C31E-0545
Application of Multi-Channel Ground-Penetrating Radar to Determine Thaw Depth and Moisture Content of the Active Layer
In permafrost regions, the thaw depth of the active layer depends on various factors, for instance soil texture, moisture content, albedo, and vegetation cover which may vary over short distances of only a few meters. Ground-penetrating radar (GPR) is a ground-based, non-invasive geophysical method which can be operated at scales from several meters up to a few kilometers. The travel time of the emitted electromagnetic waves through the soil depends on the dielectric properties of the ground which are basically determined by the unfrozen water content. Hence, in permafrost soils, GPR is suitable to distinguish between wet and dry areas as well as between frozen and unfrozen regions. In multi-channel ground-penetrating radar surveys a number of standard GPR antennas are coupled in a row and several radargrams using different antenna separations are measured simultaneously in the profiling mode. Soil dielectric permittivity and reflector depth are estimated for each position of the radargram by numerical inversion using the measured signal travel times of all channels. This allows a fast and non- invasive mapping of the depth of the permafrost table. Additionally, average soil water content of the active layer along the survey line can be inferred using standard petrophysical relationships. We demonstrate the method with measurements from a continuous permafrost site in the Aksai Chin Region, W-Tibetan Plateau. The survey was conducted at the foot of an alluvial fan which was partly covered by vegetation. We discuss the influence of surface properties and soil texture on thaw depth and average soil moisture content of the active layer. The method has the potential to link point measurements of active layer properties, for instance from local soil-atmosphere monitoring stations, to larger scale remote sensing data.
C31E-0546
Marine geophysical evidence for former expansion and flow of the Greenland Ice Sheet across the northeast Greenland continental shelf
Fast-flowing glaciers in NE Greenland drain approximately 300,000 km2 or 20% of the Greenland Ice Sheet to the margin. Swath bathymetry and sub-bottom profiler acoustic data from the continental margin of northeast Greenland (78° N to 80° N) provide a record of the long-term behaviour of the Greenland Ice Sheet in this region. Geophysical data record the presence of subglacial landforms on the continental shelf that are formed in the surface of a soft sediment layer. Mega-scale glacial lineations are found in Westwind Trough that connects the outlet glaciers Nioghalvfjerdsfjorden Gletscher and Zachariae Isstrom to the continental shelf edge. The geomorphological and stratigraphical records show that the Greenland Ice Sheet covered the inner-middle shelf during the most recent ice advance of the Late Weichselian glaciation, and that ice flow through Westwind Trough was in the form of a grounded, fast-flowing ice stream. Glacimarine sediment gravity flow deposits on the continental slope imply that the ice sheet extended beyond the middle continental shelf, and supplied subglacial sediment direct to the shelf edge with subsequent remobilisation downslope. Collectively the geophysical data record for the first time that ice streams were an important glacio-dynamic feature that drained interior basins of the Late Weichselian Greenland Ice Sheet across the NE Greenland continental margin, and that the ice sheet was far more extensive in this region during the last glacial maximum than the previous terrestrial-glacial reconstructions showed.
C31E-0547
Distribution and Geometry of Glacial (Bathymetric) Troughs on the West Antarctic Continental Shelf – An Indication of Changes in Ice Flow?
The availability of high-resolution multibeam bathymetry from the high-latitude continental margins provides an increasingly detailed picture of glacial related morphology of the continental shelves and slopes. This includes the discovery of deep glacial troughs on the shelf. High-resolution details of these troughs show a variety of morphological features such as mega-scale glacial lineation, which indicate that these troughs were formed by ice streams during past glaciations and that provide insights on ice flow directions and mechanisms. Information on present ice flow in Antarctica can be derived through remote sensing data and accumulation models that result into balance ice flow velocity models. In addition, satellite images and improved elevation models of Antarctica provide outlines of ice drainage areas. Here we analyze the relationship of present ice flow derived from remote sensing data and the location of glacial troughs identified in bathymetry data along the West Antarctic continental margin. The bathymetric data from the Amundsen Sea continental shelf are a compilation of data collected during several cruises aboard the Palmer (available trough the Antarctic and Southern ocean Data Synthesis) and cruises from BAS and AWI. This compilation revealed two major trough systems that dominate the continental shelf. One trough emerges from the Pine Island, Thwaites and Smith Glaciers, and the other from the eastern Getz and Dotson ice shelves. Both are similar in size and depth, and show clear indications of formation or at least modification by grounded ice streams. The trough morphologies suggest similar ice burdens and movements. However, the greater Pine Island Bay Trough now leads to large ice drainage basins that together accommodate about a third of the West Antarctic Ice Sheet outflow, while the Getz-Dotson-Trough is only linked to much smaller glaciers. If ice streams of similar magnitude were necessary to form these troughs, their similar features would indicate a different drainage pattern in the past, with larger ice streams then flowing through the Getz-Dotsen Trough. Such ice streams would have drained a much larger portion of the WAIS than today, denoting shifts in drainage patterns during or between glaciations. Analyzing the characteristics of troughs on the continental shelf and their connections to present and modeled past ice flow could be an important tool for verifying and calibrating reconstructions of long-term ice sheet behavior.
C31E-0548
Monitoring of Surface Wetness from active microwave satellite data in permafrost regions
Soil moisture content impacts land surface energy dynamics, regional runoff dynamics and vegetation
productivity. Coarse to medium resolution data from active microwave instruments onboard satellites which
are currently in space are able to provide such valuable information for operational use. Scatterometer (ERS,
Metop ASCAT) can be applied on regional to global scale. ScanSAR systems are suitable for regional to
continental monitoring and for the investigation of scaling issues. The original approach
which was developed for scatterometer data (Wagner et al. 1999) has been transferred to ScanSAR data
within the framework of the ESA Tiger innovator project SHARE (www.ipf.tuwien.ac.at/radar/share). Data from
the ENVISAT ASAR instrument operating in Global Mode (1km resolution) have not only been used over the
southern African subcontinent, but also over entire Australia and within other regional studies. Current
research focuses on the validation and investigation of scaling issues of satellite derived surface wetness in
permafrost environment. A comparison to soil moisture measurements has been carried out over the Lena-
Delta, Russia. Measurements are from a site on Samoylov Island, which is characterized by polygonal tundra.
Best aggreement of the 1km resolution satellit data was found for polygon centres, with a Pearson
correlation of 0.72. Timeseries analyses from this and other sites in Siberia will be presented.
http://www.ipf.tuwien.ac.at/radar
C31E-0549
Benefits of satellite measurements in the Arctic region: A novel approach opens a window into crustal architecture.
For a global tectonic study in poorly explored areas there is a clear advantage in using the worldwide coverage of satellite data. The most important item that is addressed here is the investigation of the crustal architecture in terms of plate boundaries, faults, seamounts, ridges and other tectonic elements. The satellite-measured seafloor topography and gravity data can be used, particularly when combined with information from seismic and seismology to investigate the crustal architecture. The derived spatial distribution of elastic thickness (Te) indicates significant structural units within the crust as a function of their isostatic response. Te of the Earth's crust can be estimated using a novel approach called "ASEP". This method overcomes drawbacks of spectral methods and allows the calculation of flexural rigidity and Te with a higher spatial resolution. In areas with limited access to acquire seismic data, exploration can benefit from the use of satellite measured data. Low costs and low environmental impact are also obvious advantages. The Greater Barents Sea in the Arctic region will be used as a case example. We used the Arctic Gravity Project data compilation (International Association of Geodesy) that consists of free-air anomalies offshore and Bouguer anomalies onshore. Also satellite measured topography (GEBCO) was used. To constrain our analysis we make use of a 3D density model based on the Barents50 model, which provides information about the crustal configuration, e.g. the Moho and the loading in the crust including all internal density variations. This approach reveals a signature within the crust and lithosphere that reflects the long and complex tectonic history of the Barents Sea. Integrated 3D density modelling and equivalent elastic thickness calculation with the ASEP method allow us to identify regions with different petrophysical properties, which may reflect Caledonian sutures, rift zones and other areas of crustal deformation. The Te distribution indicates a weak crust in the Western Barents Sea, which correlates with suggested rift basins, while the Eastern Barents Sea is characterized by a rigid crust typifying a stable continental platform. The regional structures and/or lineaments proposed by the Tee distribution in the Barents Sea require further interpretation before their nature can be verified. Linear features within the Barents and Kara Seas are observed parallel to the Khatanga -Yenisey shear zone. However, an older origin appears likely for these structures. We plan to extend the tectonic studies to the entire circum-Arctic region. Satellite measured topography and potential field data will form important constraints on the crustal architecture, which in turn is a fundamental aspect in plate reconstructions. In the future, the use of new and improved satellite-measured data will prove to be of value to hydrocarbon exploration.
C31E-0550
Field Investigations of Ku-band Radar Penetration Into Snow Cover on Antarctic Sea Ice
We investigated the penetration of Ku-band radar into snow cover over Antarctic sea ice. Satellite radar altimetry is used to calculate sea ice thickness in the Arctic where it is assumed that the radar reflection originates at the snow/ice interface, due to the cold, dry snow conditions. However, the more complicated snow stratigraphy and frequent flooding of Antarctic snow may mean that this assumption is not valid. The data for this investigation were obtained in sea ice off East Antarctica in September and October 2007 with a radar deployed from an icebreaker. Radar data were collected with field measurements of snow depth, density, wetness and stratigraphy in order to examine the effect of the physical conditions of the snow on the radar return echo. Data were taken over a range of locations and the snow conditions included icy layers, flooding and hard crusts. Analysis of data from detailed snow pit studies showed that the snow/ice interface was the dominant scattering surface of the radar under conditions of low density snow. Data taken along a transect showed that the mean depth of the dominant scattering surface observed in radar data was less than the mean measured snow depth. In the literature Antarctic sea ice elevations calculated with ERS 2 satellite altimeter data were higher than in-situ freeboard measurements, in accordance with our results.
C31E-0551
Compare and Contrast Performance Anomalies in the Boreal Forests and Arctic Tundra of Alaska
Performance anomalies indicate areas that perform above or below a climatically adjusted norm. Anomalous areas may result from policy, management, fire, disease, ecosystem change, or other factors that influence ecosystem performance. The driving forces behind performance anomalies in the arctic tundra of the North Slope are expected to be more directly influenced by increasing temperature, whereas performance anomalies in the boreal forests of the Yukon River Basin are expected to have a stronger fire component. The growing season integral of the normalized difference vegetation index (gNDVI) derived from MODIS or AVHRR serves as a proxy for ecosystem performance. Regression tree models estimate ecosystem performance as a function of weather for multiple years (capturing climate variability) and site potential (nonvarying characteristics of the land) for the boreal forest in the Yukon River Basin and grass-shrubs in the North Slope. The regression tree models are trained with a random sample of the pixels where gNDVI is the response variable. Performance anomalies are defined as pixels where the difference between the actual gNDVI and the estimated ecosystem performance (estimated gNDVI) lies outside of the 90-percent confidence interval. We investigate the model parameters and the spatial patterns of the residuals to gain insight into how the driving forces for the anomalies differ between the two regions. Performance anomaly mapping of boreal forests in the Yukon River Basin align well with Landsat-delineated fire perimeters and a field-based composite burn index (CBI). The North Slope has been experiencing significant climate change impacts causing shrub expansion. These overperforming, anomalous areas indicate ecosystems that may be in transition from grasses, sedges, and mosses to shrubs. Performance anomaly measures can be used to separate climatic variability from non-climatic variability by identifying areas that are above or below a climatically adjusted norm. Applying this approach to a time series of gNDVI data allows these variations from the norm to be tracked through time. With the model results, we can quantitatively compare the driving forces that cause the anomalies.
C31E-0552
Monitoring of Surface Temperatures with Thermal Camera Systems at a High-Arctic Permafrost Site on Svalbard, Norway
Surface temperature is a crucial parameter in proposed schemes that are aimed at assessing the thermal
state of permafrost by remote sensing. However, the spatial resolution of satellite-based surface temperature
measurements is usually not sufficient to capture the variations that occur in highly structured terrain typical
of permafrost regions. Moreover, in arctic regions, cloud cover is likely to preclude measurements for
prolonged periods that can result in a biased surface temperature record. To further explore these problems
and develop suitable correction algorithms, ground-based surface temperature studies with adequate spatial
and temporal resolution are required.
We present a continuous surface temperature record from a high-arctic continuous permafrost site on
Svalbard, Norway, obtained with two thermal camera systems, each mounted on a 10m mast. Both systems
featured a sensor size of 384 x 288 pixels, allowing for spatial resolutions ranging from several cm2 per
pixel to several m2 per pixel. The first thermal camera system covered a single scene that included
different expositions, surface covers and soil water contents with a temporal resolution of 10min. The second
system was mounted on a rotating head that captured 15 different images every hour. The total area
monitored with this system was approximately 300 x 100 m2 .
The study was performed from mid-July to September 2008, thus covering a large part of the snow-free
season. The study area is characterized by hilly tundra with sparse vegetation, alternating with exposed soil
and rock fields. The volumetric soil water content spatially varied from approximately 10% to more than
50%.
The data set is discussed with respect to the following issues:
1. Do systematic differences in average surface temperature exist between regions with different soil water
contents, surface covers and expositions?
2. What is the minimum monitoring frequency to correctly determine average surface temperatures for
different time periods?
3. Is it possible to determine a correct average surface temperature if only measurements from periods with
little or no cloud cover are considered?
C31E-0553
Identification of Surface Signatures Indicative of Near-Surface Permafrost in the Alaska Highway Corridor
Vegetation, airborne electromagnetic resistivity, and topography can each be indicators of the presence or absence of near-surface permafrost in discontinuous permafrost zones of interior Alaska. The objective of this study is to identify specific remotely sensed signatures indicative of near-surface permafrost, and use these in combination to map permafrost in the study area. To verify the presence of near-surface permafrost in areas of different vegetative, topographic, geologic and electromagnetic resistivity characteristics, we used a handheld soil auger to sample the subsurface to a depth of 160 cm in mid- to late August 2008 when seasonal thaw was essentially complete. Our targeted areas were selected based on land classification analyses, surficial geologic mapping, and airborne geophysical surveys. Field observations allow us to choose the parameters used for further image processing and data integration to predict the presence of near-surface permafrost. We observed that on tussock land with widely scattered, short, stunted black spruce (height: < 3 m; diameter: 0.03 – 0.05 m), the active layer can be as shallow as 27 cm from the top of the moss layer with permafrost present just below the living moss. In closely spaced, medium-size black spruce (height: 3-5 m; diameter: 0.03-0.07 m), the active layer can be as shallow as 70 cm from the top of the moss layer with permafrost present just below the active layer. In patches of moderately dense, tall black spruce and white spruce (height: 5-10 m; diameter: 0.07-0.2 m), the active layer is generally deeper than 160 cm. Permafrost is either deeper than this or absent. In the study area, bedrock generally shows high resistivity values, in the range of 1000-59000 Ωm. Field investigations of highly resistive, non-bedrock areas (e.g. glacial moraine and outwash deposits) revealed that high resistivity values (3000-7000 Ωm) in these areas are mostly due to a combined response of cobble, boulder and ground ice. Highly resistive values (2500-3000 Ωm) in peat deposits are due to the presence of significant ground ice. Where ground ice is absent, airborne resistivity values are relatively lower. Thus, resistivity data acts as a complementary data set along with other surface indicators and is very effective in mapping ground ice but fails to detect permafrost in the absence of ground ice.
C31E-0554
Cryofacial Analysis of Permafrost Soils
Cryogenic structure of soils, specifically the patterns formed by ice inclusions and massive ice in permafrost, depends on the genesis of soils and the way they are transformed into a perennially frozen state. Katasonov (1963) recognized that the analysis of relationship between the patterns of cryogenic structure and the processes of permafrost formation (he termed 'cryofacial analysis') is a powerful tool for understanding of genesis of permafrost in relation to different sediment types. He applied cryofacial analysis to Late Pleistocene syngenetic permafrost (yedoma) and to permafrost formed during freezing of thaw bulbs under drained lakes in the continuous permafrost zone. Our long-term studies of cryogenic structure in Alaska and Russia found that cryofacial analysis can be applied to all types of permafrost soil. We described the evolution of cryogenic structure associated with alluvial chronosequences on arctic floodplains in Russia and Alaska and found the differing cryofacies are highly related to patterns of ecosystem development. Cryogenic structure of glacial-lacustrine deposits in several parts of Alaska is similar to cryogenic structure of these deposits in differing permafrost areas in Russia. Cryofacial analysis is extremely useful in recognition of later modifications of permafrost when compared soils are identical in composition. For example, we differentiated original syngenetic permafrost from permafrost modified by thermokarst and thermal erosion in the CRREL permafrost tunnel at Fox, Alaska on the basis of differences in cryogenic structure. We identified unique cryogenic structures associated with the transient zone of the upper permafrost and with the formation of thermokarst-cave ice. Cryofacial analysis showed that parts of permafrost which were previously thawed after fire can be easily distinguished from parts unaffected by thawing. Cryofacial analysis helped in recognizing areas in central and northern Alaska unaffected by the last glaciation. Finally, the study of basal ice under contemporary glaciers makes possible detection of buried glacial ice along the margins of the Arctic Ocean.
C31E-0555
Simulation and Classification of Arctic Sea Ice Data for Change Detection and Kinematic Analysis (SAR, ICESat-1/2)
To correctly assess mass loss of the Arctic sea ice, two components need to be measured and modeled: (1) freeboard, and (2) spatial distribution of ice thickness. Complex morphogenetic and kinematic processes lead to a rough surface that is intersected by leads. The first part of our analysis is the simulation of sea-ice surfaces, combining (1) surface elevation and roughness from GLAS data analysis and from field and aerial snow-layer thickness and spatial roughness, and (2) spatial distribution of leads from upward-looking sonar data and from RADARSAT SAR data. The surface simulation uses fractal dimension, anisotropy direction and factor. The capability of a multi-beam lidar system as proposed for ICESat-2 to accurately capture sea-ice roughness and lead distribution and hence to improve mass change estimates is then investigated. In addition to their role in the simulation, the spatial characteristics of leads in time series of SAR data facilitates classification of kinematic states of sea-ice provinces, which is important to understand the movement of sea ice.
C31E-0556
Conditional Simulation of Ice Surfaces With Natural Roughness as an Aid in Establishing Measurement Requirements for a Multi-Beam System for ICESat-2
Observation of the mass loss of the Greenland and Antarctic Ice Sheets is a primary goal of the "Decadal Survey". For a better understanding of the processes leading to current ice loss, we need to be able to observe non-linear slope and change in slope from a single observation, and to derive accurate high-resolution DEMs suitable for elevation change monitoring and geophysical modeling and prediction. A multi-beam lidar system has been proposed as an additional or primary channel for ICESat- 2, to be launched in 2014. To assess the potential of a multi-beam channel to measure high-resolution topography, we need information on subscale roughness (ice surface roughness at a resolution higher than that of observations with the Geoscience Laser Altimeter System (GLAS) aboard ICESat-1, launched in January 2003). In this talk, we describe a mathematical approach to simulate glacier, ice stream and ice sheet surfaces that (1) are constrained by GLAS elevations at the kilometer scale, (2) have scale-dependent roughness derived from observations and (3) fractal dimension and anisotropy at each scale. We utilize Glacier Roughness Sensor (GRS) data collected in the Greenland Inland Ice, UAV laser profilometer observations and cloud simulations. Results on accuracy of elevation and slope determination are derived for two possible MB channels for ICESat-2.
C31E-0557
Interaction Between Ocean Waves and sea ice Observed With ICESat
The Ice, Cloud, and land Elevation Satellite (ICESat) has provided high-precision measurements of land and sea ice elevation since 2003. ICESat elevation profiles collected at the sea ice edge around Antarctica reveal the attenuation of ocean swells moving into the ice-covered area as well as the penetration of long- period waves (periods of several minutes) hundreds of kilometers into the ice pack. Possible sources for the long-period waves include infra-gravity waves and meteotsunamis (rissaga). Using the ICESat elevation data, attenuation coefficients for both types of wave were calculated and found to be on the order of, but lower than, coefficients previously obtained from aircraft laser altimetry, shipboard measurements, and autonomous submersibles. Differences in the attenuation coefficients are attributed to geometric effects (the angle of the satellite track relative to wave propagation direction) and the properties of the sea ice cover.
C31E-0558
Delineating Water Tracks in Headwater Drainage Basins of the Alaskan Arctic
The Imnavait and Upper Kuparuk Basins in the Alaskan Arctic are underlain by continuous permafrost in the northern foothills of the Brooks Range. One of the dominant landscape features are water tracks, which comprise the majority of the immature surficial drainage network as saturated linear-curvilinear features running roughly perpendicular to the slope. They effectively transport precipitation rapidly through a mantled organic layer, as flow is confined by the permafrost table. Mapping the physical characteristics and extent of water tracks may allow characterization of how the landscape could change over time with variations in local, regional and global climate. Water tracks appear susceptible to thermokarst development, which has been documented in the adjacent Toolik River and the Noatak region of the central Brooks Range. Remote sensing is used to assess the spatial distribution of soil and vegetation, especially within water tracks to begin determining their impacts on ground heat flux. Analysis included examination of images acquired in the optical, thermal and microwave regions to establish which parts of the spectrum were most effective for quantifying specific properties of the water tracks. Fieldwork carried out in the summer of 2008 involved differential GPS measurement to establish a network of ground-verified points to precisely locate specific vegetation and soil types in the water tracks; and field spectra collection to characterize the vegetation and soils that could further guide the remote sensing data processing
C31E-0559
Dynamics and development of the last North Sea ice sheet
The last decade there has been an increasing attention on the dynamics and history of the marine based parts of the large Pleistocene ice sheets. This interest has grown both from the potential influence the stability of these features could have on ocean circulation through rapid meltwater delivery and from the understanding of the critical role these parts have in terms of the dynamics of the large ice sheets. During the last glacial stage the northern North Sea has experienced a number of glacial advances of ice from UK and Fennoscandia. Acoustic data and core data from two contrasting areas are presented. The Norwegian Channel represents the highly dynamic ice stream system draining large parts of the southern Fennoscandian ice sheet. The adjacent Witch Ground basin shows in contrast evidence of smaller scale tidewater glaciers active in a shallow environment, which constituted the eastern limit of the north-eastern British Ice sheet during the deglaciation. Seabed imagery (Olex data) reveals fresh glacial morphology inside (west of) the interpreted ice limits, while the seabed outside (east of) the interpreted ice limits shows very few features, due to a thick cover of glacimarine sediments. The seabed imprint of these systems as well as geometry, genesis and chronology of the sediments from this region will be discussed and their implications for our understanding of the glacial development of the region will be explored.
C31E-0560
Factors Associated With Recent Ice-Marginal Glacier Dammed Lake Loss, Persistence, and Emergence Across Alaska
Ice-marginal glacier-dammed lakes (GDLs), prone to repeated catastrophic sudden drainages, and amenable to remote monitoring, pose unique hazards to human habitation downstream. Both GDLs and flood potential can be evaluated with satellite imagery and GIS tools. Using a baseline map and ASTER imagery, I determined impoundment longevity (absent, persisting, new) of nearly 700 Alaska/adjacent Canada GDL basins. I present here characterizations of these groups of basins and their 214 damming glaciers. Over 50% of historic GDLs, mapped by USGS in 1971, persisted. Of particular importance to proposed/existing infrastructure downstream, 34% of GDLs showing on recent satellite imagery were new since 1971; 44% of the glaciers damming these new GDLs did not previously dam GDLs. For absent GDLs, 70% of ice dam loss was related to glacier thinning; 27% was related to terminus retreat. Numbers of lakes and form of dam loss differed by damming glacier complexity and terminus type. Persisting lakes differed significantly (p=.005) from absent lakes in their: distance up the damming glacier in percent of its total length and in horizontal distance from terminus; and vertical distance below the mean glacier altitude. The predominant aspect of now-absent historic ice dams appeared to have strong oro-topographic origins. Emerging lake ice dam aspects, and the persistence of ice dams, by contrast, appear driven more by climate in that they predominantly face aspects of minimal solar input. Newly forming GDLs were significantly higher and 20% further up the length of damming glaciers than the now-absent historic lakes were, and 95% of all GDLs had glacier surface gradients of 6° or less below the GDL. This is of interest as GDL releases can flush waters stored within the glacier system, creating a larger than expected flood peak and/or duration, and gradients of 6° or less have been found to promote water storage within a glacier system. This work corroborates findings of dramatic Alaska glacier thinning, and findings of higher GDL emergence elsewhere. It highlights the dynamic hazards posed by these lakes and their recurring floods.
C31E-0561
Assessing Seasonal Lake Dynamics in Arctic Alaska: Preliminary Results
Lakes on the coastal plain of arctic Alaska have developed atop continuous permafrost. Recent research suggests that lake levels, rates of bank erosion and drainage, and depth of the thaw bulb in sediments beneath the lake may increase in response to a warmer and wetter climate. Assessment of lake dynamics entails separating seasonal and interannual fluctuations from the long-term response. A program to study lake dynamics was initiated in 2008 and includes: (1) analysis of both long-term lake changes and seasonal/ interannual fluctuations using high-resolution satellite imagery and aerial photographs, (2) repeated high- resolution mapping of shoreline configuration in spring and late summer using differential GPS combined with water level sensors, (3) conducting bathymetric surveys to determine basin shape and water volume, (4) evaluating the relation between wind vectors and surface water currents with real-time satellite networked GPS-enabled floats and a wide-area wireless network, and (5) quantifying the energy and water balance on a representative lake using data collected from a fully instrumented buoy. Lake basins surveyed near Barrow, Alaska have a maximum depth of 1.5-3.0 m and are characterized by a steep drop-off near the shore and very gradual deepening toward the center. Seasonal shoreline fluctuations are observed in most lakes, with the maximum effect noted in low-lying regions of the lake margin as the water level gradually falls through summer. Preliminary analysis of the lake energy and water balance is presented, including measurements of incoming and outgoing radiation, latent and sensible heat flux, and associated lake temperature and atmospheric parameters. In subsequent years, measurements will be made on lakes further inland where the surficial geology and climate differs from the coastal environment.
C31E-0562
A geomorphological overview of glacial landforms on the Icelandic continental shelf
With the increasing availability of bathymetric data, it becomes possible to produce accurate maps of the submarine morphology. However, geomorphological maps of formerly glaciated shelves, although essential to fully understand ice sheet palaeo-geography and behaviour, are still a rarity. In this poster we present glacial features mapped on a high resolution (5 m) bathymetric database that covers 80% of the Icelandic shelf. Through edges, bulging trough mouths, moraines, eskers, melt water channels, streamlined bedrock and streamlined drift, mostly hitherto unmapped, distributed all around the island have been identified. Overall, the pattern of landforms is remarkably radial, indicating that the maximum state ice sheet had its main ice divide in the centre of Iceland, although a subsidiary divide at the NW (Reykjanes Peninsula) is required to explain the orientation of trough incisions here. Most troughs extend to the shelf edge where they end with a bulging mouth. Numerous moraines have been identified within the troughs, but some others, along with eskers and melt water channels, were recognized on the shelf outside the troughs. This suggests that the entire shelf was ice covered, which leads to the conclusion that the troughs were cut by ice streams rather than piedmont style outlet glaciers. In contrast to other glaciated continental margins surrounding Antarctica and Fennoscandia there is a surprising rarity of streamlined bedforms. We wonder if the absence is that they did not form due to inappropriate bed conditions or nature of ice bed coupling, or whether they have been buried and blanketed by marine sediments. The age of ice margins recorded by the mapped moraines is largely unknown, especially on the eastern and southern shelves. We hope that our map will help researchers to conduct targeted seismic and core investigations such that the timing of retreat can be ascertained.
C31E-0563
High-Resolution Bathymetry of Disko Bay and Ilulissat Icefjord, West- Greenland
About 10% of the annual production of Greenland calf ice passes Disko Bay in the northern part of West- Greenland. The amount of over 35 km3 of ice annually which is more than any other glacier outside Antarctica produces, floats with a speed of more than 1 m per hour into Disko Bay through Ilulissat Icefjord, a 60 km long and 3-6 km wide tide-water ice-stream. This highly dynamic system with the large calving production and the high velocity implies a rapid response to climate changes and is thus a key area for the understanding of West Greenland Holocene climate history. The seafloor in the icefjord and off its mouth is extensively shaped by the movement of the icebergs and characterized by abundant plow marks. Large icebergs accumulate over a sill off the fjord mouth where they reside several months until they are finally released through the combined effect of tides and streams, melting, and melt-water lubrication. All these processes shape the morphology of the seafloor and create characteristic submarine landforms. Revealing the morphology helps to understand these processes. High-resolution bathymetric maps display the relief and morphology of the seafloor, however multibeam bathymetry surveys are difficult to perform in front of moving icebergs. As recently as 2007 a first high-resolution multibeam survey was carried out with RV Maria S. Merian to map a large area of Disko Bay off the mouth of Ilulissat Icefjord. In summer 2008 the survey was extended into the fjord using a small local vessel equipped with a temporarily installed portable Seabeam 1180 multibeam system. Both datasets merged together well display the morphology of the area mostly affected by the activity of the floating ice and the movements of icebergs.
C31E-0564
A Radial Pattern of Six Paleo Ice Streams Emanating from the Bruce Plateau Ice Dome, Antarctic Peninsula Ice Sheet: Constraints from Multibeam Bathymetry and GPS Rebound
We reconstructed ice thicknesses along six paleo ice streams emanating out of the Bruce Plateau in the Northern Antarctic Peninsula. This was done in order to generate models of potential isostatic rebound along the flow paths since the LGM and thereby provide a theoretical test for empirical observations of vertical displacement (rebound) as measured by seven coastal GPS stations (to be deployed during the current IPY- LARISSA project). This study is pertinent to realizing the effect of moderate ice sheet size during collapse and resulting sea level rise. The Palmer, Vernadsky, Hugo Island and Gerlache and Boyd Strait ice stream paths (flow lines) were highlighted on the Western side of the Peninsula. The Drygalski, Crane and Hektoria ice streams were studied on the Eastern side. Using detailed and near complete swath bathymetry data available for the Western Peninsula coastal region and partial swath mapping data generated at the site of the former Larsen B ice shelf (and Roberston Trough), we constructed hypothetical longitudinal profiles of all six ice streams along precisely located flow paths. These profiles extended from the accumulation zones in the upper elevations of the Bruce Plateau to the terminus along the continental shelf edge. The profiles included detailed elevations of the bedrock and hypothetical ice thickness values along the ice streams as they would have been during the Last Glacial Maximum (~ 16 ka). Ice thickness values were based on the elevations of bedrock, trim lines, surrounding topography, influence of surrounding glaciers and previous estimates of LGM ice thickness values around the Antarctic Peninsula. Using the components of the hypothetical longitudinal profiles, total isostatic rebound since the LGM can be calculated for the region (assuming reasonable mantle viscosities). In all the profiles reconstructed ice thicknesses are characterized by an order of magnitude increase across inner shelf troughs (such as the Palmer Deep and Larsen B embayment), that is from several hundred meters across the shelves and elevated accumulation regions, to over 2000 meters in the deeps. Since swath bathymetry indicates glacial scouring within the deeps the reconstruction must imply significant contrasts in regional rebound following deglaciation (the scales of distance are appropriate to resolution via crustal rebound, in particular for the Gerlache Ice Stream). The later aspect can be quantified by detailed chronology for deglaciation in several of the flow path sectors as rebound rates vary with time. In March 2009 GPS units (via UNAVCO and USAP support) will be installed on the peninsula to generate and test vertical displacement rates, after three additional years of data collection. This study provides the framework for the most detailed and well constrained ice sheet reconstruction for any sector of the Antarctic margin and will therefore serve as a test case for temporal variations in ice thickness, potential flow rates, and substrate conditions.
C31E-0565
Changing Lake Bathymetry with Deglaciation: The Mendenhall Glacier System
Ongoing rapid ice ablation and glacier thinning has continued the buoyancy-driven, large-scale calving
events and ice terminus collapse of the Mendenhall Glacier. New bathymetric data collected from Mendenhall
Lake between 2004 and 2008 reveal lake shallowing adjacent to the 2008 glacier terminus. Since 2000, the
lake has expanded beyond its former 3.4 km2 footprint to 4.02 km2 and enlarged its volume from
0.05 km3 to 0.23 km3 as it elongates to the north, following the receding lakefront terminus and
filling its Pleistocene ice-scoured cirque basin. In 2004, the northeastern-most deep in the lake basin
reached a maximum depth of ~97 meters below mean lake level. Since that time this deep has
shallowed to the north decreasing along the 2008 glacier terminus to depths ranging from 79.85 to 0 m below
mean lake level. This new bathymetric data will be used for ongoing mass balance studies as well as for
determination of changes in lake sedimentation rates and lake basin morphology since the 1970s when
original lake surveys were conducted by the Alaska Dept of Fish and Game personnel. Comparison of lake
basin volume with river discharge data will help to better define the seasonal contribution of glacier melt water
to Mendenhall River summer discharge, which reached 50 percent during the summer of 1998.
http://robfatland.net/seamonster/
C31E-0566
Identification and Characterization of Dynamic Alpine Subglacial Lakes Using a Fusion of InSAR and GIS
We use interferometric synthetic aperture radar (InSAR) and a geographic information system (GIS) to identify and characterize three dynamic alpine subglacial lakes in Glacier Bay National Park, Alaska. Subglacial and subaerial glacier-dammed lakes and the catastrophic floods (jokulhlaups) they release are a hazard in glacierized mountain regions around the world. Many subglacial lakes are not identified until they become subaerially exposed or release a jokulhlaup. The lakes discussed here are dammed by the Brady Glacier in southeast Alaska, 120 km west of Juneau. For InSAR analysis, we utilized 20 ascending and descending ERS-1/-2 tandem radar images (1-day repeat interval) provided by the European Space Agency and a Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM). We processed SAR data into unwrapped interferograms using standard techniques. Two interferograms have very poor coherence and the remaining eight show significant line of sight (LOS) displacement over the surface of the subglacial lakes through time. However, because the displacement is LOS, the relative contributions of horizontal and vertical displacement are ambiguous. We then created horizontal and vertical displacement maps using near concurrent ascending and descending track interferograms and a glacier flow map, which describes horizontal glacier movement. We created the flow map manually by drawing arrows in a GIS in the direction of glacier flow based on observed crevasse patterns, medial moraines, and constraining topography, then interpolated between arrows. The displacement maps have significant areas of error caused by suboptimal imaging geometry that we masked out using a simple script. Horizontal displacement over the subglacial lakes was negligible. We exported the resulting vertical displacement maps to a GIS and quantified the change in volume of the lakes through time. Because there was negligible horizontal displacement around the three lakes, we were able to quantify the vertical displacement directly from the individual interferograms. This has two distinct advantages: 1) no masking is required for interferograms, so we can calculate volume more accurately; and 2) because two interferograms are required to produce one displacement map, we gain additional temporal control using the interferograms. This study demonstrates that InSAR and GIS can be effectively fused to identify and characterize dynamic alpine subglacial lakes. Knowledge of these lakes is important for understanding glacier motion, outburst flood potential and routing, and glacier mass balance.
C31E-0567
Characterization of the Greenland Ice Sheet Basal and Surface Layer Microwave Angular Scattering Characteristics
The use of microwave backscatter signatures to characterize the physical attributes of surfaces and layers, such as roughness and dielectric constant, has been used for many geophysical applications. For ice sheet studies, the characterization of these parameters for the basal and surface layers could aid in the identification of the presence of liquid water, bed roughness, and surface snow layer characteristics. To date, the main source of basal layer scattering data have been low-frequency microwave sounders, such as the various systems deployed through the years by the University of Kansas. The conventional use of these data has been to process them to retrieve the backscatter signature from the nadir direction alone, which has yielded extremely useful data for the characterization of ice sheet thickness and attenuation. However, due to the uncertainties in the basal layer attenuation, it is problematic to use this data for basal layer backscatter characterization. In this study, we report on a novel technique, which we call Squinted Unfocused SAR Interferometry (SUSI), which has promise in retrieving the angular characteristics of the microwave backscatter signature from the basal and surface layers for incidence angles in the range from 0 to ~15 degrees. It is well known that the angular decay of the radar cross section in the near nadir regime is an indicator of the interface root mean squared slope (i.e., surface roughness), independent of the absolute magnitude of the return. Therefore, these angular signatures provide a unique tool for characterizing the basal layer unavailable from other measurements. We present the theoretical basis for the SUSI technique, and then apply it to data collected over the Greenland ice sheet by the University of Kansas radar system during May 2006, September 2007, and July 2008. These data were collected at 150 MHz and 450 MHz, allowing the retrieval of basal characteristics at two different scales of roughness. The SUSI technique can also be used to retrieve the scattering characteristics of the surface layer, which yields insights about the angular characteristics of surface clutter. This characterization has implications about the feasibility of spaceborne radar sounders for Earth or planetary applications
C31E-0568
ICESat Laser Altimetry over the Arctic Ocean: Recent Sea Ice Results
Since its launch in 2003, the Geoscience Laser Altimeter System (GLAS), onboard ICESat has been providing measurements of Arctic sea ice topography up to 86 ° N. We demonstrate a new method to retrieve sea surface height from ICESat data via the identification of surface reflections from leads and areas of thin ice. We compare our results to near-coincident MODIS imagery of the sea-ice pack. Knowledge of the local sea surface height of the Arctic Ocean has both oceanographic and geodetic applications such as the derivation of dynamic ocean topography, sea ice thickness, and the marine gravity field. We will focus in particular on the combination of sea surface height measurements with the sea ice elevation measurements provided by GLAS, to estimate sea ice freeboard during the fall and winter seasons. Since laser altimetric surface reflections over sea ice are assumed to originate from the air/snow interface, snow depth is included in the freeboard signal. We present a time-series of sea ice freeboard, which reveals a downward trend over a five-year period from February 2003 to March 2008. We investigate the seasonal and inter-annual variability of sea ice freeboard and analyze any changes in basin-scale average sea ice freeboard in light of the record sea ice minimum extent set in September 2007.
C31E-0569
Satellite Altimetric Mappings of Arctic Sea Surface Topography: An Evaluation
Increasingly precise mappings of sea surface topography (SST) in the Arctic Ocean are being derived from near-polar satellite altimeters such as the laser system - Geoscience Laser Altimeter System (GLAS) - onboard NASA's ICESat and the radar systems onboard ESA's ERS-2 and Envisat. These mappings of sea surface topography (SST) have important oceanographic and geodetic applications. For example, because the geoid does conform closely to sea surface topography we can use altimetric SST measurements to estimate gravity (e.g., see the ARCtic Satellite-only (ARCS) field, McAdoo et al. 2008) particularly in regions lacking "true" surface gravity observations. Also, by differencing mappings of mean SST with a gravimetric geoid - particularly a geoid underpinned by a GRACE mean field model - we can estimate the dynamic ocean topography (DOT) and circulation of the Arctic Ocean. However, accurate estimates of DOT (e.g. accuracies better than a decimeter) require that we have very precise knowledge of the geoid and mean SST. Comparing a mean SST derived from ICESat/GLAS data spanning several years with a corresponding mean SST derived from ERS-2 data reveals short- wavelength differences or discrepancies of order 40 - 60 cm in certain areas of the Arctic Ocean such as the Chukchi Borderland. In order to attribute a portion of these discrepancies to laser or radar altimeter measurement error, we convert these mean SST fields to equivalent gravity fields and compare with gravity observations from several of the unclassified SCICEX/U.S. Navy submarine cruises (Edwards and Coakley, 2003; http://www.ldeo.columbia.edu/res/pi/SCICEX/ ). This comparison enables us to quantify short-wavelength errors in both laser and radar altimetric mean SST models.
C31E-0570
MODIS-derived Greenland ice sheet equilibrium line altitude 2000-2008: comparison with surface melt and accumulation variability
Equilibrium Line Altitude (ELA), where accumulation and ablation balance on an annual basis conveniently integrates the combined effect of surface melting and net snow accumulation. ELA can be monitored in optical satellite imagery for cloud-free scenes just prior to the first winter snow. We use NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) to first manually, then using reflectance thresholds, we automatically classify in many images whole-Greenland ice sheet ELA. Inter-annual ELA variations spanning years 2000-2008 are compared with precipitation and melt anomalies simulated by Polar MM5 to better understand ELA sensitivity to climate and likely future changes in ice sheet accumulation area ratio.
C31E-0571
The fractal structure of the ice/water boundary for sea ice near Barrow, Alaska
A capacitively coupled resistivity survey was conducted on the sea ice near Barrow, Alaska in March 2008, as part of a continuing effort to understand the meter-scale structure of seasonal arctic sea ice. Data was collected on the Chukchi Sea, on ice approximately 3 months old and ~ 200m offshore from the Naval Arctic Research Laboratory. Data was collected along a single 500m line, then in a 12m-by-100m grid with 1m line spacings. Unusually small n-spacings were employed to concentrate the signal at shallow depths to determine the location and shape of the ice/water boundary. RES2DINV and RES3DINV were used to invert the data and to produce images of the ice in 2 and 3 dimensions. This fractal dimension will be compared to that of 2 month old sea ice surveyed in March, 2006 in the same area with the same type of survey.
C31E-0572
Validation of Fractional Snow Cover from AVHRR using Landsat TM
The suite of NOAA satellites carrying the AVHRR sensor provides daily coverage of the world's snowpack. While another satellite-borne sensor, MODIS, may provide more accurate estimates of snow cover for operational forecasting, AVHRR provides a retrospective view, gaining a perspective of historical snowpack, which in turn can supplement operational forecasting. Here we validate a fractional snow cover algorithm for AVHRR in use by the Cold Regions Research and Engineering Laboratory. The approach uses a binary decision tree trained from the theoretical reflectance of snow and non-snow spectra convolved to AVHRR bandwidths. The binary decision tree, which estimates fractional snow cover, uses bands 1 and 2 calibrated with an atmosphere optical model 6S, and a derived band 3, which estimates a reflectance component separated from the emitance component by using temperature data from channel 4, and assumptions about the surface emissivity. Using 26 Landsat TM scenes we validate 79 scenes from NOAA 9, 11, 12 and 14. We investigate the absolute differences from the fine resolution data as well as the relative differences between sensors on the two satellites. Errors of commission are eliminated with a temperature and/or elevation mask. Like most moderate resolution satellite data, georegistration errors contribute to the overall error and can be accounted for when comparing images. The AVHRR algorithm demonstrates sensitivity to fractional snow cover and performs well in comparison to TM.
C31E-0573
Ice Sheet Surface Slope from ICESat Repeat Ground Tracks
Elevations for twelve ICESat campaign periods from October 2003 to November 2008 are used in this study. Each campaign covers the same 492 tracks of a 33-day sub-cycle of the 91-day orbit. With ICESat's laser footprint of ~70 meters and sample interval of 170 meters, this generated unprecedented elevation coverage of the Greenland and Antarctic ice sheets. The spacecraft pointing is controlled in the polar regions so that the repeat passes along a reference ground track (RGT) are within +/-100 meters (1 sigma) of the reference ground track. The uniqueness of the ICESat repeat track distribution enabled us to calculate surface slope in the cross-track direction. Our algorithm calculates cross-track surface slope, mean elevation change rate dH/dt and surface height at each point on a reference track. We use a minimum of N=4 repeat passes to solve for the 3 parameters; there are up to N=12 repeat passes. Our results show that, for same surface slope, errors in both slope and dH/dt decrease as 1/sqrt (N-3). Errors in surface slope and dH/dt also decrease when slope decreases. Combining with along-track elevations sampled at 170-meter spacing, we then calculated the 3-dimensional slopes at a 200-meter scale for both the Greenland and Antarctic ice sheets. Knowing the cross-track surface slope makes it possible to construct elevation time series at each footprint on the ICESat reference ground tracks (or calculate dH/dt for any 2 passes along a repeat track, i.e., for N=2). This lays the foundation for using repeat ground tracks to study ice sheet mass balance. The surface slopes derived from ICESat RGT are compared with surface slopes derived from ICESat DEMs of Greenland and Antarctica.
C31E-0574
A Runtime Data Verification Cyberinfrastructure for an Automated Robotic Tram System Measuring Surface Reflectance in the Arctic
Global change is amongst the greatest challenges facing humanity. Understanding the future state of the Earth System and how humans will need to adapt will require improved environmental observation capacity, more thorough understanding of environmental connectivity and integration of such data in to predictive models. Increasingly, environmental science is becoming data driven as the need for answering bigger picture questions increases – more than ever, researchers are collecting larger data streams through automated means, relying on data from other researchers or agencies, and integrating data from different disciplines. Associated with this advancement in the environmental sciences is the need for improved mechanisms and procedures to verify the integrity of data streams and improve trust in and optimization of data and work flows. A collaborative research effort between the Systems Ecology Lab at the University of Texas at El Paso and the University of Alberta performs ground-based hyperspectral remote sensing studies to investigate the effect of soil moisture on arctic ecosystem structure and function using a robotic cart and tramline infrastructure. This system generates about 60,000 data files during a normal field season and because of this high volume of data, it has become nearly impossible to quality check all spectral data collected using traditional data quality checking approaches. This presentation introduces a prototype run-time Data Quality Specification and Monitoring System (DQSMS) that has been developed in a collaborative effort with the NSF-funded Cyber-ShARE Center of Excellence at the University of Texas at El Paso. Using this software, users can customize data quality requirements and flag problematic data for post collection filtering and correction. The software also supports remote real time verification through wireless connectivity. We welcome input from other researchers and the opportunity to adapt this tool to other remote field instrumentation collecting environmental observations using automated means.
C31E-0575
Changes in Sea Ice Freeboard and Thickness Derived From ICESat Laser Altimeter Measurements
The thickness of sea ice on the Arctic Ocean has been mapped from measurements of sea ice freeboard made by NASA's ICESat during February/March and October/November each year and in several May/June periods since 2003. ICESat's laser altimeter measures the sea ice freeboard height (sea ice plus snow cover) over 70 m footprints at 172 m spacings with a range precision of 2 cm. For each measurement location, an ocean reference level is selected by constructing distributions of the measured surface elevations within ± 50 km of the location and taking the average elevation of the lowest 1% of the elevations corresponding to open water or very thin ice. The method also provides an improved estimate of the ocean geoid, which is iteratively used as the initial ocean reference level. Snow cover estimates from both climatology and derived from ECMWF analysis are used to estimate sea-ice thicknesses from the sea-ice freeboards. While the area of sea ice at the end of the summer has been declining at an increasing rate in recent years, the thickness has also been decreasing at a similar rate. Therefore, the volume of sea ice has been decreasing even faster than the area of sea ice. Most of the sea ice thicker than 3 m has disappeared throughout the Arctic Ocean. A large area of former perennial ice pack from the Beaufort to Laptev Seas is now a seasonal sea ice zone. The remaining perennial pack is more vulnerable to disappearance in summer because of the thinning. As the multiyear ice pack thins, it may be passing through a tipping point where the growth in thickness during winter may not be sufficient to survive the summer melting.
C31E-0576
Advances in Determining First-year Sea Ice Melt Pond Fraction Using C-band Polarimetric SAR
Greater sea ice melt pond fractions arising from an increase in first-year sea ice relative to multiyear ice may contribute to decreasing Arctic summer sea ice extents observed in recent years. Regions of higher melt pond fraction experience enhanced absorption of shortwave energy into the ice-ocean system which accelerates ice decay and a decrease in ice volume in successive years. Understanding regional variations in melt pond fraction, and determining linkages to competing interactions such as snow depth, sea ice type, and warming/cooling trends, requires an effective sea ice monitoring tool during the critical summer melt period. Optical remote sensing data are of limited use due to the ubiquity of cloud cover over the Arctic during summer months. First results are presented on C-band (5.3 GHz) radar scattering signatures and polarimetric discriminants from a surface-based, fully-polarimetric, scatterometer deployed over melt pond covered first-year sea ice in the Canadian Arctic. Scattering properties of melt ponds, sea ice, and composite surfaces are evaluated for varying radar parameters and changing surface geophysical properties. Coincident high-resolution C-band dual-polarised (HH+VV or HH+HV) radar image data from ENVISAT-ASAR are used to demonstrate the utility of wide swath SAR data for the inversion of melt pond fraction and the proxy estimation of climatological á from Arctic first-year sea ice. The optimal combination of polarimetric discriminants and radar parameters for achieving this technique using fully polarimetric SAR data, e.g. from the recently launched RADARSAT-2, is outlined.