B. Legresy

TAS Energy, Houston, Texas, United States

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Publications (74)81.31 Total impact

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    ABSTRACT: The deployment of a seismic network along the Adélie and George V coasts in East Antarctica during the period 2009–2012 provides the opportunity to monitor cryoseismic activity and to obtain new insights on the relationship between tidal cycles and coastal glacier dynamics. Here we focus on records from a seismometer located on a rocky outcrop in the vicinity of the grounding line of the 35 km broad Mertz glacier, a major outflow of this region. We detect numerous icequakes (50,000 events within 10 months and up to 100 events/h) and demonstrate their clear tidal modulation. We suggest that they result from ice friction and fracturing around the rocky peak and from the glacier flexure in response to the falling and rising tides at its grounding area. We propose that such icequake monitoring could be used as a climate proxy since grounding lines are subject to migrate with sea level changes.
    Geophysical Research Letters 10/2013; 40. · 3.98 Impact Factor
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    ABSTRACT: In February 2010, the Mertz Glacier Tongue (MGT) calved, releasing an 80 × 40 km iceberg. We have developed a high-resolution barotropic ocean model of the region to simulate the local circulation in response to tides and atmospheric forcing. We improved the coastline, grounding line position and built a new bathymetry using satellite imagery and older bathymetry data to derive the best available tidal model for the region. We compared this and other available models to seven different sea level observations available in the area and significantly improved the tidal solutions reaching a root sum square of 2.3 cm. This model was then run in different bathymetric configurations, considering the ice draft of the major icebergs B9B and C28, to simulate the circulation before, during, and after the calving event. The currents changed substantially in the neighborhood of the MGT and icebergs. The barotropic model with tidal and atmospheric forcing and the atmospheric wind fields allow us to evaluate the forces acting on the MGT. The sea surface slope force dominates the budget. Calving occurred when high tide and strong nontidal currents (due to atmospheric forcing) combined to lead to the monthly maximum forces exerted on the MGT (i.e., between 10 and 13 February 2010). While the forces are not unusually large at the calving time, the currents are largely enhanced in the rifting area. Therefore, processes related to these currents, like melting the ice mélange inside the rifts, should be investigated to fully explain the final stage of the calving.
    Journal of Geophysical Research 08/2013; · 3.17 Impact Factor
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    ABSTRACT: Knowing the interannual variations in the Antarctic ice sheet net snow accumulation, or surface mass balance (SMB), is essential for analyzing and interpreting present-day observations. For example, accumulation events like the one in East Antarctica in 2009 (Shepherd et al. 2012, Science, doi: 10.1126/science.1228102) challenge our ability to interpret observed decadal-scale trends in terms of long-term changes versus natural fluctuations. SMB variations cause changes in the firn density structure, which need to be accounted for when converting volume trends from satellite altimetry into mass trends. Recent assessments of SMB and firn volume variations mainly rely on atmospheric modeling and firn densification modeling (FDM). The modeling results need observational validation, which has been limited by now. Geodetic observations by satellite altimetry and satellite gravimetry reflect interannual firn volume and mass changes, among other signals like changes in ice flow dynamics. Therefore, these observations provide a means of validating modeling results over the observational period. We present comprehensive comparisons between interannual volume variations from ENVISAT radar altimetry (RA) and firn densification modeling (FDM), and between interannual mass variations from SMB modeling by the regional atmospheric climate model RACMO2 and GRACE satellite gravimetry. The comparisons are performed based on time series with approximately monthly sampling and with the overlapping period from 2002 to 2010. The RA-FDM comparison spans the spatial scales from 27 km to the continental scale. The mass comparison refers to the regional (drainage basin) and continental scale. Overall, we find good agreement between the interannual variations described by the models and by the geodetic observations. This agreement proves our ability to track and understand SMB-related ice sheet variations from year to year. The assessment of differences between modeling and observations allows us to quantify upper bounds on the uncertainties of the results from either technique. Moreover, the joint analysis of the four techniques aids in attributing the remaining discrepancies to deficits in individual techniques. These analyses may guide further improvements in observing and modeling SMB-related ice sheet variations.
    04/2013;
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    ABSTRACT: The deployment of a seismic network along the Adélie and George V coasts in East Antarctica during the period 2009–2012 provides the opportunity to monitor cryoseismic activity and to obtain new insights on the relationship between tidal cycles and coastal glacier dynamics. Here we focus on records from a seismometer located on a rocky outcrop in the vicinity of the grounding line of the 35 km broad Mertz glacier, a major outflow of this region. We detect numerous icequakes (50,000 events within 10 months and up to 100 events/h) and demonstrate their clear tidal modulation. We suggest that they result from ice friction and fracturing around the rocky peak and from the glacier flexure in response to the falling and rising tides at its grounding area. We propose that such icequake monitoring could be used as a climate proxy since grounding lines are subject to migrate with sea level changes.
    Geophysical Research Letters 01/2013; · 3.98 Impact Factor
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    ABSTRACT: Interannual variations of the Antarctic ice sheet due to surface mass balance (SMB) fluctuations are important for estimates and interpretations of ice sheet mass balance. Recent assessments mainly rely on atmospheric modeling, but SMB variations on an ice-sheet scale are also reflected in satellite altimetry and GRACE satellite gravimetry data. All three approaches have their limitations. On the one hand, modeled interannual SMB variations need observational validation, which has been limited by now. On the other hand, the space-geodetic data do not exclusively reflect SMB phenomena, but also ice dynamics, glacial isostatic adjustment, and errors. Moreover, quantifying ice mass changes from altimetry requires assumptions on firn density and compaction. Finally, the spatial sensitivity of GRACE is limited to a few hundred kilometers. Nonetheless, previous work has shown promising qualitative agreement between interannual change patterns in ENVISAT radar altimetry (RA) and GRACE and between regional-scale interannual signals from GRACE and atmospheric modeling. Here we present comprehensive comparisons between all three techniques for the Antarctic ice sheet. We use the RACMO2/ANT high-resolution regional atmospheric model, ENVISAT RA estimates from an advanced along-track repeat analysis, and GRACE estimates from regional analyses based on different series of time-variable gravity field solutions. The overlapping period of the three techniques is August 2002 to October 2010. The high-resolution (27 km) spatial representations of interannual phenomena in ENVISAT RA and RACMO2/ANT match well for many regions, and show good agreement with the larger-scale patterns of mass varations determined with GRACE. We quantify this agreement by statistical parameters. Next, we combine all three techniques to characterize and quantify selected temporal SMB anomalies, such as an excess accumulation in West Antarctica and Wilkes Land in September/October 2005. The presented overall agreement indicates that, to a large extent, interannual signals in ENVISAT and GRACE are well understood as temporal SMB variations represented by RACMO2/ANT. Remaining differences between the three techniques help us to assess their limitations, and may guide further improvement in observing and modeling SMB-related ice sheet variations.
    04/2012;
  • Proceedings of '20 Years of Progress in Radar Altimetry'. ESA SP-710, Venice : Italie; 01/2012
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    ABSTRACT: The Australian TOT-Cal project seeks to provide a contribution to the calibration and validation of the CryoSat-II mission over two adjacent important regions in East Antarctica. The first focuses on the Totten glacier, arguably one of the most important outlet glaciers in the East Antarctic, known to be undergoing significant surface lowering. The second includes the coastal slope regions behind Casey station and up on the plateau areas near Law Dome where significant spatial variation in annual accumulation is known to occur. The 2010/11 austral summer is the first field season for this project, with fieldwork to be underway at the time of the AGU FM10. In this poster, we present our current field activities and forward plans for the 2011/12 season. Our field campaign includes three components. A total of six in-situ GPS sites will be deployed over the summer period throughout the Law Dome / Totten Glacier region. These sites will facilitate the computation of the integrated water vapour content of the atmosphere, enabling an assessment against the ECMWF product used in the CyroSat-II data stream. The GPS sites also serve to provide reference stations for the AWI Polar-5 aircraft that will fly over the study area equipped with a scanning LiDAR and the ESA ASIRAS instrument. Finally, a series of kinematic GPS transects, corner cube reflector placements and surface density measurements will be undertaken from our field camp on the western flank of Law Dome to provide high resolution ground measurements for cal/val activities. In a separate project, Antarctic sea ice freeboard measurements will also contribute to the calibration and validation efforts by the Australian Antarctic program. In November 2010, the first set of such measurements will be carried out in the East Antarctic sea ice zone between 77 and 90 degrees East. The primary measurement tools for this campaign will include helicopter mounted scanning LiDAR and aerial photography, combined with in-situ sea ice observations. Over the next few austral spring seasons, similar measurements will be carried out, especially during a major marine cryosphere experiment on board the Australian RSV Aurora Australis in 2012.
    AGU Fall Meeting Abstracts. 11/2010; -1:0499.
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    ABSTRACT: In November 2007, during the IPEV R0 Astrolabe voyage, we deployed a network of year-round GPS beacons along a flow line of the Mertz glacier in East Antarctica (CRAC-ICE project, Legrésy et al.). Two months of GPS data were collected at the end of the field season from 2 stations (GPS4 & GPS5) around the main rift on the Mertz floating ice tongue. We investigate sub daily time scales of motion of the two sites using the GPS records. The observed vertical signal includes tides, but also more rapid signals at sub-hourly time scales. With GPS processing using Gins-PC software and Precise Point Positioning processing (PPP); we are able to confirm getting the sub hourly scale oscillations of the ice tongue with few centimeters amplitude from two different part of the floating ice tongue. One mechanism in calving events is ocean wave energy, which leads to the movement of the ice tongue. The glacier then acts like a filter, with filtering characteristics depending mainly of the ice thickness (Holsworth and Gynn 1981). If a dominant frequency of the ocean wave spectrum coincides with one of the fundamental vibration modes of the ice-tongue, cyclic bending stresses may lead to fatigue of the ice and hence to crack propagation. This kind of event is a good candidate to explain a part of a calving process of an ice-tongue. Therefore, we focused of these oscillations using Harmonic analysis, short term FFT and wavelets. We identified a main energetic mode of vibrations around 10-40 minutes (23% of the total energy of the signal) that we compared with simple modeling of the fundamental vibrations of a beam. The model has been run in different cases of ice thickness, ice-tongue length and directions of the observed vibrations. The most visible oscillations correspond to a main mode of vibration propagating in the across flow direction of the ice tongue, driven mostly by ocean forcing. Both GPS sites are recording these vibrations. Given that each beacon is situated on from each side of the rift, we investigated the possible effects of the movement on the opening of the rift by a comparison of their own signal. Finally, we focused the possible resonance with ocean forcing and their impact on calving processes.
    05/2010;
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    ABSTRACT: It is well known that the spatial distribution of sea level measurements throughout the Southern Ocean is sparse and mostly consists of datasets with short records. The PSMSL (Permanent Service for Mean Sea Level) has only a few sea level time series below 45° South and most of them are shorter than twenty years. The lack of observations constrains the ability to determine or reconstruct global estimates of mean sea level change over the past century. For this reason, any available historical information becomes invaluable for deriving long-term estimates of sea level change in this part of the world. The aim of this presentation is to describe the way we have recovered and analysed the available historic sea level observations made in few sites of the Southern Ocean and to propose new reliable long term sea level trend estimates in this region. The first site is Saint-Paul, a small island of the Southern Indian Ocean where historical measurements were done in 1874 and connected to the permanent GLOSS tide gauge. The two other historical observations were recorded by the Australasian Antarctic Expedition lead by Sir Douglas Mawson in 1912 at Maquarie Island and Cap Denison (Antarctica). The last site concerned by this presentation is the Dumont d'Urville (Antarctica) where historical information from the beginning of the 1950's were found and analysed.
    04/2010; 12:7026.
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    ABSTRACT: The IPY CRAC-ICE project is aimed at monitoring the calving of the Mertz Glacier tongue in East Antarctica, which extends 140km from its grounding line. Legresy et al. (2004) observed dramatic ice flow changes at daily time scales linked to tide currents, using limited GPS observations and SAR interferometry. In November 2007, we deployed a network of GPS beacons on the glacier. Two months of GPS data were collected at the end of the field season from two stations straddling the main rift. We have analyzed ERS INSAR, SAR, Landsat and SPOT images, Radio echo sounding and the GPS data together to draw an overall description of the rifting and calving process for the Mertz glacier tongue. We describe the history of this rifting during the available 14 years observation period. The ice tongue is freely floating and has a longitudinal velocity of about 3m/day. It is clear that the ice flow is affected at daily time scales by the tides. A kind of stick-slip effect appears to also occur at daily scales. We see a modulation of the flow at fortnightly time scales; however, we also observe that the maximum speed occurs a few days after the spring tides. The ice tongue moves in an E-W direction in response to the force exerted by tide currents at all time scales. We find that the rifting is likely initiated by the tide current induced lateral hinging of the ice tongue, creating regularly spaced (~1km) weak lines on the glacier tongue across flow. The rifts further propagate into these weakness lines. Now that the rifts on both east and west sides of the glacier have significantly progressed, the daily to seasonal scale hinging is now happening between the down stream and upstream parts of the ice tongue. The rift is opening quickly at some 0.12 m/day at an angle of 35° from the main flow direction. We observe a residual rotation of the rift opening with a radius of 15 km. The rotation center is situated in the eastern part of the rift, which appears active at the daily scale. We present the results with an emphasis on the future possible calving scenarios.
    04/2010; 12:9856.
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    ABSTRACT: Ice within marine basins of East Antarctica, and their outlets, represent the ultimate limit on sea level change. The region of East Antarctica between the Ross Sea and Wilkes Land hosts a number of major basin, but has been poorly understood. Long range aerogeophysics from US, Australian and French stations, with significant British and IceBridge support, has, under the banner of the ICECAP project, greatly improved our knowledge of ice thickness, surface elevation, and crustal structure of the Wilkes and Aurora Subglacial Basins, as well as the Totten Glacier, Cook Ice Shelf, and Byrd Glacier. We will discuss the evolution of the Wilkes and Aurora Subglacial Basins, new constraints on the geometry of the major outlet glaciers, as well as our results from surface elevation change measurements over dynamic regions of the ice sheet. We will discuss the implications of our data for the presence of mid Pleistocene ice in central East Antarctica. Future directions for ICECAP will be discussed.
    01/2010;
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    ABSTRACT: The Mertz Glacier tongue (MGT), East Antarctica, has a large area of multi-year fast sea ice (MYFI) attached to its eastern edge. We use various satellite data sets to study the extent, age, and thickness of the MYFI and how it interacts with the MGT. We estimate its age to be at least 25 years and its thickness to be 10-55 m; this is an order of magnitude thicker than the average regional sea-ice thickness and too thick to be formed through sea-ice growth alone. We speculate that the most plausible process for its growth after initial formation is marine (frazil) ice accretion. The satellite data provide two types of evidence for strong mechanical coupling between the two types of ice: The MYFI moves with the MGT, and persistent rifts that originate in the MGT continue to propagate for large distances into the MYFI. The area of MYFI decreased by 50% following the departure of two large tabular icebergs that acted as pinning points and protective barriers. Future MYFI extent will be affected by subsequent icebergs from the Ninnis Glacier and the imminent calving of the MGT. Fast ice is vulnerable to changing atmospheric and oceanic conditions, and its disappearance may have an influence on ice tongue/ice shelf stability. Understanding the influence of thick MYFI on floating ice tongues/ice shelves may be significant to understanding the processes that control their evolution and how these respond to climate change, and thus to predicting the future of the Antarctic Ice Sheet.
    Journal of Geophysical Research C: Oceans. 01/2010;
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    ABSTRACT: We discuss various field observations that have been (and will still be) carried out during the last two field seasons over a test glacier in East Antarctica under the framework of the DACOTA program (supported by both the French Agence Nationale de la Recherche, and the French Polar Institute). We will use various techniques so as to provide a better characterization of the dynamics of an outlet glacier as well as the required data sets for running and constraining an ice flow model. These outlet glaciers play a crucial role by draining ice situated inland, thereby controlling the overall mass balance of large parts of the ice sheet. As a small, simple, and accessible glacier, Astrolabe Glacier is an ideal test case. Data of the kinds being collected provide a reference against which later measurements will be compared to infer significant trends (velocity and thickness changes). As an example, surface elevation has been measured at various places on the glacier. The order of magnitude of thickness changes expected compared to the measurement techniques accuracy should allow for significant trends after a couple of years. A permanent deformation rate network consisting of autonomous GPS stations has been started last year and should be completed next winter. By being located close to the grounding line, the deformation rate network will yield constraining data for the model by providing the surface velocity changes induced by the mobility of the grounding line. With regard to modelling input data, bedrock topography represents the most important data set but also the most difficult to access. Radar techniques have been used with first a ground-based penetrating radar later completed by two larger scale airborne surveys allowing for full coverage of the entire drainage basin (8000 km2). This airborne campaign has been possible under the frame of a collaboration between the University of Texas (60 MHz airborne radar), the Jet Propulsion Laboratory (2.5 MHz airborne radar) and the French Polar Institute IPEV (fuel and ground logistics). Some first results are presented as well as the flight plans for the forthcoming season (2009/1010) where an airborne Basler-DC-3 platform (fielded as part of the University of Texas ICECAP project) will simultaneously fly a large panel of geophysical instruments (both previously flown radars, a scanning lidar, a gravity meter, magnetometer and accurate GPS positioning). Through collaborations between institutes from different countries and from the use of the most sophisticated geophysical techniques, the Astrolabe Glacier will benefit from comprehensive geophysical coverage, becoming an "observatory" that allows for realistic dynamical and /or modelling studies to be undertaken.
    AGU Fall Meeting Abstracts. 12/2009;
  • S. Parouty, B. Legrésy, F. Rémy, F. Blarel
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    ABSTRACT: We are interested in the way winds affect the Antarctica ice sheet surface. Indeed, some specific ice surfaces such as blue ice (Van den Broeke and Bintanja, 1995) or megadunes fields (Frezzotti et al., 2002) are known to be created under given wind conditions. Besides that, the shape of the altimetric echoes from satellite observations are affected by changes in ice surface properties (Partington at al. (1989), Rémy et al. (1991), Legrésy et al. (1998), Lacroix et al. (2007)), which are mainly the surface roughness and micro roughness, the stratification of the ice sheet upper layers and the grains size. We are thus studying how changes in wind conditions induce variations in the altimetric echo shapes. For this purpose we compare winds given by reanalysis or analysis of global climate models (NCEP/NCAR, NCEP/DOE and ECMWF) and different parameters (namely the height measurement, the backscatter coefficient, the leading edge width and the trailing edge slope) describing the altimetric echo shape from the altimeter onboard ENVISAT during a five year period from january 2003 to december 2007. This altimeter covers about 80% of the Antarctic ice sheet and provides us with observations in two different frequencies (Ku and S bands) which are complementary when it comes to studying surface properties (Legrésy et al. (1998)). Using the altimetric parameters we manage to retrieve winds with a fairly good agreement in the wind magnitude (+/- 0,6m/s), and in the reconstruction of interannual variability. The obtained relationship between altimetric parameters and wind speed is not unique for the whole ice sheet, showing the existence of locally different impacts of winds on the surface properties to which the radar altimetric measurements are sensitive. As we used three global climate models to recompose wind variations, we are able to assess to which one it is possible to get closer using our observations, and explain differences between the winds we compute and the winds from these global climate models for selected regions.
    04/2009;
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    ABSTRACT: By observing volume and mass changes, respectively, satellite altimetry and satellite gravimetry are complementary tools for ice sheet mass balance studies. We combine results from ENVISAT radar altimetry (2003 - present) and from GRACE (2002 - present) on Antarctic and Greenland ice mass changes. Satellite radar altimetry over ice sheets has had its limitations due to (1) the incomplete coverage (polar gap), (2) the surface slope induced errors and (3) the ambiguity between changes in surface height and firn properties. Here, we apply the Along-Track Repeat Satellite Radar Altimetry method that largely mitigates the problems (2) and (3). Unlike traditional crossover analyses, the complete along-track information is used. Local slope induced errors and time variations of the radar echoe shapes are accounted for within a simultaneous regression at each along-track position. The method thus exploits much more data (e.g. about 100 times more over Antarctica). Results are shown in terms of trends, seasonal and interannual variations. Our GRACE analyses concentrate on the 10-daily solutions by CNES/GRGS (Releases 1 and 2) which apply innovative regularization techniques. For the comparison of the ENVISAT and GRACE results, we account for their different characteristics concerning spatial resolution and coverage, volume versus mass change, and the different sensitivities to errors in the correction for glacial isostatic adjustment. In particular, we use the full GRACE normal equation matrices to describe the filtering inherent to the regularization during GRACE processing. By the synthesis of both kinds of observations we exploit their complementarities and resolve the altimetric signal in terms of ice or firn volume change. This task is notably aided by the consideration of seasonal and interannual signals in addition to linear trends. In result, we present new estimates on ice mass changes and their origins together with an assessment of related uncertainties.
    04/2009;
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    ABSTRACT: We show how the studies of ice and snow cover of continental water bodies can benefit from the synergy of more than 15 years-long simultaneous active (radar altimeter) and passive (radiometer) observations from radar altimetric satellites (TOPEX/Poseidon, Jason-1, ENVISAT and Geosat Follow-On) and how this approach can be complemented by SSM/I passive microwave data to improve spatial and temporal coverage. Five largest Eurasian continental water bodies - Caspian and Aral seas, Baikal, Ladoga and Onega lakes are selected as examples. A step-by-step ice discrimination approach based on a combined use of the data from the four altimetric missions and SSM/I is presented, as well as validation of this approach using in situ and independent satellite data in the visible range. We also discuss drawbacks and benefits of each type of sensor and particularities of radiometric properties for each of the chosen water bodies. We then analyse the long-term evolution of ice conditions for these lakes and inland seas using historical data and recent observations from satellite radar altimetry and radiometry.
    03/2009; 11:2783.
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    ABSTRACT: We report on long-term surface elevation changes of the central Amery Ice Shelf (AIS) by comparing elevation records spanning four decades (1968-2007). We use elevation records acquired with the following methods: optical leveling (1968-69); ERS radar altimetry (1992-2003); GPS (1995-2006); and ICESat laser altimetry (2003-2007). We compute multi-decadal elevation trend (dh/dt) values at crossovers between the leveling route and each of the GPS and ICESat tracks, as well as shorter period dh/dt at ERS-ERS, GPS-GPS and ICESat-ICESat crossovers. At GPS-leveling crossovers the mean long-term dh/dt is 0.003 m a-1 and at ICESat-leveling crossovers the mean dh/dt is +0.013 m a 1; neither trend is significantly different from zero. The data do however exhibit variable trends: near-zero change between 1991 and mid-1996, then thickening to ~2003, followed by thinning ~2003-2007, with 5 year dh/dt averages exceeding ~±0.1 m a-1. The changes in dh/dt pattern in mid-1996 and again in 2003 occur with unexpected speed. The ice shelf exhibits different dh/dt patterns than does the surrounding grounded ice, suggesting that surface mass balance variations or longer term variations in firn densification processes are unlikely to be major causes. We conclude that these observed multi-year elevation changes must be due to currently unexplained or presently poorly quantified phenomena involving surface, basal processes and/or ice dynamics. With the multi-decadal stability of the AIS established, the short-term fluctuations that we observe suggests that, for other ice shelves, observed strong dh/dt signals over short time periods do not necessarily indicate ice shelf instability.
    Journal of Geophysical Research 01/2009; 114:F01010, doi:10.1029/2008JF001094. · 3.17 Impact Factor
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    ABSTRACT: We present results of snow surface properties using the ENVISAT dual frequency altimeter at S (3.2 GHz) and Ku (13.6 GHz) bands and the AMSR-E microwave radiometer at frequencies ranging between 6 and 36 GHz in the Vostok region, East Antarctica. The altimetric time series observed between 2002 and 2008 show variations at 3 different time scales (daily, seasonal and inter-annual), that correlate directly with variations in the snow surface properties. In this study we focus on the analysis of the rapid daily event, occurring on February 14th 2005, that created a jump of the backscatter coefficient of up to 5.3 dB at the S band and 2.5 dB at the Ku band. The ratio of V/H-polarization brightness temperature slowly decreased in December and January 2005, and suddenly increased on February 14th 2005.The origin of this rapid event is investigated using AWS data from Vostok station, altimetric and radiometric data simultaneously. Both snow surface density and roughness are found to vary during this event. This event is shown to be synchronous with strong wind occuring during a period of anomalous wind direction, and the presence of surface hoar. These particular conditions certainly modified the snow surface roughness and thus impacted the altimetric signal. We finally investigate the impact of this event on the calculation of the regional ice-sheet mass-balance using different corrections of height with echo shape variations. It is shown to be negligible only if the full echo shape correction (Legresy et al., 2006) is used.
    Remote Sensing of Environment. 01/2009;
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    ABSTRACT: The snow surface roughness at centimetre and millimetre scales is an important parameter related to wind transport, snowdrifts, snowfall, snowmelt and snow grain size. Knowledge of the snow surface roughness is also of high interest for analyzing the signal from radar sensors such as SAR, altimeters and scatterometers. Unfortunately, this parameter has seldom been measured over snow surfaces. The techniques used to measure the roughness of other surfaces, such as agricultural or sand soils, are difficult to implement in polar regions because of the harsh climatic conditions. In this paper we develop a device based on a laser profiler coupled with a GPS receiver on board a snowmobile. This instrumentation was tested successfully in midre Lovénbreen, Svalbard, in April 2006. It allowed us to generate profiles of 3 km sections of the snow-covered glacier surface. Because of the motion of the snowmobile, the roughness signal is mixed with the snowmobile signal. We use a distance/frequency analysis (the empirical mode decomposition) to filter the signal. This method allows us to recover the snow surface structures of wavelengths between 4 and 50 cm with amplitudes of >1 mm. Finally, the roughness parameters of snow surfaces are retrieved. The snow surface roughness is found to be dependent on the scales of the observations. The retrieved RMS of the height distribution is found to vary between 0.5 and 9.2 mm, and the correlation length is found to be between 0.6 and 46 cm. This range of measurements is particularly well adapted to the analysis of GHz radar response on snow surfaces.
    Journal of Glaciology 11/2008; 54(187):753-762. · 2.88 Impact Factor

Publication Stats

394 Citations
81.31 Total Impact Points

Institutions

  • 2010
    • TAS Energy
      Houston, Texas, United States
    • Université de La Rochelle
      La Rochelle, Poitou-Charentes, France
  • 2002–2009
    • Laboratoire d'Etudes en Géophysique et Óceanographie Spatiales
      Tolosa de Llenguadoc, Midi-Pyrénées, France
  • 2007
    • Technische Universität Dresden
      • Institut für Planetare Geodäsie
      Dresden, Saxony, Germany
    • University of Tasmania
      Hobart Town, Tasmania, Australia
  • 2006
    • Centre National de Recherches Météorologiques
      Tolosa de Llenguadoc, Midi-Pyrénées, France
  • 2005
    • Collecte Localisation Satellites
      Ramonville, Midi-Pyrénées, France