decorrelation in interferometric radar echoes a radar interferometric technique for topographic mapping of surfaces implemented utilizing a single synthetic aperture radar sar system in a nearly repeating orbit is discussed the authors characterize the various sources contributing to the echo correlation statistics and isolate the term which most closely describes surficial change they then examine the application of this approach to topographic mapping of vegetated surfaces which may be expected to possess varying backscatter over time it is found that there is decorrelation increasing with time but that digital terrain model generation remains feasible the authors present such a map of a forested area in oregon which also includes some nearly unvegetated lava flows such a technique could provide a global digital terrain map

a short duration of chondrule formation in the solar nebula evidence from 26al in semarkona ferromagnesian chondrules abstract the 26 al 26 mg systems of five ferromagnesian chondrules from the least metamorphosed ordinary chondrite semarkona ll3 0 were studied using a secondary ion mass spectrometer their glass or plagioclase portions contain excesses of 26 mg and in two chondrules the 26 mg excesses are well correlated with 27 al 24 mg which demonstrates the in situ decay of 26 al the initial 26 al 27 al ratios in these chondrules obtained from the slope of isochrons show a narrow range of between 6 10 6 and 9 10 6 indicating their short formation duration of less than 1 my if the solar nebula was initially homogeneous in al isotopes the chondrule formation ages are 2 my younger than those of cais our results based on the study of the least metamorphosed uoc are consistent with the previous studies on al rich chondrules that the chondrule formation started at least 2 my after cais alternatively the older records before 2 my were erased by chondrule recycling process it further suggests that the young apparent ages 3 to 5 my after cais for chondrules in type 3 4 uocs are due to the disturbance of the 26 al 26 mg system possibly during parent body metamorphism the result is not consistent with the extended nebular time scale of 5 my and the chondrule formation by planetary processes the ni isotopic analysis of the feo rich olivines in a type ii chondrule in semarkona did not show any detectable excess 60 ni in spite of their high fe ni ratios the upper limit of the initial 60 fe 56 fe ratio of the solar system was estimated to be 3 4 10 7 which is consistent with the previous estimate 0 2 1 9 10 7 from eucrites this result confirms that the 60 ni excess previously observed from cais was not due to the decay of the short lived nuclide 60 fe but a ni isotopic anomaly of nucleosynthetic origin

application of image cross correlation to the measurement of glacier velocity using satellite image data abstract image to image cross correlation software is applied to pairs of digital satellite images to map the velocity field of moving ice this technique uses small scale glacial surface features such as crevasse scars and snow dunes as markers on the surface of the moving ice displacements of the surface features are mapped by selecting small image areas centered on distinct features or by dividing a large area of densely featured glacial surface into a grid of areas and searching a subsequent image for matching areas using a cross correlation algorithm interpolation of the peak correlation values allows the displacements to be measured to subpixel accuracy resulting in very precise velocity measurements cross correlation is also applied to provide image coregistration in areas devoid of bedrock exposures in such areas subtle large scale topographic undulations in the ice surface related to underlying bedrock structure may be correlated by using large image areas and low pass filtered images both types of applications are demonstrated using ice stream d and ice stream e in west antarctica as test areas a high resolution map of the velocity field of the central portion of ice stream e generated by the displacement measuring technique is presented the use of cross correlation software is a significant improvement over previous manually based photogrammetric methods for velocity measurement and is far more cost effective than in situ methods in remote polar areas

satellite radar interferometry for monitoring ice sheet motion application to an antarctic ice stream satellite radar interferometry sri provides a sensitive means of monitoring the flow velocities and grounding line positions of ice streams which are indicators of response of the ice sheets to climatic change or internal instability the detection limit is about 1 5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction the grounding line detected by tidal motions where the ice goes afloat can be mapped at a resolution of 0 5 kilometer the sri velocities and grounding line of the rutford ice stream antarctica agree fairly well with earlier ground based data the combined use of sri and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior

correcting atmospheric effects on insar with meris water vapour data and elevation dependent interpolation model summary the propagation delay when radar signals travel from the troposphere has been one of the major limitations for the applications of high precision repeat pass interferometric synthetic aperture radar insar in this paper we first present an elevation dependent atmospheric correction model for advanced synthetic aperture radar asar the instrument aboard the envisat satellite interferograms with medium resolution imaging spectrometer meris integrated water vapour iwv data then using four asar interferometric pairs over southern california as examples we conduct the atmospheric correction experiments with cloud free meris iwv data the results show that after the correction the rms differences between insar and gps have reduced by 69 6 per cent 29 per cent 31 8 per cent and 23 3 per cent respectively for the four selected interferograms with an average improvement of 38 4 per cent most importantly after the correction six distinct deformation areas have been identified that is long beach santa ana basin pomona ontario san bernardino and elsinore basin with the deformation velocities along the radar line of sight los direction ranging from 20 mm yr 1 to 30 mm yr 1 and on average around 25 mm yr 1 and santa fe springs and wilmington with a slightly low deformation rate of about 10 mm yr 1 along los finally through the method of stacking we generate a mean deformation velocity map of los angeles over a period of 5 yr the deformation is quite consistent with the historical deformation of the area thus using the cloud free meris iwv data correcting synchronized asar interferograms can significantly reduce the atmospheric effects in the interferograms and further better capture the ground deformation and other geophysical signals

flow of glaciar moreno argentina from repeat pass shuttle imaging radar images comparison of the phase correlation method with radar interferometry high resolution radar images of glaciar moreno argentina acquired by the shuttle imaging radar c sir c on 9 and 10 october 1994 at 24 cm wavelength l band are utilized to map the glacier velocity both interferometrically and using the phase correlation method the precision of the interferometric ice velocities is 1 8 cm d 1 6 m a 1 1 the phase correlation method measures ice velocity with a precision of 14 cm d 1 50 m a 1 with image data at a 6 m sample spacing acquired 1 day apart averaged strain rates are measured with a precision of 10 4 d 1 at a 240 m sample spacing with the phase correlation method and 10 5 d 1 with radar interferometry the phase correlation method is less precise than radar interferometry but it performs better in areas of rapid flow is more robust to temporal changes in glacier scattering and measures the glacier velocity in two dimensions with only one image pair using this technique we find that glaciar moreno flows at 400 m a 1 in the terminal valley and 800 m a 1 at the calving front in agreement with velocities recorded a decade ago assuming steady state flow conditions the vertical strain rates measured by sir c are combined with prior data on mass ablation to estimate the glacier thickness and ice discharge the calculated discharge is 0 6 0 2 km3 ice a 1 at 300 m elevation and 1 1 0 2 km3 ice a 1 at the equilibrium line elevation 1150 m which yields a balance accumulation of 6 1m ice a 1

rb sr isotopic systematics of alkali rich fragments in the yamato 74442 ll chondritic breccia abstract we have undertaken mineralogical petrographical and rb sr isotopic studies on alkali rich igneous rock fragments in the yamato y 74442 ll chondritic breccia the fragments are a few mm in size and are composed mainly of porphyritic olivine and dendritic pyroxene set in alkali rich groundmass glass minor phases include chromite troilite and metallic nickel iron bulk chemical compositions of the fragments are almost identical to the host chondrite except for a depletion of sodium and an enrichment of potassium isotopic analyses of nine fragments from y 74442 yield a rb sr age of 4429 54 ma 2 for 87 rb 0 01402 ga 1 with an initial ratio of 87 sr 86 sr 0 7144 0 0094 2 assuming precursors of the fragments formed 4568 ma with 87 sr 86 sr 0 69889 when the solar system formed a time averaged rb sr weight ratio of the source material for the fragments is calculated to be 2 58 0 91 0 93 the extremely high rb sr value of this source is difficult to interpret by any igneous fractionation or liquid immiscibility but can be explained by mixing of a chondritic component with an alkali rich component formed in the early solar nebula in our preferred model the alkali component with rb sr 30 would have condensed from the residual nebular gas after removal of refractory strontium and must have been isolated for a long time in a region where the temperature was sufficiently low to prevent reaction with other silicates oxides a mixture of the alkali component early nebular condensates and the ferromagnesian component could reflect flash heating induced by impact on an ll chondritic parent body at least 4429 ma ago and further enrichments of rubidium and potassium relative to strontium could have occurred during this event the resulting impact melt rocks could have been fragmented by later impact event s and finally incorporated into the y 74442 parent body thus a remarkable signature of alkali enrichments both in the early solar nebula and later on the ll chondrite parent body is preserved as a minor component of some chondritic breccias such as y 74442

permanent scatterers analysis for atmospheric correction in ground based sar interferometry ground based synthetic aperture radar gb sar interferometry has already been recognized as a powerful tool complementary or alternative to spaceborne sar interferometry for terrain monitoring and for detecting structural changes in buildings it has been noted that in spite of the very short range compared with the satellite configuration in gb sar measurement the disturbances due to atmospheric effects cannot be neglected either the analysis of the interferometric phases of very coherent points called permanent scatterers pss allows the evaluation of the atmospheric disturbance and the possibility of removing it in this paper the ps analysis is carried out both on a test site facility and on a real campaign citrin valley italy that provided data with a temporal baseline of about ten months

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

surface motion of mountain glaciers derived from satellite optical imagery a complete and detailed map of the ice velocity field on mountain glaciers is obtained by cross correlating spot5 optical images this approach offers an alternative to sar interferometry because no present or planned radar satellite mission provides data with a temporal separation short enough to derive the displacements of glaciers the methodology presented in this study does not require ground control points gcps the key step is a precise relative orientation of the two images obtained by adjusting the stereo model of one slave image assuming that the other master image is well georeferenced it is performed with numerous precisely located homologous points extracted automatically the strong ablation occurring during summer time on the glaciers requires a correction to obtain unbiased displacements the accuracy of our measurement is assessed based on a comparison with nearly simultaneous differential gps surveys performed on two glaciers of the mont blanc area alps if the images have similar incidence angles and correlate well the accuracy is on the order of 0 5 m or 1 5 of the pixel size similar results are also obtained without gcps an acceleration event observed in early august for the mer de glace glacier is interpreted in term of an increase in basal sliding our methodology applied to spot5 images can potentially be used to derive the displacements of the earth s surface caused by landslides earthquakes and volcanoes

radar interferometry and its application to changes in the earth s surface geophysical applications of radar interferometry to measure changes in the earth s surface have exploded in the early 1990s this new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times the resulting interferogram is a contour map of the change in distance between the ground and the radar instrument these maps provide an unsurpassed spatial sampling density 100 pixels km 2 a competitive precision 1 cm and a useful observation cadence 1 pass month 1 they record movements in the crust perturbations in the atmosphere dielectric modifications in the soil and relief in the topography they are also sensitive to technical effects such as relative variations in the radar s trajectory or variations in its frequency standard we describe how all these phenomena contribute to an interferogram then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments including the four satellites currently in orbit ers 1 ers 2 jers 1 and radarsat the next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement respecting the limits of the technique assessing its uncertainty recognizing artifacts and discriminating different types of signal we then review the geophysical applications published to date most of which study deformation related to earthquakes volcanoes and glaciers using ers 1 data we also show examples of monitoring natural hazards and environmental alterations related to landslides subsidence and agriculture in addition we consider subtler geophysical signals such as postseismic relaxation tidal loading of coastal areas and interseismic strain accumulation we conclude with our perspectives on the future of radar interferometry the objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it

integrated satellite interferometry tropospheric noise gps estimates and implications for interferometric synthetic aperture radar products interferometric synthetic aperture radar insar like other astronomic and space geodetic techniques is limited by the spatially and temporally variable delay of electromagnetic waves propagating through the neutral atmosphere statistical analysis of these variations from a wide variety of instruments reveals a power law dependence on frequency that is characteristic of elementary kolmogorov turbulence a statistical model for a major component of the delay fluctuations the wet component has previously been developed by treuhaft and lanyi 1987 for very long baseline interferometry a continuous global positioning system gps network is now in place in southern california that allows estimation of along with geodetic parameters the total delay due to the atmosphere above each site on a subhourly basis these measurements are shown to conform to the treuhaft and lanyi tl statistical model both temporally and spatially the tl statistical model is applied to the problem of insar and used to produce the covariance between two points separated in time and or space the error due to the atmospheric variations for sar products such as topography and surface deformation is calculated via propagation of errors there are two methods commonly cited to reduce the effect of atmospheric distortion in products from sar interferometry stacking and calibration stacking involves averaging independent interferograms to reduce the noise calibration involves removing part or all of the delay using data from an independent source such as total zenith delay estimates from continuous gps networks despite the relatively poor spatial density of surface measurements calibration can be used to reduce noise if the measurements are sufficiently accurate reduction in tropospheric noise increases with increasing number of measurement points and increasing accuracy up to a maximum of n where n is the number of points stacking and calibration are shown to be complementary and can be used simultaneously to reduce the noise to below that achievable by either method alone

evidence of log periodic oscillations and increasing icequake activity during the breaking off of large ice masses in 1973 surface velocities were measured for the first time on an unstable hanging glacier to predict its collapse the observed velocities have been shown to increase as a power law function of time up to infinity at the theoretical time of failure known as finite time singularity this is the characteristic signature of critical phenomena and has been observed in the case of various other naturally occurring ruptures such as earthquakes landslides and snow avalanches recent velocity measurements performed on weisshorn and monch hanging glaciers switzerland confirmed this behaviour while log periodic oscillations superimposed on this general acceleration were also detected despite different rupture mechanisms in both cases the log frequency of the oscillations is shown to be the same the seismic activity was recorded near the unstable weisshorn hanging glacier simultaneously with the velocity measurements results show dramatically increasing icequake activity 3 days before the final collapse combined motion seismic monitoring seems to be a promising way to accurately predict the breaking off of hanging glaciers such a combined analysis is also useful for capturing the physical mechanisms of rupture in natural heterogeneous materials

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

multi interferogram method for measuring interseismic deformation denali fault alaska summary studies of interseismic strain accumulation are crucial to our understanding of continental deformation the earthquake cycle and seismic hazard by mapping small amounts of ground deformation over large spatial areas insar has the potential to produce continental scale maps of strain accumulation on active faults however most insar studies to date have focused on areas where the coherence is relatively good e g california tibet and turkey and most analysis techniques stacking small baseline subset algorithm permanent scatterers etc only include information from pixels which are coherent throughout the time span of the study in some areas such as alaska where the deformation rate is small and coherence very variable it is necessary to include information from pixels which are coherent in some but not all interferograms we use a three stage iterative algorithm based on distributed scatterer interferometry we validate our method using synthetic data created using realistic parameters from a test site on the denali fault alaska and present a preliminary result of 10 5 5 0 mm yr 1 for the slip rate on the denali fault based on a single track of radar data from ers1 2

identifying the top of the tropical tropopause layer from vertical mass flux analysis and calipso lidar cloud observations 1 we identify the top of the tropical tropopause layer ttl by analyzing the vertical mass flux profile based on radiative transfer calculations employing observed atmospheric profiles and cloud information we find that the top of the ttl is located at 18 7 km 70 mb we have analyzed the calipso lidar cloud observations from june 2006 to february 2007 which indicates that almost no clouds occur above 19 km consistent with the top of ttl based on vertical mass flux analyses the total cloud fractions between 20s and 20n are about 0 05 at 18 5 km 0 5 at 18 0 km and 5 at 17 0 km where the clouds with optical depth larger than 0 5 contribute up to one tenth of these total cloud fractions the clouds above 17 km mainly originate over the west pacific south america central africa and south asia citation fu q y hu and q yang 2007 identifying the top of the tropical tropopause layer from vertical mass flux analysis and calipso lidar cloud observations geophys res lett 34 l 14813

sliding phenomena in a steep section of balmhorngletscher switzerland annual aerial photographs of balmhorngletscher available since 1973 have furnished data on large ice avalanches originating in one particular location the avalanches characteristically occur during an active phase of fast sliding the analysis of a photogrammetric 1 2000 bedrock map of longitudinal ice surface profiles from photographs taken at various times and of velocity measurements by theodolite has shown that the fast sliding and the release of the avalanches in an area of about 250 by 100 m is quite independent of ice thickness it is suggested that besides the slope of the bed rock roughness and topographical features the particular structure of the rock surface in the fashion of tiles on a roof is a factor which influences the processes of fast sliding and avalanche formation it is suggested that meltwater gains access to cavities at the rock steps from where it is dragged along on the ice rock interface getting slowly worked into the basal ice layer many weeks after the beginning of the melt season the evolving acceleration becomes apparent characteristically at the beginning of september once the surface meltwater gains direct access to the bed through fresh crevasses the glacier accelerates progressively as water enters cracks faults and microfissures water pressure effects may become important as cavities grow while the gradual development of the active phase permits to forecast the growing avalanche risk the prediction of the event in time is a long way off if practical at all

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

glacier motion estimation using sar offset tracking procedures two image to image patch offset techniques for estimating feature motion between satellite synthetic aperture radar sar images are discussed intensity tracking based on patch intensity cross correlation optimization and coherence tracking based on patch coherence optimization are used to estimate the movement of glacier surfaces between two sar images in both slant range and azimuth direction the accuracy and application range of the two methods are examined in the case of the surge of monacobreen in northern svalbard between 1992 and 1996 offset tracking procedures of sar images are an alternative to differential sar interferometry for the estimation of glacier motion when differential sar interferometry is limited by loss of coherence i e in the case of rapid and incoherent flow and of large acquisition time intervals between the two sar images in addition an offset tracking procedure in the azimuth direction may be combined with differential sar interferometry in the slant range direction in order to retrieve a two dimensional displacement map when sar data of only one orbit configuration are available

correction for interferometric synthetic aperture radar atmospheric phase artifacts using time series of zenith wet delay observations from a gps network 1 radar interferograms provide precise millimeter level measurements of crustal deformation at fine resolution over wide areas the dominant error source in many interferograms results from spatial heterogeneity of the wet component of atmospheric refractivity resulting in excess path length of the radar signal propagating through the neutral atmosphere in this report we introduce a method to compensate for atmospheric phase artifacts in a radar interferogram using spatially interpolated zenith wet delay zwd data obtained from a network of global positioning system gps receivers in the region imaged by the radar our method based on taylor s frozen flow hypothesis uses gps data recorded prior to and after the individual radar acquisition times to infer denser spatial networks of control points for interpolation than is suggested by the sparse and irregular spatial distribution of gps receivers we test this approach by correcting phase fluctuations observed in a radar interferogram over an area covered by the southern california integrated gps network stations using maps of atmospheric delay interpolated from the denser network of gps zwd measurements generated by our method we find that the largest improvement results from removing an altitude dependent model derived from the gps data the uncorrected interferogram in our example has an rms fluctuation of 16 1 mm which falls to 8 6 mm after the altitude correction a map derived from zwd measurements recorded only at the instances of radar acquisition reduced overall fluctuations in the data from 8 6 to 8 1 mm rms while using the inferred denser network reduces the error further to 7 5 mm rms most of this residual variation is due to decorrelation of the signal and does not result from atmospheric propagation however after smoothing to remove decorrelation noise the residual drops from 4 7 to 3 9 mm gps stations only and then to 2 7 mm rms when the denser network algorithm is used

geostatistical analysis and mitigation of the atmospheric phase screens in ku band terrestrial radar interferometric observations of an alpine glacier terrestrial radar interferometry tri can measure displacements at high temporal resolution potentially with high accuracy an application of this method is the observation of the surface flow velocity of steep fast flowing aglaciers for these observations the main factor limiting the accuracy of tri observations is the spatial and temporal variabilities in the distribution of atmospheric water vapor content causing a phase delay atmospheric phase screen aps whose magnitude is similar to the displacement phase this contribution presents a geostatistical analysis of the spatial and temporal behaviors of the aps in ku band tri the analysis is based on the assumption of a separable spatiotemporal covariance structure which is tested empirically using variogram analysis from this analysis spatial and temporal aps statistics are estimated and used in a two step procedure combining regression kriging with generalized least squares gls inversion to estimate a velocity time series the performance of this method is evaluated by cross validation using phase observations on stable scatterers this analysis shows a considerable reduction in residual phase variance compared with the standard approach of combining the linear models of aps stratification and interferogram stacking

a review of terrestrial radar interferometry for measuring surface change in the geosciences this paper presents a review of the current state of the art in the use of terrestrial radar interferometry for the detection of surface changes related to mass movement different hardware types and acquisition concepts are described which use either real or synthetic aperture for radar image formation we present approaches for data processing procedures paying special attention to the separation of high resolution displacement information from atmospheric phase variations recent case studies are used to illustrate applications in terrestrial radar interferometry for change detection applications range from detection and quantification of very slow moving millimeters to centimeters per year displacements in rock walls from repeat monitoring to rapid processes resulting in fast displacements 50 m yr acquired during single measurement campaigns with durations of only a few hours fast and episodic acting processes such as rockfall and snow avalanches can be assessed qualitatively in the spatial domain by mapping decorrelation caused by those processes a concluding guide to best practice outlines the necessary preconditions that have to be fulfilled for successful application of the technique as well as in areas characterized by rapid decorrelation empirical data from a ku band sensor show the range of temporal decorrelation of different surfaces after more than two years for rock surfaces and after a few seconds to minutes in vegetated areas during windy conditions the examples show that the displacement field can be measured for landslides in dense grassland ice surfaces on flowing glaciers and snowpack creep copyright 2014 john wiley sons ltd

seismic activity and surface motion of a steep temperate glacier a study on triftgletscher switzerland the tongue of triftgletscher switzerland is particularly susceptible to major break off events due to its steep slope in order to detect precursors of such an event we monitored the local seismic activity and detected 2426 icequakes with sources located in an area ranging between 2050 and 2350ma s l events triggered by cracks and icefalls were recorded but no precise distinction between the two sources was possible using duration or frequency criteria clusters of seismic activity were located and confirmed by visual observations we performed a surface motion analysis and found that surface motion was driven significantly by runoff changes at a timescale of 2 3 days by means of a statistical analysis a power law behaviour of the released seismic energy distribution was discerned at certain times during the period investigated variations in power law exponent values indicated that low and high energy events predominantly occurred during phases of enhanced and reduced surface motion respectively substantial releases of seismic energy likely to signal the glacier recoupling were detected during phases of decreasing runoff clues to potential seismic precursors of break off events are discussed

on the instability of avalanching glaciers the instability of hanging glaciers and more generally of avalanching glaciers is discussed on the basis of observations performed on several glaciers located in the european alps a classification of avalanching glaciers is proposed which allows a primary appreciation of the danger inherent in these glaciers on the basis of field observations and results of numerical simulations of crevassing the fracture processes which lead to major icefalls as well as their recurrence are analyzed a method for predicting the time of failure is then discussed the disaggregation of the unstable ice masses usually observed prior to large icefalls is investigated and its implications for the forecasting of icefalls analyzed

the kolka karmadon rock ice slide of 20 september 2002 an extraordinary event of historical dimensions in north ossetia russian caucasus on 20 september 2002 an enormous rock ice slide and subsequent mud flow occurred on the northern slope of the kazbek massif northern ossetia russian caucasus it started on the north northeast wall of dzhimarai khokh 4780 ma s l and seriously affected the valley of genaldon karmadon immediate governmental actions available scientific information first reconstructions hazard assessments and monitoring activities as well as initial expert judgments recommendations are documented in order to enable more detailed analyses and modelling of the event by the wider scientific community among the most remarkable aspects related to this event are 1 the relation between the recent event and somewhat smaller but quite similar events that occurred earlier in historical times 1835 1902 2 the interactions between unstable local geological structures and complex geothermal and hydraulic conditions in the starting zone with permafrost cold to polythermal hanging glaciers and volcanic effects hot springs in close contact with each other 3 the erosion and incorporation of a debris covered valley glacier largely enhancing the sliding volume of rocks ice firn snow water and probably air to a total of about 100 106m3 and 4 the astonishingly high flow velocities up to 300 km h 1 and enormous length of travel path 18 km plus 15 km of debris mud flow this extraordinary case illustrates that large catastrophic events in high mountain regions typically involve a multitude of factors and require integrated consideration of complex chains of processes a task which must be undertaken by qualified groups of experts

ground based radar interferometry for landslides monitoring atmospheric and instrumental decorrelation sources on experimental data the application of ground based radar interferometry for landslide monitoring is analyzed a case study based on an experimental campaign carried out in italy during 2002 is discussed interferometric data obtained from coherent synthetic aperture radar sar images acquired by means of c band ground based equipment are analyzed the campaign was aimed at retrieving potential terrain movements of a small landslide observed hundreds of meters away critical aspects related to spatial and temporal decorrelation are discussed the use of optical photogrammetry as a technique for evaluating mechanical stability and correcting geometric distortion is presented results also confirmed that the application of ground based radar interferometry can be attractive and effective if the acquired sar images maintain an adequate coherence on different dates

estimation of ice sheet motion using satellite radar interferometry method and error analysis with application to humboldt glacier greenland satellite radar interferometry provides glaciologists with an important new tool for determining the motion and topography of large ice sheets we examine the sources of error in interferometrically derived ice motion measurements including those errors due to inaccurate estimates of the interferometric baseline several simulations are used to assess baseline accuracy in terms of tie point error and the number and distribution of tie points these results give insight into how best to select tie points and also demonstrate the level of accuracy that can be achieved examination of two representative cases likely to occur in mapping ice sheet motion leads to the conclusion that with adequate tie point information ice velocity can be measured accurately to within a few meters per year a method to correct horizontal velocity estimates for the effect of vertical displacement using surface slopes is also developed finally we estimate the single component velocity field for an area on humboldt glacier northern greenland using interferograms formed from ers i sar images we estimate that these velocity measurements are accurate to within 2 3 m year 1

atmospheric phase screen compensation in ground based sar with a multiple regression model over mountainous regions in this paper a new model based technique for the compensation of severe height dependent atmospheric artifacts using ground based synthetic aperture radar sar data over mountainous regions is proposed the method presented represents an extension of already existing techniques but now taking into account the effect of steep topography in the atmospheric phase screen compensation process in addition the technique is adapted to work with polarimetric sar data showing in that case a noticeable improvement in the compensation process the method is validated in the mountainous environment of el forn de canillo located in the andorran pyrenees where there is a slow moving landslide that nowadays is being reactivated coinciding with strong rain episodes in this framework ten zero baseline fully polarimetric data sets have been acquired at x band during a one year measurement campaign october 2010 october 2011 with the gb sar sensor developed at the universitat politecnica de catalunya first the impact of the severe atmospheric fluctuations among multitemporal gb sar measurements is carefully studied and analyzed hence the need to correctly estimate and compensate the resulting phase differences when retrieving interferometric information is put forward in the frame of differential sar interferometry applications

avalanching glacier instabilities review on processes and early warning perspectives avalanching glacier instabilities are gravity driven rupture phenomena that might cause major disasters especially when they are at the origin of a chain of processes reliably forecasting such events combined with a timely evacuation of endangered inhabited areas often constitute the most efficient action recently considerable efforts in monitoring analyzing and modeling such phenomena have led to significant advances in destabilization process understanding improving early warning perspectives the purpose of this paper is to review the recent progress in this domain three different types of instabilities can be identified depending on the thermal properties of the ice bed interface if cold 1 the maturation of the rupture is associated with a typical time evolution of surface velocities and passive seismic activity a prediction of the final break off is possible using these precursory signs for the two other types water plays a key role in the development of the instability if the ice bed interface is partly temperate 2 the presence of meltwater may reduce the basal resistance which promotes the instability no clear and easily detectable precursory signs are known in this case and the only way to infer any potential instability is to monitor the temporal evolution of the thermal regime the last type of instability 3 concerns steep temperate glacier tongues switching for several days weeks during the melting season into a so called active phase followed in rare cases by a major break off event although the prediction of such events is still far from being achievable critical conditions promoting the final instability can be identified