than in the manually recorded profiles nir imaging of snow trenches using the described protocols is an efficient tool for quantifying continuous microscale variations in snow layers and associated properties

modeling time series of microwave brightness temperature at dome c antarctica using vertically resolved snow temperature and microstructure measurements time series of observed microwave brightness temperatures at dome c east antarctic plateau were modeled over 27 months with a multilayer microwave emission model based on dense medium radiative transfer theory the modeled time series of brightness temperature at 18 7 and 36 5 ghz were compared with advanced microwave scanning radiometer eos observations the model uses in situ high resolution vertical profiles of temperature snow density and grain size the snow grain size profile was derived from near infrared nir reflectance photography of a snow pit wall in the range 850 1100 nm to establish the snow grain size profile from the nir reflectance and the specific surface area of snow two empirical relationships and a theoretical relationship were considered in all cases the modeled brightness temperatures were overestimated and the grain size profile had to be scaled to increase the scattering by snow grains using a scaling factor and a constant snow grain size below 3 m depth i e below the image derived snow pit grain size profile brightness temperatures were explained with a root mean square error close to 1 k most of this error is due to an overestimation of the predicted brightness temperature in summer at 36 5 ghz

fluvial response to late quaternary climate changes western india we review here the fluvial response to late quaternary climatic changes in the semi arid regions of western india i e the thar desert and its margins and maharashtra the rivers in the thar desert show a spectrum of environments from gravel bedload braided to ephemeral sand bed streams to sheet flows and sheet floods while those in the thar margin and maharashtra show dominantly two modes i e braided and meandering rivers the streams became defunct and aeolian sands were deposited during periods of relatively greater aridity in the thar desert and its margins incisions occurred during the wet phases in ois 1 it is inferred that changes in the monsoon precipitation led to relative changes in the discharge and sediment supply which were routed through those in the vegetation cover and played a key role in determining the fluvial style an inter comparison of the late quaternary alluvial deposits in the semi arid regions of western india suggests a continuum of fluvial environments interrelated through a precipitation gradient further a global comparison indicates that the response of semi arid western indian rivers was synchronous with the rivers in other climatic settings

ice layer and surface crust permeability in a seasonal snow pack ice layers in snowpacks are thought to retard or obstruct gas and melt water flow through the pack yet there has been little published information on the permeability of ice layers in seasonal snow in this paper investigations of ice layer permeabilities are reported for prominent ice layers 1 to 3 mm thick in a seasonal snowpack for distinct fairly solid ice layers 1 to 3 mm thick permeabilities ranged from 1 to 19 x 10 10 m 2 these values are significantly lower than values for the surrounding snow within 24 h early in the melt season the permeability of the surface crust increased 160 from approximately 70 to 120 x 10 10 m 2 this increase in permeability was accompanied by a small increase in grain size and a decrease in albedo the snow air interface can exhibit dramatic changes in transport properties over relatively short periods of time even without precipitation events these changes driven by the surface meteorology affect transport properties such as permeability as well as albedo

spatial scales of snow texture as indicator for snow class a method for automated and fast classification of snow texture would be useful for applications where snow structure must be quantified large numbers of field measurements were carried out on natural snow in order to investigate small scale variations of the micro penetration force snow characterization was done for snow from the himalaya and the alps using a high resolution snow penetrometer snowmicropen measurements of snow resistance at equal intervals of 4 mm were geostatistically evaluated the range parameter correlation length or cl of penetration force was estimated for all major snow classes from the sample semivariogram average cl was lowest for new snow and highest for melt freeze snow for major snow classes cl was found to increase with snow density ground perpendicular and ground parallel snow profiles were also obtained for homogeneous snow and cl was estimated along these directions new snow showed larger cl in the ground parallel direction and depth hoar snow showed larger cl in the ground perpendicular direction based on cl the directional anisotropy was calculated an attempt was also made to show the relationship between cl and texture index the semivariogram was used to estimate the fractal dimension both cl and fractal dimension were found to be potential parameters to describe snow

a δ 13 c record of late quaternary climate change from tropical peats in southern india stable isotope ratios of carbon in soils or lake sediments1 3 and of oxygen and hydrogen in peats4 5 have been found to reflect past moisture variations and hence to provide valuable palaeoclimate records previous applications of the technique to peat have been restricted to temperate regions largely because tropical climate variations are less pronounced making them harder to resolve here we present a 13c record spanning the past 20 kyr from peats in the nilgiri hills southern india because the site is at high altitude 2 000 m above sea level it is possible to resolve a clear climate signal we observe the key climate shifts that are already known to have occurred during the last glacial maximum 18 kyr ago and the subsequent deglaciation in addition we observe an arid phase from 6 to 3 5 kyr ago and a short wet phase about 600 years ago the latter appears to correspond to the mediaeval warm period which previously was believed to be confined to europe and north america6 7 our results therefore suggest that this event may have extended over the entire northern hemisphere

snow stratigraphic heterogeneity within ground based passive microwave radiometer footprints implications for emission modeling two dimensional measurements of snowpack properties stratigraphic layering density grain size and temperature were used as inputs to the multilayer helsinki university of technology hut microwave emission model at a centimeter scale horizontal resolution across a 4 5 m transect of ground based passive microwave radiometer footprints near churchill manitoba canada snowpack stratigraphy was complex between six and eight layers with only three layers extending continuously throughout the length of the transect distributions of one dimensional simulations accurately representing complex stratigraphic layering were evaluated using measured brightness temperatures large biases 36 to 68 k between simulated and measured brightness temperatures were minimized 0 5 to 0 6 k within measurement accuracy through application of grain scaling factors 2 6 to 5 3 at different combinations of frequencies polarizations and model extinction coefficients grain scaling factors compensated for uncertainty relating optical specific surface area to hut effective grain size inputs and quantified relative differences in scattering and absorption properties of various extinction coefficients the hut model required accurate representation of ice lenses particularly at horizontal polarization and large grain scaling factors highlighted the need to consider microstructure beyond the size of individual grains as variability of extinction coefficients was strongly influenced by the proportion of large hoar grains in a vertical profile it is important to consider simulations from distributions of one dimensional profiles rather than single profiles especially in sub arctic snowpacks where stratigraphic variability can be high model sensitivity experiments suggested that the level of error in field measurements and the new methodological framework used to apply them in a snow emission model were satisfactory layer amalgamation showed that a three layer representation of snowpack stratigraphy reduced the bias of a one layer representation by about 50

contact spectroscopy for determination of stratigraphy of snow optical grain size we present a technique for in situ measurement of the vertical and spatial stratigraphic distribution of snow optical grain size with a coupled contact illumination probe and field spectroradiometer accurate measurements of optical equivalent grain size are critical for modeling radiative properties of snow such as spectral albedo and microwave emission measurements of the spectral reflectance of the snow pit surface are made at 2 cm intervals in the vertical plane under constant illumination and view geometries we invert the integral of the continuum normalization of the ice absorption feature with maximum at 1 03 mm wavelength for optical equivalent grain size using the validated model of nolin and dozier 2000 that has accuracy of 10 50 mm across the grain size range 50 900 mm results are presented for an alpine site in southwest colorado usa across the ablation season and for a greenland ice sheet site at the onset of snowmelt these results suggest that traditional measurements of grain size using a hand lens are nearly accurate only for rounded grains r 2 0 41 rmse 160 mm for polycrystals and faceted grains the hand lens approach is very inaccurate r 2 0 03 and 0 24 rmse 1206 and 1010 mm respectively we demonstrate an order of magnitude improvement in modeling of shortwave spectral albedo and net shortwave flux with contact spectroscopy measurements of grain size stratigraphy over those from a hand lens

relation between grain size and correlation length of snow in the past it has often been difficult to compare results of different types of snow structural information grain size and correlation length are such parameters of granular media and there exist different definitions and different measurement methods for both of them the relation between these parameters is analyzed from theoretical and from experimental points of view considering optical and microwave properties for spherical ice grains the connecting formulas are simple but for other shapes the two parameters are not directly related care must be taken in the measurement procedure especially if grain size is regarded as the maximum extent of connected ice particles the results are likely to lead to extreme overestimates therefore it is concluded that grain size should be complemented by an additional size parameter namely the surface to volume ratio of equivalent spheres i e a measure of the correlation length methods to determine this quantity in the laboratory have been known for a long time methods to obtain such measurements in the field are described here

new algorithm to retrieve the effective snow grain size and pollution amount from satellite data this paper presents a new simple and efficient algorithm to retrieve the effective snow grain size and soot concentration from spectral reflectance on snow measured by optical instrument on a satellite this algorithm was recently developed and will be used for integrated ice atmosphere ocean monitoring in the framework of the damocles program the algorithm is based on an analytical approach to snow optics in this approach snow is considered as a close packed medium with irregularly shaped grains rather than with independent spherical particles unlike the known conventional algorithms the developed algorithm uses no a priori snow optical model the analytical nature of this algorithm provides a very fast inversion of the reflection data the developed algorithm was realized and validated for the gli and modis instruments the algorithm can be generalized for other satellite instruments with appropriate spectral channels finally the results of verifications using a computer simulation are discussed

linking the effective thermal conductivity of snow to its shear strength and density 1 the effective thermal conductivity of snow keff is a crucial climatic and environmental variable here we test the intuition that keff is linked to microstructural and mechanical properties by attempting to relate keff to density snow and to shear strength measured with a handheld shear vane we performed 106 combined measurements of keff snow and in the alps svalbard arctic alaska and near the north pole covering essentially all snow types we find a good correlation between keff and snow which is not significantly different from that of sturm et al 1997 the correlation between keff and a combination of and snow is stronger than with density alone we propose an equation linking keff w m 1 k 1 snow kg m 3 and pa keff 7 114 10 5 snow 0 333 2 367 10 2 this equation places constraints on the calculation of keff snow and in avalanche warning models where is a key variable for our samples we calculate from measured values of keff and snow using our equation and compare the value to that predicted by the french mepra avalanche warning model which uses density and grain type as input data mepra and the prediction of based on keff and snow agree within 8 mepra agrees with observations within 11 calculating from density only yields values 55 lower than measured showing the interest of using additional data to predict

late pleistocene and holocene dune activity and wind regimes in the western sahara desert of mauritania the western sahara desert in mauritania is dominated by extensive sand seas consisting largely of linear dunes analyses of landsat images geomorphic and stratigraphic studies and optically stimulated luminescence dating of dunes in the azefal agneitir and akchar sand seas provide evidence that three main generations of dunes were formed during the periods 25 15 ka centered around the last glacial maximum 10 13 ka spanning the younger dryas event and after 5 ka the wind regimes that occurred during each of these periods were significantly different leading to the formation of dunes on three distinct superimposed trends northeast north northeast and north and the development of the sand seas as composite geomorphic features

the layered character of snow covers snow studies have generally ignored the layered nature of snow covers having achieved a good understanding of the properties and processes in homogeneous snow snow scientists should develop more insight into the evolution of the layers and their effects on overall snow response many of the outstanding problems in snow studies can only be solved by dealing with snow as a layered medium the various mechanisms by which layers are generated their effects and some of the outstanding research problems are described here

measurement of vertical profiles of snow specific surface area with a 1 cm resolution using infrared reflectance instrument description and validation the specific surface area ssa defined as the surface area of ice per unit mass is an important variable characterizing the complex microstructure of snow its application range covers the physical evolution of snow metamorphism photochemistry and optical and microwave remote sensing this paper presents a new device posssum profiler of snow specific surface area using swir reflectance measurement designed to allow the rapid acquisition of ssa profiles down to 20 m depth and with an effective vertical resolution of 10 20 mm posssum is based on the infrared ir reflectance technique a laser diode operating at 1310 nm illuminates the snow at nadir incidence angle along the face of a drilled hole the reflected radiance is measured at three zenith angles 20 40 and 60 each for two azimuth angles 0 and 180 a second laser operating at a shorter wavelength 635 nm which is almost insensitive to ssa allows the distance to the snow face to be estimated the reflected ir radiance and the distance are combined to estimate bidirectional reflectances these reflectances are converted into hemispherical reflectances and in turn into ssa using a theoretical formulation based on an asymptotic solution of the radiative transfer equation the evaluation and validation of posssum s ssa measurements took place in spring 2009 in the french alps the new method was compared with the methane adsorption technique and dufisss another well validated instrument based on the ir technique the overall measurement error is in the range 10 15

continental record of the southwest monsoon during the last 130 ka evidence from the southern margin of the thar desert india abstract field stratigraphy sedimentology and luminescence dating of the exposed fluvial and aeolian sequences from the southern desert margin were used to discern the pattern of southwest monsoon variability during the last 130 ka the sedimentary architecture and textural attributes of the sediments belonging to the period 130 120 ka suggests the existence of a meandering river system consequent to enhanced southwest monsoon conditions a shift from a meandering to a braided pattern during 120 100 ka indicates a phase of reduced precipitation presence of flood plain fines and bedded calcretes during 100 70 ka suggest a period of enhanced monsoon with seasonality following this a phase of weak monsoon activity was observed during 70 60 ka regional flood plain aggradation and pedogenesis during the period termination of a regional fluvial phase around 30 ka and incision of dunes dated to 20 11 ka suggest that the present rivers occupied their course between 11 ka drowned valleys in the estuarine zones suggest that the incision began during the low sea stand around 20 ka when the rivers were graded to the exposed shelf the incision intensified with the re establishment of monsoon during the early holocene

instruments and methods recording microscale variations in snowpack layering using near infrared photography deposition of snow from precipitation and wind events creates layering within seasonal snowpacks the thickness and horizontal continuity of layers within seasonal snowpacks can be highly variable due to snow blowing around topography and vegetation and this has important implications for hydrology remote sensing and avalanche forecasting in this paper we present practical field and post processing protocols for recording lateral variations in snow stratigraphy using near infrared nir photography a fuji s9100 digital camera modified to be sensitive to nir wavelengths was mounted on a rail system that allowed for rapid imaging of a 10 m long snow trench excavated on the north side of toolik lake alaska 68838 0 n 149836 0 w post processing of the images included removal of lens distortion and vignetting a tape measure running along the base of the trench provided known locations control points that permitted scaling and georeferencing snow layer heights estimated from the nir images compared well with manual stratigraphic measurements made at 0 2 m intervals along the trench n 357 r 2 0 97 considerably greater stratigraphic detail was captured by the nir images than in the manually recorded profiles nir imaging of snow trenches using the described protocols is an efficient tool for quantifying continuous microscale variations in snow layers and associated properties

measuring specific surface area of snow by near infrared photography the specific surface area ssa is considered an essential microstructural parameter for the characterization of snow photography in the near infrared nir spectrum is sensitive to the ssa we calculated the snow reflectance from calibrated nir images of snow pit walls and measured the ssa of samples obtained at the same locations this new method is used to map the snow stratigraphy the correlation between reflectance and ssa was found to be 90 calibrated nir photography allows quantitative determination of ssa and its spatial variation in a snow profile in two dimensions within an uncertainty of 15 in an image covering 0 5 1 0 m 2 even layers of 1 mm thickness can be documented and measured spatial maps of ssa are an important tool in initializing and validating physical and chemical models of the snowpack

calibration of a conodont apatite based ordovician 87sr 86sr curve to biostratigraphy and geochronology implications for stratigraphic resolution the ordovician 87 sr 86 sr isotope seawater curve is well established and shows a decreasing trend until the mid katian however uncertainties in calibration of this curve to biostratigraphy and geochronology have made it diffi cult to determine how the rates of 87 sr 86 sr decrease may have varied which has implications for both the stratigraphic resolution possible using sr isotope stratigraphy and efforts to model the effects of ordovician geologic events we measured 87 sr 86 sr in conodont apatite in north american ordovician sections that are well studied for conodont biostratigraphy primarily in nevada oklahoma the appalachian region and ohio valley our results indicate that conodont apatite may provide an accurate medium for sr isotope stratigraphy and strengthen previous reports that point toward a signifi cant increase in the rate of fall in seawater 87 sr 86 sr during the middle ordovician darriwilian stage our 87 sr 86 sr results suggest that sr isotope stratigraphy will be most useful as a high resolution tool for global correlation in the mid darriwilian to mid sandbian when the maximum rate of fall in sr

using quartz grain size and shape analysis to distinguish between aeolian and fluvial deposits in the dallol bosso of niger west africa size and fourier shape characteristics of quartz sand grains were determined by computerized image analysis in order to distinguish between aeolian and fluvial soil parent materials in the dallol bosso in niger factor analysis of grain size distributions gave four sand end members that can be related to fluvial transport dynamics operating when the sediments were initially deposited the medium to fine and more angular shaped sand fractions are being reworked by wind aeolian deposits were well sorted whereas fluvial deposits were poorly sorted in both size and shape although gross shape characteristics lower harmonics of fourier series expansion indicated a common source rock for all sands the aeolian sands were well rounded whereas the fluvial sands tended to be more angular upper harmonics of fourier series

isotopic fingerprints of paleoclimates during the last 30 000 years in deep confined groundwaters of southern india isotopic and geochemical evidence of paleoclimates especially for the last glaciation has been obtained from deep confined groundwaters of southern india the 13c 18o chloride and deuterium analyses of groundwaters show distinct excursions inferred to be related to climatic variations the arid climatic episode associated with the last glaciation 18 000 2000 yr b p is conspicuously identified by signatures of relatively enriched 13c 10 to 12 pdb and 18o 5 3 to 4 8 smow values and high chloride concentration 80 to 160 mg l the transition from an arid to humid period ca 12 000 8000 yr b p is shown by a decreasing trend in the 13c 9 5 to 17 and 18o 4 5 to 6 3 contents of groundwaters the late holocene since 4000 yr b p marked by a more humid but unstable climate is identified by further depletion of 13c 13 to 20 and 18o 5 2 to 6 3 similar variation between 18o and chloride values in confined groundwaters further demonstrates two distinct climatic excursions arid and humid governed by the amount effect this is the first time that isotopic and geochemical signatures related to changing paleoclimates have been identified in the confined groundwaters of the southern indian landmass

high resolution holocene monsoon record from the eastern arabian sea through stable oxygen and carbon analyses of rapidly accumulating sediment cores from the eastern arabian sea we show that the excess of evaporation over precipitation e p steadily appears to have decreased during the last 10 000 to 2000 years most probably due to an increasing trend in the summer monsoon rainfall contrary to the land based paleoclimatic data from this region which indicate onset of aridity around 4000 years ago our results are consistent with the hypothesis that significant spatial variability in the monsoon rainfall observed today was persistent during most of the holocene alternatively the trend can be seen as an adjustment between two phases one between 10 000 and 6000 years ago of increasing precipitation and another between 3500 and 2000 years ago after the arid episode we also report a significant 700 year periodicity similar to that reported recently from the south china sea indicating that the centennial millennial scale response of the indian and chinese monsoons to high latitude forcing may be alike

an energy and mass model of snow cover suitable for operational avalanche forecasting a numerical model has been developed to simulate energy and mass evolution of snow cover at a given location as a function of meteorological conditions precipitation air temperature humidity wind velocity and incoming short wave and long wave radiation this model named crocus was first tested on a well instrumented field during a whole winter showing its ability to simulate the important phenomena affecting the evolution of the snow layers high temperature gradients wetting compaction and melting freezing cycles a second test was conducted at two locations in the french network used for operational avalanche forecasting though the weather observations are made there only twice daily the snow profiles calculated by the model were very close to those obtained once a week by a pit observation crocus proved itself sufficient to be considered now as a useful objective tool for operational avalanche forecasting

density specific surface area and correlation length of snow measured by high resolution penetrometry precise measurements of snow structural parameters are crucial to understand the formation of snowpacks by deposition and metamorphism and to characterize the stratigraphy for many applications and remote sensing in particular the area wide acquisition of structural parameters at high spatial resolution from state of the art methods is however still cumbersome since the time required for a single profile is a serious practical limitation as a remedy we have developed a statistical model to extract three major snow structural parameters density correlation length and specific surface area ssa solely from the snowmicropen smp a high resolution penetrometer which allows a meter profile to be measured with millimeter resolution in less than 1 min the model was calibrated by combining smp data with 3 d microstructural data from microcomputed tomography which was used to reconstruct full depth snow profiles from different snow climates alpine arctic and antarctic density correlation length and ssa were derived from the smp with a mean relative error of 10 6 16 4 and 23 1 respectively for validation we compared the density and ssa derived from the smp to traditional measurements and near infrared profiles we demonstrate the potential of our method by the retrieval of a two dimensional stratigraphy at kohnen station antarctica from a 46 m long smp transect the result clearly reveals past depositional and metamorphic events and our findings show that the smp can be used as an objective high resolution tool to retrieve essential snow structural parameters efficiently in the field

energy based binary segmentation of snow microtomographic images x ray microtomography has become an essential tool for investigating the mechanical and physical properties of snow which are tied to its microstructure to allow a quantitative characterization of the microstructure the grayscale x ray attenuation coefficient image has to be segmented into a binary ice pore image this step called binary segmentation is crucial and affects all subsequent analysis and modeling common segmentation methods are based on thresholding in practice these methods present some drawbacks and often require time consuming manual post processing here we present a binary segmentation algorithm based on the minimization of a segmentation energy this energy is composed of a data fidelity term and a regularization term penalizing large interface area which is of particular interest for snow where sintering naturally tends to reduce the surface energy the accuracy of the method is demonstrated on a synthetic image the method is then successfully applied on microtomographic images of snow and compared to the threshold based segmentation the main advantage of the presented approach is that it benefits from local spatial information moreover the effective resolution of the segmented image is clearly defined and can be chosen a priori

granulometric investigations of snow avalanches avalanche deposits consist of rounded granules composed of aggregates of snow and ice particles the size of the granules is related to vertical shear gradients within the flow studying the granule size distribution may be useful in understanding the flow and stopping of avalanches we applied a sediment size sampling method to measure snow granule size distributions at different depositional environments on two dry and two wet avalanche deposits at three field sites the granule size distributions are approximately log normal similar to many natural sediment deposits the median granule size in the wet and dry avalanches varies between 65 and 162 mm wet avalanches tend to produce more large granules than dry avalanches indicating both smaller flow velocities and near surface shear gradients granule size is similar in frontal lobes and levee deposits suggesting that levee formation occurs independently of the size segregation at the avalanche front

ku x and c band measured and modeled microwave backscatter from a highly saline snow cover on first year sea ice abstract in this study we inter compare observed and modeled ku x and c band microwave backscatter for two snow temperature conditions for a highly saline snow cover on smooth first year sea ice a new surface based multi frequency ku x and c bands microwave scatterometer system is used quasi coincident with in situ geophysical snow measurements a multilayer snow and ice backscatter model is used to calculate the total co polarized backscatter coefficient for two snow temperature conditions the model provides the surface and volume scattering contributions for each snow layer as well as the frequency dependent penetration depth these results aid interpretation of observed backscatter joint use of ku x and c band microwaves provide an enhanced understanding of diverse variations in geophysical thermodynamic and electrical state of snow sea ice system our results indicate that the effect of dielectric loss associated with highly saline snow covers is the dominant factor affecting microwave penetration and backscatter from all three frequencies the observed and modeled c band backscatter shows good agreement followed by x and ku bands at both snow temperature conditions microwave backscatter shows greater sensitivity to variations in plot scale surface roughness for all three frequencies additionally ku band wavelength exhibits greater sensitivity to snow grain radius over x and c bands our results demonstrate the future potential of a multi frequency approach towards the development of snow thickness and snow water equivalent algorithms on first year sea ice

east antarctic sea ice in spring spectral albedo of snow nilas frost flowers and slush and light absorbing impurities in snow spectral albedos of open water nilas nilas with frost flowers slush and first year ice with both thin and thick snow cover were measured in the east antarctic sea ice zone during the sea ice physics and ecosystems experiment ii sipex ii from september to november 2012 near 658 s 1208 e albedo was measured across the ultraviolet uv visible and near infrared nir wavelengths augmenting a dataset from prior antarctic expeditions with spectral coverage extended to longer wavelengths and with measurement of slush and frost flowers which had not been encountered on the prior expeditions at visible and uv wavelengths the albedo depends on the thickness of snow or ice in the nir the albedo is determined by the specific surface area the growth of frost flowers causes the nilas albedo to increase by 0 2 0 3 in the uv and visible wavelengths the spectral albedos are integrated over wavelength to obtain broadband albedos for wavelength bands commonly used in climate models the albedo spectrum for deep snow on first year sea ice shows no evidence of light absorbing particulate impurities lai such as black carbon bc or organics which is consistent with the extremely small quantities of lai found by filtering snow meltwater estimated bc mixing ratios were in the range 0 1 0 5 ng of carbon per gram of snow

light propagation in firn application to borehole video borehole optical stratigraphy bos is a borehole video system and processing routine for investigating polar firn bos records brightness variations in the firn and is effective at identifying stratigraphic markers bos brightness logs have been used to count annual layers and measure vertical strain even though a specific cause of the brightness variations has not been determined here we combine two models of light transport to examine potential errors with bos and identify improvements which will allow the system to estimate optical grain size we use a monte carlo radiative transfer model to estimate the influence of firn microstructure variations on borehole reflectance we then use a ray tracing algorithm to model the multiple reflections within the borehole that cause measured brightness variations multiple reflections cause the brightness measured at a point on the borehole wall to not necessarily be equal to the local wall reflectance the ray tracing further shows that wall imperfections or variations in the camera position can produce brightness variations that are unrelated to changes in firn properties smooth walls and good stabilization of the camera help ensure that brightness variations result from variations in firn properties and thus are a measure of firn stratigraphy rather than artifacts

snow replica method for three dimensional x ray microtomographic imaging visualization and quantification of snow structures at a scale of a few millimetres is important in understanding the mechanical thermal and electromagnetic properties of snow surface sections and to an even greater degree three dimensional 3 d reconstructions of cast snow samples are difficult to prepare and automatic image processing is notoriously difficult and often requires manual evaluation here we present a new method to measure the 3 d structure of cast snow samples snow samples cast with diethyl phthalate dep and frozen are cut to a sample size a few centimetres in diameter and up to 10 cm in height the ice of these samples is then sublimated in high vacuum and the remaining negative structure replica is imaged using x ray microtomography micro ct the accuracy of the method is demonstrated by comparing micro ct scans of the original snow structure and the replica the method described here allows easy transportation of samples requires little manual interaction has a very high spatial resolution of up to 10 m and is environmentally friendly

a synthetic study to assess the applicability of full waveform inversion to infer snow stratigraphy from upward looking ground penetrating radar data snow stratigraphy and liquid water content are key contributing factors to avalanche formation upward looking groundpenetrating radar upgpr systems allow nondestructive monitoring of the snowpack but deriving density and liquid water content profiles is not yet possible based on the direct analysis of the reflection response we have investigated the feasibility of deducing these quantities using full waveform inversion fwi techniques applied to upgpr data for that purpose we have developed a frequency domain fwi algorithm in which we additionally took advantage of time domain features such as the arrival times of reflected waves our results indicated that fwi applied to upgpr data is generally feasible more specifically we could show that in the case of a dry snowpack it is possible to derive snow densities and layer thicknesses if sufficient a priori information is available in case of a wet snowpack in which it also needs to be inverted for the liquid water content the algorithm might fail even if sufficient a priori information is available particularly in the presence of realistic noise finally we have investigated the capability of fwi to resolve thin layers that play a key role in snow stability evaluation our simulations indicate that layers with thicknesses well below the gpr wavelengths can be identified but in the presence of significant liquid water the thin layer properties may be prone to inaccuracies these results are encouraging and motivate applications to field data but significant issues remain to be resolved such as the determination of the generally unknown upgpr source function and identifying the optimal number of layers in the inversion models furthermore a relatively high level of prior knowledge is required to let the algorithm converge however we feel these are not insurmountable and the new technology has significant potential to improve field data analysis