a comparison of terrasar x radarsat 2 and alos palsar interferometry for monitoring permafrost environments case study from herschel island canada abstract interferometric synthetic aperture radar insar data sets from terrasar x radarsat 2 and alos palsar are compared for their ability to detect ground movement over the continuous permafrost site of herschel island yukon territory canada all three sensors maintain good coherence within a summer season and can be used to create summer displacement products stacking is advantageous for the terrasar x and radarsat 2 data sets although mottling possibly an interaction of the sar with vegetation or residual tropospheric noise is visible reducing the reliability of the results radarsat 2 and alos palsar provide the most promising results with the ability to form one year interval interferograms palsar can also form two and three year interval interferograms long interval data sets spanning 2007 to 2010 identify a band of movement of 20 to 30 cm year along the north east coast and a region of movement of up to 5 cm year near the northern tip of the island the ability to form long interval displacement products holds the most promise for permafrost monitoring since long term trends are of greater interest for permafrost stability than short term seasonal changes terrasar x data have the disadvantage that year to year interferograms cannot be formed insar is not the ideal monitoring technique for the large thaw slumps of herschel island although general areas of instability can be identified specific slump detection is limited by radar look direction and the large and abrupt slump movement often accompanied by disintegration and collapse of slump sections causes loss of coherence in the insar data thaw slumps may require a different interferometric approach such as slump extent mapping from coherence loss or the installation of corner reflectors and point target techniques the frequent revisit and high spatial resolution of terrasar x provide the best chance of maintaining coherence over thaw slumps in general insar is more successful at identifying broad areas of subtle subsidence in gentle relief areas of terrain instability possibly due to permafrost thaw or ground ice melt and the removal of water volume and prior to significant slumping

optical algorithm for cloud shadow detection over water the application of ocean color product retrieval algorithms for pixels containing cloud shadows leads to erroneous results thus shadows are an important scene type that should be identified and excluded from the set of clear sky pixels in this paper we present an optical cloud shadow detection technique called the cloud shadow detection index csdi this approach is for homogeneous water bodies such as deep waters where shadow detection is very challenging due to the relatively small differences in the brightness values of the shadows and neighboring sunlit or some other regions the csdi technique is developed based on the small differences between the total radiances reaching the sensor from the shadowed and neighboring sunlit regions of similar optical properties by amplifying the differences through integrating the spectra of the two regions the integrated value iv is then normalized by the mean of the ivs within a spatial adaptive sliding box where atmospheric and marine optical properties are assumed homogeneous assuming that the true color and the iv images represent accurate shadow locations the results were visually compared the csdi images agree reasonably well with the corresponding true color and the iv images over open ocean also the shape of the cloud shadow particularly for the isolated cloud closely follows that of the cloud as expected reconfirming the potential of the csdi technique

recent progress in snow and ice research a review of snow and ice research in 1987 1990 is presented focusing on the effects of layers in seasonal snow covers ice mechanics on fresh water and sea ice and remote sensig of polar ice sheets these topics provide useful examples of general needs in snow and ice research applicable to most areas such as better representation in models of detailed processes controlled laboratory experiments to quantify processes and field studies to provide the appropriate context for interpretation of processes from remote sensing

constraints on central uplift structure from the manicouagan impact crater recent drilling operations at the 90 km diameter late triassic manicouagan impact crater of quebec canada have provided new insight into the internal structure of a complex craters central region previous work had indicated that the impact event generated a 55 km diameter sheet of molten rock of relatively consistent originally 400 m thickness floran et al 1978 the drilling data reveals melt sheet thicknesses of up to 1500 m with kilometer scale lateral and substantial vertical variations in the geometry of the crater floor beneath the melt sheet the thickest melt section occurs in a 1500 m deep central trough encircled by a horseshoe shaped uplift of precambrian basement the uplift constitutes a modified central peak structure at least part of which breached the melt sheet mineralogical and compositional segregation differentiation of the thicker melt sheet section coupled with a lack of fractionation in the thinner units shows that the footwall geometry and associated trough structure were in place prior to melt sheet solidification marked lateral changes in sub melt sheet basement relief support the existence of a castellated footwall that was created by high angle impact related offsets of 100s to 1000s of meters this indicates that deformation during the modification stage of the cratering process was primarily facilitated by large displacement fault systems this work suggests that manicouagan is a central peak basin with rings which does not appear to fit with current complex crater classification schemes

implementation and evaluation of concurrent gradient search method for reprojection of modis level 1b imagery this paper presents details regarding implementation of a novel algorithm for reprojection of moderate resolution imaging spectroradiometer modis level 1b imagery the method is based on a simultaneous 2 d search in latitude and longitude geolocation fields by using their local gradients due to the segmented structure of modis imagery caused by the instrument whiskbroom electrooptical design the gradient search is realized in the following two steps intersegment and intrasegment search this approach resolves the discontinuity of the latitude longitude geolocation fields caused by overlap between consecutively scanned modis multidetector image segments the structure of the algorithm allows equal efficiency with nearest neighbor and bilinear interpolation a special procedure that combines analytical and numerical schemes is designed for reprojecting imagery near the polar region where the standard gradient search may become unstable the performance of the method was validated by comparison of reprojected modis terra and modis aqua images with georectified landsat 7 enhanced thematic mapper plus imagery over canada it was found that the proposed method preserves the absolute geolocation accuracy of modis pixels determined by the modis geolocation team the method was implemented to reproject modis level 1b imagery over canada north america and arctic circumpolar zone in the following four popular geographic projections plate care cylindrical equidistant lambert conic conformal universal transverse mercator and lambert azimuthal equal area it was also found to be efficient for reprojection of advanced very high resolution radiometer and medium resolution imaging spectrometer satellite images and general type meteorological fields such as the north american regional reanalysis data sets

shock metamorphism of bosumtwi impact crater rocks shock attenuation and uplift formation shock wave attenuation rate and formation of central uplifts are not precisely constrained for moderately sized complex impact structures the distribution of shock metamorphism in drilled basement rocks from the 10 5 kilometer diameter bosumtwi crater and results of numerical modeling of inelastic rock deformation and modification processes during uplift constrained with petrographic data allowed reconstruction of the pre impact position of the drilled rocks and revealed a shock attenuation by 5 gigapascals in the uppermost 200 meters of the central uplift the proportion of shocked quartz grains and the average number of planar deformation feature sets per grain provide a sensitive indication of minor changes in shock pressure the results further imply that for moderately sized craters the rise of the central uplift is dominated by brittle failure

using cosmo skymed x band and envisat c band sar interferometry for landslides analysis abstract we explore new possibilities offered by the recently available x band satellite radar sensors for landslide hazard assessments on a detailed scale with particular reference to the exploitation of persistent scatterers interferometry psi techniques special attention is paid to the impact of the improved resolution of new x band radar imagery on the psi results in terms of quality and quantity of useful information this evaluation is supported by theoretical modelling as well as by the comparison of results from x band csk and c band envisat psi for two areas of interest one in italy and the other in switzerland it is demonstrated that with respect to medium resolution envisat ps processing fewer csk high resolution images are sufficient to achieve comparable precision of the mean displacement velocity estimates this together with the shorter revisit times provided by the csk constellation can be very important when dealing with emergency situations furthermore it is quantified that from about 3 to 11 times greater ps densities are obtained with the higher resolution x band data this implies more information about ground surface displacements as well as improved landslide monitoring and slope instability investigation capabilities furthermore ground displacement measurements can be interpreted without local knowledge of the focus area or in situ controls and nonetheless guide single hillslope instability assessments with support of google earth and its high resolution optical imagery this blind approach will allow one to monitor remote and poorly known regions at high risk of potentially disastrous slope failures

frictional melting processes in planetary materials from hypervelocity impact to earthquakes frictional melting is the result of the conversion of mechanical deformation to heat under adiabatic conditions of slip within planetary materials which are mainly natural ceramics frictional melting occurs at high strain rates typically 10 2 s 1 and at slip velocities greater than 0 1 m s 1 t he pathway to friction melting is controlled by the mechanical properties of a rock s constituent minerals especially fracture toughness minerals with the lowest fracture toughnesses and breakdown temperatures are preferentially comminuted and fused to form the melt the product is a polyphase suspension comprising mineral and rock fragments enclosed in a liquid matrix this cools to form the rock type known as pseudotachylyte and at even higher strain rates it forms shock veins in meteorites and in impact craters which may contain high pressure mineral polymorphs the generation of melt on sliding surfaces can lubricate earthquake faults facilitate the post shock modification of impact craters and make landslides more hazardous

early soil consolidation from magnetic extensometers and full resolution sar interferometry over highly decorrelated reclaimed lands abstract reclaimed lands account for a large portion of the developable territories in hong kong towards better construction planning for the follow up civil works stability monitoring is usually required at these artificial sites the synthetic aperture radar interferometry insar technique can provide bi weekly updates of high resolution up to 1 m and high precision millimeter level ground motion maps at low costs which overcomes the limitations of ground based instruments however rapid settlement during the early stage of soil consolidation can result in significant temporal decorrelation to phase signals and impact insar detection especially over newly reclaimed areas here we give a first demonstration on how the introduction of in situ extensometer measurements can help improve insar capabilities for signal recovery of the early consolidation process we integrate persistent scatterers ps and distributed scatterers ds in our processing chain to establish a two tier monitoring network magnetic extensometers are used to estimate local consolidation models which are then utilized to replace the linear part in the conventional functional phase model for nonlinear deformation both hyperbolic and exponential models were considered the proposed method was applied to 61 terrasar x images covering the penny s bay reclamation stage 2 pbr2 in hong kong the consolidation history of the new reclamation site has been successfully extracted with cumulative subsidence exceeding 1 6 m between may 2008 and dec 2011 approximately 84 of the settlement of the non dredged region was found to be from compaction of underlying soft marine deposits not the filling materials in addition to highlighting the spatiotemporal characteristics of the deformation insar also helps reveal the compaction evolution of the underlying deposit the results benefit our understanding of the early consolidation process in pbr2 and inform extra reinforcement plans if necessary

characteristics of thermokarst lakes and their influence on permafrost in qinghai tibet plateau abstract about 250 thermokarst lakes with an average size of 5580 m2 and a total size of 139 104 m2 are spread between the kunlun mountain pass and the fenghuo mountain pass along the qinghai tibet railway where ice rich and warm permafrost exists approximately 56 of the lakes are elliptical and 23 are elongated the water depth varies between 0 4 and 3 m most of the lakes in the chumarhe high plain and other mountain regions are shallower than the thickness of winter ice 60 to 80 cm and are frozen to the bottom during the cold seasons however in the hoh xil hill region and beiluhe basin the water depth is greater than the thickness of winter ice and the relatively warm lake bottoms can cause considerable disturbance to the surrounding continuous permafrost the lakes in the chumarhe high plain are saltwater or brine lakes and in other regions the lakes contain freshwater or brackish water ages of formation enlargement rates water and lake bottom temperatures the configuration of permafrost and active layer thickness were measured at a typical thermokarst lake in the beiluhe basin between 2007 and 2009 the lake formed about 890 years ago and is 150 m long 100 m wide with a water depth of 2 5 m now the size of the lake is growing at a rate of about 1 m a at some shores the lakeshores are underlain by permafrost which terminates almost vertically at their edge the mean annual temperature measured at lake bottom in the centre was 5 45 c while the temperature of permafrost at 15 m depth in the lakeshore varied from 0 84 c near the edge of the lake to 1 26 c at 80 m from the edge the corresponding active layer depths varied from 2 45 to 1 80 m the configuration of the talik indicates that no permafrost is found beneath the centre of the lake

numerical modeling of crustal block and fault dynamics earthquakes and slip rates in the tibet himalayan region the tibetan plateau and himalayans have resulted from the continuous indian and eurasian plate convergence following their initial collision about 55 million years ago earthquakes in the region occur mainly in response to the crustal motion and stress localization associated with this convergence to understand the basic features of the crustal motion and seismicity in the tibet himalayan region we develop a numerical model of block and fault dynamics the model structure is composed of six major upper crustal blocks separated by fault planes these blocks are assumed to be perfectly rigid and move as a consequence of the indian plate push and of a flow of the lower crust deformations take place along the fault planes separating the blocks the interaction of the blocks along the fault planes is visco elastic as long as the ratio of the shear stress to the difference between the pore pressure and normal stress remains below a critical strength level when the critical level is exceeded in some part of a fault plane an earthquake stress drop occurs causing also failures in adjacent parts of the fault plane the stress drop affected parts of the fault plane enter in a state of creep immediately after the earthquake and the creep lasts until the stress falls below a certain level we develop several sets of numerical experiments to analyze the earthquake clustering frequency to magnitude relationships earthquake focal mechanisms and fault slip rates in the model large events in the numerical experiments cluster on the fault segments associated with the himalayan frontal thrust as well as at some internal faults of the tibetan plateau the clustering of earthquakes on a given fault is a consequence of the dynamics of the regional fault system rather than that of the fault only we show that variations in the relationship of magnitude to frequency of the events are associated with changes in the motion of the upper crustal blocks and depend on the rheological properties of fault plane zones the focal mechanisms of model events are found to be consistent with that of earthquakes in the region the synthetic moment rate captures the observed rate of seismic moment release we demonstrate in the model that the present crustal motion in the region is indeed governed by the north northeastern movement of india toward eurasia and the movement of the lower crust variations in the rheological properties of fault plane zones and or in the motion of the lower crust influence rates of the crustal block displacements and slips at the faults separating the blocks this can explain the discrepancies in estimates of slip rates over short and long time scales at major faults in the region

integrated pan arctic melt onset detection from satellite active and passive microwave measurements 2000 2009 1 an integrated pan arctic melt onset data set is generated for the first time by combining estimates derived from active and passive microwave satellite data using algorithms developed for the northern high latitude land surface ice caps large lakes and sea ice the data set yields new insights into the spatial and temporal patterns of mean melt onset date mmod and the associated geographic and topographic controls for example in the terrestrial arctic tree fraction and latitude explain more than 60 of the variance in mmod with the former exerting a stronger influence on mmod than the latter elevation is also found to be an important factor controlling mmod with most of the arctic exhibiting significant positive relationships between mmod and elevation with a mean value of 24 5 m d 1 melt onset progresses fastest over land areas of uniform cover or elevation 40 80 km d 1 or both and slows down in mountainous areas on ice caps and in the forest tundra ecotones over sea ice melt onset advances very slowly in the marginal seas while in the central arctic the rate of advance can exceed 100 km d 1 comparison of the observed mmod with simulated values from the third version of the canadian coupled global climate model showed good agreement over land areas but weaker agreement over sea ice particularly in the central arctic where simulated mmod is about 2 3 weeks later than observed because of a cold bias in simulated surface air temperatures over sea ice

topographic correction for alos palsar interferometry l band synthetic aperture radar sar interferometry is very successful for mapping ground deformation in densely vegetated regions however due to its larger wavelength the capacity to detect slow deformation over a short period of time is limited stacking and small baseline subset sbas techniques are routinely used to produce time series of deformation and average deformation rates by reducing the contribution of topographic and atmospheric noise for large sets of images that are presently available from c band european remote sensing satellites ers 1 2 and environmental satellite envisat the standard stacking and sbas algorithms are accurate however the same algorithms are often inaccurate when used for processing of interferograms from l band advanced land observing satellite phased array type l band sar alos palsar this happens because only a limited number of interferograms is acquired and also because of large spatial baselines often correlated with the time of acquisition in this paper two techniques are suggested that can be used for removing the residual topographic component from stacking and sbas results thereby increasing their accuracy

observations at terrestrial impact structures their utility in constraining crater formation hypervelocity impact involves the near instantaneous transfer of considerable energy from the impactor to a spatially limited near surface volume of the target body local geology of the target area tends to be of secondary importance and the net result is that impacts of similar size on a given planetary body produce similar results this is the essence of the utility of observations at impact craters particularly terrestrial craters in constraining impact processes unfortunately there are few well documented results from systematic contemporaneous campaigns to characterize specific terrestrial impact structures with the full spectrum of geoscientific tools available at the time nevertheless observations of the terrestrial impact record have contributed substantially to fundamental properties of impact there is a beginning of convergence and mutual testing of observations at terrestrial impact structures and the results of modeling in particular from recent hydrocode models the terrestrial impact record provides few constraints on models of ejecta processes beyond a confirmation of the involvement of the local substrate in ejecta lithologies and shows that z models are at best first order approximations observational evidence to date suggests that the formation of interior rings is an extension of the structural uplift process that occurs at smaller complex impact structures there are however major observational gaps and cases e g vredefort where current observations and hydrocode models are apparently inconsistent it is perhaps time that the impact community as a whole considers documenting the existing observational and modeling knowledge gaps that are required to be filled to make the intellectual breakthroughs equivalent to those of the 1970s and 1980s which were fueled by observations at terrestrial impact structures filling these knowledge gaps would likely be centered on the later stages of formation of complex and ring structures and on ejecta

contribution of small glaciers to global sea level observed long term changes in glacier volume and hydrometeorological mass balance models yield data on the transfer of water from glaciers excluding those in greenland and antarctica to the oceans the average observed volume change for the period 1900 to 1961 is scaled to a global average by use of the seasonal amplitude of the mass balance these data are used to calibrate the models to estimate the changing contribution of glaciers to sea level for the period 1884 to 1975 although the error band is large these glaciers appear to account for a third to half of observed rise in sea level approximately that fraction not explained by thermal expansion of the ocean

potential of small baseline sar interferometry for monitoring land subsidence related to underground coal fires wuda northern china case study uncontrolled coal fires can result in massive surface displacements due to the change in volume of burning coal and thermal effects in the adjacent rock mass simultaneously the resultant surface breakings provide greater access to air and water that in turn can aggravate the problem of underground coal seam burning in this case study we have investigated the feasibility and potential of detecting the land subsidence accompanying coal fires by means of satellite insar observations three groups of small baseline insar approaches psi stacking and 2 passdinsar were applied to the wuda coalfield northern china to reveal the spatial and temporal signals of the land subsidence in the areas affected by the coal fires the interferometric results agree well with gps observations and coal fire data obtained by field investigation which demonstrates that the small baseline insar techniques have remarkable potential to detect this land subsidence of interest in particular our results show that the development of coal fires can lead to new subsiding areas and also accelerate the ongoing surface subsidence typically within the areas of mature coal fires through a comparison of the interferometric observations and the multi temporal coal fire maps this timely and reliable information on land subsidence will be useful for the detection and mapping of the coal fire affected regions and thereby assist in fighting and controlling coal seam burning

insar measurements of surface deformation over permafrost on the north slope of alaska 1 ground based measurements of active layer thickness provide useful data for validating calibrating remote sensing and modeling results however these in situ measurements are usually site specific with limited spatial coverage here we apply interferometric synthetic aperture radar insar to measure surface deformation over permafrost on the north slope of alaska during the 1992 2000 thawing seasons we find significantly systematic differences in surface deformation between floodplain areas and the tundra covered areas away from the rivers using floodplain areas as the reference for insar s relative deformation measurements we find seasonally varying vertical displacements of 1 4 cm with subsidence occurring during the thawing season and a secular subsidence of 1 4 cm decade we hypothesize that the seasonal subsidence is caused by thaw settlement of the active layer and that the secular subsidence is probably due to thawing of ice rich permafrost near the permafrost table these mechanisms could explain why in situ measurements on alaskan north slope reveal negligible trends in active layer thickness during the 1990s despite the fact that atmospheric and permafrost temperatures in this region increased during that time this study demonstrates that surface deformation measurements from insar are complementary to more traditional in situ measurements of active layer thickness and can provide new insights into the dynamics of permafrost systems and changes in permafrost conditions

synergistic approach for mapping debris covered glaciers using optical thermal remote sensing data with inputs from geomorphometric parameters abstract debris cover on glacier boundaries critically impedes the global inventorying of glaciers and confounds most of the techniques developed for semi automated mapping of glaciers debris on the glacier referred as supraglacial debris and that occurring outside the glacier boundaries referred as periglacial debris being derived from a common source i e the valley rock tend to have a similar spectral response in the reflection region which renders them mutually indistinguishable however there exist temperature differences between them this aspect has been considered in this remote sensing based study to distinguish between the supraglacial and periglacial debris in a test area in the chenab basin himalayas by inclusion of thermal infrared tir bands in remote sensing data processing a synergistic multisensor approach for the delineation of debris covered glacier boundaries is used here which integrates the inputs from thermal terra aster sensor and optical irs p6 awifs sensor remote sensing data multispectral classification techniques and the dem derived geomorphometric parameters the results of this study corroborate earlier findings on utilization of temperature differences as one of the parameters in glacial studies the proposed synergistic approach therefore appears useful in accurate mapping of debris covered glaciers in the himalayan region

comparison between the results of a snow metamorphism model and remote sensing derived snow parameters in the alps abstract the numerical snow metamorphism model crocus derives a complete description of the snow cover according to its geographical location range elevation slope and orientation from the remote sensing data snow parameters that were comparable to the model results were derived the lower elevation of the snow cover the surface grain size and the surface temperature the landsat thematic mapper sensor was used because it has a good spatial resolution a short wave infrared channel which is sensitive to grain size and a thermal infrared channel a first landsat tm thematic mapper scene was acquired on 24 april 1992 and a second one on 11 december 1992 a dem digital elevation model was used to obtain the local incidence angles and the elevation of each snow pixel the pixels were then grouped according to the crocus classification range elevation slope orientation and the mean snow characteristics for each class were compared with the crocus results the lower limit of snow and the surface grain size derived from tm data compared favorably with the model results even if those parameters were not always easy to define larger differences were found for the temperature because it varies rapidly and is very sensitive to shadowing by surrounding mountains and also because its remote measurement is dependent on atmospheric conditions

a small baseline approach for investigating deformations on full resolution differential sar interferograms this paper presents a differential synthetic aperture radar sar interferometry difsar approach for investigating deformation phenomena on full resolution difsar interferograms in particular our algorithm extends the capability of the small baseline subset sbas technique that relies on small baseline difsar interferograms only and is mainly focused on investigating large scale deformations with spatial resolutions of about 100 spl times 100 m the proposed technique is implemented by using two different sets of data generated at low multilook data and full single look data spatial resolution respectively the former is used to identify and estimate via the conventional sbas technique large spatial scale deformation patterns topographic errors in the available digital elevation model and possible atmospheric phase artifacts the latter allows us to detect on the full resolution residual phase components structures highly coherent over time buildings rocks lava structures etc as well as their height and displacements in particular the estimation of the temporal evolution of these local deformations is easily implemented by applying the singular value decomposition technique the proposed algorithm has been tested with data acquired by the european remote sensing satellites relative to the campania area italy and validated by using geodetic measurements

recent advances in sar interferometry time series analysis for measuring crustal deformation abstract synthetic aperture radar sar interferometry is a technique that permits remote detection of deformation at the earth s surface and has been used extensively to measure displacements associated with earthquakes volcanic activity and many other crustal deformation phenomena analysis of a time series of sar images extends the area where interferometry can be successfully applied and also allows detection of smaller displacements through the reduction of error sources here we review recent advances in time series sar interferometry methods that further improve accuracy this is particularly important when constraining displacements due to processes with low strain rates such as interseismic deformation we include examples of improved algorithms applied to image deformation associated with the 2010 eruption of eyjafjallajokull volcano in iceland slow slip on the guerrero subduction zone in mexico and tectonic deformation in western anatolia turkey

shock barometry of the siljan impact structure sweden the siljan impact structure in sweden is the largest confirmed impact structure in western europe despite this the structure has been poorly studied in the past and detailed studies of shock metamorphic features in the target lithologies are missing here we present the results of a detailed systematic search for shock metamorphic features in quartz grains from 73 sampled localities at siljan at 21 localities from an area approximately 20 km in diameter located centrally in the structure the orientations of 2851 planar deformation feature sets in 1179 quartz grains were measured observations of shatter cones outside of the zone with shocked quartz extend the total shocked area to approximately 30 km in diameter the most strongly shocked samples recording pressures of up to 20 gpa occur at the very central part of the structure and locally in these samples higher pressures causing melting conditions in the affected rocks were reached pressures recorded in the studied samples decrease outwards from the center of the structure forming roughly circular envelopes around the proposed shock center based on the distribution pattern of shocked quartz at siljan the original transient cavity can be estimated at approximately 3238 km in diameter after correcting for erosion we conclude that the original rim to rim diameter of the siljan crater was somewhere in the size range 5090 km less

global assessment of supraglacial debris cover extents rocky debris on glacier surfaces influences ice melt rates and the response of glaciers to climate change however scarce data on the extent and evolution of supraglacial debris cover have so far limited its inclusion in regional to global glacier models here we present global data sets of supraglacial debris cover extents based on landsat 8 and sentinel 2 optical satellite imagery we find that about 4 4 26 000 km2 of all glacier areas excluding the greenland ice sheet and antarctica are covered with debris but that the distribution is heterogeneous the largest debris covered areas are located in high mountain ranges away from the poles at a global scale we find a negative scaling relationship between glacier size and percentage of debris therefore the influence of debris cover on glacier mass balances is expected to increase in the future as glaciers continue to shrink

structural geology of impact craters abstract the formation of impact craters is a highly dynamic and complex process that subjects the impacted target rocks to numerous types of deformation mechanisms understanding and interpreting these styles of micro meso and macroscale deformation has proved itself challenging for the field of structural geology in this paper we give an overview of the structural inventory found in craters of all size ranges on earth and look into the structures of craters on other planetary bodies structural features are discussed here that are caused by i extremely high pressures and temperatures that occur during the initial passage of the shock wave through the target rock and projectile ii the resulting flow field in the target that excavates and ejects rock materials and iii the gravitationally induced modification of the crater cavity into the final crater form a special focus is put on the effects that low angle impacting bodies have on crater formation we hope that this review will help both planetary scientists and structural geologists understand the deformation processes and resulting structures generated by meteorite impact

ries crater and suevite revisited observations and modeling part ii modeling we present the results of numerical modeling of the formation of the ries crater utilizing the two hydrocodes sova and isale these standard models allow us to reproduce crater shape size and morphology and composition and extension of the continuous ejecta blanket some of these results cannot however be readily reconciled with observations the impact plume above the crater consists mainly of molten and vaporized sedimentary rocks containing very little material in comparison with the ejecta curtain at the end of the modification stage the crater floor is covered by a thick layer of impact melt with a total volume of 6 11 km3 the thickness of true fallback material from the plume inside the crater does not exceed a couple of meters ejecta from all stratigraphic units of the target are transported ballistically no separation of sedimentary and crystalline rocks as observed between suevites and bunte breccia at ries is noted we also present numerical results quantifying the existing geological hypotheses of ries ejecta emplacement from an impact plume by melt flow or by a pyroclastic density current the results show that none of these mechanisms is consistent with physical constraints and or observations finally we suggest a new hypothesis of suevite formation and emplacement by postimpact interaction of hot impact melt with water or volatile rich sedimentary rocks

ejecta from experimental impact craters particle size distribution and fragmentation energy abstract the particle size distribution psd of impact crater ejecta is an important parameter that is useful for understanding the formation of natural craters the distribution of space debris the influence of impact events on climate and energy partitioning in impact events 11 impact experiments into dry and water saturated sandstone were performed and analyzed the experiments span a range of impact velocities from 2 5 to 5 3 km s 1 using projectile sizes from 2 5 to 12 mm kinetic impact energies between 874 and 80 338 j were achieved ejecta of these experiments was collected and the psd was measured and quantified with power law fits the resulting power law exponents lie between 2 54 and 2 74 our results do not show an influence of impact energy or impact velocity on the psd of impact ejecta a significant increase in the psd values was found from dry to water saturated sandstone targets we suggest that water saturation of the target has multiple effects on ejecta fragmentation a comparison of our experimental data with data from the literature shows no correlation between the target material lithology and the ejecta psd interestingly literature data for disruption experiments revealed a strong influence imparted energy density on the d values psd values were used to calculate the energy spent for target fragmentation and show that the fraction of impact energy used for comminution is in the lower single digit percentage

progressive deformation of feldspar recording low barometry impact processes tenoumer impact structure mauritania the tenoumer impact structure is a small well preserved crater within archean to paleoproterozoic amphibolite gneiss and granite of the reguibat shield north central mauritania the structure is surrounded by a thin ejecta blanket of crystalline blocks granitic gneiss granite and amphibolite and impact melt rocks evidence of shock metamorphism of quartz most notably planar deformation features pdfs occurs exclusively in granitic clasts entrained within small bodies of polymict glass rich breccia impact related deformation features in oligoclase and microcline grains on the other hand occur both within clasts in melt breccia deposits where they co occur with quartz pdfs and also within melt free crystalline ejecta in the absence of co occurring quartz pdfs feldspar deformation features include multiple orientations of pdfs enhanced optical relief of grain components selective disordering of alternate twins inclined lamellae within alternate twins and combinations of these individual textures the distribution of shock features in quartz and feldspar suggests that deformation textures within feldspar can record a wide range of average pressures starting below that required for shock deformation of quartz we suggest that experimental analysis of feldspar behavior combined with detailed mapping of shock metamorphism of feldspar in natural systems may provide critical data to constrain energy dissipation within impact regimes that experienced low average shock pressures

growth and evolution of asteroids asteroids are what is left of the precursors to the terrestrial planets they are stunning in their diversity ranging from charcoal black worlds the size of a hilltop spinning like a carnival ride to dog bone shaped metallic remnants of some cataclysmically disrupted planetary core to worlds as stately as ceres and vesta and fragments thereof to garden variety fractured and blocky nuggets that dominate near earth space asteroid belts are common around sun like stars when properly seen as unaccreted residues as scraps on the floor of the planetary bakery the diversity of asteroids can be fully appreciated for to paraphrase tolstoy accreted planets are all alike every unaccreted planet is unaccreted in its own way

measurements of glacier variation in the tibetan plateau using landsat data glaciers on the tibetan plateau play an important role in the earth s climate system because of high altitude and difficulties in access regular systematic surveys of glacier variation are almost impossible in some regions of the tibetan plateau as a result remote sensing is at present the primary in many cases the only way to measure the state of glaciers in combination with geographic information system gis it provides an efficient tool to analyze the current state and changes in glaciers we used a technique of integrated remote sensing and gis to map and measure changes in glaciers using a 21 year series of landsat images from 1973 to 1994 and topographic maps of a study site on the tibetan plateau the details of glacier fluctuation such as area of glaciers and changes in the magnitude of recession or advance of a glacier terminus on different dates are described based on the results of image analysis including coregistration classification vector analysis and area calculation within the study area during the 21 years it was determined that the northern glaciers advanced and the southern glaciers retreated the average rate of change was 50 m a 1 to 105 m a 1 the results show that landsat data provide an important source of information for studies of glacier variation

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

variability of biome reflectance directional signatures as seen by polder reflectance measurements acquired with the spaceborne polder instrument are used to analyze the variability of land surface directional signatures as a function of vegetation cover type the reflectance directional signatures are quantified by the three parameters of a modified version of the ross li reflectance model the variability of the estimated parameters with respect to the seven modis biome classes was found to be higher within the classes than between classes with the exception of the desert targets that show more isotropic reflectances a limited number of standard brdfs typically 5 in the red and near infrared capture most of the variability of the directional reflectance measurements supporting the idea that different land surfaces have similar directional signatures over vegetation targets they are characterized by a strong increase toward backscattering and much smaller variations in forward directions the results express the diversity in structural situations within a given biome class and indicate that at the resolution of the polder sensor i e a few kilometers the brdf contains little information on the dominant vegetation type we show that standard directional signatures may be used to correct the reflectance measurements for directional effects with an rms error on the order of 0 011 in the red and 0 015 in the near infrared

mapping blue ice areas in antarctica using etm and modis data blue ice areas bias and their geographical distribution in antarctica were mapped using landsat 7 etm images with 15 m spatial resolution obtained during the 1999 2003 austral summers and covering the area north of 82 58 s and a snow grain size image of the modis based mosaic of antarctica moa dataset with 125 m grid spacing acquired during the 2003 04 austral summer from 82 58 s to the south pole a map of bias was created with algorithms of thresholds based on band ratio and reflectance for etm data and thresholds based on snow grain size for the moa dataset the underlying principle is that blue ice can be separated from snow or rock by their spectral discrepancies and by different grain sizes of snow and ice we estimate the total area of bias in antarctica during the data acquisition period is 234 549 km 2 or 1 67 of the area of the continent blue ice is scattered widely over the continent but is generally located in coastal or mountainous regions the bia dataset presented in this study is the first map covering the entire antarctic continent sourced solely from etm and modis data this dataset can potentially benefit other studies in glaciology meteorology climatology and paleoclimate meteorite collection and airstrip site selection

interaction between permafrost and infrastructure along the qinghai tibet railway detected via jointly analysis of c and l band small baseline sar interferometry abstract the qinghai tibet railway qtr is the highest and longest plateau linear structure in the world the embankment is prone to instability primarily due to the freezing and thawing of the permafrost overlying active layer the infrastructure construction changes environmental conditions and in turn has influenced permafrost evolutions in this study we have investigated the feasibility of extracting surface motions in permafrost regions by means of satellite sar interferometry the relationship between surface deformation permafrost active layer and other environmental conditions were further analyzed in total 19 l band alos palsar slc images acquired from 21 june 2007 to 30 december 2010 and 38 c band envisat asar slc images acquired from 18 november 2004 to 17 december 2009 were employed to cover the beiluhe experimental site qinghai china a hybrid persistent scatterer interferometry model based on interferometric point target analysis ipta and small baseline strategy was firstly developed for surface motion estimation minimizing the seasonal decorrelation effect then the results from c and l band data were analyzed and compared based on a statistical calibration model ground leveling data acquired from fenghuo mount tunnel front with a one month interval were used for insar derived results validation revealing good agreement in displacement rates as well as time series the qtr has been in operation since 2006 our study has observed distinct surface motions along the embankment primarily in the range of 20 to 20 mm yr implying the necessity of continued satellite based surveillance along the qtr

measurement of interseismic strain across the haiyuan fault gansu china by insar the haiyuan fault is part of a major left lateral fault system at the northeastern edge of the tibet qinghai plateau two m8 earthquakes 1920 and 1927 occurred along the fault bracketing an unbroken section of the fault identified as the tianzhu seismic gap we use interferometric synthetic aperture radar data from descending orbits of the ers satellites acquired between 1993 and 1998 along two adjacent tracks covering the gap to measure the current surface movements and better understand the present day mechanical behavior of this fault section the analysis of the radar data involves first the combined correction of orbital errors and errors associated with the phase delay through the troposphere a subset of the data is then selected based on the analysis of the residual noise spectra for each pair of data the selected interferograms are stacked and the average phase change rate is converted in fault parallel velocity assuming that the ground movement is horizontal and parallel to the fault velocity maps from both tracks show a zone of high velocity gradient across the fault a few kilometers wide consistent with left lateral slip on the haiyuan fault the average velocity field from the two tracks in their overlapping area is well fit with a single screw dislocation model in an elastic half space the derived fault slip rate at depth 4 2 8 mm yr is consistent with recent gps results the corresponding shallow apparent locking depth 0 4 2 km can be explained by a current low stress accumulation on the fault due to creep almost on the entire fault plane however unless it is transient this creep would be paradoxical with the occurrence of past large earthquakes along this fault section as revealed by paleoseismology an alternative model implying both shallow creep in the brittle upper crust and deep aseismic slip beneath the seismogenic layer separated by a locked section would be consistent with insar observations and with the potential for large earthquakes on the fault as well a two dislocation model with slip at 5 mm yr beneath 15 km and a transient creep rate of 11 mm yr between 2 and 7 km fits the insar data however the width and creep rate of the shallow creeping zone and their possible along strike variations are still poorly resolved with the present data set

modelling the spatial distribution of permafrost in labrador ungava using the temperature at the top of permafrost permafrost zonation in labrador ungava ranges from very isolated patches through to continuous permafrost here we present a new estimate of the distribution of permafrost at high resolution 250 m 250 m using spatial numerical modelling supported by station data from 29 air and ground climate monitoring stations permafrost presence was estimated using a modified version of the temperature at the top of permafrost ttop model mean ground surface temperatures were modelled using gridded air temperatures and a novel n factor parameterization scheme that compensates for regional differences in continentality snowfall and land cover and is transferable to other subarctic environments the thermal offset was modelled using land cover and surficial material datasets predicted ttop values for the average climate range regionally from 9 c for high elevations in northern quebec to 5 c for southeastern labrador quebec modelling for specific temporal windows 1948 1962 1982 1996 2000 2014 suggests that permafrost area increased from the middle of the 20th century to a potential peak extent 36 of the total land area in the 1990s subsequent warming is predicted to have caused a decrease in permafrost extent of one quarter 95 000 km2 even if air temperatures rise no further providing air and ground temperatures equilibrate zonal boundaries derived by upscaling the high resolution model are highly scale dependent precluding direct comparison with the permafrost map of canada that was generated without the use of geographic information system based analyses

comparison of geomorphological field mapping and 2d insar mapping of periglacial landscape activity at nordnesfjellet northern norway

soil organic carbon pools in the northern circumpolar permafrost region of all soils in the northern permafrost region is approximately 18 782 10 3 km 2 o r approximately 16 of the global soil area in the northern permafrost region organic soils peatlands and cryoturbated permafrost affected mineral soils have the highest mean soil organic carbon contents 32 2 69 6 kg m 2 here we report a new estimate of the carbon pools in soils of the northern permafrost region including deeper layers and pools not accounted for in previous analyses carbon pools were estimated to be 191 29 pg for the 0 30 cm depth 495 80 pg for the 0 100 cm depth and 1024 00 pg for the 0 300 cm depth our estimate for the first meter of soil alone is about double that reported for this region in previous analyses carbon pools in layers deeper than 300 cm were estimated to be 407 pg in yedoma deposits and 241 pg in deltaic deposits in total the northern permafrost region contains approximately 1672 pg of organic carbon of which approximately 1466 pg or 88 occurs in perennially frozen soils and deposits this 1672 pg of organic carbon would account for approximately 50 of the estimated global belowground organic carbon pool

monitoring surface deformation over permafrost with an improved sbas insar algorithm with emphasis on climatic factors modeling abstract changes of permafrost not only affect regional and global water circulation carbon deposit and climate warming but also influence ground ecological geophysical and biogeochemical processes in cold region monitoring surface deformation over permafrost will help to understand the dynamics of these processes assess climate changes and prevent potential damages to engineering structures underlain by permafrost this article employs an improved small baseline subset interferometric synthetic aperture radar sbas insar technique to monitor the surface deformation over the danxiong yangbajing area in the southern qinghai tibet plateau qtp with emphasis on climatic factors modeling a new deformation model considering both the external mainly climatic and internal factors such as tectonic activities and thermal character of frozen soil is constructed and introduced into the sbas insar to estimate the surface deformation over permafrost the results show that the peak to peak annual deformation over natural surface is 3 6 5 0 cm while that along the qinghai tibet highway qth and the qinghai tibet railway qtr is 2 8 3 7 cm we also find that the surface deformation over frozen soil is negatively correlated to air temperature and precipitation with the correlation being 0 80 to 0 45 and 0 95 to 0 75 respectively the root mean squares rmss of the residual un modeled deformation got by the proposed method are much smaller than that by the existing methods we also successfully examine a time lag of about 60 days between the retrieved maximal subsidence and the highest air temperature in warm seasons from may to september after compensating for this time lag the rmss of the residual deformation reduce significantly and the correlation between the deformation and the temperature rises considerably varying from 0 95 to 0 65 the method presented in this paper is more suitable to model and analyze the surface deformation in permafrost areas

nonlinear subsidence rate estimation using permanent scatterers in differential sar interferometry discrete and temporarily stable natural reflectors or permanent scatterers ps can be identified from long temporal series of interferometric sar images even with baselines larger than the so called critical baseline this subset of image pixels can be exploited successfully for high accuracy differential measurements the authors discuss the use of ps in urban areas like pomona ca showing subsidence and absidence effects a new approach to the estimation of the atmospheric phase contributions and the local displacement field is proposed based on simple statistical assumptions new solutions are presented in order to cope with nonlinear motion of the targets

surface deformation detected by alos palsar small baseline sar interferometry over permafrost environment of beiluhe section tibet plateau china abstract the evolution of permafrost and the active layer is highly related to biological diversity and climate change because of its feedback effects involving water and carbon storage in this study we firstly examined the relationship of active layer variation geomorphological processes and anthropogenic activities by means of small baseline synthetic aperture radar interferometry in beiluhe hoh xil natural reserve in tibet plateau tp china 3 5 yr observation span of l band alos palsar data june 2007 to december 2010 was used the estimated surface displacements primarily in the range of 20 mm yr 1 to 20 mm yr 1 and time series implied evolution of the active layer and permafrost beneath the motion trend along slopes was complicated due to the geomorphological processes and thus interdisciplinary interpretations were needed anthropogenic influences on this frail permafrost environment were significant as evident from the remarkable surface settlement along the embankment of qinghai tibet railway it is crucial and necessary to monitor this permafrost plateau owing to the consequences arising from a combination of factors related to climate change geo hazard prediction nature conservation and regional sustainable development

reconstruction of landsat time series in the presence of irregular and sparse observations development and assessment in north eastern alberta canada abstract time series analysis of landsat is limited by sparse and irregular sampling of clear sky observations due to acquisition limitations clouds shadows atmosphere and sensor artifacts many remote sensing applications utilizing coarse spatial resolution time series methods are not suitable for landsat due to observation sparsity in this research we develop an imputation based approach to constrain the harmonic modeling method of zhu et al 2012 zhu et al 2015 and zhu and woodcock 2014b to reconstruct landsat time series at a regular temporal interval the approach was assessed for a boreal forest region in central canada for different sparsity conditions the imputed landsat estimates for a specific pixel were predicted from climate or avhrr data these estimates were given a small weight relative to available landsat observations in fitting the final harmonic model essentially constraining it to a more plausible range in addition we implemented the model in a piecewise manner to handle non linear temporal drift related to factors such as climate change drought or the allometric nature of vegetation regrowth results show that the inclusion of imputed estimates improved model predictions in the presence of observation sparsity where there were less than 3 observations within 20 days the imputation approach performed better with a reduction in average reflectance error of 0 001 to 2 5 error assessment with hold out observations comparison to modis time series and example predicted images are presented

semi automated open water iceberg detection from landsat applied to disko bay west greenland changes in greenland s marine terminating outlet glaciers have led to changes in the flux of icebergs into greenland s coastal waters yet icebergs remain a relatively understudied component of the ice ocean system we developed a simple iceberg delineation algorithm for landsat imagery a machine learning based cloud mask incorporated into the algorithm enables us to extract iceberg size distributions from open water even in partially cloudy scenes we applied the algorithm to the landsat archive covering disko bay west greenland to derive a time series of iceberg size distributions from 2000 02 and 2013 15 the time series captures a change in iceberg size distributions which we interpret as a result of changes in the calving regime of the parent glacier sermeq kujalleq jakobshavn isbrae the change in calving style associated with the disintegration and disappearance of sermeq kujalleq s floating ice tongue resulted in the production of more small icebergs the increased number of small icebergs resulted in increasingly negative power law slopes fit to iceberg size distributions in disko bay suggesting that iceberg size distribution time series provide useful insights into changes in calving dynamics

sentinel 1 insar measurements of deformation over discontinuous permafrost terrain northern quebec canada abstract differential synthetic aperture radar interferometry d insar has been applied in permafrost environments to detect surface deformation caused by freeze thaw processes in the active layer and underlying permafrost the effectiveness of sentinel 1 insar in monitoring ground surface deformation over continuous permafrost terrain above the treeline has been proven the heterogeneous landscape and developed vegetation cover increase the difficulty of applying d insar in sub arctic discontinuous permafrost terrain the potential of sentinel 1 insar in such an environment has not been fully explored in this study we explore the capabilities and limitations of applying sentinel 1 time series data for monitoring surface deformation over discontinuous permafrost terrain the interferometric coherence time series from september 2016 to april 2018 were analyzed over typical landscapes in discontinuous permafrost environments and their thaw subsidence curves are revealed by the small baseline subset sbas insar technique the seasonal thaw subsidence in the summer of 2017 was in the range of 15 80 mm in the study area the land cover types with thaw subsidence magnitudes from low to high are exposed land peatland lichen low shrub lichen dominated and wetland low vegetation the difference in displacement pattern between lichen dominated and wetland low vegetation dominated permafrost terrains is especially clear at the end of the thawing stage in september and october the differences in thaw subsidence magnitude and pattern reveal the influence of the soil water content in the active layer and permafrost properties on the thaw subsidence patterns we also compared the sentinel 1 retrieved cumulative displacement with the x band terrasar x and l band alos palsar results the difference of retrieved deformation magnitude using the three sensors is amplified when shrubs are more developed the findings indicate that sentinel 1 time series with a 6 day or 12 day span work well over discontinuous permafrost terrain above the tree line i e tundra tundra wetlands and less developed shrub tundra environments during the thawed season but the results and accuracy are not promising over developed shrub tundra and especially forest tundra environments

generating synthetic landsat images based on all available landsat data predicting landsat surface reflectance at any given time abstract a new algorithm for generating synthetic landsat images is developed based on all available landsat data this algorithm is capable of predicting landsat surface reflectance for any desired date it first excludes cloud cloud shadow and snow observations and then uses the remaining clear observations to estimate time series models for each landsat pixel three time series models a simple model advanced model and full model are used for estimating surface reflectance for each pixel and the selection of a time series model is dependent on the number of clear observations available the more clear observations the more complex the model will be that is used for each time series model there are three components seasonality trend and breaks that are used for modeling intra annual and inter annual differences and abrupt surface change abrupt surface changes are detected by differencing predicted and observed landsat observations and if the difference is larger than twice the root mean square error rmse for six consecutive observations it will be detected as a break in the time series model the rmse values are temporally adjusted to provide better threshold range for each synthetic image a quality assessment qa band is provided that contains information on how the time series model was estimated and used for generating the synthetic data we have applied this approach to six landsat scenes within the united states we visually compared the synthetic images with real landsat images for different kinds of environments and they are similar for all image pairs we also quantitatively assessed the accuracy of the synthetic data by calculating the rmse value for all clear landsat observations the rmse values for the three visible bands are the lowest approximately 0 01 and the short wave infrared swir bands are slightly higher in magnitude between 0 01 and 0 02 the near infrared nir band has the highest rmse values between 0 02 and 0 03 the goal of this paper is to provide landsat images that are free of cloud cloud shadow snow and scan line corrector slc off gaps that can be used to derive land cover and bio physical products

a new method for measuring deformation on volcanoes and other natural terrains using insar persistent scatterers 1 we present here a new insar persistent scatterer ps method for analyzing episodic crustal deformation in non urban environments with application to volcanic settings our method for identifying ps pixels in a series of interferograms is based primarily on phase characteristics and finds low amplitude pixels with phase stability that are not identified by the existing amplitude based algorithm our method also uses the spatial correlation of the phases rather than a well defined phase history so that we can observe temporally variable processes e g volcanic deformation the algorithm involves removing the residual topographic component of flattened interferogram phase for each ps then unwrapping the ps phases both spatially and temporally our method finds scatterers with stable phase characteristics independent of amplitudes associated with man made objects and is applicable to areas where conventional insar fails due to complete decorrelation of the majority of scatterers yet a few stable scatterers are present

modeling dense pyroclastic basal flows from collapsing columns 1 a two layer model for the formation of dense pyroclastic basal flows from dilute collapsing volcanic eruption columns is presented the collapsing dilute current is described by depth averaged isothermal continuum conservation equations the dense basal flow is modelled as a granular avalanche of constant density simulations demonstrate that pyroclastic flow formation and behavior is dependent upon slope conditions when the dilute part of the current has lost most of its mass the dilute current runout increases with decreasing particle size and increasing initial column height if the dilute current has transferred its mass to the dense basal flow on volcanic slopes with inclination angle greater than the friction angle of the basal flow then the basal flow will continue to propagate until frictional forces bring it to rest if the dilute current terminates on lower angled slopes frictional forces dominate the basal flow preventing further front propagation

insar detects increase in surface subsidence caused by an arctic tundra fire wildfire is a major disturbance in the arctic tundra and boreal forests having a significant impact on soil hydrology carbon cycling and permafrost dynamics this study explores the use of the microwave interferometric synthetic aperture radar insar technique to map and quantify ground surface subsidence caused by the anaktuvuk river fire on the north slope of alaska we detected an increase of up to 8 cm of thaw season ground subsidence after the fire which is due to a combination of thickened active layer and permafrost thaw subsidence our results illustrate the effectiveness and potential of using insar to quantify fire impacts on the arctic tundra especially in regions underlain by ice rich permafrost our study also suggests that surface subsidence is a more comprehensive indicator of fire impacts on ice rich permafrost terrain than changes in active layer thickness alone

interferometric synthetic aperture radar atmospheric correction using a gps based iterative tropospheric decomposition model abstract atmospheric effects represent one of the major error sources of repeat pass interferometric synthetic aperture radar insar and could mask actual displacements due to tectonic or volcanic deformation the tropospheric delays vary both vertically and laterally and can be considered as the sum of i a vertically stratified component highly correlated with topography and ii a turbulent component resulting from turbulent processes in the troposphere varying both in space and time in this paper we outline a framework to routinely use pointwise gps data to reduce tropospheric effects on satellite radar measurements an iterative tropospheric decomposition itd model is used and further developed to separate tropospheric stratified and turbulent signals and then generate high resolution correction maps for sar interferograms cross validation is employed to assess the performance of the itd model and act as an indicator to users of when and where correction is feasible tests were carried out to assess the impact of gps station spacing on the itd model insar correction performance which provides insights into the trade off between station spacing and the achievable accuracy the application of this framework to sentinel 1a interferograms over the southern california usa and southern england uk regions shows approximately 45 78 of noise reduction even with a sparse 50 80 km station spacing gps network and or with strong and non random tropospheric turbulence this is about a 50 greater improvement than previous methods it is believed that this framework could lead to a generic insar atmospheric correction model while incorporating continuous and global tropospheric delay datasets e g numerical weather models

estimating 1992 2000 average active layer thickness on the alaskan north slope from remotely sensed surface subsidence 1 the measurement of temporal changes in active layer thickness alt is crucial to monitoring permafrost degradation in the arctic we develop a retrieval algorithm to estimate long term average alt using thaw season surface subsidence derived from spaceborne interferometric synthetic aperture radar insar measurements our algorithm uses a model of vertical distribution of water content within the active layer accounting for soil texture organic matter and moisture we determine the 1992 2000 average alt for an 80 100 km study area of continuous permafrost on the north slope of alaska near prudhoe bay we obtain an alt of 30 50 cm over moist tundra areas and a larger alt of 50 80 cm over wet tundra areas our estimated alt values match in situ measurements at circumpolar active layer monitoring calm sites within uncertainties our results demonstrate that insar can provide alt estimates over large areas at high spatial resolution

u pb geochronology of apatite and zircon from the brent impact structure canada a late ordovician sandbian katian boundary event associated with l chondrite parent body disruption in situ la icp ms u pb geochronology has been performed on apatite and zircon within thermally recrystallized clast laden and clast poor impact melt rocks from the brent impact structure a total of 377 laser analyses on 120 impact melt grown n 9 and impact recrystallized zircon grains n 111 were obtained from which a concordia age of 452 8 2 7 ma mswd 0 57 n 11 and a weighted average mean 206pb 238u age of 453 2 2 9 ma mswd 0 60 n 11 are calculated a total of 300 laser analyses from 100 relict apatite grains were obtained with an unanchored regression through all data yielding a lower intercept age of 453 2 6 0 ma mswd 5 8 n 300 that overlaps within error of zircon 207pb 206pb ratios obtained from feldspar clasts within clast laden impact melt retain the same initial pb composition as the target rocks from which they are derived while feldspars that crystallized from impact melt have 207pb 206pb ratios indicative of isotopic re equilibration between basement lithologies of two different ages a similar variability in 207pb 206pb is recorded by apatite this provides evidence for the involvement of neoproterozoic lake nipissing alkaline suite as well as mesoproterozoic grenville gneisses in the production of impact melt at brent recrystallized apatite grains exhibit enrichments in light rare earth elements lrees along neoblast grain boundaries indicative of trace element substitution and phase precipitation during impact induced recrystallization an age of 452 8 2 7 ma from zircon and 453 2 6 0 ma from apatite places the impact event in the late ordovician at or near the sandbian katian boundary confirming brent s involvement in the middle to late ordovician crater cluster event a period of enhanced impactor flux to earth related to the l chondrite parent body disruption

analysis of sub pixel snow and ice extent over the extratropical andes using spectral unmixing of historical landsat imagery abstract with more than 30 years of imagery the landsat database offers potential insights into changes in the global cryosphere in this study a landsat based sub pixel fractional snow covered area retrieval model based on spectral unmixing is applied and validated over a southern andes study region an application analyzing minimum annual snow ice covered areas is presented as an example of the utility of the existence of such a model and the landsat database the model was validated using high resolution imagery aggregated to the nominal landsat resolution showing good correlation for both fresh snow and ice old snow presence using annual minimum snow ice retrievals from landsat 5 and 7 the presence of trends in each snow ice covered pixel area was assessed for the 1986 2013 historical period and three metrics were examined pixels with significant negative trends total area loss and areas with any absolute negative change significant negative area reduction trends in most of the glacier fronts were found with a loss of approximately 15 of the original 241 km2 glacierized snow area between 1986 and 2011 trends in fractional values were compared with those derived from traditional binary classification of snow and significant discrepancies were observed even though the binary classification identified a greater total areal loss 33 vs 23 km2 when comparing scenes from the beginning and the end of the study period the fractional algorithm identified a larger number of pixels with significant negative trends between 1986 and 2013 42 3 vs 10 5 km2 the binary algorithm resulted in consistent overestimations of ice and snow area and does not offer the ability for identifying subpixel changes the method could enable future monitoring of andean and other glaciers and snow cover at a sub pixel scale over large scales and with landsat 8 in orbit a continuous stream of more than 30 years of data is already available

quantification of mass wasting volume associated with the giant landslide daguangbao induced by the 2008 wenchuan earthquake from persistent scatterer insar abstract the spaceborne interferometric synthetic aperture radar insar with persistent scatterer ps is utilized to retrieve the spatial characteristics of the largest coseismic landslide daguangbao induced by the ms 8 0 wenchuan earthquake in sichuan province china the available twenty interferometric pairs with good coherence selected from the alos palsar imagery data covering the longmen shan mountainous area are used in the study we have constructed a natural geodetic observation network with numerous scattered bare rocks emerging after the earthquake and coseismic landslide events which are effectively recognized as the radar persistent scattering objects the spatial connections between adjacent ps are established to form observation baselines with differential parameters related to topography and deformation which are determined by the least squares method from time series interferometric phase analysis the post seismic topographic change relative to the pre seismic over the landslide area is spatially mapped from the ps network adjustment solution the quantitative estimation of local elevation change mass sliding volume and deposit thickness associated with the landslide is conducted the spatial pattern of mass movement suggests that the giant landslide is characterized by a major sliding length of 4350 m along the ne sw directions with an extension width of 3400 m along the huangdongzi gully and a peak height change of 535 m in the vertical direction the affected area of landslide mass movement reaches 7 2 km2 with the volume up to 1 28 billion m3 the study also demonstrates the potential of persistent scatterer insar technique as an alternative to allow the quantitative measurement of mass wasting volume associated with earthquake induced giant landslides

spectral signature of alpine snow cover from the landsat thematic mapper mapping of snow and estimation of snow characteristics from satellite remote sensing data require that we distinguish snow from other surface cover and from clouds and compensate for the effects of the atmosphere and rugged terrain the spectral signature of the snowpack is calculated from a radiative transfer model accounting for scattering and absorption by the ice grains water inclusions and particulates in interpreting the spectral reflectance measured from the thematic mapper or from any other satellite we need to account for topographic effects without requiring that satellite data be precisely registered to digital elevation data because the poor quality of most digital elevation data introduces considerable noise into calculations of slope and azimuth for a range of snow types atmospheric profiles and topographic illumination conditions i estimate typical spectral signatures for the landsat thematic mapper tm images of the southern sierra nevada are analyzed to distinguish several classes of snow from other surface covers snow can be reliably distinguished from other surfaces and from clouds at all sun angles encountered in the mid latitudes in tm band 1 or 2 snow is brighter than other natural surfaces and in band 5 clouds are usually much more reflective than snow therefore the intersection of the following criteria maps the snow cover planetary reflectance rp in tm band 1 is greater than about 0 16 rp tm5 is less than about 0 2 the normalized band 2 5 difference rp tm2 rp tm5 rp tm2 rp tm5 is greater than about 0 4 large surface grain sizes can be distinguished from areas where the grain size is finer at the snow surface using tm bands 2 4 and 5 because of saturation in tm band 1 estimation of the degree of contamination by absorbing aerosols is not feasible rp tm2 rp tm5 rp tm2 rp tm5 is

remote sensing of greenland ice sheet using multispectral near infrared and visible radiances 1 we present the physical basis of and validate a new remote sensing algorithm that utilizes reflected visible and near infrared radiation to discriminate between dry and wet snow when applied to the moderate resolution imaging spectroradiometer modis satellite data our discrimination algorithm has the potential to retrieve melting regions of the ice sheet at a spatial resolution of 0 25 km 2 over three orders of magnitude higher than the resolution of current microwave methods the method should be useful for long term monitoring of the melt area of the greenland ice sheet especially regions close to ice sheet margins and of the outflow glaciers our analysis of modis retrievals of the western portion of the greenland ice sheet over the period 2000 to 2006 indicates significant interannual variability with a maximum melt extent in 2005 collocated in situ meteorological data reveal a high correlation 0 80 between the modis melt day area and the average summer temperature our analysis suggests that it is the magnitude of the summer temperature that dominates the melting not the variability of the length of the melting season furthermore we find that the melt day area increases by about 3 8 for each 0 1 k increase in the average surface air summer temperature we combine this empirical relationship with historic temperature data to infer that the melt day area of the western part of the ice sheet doubled between the mid 1990s and mid 2000s and that the largest ice sheet surface melting probably occurred between 1920s and 1930s concurrent with the warming in that period

dynamic tensile strength of terrestrial rocks and application to impact cratering dynamic tensile strengths and fracture strengths of 3 terrestrial rocks san marcos gabbro coconino sandstone and sesia eclogite were determined by carrying out flat plate pmma and aluminum impact experiments on disc shaped samples in the 5 to 60 m sec range tensile stresses of 125 to 300 mpa and 245 to 580 mpa were induced for gabbro and eclogite respectively with duration time of 1 s for sandstone porosity 25 tensile stresses normal to bedding of 13 to 55 mpa were induced with duration times of 2 4 and 1 4 s tensile crack failure was detected by the onset of shock induced damage p and s wave velocity reduction the dynamic tensile strength of gabbro determined from p and s wave velocity deficits agrees closely with the value of previously determined values by post impact microscopic examination 150 mpa tensile strength of coconino sandstone is 20 mpa for a 14 s duration time and 17 mpa for a 2 4 s duration time for sesia eclogite the dynamic tensile strength is 240 mpa the fracture strength for gabbro is 250 mpa 500 mpa for eclogite and 40 mpa for sandstone relative crack induced reduction of s wave velocities is less than that of post impact p wave velocity reductions for both gabbro and eclogite indicating that the cracks were predominantly spall cracks impacts upon planetary surfaces induce tensile failure within shock processed rocks beneath the resulting craters the depth of cracking beneath impact craters can be determined both by seismic refraction methods for rocks of varying water saturation and for dry conditions e g the moon from gravity anomalies in principle depth of cracking is related to the equations of state of projectile and target projectile dimension and impact velocity we constructed a crack depth model applicable to meteor crater for the observed 850 m depth of cracking our preferred strength scaling model yields an impact velocity of 33 km s and impactor radius of 9 m for an iron projectile

interannual changes of the floating ice shelf of petermann gletscher north greenland from 2000 to 2012 petermann gletscher northwest greenland drains 4 of the greenland ice sheet into nares strait its floating ice shelf retreated from 81 to 48 km in length during two large calving events in 2010 and 2012 we document changes in the three dimensional ice shelf structure from 2000 to 2012 using repeated tracks of airborne laser altimetry and ice radio echo sounding icesat laser altimetry and modis visible imagery the recent ice shelf velocity measured by tracking surface features between flights in 2010 and 2011 is 1 25 km a 1 15 30 faster than estimates made before 2010 the steady state along flow ice divergence represents 6 3 gt a 1 mass loss through basal melting 5 gt a 1 and surface melting and sublimation 1 0 gt a 1 airborne laser altimeter data reveal thinning both along a thin central channel and on the thicker ambient ice shelf from 2007 to 2010 the ice shelf thinned by 5 m a 1 which represents a non steady mass loss of 4 1 gt a 1 we suggest that thinning in the basal channels structurally weakened the ice shelf and may have played a role in the recent calving events

land subsidence characteristics of bandung basin as revealed by envisat asar and alos palsar interferometry abstract in this work land subsidence in bandung basin indonesia between 2002 and 2011 was mapped using the c band envisat asar and l band alos palsar data twenty four alos palsar and thirty envisat asar images acquired between 2002 2008 and 2007 2011 respectively were analysed several locations that were experiencing land displacement were identified including cimahi dayeuh kolot rancaekek solokan jeruk and gedebage the subsidence rates in the basin range from 240 mm year to 40 mm year the comparison between the alos palsar and envisat asar measurements which showed good agreement suggested the subsidence in many areas of the basin were steady between 2002 and 2011 except south bandung acceleration of subsidence in south bandung was observed between the measurements from the two datasets likely as a result of increasing population and industries the subsidence in the basin was expected mainly as a result of excessive groundwater extraction and soil consolidation caused by surficial loading gps survey data collected between 2002 and 2010 were used to validate the alos palsar and envisat asar measurements good correlations were observed between insar and gps measurements the comparison between the land subsidence measurements and the groundwater level information showed there were some correlations between them for every 1 m reduction in groundwater level per annum ground subsidence of 20 23 mm per annum has been observed the comparison results suggested that there was no evidence showing the aquifer in the basin is being recovered

partitioning of localized and diffuse deformation in the tibetan plateau from joint inversions of geologic and geodetic observations abstract the spatial complexity of continental deformation in the greater tibetan plateau region can be defined as the extent to which relative motion of the indian and asian plates is partitioned between localized slip on major faults and distributed deformation potency rates provide a quantitative metric for determining the magnitudes of diffuse and on fault crustal deformation which are proportional to strain rates within crustal micro plates and fault slip rates respectively we simultaneously estimate micro plate rotation rates interseismic elastic strain accumulation fault slip rates on major structures and strain rates within 24 tectonic micro plates inferred from active fault maps in the greater tibetan plateau region using quasi static block models constrained by interseismic surface velocities at 731 gps sites and 9 holocene late quaternary geologic fault slip rates the joint geodetic geologic inversion indicates that geologic slip rates are kinematically consistent with differential micro plate motions estimated left lateral slip rates on the altyn tagh west central kunlun and xianshuihe faults are relatively homogeneous along strike 11 5 10 5 and 11 mm yr respectively while segmentation of the eastern kunlun fault by the intersecting elashan and riyueshan faults results in a decreased slip rate consistent with geologic observations the fraction of total potency rate associated with intrablock strain uncorrected for observational noise ranges from 0 27 in the himalayan range block to 0 91 in the aksai chin block monte carlo simulations are used to quantify the likelihood that internal deformation is statistically distinguishable from the uncertainties in geodetic velocities these simulations indicate that internal block deformation is statistically significant only within the himalayan range front where internal deformation accounts for id 0 11 of block potency rate budget west central plateau id 0 68 ganzi yushu xianshuihe 0 58 burma 0 09 jiali 0 38 and aksai chin 0 68 blocks in the other 18 tectonic micro plates within the plateau region estimated internal block potency is not currently distinguishable from the expected contribution of observational noise to residual velocities of the total potency budget within the tibetan plateau 85 is taken up by slip on major faults with the remaining 15 accommodated by internal processes at sub block scale distinguishable from observational noise the localization of the majority of plate boundary activity is also supported by the spatial distribution of modern and historical crustal earthquakes sixty seven percent of the total moment released by earthquakes in the cmt catalog and 90 of historical moment since 1900 have been released within 25 km of the major faults included in the block model representing only 12 of the characteristic half block length scale of 215 km the localization of deformation inferred from geologic geodetic and seismic observations suggests that forces applied to tectonic micro plates drive fault system activity at the india asia collision zone over decadal to quaternary time scales

sar interferometry on a very long time scale a study of the interferometric characteristics of man made features anthropogenic features show up as highly coherent objects even in heavily decorrelated interferograms in order to assess whether the information from such features is still usable the stability of their phase and coherence is analyzed through a series of interferograms the results indicate that these features can remain interferometrically stable over several years

coseismic slip from the 6 october 2008 mw6 3 damxung earthquake tibetan plateau constrained by insar observations coseismic deformation fields of the 6 october 2008 m w6 3 damxung earthquake were obtained from interferometric synthetic aperture radar by using three descending and two ascending envisat images significant coseismic surface deformation occurred within 20 km 20 km of the epicenter with a maximum displacement of 0 3 m along the satellite line of sight we model a linear elastic dislocation in a homogeneous half space and use a nonlinear constraint optimized algorithm to estimate the fault location geometry and slip distribution the results indicate a moment magnitude m w6 3 and the earthquake is dominated by oblique normal and right lateral slip with a maximum slip of 2 86 m at depth of 8 km the rupture plane is about 15 km 14 km with strike s190 w and dip 55 to nw located at a secondary fault of the southeastern piedmont of the nyainqentanglha mountains slip on normal faults in the tibetan plateau contributes to the rift evolution

el nino southern oscillation enso influence on a sajama volcano glacier bolivia from 1963 to 1998 as seen from landsat data and aerial photography sajama volcano located in the bolivian altiplano is the southernmost tropical glacier and owing to its situation approximately 100 km east of the pacific coast is well suited to study the el nino southern oscillation phenomenon landsat data from 1972 to 1998 and a 1963 aerial photograph are used to monitor the snow line fluctuations on a selected part of sajama volcano we assume that a few months after the rainy season the snow line is representative of the previous rainy season if no recent snowfall has occurred by observing precipitation from the stations surrounding sajama volcano and by verifying snow presence on surrounding summits we detect images with recent snowfall likely to disturb the climatic significance of the snow line a snow line evolution model takes into account the different image acquisition dates and adjusts the snow line elevation accordingly for the middle of the dry season a progressive rise of the snow line elevation is observed from 1963 to 1998 with a sustained rise from 1984 to 1990 the snow line altitude is related to the southern oscillation index even after the high precipitation of the 1996 1997 wet season the following el nino 1997 1998 leads to a substantial rise of the snow line the snow line elevation is related primarily to the total rainy season precipitation and to a lesser degree to the maximum monthly mean temperature of the warmest month thus confirming a greater snow line sensitivity to precipitation than to temperature

el gygytgyn impact crater chukotka arctic russia impact cratering aspects of the 2009 icdp drilling project the el gygytgyn impact structure in chukutka arctic russia is the only impact crater currently known on earth that was formed in mostly acid volcanic rocks mainly of rhyolitic with some andesitic and dacitic compositions in addition because of its depth it has provided an excellent sediment trap that records paleoclimatic information for the 3 6 myr since its formation for these two main reasons because of the importance for impact and paleoclimate research el gygytgyn was the subject of an international continental scientific drilling program icdp drilling project in 2009 during this project which due to its logistical and financial challenges took almost a decade to come to fruition a total of 642 3 m of drill core was recovered at two sites from four holes the obtained material included sedimentary and impactite rocks in terms of impactites which were recovered from 316 08 to 517 30 m depth below lake bottom mblb three main parts of that core segment were identified from 316 to 390 mblb polymict lithic impact breccia mostly suevite with volcanic and impact melt clasts that locally contain shocked minerals in a fine grained clastic matrix from 385 to 423 mblb a brecciated sequence of volcanic rocks including both felsic and mafic basalt members and from 423 to 517 mblb a greenish rhyodacitic ignimbrite mostly monomict breccia the uppermost impactite 316 328 mblb contains lacustrine sediment mixed with impact affected components over the whole length of the impactite core the abundance of shock features decreases rapidly from the top to the bottom of the studied core section the distinction between original volcanic melt fragments and those that formed later as the result of the impact event posed major problems in the study of these rocks the sequence that contains fairly unambiguous evidence of impact melt which is not very abundant anyway usually less than a few volume is only about 75 m thick the reason for this rather thin fallback impactite sequence may be the location of the drill core on an elevated part of the central uplift a general lack of large coherent melt bodies is evident similar to that found at the similarly sized bosumtwi impact crater in ghana that however was formed in a target composed of a thin layer of sediment above crystalline rocks

usage of high resolution landsat 7 band 8 for single band snow cover classification with the launch of landsat 7 a new band was added to the landsat enhanced thematic mapper plus etm the new panchromatic band 8 covers wavelengths of 0 52 0 92 m and extends over band 2 0 525 0 605 m band 3 0 630 0 690 m and band 4 0 750 0 900 m its high resolution with a pixel length of 15 m is of interest for high spatial resolution analysis this project focused on using landsat 7 band 8 as a precise tool to obtain remotely the size and shape of permanent snowpatches in the mountainous area west of abisko sweden in the supervised classification employed shadowed and non shadowed areas were classified separately supervision of the classification was based on ground truthing consisting of photographic mapping of the snow cover in the study area the results from this single band classification were compared to the results from the normalized difference snow index ndsi and false color images using bands 2 4 and 5 this comparison showed similar estimates of the total amount of snow covered area with the additional advantage that the landsat 7 band 8 lb8 classification detects details in the extent of individual snowfields this new application and the insights documented here support the use of landsat 7 band 8 for snow cover investigations in the future

developing clear sky cloud and cloud shadow mask for producing clear sky composites at 250 meter spatial resolution for the seven modis land bands over canada and north america abstract a new technology was developed at the canada centre for remote sensing ccrs for generating canada wide and north america continental scale clear sky composites at 250 m spatial resolution for all seven modis land spectral bands b1 b7 the modis level 1b mod02 swath level data are used as input to circumvent the problems with image distortion in the mid latitude and polar regions inherent to the global sinusoidal sin projection utilized for the standard modis data products the modis 500 m land bands b3 to b7 are first downscaled to 250 m resolution using an adaptive regression and normalization scheme for compatibility with the 250 m bands b1 and b2 a new method has been developed to produce the mask of clear sky cloud and cloud shadow at 250 m resolution it shows substantial advantages in comparison with the modis 250 m standard cloud masks the testing of new cloud mask showed that it is in reasonable agreement with the modis 1 km standard product once it is aggregated to 1 km scale while the cloud shadow detection looks more reliable with the new methodology nevertheless more quantitative analyses of the presented scene identification technique are required to understand its performance over the range of input scenes in various seasons the new clear sky compositing scheme employs a scene dependent decision matrix it is demonstrated that this new scheme provides better results than any others based on a single compositing criterion such as maximum ndvi or minimum visible reflectance to account for surface bi directional properties two clear sky composites for the same time period are produced by separating backward scattering and forward scattering geometries which separate pixels with the sun satellite relative azimuth angles within 90 270 and outside of this range comparison with landsat imagery and with modis standard composite products demonstrated the advantage of the new technique for screening cloud and cloud shadow and generating high spatial resolution modis clear sky composites the new data products are mapped in the lambert conformal conic lcc projection for canada and the lambert azimuthal equal area laea projection for north america presently this activity is limited to modis terra due to known problems with band to band registration and noisy swir channels on modis aqua

on critical observations that constrain models of terrestrial hypervelocity impact craters impact structures in the crystalline rocks of the canadian shield range over two orders of magnitude in size and display morphologies recognized elsewhere in the solar system this contribution draws upon new examinations of drill core from canadian craters to reaffirm some relationships modify others and refine the transitions from simple to complex with central peak to peak ring structures these include recognizing the hyperbolic form of transient craters sharpening the allochthon parautochthon distinction and proposing new formulae for key relationships it emphasizes the role of dynamic tensile strength and the attenuation of tensile rarefaction waves in determining the size of both transient and final crater dimensions on earth depth d to diameter d ratios are not invariant at about 1 10 but change smoothly with size from 1 3 at brent through 1 5 to 1 10 in the largest that is d 0 4 d0 75 in craters in crystalline rocks the central peak grows at about uplift 0 175 d until at d about 28 km the uplift rises above the original surface then collapses to form a peak ring structure these relationships demonstrate the dominant role of gravity in attenuating tensile rarefaction waves and controlling transient crater depth and overall size relative to the volume shocked

structural evidence from shock metamorphism in simple and complex impact craters linking observations to theory the structure of canadian impact craters formed in crystalline rocks is analyzed using shock metamorphism and evidence for movement along shear zones the analysis is based on an interpretation that beyond the near field region shock pressure attenuates down axis as p r 2 in agreement with nuclear test and computed results and as p r 3 near the surface in both simple and complex craters the transient cavity is defined by the limit of fragmentation due to direct and reflected shock waves the intersection of the transient cavity with hemispheric shock isobars indicates that the transient cavity has a parabolic form weakening by dilation during early uplift allows late stage slumping of the walls of simple craters this is controlled by a spheroidal primary shear of radius rs 2dt where dt is the depth of the transient crater due to excavation and initial compression with increasing crater diameter the size of the transient cavity decreases relative to the shock imprint suggesting that fragmentation and excavation is limited by progressively earlier collapse of the margins under gravity central peak formation in complex craters may be initiated by relaxation of the shock compressed central parautochthone so the primary shear lubricated by friction melting meets below the crater floor and drives the continuing upward motion

an international and multidisciplinary drilling project into a young complex impact structure the 2004 icdp bosumtwi crater drilling project an overview the bosumtwi impact crater in ghana arguably the best preserved complex young impact structure known on earth displays a pronounced rim and is almost completely filled by lake bosumtwi a hydrologically closed basin it is the source crater of the ivory coast tektites the structure was excavated in 2 1 2 2 gyr old metasediments and metavolcanics of the birimian supergroup a drilling project was conceived that would combine two major scientific interests in this crater 1 to obtain a complete paleoenvironmental record from the time of crater formation about one million years ago at a near equatorial location in africa for which very few data are available so far and 2 to obtain a complete record of impactites at the central uplift and in the crater moat for ground truthing and comparison with other structures within the framework of an international and multidisciplinary drilling project led by the international continental scientific drilling program icdp 16 drill cores were obtained from june to october 2004 at six locations within lake bosumtwi which is 8 5 km in diameter the 14 sediment cores are currently being investigated for paleoenvironmental indicators the two impactite cores lb 07a and lb 08a were drilled into the deepest section of the annular moat 540 m and the flank of the central uplift 450 m respectively they are the main subject of this special issue of meteoritics planetary science which represents the first detailed presentations of results from the deep drilling into the bosumtwi impactite sequence drilling progressed in both cases through the impact breccia layer into fractured bedrock lb 07a comprises lithic in the uppermost part and suevitic impact breccias with appreciable amounts of impact melt fragments the lithic clast content is dominated by graywacke besides various metapelites quartzite and a carbonate target component shock deformation in the form of quartz grains with planar microdeformations is abundant first chemical results indicate a number of suevite samples that are strongly enriched in siderophile elements and mg but the presence of a definite meteoritic component in these samples cannot be confirmed due to high indigenous values core lb 08a comprises suevitic breccia in the uppermost part followed with depth by a thick sequence of graywacke dominated metasediment with suevite and a few granitoid dike intercalations it is assumed that the metasediment package represents bedrock intersected in the