Papers by Frederique Remy
Marine Geodesy, Sep 10, 2015
HAL (Le Centre pour la Communication Scientifique Directe), Mar 12, 2014
International audienc
AGU Fall Meeting Abstracts, Dec 1, 2008
Due to their remoteness, the recent evolution of glaciers and ice caps on sub-Antarctic islands i... more Due to their remoteness, the recent evolution of glaciers and ice caps on sub-Antarctic islands is poorly known. The objective of our study is to assess the changes of some of these austral ice masses located on the Kerguelen Islands (Indian Ocean, °S) using historical information (map published in 1967, glaciological campaigns carried out in the 1970s) and recent (1991-2007)
ESASP, Dec 1, 2010
The LEGOS based OSCAR project (observing continental surfaces with radar altimetry) delivers a va... more The LEGOS based OSCAR project (observing continental surfaces with radar altimetry) delivers a validation of the ENVISAT RA2 altimetry, in particular over Antarctic and Greenland. We investigated the stability and reliability of every correction on the altimetric measurements. Here we show the investigations on the dry troposphere correction. Although the overall trend in this correction is difficult to qualify, we found large unreliability of this correction at smaller scale on the Antarctic icecap. Large jumps are observed at cycle 40 and 55 of the satellite's life local trends of very significant and suspect values are found as well. We show the results of our investigations and map the impact this suspect correction has on the surface height changes. The impact is found to be non negligible and locally very significant. We investigate the possibility to re-compute a correction with the ECMWF pressure fields and show the improvement on the height recovery and height change surveys.
La Météorologie, 2017
Cet article présente une vue d'ensemble des avancées récentes en télédétection spatiale appliquée... more Cet article présente une vue d'ensemble des avancées récentes en télédétection spatiale appliquée à l'étude des surfaces enneigées et englacées auxquelles la communauté scientifique française a participé. Qu'ils s'agissent de données satellitaires optique, radar, lidar ou gravimétrique, ces travaux sur la couverture nivale saisonnière ou pérenne, les glaciers de montagne, les calottes polaires, la glace de mer ou de lac et de rivière ont pour objectifs de documenter aussi bien les caractéristiques physiques de ces objets que leur variabilité spatiotemporelle aux échelles locale, régionale ou globale.
Journal of Glaciology, 1993
In order to estimate the accuracy of altimetric height measurements over ice shee ts, an altimete... more In order to estimate the accuracy of altimetric height measurements over ice shee ts, an altimeter wave-form simulator has been developed, and different tracking methods have been tested. A large range of surface features, including large-scale and medium-scale features and micro-roughness have been taken into account for modeling of either surface-or volume-scattering. A large set of parameters affects the trailing edge of the radar wave form, so that re-tracking algorithms based on the detection of its leading edge provide better retrievals of the surface height than those based on the analysis of the whole wave form. A volume component is clearly present in the radar wave forms; its effect on the leading edge depends mostly on the snow grain-size (and therefore on the snow temperature) and on the pointing angle. However, on average, the induced error on the snow-surface height estimation should only be around 25 cm.
Geophysical Research Letters, May 22, 1992
ESA Living Planet Symposium, Dec 1, 2013
Geophysical Research Letters, 2007
The largest channels on Mars are the Northwestern Slope Valleys (NSVs) of Tharsis, which have pre... more The largest channels on Mars are the Northwestern Slope Valleys (NSVs) of Tharsis, which have previously been interpreted as the probable erosional trace of catastrophic flooding. It is argued here that ice‐streaming within ancient ice sheets emplaced by atmospheric precipitation at high mean obliquity may instead account for these channels, explaining similarities between the region and terrestrial Pleistocene subglacial landscapes. An ice‐sheet model shows extensive basal melting in and only in the NSV region, and ice streams which have significant erosive power.
The evolution of the thickness and area of two large Southern Ocean icebergs that have drifted in... more The evolution of the thickness and area of two large Southern Ocean icebergs that have drifted in open water for more than a year is estimated through the combined analysis of altimeter data and visible satellite images. The observed thickness evolution is compared with iceberg melting predictions from two commonly used melting formulations, allowing us to test their validity for large icebergs. The first formulation, based on a fluid dynamics approach, tends to underestimate basal melt rates, while the second formulation, which considers the thermodynamic budget, appears more consistent with observations. Fragmentation is more important than melting for the decay of large icebergs. Despite its importance, fragmentation remains poorly documented. The correlation between the observed volume loss of our two icebergs and environmental parameters highlights factors most likely to promote fragmentation. Using this information, a bulk model of fragmentation is established that depends on ocean temperature and iceberg velocity. The model is effective at reproducing observed volume variations. The size distribution of the calved pieces is estimated using both altimeter data and visible images and is found to be consistent with previous results and typical of brittle fragmentation processes. These results are valuable in accounting for the freshwater flux constrained by large icebergs in models.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 21, 2019
In this work a method for the estimation of 2003-2010 monthly-mean total discharge from Greenland... more In this work a method for the estimation of 2003-2010 monthly-mean total discharge from Greenland and Antarctica is presented. We show that measurements of time-variable gravity from GRACE when combined with estimates of precipitation and sublimation can realistically reconstruct the total discharge from the ice-sheets into the ocean. In particular, the total discharge has been calculated as a 8-member ensemble-mean obtained by combining multiple GRACE solutions with water fluxes from both an high resolution regional atmospheric climate model (RACMO2) and a global reanalysis (ERA-Interim). The gravimetric measurements of mass variations and the precipitation and sublimation atmospheric fields have been combined in the ice-sheets water mass balance equation, according to the main drainage basin systems. The use of the combined land-atmosphere water mass balance has also been tested, which however led to a large underestimation of total discharge. A comparison among the different GRACE solutions is also performed, highlighting similarities and differences and analyzing the possible causes. GRACE datasets show similar ice-sheet mass trends on Antarctica and over the majority of the Greenland basins, while significant differences (up to a factor of 1.9) have been found in mass-loss areas characterized by strongly negative water height trends. This is likely primarily caused by the 1
Journal of Glaciology, Mar 29, 2021
GRACE and ICESat Antarctic mass-balance differences are resolved utilizing their dependencies on ... more GRACE and ICESat Antarctic mass-balance differences are resolved utilizing their dependencies on corrections for changes in mass and volume of the same underlying mantle material forced by ice-loading changes. Modeled gravimetry corrections are 5.22 times altimetry corrections over East Antarctica (EA) and 4.51 times over West Antarctica (WA), with inferred mantle densities 4.75 and 4.11 g cm −3. Derived sensitivities (S g , S a) to bedrock motion enable calculation of motion (δB 0) needed to equalize GRACE and ICESat mass changes during 2003-08. For EA, δB 0 is −2.2 mm a −1 subsidence with mass matching at 150 Gt a −1 , inland WA is −3.5 mm a −1 at 66 Gt a −1 , and coastal WA is only −0.35 mm a −1 at −95 Gt a −1. WA subsidence is attributed to low mantle viscosity with faster responses to post-LGM deglaciation and to ice growth during Holocene grounding-line readvance. EA subsidence is attributed to Holocene dynamic thickening. With Antarctic Peninsula loss of −26 Gt a −1 , the Antarctic total gain is 95 ± 25 Gt a −1 during 2003-08, compared to 144 ± 61 Gt a −1 from ERS1/2 during 1992-2001. Beginning in 2009, large increases in coastal WA dynamic losses overcame long-term EA and inland WA gains bringing Antarctica close to balance at −12 ± 64 Gt a −1 by 2012-16. List of symbols and units Symbol Meaning Usual units
Journal of Glaciology, 2012
Since 2002, the Envisat radar altimeter has measured the elevation of the Antarctic ice sheet wit... more Since 2002, the Envisat radar altimeter has measured the elevation of the Antarctic ice sheet with a repeat cycle of 35 days. This long and regular time series is processed using an along-track algorithm to depict in detail the spatial and temporal pattern of elevation change for the whole ice sheet. We use this dataset to examine the spatial and temporal pattern of Pine Island Glacier (PIG) thinning and compare it to the neighbouring glaciers. We also examine additional areas, especially in East Antarctica whose mass balance is poorly known. One advantage of the finer along-track spacing of measurements is that it reveals places of dynamic thinning in regions of rapid ice flow. We observe the acceleration of thinning on PIG. Over the entire basin, the volume loss increased from 7 km 3 a-1 during 2002-06 to $ $48 km 3 a-1 during 2006-10. We also observe accelerated thinning on the lower tens of kilometres of Thwaites Glacier, with a mean thinning of 0.18 m a-1 over its entire basin during our observation period. We confirm the dynamic thinning of Totten Glacier but we do not detect significantly accelerated thinning on any glacier elsewhere than on the coast of the Amundsen Sea.
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Papers by Frederique Remy