topographic context of glaciers and perennial snowfields glacier national park montana abstract equilibrium line altitudes elas of modem glaciers in the northern rocky mountains are known to correspond with regional climate but strong subregional gradients such as across the continental divide in glacier national park montana also exert topoclimatic influences on the ela this study analyzed the relationships between glacier and snowfield morphology ela and surrounding topography glaciers and perennial snowfields were mapped using multitemporal satellite data from the landsat thematic mapper and aerial photography within an integrated geographic information system gis relationships between glacier morphology and ela were investigated using discriminant analysis four morphological categories of perennial snow and ice patches were identified cirque glacier niche glacier ice cap and snowfield ela was derived from overlaid glacier boundaries and digital elevation models dems within the gis dems provided topographic variables and models of solar radiation and wind exposure shelteredness regression analysis showed the effects of exposure on snow accumulation the strong influence of local topography through upslope zone morphology such as cirque backwalls and the tendency for glaciers with high elas to exhibit compactness in morphology results highlight the relatively compact shape and larger area of glaciers adjacent to the continental divide discriminant analysis correctly predicted the type of glacier morphology in more than half the observations using factored variables of glacier shape elevation range and upslope area

assessment of radar derived snow depth over arctic sea ice knowledge of contemporaneous snow depth on arctic sea ice is important both to constrain the regional climatology and to improve the accuracy of satellite altimeter estimates of sea ice thickness we assess new data available from the nasa operation icebridge snow radar instrument and derive snow depth estimates across the western arctic ice pack using a novel methodology based on wavelet techniques that define the primary reflecting surfaces within the snow pack we assign uncertainty to the snow depth estimates based upon both the radar system parameters and sea ice topographic variability the accuracy of the airborne snow depth estimates are examined via comparison with coincident measurements gathered in situ across a range of ice types in the beaufort sea we discuss the effect of surface morphology on the derivation and consequently the accuracy of airborne snow depth estimates we find that snow depths derived from the airborne snow radar using the wavelet based technique are accurate to 1 cm over level ice over rougher surfaces including multiyear and ridged ice the radar system is impacted by ice surface morphology across basin scales we find the snow radar derived snow depth on first year ice is at least 60 of the value reported in the snow climatology for the beaufort sea canada basin and parts of the central arctic since these regions were previously dominated by multiyear ice during the measurement period of the climatology snow on multiyear ice is more consistent with the climatology

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

snow depth of the weddell and bellingshausen sea ice covers from icebridge surveys in 2010 and 2011 an examination we examine the snow radar data from the weddell and bellingshausen seas acquired by eight icebridge oib flightlines in october of 2010 and 2011 in snow depth retrieval the sidelobes from the stronger scattering snow ice s i interfaces could be misidentified as returns from the weaker air snow a s interfaces in this paper we first introduce a retrieval procedure that accounts for the structure of the radar system impulse response followed by a survey of the snow depths in the weddell and bellingshausen seas limitations and potential biases in our approach are discussed differences between snow depth estimates from a repeat survey of one weddell sea track separated by 12 days without accounting for variability due to ice motion is 0 7 13 6 cm average snow depth is thicker in coastal northwestern weddell and thins toward cape norvegia a decrease of 30 cm in the bellingshausen the thickest snow is found nearshore in both octobers and is thickest next to the abbot ice shelf snow depth is linearly related to freeboard when freeboards are low but diverge as the freeboard increases especially in the thicker rougher ice of the western weddell we find correlations of 0 71 0 84 between snow depth and surface roughness suggesting preferential accumulation over deformed ice retrievals also seem to be related to radar backscatter through surface roughness snow depths reported here generally higher than those from in situ records suggest dissimilarities in sample populations implications of these differences on antarctic sea ice thickness are discussed

a first assessment of icebridge snow and ice thickness data over arctic sea ice we present a first assessment of airborne laser and radar altimeter data over snow covered sea ice gathered during the national aeronautics and space administration operation icebridge mission we describe a new technique designed to process radar echograms from the university of kansas snow radar to estimate snow depth we combine icebridge laser altimetry with radar derived snow depths to determine sea ice thickness results are validated through comparison with direct measurements of snow and ice thickness collected in situ at the danish greenarc 2009 sea ice camp located on fast ice north of greenland the icebridge instrument suite provides accurate measurements of snow and ice thickness particularly over level ice mean icebridge snow and ice thickness agree with in situ measurements to within 0 01 and 0 05 m respectively while modal snow and ice thickness estimates agree to within 0 02 and 0 10 m respectively icebridge snow depths were correlated with in situ measurements r 0 7 for an averaging length of 55 m the uncertainty associated with the derived icebridge sea ice thickness estimates is 0 40 m the results demonstrate the retrieval of both first year and multiyear ice thickness from icebridge data the airborne data were however compromised in heavily ridged ice where snow depth and hence ice thickness could not be measured techniques developed as part of this study will be used for routine processing of icebridge retrievals over arctic sea ice the limitations of the greenarc study are discussed and recommendations for future validation of airborne measurements via field activities are provided

responses to climatic changes since the little ice age on maladeta glacier central pyrenees abstract the evolution of maladeta glacier maladeta massif central spanish pyrenees since the little ice age maximum is analyzed in this work the extent of the glacier was mapped into 10 stages using morainic deposits and graphic documents climatic data temperature and precipitation were reconstructed by using dendroclimatic techniques complemented by recent instrumental records the results thus obtained confirm the control of the above mentioned climatic factors particularly annual temperature and winter precipitation in the evolution of maladeta glacier which has receded from an extent of 152 3 ha in 1820 1830 to 54 5 ha in 2000 a 35 7 reduction in size the rate of ice wastage has varied during that period defining several phases of glacial stabilization 1820 1830 to 1857 1914 1920 to 1934 1935 1957 to 1981 moderated glacial depletion 1901 1904 to 1914 1920 1934 1935 to 1957 and marked glacial depletion 1857 to 1901 1904 1981 to 2000 the evolution of maladeta glacier is also in keeping with trends observed from other alpine mediterranean glaciers which have experienced a consistent rise in their equilibrium line altitudes during the 19th and 20th centuries as well as associated and prolonged periods of negative mass balance

attenuation tomography of the western united states from ambient seismic noise 1 we show that the spatial coherency of the ambient seismic field can be used for attenuation tomography in the western united states we evaluate the real portion of the spatial coherency with an elastic geometric spreading term a bessel function and a distance dependent decay an attenuation coefficient in order to invert the spatial coherency a weight stack inversion technique is applied we recover phase velocity and attenuation coefficient maps at periods of 8 32s which correspond to the elastic and anelastic structure at crustal and upper mantle depths the phase velocity maps obtained by this method are of similar resolution to more standard two station methods the attenuation results provide an important complement to the information extracted from earthquake based tomography several geological features are easily identifiable in the attenuation coefficient maps such as the highly attenuating sedimentary basins along the west coast of the united states and the highly attenuating yellowstone region and the boundaries of the snake river plains

combined airborne laser and radar altimeter measurements over the fram strait in may 2002 knowledge of sea ice thickness is critical for the prediction of future climate and for assessing the significance of changes in thickness sea ice thickness can be calculated from radar or laser satellite altimetry measurements of freeboard however a lack of knowledge of snow depth introduces significant uncertainties into these calculations this paper compares the first coincident airborne laser and radar altimetry data over sea ice collected during the laser radar altimetry lara field campaign lara was a flight of opportunity that provided valuable data to explore techniques to validate satellite measurements of ice freeboard and the possibility of combining laser and radar measurements over snow covered sea ice to calculate the snow depth two new methods were created to analyse these data sets a new radar retracker and a radar power simulator which models radar returns from the laser data we present the first quantitative analysis of data from the lara laser and radar altimeters and demonstrate the potential of combining laser and radar altimetry to estimate snow depth lara elevation estimates compare well with elevations from the radar altimeter onboard ers 2 at the sub meter level and the study provides lessons for future validation of satellite altimetry data over sea ice laser elevations are consistently higher than the radar elevations over snow covered sea ice as lara was a flight of opportunity no coincident in situ measurements were available nevertheless the difference between the reflecting surface of the laser and radar is consistent with snow depth from climatology and the analysis techniques developed in this paper will be useful for future radar and laser altimetry comparisons

ice and snow thickness variability and change in the high arctic ocean observed by in situ measurements in april 2017 we collected unique extensive in situ data of sea ice and snow thickness at 10 sampling sites located under a cryosat 2 overpass between ellesmere island and 87 1 n mean and modal total ice thicknesses ranged between 2 to 3 4 m and 1 8 to 2 9 m respectively coincident snow thicknesses ranged between 0 3 to 0 47 m mean and 0 1 to 0 5 m mode the profile spanned the complete multiyear ice zone in the lincoln sea into the first year ice zone farther north complementary snow thickness measurements near the north pole showed a mean thickness of 0 31 m compared with scarce measurements from other years multiyear ice was up to 0 75 m thinner than in 2004 but not significantly different from 2011 and 2014 we found excellent agreement with a commonly used snow climatology and with published long term ice thinning rates there was reasonable agreement with cryosat 2 thickness retrievals

earthquake ground motion prediction using the ambient seismic field 1 the waves generated by faulting represent the primary threat posed by most large earthquakes the effect of complex geological structures such as sedimentary basins on earthquake ground motion is a source of particular concern we show that it is possible to extract reliable phase and amplitude response that includes the effects of complex structure for the elastodynamic green s function from the ambient seismic field using deconvolution we demonstrate the accuracy of the approach by predicting complex ground motion for a moderate mw 4 6 earthquake in southern california as recorded in the los angeles basin this suggests a novel approach to seismic hazard analysis in which ground motion from hypothetical future earthquakes is simulated directly without the need for modeling the detailed heterogeneity of the earth s crust as an intermediate step

attenuation of lg in the western us using the usarray 1 the unprecedented breadth and density of the usarray allows us to resolve lateral variations of 1 hz lg attenuation to 0 5 degrees over much of the western united states we collected over 31 000 lg amplitudes from 547 events and 408 stations of the initial usarray footprint two dimensional tomographic inversion yielded q ranging from 60 to 550 with a variance reduction of 47 relative to the best fit constant q model q 155 q is low over most of the region with lowest values associated with recent volcanic activity and active shear zones high q is found in older stable crust notably the colorado and columbia plateaus while smaller islands of high q are associated with batholiths including the sierra nevada peninsular and bitterroot ranges the western mojave and okanogan highlands as well as other areas of competent crust such as the harcuvar range and two topographically bounded blocks in the basin and range

interdecadal changes in snow depth on arctic sea ice snow plays a key role in the growth and decay of arctic sea ice in winter it insulates sea ice from cold air temperatures slowing sea ice growth from spring to summer the albedo of snow determines how much insolation is absorbed by the sea ice and underlying ocean impacting ice melt processes knowledge of the contemporary snow depth distribution is essential for estimating sea ice thickness and volume and for understanding and modeling sea ice thermodynamics in the changing arctic this study assesses spring snow depth distribution on arctic sea ice using airborne radar observations from operation icebridge for 2009 2013 data were validated using coordinated in situ measurements taken in march 2012 during the bromine ozone and mercury experiment bromex field campaign we find a correlation of 0 59 and root mean square error of 5 8 cm between the airborne and in situ data using this relationship and icebridge snow thickness products we compared the recent results with data from the 1937 1954 1991 soviet drifting ice stations the comparison shows thinning of the snowpack from 35 1 9 4 to 22 2 1 9 cm in the western arctic and from 32 8 9 4 to 14 5 1 9 cm in the beaufort and chukchi seas these changes suggest a snow depth decline of 37 29 in the western arctic and 56 33 in the beaufort and chukchi seas thinning is negatively correlated with the delayed onset of sea ice freezeup during autumn

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

an ultra wideband microwave radar for measuring snow thickness on sea ice and mapping near surface internal layers in polar firn sea ice is generally covered with snow which can vary in thickness from a few centimeters to 1 m snow cover acts as a thermal insulator modulating the heat exchange between the ocean and the atmosphere and it impacts sea ice growth rates and overall thickness a key indicator of climate change in polar regions snow depth is required to estimate sea ice thickness using freeboard measurements made with satellite altimeters the snow cover also acts as a mechanical load that depresses ice freeboard snow and ice above sea level freeboard depression can result in flooding of the snow ice interface and the formation of a thick slush layer particularly in the antarctic sea ice cover the center for remote sensing of ice sheets cresis has developed an ultra wideband microwave radar capable of operation on long endurance aircraft to characterize the thickness of snow over sea ice the low power 100 mw signal is swept from 2 to 8 ghz allowing the air snow and snow ice interfaces to be mapped with 5 cm range resolution in snow this is an improvement over the original system that worked from 2 to 6 5 ghz from 2009 to 2012 cresis successfully operated the radar on the nasa p 3b and dc 8 aircraft to collect data on snow covered sea ice in the arctic and antarctic for nasa operation icebridge the radar was found capable of snow depth retrievals ranging from 10 cm to 1 m we also demonstrated that this radar can be used to map near surface internal layers in polar firn with fine range resolution here we describe the instrument design characteristics and performance of the radar

arctic sea ice freeboard from altika and comparison with cryosat 2 and operation icebridge satellite radar altimeters have improved our knowledge of arctic sea ice thickness over the past decade the main sources of uncertainty in sea ice thickness retrievals are associated with inadequate knowledge of the snow layer depth and the radar interaction with the snow pack here we adapt a method of deriving sea ice freeboard from cryosat 2 to data from the altika ka band radar altimeter over the 2013 14 arctic sea ice growth season altika measures basin averaged freeboards between 4 4 cm and 6 9 cm larger than cryosat 2 in october and march respectively using airborne laser and radar measurements from spring 2013 and 2014 we estimate the effective scattering horizon for each sensor while cryosat 2 echoes penetrate to the ice surface over first year ice and penetrate the majority 82 3 of the snow layer over multiyear ice altika echoes are scattered from roughly the midpoint 46 5 of the snow layer over both ice types

evaluation of operation icebridge quick look snow depth estimates on sea ice we evaluate operation icebridge oib quick look ql snow depth on sea ice retrievals using in situ measurements taken over immobile first year ice fyi and multi year ice myi during march of 2014 good agreement was found over undeformed fyi 4 5 cm mean bias with reduced agreement over deformed fyi 6 6 cm mean bias over myi the mean bias was 5 7 cm but 54 of retrievals were discarded by the oib retrieval process as compared to only 10 over fyi footprint scale analysis revealed a root mean square error rmse of 6 2 cm over undeformed fyi with rmse of 10 5 cm and 17 5 cm in the more complex deformed fyi and myi environments correlation analysis was used to demonstrate contrasting retrieval uncertainty associated with spatial aggregation and ice surface roughness

extracting surface wave attenuation from seismic noise using correlation of the coda of correlation 1 extracting surface wave travel time information from the cross correlation cc of seismic ambient noise has been a great success and remains fast growing however it is still challenging to exploit the amplitude content of the noise cc although spatial average is able to constrain somewhat meaningful attenuation using noise cc amplitudes clear bias is observed when spatially varying attenuation is estimated with the traditional noise cc calculation methods perhaps the key lies in the development of novel techniques that can mitigate the effect of the uneven distribution of natural noise sources in this paper we propose a new method to use the correlation of the coda of correlation of noise c3 for amplitude measurement we examine the ability of the method to retrieve surface wave attenuation using data from selected line array stations of the usarray by comparing c3 derived attenuation coefficients with those estimated from earthquake data we demonstrate that c3 effectively reduces bias and allows for more reliable attenuation estimates from noise this is probably because of the fact that the coda of noise correlation contains more diffused noise energy and thus the c3 processing effectively makes the noise source distribution more homogeneous when selecting auxiliary stations for c3 calculation we find that stations closer to noise sources near the coast tend to yield better signal to noise ratios we suggest to preprocess noise data using a transient removal and temporal flattening method to mitigate the effect of temporal fluctuation of the noise source intensity and to retain relative amplitudes in this study we focus our analysis on 18 s measurements

glacier development and topographic context 10 paginas 4 figuras 2 tablas the definitive version is available at www3 interscience wiley com

snow thickness retrieval from l band brightness temperatures a model comparison the soil moisture and ocean salinity smos satellite s l band 1 4 ghz measurements have been used to retrieve snow thickness over thick sea ice in a previous study here we consider brightness temperature simulations for 2 5 4 5 m thick arctic multi year ice and compare the results of the relatively simple emission model m2013 used previously for the retrieval with simulations from a more complex model t2011 that combines a sea ice version of the microwave emission model for layered snowpacks memls with a thermodynamic model we find that l band brightness temperature is mainly determined by ice temperature in the m2013 model ice temperature in turn is mainly determined by surface temperature and snow thickness and this dependence has been used previously to explain the potential for a snow thickness retrieval our comparisons suggest that the m2013 retrieval model may benefit from a more sophisticated thermodynamic calculation of the ice temperature or from using independent temperature data e g from 6 ghz channels in both models horizontally polarized brightness temperatures increase with snow thickness while holding surface temperature ice thickness and snow density near constant the increase in the t2011 model is steeper than in m2013 suggesting a higher sensitivity to snow thickness than found earlier

thin and thinner sea ice mass balance measurements during sheba 1 as part of a large interdisciplinary study of the surface heat budget of the arctic ocean sheba we installed more than 135 ice thickness gauges to determine the sea ice mass balance while installing these gauges during the fall of 1997 we found that much of the multiyear ice cover was only 1 m thick considerably thinner than expected over the course of the yearlong field experiment we monitored the mass balance for a wide variety of ice types including first year ice ponded ice unponded ice multiyear ice hummocks new ridges and old ridges initial ice thicknesses for these sites ranged from 0 3 to 8 m and snow depths varied from a few centimeters to more than a meter however for all of their differences and variety these thickness gauges sites shared a common trait at every site there was a net thinning of the ice during the sheba year the thin ice found in october 1997 was even thinner in october 1998 the annual cycle of ice thickness was also similar at all sites there was a steady increase in thickness through the winter that gradually tapered off in the spring this was followed by a steep drop off in thickness during summer melt and another tapering in late summer and early fall as freeze up began maximum surface melting was in july while bottom ablation peaked in august combining results from the sites we found an average winter growth of 0 51 m and a summer melt of 1 26 m which consisted of 0 64 m of surface melt and 0 62 m of bottom melt there was a weak trend for thicker ice to have less winter growth and greater net loss for the year however ice growth was also impacted by the snow depth considerable variability was observed between sites in both accretion and ablation the total accretion during the 9 month growth season ranged from zero for thick ridged ice to more than a meter for young ice ponds tended to have a large amount of surface melting while ridges had considerable bottom ablation

retrieving surface waves from ambient seismic noise using seismic interferometry by multidimensional deconvolution retrieving virtual source surface waves from ambient seismic noise by cross correlation assumes among others that the noise field is equipartitioned and the medium is lossless violation of these assumptions reduces the accuracy of the retrieved waves a point spread function computed from the same ambient noise quantifies the associated virtual source s spatial and temporal smearing multidimensional deconvolution mdd of the retrieved surface waves by this function has been shown to improve the virtual source s focusing and the accuracy of the retrieved waves using synthetic data we tested mdd on data recorded during the batholiths experiment a passive deployment of broadband seismic sensors in british columbia canada the array consisted of two approximately linear station lines using 4 months of recordings we retrieved fundamental mode rayleigh waves 0 05 0 27 hz we only used noise time windows dominated by waves that traverse the northern line before reaching the southern 2 5 of all data compared to the conventional cross correlation result based on this subset the mdd waveforms are better localized and have significantly higher signal to noise ratio furthermore mdd corrects the phase and the spatial deconvolution fills in a spectral f k domain gap between the single frequency and double frequency microseism bands frequency whitening of the noise also fills the gap in the cross correlation result but the signal to noise ratio of the mdd result remains higher comparison of the extracted phase velocities shows some differences between the methods also when all data are included in the conventional cross correlation

winter snow cover on the sea ice of the arctic ocean at the surface heat budget of the arctic ocean sheba temporal evolution and spatial variability 1 the evolution and spatial distribution of the snow cover on the sea ice of the arctic ocean was observed during the surface heat budget of the arctic ocean sheba project the snow cover built up in october and november reached near maximum depth by mid december then remained relatively unchanged until snowmelt ten layers were deposited the result of a similar number of weather events two basic types of snow were present depth hoar and wind slab the depth hoar 37 of the pack was produced by the extreme temperature gradients imposed on the snow the wind slabs 42 of the snowpack were the result of two storms in which there was simultaneous snow and high winds 10 m s 1 the slabs impacted virtually all bulk snow properties emphasizing the importance of episodic events in snowpack development the mean snow depth n 21 169 was 33 7 cm with a bulk density of 0 34 g cm 3 n 357 r2 of 0 987 giving an average snow water equivalent of 11 6 cm 25 higher than the amount record by precipitation gauge both depth and stratigraphy varied significantly with ice type the greatest depth and the greatest variability in depth occurring on deformed ice ridges and rubble fields across all ice types a persistent structural length in depth variations of 20 m was found this appears to be the result of drift features at the snow surface interacting with small scale ice surface structures a number of simple ways of representing the complex temporal and spatial variations of the snow cover in ice ocean atmosphere models are suggested

3 d crustal structure of the western united states application of rayleigh wave ellipticity extracted from noise cross correlations we present a new 3 d seismic model of the western united states crust derived from a joint inversion of rayleigh wave phase velocity and ellipticity measurements using periods from 8 to 100 s improved constraints on upper crustal structure result from use of short period rayleigh wave ellipticity or rayleigh wave h v horizontal to vertical amplitude ratios measurements determined using multicomponent ambient noise cross correlations to retain the amplitude ratio information between vertical and horizontal components for each station we perform daily noise pre processing temporal normalization and spectrum whitening simultaneously for all three components for each station pair amplitude measurements between cross correlations of different components radial radial radial vertical vertical radial and vertical vertical are then used to determine the rayleigh wave h v ratios at the two station locations we use all earthscope usarray tranportable array data available between 2007 january and 2011 june to determine the rayleigh wave h v ratios and their uncertainties at all station locations and construct new rayleigh wave h v ratio maps in the western united states between periods of 8 and 24 s combined with previous longer period earthquake rayleigh wave h v ratio measurements and rayleigh wave phase velocity measurements from both ambient noise and earthquakes we invert for a new 3 d crustal and upper mantle model in the western united states correlation between the inverted model and known geological features at all depths suggests good resolution in five crustal layers use of short period rayleigh wave h v ratio measurements based on noise cross correlation enables resolution of distinct near surface features such as the columbia river basalt flows which overlie a thick sedimentary basin

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

anelastic earth structure from the coherency of the ambient seismic field 1 cross correlation of the ambient seismic field is now routinely used to measure seismic wave travel times however relatively little attention has been paid to other information that could be extracted from these signals in this paper we demonstrate the relationship between the spatial coherency of the ambient field and the elastodynamic green s function in both time and frequency domains through measurement of the frequency domain coherency as a function of distance we sequentially recover phase velocities and attenuation coefficients from these measurements we generate 1 d shear wave velocity and attenuation models for southern california the ambient field measurements of attenuation and the exceptional path coverage that results from the many possible interstation measurements allow us to extend q estimates over a range of frequencies that has previously been difficult to analyze using earthquake data measurements from paths that cross major sedimentary basins show both lower wave speeds and lower quality factors than other paths as expected our results indicate that there is a wealth of information available in the spatial coherency of the ambient seismic field

mass balance and equilibrium line altitudes of glaciers in high mountain environments abstract the mass balance characteristics of glaciers in high mountain environments complicate the relationship between glacier equilibrium line altitudes elas and climatic variables such as precipitation and air temperature therefore methods of ela reconstruction employed in low relief environments are commonly not applicable in high mountains or require some modification we review the concept of the ela with reference to the mass balance of a range of glacier types found in high mountain regions we examine the applicability of several commonly used methods of ela reconstruction for different glacier types and propose some general principles to guide the choice of appropriate methods

ambient field green s functions from asynchronous seismic observations 1 we demonstrate that the coda of station to station green s functions extracted from the ambient seismic field in southern california reach stability in the microseism band 5 10 s after correlating six months of noise data the coda stability makes it possible to retrieve green s functions between stations that operate asynchronously through scattered waves as recorded by a network of fiducial stations the green s functions extracted from asynchronous and synchronous data have comparable quality as long as stable virtual coda are used and both show good convergence to the green s functions extracted from 1 year of seismic noise with 50 fiducial stations this approach suggests that green s functions can be extracted across seismic stations regardless of whether or not they are occupied simultaneously which raises the prospect of a new mode for seismic experiments that seek to constrain earth structure

surface wave tomography from microseisms in southern california received 5 april 2005 revised 23 may 2005 accepted 9 june 2005 published 26 july 2005 1 since it has already been demonstrated that point topoint seismic propagation green functions can be extracted from seismic noise it should be possible to image earth structure using the ambient noise field seismic noise data from 148 broadband seismic stations in southern california were used to extract the surface wave arrival times between all station pairs in the network the seismic data were then used in a simple but densely sampled tomographic procedure to estimate the surface wave velocity structure within the frequency range of 0 1 0 2 hz for a region in southern california the result compares favorably with previous estimates obtained using more conventional and elaborate inversion procedures this demonstrates that coherent noise field between station pairs can be used for seismic imaging purposes citation sabra k g p gerstoft p roux w a kuperman and m c fehler 2005 surface wave tomography from microseisms in southern california geophys res lett 32 l14311 doi 10 1029 2005gl023155

reconstructing green s function by correlation of the coda of the correlation c3 of ambient seismic noise analysis of long range correlation of the microseisms has been shown to provide reliable measurements of surface wave speeds that can be used for seismic imaging and monitoring in the case of an even distribution of noise sources it has been theoretically demonstrated that the correlation is the exact green s function including all types of waves this method is limited in its application by the actual source distribution in practice the azimuthal distribution of energy flux of the noise is dominated by some particular directions resulting in a clear azimuthal dependence of the quality of the reconstruction of rayleigh waves with a poor reconstruction in some azimuths to solve this problem we use noise correlations measured on the entire network we consider two stations a and b for which the rayleigh waves could not be discerned in the in the correlation of continuous records of ambient noise we computed all correlations between the station a respectively b and all the 150 other stations located at regional distances theoretically these virtual seismograms contain direct waves and coda although they are clearly contaminated by the influence of the imperfect ambient noise field and most are inadequate for direct analysis we used these correlation functions as equivalents to seismograms produced by sources acting at the 150 stations locations and recorded in a respectively b we select time windows in those virtual seismograms that correspond to coda and compute correlations between them this metacorrelation is found to exhibit the surface wave part of the green s function that was not visible in the raw correlation of ambient noise we illustrate the legitimacy of the reconstruction by comparison with raw noise correlations this procedure can be used to assess seismic velocity between stations even in presence of a directive and poorly oriented ambient noise the result shows that in spite of the small signal to noise ratios often seen in correlations of ambient noise especially at large lag time corresponding to coda their codas are better equipartitioned than was the ambient noise upon which they were based they are therefore presumably multiply scattered and contain information on both direct surface waves and also on more complex travel paths

estimating the spatial distribution of snow water equivalence in a montane watershed an approach to model distributed snow water equivalence swe that merges field measurements of depth and density with remotely sensed snow covered area sca is described in 1993 two teams conducted an intensive snow survey in the 92 8k m 2 blackcap basin of the kings river snow depth was measured at 709 points and density in five snow pits and along five transects using a federal sampler sample locations were chosen to be representative of the range of elevation slope and aspect of the basin regression tree models showed that net radiation elevation and slope angle account for 60 70 of the variance in the depth measurements density was distributed over the basin on a 30 m grid with a multiple linear regression model that explained 70 of the observed variance as a function of the same three variables the gridded depth estimates combined with modelled density produced spatially distributed estimates of swe an unsupervised spectral unmixing algorithm estimated snow cover fractions from landsat 5 thematic mapper data acquired at the time as the snow survey this method provides a snow cover fraction estimate for every pixel this subpixel map was used as the best estimate for sca and combining it with the swe map allowed computation of the swe volume the estimated volume using the subpixel sca map was compared with several sca maps produced with simulations of binary sca mapping techniques thresholds of 40 50 and 60 fractional cover were used to map binary cases of full snow cover or no snow cover the diaerence in basin swe volume was up to 13 depending on the threshold used to classify snow covered versus snow free areas the percentage diaerences in volumes show a significant correlation to the percentage diaerences in sca between the methods 1998 john wiley sons ltd

airborne surveys of snow depth over arctic sea ice 1 during the spring of 2009 an ultrawideband microwave radar was deployed as part of operation icebridge to provide the first cross basin surveys of snow thickness over arctic sea ice in this paper we analyze data from three 2000 km transects to examine detection issues the limitations of the current instrument and the regional variability of the retrieved snow depth snow depth is the vertical distance between the air snow and snow ice interfaces detected in the radar echograms under ideal conditions the per echogram uncertainty in snow depth retrieval is 4 5 cm the finite range resolution of the radar 5 cm and the relative amplitude of backscatter from the two interfaces limit the direct retrieval of snow depths much below 8 cm well defined interfaces are observed over only relatively smooth surfaces within the radar footprint of 6 5 m sampling is thus restricted to undeformed level ice in early april mean snow depths are 28 5 16 6 cm and 41 0 22 2 cm over first year and multiyear sea ice myi respectively regionally snow thickness is thinner and quite uniform over the large expanse of seasonal ice in the beaufort sea and gets progressively thicker toward the myi cover north of ellesmere island greenland and the fram strait snow depth over myi is comparable to that reported in the climatology by warren et al 1999 ongoing improvements to the radar system and the utility of these snow depth measurements are discussed

snow depth on arctic sea ice derived from radar in situ comparisons and time series analysis the snow radar being flown on nasa s operation icebridge ongoing aircraft campaigns to the arctic and the antarctic are providing unique observations of the depth of snow on the sea ice cover in this paper we focus on the radar derived snow depth results from the 2009 2012 arctic campaigns we develop and evaluate the use of a distinct snow layer tracker to measure snow depth based on a support vector machine svm supervised learning algorithm the snow radar is designed to detect both the air snow and snow ice interfaces using ultrawideband frequencies from 2 to 8 ghz the quality errors and repeatability of the snow radar snow depth estimates are examined based on comparisons with in situ data obtained during two separate sea ice field campaigns the greenarc 2009 and the cryovex 2011 campaigns off greenland in the lincoln sea finally we analyze 4 years 2009 2012 of three annually repeated sea ice flight lines obtained in early spring located off greenland and the canadian arctic we examine the annual variations of snow depth differences between perennial and seasonal ice when available overall the snow layer tracker produced consistent accurate results for snow depths between 0 10 and 0 60 m this was confirmed with comparisons with the two data sets from the in situ measurement campaigns as well as with the time series analysis and is consistent with other published results

three station interferometry and tomography coda versus direct waves traditional two station ambient noise interferometry estimates the greens function between a pair of synchronously deployed seismic stations three station interferometry considers records observed three stations at a time where two of the stations are considered receiver stations and the third is a source station cross correlations between records at the source station with each of the receiver stations are correlated or convolved again to estimate the greens function between the receiver stations which may be deployed asynchronously we use data from the earthscope usarray in the western us to compare rayleigh wave dispersion obtained from two station and three station interferometry three three station interferometric methods are distinguished by the data segment utilized coda wave or direct wave and whether the source stations are constrained to lie in stationary phase zones approximately inline with the receiver stations the primary finding is that the three station direct wave methods perform considerably better than the three station coda wave method and two station ambient noise interferometry for obtaining surface wave dispersion measurements in terms of signal to noise ratio bandwidth and the number of measurements obtained but possess small biases relative to two station interferometry we present a ray theoretic correction method that largely removes the bias below 40 s period and reduces it at longer periods three station direct wave interferometry provides substantial value for imaging the crust and uppermost mantle and its ability to bridge asynchronously deployed stations may impact the design of seismic networks in the future

ambient noise rayleigh wave tomography of new zealand summary we present the first new zealand wide study of surface wave dispersion using ambient noise observed at 42 broad band stations in the national seismic network geonet and the global seismic network gsn year long vertical component time series recorded between 2005 april 1 and 2006 march 31 have been correlated with one another to yield estimated fundamental mode rayleigh wave green s functions we filter these green s functions to compute rayleigh wave group dispersion curves at periods of 5 50 s using a phase matched filter frequency time analysis technique the uncertainties of the measurements are estimated based on the temporal variation of the dispersion curves revealed by 12 overlapping 3 month stacks after selecting the highest quality dispersion curve measurements we compute group velocity maps from 7 to 25 s period these maps and 1 d shear wave velocity models at four selected locations exhibit clear correlations with major geological structures including the taranaki and canterbury basins the hikurangi accretionary prism and previously reported basement terrane boundaries