deriving a time series of 3d glacier motion to investigate interactions of a large mountain glacial system with its glacial lake use of synthetic aperture radar pixel offset small baseline subset technique abstract we investigated the interactions of lake merzbacher with the southern inylchek glacier central tien shan using the synthetic aperture radar sar pixel offset small baseline subset po sbas to derive a time series of three dimensional 3d glacier motion the measurements of 3d glacier velocity were 17 more precise than a previous study that did not use the sbas estimation the velocities of the glacier were up to 58 cm day east 70 cm day north and 113 cm day vertically combining these data with landsat images indicated that movement of the glacier is sensitive to changes of lake merzbacher specifically the entry of more lake water into the glacier during the ablation season increased englacial ablation due to thermal erosion moreover ice calving begins when the lake water gradually lifts the ice dam calving can cause greater loss of glacier mass than normal ablation trying to replenish the front mass loss the distributary accelerates and the mass loss further intensifies a time series of the vertical velocity indicates that the glacier tongue has a huge englacial cavity we suggest that the lake outburst is directly related to the crack of this cavity bursting of the lake triggers a mini surge at the glacier tongue the vertical velocity at the ice dam was 60 cm day before the lake outburst and 113 cm day afterwards after drainage of the lake flow velocities at the distributary do not sharply decrease because pre drainage mass loss needs to be replenished by fast flow based on comparisons with previous measurements our results indicate that the lake had an increasing influence on the glacier from 2005 to 2009 this study demonstrates that a time series of 3d glacier motion based on the po sbas technique is effective for assessing the dynamics of a mountain glacial system and interactions with its glacial lake

greenland flow variability from ice sheet wide velocity mapping using radarsat synthetic aperture radar data we have mapped the flow velocity over much of the greenland ice sheet for the winters of 2000 01 and 2005 06 these maps provide a detailed view of the ice sheet flow including that of the hundreds of glaciers draining the interior the focused patterns of flow at the coast suggest a strong influence of bedrock topography differences between our two maps confirm numerous early observations of accelerated outlet glacier flow as well as revealing previously unrecognized changes the overall pattern is one of speed up accompanied by terminus retreat but there are also several instances of surge behavior and a few cases of glacier slowdown comprehensive mappings such as these at regular intervals provide an important new observational capability for understanding ice sheet variability

three dimensional surface velocities of storstrommen glacier greenland derived from radar interferometry and ice sounding radar measurements non steady state vertical velocities of up to 5 m y 1 exceed the vertical surface parallel flow components over much of the ablation area of storstrommen a large outlet glacier from the east greenland ice sheet neglecting a contribution to the vertical velocity of this magnitude results in substantial errors up to 20 also on the south north component of horizontal velocities derived by satellite synthetic aperture radar interferometry insar measurements in many glacier environments the steady state vertical velocity component required to balance the annual ablation rate is 5 to 10 m y 1 or more this indicates that the surface parallel flow assumption may be problematic also for glaciers in steady state here we derive the three dimensional surface velocity distribution of storstrommen by using the principle of mass conservation to combine insar measurements from ascending and descending satellite tracks with airborne ice sounding radar measurement of ice thickness the results are compared to insar velocities previously derived by using the assumption of surface parallel flow and to velocities obtained by inin situ gps measurements the velocities derived by using the principle of mass conservation are in better agreement with the gps velocities than the previously calculated velocities derived with the assumption of surface parallel flow

pine island glacier antarctica a study of the catchment using interferometric synthetic aperture radar measurements and radar altimetry we have mapped the catchment region of pine island glacier antarctica using ers 1 and ers 2 radar altimetry and synthetic aperture radar sar interferometry the radar altimeter data were converted to a digital elevation model dem using an algorithm we developed that corrects for slopes and grids the surface elevation estimates in a single step we used the dem and precise postprocessed orbital ephemerides to generate terrain corrected and geolocated complex radar imagery interferometric pairs on both ascending and descending orbits corrected by means of the dem yielded components of ice surface motion in the radar look direction where possible we combined velocity components from ascending and descending tracks to produce vector velocities elsewhere the velocity was calculated by assuming the direction of motion is down the surface slope the velocity map reveals a system of tributaries that channel ice from the basin like catchment area into the fast flowing downstream trunk of pine island glacier none of the tributaries shows a clear onset region instead the ice speed gradually increases along with a gradual decrease in driving stress along each tributary we combined the velocity data with sparse information on ice thicknesses and snow accumulation rates to calculate an approximate mass balance we find that the region is in balance within an uncertainty of 30 of the total mass throughput

observations of atmosphere ocean coupling in midlatitude western boundary currents oceanographic fields derived from the geosat altimeter and atmospheric fields from the european centre for medium range weather forecasts ecmwf were examined for both the western north pacific ocean and the western north atlantic ocean to determine the nature of the coupling despite the short data records approximately 2 5 years correlation analyses of nonseasonal fluctuations showed similar relationships for both oceans correlations between the height difference across the jets surface transport and the path of the western boundary currents suggested that there is a structural change of the recirculation gyres associated with a path change with timescales of 5 9 months both wind stress and wind stress curl were clearly correlated with the surface transport and path in each ocean although net surface heat flux and wind stress were correlated there was no clear correlation between net surface heat flux from ecmwf and surface transport over the entire study region additional regional analyses of the north atlantic showed a consistent relationship between cooling sea surface temperature sst and surface transport west of 62 w anomalous cooling accompanied by cyclonic wind anomalies corresponds to a weaker sst gradient across the gulf stream and decreasing surface transport because the surface transport fluctuations to the west and east of 62 w in the western north atlantic are not correlated structural changes in the recirculation gyres which have their maximum variations east of 62 w may not be related to surface heat flux variations

observations of ice sheet motion in greenland using satellite radar interferometry we present interferometric observations of ice sheet motion in western greenland based on pairs of ers 1 synthetic aperture radar sar images these observations provide the first detailed regional view of ice motion associated with dynamically supported topography near the margin of an ice sheet the interferograms of this area are much more complicated than other interferograms of ice sheets presented to date we devote the largest part of this paper to explaining the source of the complexity in these interferograms a synthetic interferogram based on a simple model helps to illustrate the effects of different components of the ice velocity field in interferometric data and suggests a method for estimating the large scale ice velocity field from such data

seasonal acceleration of inland ice via longitudinal coupling to marginal ice we use an ice flow model to demonstrate how flow variations initiated in the marginal zone of an ice sheet affect flow farther inland through longitudinal along flow coupling our findings allow for an alternate interpretation of seasonal accelerations observed near the equilibrium line of the greenland ice sheet zwally and others 2002 we demonstrate that these observations can be explained by accelerations initiated up to 12 km closer to the margin where the ice is 40 thinner is heavily crevassed experiences a seasonal doubling of velocity and where the ablation rate surface meltwater flux and ice temperature are likely higher our modeling and observations suggest that conditions and processes normally found near ice sheet margins are adequate for explaining the observations of zwally and others 2002 this and considerations of the likely subglacial hydrology in the marginal zone lead us to suggest that seasonal accelerations may have limited impact on ice sheet mass balance even in the face of climate warming

estimation of arctic glacier motion with satellite l band sar data offset fields between pairs of jers 1 satellite sar data acquired in winter with 44 days time interval were employed for the estimation of arctic glacier motion over svalbard novaya zemlya and franz josef land the displacement maps show that the ice caps are divided into a number of clearly defined fast flowing units with displacement larger than about 6 m in 44 days i e 50 m year the estimated error of the jers 1 offset tracking derived displacement is on the order of 20 m year occasionally azimuth streaks related to auroral zone ionospheric disturbances were detected and dedicated processing steps were applied to minimize their influence on the estimated motion pattern our analysis demonstrated that offset tracking of l band sar images is a robust and direct estimation technique of glacier motion the method is particularly useful when differential sar interferometry is limited by loss of coherence i e for rapid and incoherent flow and large acquisition time intervals between the two sar images the jers 1 results obtained using sar data acquired by a satellite operated until 1998 raise expectations of l band sar data from the alos satellite launched in early 2006

low frequency circulation at the edge of the scotian shelf abstract records of current temperature and salinity from a two year mooring program at the shelf break off nova scotia are examined to determine the low frequency oceanic responses to the driving surface wind field and fluctuating offshore currents associated with the gulf stream the seasonal mean and subtidal variance at periods of 2 10 days of the cross shelf currents reflect the strong annual cycle in the wind field measured at sable island the mean vertical shear suggests a simple ekman response to winter increases in the longshore wind component but this model fails quantitatively because 1 the inferred surface layer 20 m transport is much too large and 2 the deep 150 m return flow shows no annual signal the excessive offshore near surface transport in winter must be reconciled with the relatively stationary position of the shelf slope water boundary ssb by invoking intense cross frontal mixing and or a seasonal mean alongshore pressure gradient the seasonal mean longshore currents

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

a high resolution record of greenland mass balance we map recent greenland ice sheet elevation change at high spatial 5 km and temporal monthly resolution using cryosat 2 altimetry after correcting for the impact of changing snowpack properties associated with unprecedented surface melting in 2012 we nd good agreement 3 cm yr bias with airborne measurements with the aid of regional climate and rn modeling we compute high spatial and temporal resolution records of greenland mass evolution which correlate r 0 96 with monthly satellite gravimetry and reveal glacier dynamic imbalance during 2011 2014 greenland mass loss averaged 269 51 gt yr atmospherically driven losses were widespread with surface melt variability driving large uctuations in the annual mass de cit terminus regions of ve dynamically thinning glaciers which constitute less than 1 of greenland s area contributed more than 12 of the net ice loss this high resolution record demonstrates that mass de cits extending over small spatial and temporal scales have made a relatively large contribution to recent ice sheet imbalance

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

an investigation into the mechanisms controlling seasonal speedup events at a high arctic glacier bingham r g hubbard a l nienow p w sharp m j 2008 an investigation into the mechanisms controlling seasonal speedup events at a high arctic glacier journal of geophysical research earth surface 113 f2 f02006 sponsorship nerc nserc the university of alberta circumpolar institute and northern science training programme the geological society of america

contribution to the glaciology of northern greenland from satellite radar interferometry interferometric synthetic aperture radar insar data from the ers 1 and ers 2 satellites are used to measure the surface velocity topography and grounding line position of the major outlet glaciers in the northern sector of the greenland ice sheet the mass output of the glaciers at and above the grounding line is determined and compared with the mass input we find that the grounding line output is approximately in balance with the input except for the three largest glaciers for which the mass loss is 4 3 km3 ice year 1 or 11 8 of the mass input along the coast we detect a systematic retreat of the grounding lines between 1992 and 1996 with insar which implies that the outlet glaciers are thinning the inferred coastal thinning is too large to be explained by a few warm summers glacier thinning must be of dynamic origin that is caused by spatial and temporal changes in ice velocity iceberg production from the glaciers is uncharacteristically low it accounts for only 8 of the ice discharge to the ocean about 55 of the ice is lost through basal melting 5 8 m ice year 1 on average from the underside of the floating glacier tongues that are in contact with warm ocean waters mass losses are highest in the first 10 km of floating ice where ice reaches the greatest depths and basal melting is 3 times larger than on average only a small increase in basal melting would suffice to disintegrate the floating glacier tongues copyright 2001 by the american geophysical union

seasonal and interannual variations in geostrophic velocity in the middle atlantic bight 1 more than 6 years of measurements from the topex poseidon t p altimeter are used to study the seasonal and interannual variations of the geostrophic velocity anomalies in the middle atlantic bight region geostrophic velocities from t p data are compared with the simultaneous low pass filtered current meter data the correlations are all above 95 significance for the three current meter observations at the 1000 m 2210 m and 2990 m isobaths the seasonal mean geostrophic currents from 63 75 w show coherent variations along isobaths with seasonal reversals toward the southwest during the winter and toward the northeast during the summer the eof analysis indicates that the seasonal reversals disappeared during 1996 this disruption is part of the intensification of the slope sea gyre and is related to the southward shift of the gulf stream which acts as the boundary between the subpolar and subtropical gyres the gulf stream moved farther south during 1996 1998 the variations in the gulf stream position may be caused by the wind stress wind stress curl change

measurement of ice sheet topography using satellite radar interferometry detailed digital elevation models dems do not exist for much of the greenland and antarctic ice sheets radar altimetry is at present the primary in many cases the only source of topographic data over the ice sheets but the horizontal resolution of such data is coarse satellite radar interferometry uses the phase difference between pairs of synthetic aperture radar sar images to measure both ice sheet topography and surface displacement we have applied this technique using ers 1 sar data to make detailed i e 80 m horizontal resolution maps of surface topography in a 100 km by 300 km strip in west greenland extending northward from just above jakobshavns isbrae comparison with a 76 km long line of airborne laser altimeter data shows that we have achieved a relative accuracy of 2 5m along the profile these observations provide a detailed view of dynamically supported topography near the margin of an ice sheet in the final section we compare our estimate of topography with phase contours due to motion and confirm our earlier analysis concerning vertical ice sheet motion and complexity in ers 1 sar interferograms

ice sheet motion and topography from radar interferometry both topography and motion information are present in repeat pass ers 1 interferograms over ice sheets the authors demonstrate that the topography is separable from the surface displacement field when a sequence of radar images are available if the velocity field is constant over the time span of observation the topography can be derived from differential interferograms formed from sequential observations with this measurement a pure displacement field can then be obtained by removal of the topographic contribution to the interferometric phase at each pixel further they discuss how the vertical and horizontal components of displacement affect the interferometrically derived motion field they illustrate their approach with four successive 3 day repeat ers 1 images of a flow feature in northeastern greenland

role of the gulf stream and kuroshio oyashio systems in large scale atmosphere ocean interaction a review abstract ocean atmosphere interaction over the northern hemisphere western boundary current wbc regions i e the gulf stream kuroshio oyashio and their extensions is reviewed with an emphasis on their role in basin scale climate variability sst anomalies exhibit considerable variance on interannual to decadal time scales in these regions low frequency sst variability is primarily driven by basin scale wind stress curl variability via the oceanic rossby wave adjustment of the gyre scale circulation that modulates the latitude and strength of the wbc related oceanic fronts rectification of the variability by mesoscale eddies reemergence of the anomalies from the preceding winter and tropical remote forcing also play important roles in driving and maintaining the low frequency variability in these regions in the gulf stream region interaction with the deep western boundary current also likely influences the low frequency variability surface heat fluxes damp the low frequency sst anomalies ove

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

a spatially adjusted elevation model in dronning maud land antarctica based on differential sar interferometry in this paper a new digital elevation model dem is derived for the ice sheet in western dronning maud land antarctica it is based on differential interferometric synthetic aperture radar sar from the european remote sensing 1 2 ers 1 2 satellites in combination with icesat s geoscience laser altimeter system glas a dem mosaic is compiled out of 116 scenes from the ers 1 ice phase in 1994 and the ers 1 2 tandem mission between 1996 and 1997 with the glas data acquired in 2003 that served as ground control using three different sar processors uncertainties in phase stability and baseline model resulting in height errors of up to 20 m are exemplified atmospheric influences at the same order of magnitude are demonstrated and corresponding scenes are excluded for validation of the dem mosaic covering an area of about 130 000 km2 on a 50 m grid independent icesat heights 2004 2007 ground based kinematic gps 2005 and airborne laser scanner data als 2007 are used excluding small areas with low phase coherence the dem differs in mean and standard deviation by 0 5 10 1 1 1 6 4 and 3 1 4 0 m from icesat gps and als respectively the excluded data points may deviate by more than 50 m in order to suppress the spatially variable noise below a 5 m threshold 18 of the dem area is selectively averaged to a final product at varying horizontal spatial resolution apart from mountainous areas the new dem outperforms other currently available dems and may serve as a benchmark for future elevation models such as from the tandem x mission to spatially monitor ice sheet elevation

recirculation and seasonal change of the kuroshio from altimetry observations surface height fluctuations across an eastward flowing boundary current such as the gulf stream and the kuroshio can be caused by changes both in the upstream inflow and in the neighboring recirculation gyres clarifying these causes is important in understanding the time dependent nature of the boundary currents and their relationship to the surface wind and buoyancy forcing using satellite altimetry data to identify these causes however requires mean surface height field information which is not readily available from the altimetry observation owing to lack of accurate geoid data the present study presents a method to estimate the mean surface height profile across a boundary current system including recirculation gyres by combining altimetrically measured residual height data and historical hydrographic data applying this method to the kuroshio revealed that the absolute surface height profiles thus estimated agree well with the results from quarterly in situ hydrographic observations by separating the signals of the surface height fluctuations into those of the eastward flowing jet and the recirculation gyres we found that the seasonal cycle in the surface transport of the kuroshio which has a maximum in july and august is primarily due to the seasonal change in the intensity of the recirculation gyre south of the kuroshio

using multiple radarsat insar pairs to estimate a full three dimensional solution for glacial ice movement 1 multiple sar interferograms are used to solve for the full 3 dimensional displacement of the surface of the henrietta nesmith glacier in northern ellesmere island canada the approach exploits the incidence angle flexibility of different ascending and descending beam modes and the azimuth angle diversity which occurs when different incidence angles are used at high latitudes line of sight displacements are estimated in 3 different orientations from the terrain corrected unwrapped differential phase and used to solve for the displacements in a local east north up frame uncertainty in the absolute line of sight displacements limits the absolute accuracy for vertical displacement however the relative solution coupled with knowledge of the surface slope allows spaceborne mapping of relative glacier thickening or thinning with unprecedented spatial resolution and with an accuracy of order a millimeter per day

short term surface ice motion variations measured with a ground based portable real aperture radar interferometer we report measurements using a portable real aperture radar gamma portable radar interferometer gpri for interferometric imaging of the surface ice motion on gornergletscher switzerland during the drainage of the adjacent ice marginal lake gornersee the gpri tracked the surface ice motion in line of sight over an area of 3k m 2 down glacier of gornersee almost continuously during the drainage event the displacement maps derived from the acquired interferograms capture the spatial distribution of the surface ice motion due to fast acquisition times of the microwave images the gpri was able to record sub daily variations of the ice displacements most likely caused by the impact of the gornersee drainage on the ice motion of gornergletscher in situ point measurements of the ice displacement agree reasonably well with the results obtained by the gpri and highlight the use of the gpri for high resolution measurements of glacier surface ice motion motion of gornergletscher these variations in surface ice motion were triggered by the subglacial drainage of the adjacent marginal ice dammed lake gornersee we present ice displacement maps derived from the gpri interfero grams and analyze the performance of the radar device for remote sensing of surface ice motions of a glacier on spatial and temporal scales lower than in conventional d insar applications we compare the radar displacements against local in situ ice displacement measurements to complete the study a brief discussion of the observed displacements in relation to the drainage phenomena is given

western boundary currents and frontal air sea interaction gulf stream and kuroshio extension abstract in the northern hemisphere midlatitude western boundary current wbc systems there is a complex interaction between dynamics and thermodynamics and between atmosphere and ocean their potential contribution to the climate system motivated major parallel field programs in both the north pacific kuroshio extension system study kess and the north atlantic climate variability and predictability clivar mode water dynamics experiment climode and preliminary observations and analyses from these programs highlight that complexity the gulf stream gs in the north atlantic and the kuroshio extension ke in the north pacific have broad similarities as subtropical gyre wbcs but they also have significant differences which affect the regional air sea exchange processes and their larger scale interactions the 15 yr satellite altimeter data record which provides a rich source of information is combined here with the longer historical record from in situ data to describe and compare the curr

changes in west antarctic ice stream velocities observation and analysis 1 we have produced a map of velocity covering much of the siple coast ice streams the map confirms earlier estimates of deceleration on whillans ice stream comparison with bed elevation data indicates that subglacial topography and the location of consolidated sediment play a strong role in determining the location of the tributaries feeding the ice streams force balance estimates based on these data indicate that the tributaries have beds nearly an order of magnitude stronger than those beneath many of the ice streams we have used a theoretical analysis to examine the controls on fast flow this analysis suggests that ice plains very wide ice streams are inherently unstable this instability may be responsible for the current deceleration on the ice plain of whillans ice stream and the shutdown of ice stream c 150 years ago thinning induced reductions in driving stress may also explain some of the observed deceleration particularly in upstream areas the active portions of ice stream c coincide well with the areas where we estimate that melt should be taking place current topography and inferences of large thickening following a shutdown suggest the upstream migration of a stagnation front that initiated at the ice plain uncertainty remains about the basal conditions on ice stream d while the basal resistance on ice stream e is large enough to ensure basal melting

tidal motion ice velocity and melt rate of petermann gletscher greenland measured from radar interferometry over a floating glacier ice tongue or an ice shelf the glacier motion measured by a single repeat pass radar interferogram is difficult to analyze because the long term steady motion of the ice is intermixed with its cyclic downward motion induced by tidal forcing multiple interferograms and a quadruple difference technique are necessary to separate the tidal signal from the long term steady motion of the ice an example of application of this technique is given here using ers 1 radar images of petermann gletscher a major outlet glacier of northern greenland tidal displacements are measured with 5 mm statistical noise the long term ice velocity is measured with a precision of 1 m a 1 the inferred tidal displacements agree well with model predictions from a fixed elastic beam with an elastic damping factor of 0 47 0 01 km 1 the hinge line is mapped with a precision of 20 80 m combining the interferometric ice velocities with ice thickness data the glacier ice discharge is calculated at and below the hinge line at the hinge line the ice flux is 12 1 1 km3 a 1 at the ice front calf ice production is only 0 59 km3 a 1 meaning that 95 of the ice that crosses the grounding line melts before it reaches the calving front assuming steady state conditions the melt rate of the glacier tongue averages 12 1 m a 1 with peak values exceeding 20 m a 1 near the hinge line this high melt rate cannot be accommodated by surface ablation alone only about 2 3 m a 1 and is attributed to pronounced basal melting of the ice tongue basal melting often assumed to be negligible in greenland is the dominant process of mass release from the floating section of petermann gletscher

new velocity map and mass balance estimate of mertz glacier east antarctica derived from landsat sequential imagery automatic feature tracking on two landsat images acquired in january 2000 and december 2001 generates a complete velocity field of mertz glacier east antarctica this velocity field shows two main tributaries to the ice stream between the tributaries a likely obstruction feature in the bedrock results in a slow down of the flow a third landsat image acquired in 1989 and combined with the 2000 image permits the determination of the glacier mean velocity during the 1990s although some parts of the mertz glacier system show evidence of slight speed increase we conclude that the mertz flow speed is constant within our uncertainty 35 m a 1 using this complete velocity field new estimates of the ice discharge flux 17 8 km 3 a 16 4 gt a and of the basal melting of the tongue 11m a of ice are given our results lead to an apparent imbalance of the drainage basin ice discharge 3 5 km 3 a lower than the accumulation considering previous studies in the mertz glacier area we discuss the uncertainty of this imbalance and the problems with accumulation mapping for this region

is there a single surge mechanism contrasts in dynamics between glacier surges in svalbard and other regions 1 during the 1990s monacobreen a 40 km long tidewater glacier in svalbard underwent a major surge we mapped the surge dynamics using ers synthetic aperture radar images differential dual azimuth interferometry and intensity correlation tracking a series of 11 three dimensional 3 d velocity maps covering the period 1991 1997 show a months long initiation and years long termination to the surge with no indication of a surge front travelling downglacier during the surge the front of the glacier advanced 2 km the velocity and derived strain rate increased by more than an order of magnitude and maximum ice flow rates measured during 1994 were 5 m d 1 the spatial pattern of both velocity and strain rate was remarkably consistent and must therefore be controlled by spatially fixed processes operating at the glacier bed we combine these results with those published in the literature to construct a typical svalbard glacier surge cycle and compare this to surge dynamics of glaciers from other cluster regions especially those of variegated glacier in alaska the strong contrast in dynamics suggests that there exist at least two distinct surge mechanisms

investigating mountain glacier motion with the method of sar intensity tracking removal of topographic effects and analysis of the dynamic patterns abstract accurate knowledge of glacier motion variations can provide critical information for assessing glacier mass balance changes for fast flowing high mountain glaciers sar intensity tracking may be the most appropriate technique to measure their motions however due to the slant range imaging mode topographic relief can give rise to pixel disalignments in sar image and then bring errors to sar intensity tracking as a result the application of sar intensity tracking has been limited to sar pairs with short baselines because the use of image pairs with long baselines would suffer significant topographic effects over mountainous regions this paper presents an improvement to sar intensity tracking by adding an explicit procedure of topographic correction such correction will not only significantly increase the accuracy of the sar pairs with shorter baselines but also allow the image pairs with longer baselines to be taken advantage of instead of letting them to be dismissed otherwise using the improved sar intensity tracking technique we derive the highly precise motion variation patterns of 11 giant glaciers in tuomuer khan tengri mountain ranges one of the largest glacial centers in tien shan the results manifest that most glaciers there saw flow deceleration during the observation interval 6 january 2007 4 march 2011 except the northern and southern inylchek glacier regarding the glacier motion mechanism ice thermal character and climate features there we deduce that the flow acceleration and deceleration should be the sign of glacier mass gain and loss respectively and the sharp and slight flow decelerations should correspond to remarkable and mild mass loss respectively we confirm these deductions by exploring the close link between the long term motion variations and the dynamic patterns of these glaciers the obvious diversities of the dynamic patterns among the studied glaciers are ascribed to the discrepancies of the glaciers location and scale longer observations are still needed to confirm or redefine these findings in the future though provided that the precipitation keeps increasing whether the glaciers in tuomuer khan tengri mountain ranges will regain mass or not has not been determined yet

multi model photogrammetric analysis of the 1990s surge of sortebrae east greenland sortebrae is a surge type tidewater glacier complex draining southeastward from the geikie plateau east greenland sortebrae s main flow unit surged around 1950 and again between 1992 and 1995 the 1990s surge affected the lower 50 km of sorte brae over an area of approximately 335 km2 over a period of 5 km surge velocities in the order of kilometres per annum are about 100 fold the quiescent velocities multi model photogrammetric analysis shows a thinning of the reservoir zone of up to 219 m and thickening of the receiving zone of up to 74 m the surge transported approximately 18 6 km 3 of ice down glacier the total calving volume as a result of the surge amounted to 11 7 km 3 equivalent to a calving flux of 3 9 7 3 km a 1 the surge characteristics and environmental setting suggest that the surge mechanism involves a switch in the subglacial drainage this surge of sortebrae is more similar to the fast short alaskan type surges than to the sluggish long svalbard type surges

gulf stream surface transport and statistics at 69 w from the geosat altimeter geosat altimeter height measurements for the gulf stream for three subtracks from the exact repeat mission were processed to remove the geoid and mean gulf stream height a gaussian model for the gulf stream velocity profile was used to predict the form of the residual height profiles seen by geosat and the mean height profile using estimates of the width and position derived from the height residuals estimates of the maximum surface velocity and the surface transport were obtained by a least squares fit of the synthetic height profiles to the data location statistics from the geosat data were in good agreement with values obtained from infrared images of the gulf stream maximum surface velocities were typically between 1 2 and 2 0 m s 1 the time series showed that surface transport is correlated primarily with the magnitude of the surface velocities although an anomalously large increase in surface transport in the winter of 1987 1988 was caused by an increase in the width of the gulf stream an analysis of the average annual signal in transport showed maximum values in the late fall and minimum transport in the late spring maximum minimum surface transport generally occurred when the gulf stream was north south of its mean position

interannual variations of volume transport in the western labrador sea based on topex poseidon and woce data abstract the interannual variations of volume transport in the western labrador sea are estimated using six years of topex poseidon altimeter data and hydrographic data from a woce repeat section and a method based on the linear momentum equation in which the sea surface is the level of known motion the interannual variation of the total transport in spring summer has a range of 6 2 sv sv 106 m3 s 1 and is positively correlated with the fall winter north atlantic oscillation nao index and wind patterns in the northwest north atlantic the total transport anomaly is decomposed into a barotropic and a baroclinic component the interannual change of the barotropic transport is similar to that of the total transport and is positively correlated with the fall winter nao index the baroclinic transport anomaly in comparison has a smaller magnitude and the opposite sign the authors conjecture that the deepened icelandic low in high index years generates a strong cyclonic wind stress curl which in tur

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

motion patterns of nabesna glacier alaska revealed by interferometric sar techniques abstract nabesna glacier is one of the longest land terminus mountain glaciers in north america however its flow has never been studied we derived detailed motion patterns of nabesna glacier in winter and spring 1994 1996 from the synthetic aperture radar sar images acquired by the european remote sensing satellites ers 1 and ers 2 using interferometric sar insar techniques special effort was made to assess the accuracy of the motion estimates and remove data points with high uncertainty from the motion profiles enabling us to obtain reliable glacier flow patterns along the highly curved main course of nabesna glacier the results covering 80 km of the 87 km main course of the glacier were used to delineate four distinctive sections in terms of spatial and temporal variability of the glacier speed 1 the upper section where glacier flow was apparently random both temporally and spatially presumably due to development of crevasses 2 the upper middle section with relatively steady flow around 0 27 to 0 4 m day 3 the middle section with a stable pattern of acceleration from 0 27 0 3 m day to the maximum about 0 67 0 73 m day followed by a general deceleration to 0 17 0 33 m day before reaching 4 the lower section where the glacier motion was generally slow yet highly variable although uncertainty in the estimation is high occurrence of the flow maximum as well as many local maxima and minima at consistent locations over different periods suggests that the valley geometry affect the overall flow pattern on top of this general trend many small scale temporal spatial variations in the glacier flow patterns were observed along the glacier especially in the lower sections on average the flow speeds were in the range of 0 3 to 0 7 m day however this lacks any measurements of summer flow speeds which are expected to be significantly higher

observation and analysis of ice flow in the largest greenland ice stream we have applied satellite radar interferometry methods to map the velocity field of the recently discovered northeast greenland ice stream we have used these data in conjunction with ice thickness and accumulation data to determine that the ice stream is in balance within the measurement errors we used control methods to invert a finite element model of ice sheet flow constrained by the data to infer the ice stream s basal shear stress distribution our results reveal that flow in a section of the downstream end has much in common with the streaming flow of the ross ice streams of west antarctica e g a weak bed and fast flow in the presence of low driving stresses for several hundred kilometers along the middle of the ice stream the basal shear stress balances the driving stress in the upstream area where the ice stream is first visible in the velocity data the bed appears to be weak which may contribute to the initiation of the ice stream

ice flow of humboldt petermann and ryder gletscher northern greenland radar interferometry ice penetrating radar profiles and an elevation model are used to determine the velocity fields rates of ice discharge approximate states of balance and catchment area for three large outlet glaciers in northeast greenland discharge through flux gates is calculated for humboldt and petermann gletscher which are found to be in balance at the level that the accumulation is known a large difference between the measured and estimated fluxes for ryder gletscher may be a reflection of unsteady flow behavior for this glacier the patterns ofice flow for the three glaciers considered are each unique showing that the nature of ice discharge varies substantially from basin to basin controlled by bed conditions and the presence of subglacial troughs and obstructions

three dimensional glacial flow and surface elevation measured with radar interferometry outlet glaciers which serve to drain ice from ice sheets seem to be dynamically less stable in north greenland than in south greenland1 2 3 storstrommen a large outlet glacier in northeastern greenland which surged between 1978 and 1984 ref 2 has been well studied in general neither glacier surge mechanisms nor the geographical distribution of the surges are well known conventional satellite radar interferometry can provide large scale topography models with high resolution4 and can measure the radar line of sight component of ice flow vectors5 but cannot map full vector flow fields here we present an interferometry method that combines observations from descending and ascending satellite orbits which assuming ice flow parallel to the topographic surface allows us to use the differing view angles to estimate full three dimensional surface flow patterns the accuracy of our technique is confirmed by the good agreement between our radar based flow model and in situ global positioning system gps reference data at storstrommen radar measurements such as these made regularly and at high spatial density have the potential to substantially enhance our understanding of glacier dynamics and ice sheet flow as well as improve the accuracy of glacier mass balance estimates

estimation and analysis of the surface velocity field of mountain glaciers in muztag ata using satellite sar data muztag ata is a mountain known as the father of glaciers in the west of china however its glacier flow pattern has never been studied in this paper the velocity of mountain glaciers on muztag ata is mapped by two methods insar and offset tacking using sar data this map provides a detailed view of the features of glacier motion on muztag ata a special effort was also made to assess the accuracy of the glacier velocity estimates to ensure the accuracy of the derived results the validation of the results was conducted over two glaciers saliymek glacier and kuksay glacier the two methods yielded similar results that agree well with each other the patterns of glacier velocity on muztag ata suggest that mountain topography westerly winds and the monsoon have a strong influence our results show that motion of glaciers in the southern and western regions of muztag ata is faster than that in the northern and eastern regions eleven glaciers were identified along which glacier velocities exhibited distinctive behavior in terms of the spatial variability of the glacier motion the occurrence of the local flow maxima and minima at consistent locations over different parts of different glaciers suggests that the subglacial topography glacier size and glacier orientation affect the overall flow patterns the velocities are very low in the surface debris cover of some glaciers which suggests debris cover has an impact on glacier motion

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

interferometric estimation of three dimensional ice flow using ascending and descending passes satellite radar interferometry sri provides an important new tool for determining ice flow velocity interferometric measurements made from a single track direction are sensitive only to a single component of the three component velocity vector observations from along three different track directions would allow the full velocity vector to be determined a north south looking synthetic aperture radar sar could provide these observations over large portions of the globe but not over large areas of the polar ice sheets the authors develop and demonstrate a technique that allows the three component velocity vector to be estimated from data acquired along two track directions ascending and descending under a surface parallel flow assumption this technique requires that there are accurate estimates of the surface slope which are also determined interferometrically to demonstrate the technique the authors estimate the three component velocity field for the ryder glacier greenland their results are promising although they do not have yet ground truth data with which to determine the accuracy of their estimates

ground motion phenomena in caltanissetta italy investigated by insar and geological data integration abstract urban areas are frequently affected by ground instabilities of various origins the location of urban zones affected by ground instability phenomena is crucially important for hazard mitigation policies satellite based interferometric synthetic aperture radar insar has demonstrated its remarkable capability to detect and quantify ground and building motion in urban areas especially since the development of advanced differential interferometric sar techniques a dinsar in fact the high density of reflectors like buildings and infrastructures in urban areas improves the quality of the insar signal allowing sub centimetric displacements to be reliably detected the a dinsar techniques allow urban zones affected by ground deformation to be located and mapped but clearly they are not able to point out the causes of the instability phenomena these can only be highlighted by an integrated analysis of multidisciplinary data like geological geotechnical sar interferometric and historical data the overlay of these data which is possible within a geographic information system gis is a useful tool to identify ground motion phenomena affecting urban zones in this study we apply this kind of approach to caltanissetta a provincial capital in sicily italy where local damage has been detected the reconstruction of the local near surface geology shows the presence of zones affected by local natural hazard factors essentially due to the local presence of soils with poor mechanical properties or swelling soils high topographic gradients and steep slopes on loose soils processing 17 asar envisat sar images covering the time interval october 2002 december 2005 by means of an a dinsar procedure the caltanissetta deformation map has been realized it shows that most of the city is stable with the exception of three zones situated in the northwestern northeastern and southern parts of the city respectively two of them characterized by high topographic gradients and steep slopes on sandy soils are affected by subsidence ground motion an uplift motion is recognized in the other zone characterized by the local presence of expansible clays geotechnical swelling tests carried out on them have shown a swelling behavior on site surveys have highlighted the presence of damage in the zones affected by ground motion

implications of changing scattering properties on greenland ice sheet volume change from cryosat 2 altimetry abstract long term observations of surface elevation change of the greenland ice sheet gris is of utmost importance when assessing the state of the ice sheet satellite radar altimetry offers a long time series of data over the gris starting with ers 1 in 1991 esa s cryosat 2 mission launched in 2010 provides an invaluable radar altimetry dataset for monitoring the current changes of the ice sheets due to its dense spatial and temporal coverage of these areas here we investigate the effects of including different parameters which describe the shape of the return radar waveform waveform parameters in the elevation change algorithm to correct for temporal changes in the ratio between surface and volume scatter in cryosat 2 observations we present elevation and volume changes for the greenland ice sheet in the period from 2010 until 2014 the waveform parameters considered here are the backscatter coefficient and the leading edge width which are both available in the esa cryosat 2 level 2i data product investigations into relocation of radar reflection points are also included inter comparison of the cryosat 2 derived elevation changes with those derived from operation icebridge laser data suggests waveform parameters to be applicable for correcting for changes in volume scattering the best results in the synthetic aperture radar interferometric mode area of the gris are found when applying only the backscatter correction whereas the best result in the low resolution mode area is obtained by only applying a leading edge width correction using this approach to correct for the scattering properties a volume loss of 292 38 km 3 yr 1 is found for the gris for the time span november 2010 until november 2014 the inclusion of waveform parameter corrections and improved relocation for the gris helps to reconcile the satellite derived elevation changes with those observed by operation icebridge however the bias of temporal changes in the scattering horizons of cryosat 2 is not entirely removed and suggests that future improvements could be made by including climate data and or additional waveform parameters to make additional corrections in the cryosat 2 radar altimetry

glacier surface motion pattern in the eastern part of west kunlun shan estimation using pixel tracking with palsar imagery mountain glacier is considered as one of the most sensitive natural indicators of climate change glacier surface motion distribution in west kunlun shan wks has been attracting considerable attention and represents a fundamental glacier parameter for better understanding glacier dynamics ice mass balance and even for the climate change this paper would present the accurate ice motion observation of mountain glacier in eastern part of wks by the refined pixel tracking method with phased array type l band synthetic aperture radar images acquired on december 13 2008 and january 28 2009 the standard deviation values in nonglacial area before after topographic effect compensation are 0 61 and 0 43 m respectively during 46 day temporal interval in addition the terrain almost is a determining factor of ice velocity distribution in study area because the elevation of topography is generally shown to be positive correlated with glacier surface velocity along the central line furthermore with estimated detailed glacier surface movement distribution pattern we found that the continental glaciers were actively moving with spatially variable ice motion while the icecaps maintain the stable status without apparent motion on most part of surface therefore the refined sar based pixel tracking method including topographic effect compensation operation provides a useful and robust tool to map and measure the glacier motion in mountain area with complex terrain

the glaciers climate change initiative methods for creating glacier area elevation change and velocity products glaciers and their changes through time are increasingly obtained from a wide range of satellite sensors due to the often remote location of glaciers in inaccessible and high mountain terrain satellite observations frequently provide the only available measurements furthermore satellite data provide observations of glacier characteristics that are difficult to monitor using ground based measurements thus complementing the latter in the glaciers cci project of the european space agency esa three of these characteristics are investigated in detail glacier area elevation change and surface velocity we use a data from optical sensors to derive glacier outlines b digital elevation models from at least two points in time c repeat altimetry for determining elevation changes and d data from repeat optical and microwave sensors for calculating surface velocity for the latter the two sensor types provide complementary information in terms of spatio temporal coverage while c and d can be generated mostly automatically a and b require the intervention of an analyst largely based on the results of various round robin experiments multi analyst benchmark studies for each of the products we suggest and describe the most suitable algorithms for product creation and provide recommendations concerning their practical implementation and the required post processing for some of the products area velocity post processing can influence product quality more than the main processing algorithm

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

a mini surge on the ryder glacier greenland observed by satellite radar interferometry satellite radar interferometry reveals that the speed of the ryder glacier increased roughly threefold and then returned to normal 100 to 500 meters year over a 7 week period near the end of the 1995 melt season the accelerated flow represents a substantial though short lived change in ice discharge during the period of rapid motion meltwater filled supraglacial lakes may have drained which could have increased basal water pressure and caused the mini surge there are too few velocity measurements on other large outlet glaciers to determine whether this type of event is a widespread phenomenon in greenland but because most other outlet glaciers are at lower latitudes they should experience more extensive melting making them more susceptible to meltwater induced surges

slow variations in mean path of the gulf stream east of cape hatteras the gulf stream between cape hatteras and the new england seamounts varies in position over a wide range of time scales we present evidence that interannual path changes may be governed by a time varying outflow of waters from the labrador shelf region when the shelf and slope waters south of new england turn cold and fresh the stream frequently assumes a more southerly track and conversely when the waters are warm and saline these changes in path and surface water properties most likely result from large variations in shelf transport and thus greater or less dilution of the warm saline gulf stream waters that continually leak from the current into the slope sea these observations point to a thermohaline rather than winddriven mechanism for governing the path of the gulf stream after it leaves the coast

fracture propagation as means of rapidly transferring surface meltwater to the base of glaciers 1 propagation of water filled crevasses through glaciers is investigated based on the linear elastic fracture mechanics approach a crevasse will penetrate to the depth where the stress intensity factor at the crevasse tip equals the fracture toughness of glacier ice a crevasse subjected to inflow of water will continue to propagate downward with the propagation speed controlled primarily by the rate of water injection while the far field tensile stress and fracture toughness determine where crevasses can form once initiated the rate of water driven crevasse propagation is nearly independent of these two parameters thus rapid transfer of surface meltwater to the bed of a cold glacier requires abundant ponding at the surface to initiate and sustain full thickness fracturing before refreezing occurs

large fluctuations in speed on greenland s jakobshavn isbrae glacier it is important to understand recent changes in the velocity of greenland glaciers because the mass balance of the greenland ice sheet is partly determined by the flow rates of these outlets jakobshavn isbrae is greenland s largest outlet glacier draining about 6 5 per cent of the ice sheet area and it has been surveyed repeatedly since 1991 ref 2 here we use remote sensing data to measure the velocity of jakobshavn isbrae between 1992 and 2003 we detect large variability of the velocity over time including a slowing down from 6 700 m yr 1 in 1985 to 5 700 m yr 1 in 1992 and a subsequent speeding up to 9 400 m yr 1 by 2000 and 12 600 m yr 1 in 2003 these changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter our observations indicate that fast flowing glaciers can significantly alter ice discharge at sub decadal timescales with at least a potential to respond rapidly to a changing climate

ice flow in the northeast greenland ice stream as the use of satellite data for icesheet research has accelerated new discoveries have changed the way that we think about ice discharge and new tools have changed the way that we measure it we have begun to apply a combination of remote sensing and ice sheet modeling techniques to study ice flow in the recently identified northeast greenland ice stream this ice stream shows evidence of organized flow far into the interior and has low slope areas of rapid flow and regions of enhanced shear that resemble the ice streams of west antarctica the onset of rapid flow close to the ice divide and the evolution of its flow pattern however make this ice stream unique our investigation is aimed at increasing our understanding of this ice stream and its origins and role in the discharge of ice from the ice sheet and the effects that discharge may have on the history and evolution of the ice in northern greenland the ice flow data comes from satellite radar interferometry tied to reference points we have applied this technique to measure the velocity over the entire ice stream which is more than 700 km in length the velocity contours reveal distinct well developed shear margins which are coincident with linear features in the synthetic aperture radar sar amplitude imagery it is surprising to see such defined enhanced flow so far inland and so close to the ice divide the velocity data and topography data are being used to feed a modeling effort that allows us to study the dynamics and character rapid flow additional information is contained in the original

abrupt changes in indian summer monsoon strength during the last 900 years and their linkages to socio economic conditions in the indian subcontinent abstract abrupt shifts in indian summer monsoon ism precipitation largely affected regional hydrometeorology accelerating socio economic and cultural adaptations of agrarian economies in south asia in the last millennium linking ism variability to human history in the indian subcontinent is still limited by the scarcity of high resolution paleoclimatic data for the period encompassing the last 1000 years or earlier we present a new high resolution oxygen isotope proxy record from the wah shikar cave northeastern india and identified abrupt shifts in the ism that had profound impact on human societies during the last 900 yrs the ism was strong during the medieval climate anomaly mca and the current warm period cwp and show multiple shifts during the little ice age lia the abrupt shifts in the ism were more frequent during warm intervals showing a secular trend with few exceptions during the cold periods intervals of prolonged summer monsoon weakening are correlated to the decline of major dynasties in india possibly due to decrease in agriculture productivity declining economy and societal crisis changes in atmospheric temperature due to volcanic eruptions and sun spot activity have played major role in the onset of the lia and other prolonged weak intervals of the ism during the last 900 yrs

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

glacier specific ablation rate derived by remote sensing measurements 1 the specific ablation rate in a transect of storstrommen a large outlet glacier from the northeast greenland ice sheet is derived by combining airborne laser altimetry measurements with emergence submergence velocities derived from satellite synthetic aperture radar interferometry insar and airborne ice sounding radar measurement of ice thickness the results are compared with in situ point observations of ablation measured at poles drilled into the glacier considering the different measurement periods for the different data sets the agreement between derived and observed ablation rates is satisfactory the new method of deriving specific mass balance particularly ablation rate by remote sensing measurements alone has the potential to substantially increase the density of observational based ablation rates on ice sheet and ice cap margins

ice flow dynamics of the greenland ice sheet from sar interferometry synthetic aperture radar sar interferograms produced from esa s ers 1 satellite provide the first synoptic view of ice flow dynamics of the western sector of the greenland ice sheet glacial motion is detected in the radar ranging direction at millimetric scales across a complete sequence of snow accumulation and melting regimes despite significant variations in their radar scattering properties ice flow evolves from a slow regular motion at the higher elevations at lower elevations motion is strongly convoluted by meter scale undulations in surface topography which have a unique interferometric signature that enables a novel approach for retrieving flow direction inferred flow directions combined with surface displacements in the radar ranging direction yield ice velocity estimates that are within 6 of in situ measurements gathered along a 40 km survey line application of repeat pass sar interferometry to the entire greenland ice sheet should enable precise mapping of its ice flow dynamics at an unprecedented level of spatial detail

variability in the slope water and its relation to the gulf stream path 1 sea surface temperature sst and sea surface height ssh data for 1993 2007 for the north atlantic are combined with hydrographic data at 69w to investigate the relation between the gulf stream gs position and the slope water properties sst anomalies north of the gs are correlated with changes in its path the lag of this correlation is such that positive temperature anomalies precede northward shifts of the gs and suggests that sst anomalies move westward with speeds of several cm s eof analysis of the sst and ssh fields shows that cooling and strengthening of the sw flow are in phase over the slope water which is mirrored in the vertical structure of these fields at 69w indicating larger transports in the deep western boundary current lead to southward shifts of the mean gs path this relation between the slope water and the gs path provides some predictability for the latter

the basal speed of valley glaciers an inverse approach geophysical inverse methods are used to calculate the basal motion of a glacier they are applied to a one dimensional forward model that can be linearized to make the analysis simpler the inverse method finds a solution that fits the data within a given error it selects for smooth solutions to discriminate against unrealistic oscillations the method is applied to a simple model glacier of uniform shape and thickness to test how well a given basal motion field can be reconstructed it shows as expected that optimizing for smoothness lowers maxima and increases minima of the solution a step change in basal velocity is drawn out in the inversion over a distance that is given by the half width of a resolving function this is typically about three times the ice thickness but is also affected by the sampling rate of the data the method is then applied to two glaciers where suitable data are available brown glacier on heard island southern indian ocean and mccall glacier in the brooks range alaska u s a the mccall results agree well with earlier estimates of basal motion