Sea ice is both a key witness and driver of climate change. While sea ice extent and area is well... more Sea ice is both a key witness and driver of climate change. While sea ice extent and area is well described with observations during the last four decades, sea ice thickness and volumes changes remain poorly known. However, thickness is a mandatory variable to fully understand the past, present and future changes of sea ice. Despite improvements in sea ice thickness estimation from altimetry during the past few years thanks to SAR and laser altimetry, former radar altimetry missions such as Envisat and especially ERS-1 and ERS-2 have remained under exploited so far. ERS-2 arctic sea ice thickness has been recently retrieved thanks to a machine learning approach aiming at calibrating ERS-2 and Envisat against CryoSat-2. We are now able to extend the time series from ERS-1 for both polar oceans, allowing to propose a 29 years-long sea ice thickness and volume time series. Estimates are combined with uncertainties derived from a Monte Carlo methodology. Nearly 30 years of sea ice volum...
Ce focus a été publié en ligne, dans le cadre du projet ANR BDL (1795-1932), à l'adresse suiv... more Ce focus a été publié en ligne, dans le cadre du projet ANR BDL (1795-1932), à l'adresse suivante :[http://bdl.ahp-numerique.fr/focus-histoire-fr-meteorologie-bdl
Cinq Voyages extraordinaires de Jules Verne, publies de 1855 a 1897, ont pour theme central les r... more Cinq Voyages extraordinaires de Jules Verne, publies de 1855 a 1897, ont pour theme central les regions polaires et cinq autres voyages se passent a un moment ou a un autre aux poles. En ce milieu du XIXe siecle, les poles sont encore loin d’etre atteints et les regions avoisinantes restent relativement peu connues. Quelques recits de voyage commencent a etre publies, Jules Verne va fortement s’en inspirer. Il va alors creer un monde « d’une sinistre beaute », oxymore qui traduit toute l’angoisse et la frayeur qui envahissent les explorateurs et toute la beaute qui neanmoins les fascine. La glace de Jules Verne, vit, bouge, danse avec la houle, elle est en perpetuel mouvement, ses formes varient brusquement, les couleurs du ciel, de la glace ou des animaux evoluent tres vite. Les phenomenes physiques : la refraction, la phosphorescence, l’electricite… participent aussi a cette sinistre beaute. Comment, a partir des quelques elements qu’il possede, Jules Verne su creer un monde fasci...
Reference Module in Earth Systems and Environmental Sciences, 2017
The Antarctic ice sheet represents a potential contribution to sea level rise. Understanding proc... more The Antarctic ice sheet represents a potential contribution to sea level rise. Understanding processes interacting on the ice sheet is fundamental to precisely determine its response to a rapid changing climate and estimate its present and future contribution to sea level change. Satellite altimetry and gravimetry have been providing with maps of spatial and temporal changes of the ice sheet elevation and mass. They reveal that several places in Antarctica are changing at an accelerating rate in response to current climate change. The future monitoring programs of the ice sheet will significantly improve our knowledge of the ice sheet.
Observations of giant ice rings on Lake Baikal (Russia) have recently sparked scientific and publ... more Observations of giant ice rings on Lake Baikal (Russia) have recently sparked scientific and public interest. However, there is still no clear consensus on their origins. Here, we provide an inventory of the ice rings based on satellite imagery and photography for 1974–2014. We have identified 45 rings on Lake Baikal (compared with 13 previously known) and also for the first time four rings for the neighbouring Lake Hovsgol (Mongolia). The results of our hydrographic surveys beneath the ice rings in Lake Baikal in 2012–2014 and in Lake Hovsgol in 2015 show the presence of warm double‐convex lens‐like eddies before and during manifestation of ice rings. We suggest that these eddies are the driving factor for the formation of ice rings in these lakes. We reassess the existing hypotheses of ice ring formation and discuss the potential mechanisms of eddy formation.
Abstract The scattering properties of the radar signal at Ka and Ku-band frequencies are investig... more Abstract The scattering properties of the radar signal at Ka and Ku-band frequencies are investigated using a theoretical model and snow grain observations obtained during previous field campaigns. Our results show that the combination of radar altimeters operating at these two frequencies should allow for the retrieval of snow depth over Arctic sea ice. We estimate uncertainties of the ice surface position in relation to crossover observations over sea ice and show that the accuracy of the crossover methodology with short time gap (3 days or less) is better than 3 cm. Comparison of the CryoSat-2/AltiKa retrieved snow depth with in situ measurements provided by Operation IceBridge shows a good agreement with a Root Mean Square Error (RMSE) of 5 cm. Analysis of the CryoSat-2/AltiKa retrieved snow depths over three winters (2013–2015) reveals a thinner snow cover on both Multi-Year (32%–57%) and First-Year Ice (63%–75%) relative to the 1954–91 Warren climatology, suggesting the need for more contemporary year-round and basin-scale snow depth fields.
ABSTRACT Sea ice leads play an essential role in ocean-ice-atmosphere exchange, in ocean circulat... more ABSTRACT Sea ice leads play an essential role in ocean-ice-atmosphere exchange, in ocean circulation, geochemistry and in ice dynamics. Their precise detection is crucial for altimetric estimations of sea ice thickness and volume. This study evaluates the performance of the SARAL/AltiKa altimeter to detect leads and to monitor their spatio-temporal dynamics. We show that a pulse peakiness parameter (PP) used to detect leads by Envisat RA-2 and ERS-1,-2 altimeters is not suitable because of saturation of AltiKa return echoes over the leads. The signal saturation results in loss of 6-10% of PP data over sea ice. We propose a different parameter: maximal power of waveform, and define the threshold to discriminate the leads. Our algorithm can be applied from December until May. It detects well the leads of small and medium size: from 200 m to 3-4 km. So, the combination of the high-resolution altimetric estimates with low-resolution thermal infra-red or radiometric lead fraction products could enhance the capability of remote sensing to monitor sea ice fracturing.
Sea ice is both a key witness and driver of climate change. While sea ice extent and area is well... more Sea ice is both a key witness and driver of climate change. While sea ice extent and area is well described with observations during the last four decades, sea ice thickness and volumes changes remain poorly known. However, thickness is a mandatory variable to fully understand the past, present and future changes of sea ice. Despite improvements in sea ice thickness estimation from altimetry during the past few years thanks to SAR and laser altimetry, former radar altimetry missions such as Envisat and especially ERS-1 and ERS-2 have remained under exploited so far. ERS-2 arctic sea ice thickness has been recently retrieved thanks to a machine learning approach aiming at calibrating ERS-2 and Envisat against CryoSat-2. We are now able to extend the time series from ERS-1 for both polar oceans, allowing to propose a 29 years-long sea ice thickness and volume time series. Estimates are combined with uncertainties derived from a Monte Carlo methodology. Nearly 30 years of sea ice volum...
Ce focus a été publié en ligne, dans le cadre du projet ANR BDL (1795-1932), à l'adresse suiv... more Ce focus a été publié en ligne, dans le cadre du projet ANR BDL (1795-1932), à l'adresse suivante :[http://bdl.ahp-numerique.fr/focus-histoire-fr-meteorologie-bdl
Cinq Voyages extraordinaires de Jules Verne, publies de 1855 a 1897, ont pour theme central les r... more Cinq Voyages extraordinaires de Jules Verne, publies de 1855 a 1897, ont pour theme central les regions polaires et cinq autres voyages se passent a un moment ou a un autre aux poles. En ce milieu du XIXe siecle, les poles sont encore loin d’etre atteints et les regions avoisinantes restent relativement peu connues. Quelques recits de voyage commencent a etre publies, Jules Verne va fortement s’en inspirer. Il va alors creer un monde « d’une sinistre beaute », oxymore qui traduit toute l’angoisse et la frayeur qui envahissent les explorateurs et toute la beaute qui neanmoins les fascine. La glace de Jules Verne, vit, bouge, danse avec la houle, elle est en perpetuel mouvement, ses formes varient brusquement, les couleurs du ciel, de la glace ou des animaux evoluent tres vite. Les phenomenes physiques : la refraction, la phosphorescence, l’electricite… participent aussi a cette sinistre beaute. Comment, a partir des quelques elements qu’il possede, Jules Verne su creer un monde fasci...
Reference Module in Earth Systems and Environmental Sciences, 2017
The Antarctic ice sheet represents a potential contribution to sea level rise. Understanding proc... more The Antarctic ice sheet represents a potential contribution to sea level rise. Understanding processes interacting on the ice sheet is fundamental to precisely determine its response to a rapid changing climate and estimate its present and future contribution to sea level change. Satellite altimetry and gravimetry have been providing with maps of spatial and temporal changes of the ice sheet elevation and mass. They reveal that several places in Antarctica are changing at an accelerating rate in response to current climate change. The future monitoring programs of the ice sheet will significantly improve our knowledge of the ice sheet.
Observations of giant ice rings on Lake Baikal (Russia) have recently sparked scientific and publ... more Observations of giant ice rings on Lake Baikal (Russia) have recently sparked scientific and public interest. However, there is still no clear consensus on their origins. Here, we provide an inventory of the ice rings based on satellite imagery and photography for 1974–2014. We have identified 45 rings on Lake Baikal (compared with 13 previously known) and also for the first time four rings for the neighbouring Lake Hovsgol (Mongolia). The results of our hydrographic surveys beneath the ice rings in Lake Baikal in 2012–2014 and in Lake Hovsgol in 2015 show the presence of warm double‐convex lens‐like eddies before and during manifestation of ice rings. We suggest that these eddies are the driving factor for the formation of ice rings in these lakes. We reassess the existing hypotheses of ice ring formation and discuss the potential mechanisms of eddy formation.
Abstract The scattering properties of the radar signal at Ka and Ku-band frequencies are investig... more Abstract The scattering properties of the radar signal at Ka and Ku-band frequencies are investigated using a theoretical model and snow grain observations obtained during previous field campaigns. Our results show that the combination of radar altimeters operating at these two frequencies should allow for the retrieval of snow depth over Arctic sea ice. We estimate uncertainties of the ice surface position in relation to crossover observations over sea ice and show that the accuracy of the crossover methodology with short time gap (3 days or less) is better than 3 cm. Comparison of the CryoSat-2/AltiKa retrieved snow depth with in situ measurements provided by Operation IceBridge shows a good agreement with a Root Mean Square Error (RMSE) of 5 cm. Analysis of the CryoSat-2/AltiKa retrieved snow depths over three winters (2013–2015) reveals a thinner snow cover on both Multi-Year (32%–57%) and First-Year Ice (63%–75%) relative to the 1954–91 Warren climatology, suggesting the need for more contemporary year-round and basin-scale snow depth fields.
ABSTRACT Sea ice leads play an essential role in ocean-ice-atmosphere exchange, in ocean circulat... more ABSTRACT Sea ice leads play an essential role in ocean-ice-atmosphere exchange, in ocean circulation, geochemistry and in ice dynamics. Their precise detection is crucial for altimetric estimations of sea ice thickness and volume. This study evaluates the performance of the SARAL/AltiKa altimeter to detect leads and to monitor their spatio-temporal dynamics. We show that a pulse peakiness parameter (PP) used to detect leads by Envisat RA-2 and ERS-1,-2 altimeters is not suitable because of saturation of AltiKa return echoes over the leads. The signal saturation results in loss of 6-10% of PP data over sea ice. We propose a different parameter: maximal power of waveform, and define the threshold to discriminate the leads. Our algorithm can be applied from December until May. It detects well the leads of small and medium size: from 200 m to 3-4 km. So, the combination of the high-resolution altimetric estimates with low-resolution thermal infra-red or radiometric lead fraction products could enhance the capability of remote sensing to monitor sea ice fracturing.
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Papers by Frederique Remy