reach scale floodplain inundation dynamics observed using airborne synthetic aperture radar imagery data analysis and modelling summary in this paper we use an airborne synthetic aperture radar to map river flood inundation synoptically at fine spatial resolution 1 2 m along a 16 km reach of the river severn west central england images were obtained at four times through a large flood event between 8th and 17th november 2000 and processed using a statistical active contour algorithm to yield the flood shoreline at each time intersection of these data with a high vertical accuracy survey of floodplain topography obtained from airborne laser altimetry permitted the calculation of dynamic changes in inundated area total reach storage and rates of reach dewatering in addition comparison of the data to gauged flow rates the measured floodplain topography and map data giving the location of embankments and drainage channels on the floodplain yields new insights into the factors controlling the development of inundation patterns at a variety of scales finally the data were used to assess the performance of a simple two dimensional flood inundation model lisflood fp and allows us for the first time to validate the dynamic performance of the model this process is shown to give new information into structural weaknesses of the model and suggests possible future developments including the incorporation of a better description of floodplain hydrological processes in the hydraulic model to represent more accurately the dewatering of the floodplain

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

fram strait satellite image derived ice motions in order to develop an operational method for the u s navy noaa joint ice center to extract ice velocity vectors from sequential advanced very high resolution radiometer avhrr imagery we have combined the maximum cross correlation mcc method with a spatial filtering technique on the image inferred ice motion vectors we compute the cross correlations between images directly from the image brightness values rather than computing ffts the direct method allows greater flexibility in computational parameter settings and allows one to compute motion vectors near coastlines where irregular windows are required by using a combination of statistical and spatial filters we can then retrieve coherent ice motion vectors in the presence of cloud contaminated imagery a series of six satellite images of the fram strait region from april 1986 was used to compute sea ice motion from pairs of sequential images the resulting ice motion vectors were taken as a representation of the surface flow field derived objectively from the satellite imagery resulting vector motion fields were found to match well with manually tracked vectors for the same images thus verifying the validity of the objective mcc method of computing ice motion these techniques were applied to both the visible and infrared avhrr channels and to images with different spatial resolutions yielding an overall bias accuracy of about 0 5 cm s and standard deviations of about 0 9 cm s the mcc ice motion results were also compared with wind driven numerical model simulations of the region marked differences between the mcc image derived velocities and those from the numerical model were thought to be primarily due to a stronger ocean current than was present in the model

satellite image derived velocity field of an antarctic ice stream the surface velocity of a rapidly moving ice stream has been determined to high accuracy and spatial density with the use of sequential satellite imagery variations of ice velocity are spatially related to surface undulations and transverse velocity variations of up to 30 percent occur such large variations negate the concept of plug flow and call into question earlier mass balance calculations for this and other ice streams where sparse velocity data were used the coregistration of images with the use of the topographic undulations of the ice stream and the measurement of feature displacement with cross correlation of image windows provide significant improvements in the use of satellite imagery for ice flow determination

partitioning effects from ocean and atmosphere on the calving stability of kangerdlugssuaq glacier east greenland we use the 7 km retreat of kangerdlugssuaq glacier kg east greenland to examine the mechanisms interactions and relative significance of atmospheric forcing and ice ocean interactions hydrographic data from 1991 1993 and 2004 show that subtropical waters are common in kangerdlugssuaq fjord kf and that surface waters were warm in 2004 relative to 1991 and 1993 the main water column was nonetheless warmest in 1991 we contend that while flow of subtropical waters into fjords provides a setting in which rapid glacier retreat can occur the triggering of retreat depends on additional environmental factors the climatic variables standing out in our study of kg and kf are air temperature and katabatic winds both had strong positive anomalies during winter 2004 05 when kg retreated we show that proglacial ice melange was absent and that fjord freeze up did not occur until 11 april 2005 due to warm and windy conditions we demonstrate that this setting is unusual and hypothesize that exposure to open water in winter months caused the retreat calculation of ice front melt rates shows that discharge of basal meltwater first from runoff and subsequently from frictional basal heating should intensify the interaction between glacier and fjord

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

a simple raster based model for flood inundation simulation in this paper the development of a new model for simulating flood inundation is outlined the model is designed to operate with high resolution raster digital elevation models which are becoming increasingly available for many lowland floodplain rivers and is based on what we hypothesise to be the simplest possible process representation capable of simulating dynamic flood inundation this consists of a one dimensional kinematic wave approximation for channel flow solved using an explicit finite difference scheme and a two dimensional diffusion wave representation of floodplain flow the model is applied to a 35 km reach of the river meuse in the netherlands using only published data sources and used to simulate a large flood event that occurred in january 1995 this event was chosen as air photo and synthetic aperture radar sar data for flood inundation extent are available to enable rigorous validation of the developed model 100 50 and 25 m resolution models were constructed and compared to two other inundation prediction techniques a planar approximation to the free surface and a relatively coarse resolution two dimensional finite element scheme the model developed in this paper outperforms both the simpler and more complex process representations with the best fit simulation correctly predicting 81 9 of inundated and non inundated areas this compares with 69 5 for the best fit planar surface and 63 8 for the best fit finite element code however when applied solely to the 7 km of river below the upstream gauging station at borgharen the planar model performs almost as well 83 7 correct as the raster model 85 5 correct this is due to the proximity of the gauge which acts as a control point for construction of the planar surface and the fact that here low lying areas of the floodplain are hydraulically connected to the channel importantly though it is impossible to generalise such application rules and thus we cannot specify a priori where the planar approximation will work simulations also indicate that for this event at least dynamic effects are relatively unimportant for prediction of peak inundation lastly consideration of errors in typically available gauging station and inundation extent data shows the raster based model to be close to the current prediction limit for this class of problem q 2000 elsevier science b v all rights reserved

greenland ice sheet surface properties and ice dynamics from ers 1 sar imagery c band synthetic aperture radar sar imagery from the european space agency s ers 1 satellite reveals the basic zonation of the surface of the greenland ice sheet the zones have backscatter signatures related to the structure of the snowpack which varies with the balance of accumulation and melt at various elevations the boundaries of zones can be accurately located with the use of this high resolution imagery the images also reveal a large flow feature in northeast greenland that is similar to ice streams in antarctica and may play a major role in the discharge of ice from the ice sheet

a new ice thickness and bed data set for the greenland ice sheet 2 relationship between dynamics and basal topography new data sets of bed and surface elevation have been combined with balance velocities bed topography and radar reflectivity to investigate the relationship between ice flow and bed conditions it has been found that the bed topography affects the local driving stresses and initiates the onset of streaming flow in specific areas where there are large undulations this onset region only appears significantly inland in three areas the northeast greenland ice stream kangerdlugssuaq gletscher and a region in the southwest associated with abnormally low driving stresses and an apparently unnamed but active glacier bed reflectance values below the northeast ice stream suggest that basal melting could be occurring along its length and it seems likely therefore that the enhanced flow observed inland from the onset of streaming may be due in part to basal sliding

improved 2d shallow water model able to capture the effects of complex bathymetric features through their subgrid modeling abstractin this study an improved two dimensional 2d model is proposed for simulating shallow water flows over complex bathymetry through their subgrid modeling the proposed model delineates the detailed unevenness in the topography of selected 2d elements that are usually ignored in other common 2d hydrodynamic models by specifying the bed elevation at more than one point in an element the relationship between submerged area and water stage and the relationship between water volume and water stage can then be preprocessed for every specified element the process is similar to how cross sections are handled in standard one dimensional models thus the 2d model can simulate the open channel flow accurately and efficiently with only one element been applied over the channel width the proposed model was tested using a hypothetical channel flow with an analytical solution and a real river coast system with measured data the simulations showed that the model could achieve the same level of accuracy us

sediment thicknesses and holocene glacial marine sedimentation rates in three east greenland fjords ca 68 n we compared measured and estimated sediment budgets in heavily glaciated fjords in east greenland mass balance calculations and regional glacio climatic conditions suggest that the sediment flux to the seafloor in kangerdlugssuaq and nansen fjords should be dominated by iceberg rafting and not by the rain out of suspended particulates in meltwater as the glacier calving flux is estimated at 15 and 2 km 3 yr compared to meltwater volumes of 4 4 and 1 7 km 3 yr respectively gravity cores in the three fjords indicate that the uppermost 1 2 5 m of sediment consists of diamictons or fine grained laminated muds ams radiocarbon dates on calcareous foramininfera or shells 16 total indicate sedimentation rates of 110 to 340 cm ka within the fjords over the last 1 ka and 10 20 cm ka during the holecene on the inner and middle shelf annual sediment discharge is around 0 67 times 10 6 tonnes yr within the kangerdlugssuaq fjord and trough system which translates into an average basin wide rate

jakobshavns glacier drainage basin a balance assessment maximum and minimum estimates are made of the drainage basin feeding the jakobshavns glacier by using surface elevation maps derived from seasat altimetry benson s 1962 net balance measurements are used to calculate the balance flow within the basin comparisons of the balance flux at the terminus with estimates of actual flux suggest the basin is in overall equilibrium or slightly thickening this agrees with measurements along the nearby egig traverse balance velocities accelerate rapidly within 100 km of the coast farther upstream balance velocities are consistent with both measured velocities along the egig traverse and calculated deformation velocities it is estimated that jakobshavns glacier discharges between 4 8 and 7 6 of the annual net balance over greenland and drains between 3 7 and 5 8 of the ice sheet area

fast glacier flow ice streams surging and tidewater glaciers fast flowing glaciers are unusual but important jakobshavns glacier in western greenland illustrates this point figure 1 considered to be the world s fastest glacier its maximum observed flow rate measured in midsummer near the floating terminus is 8360 m yr 1 lingle et al 1981 except for a tidal influence near the terminus the flow is believed to be fairly steady bindschadler 1984

fast flowing outlet glaciers on svalbard ice caps four well defined outlet glaciers are present on the 2510 km2 ice cap of vestfonna in nordaustlandet svalbard airborne radio echo sounding and aerial photograph and satellite image analysis methods are used to analyze the morphology and dynamics of the ice cap and its component outlet glaciers the heavily crevassed outlets form linear depressions in the ice cap surface and flow an order of magnitude faster than the ridges of uncrevassed ice between them ice flow on the ridges is accounted for by internal deformation alone whereas rates of outlet glacier flow require basal motion one outlet has recently switched into and out of a faster mode of flow rapid terminal advance a change from longitudinal compression to tension and thinning in the upper basin indicate surge behavior observed outlet glacier discharge is significantly greater than current inputs of mass to the ice cap indicating that present rates of flow cannot be sustained under the contemporary climate

transient two dimensional simulation of real flood events in a mediterranean floodplain the application of a two dimensional 2d finite volume numerical model to real flood events in the ebro river is presented the hydraulic model used is based on the 2d transient shallow water equations on the irregular bed that are able to compute flow advance over a dry bed this study involves the reliable simulation of not only the flood wave advance but also the drying process in a series of events of different magnitude the importance of the correct characterization of the roughness coefficient and the topography is emphasized in the study the former is estimated from a previous classification of structurally homogeneous habitats and the latter is defined by merging the digital terrain model data with a hydraulic river bed elevation reconstruction algorithm the calibration of the full model resulting from the roughness bed river and flow simulation models is based on field measurements of the flooded area for two steady discharges the validation is performed by comparing the numerical results with the water levels measured during five flood events at certain times with the flooded area and time series of continuous point measurements of water depth during different situations throughout the year because the model provides correct predictions of the surface processes both for low and high flow discharges the simulation results are used to analyze the present floodplain hydrodynamics in the same way different topographic scenarios on the basis of changes in the hydraulic river floodplain connectivity are generated to analyze their potentially beneficial effect in the floodplain geomorphic dynamics doi 10 1061 asce hy 1943 7900 0000565 2012 american society of civil engineers ce database subject headings unsteady flow overland flow hydration dewatering flood plains shallow water mediterranean sea simulation author keywords unsteady surface flow wetting drying finite volume shallow water hydrodynamic floodplain hydraulic bed reconstruction

synchronous retreat and acceleration of southeast greenland outlet glaciers 2000 06 ice dynamics and coupling to climate a large portion of the recent increase in the rate of mass loss from the greenland ice sheet is from increased outlet glacier discharge along its southeastern margin while previous investigations of the region s two largest glaciers suggest that acceleration is a dynamic response to thinning and retreat of the calving front it is unknown whether this mechanism can explain regional acceleration and what forcing is responsible for initiating rapid thinning and retreat we examine seasonal and interannual changes in ice front position surface elevation and flow speed for 32 glaciers along the southeastern coast between 2000 and 2006 while substantial seasonality in front position and speed is apparent nearly all the observed glaciers show net retreat thinning and acceleration with speed up corresponding to retreat the ratio of retreat to the along flow stress coupling length is proportional to the relative increase in speed consistent with typical ice flow and sliding laws this affirms that speed up results from loss of resistive stress at the front during retreat which leads to along flow stress transfer large retreats were often preceded by the formation of a flat or reverse sloped surface near the front indicating that subsequent retreats were influenced by the reversed bed slope many retreats began with an increase in thinning rates near the front in the summer of 2003 a year of record high coastal air and sea surface temperatures this anomaly was driven in part by recent warming suggesting that episodes of speed up and retreat may become more common in a warmer climate

monitoring the glacier changes in the muztag ata and konggur mountains east pamirs based on chinese glacier inventory and recent satellite imagery glaciers in the muztag ata and konggur mountains of the eastern pamir plateau northwestern china have been monitored by applying aerial photo stereo models 1962 66 and landsat tm 1990 and etm 1999 images all of which have been compared in order to detect areal and frontal changes through the past four decades the mean frontal retreat of glaciers in the muztag ata and konggur mountains increased from 6 0 m a 1 between 1962 66 and 1990 to 11 2 m a 1 between 1990 and 1999 with an overall glacier length reduction of 9 9 for the whole study period the glacier area has decreased by 7 9 mainly due to changes observed in the most recent period 1990 99 when the annual area loss almost tripled to 1 01 km 2 a 1 based on meteorological data from taxkogan station since 1957 we conclude that climate change particularly the rise in summer temperature after 1994 is the main forcing factor in glacier shrinkage

finite volume model for shallow water equations with improved treatment of source terms a simple yet precise relation between the flux gradient and the bed slope source term is presented which produces a net force within the cell with an inclined water surface but ensures still water condition when there is no flow across the boundaries the proposed method consists of calculating the pressure term based on the water depths at the cell vertices which may be computed by a higher order scheme and the bed slope source term by a centered discretization technique the methodology is demonstrated with a godunov type upwind finite volume formulation the inviscid fluxes are calculated using roe s approximate riemann solver and a second order spatial accuracy is obtained by implementing multidimensional gradient reconstruction and slope limiting techniques the accuracy and applicability of the numerical model is verified with a couple of test problems and a real flow example of tidal water movement in a stretch of river hooghly in india

comparing the performance of a 2 d finite element and a 2 d finite volume model of floodplain inundation using airborne sar imagery the performances of a finite volume model sfv and finite element model telemac 2d in reproducing inundation on a 16 km reach of the river severn united kingdom are compared predicted inundation extents are compared with 4 airborne synthetic aperture radar images of a major flood event in november 2000 and these are used to calibrate 2 values of manning s n for the channel and floodplain the four images are shown to have different capacities to constrain roughness parameters with the image acquired at low flow rate doing better in determining these parameters than the image acquired at approximately peak flow this is assigned to the valley filling nature of the flood and the associated insensitivity of flood extent to changes in water level the level of skill demonstrated by the models when compared with inundation derived using a horizontal water free surface also increases as flow rate drops the two models show markedly different behaviours to the calibration process with telemac showing less sensitivity and lower optimum values for manning s n than sfv when the models are used in predictive mode calibrated against one image and predicting another sfv performs better than telemac copyright 2007 john wiley sons ltd

regional source discrimination of small events based on the use of lg wavetrain nuclear monitoring requires identification of small events observed at regional distances for which lg is generally the largest seismic phase recent research including ours has provided significantly better understanding of the generation of lg from explosions but the new concepts have not yet been fully exploited for improving discrimination between low magnitude explosions and earthquakes in different regions of the world our analysis of spectrograms which display spectral energy versus time shows that lg from explosions alone is generally followed by several distinct arrivals with progressively lower frequency contents probably due to the scattering of explosion generated rg into s at several discrete near source locations this promising new discriminant may offer a distinct advantage over other seismic methods of discrimination since it may not require the region of interest to be calibrated with the help of earlier known type seismic events moreover regional discrimination based on the lg wavetrain can be especially useful when signal to noise considerations for a small event preclude the use of other seismic phases

predicting floodplain inundation raster based modelling versus the finite element approach we compare two approaches to modelling floodplain inundation a raster based approach which uses a relatively simple process representation with channel flows being resolved separately from the floodplain using either a kinematic or diffusive wave approximation and a finite element hydraulic model aiming to solve the full two dimensional shallow water equations a flood event on a short c 4 km reach of the upper river thames in the uk is simulated the models being validated against inundation extent as determined from satellite synthetic aperture radar sar imagery the unconstrained friction parameters are found through a calibration procedure where a measure of fit between predicted and observed shorelines is maximized the raster and finite element models offer similar levels of performance both classifying approximately 84 of the model domain correctly compared with 65 for a simple planar prediction of water surface elevation further discrimination between models is not possible given the errors in the validation data the simple raster based model is shown to have considerable advantages in terms of producing a straightforward calibration process and being robust with respect to channel specification copyright 2001 john wiley sons ltd

the jakobshanvs effect the jakobshavns effect may have been a significant factor in hastening the collapse of palaeo ice sheets with the advent of climatic warming after 18 000 years ago and may precipitate partial collapse of the present day greenland and antarctic ice sheets following co2 induced climatic warming in the decades ahead the jakobshavns effect is observed today on jakobshavns glacier which is located at 69 10 n on the west coast of greenland the jakobshavns effect is a group of positive feedback mechanisms which allow jakobshavns glacier to literally pull ice out of the greenland ice sheet at a rate exceeding 7 km a across a floating terminus 800 m thick and 6 km wide the pulling power results from an imbalance of horizontal hydrostatic forces in ice and water columns at the grounding line of the floating terminus positive feedback mechanisms that sustain the rapid ice discharge rate are ubiquitous surface crevassing high summer rates of surface melting extending creep flow progressive basal uncoupling progressive lateral uncoupling and rapid iceberg calving

increased ablation at the margin of the greenland ice sheet under a greenhouse effect climate increased ablation under a greenhouse effec t climate is calculated by an energy balance model for two sites at the margin of the greenland ice sheet nordbogletscher south greenland and qaman lrssop sermia west greenland the change in summer ablation is nearly linear with change in summer temperature with gradients of 0 43 and 0 57 m water a i deg i for nordbogletscher and qamanarssup sermia respectively however the increase in ablation rate must be less in the higher parts of the ice sheet a future climatic warming will therefore cause a rapid retreat of the ice sheet margin and a steeper ice sheet profile

floodplain friction parameterization in two dimensional river flood models using vegetation heights derived from airborne scanning laser altimetry two dimensional 2 d hydraulic models are currently at the forefront of research into river flood inundation prediction airborne scanning laser altimetry is an important new data source that can provide such models with spatially distributed floodplain topography together with vegetation heights for parameterization of model friction the paper investigates how vegetation height data can be used to realize the currently unexploited potential of 2 d flood models to specify a friction factor at each node of the finite element model mesh the only vegetation attribute required in the estimation of floodplain node friction factors is vegetation height different sets of flow resistance equations are used to model channel sediment short vegetation and tall and intermediate vegetation the scheme was tested in a modelling study of a flood event that occurred on the river severn uk in october 1998 a synthetic aperture radar image acquired during the flood provided an observed flood extent against which to validate the predicted extent the modelled flood extent using variable friction was found to agree with the observed extent almost everywhere within the model domain the variable friction model has the considerable advantage that it makes unnecessary the unphysical fitting of floodplain and channel friction factors required in the traditional approach to model calibration copyright 2003 john wiley sons ltd

mapping tide water glacier dynamics in east greenland using landsat data landsat multispectral scanner and thematic mapper images were co registered for the kangerdlugssuaq fjord region in east greenland and were used to map glacier drainage basin areas changes in the positions of tide water glacier termini and to estimate surface velocities of the larger tide water glaciers statistics were compiled to document distance and area changes to glacier termini the methodologies developed in this study are broadly applicable to the investigation of tide water glaciers in other areas the number of images available for consecutive years and the accuracy with which images are co registered are key factors that influence the degree to which regional glacier dynamics can be characterized using remotely sensed data three domains of glacier state were interpreted net increase in terminus area in the southern part of the study area net loss of terminus area for glaciers in upper kangerdlugssuaq fjord and a slight loss of glacier terminus area northward from ryberg fjord local increases in the concentrations of drifting icebergs in the fjords coincide with the observed extension of glacier termini positions ice surface velocity estimates were derived for several glaciers using automated image cross correlation techniques the velocity determined for kangerdlugssuaq gletscher is approximately 5 0 km a 1 and that for kong christian iv gletscher is 0 9 km a 1 the continuous presence of icebergs and brash ice in front of these glaciers indicates sustained rates of ice front calving

modeling iceberg rafted sedimentation in high latitude fjord environments 1 an iceberg model sedberg has been developed to simulate sedimentation in high latitude glaciated fjords sediments deposited in fjords provide an important record of glaciological response to changing climatic conditions the model simulates the formation drift and melt of a population of icebergs utilizing monte carlo based techniques with a number of underlying parametric probability distributions to describe the stochastic behavior of iceberg formation and dynamics the model captures iceberg dynamics and melt in fjord environments and has been applied to kangerdlugssuaq fjord in east greenland as an example of an iceberg dominated sedimentary environment sedimentation has been simulated over the past 1500 years encompassing the climatic intervals of the medieval warm period mwp and the little ice age lia model results have been compared with the observed sedimentary record the model demonstrates that the glaciological regime e g basal debris thickness mean annual calving rate mean iceberg size plays a more important role than the direct influence of climate ocean and air temperatures on iceberg sedimentation rate although often changes in climate result in changes to the glaciological regime

reflectances of glaciers as calculated using landsat 5 thematic mapper data landsat 5 thematic mapper tm data have been used in previous work in order to locate zones of similar spectral reflectance on glaciers in austria and alaska and to relate these zones to the glacier facies which are indicative of glacier mass balance in this paper landsat 5 digital numbers dns have been used to compute the at satellite planetary reflectances p on spectrally similar zones on the meares and schwanda glaciers in alaska and the grossglockner glacier group in austria the patterns of tm derived reflectances in the ablation areas of the grossglockner glacier group and the meares glacier compare favorably with published reflectance curves measured on the surface of glacier ice though the surface reflectance of snow covered ice is higher than the landsat derived reflectance for the glaciers studied the accuracy of the at satellite planetary reflectances is shown to be affected by topographic and atmospheric effects and by the anisotropic nature of snow reflectance use of reflectance values for analysis of snow and ice facilitates scene to scene comparisons of glaciers

coupled 1d quasi 2d flood inundation model with unstructured grids a simplified numerical model for simulation of floodplain inundation resulting from naturally occurring floods in rivers is presented flow through the river is computed by solving the de saint venant equations with a one dimensional 1d finite volume approach spread of excess flood water spilling overbank from the river onto the floodplains is computed using a storage cell model discretized into an unstructured triangular grid flow exchange between the one dimensional river cells and the adjacent floodplain cells or that between adjoining floodplain cells is represented by diffusive wave approximated equation a common problem related to the stability of such coupled models is discussed and a solution by way of linearization offered the accuracy of the computed flow depths by the proposed model is estimated with respect to those predicted by a two dimensional 2d finite volume model on hypothetical river floodplain domains finally the predicted extent of inundation for a flood event on a stretch of river severn united kingdom by the model is compared to those of two proven two dimensional flow simulation models and with observed imagery of the flood extents

evidence for the asynchronous retreat of large outlet glaciers in southeast greenland at the end of the last glaciation recent rapid changes in the marine terminating sectors of the greenland ice sheet gris have prompted concerns about the future stability of the ice sheet long term records of ice sheet behaviour provide valuable context to assess the magnitude of current change and may help resolve the mechanisms driving deglaciation we report 23 new 10be exposure ages which constrain the deglacial history of two large fjord systems in southeast se greenland we compare our chronologies with existing data from the centre of the sector to examine the timing and style of deglaciation at a regional scale glacial erratic 10be exposure ages demonstrate that kangerdlugssuaq fjord deglaciated at 11 8 ka at the end of the younger dryas yd 12 8 11 6 ka retreat at kangerdlugssuaq fjord coincided with known incursion of the warm irminger current ic onto the continental shelf this is inferred to have initiated retreat comparison with recently published results from sermilik fjord and new 10be ages from bernstorffs fjord indicates deglaciation occurred 1 ka later in the south of the se region sermilik fjord 10 9 ka and bernstorffs fjord 10 4 ka deglaciated later retreat likely occurred in response to dramatic climatic amelioration at the termination of the yd stadial we suggest that the disparate timing of deglaciation across the se region may be primarily explained by the varying influence of the warm ic glaciers in southern se greenland were isolated from warm atlantic waters during the yd by complex shelf bathymetry in all fjord settings ice retreat was rapid and persistent consistent with the absence of geomorphological evidence for stillstand or readvance events ice retreat was accompanied by rapid thinning and likely continued to well within present day ice sheet margins glacial erratic 10be age determinations and geomorphological observations show no evidence for holocene readvance events prior to the little ice age lia

two dimensional flood routing on steep slopes program routweir represents a two dimensional flood routing model designed to analyze two dimensional flow caused by rainfall and runoff flooding events input to the program consists of known geometry topography initial conditions and boundary conditions the geometry and bathymetry of the flood plain are represented by a grid of interconnecting triangular elements initial water levels are prescribed to correspond to the normal water elevations in the river channel boundary conditions are prescribed by a discharge hydrograph at the upstream boundary of the river basin and by the water surface elevations at the ocean boundary the interior water elevations and discharges are computed allowing flooding and drying to take place in the triangular elements of the grid based on a conservation of water volume equation and a surface slope dependent dynamic equation output consists of time histories of watersurface elevations and peak elevations in both tabular and graphical form routweir has been successfully calibrated against recorded flood levels in the rio culebrinas basin in puerto rico and has been used in that basin in a federal flood insurance study a versatile computer program routweir can be applied to many flood routing problems it is particularly suited for wide river basins with large bottom slopes and for normally dry areas subject to extensive flooding

antarctica measuring glacier velocity from satellite images many landsat images of antarctica show distinctive flow and crevasse features in the floating part of ice streams and outlet glaciers immediately below their grounding zones some of the features which move with the glacier or ice stream remain visible over many years and thus allow time lapse measurements of ice velocities measurements taken from landsat images of features on byrd glacier agree well with detailed ground and aerial observations the satellite image technique thus offers a rapid and cost effective method of obtaining average velocities to a first order of accuracy of many ice streams and outlet glaciers near their termini