validating and improving elevation data of a satellite image map of filchner ronne ice shelf antarctica with results from ers 1 a satellite image map with surface elevation contours of filchner ronne ice shelf has been published previously as a topographic map the image map was constructed from a mosaic of 69 landsat multispectral scanner mss images and noaa avhrr data the standard deviation in position in the central part of the mosaic is 125m topographic glaciologic features were taken from landsat scenes and represent the best coastline of this region surface elevations have been calculated from airborne and ground measurements of either ice thickness by assuming hydrostatic equilibrium or barometric pressure accuracies vary from 2 to 7 m oversnow trigonometric levelling in the northeastern part of the ice shelf tied to sea level at the ice front has given accuracies of 1m accuracies reduce to about 20 m in the grounded ice areas ers i radar altimeter data over the ice shelf have been processed to give ellipsoidal heights elevation above the ellipsoid geoidal reductions have been used to convert these to orthometric heights elevation above sea level no tidal corrections have been applied the overall accuracy of the radar altimeter derived elevations is estimated to be better than 5m there are noticeable differences from the topographic map in the central part where the radar data indicate a lower surface however the maps agree to within the stated error figures

modeling the formation and deposition of frazil ice beneath filchner ronne ice shelf large areas of the filchner ronne ice shelf are underlain by layers of marine ice which form when supercooled seawater circulating beneath the ice shelf freezes the freezing process initially produces a suspension of disc shaped frazil ice crystals and these are subs quently deposited onto the ice shelf base in areas where the flow of water is slack enough this has been modeled assuming that the freezing takes place within buoyant plumes of ice shelf water ascending the ice shelf base from source regions near the grounding lines of the major inlet glaciers the deposition of the majority of the suspended frazil ice is found to occur in spatially discrete bursts where peak rates of accumulation at the ice shelf base exceed 1 m yr 1 of solid ice there is a good correlation between the location of the zones of crystal deposition and the position of the upstream limits of the marine ice layers the high rates of localized accumulation account for the rapid buildup observed in the layer thickness which then gradually declines as the marine ice is carried downstream with the flow of the ice shelf model results also suggest an origin for the ice platelets observed at depth in the water column near the filchner ice shelf

ocean circulation beneath filchner ronne ice shelf from three dimensional model results a high resolution three dimensional ocean circulation model is applied to the cavity beneath filchner ronne ice shelf fris the model predicts predominantly barotropic currents which form a series of cyclonic gyres in the deep basins and anticyclonic circulations around the islands the surface circulation can be such that the water moves in the direction of decreasing or increasing ice thicknesses in the former case leading to freezing while melting at the ice shelf base results in the latter case the pattern of melting and freezing is consistent with known distributions of marine ice and melting areas beneath fris an anticyclonic circulation around the korff and henry ice rises with melting west of korff ice rise and freezing on the eastern side and north of henry ice rise is the main source for an ice pumping mechanism that produces the observed large marine ice body in the central filchner ronne ice shelf the estimates for net melting for realistic conditions at the open ocean boundary are 40 50 km 3 yr 1 indicating that ice shelf ocean interaction is an important contribution to the mass balance of the ice shelf

surface deformation and coherence measurements of kilauea volcano hawaii from sir c radar interferometry the shuttle imaging radar c x synthetic aperture radar sir c x sar radar on board the space shuttle endeavor imaged kilauea volcano hawaii in april and october 1994 for the purpose of measuring active surface deformation by the methods of repeat pass differential radar interferometry observations at 24 cm l band and 5 6 cm c band wavelengths were reduced to interferograms showing apparent surface deformation over the 6 month interval and over a succession of 1 day intervals in october a statistically significant local phase signature in the 6 month interferogram is coincident with the pu u o o lava vent interpreted as deformation the signal implies centimeter scale deflation in an area several kilometers wide surrounding the vent peak deflation is roughly 14 cm if the deformation is purely vertical centered southward of the pu u o o caldera delays in the radar signal phase induced by atmospheric refractivity anomalies introduce spurious apparent deformation signatures at the level of 12 cm peak to peak in the radar line of sight direction though the phase observations are suggestive of the wide area deformation measured by global positioning system gps methods the atmospheric effects are large enough to limit the interpretation of the result it is difficult to characterize centimeter scale deformations spatially distributed over tens of kilometers using differential interferometry without supporting simultaneous spatially distributed measurements of refractivity along the radar line of sight studies of the interferometric correlation of images acquired at different times show that l band is far superior to c band in the vegetated areas even when the observations are separated by only 1 day these results imply longer wavelength instruments are more appropriate for studying surfaces by repeat pass observations

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 side scan sonar and high resolution chirp sub bottom profile study of the natural and anthropogenic sedimentary record of lower lough erne northwestern ireland a geophysical survey side scan sonar and high resolution sub bottom profiling combined with established chrono and bio stratigraphic markers are used to reconstruct the evolutionary history of lower lough erne northwestern ireland since the end of the last glacial discrete acoustic units define four prominent sedimentation cycles one late glacial and three holocene within the seismic stratigraphy basin development is predominantly controlled by climate until the mid holocene when the effects of cultural activity are related to pronounced signatures in the seismic record an enhanced reflector marking the termination of the early holocene sedimentation cycle is associated with the elm decline and forest clearance during the neolithic between approximately 5800 cal bp and 5300 cal bp the associated increase in sediment input by infilling minor topographic lows and basins has a smoothing effect on the morphologic expression of the original basin onlapping and truncated reflectors in the penultimate acoustic unit define further modification of lake bed relief by removal of sediment from the system during engineered lowering of the lake levels that began in the 1880s acoustic anomalies identified on the side scan sonar data are linked with cultural activity and are identified as having the potential to facilitate the recent establishment and migration of invasive zebra mussels through the erne system c 2005 elsevier ltd all rights reserved

multidecadal observations of the antarctic ice sheet from restored analog radar records airborne radar sounding can measure conditions within and beneath polar ice sheets in antarctica most digital radar sounding data have been collected in the last 2 decades limiting our ability to understand processes that govern longer term ice sheet behavior here we demonstrate how analog radar data collected over 40 y ago in antarctica can be combined with modern records to quantify multidecadal changes specifically we digitize over 400 000 line kilometers of exploratory antarctic radar data originally recorded on 35 mm optical film between 1971 and 1979 we leverage the increased geometric and radiometric resolution of our digitization process to show how these data can be used to identify and investigate hydrologic geologic and topographic features beneath and within the ice sheet to highlight their scientific potential we compare the digitized data with contemporary radar measurements to reveal that the remnant eastern ice shelf of thwaites glacier in west antarctica had thinned between 10 and 33 between 1978 and 2009 we also release the collection of scanned radargrams in their entirety in a persistent public archive along with updated geolocation data for a subset of the data that reduces the mean positioning error from 5 to 2 5 km together these data represent a unique and renewed extensive multidecadal historical baseline critical for observing and modeling ice sheet change on societally relevant timescales

detection of aquifer system compaction and land subsidence using interferometric synthetic aperture radar antelope valley mojave desert california interferometric synthetic aperture radar insar has great potential to detect and quantify land subsidence caused by aquifer system compaction insar maps with high spatial detail and resolution of range displacement 10 mm in change of land surface elevation were developed for a groundwater basin 103 km2 in antelope valley california using radar data collected from the ers 1 satellite these data allow comprehensive comparison between recent 1993 1995 subsidence patterns and those detected historically 1926 1992 by more traditional methods the changed subsidence patterns are generally compatible with recent shifts in land and water use the insar detected patterns are generally consistent with predictions based on a coupled model of groundwater flow and aquifer system compaction the minor inconsistencies may reflect our imperfect knowledge of the distribution and properties of compressible sediments when used in conjunction with coincident measurements of groundwater levels and other geologic information insar data may be useful for constraining parameter estimates in simulations of aquifer system compaction

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

transgressions rethinking beringian glaciation abstract the purpose of this investigation is to encourage a fresh look at pleistocene beringia heretofore flooding of bering strait has been cited as the only barrier to migration with marine sea transgressions being a sea gate that closed off migration during glacial interstadials and interglaciations however the possibility exists that glacial advances were also barriers with marine ice transgressions being an ice gate that closed off migration during glacial stadials and glacial maxima this possibility proceeds from the marine ice transgression hypothesis mith which states that marine ice sheets form on the broad arctic continental shelf of northern hemisphere continents when sea ice thickens grounds and domes in shallow water and then transgresses landward as continental ice sheets and seaward as floating ice shelves hughes 1987 landward transgression is onto coastal lowlands during pleistocene glaciations a marine ice sheeet extending from spitsbergen to greenland may have transgressed the circumpolar continental landmass at its lowest and narrowest gap central beringia and calved into the pacific ocean four models of beringian glaciation are presented based on the distinction between marine glaciation and highland glaciation central beringia was glaciated only in highlands in the traditional model hopkins et al 1982 was also glaciated by a self sustaining ice shelf floating over the deep ocean basins of the bering sea in the model by grosswald and vozovik 1984 was glaciated by a marine ice sheet that covered highlands the continental shelf and supplied the ice shelf in a model for maximum pleistocene glaciation and was glaciated by a marine ice sheet in the chukchi sea that merged with highland glaciers transgressed the continental shelf of the western bering sea and calved into the southern bering sea along the edge of the continental shelf in a model for the last glaciation field tests are suggested to assess the viability of these four models the first model is already established for highland glaciation in alaska but less established in siberia the last model should be the easiest to evaluate for marine glaciation the last model limits human migration across the beringian land bridge to brief intervals between stadials and interstadials of the last glaciation cycle when both the ice gate and the sea gate were opened to human migration this model can influence the sea change now underway among quaternary scientists studying peopling of the americas based on the archaeological linguistic and ethnic diversity among native american populations

marine electrical resistivity tomography for shipwreck detection in very shallow water a case study from agropoli salerno southern italy abstract a marine electric resistivity survey was carried out over a submerged beach along the agropoli shore salerno italy to detect buried objects of archaeological interest below the sandy seabed we found a shipwreck a military vessel that probably sunk during the salerno landing operations of the allied forces in the second world war resistivity data provide information on the vertical and horizontal extension of the shipwreck which is characterized by very low calculated resistivity values about 2 5 ohm m such values differ significantly from the sand and the bedrock values 5 40 ohm m although the presence of the shipwreck is clearly visible from geoelectric data the joint application of electric magnetic and multibeam bathymetric techniques reduces the ambiguities inherent in each method as shown in the electrical resistivity tomography ert and confirmed by the digital elevation model obtained from the processing of bathymetric data the shipwreck extends more than 30 m in ne sw direction and it is about 13 m wide the global extension of the relic is consistent with the magnetic data that are characterized by a magnetic anomaly with an amplitude of about 1800 nt and similar dimension as inferred from the estimation of source boundaries obtained from the computation of the analytic signal the results of our survey encourage the use of marine geoelectrical methods for the detection of buried archaeological targets particularly in locations where the use of seismic prospecting is not effective e g very shallow water with sandy sea bottoms the integration of different geophysical methods allows to better define the extension depth and thickness of buried objects suggesting that such an approach is the most effective for underwater archaeological investigations

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

horizontal aquifer movement in a theis thiem confined system the skeletal matrix of an aquifer is known to move laterally toward a discharging well the mechanisms by which it moves relative to the well have been only partially studied in the past examining the relation of drawdown to volume strain for an assumed poroelastic solid has been a common approach by way of contrast the present study examines the relation of the velocity of solids aquifer matrix to their hydraulic driving forces the present approach can be considered darcian and allows the displacement field of the aquifer matrix to be calculated directly a new formulation of the darcy gersevanov law of water flowing relative to moving solids is applied to a theis thiem confined aquifer the aquifer is found to start with a maximum velocity when the pump is turned on and then to decelerate as time progresses dimensionless type curves of horizontal movement of the skeletal matrix are calculated the resulting equation of aquifer deformation is checked against 1 results from alternatively using the standard poroelastic stress strain approach and 2 the fundamental storage equation for transient groundwater flow

backscatter responses and resolution considerations in archaeological side scan sonar surveys a control experiment the backscatter responses of submerged archaeological material remain poorly understood to address this a control experiment was conducted in belfast lough during july and august 2001 a selection of material and targets was arranged oil the seabed in varying orientations in an attempt to replicate the situation found oil a range of archaeological sites where material is exposed on the seafloor repeat side scan sonar surveys of the control array were conducted at variable ranges and fish heights to examine the backscatter responses and resolution of three commercially available side scan sonar systems results indicate that the electro acoustic specification of the pulse length and the beam angle of the acoustic sources govern the theoretical resolution of side scan data backscatter data from the control experiment indicate both organic wood and leather and inorganic metals ceramics glass and varying aggregate and ballast grades natural and man made materials can be imaged using side scan sonar and a wide variety of archaeological material types and concentrations may be differentiated by their backscatter responses c 2005 elsevier ltd all rights reserved

a glaciological map of filchner ronne ice shelf antarctica a set of landsat 5 multispectral scanner mss images of filchner ronne ice shelf was commissioned by the institut fur angewandte geodasie and recorded over a short period in early 1986 a mosaic of digitally enhanced images was constructed using all available ground control in due course it is planned to use the data for the production of a series of digital image maps at a scale of 1 1 000 000 meanwhile a line map has been prepared at a scale of 1 2 000 000 to show the principal glaciological features the new mosaic shows much more detail than earlier landsat images and extends coverage to higher latitudes more of the poorly known southern boundary of the ice shelf can be identified but floating ice still extends beyond the limit of coverage extensive ice rumples are revealed many of them undetected in earlier imagery flow bands can be tracked without a break from their ice stream source to the ice front over distances of up to 800 km even minor tributaries and sheet flow from the inland ice sheet between the ice streams yield narrow but identifiable flow bands ice thickness velocity and mass flux data are reviewed in order to underline their dependence on good mapping

the role of scour in shipwreck site formation processes and the preservation of wreck associated scour signatures in the sedimentary record evidence from seabed and sub surface data fully submerged shipwreck sites act as open systems with the exchange of material sediment water organic and inorganic objects and energy wave tidal storm across system boundaries formation processes at wreck sites are driven by some combination of chemical biological and physical processes with physical processes dominant in initial phases of site formation scouring and associated depositional patterns that form in response to hydrodynamic forcing are commonly the dominant physical processes acting at shipwreck sites scour is initiated by the introduction of a shipwreck to the seafloor leading to increases in flow velocity and turbulent intensity around the structure near field and far field scour pits form at wreck sites due to the interaction of horseshoe and lee wake vortices with the mobile substrate the morphology of resultant scour signatures are controlled by the orientation of the wreck structure in relation to the prevailing hydrodynamic regime the morphology and size of the wreck and individual site components the hydrodynamic regime currents waves or combined waves and currents bathymetry and the geology of the site seafloor and sub surface conditions individual objects or artefacts may act as nuclei to promote scour at a local scale under high energy conditions groups of artefacts and or disarticulated structural components emanating from a wreck may compound natural scour processes by rolling or sliding under suitable environmental conditions wreck associated scour features can be preserved in the sedimentary record

postseismic rebound in fault step overs caused by pore fluid flow near field strain induced by large crustal earthquakes results in changes in pore fluid pressure that dissipate with time and produce surface deformation synthetic aperture radar sar interferometry revealed several centimeters of postseismic uplift in pull apart structures and subsidence in a compressive jog along the landers california 1992 earthquake surface rupture with a relaxation time of 270 45 days such a postseismic rebound may be explained by the transition of the poisson s ratio of the deformed volumes of rock from undrained to drained conditions as pore fluid flow allows pore pressure to return to hydrostatic equilibrium

deflation of mount etna monitored by spaceborne radar interferometry ground based measurements of volcano deformation can be used to assess eruptive hazard but require the costly and often hazardous installation and maintenance of an instrument network here we show that spaceborne radar interferometry which has already shown its utility in mapping earthquake related deformation1 can be used to monitor long term volcano deformation two families of synthetic aperture radar images acquired from ascending and descending orbits by the satellite ers 1 and looking at mount etna from opposite sides cover the time period from 17 may 1992 to 24 october 1993 and include the second half of etna s most recent eruption despite artefacts of the interferometric technique we can observe a volcano wide deflation which is an expected consequence of the eruption but which had not previously been appreciated we quantify it using a simple model based on the change of pressure in a sphere located in an elastic half space the modelled deformation increases linearly with time until the end of the eruption our results show that it will be possible to use this technique to detect the inflation of volcanic edifices that usually precedes eruptions

permanent scatterer insar reveals seasonal and long term aquifer system response to groundwater pumping and artificial recharge received 4 may 2007 revised 30 july 2007 accepted 10 october 2007 published 5 february 2008 1 permanent scatterer insar psinsark p rovides an ew high resolution methodology for detecting and precisely measuring long term and seasonal aquifer system response to pumping and recharge in contrast to conventional insar the permanent scatterer methodology utilizes coherent radar phase data from thousands of individual radar reflectors on the ground to develop displacement time series and to produce velocity field maps that depict aquifer system response with a high degree of spatial detail in this study we present the first results of a prototype study in las vegas valley nevada that demonstrate how this methodology can be utilized in heavily pumped groundwater basins to analyze aquifer system response to long term and seasonal pumping we have developed a series of velocity field maps of the valley for the 1992 1996 1996 2000 and 2003 2005 time periods that show that despite rising water levels associated with an artificial recharge program long term residual inelastic aquifer system compaction subsidence is continuing in several parts of the valley in other areas however long term subsidence has been arrested and locally reversed the seasonal elastic responses to alternating pumping and recharge cycles were segregated from the long term trends and analyzed for spatial and temporal patterns the results show oscillations in which the maximum seasonal responses are associated with the late stages of the annual artificial recharge cycles and that similar seasonal subsidence signals are related to summer pumping cycles the differentiation of the seasonal response through the use of time series data further allows the estimation of elastic and inelastic skeletal storage coefficients providing a basis for future work that could characterize the storage properties of an aquifer system with a high degree of spatial resolution

regime of the filchner ronne ice shelves antarctica seismic radio echo twerle balloon and oceanographic data of the filchner ronne ice shelves are analysed a large thin area in the central ronne ice shelf is found to differ from the morphology of the ross and filchner ice shelves this area is partly filled by basal saline ice which can be attributed to regional regelation caused by oceanic circulation

integrated geophysical surveys of the french frigate la surveillante 1797 bantry bay co cork ireland between 1998 and 2000 a series of geophysical surveys were conducted over the site of la surveillante a french frigate wrecked in 1797 in bantry bay co cork ireland the objectives of the surveys were to accurately relocate the wreck site delineate the extent of site map the seafloor and subsurface lithologies in the wreck environs and provide basemaps for more detailed diver investigations the integrated surveys employed a suite of equipment consisting of a digital echo sounder side scan sonar chirp sub bottom profiler and an overhause effect magnetometer integration and interpretation of the geophysical data indicate la surveillante was wrecked on a fine grained substrate in a low energy environment with site distribution limited to an area measuring 50 x 25 m centred on the wreck integration of geophysical and diver survey data with tidal and sediment records indicates site formation is dominated by biological and chemical processes

ice thickness and sea depth derived from reflection seismic measurements on the central part of filchner ronne ice shelf antarctica in january 1986 reflection seismic measurements were made in the central part of filchner ronne ice shelf north of henry and korff ice rises by a german oversnow traverse with the help of a newly developed ice streamer two people were able to obtain seismic records nearly every 5km over a distance of 150km within 3d processing of digitally recorded seismograms yielded profiles of ice thickness and sea depth the ice thickness varies from 400 to 500 m and is in good agreement with the thickness of 465 m at a drill hole the reflection seismic results are comparable with those obtained from aerogeophysical measurements

crustal deformation from 1992 to 1995 at the mid atlantic ridge southwest iceland mapped by satellite radar interferometry satellite radar interferometry observations of the reykjanes peninsula oblique rift in southwest iceland show that the reykjanes central volcano subsided at an average rate of up to 13 millimeters per year from 1992 to 1995 in response to use of its geothermal field interferograms spanning up to 3 12 years also include signatures of plate spreading and indicate that the plate boundary is locked at a depth of about 5 kilometers below that depth the plate movements are accommodated by continuous ductile deformation which is not fully balanced by inflow of magma from depth causing subsidence of the plate boundary of about 6 5 millimeters per year

coupled multiphase flow and poromechanics a computational model of pore pressure effects on fault slip and earthquake triggering the coupling between subsurface flow and geomechanical deformation is critical in the assessment of the environmental impacts of groundwater use underground liquid waste disposal geologic storage of carbon dioxide and exploitation of shale gas reserves in particular seismicity induced by fluid injection and withdrawal has emerged as a central element of the scientific discussion around subsurface technologies that tap into water and energy resources here we present a new computational approach to model coupled multiphase flow and geomechanics of faulted reservoirs we represent faults as surfaces embedded in a three dimensional medium by using zero thickness interface elements to accurately model fault slip under dynamically evolving fluid pressure and fault strength we incorporate the effect of fluid pressures from multiphase flow in the mechanical stability of faults and employ a rigorous formulation of nonlinear multiphase geomechanics that is capable of handling strong capillary effects we develop a numerical simulation tool by coupling a multiphase flow simulator with a mechanics simulator using the unconditionally stable fixed stress scheme for the sequential solution of two way coupling between flow and geomechanics we validate our modeling approach using several synthetic but realistic test cases that illustrate the onset and evolution of earthquakes from fluid injection and withdrawal

atmospheric limitations to repeat track radar interferometry in its recent radar imaging mission the shuttle imaging radar satellite sir c devoted three days to repeat track interferometry we have analyzed the data from a test site in the mojave desert of california although good topography 10 m on 21 m postings was obtained most of the error was caused by turbulent water vapor in the lower atmosphere spatial structure of 6 km and all smaller sizes was observed the rms one way time delay was found to be 0 24 cm essentially identical results were obtained at two wavelengths 24 and 5 7 cm

mapping small elevation changes over large areas differential radar interferometry a technique that uses synthetic aperture radar sar images to measure very small 1 cm or less surface motions with good resolution 10 m over large swaths 50 km is presented along with experimental results the method could be used for accurate measurements of many geophysical phenomena including swelling and buckling in fault zones residual displacements from seismic events and prevolcanic swelling the method is based on sar interferometry where two images are made of a scene by simultaneously flying two physically separated antennas then the phases of corresponding pixels are differenced and altitude formation is deduced from some simple computation and image rectification it is also possible to use one antenna flown twice over the same scene then if the second flight exactly duplicates the track of the first an interesting possibility occurs there would be no phase changes between the images at all unless there was a physical change in the scene such as ground swelling that would alter the distance from some resolution element to the antenna since the phase changes all occur at the short carrier wavelength the basic limitation on sensitivity is only the phase noise in the system when the two imaging passes are made from flight tracks that are separated which is the case with the seasat images used here it is no longer possible to distinguish surface changes from the parallax caused by topography however with some additional computation a third image made at some other baseline may be used to remove the topography and leave only the surface changes this method was applied using seasat data to an imaging site in imperial valley california where motion effects were observed that were ascribed to the expansion of water absorbing clays phase change images of this area are shown along with associated ground truth about the presence of water problems with the technique are explored along with a discussion of future experimental possibilities on upcoming sar missions like earth observing system eos earth resources satellite ers 1 sir c and the venus imaging radar magellan

interbed storage changes and compaction in models of regional groundwater flow water released from permanent compaction of compressible fine grained interbeds within confined aquifers may be a significant source of pumped water permanent or inelastic compaction of the interbeds occurs when head declines from pumping cause the effective stress or grain to grain load to exceed the elastic limits of the interbeds as a result the grains in the interbeds rearrange and excess water is expelled the amount of inelastic compaction generally is proportional to the increase in effective stress and the decrease in head a common approach for the simulation of elastic and inelastic compaction in groundwater flow models is to assume that head changes in the aquifer result in instantaneous storage changes in the compressible interbeds a term is added to the groundwater flow equation to account for the storage changes changes in specific storage may be computed explicitly from the results at the previous time step in the finite difference formulation of the groundwater flow equation a better approach is to implicitly apportion storage changes between elastic and inelastic components within a time step if storage changes cannot be considered to occur instantaneously with change in head in the aquifer another approach is taken equations for horizontal flow in the aquifer are coupled with equations for vertical flow in the compressible interbeds to simulate flow in half a representative doubly draining interbed storage changes and compaction are calculated for the representative half thickness and are extrapolated to the entire thickness of all interbeds within each cell this approach was applied to an existing model of groundwater flow in the central valley of california the simulation demonstrates that solving coupled systems of equations is feasible for a regional flow model

surface displacement of the 17 may 1993 eureka valley california earthquake observed by sar interferometry satellite synthetic aperture radar sar interferometry shows that the magnitude 6 1 eureka valley earthquake of 17 may 1993 produced an elongated subsidence basin oriented north northwest parallel to the trend defined by the aftershock distribution whereas the source mechanism of the earthquake implies a north northeast striking normal fault the 3 millimeter accuracy of the radar observed displacement map over short spatial scales allowed identification of the main surface rupture associated with the event these observations suggest that the rupture began at depth and propagated diagonally upward and southward on a west dipping north northeast fault plane reactivating the largest escarpment in the saline range

ice ocean interaction on ronne ice shelf antarctica detailed glaciological studies have been completed at 28 sites lying on an approximate flow line extending 760 km across ronne ice shelf parameters measured at each location include ice velocity thickness principal strain rates surface elevation temperature and accumulation rate the data have been used in a steady state model to derive the basal mass flux and the temperature profile with depth at each site from the principles of mass and energy conservation these calculations indicate basal melting in excess of 1 m yr 1 over the first 100 km of the flow line downstream of the grounding line where the ice shelf is between 1200 m and 1600 m thick the maximum melt rates in this region occur near the inland margin and exceed 4 m yr 1 melting continues at a lesser rate over the next 200 km before freezing commences freezing then dominates up to the final 100 km before the ice front resulting in the accumulation of a layer of basal sea ice up to 50 m thick this is rapidly removed as melt rates increase to over 6 m yr 1 at the ice front the cumulative effect of this pattern of basal accumulation and ablation is the wastage by melting of 85 of the mass discharged across the grounding line before it reaches the ice front supporting evidence for a layer of saline ice underlying the ice shelf is provided by the strength of basal radar reflections observed during radio echo sounding of ice thickness in the region where mass balance calculations suggest an accretion of basal sea ice reflection coefficients are consistently low ranging from 6 db to 38 db most of these weak reflections are believed to originate from the true base of the ice shelf the additional energy loss being the result of increased attenuation of the radar signal within the saline layer the derived pattern of basal melting and freezing is consistent with a simple model of sub ice shelf oceanic circulation involving a deep thermohaline convection cell dense saline water which is formed over the continental shelf during winter when the sea surface freezes drains into the deepest parts of the sub ice shelf cavity at the inland margin where this water mass comes into contact with the ice shelf its temperature is 1 c above the local pressure freezing point melting of ice results producing a buoyant outflow of cold relatively fresh water along the ice shelf base basal freezing occurs towards the ice front where the ascending water becomes supercooled this circulation has important implications for the production of antarctic bottom water and for the response of the ice shelf to driving stresses through the temperature dependent viscosity of ice

on the derivation of coseismic displacement fields using differential radar interferometry the landers earthquake we present a map of the coseismic displacement field resulting from the landers california june 28 1992 earthquake derived using data acquired from an orbiting high resolution radar system we achieve results more accurate than previous space studies and similar in accuracy to those obtained by conventional field survey techniques data from the ers 1 synthetic aperture radar instrument acquired in april july and august 1992 are used to generate a high resolution wide area map of the displacements the data represent the motion in the direction of the radar line of sight to centimeter level precision of each 30 m resolution element in a 113 km by 90 km image our coseismic displacement contour map gives a lobed pattern consistent with theoretical models of the displacement field from the earthquake fine structure observed as displacement tiling in regions several kilometers from the fault appears to be the result of local surface fracturing comparison of these data with global positioning system and electronic distance measurement survey data yield a correlation of 0 96 thus the radar measurements are a means to extend the point measurements acquired by traditional techniques to an area map format the technique we use is 1 more automatic 2 more precise and 3 better validated than previous similar applications of differential radar interferometry since we require only remotely sensed satellite data with no additional requirements for ancillary information the technique is well suited for global seismic monitoring and analysis

a new process based model for wreck site formation abstract in order for a model of wreck disintegration to have some predictive ability it is advantageous that such a model should be process orientated scale independent i e be applicable to the wreck as a whole and to individual wreck components and or spatially and temporally independent existing models and flowcharts for wreck site formation focus on the products rather than the processes of wreck disintegration the major classes of environmental processes affecting wreck site formation are physical biological and chemical which are each closely linked to the depositional environment here a modified flow chart for wreck evolution is presented in which the major variables influencing wreck site formation are the wreck itself sediment supply and the hydrodynamic environment the rate of wreck disintegration dd dt may be given by the sum of the rates of disintegration due to physical biological and chemical processes gsdp dt db dt dc dt a model is developed where wreck disintegration may be plotted against the relative sedimentation rate ds dt which is a first order control on the forces of degradation the model possesses the advantageous features noted above and acts to illustrate the characteristics of a wreck site and provide a framework in which to begin prediction of the nature of the material preserved although its application to marine wreck is outlined the model is applicable to both terrestrial and marine wreck site formation

numerical simulations of the ross sea tides tidal currents below the floating ross ice shelf are reconstructed by using a numerical tidal model they are predominantly diurnal achieve maximum strength in regions near where the ice shelf runs aground and are significantly enhanced by topographic rossby wave propagation along the ice front a comparison with observations of the vertical motion of the ice shelf surface indicates that the model reproduces the diurnal tidal characteristics within 20 similar agreement for the relatively weak semi diurnal tides was not obtained and this calls attention to possible errors of the open boundary forcing obtained from global ocean tidal simulations and to possible errors in mapping zones of ice shelf grounding air sea contact below the ice shelf is eliminated by the thick ice cover the dominant sub ice shelf circulation may thus be tidally induced a preliminary assessment of sub ice shelf conditions based on the numerical tidal simulations suggests that 1 strong barotropic circulation is driven along the ice front and 2 tidal fronts may form in the sub ice shelf cavity where the water column is thin and where the buoyancy input is weak

numerical models of the filchner ronne ice shelf an assessment of reinterpreted ice thickness distributions recent radio echo soundings of the filchner ronne ice shelf by the german antarctic expedition 1983 1984 suggest that previous ice thickness measurements may have misinterpreted an internal radio echo reflecting horizon as the true ice shelf bottom this and the analysis of total ice thickness from surface altimetry suggests that a previously defined thin ice region comprising approximately 1 5 of the total ice shelf area may be underlain by a thick layer of possibly saline ice one possible way to verify the existence of such a layer is by measurement of its influence on the ice shelf flow regime here we evaluate this influence by conducting finite element simulations of two alternative ice thickness configurations we conclude that flow differences are sufficiently large to allow verification of the possible saline basal ice layer provided that surface strain rate measurements are conducted in certain key areas

the structure of west antarctica from geophysical studies the subglacial topographical and geological configurations of west antarctica and the boundary zone between east and west antarctica are poorly known yet they are crucial to our understanding of the tectonic evolution of the pacific proto atlantic margin of gondwanaland preliminary results are presented of simultaneous airborne radio echo and magnetic sounding of 106 km2 of west antarctica including detailed maps of ice sheet and bedrock surfaces magnetics radio echo and other available geophysical data suggest interpretations of sub glacial geology

preconsolidation stress of aquifer systems in areas of induced land subsidence aquifer systems in the eloy picacho area arizona the houston galveston area texas and the tulare wasco area and santa clara valley california appear to have been overconsolidated by an amount that ranged approximately from 1 6 to 6 2 bars 16 to 63 m of water before man began to withdraw groundwater from them the relation between land subsidence and water level decline in these areas consists of two linear segments in these areas subsidence per unit water level decline was approximately constant until water levels had declined an amount that ranged from 16 to 63 m when water levels declined past these values subsidence per unit water level decline increased to larger constant values although slow drainage from aquitards may have contributed to this response it is interpreted here to be caused primarily by natural overconsolidation of the compacting part of the aquifer system the water level decline at which the ratio of subsidence to unit water level decline changed indicates approximately the amount by which the preconsolidation stress exceeded the overburden stress on the aquifer system that existed before groundwater withdrawals began

optimal sidescan sonar and subbottom profiler surveying of ancient wrecks the fiskardo wreck kefallinia island ionian sea abstract marine geophysical data collected during an underwater natural and cultural heritage assessment survey along the coastal zone of kefallinia island in the ionian sea greece showed among other seafloor features the presence of a roman shipwreck and its amphorae cargo on the seafloor the study and analysis of the collected data demonstrated that i sidescan sonar and chirp sub bottom profiling systems can successfully detect ancient shipwrecks and their amphorae cargo on the seafloor ii the use of objective computer vision techniques in processing sidescan sonar seafloor images is a valuable tool for the separation of potential ancient shipwreck targets from other seafloor features with similar acoustic signatures furthermore a guideline for the data acquisition parameters that should be used to obtain optimal seafloor sonar images to maximize the separation of potential shipwreck targets from other seafloor features is provided the underwater sonar remote sensing techniques may also provide adequate indication regarding the amphorae hull stowage and its vulnerability to human activity in the area the shipwreck is dated between 1st century bc and 1st century ad and is one of the largest found so far in the mediterranean sea for that period it is estimated that it was carrying about 6 000 amphorae the amphorae cargo visible on the seafloor is in very good state of preservation and the shipwreck has the potential to yield a wealth of information about the shipping routes trading amphorae hull stowage and ship construction during the relevant period and is therefore considered to be of significant archaeological importance

land subsidence caused by the east mesa geothermal field california observed using sar interferometry interferometric combination of pairs of synthetic aperture radar sar images acquired by the ers 1 satellite maps the deformation field associated with the activity of the east mesa geothermal plant located in southern california sar interferometry is applied to this flat area without the need of a digital terrain model several combinations are used to ascertain the nature of the phenomenon short term interferograms reveal surface phase changes on agricultural fields similar to what had been observed previously with seasat radar data long term 2 years interferograms allow the study of land subsidence and improve prior knowledge of the displacement field and agree with existing sparse levelling data this example illustrates the power of the interferometric technique for deriving accurate industrial intelligence as well as its potential for legal action in cases involving environmental damages

the role of time lapse bathymetric surveys in assessing morphological change at shipwreck sites abstract data from time lapse single beam and multi beam bathymetric surveys are used to assess the rate and scale of morphological change at shipwreck sites caused by anthropogenic forcing the technique is illustrated by characterizing changes in wreck site morphology over two sites located on the east coast of ireland the drogheda boat site on the river boyne and the arklow bank site in the irish sea results indicate that repeated bathymetric surveys accurately and rapidly capture morphological change with time lapse accretion erosion models indicating possible erosion rates of up to 0 04 m per day and accretion rates of 0 36 m per day at dynamic riverine and marine sites in response to external triggers these data are valuable in understanding site formation processes at fully submerged archaeological sites and in the derivation of high resolution site formation models

crustal deformation measurements using repeat pass jers 1 synthetic aperture radar interferometry near the izu peninsula japan we have examined the precision of interferometric synthetic aperture radar sar measurements of surface deformation of the earth using 24 cm wavelength data acquired by the japanese earth resources satellite 1 jers 1 spacecraft over the izu peninsula japan radar images acquired from 1993 to 1994 were made into 11 independent interferograms apparent water vapor signatures with equivalent path delay up to 16 cm preclude reliable estimates of small deformation from only one interferogram averaging of interferograms improves the measurement such that residuals between precise leveling data and corresponding radar observations are less than 1 cm rms there is a clear correlation between cloud cover extent on a given day and the spectral power of the water vapor signature in an interferogram formed from the corresponding day s sar image also several water vapor features associated with local topography are consistent with accumulation of moisture on the windward side of an on shore flow analysis shows that decorrelation in mixed conifer and deciduous forest is a weak function of the time between observations imposing a roughly constant level of additional decorrelation relative to scatter stable urban areas furthermore in high relief areas correlation is high when the baseline is tens of meters but drops rapidly with increasing baseline length with strict control of the interferometric baseline length adequate correlation in interferograms over very long time periods is possible even in forested high relief regions observed inflation over ito city is consistent with a localized magma source at depth suggesting a different mechanism from the previous episode in 1989

rock debris in an antarctic ice shelf we have discovered a band of stones and coarse sand in the ronne ice shelf antarctica some 60m above the ice shelf s base 40km from its seaward edge and 420km from the point where the ice originally went afloat a study of ice sounding radar data from across the ronne ice shelf has revealed other areas likely to contain debris in significant quantities it appears that basal debris at the margins of ice streams feeding the ice shelf can be buried in the ice shelf by sea water freezing on at the ice shelf base these findings are evidence for a mechanism active in a present day ice sheet shelf system which enables icebergs to transport large volumes of ice rafted debris and which also provides a potential mechanism for the formation of ice rises near ice fronts we anticipate that a seismics study of debris melted from the ice shelf and deposited beneath will provide a valuable control on the history of ice shelf ocean interactions