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Featured researches published by Imen Turki.


Hydrological Sciences Journal-journal Des Sciences Hydrologiques | 2014

Hydrological variability of major French rivers over recent decades, assessed from gauging station and GRACE observations

L. Chevalier; Benoit Laignel; Nicolas Massei; S. Munier; M. Becker; Imen Turki; A. Coynel; A. Cazenave

Abstract This study was carried out in the framework of the Surface Water and Ocean Topography (SWOT) programme of the French National Centre of Space Studies (CNES). Based on discharge measurements and Gravity Recovery and Climate Experiment (GRACE) determination of total water storage (TWS), we have investigated the hydrological variability of the main French drainage basins (Seine, Loire, Garonne and Rhône) using a wavelet approach (continuous wavelet analyses and wavelet coherence analyses). The results of this analysis have shown a coherence ranging between 82% and 90% for TWS and discharge, thus demonstrating the potential use of TWS for characterization of the hydrological variability of French rivers. Strong coherence between the four basin discharges (between 73% and 92%) and between their associated TWS data (from 82% to 98%) suggested a common external influence on hydrological variability. To determine this influence, we investigated the relationship between hydrological variability and the North Atlantic Oscillation (NAO), considered as an index of prevailing climate in Europe. Basin discharges show strong coherence with NAO, ranging between 64% and 72% over the period 1959–2010. The coherence between NAO and TWS was 62% to 67% for 2003–2009. This is similar to the coherence between NAO and basin discharges detected for the same period. According to these results, strong influence of the NAO was clearly observed on the TWS and discharges of the major French river basins. Editor Z.W. Kundzewicz


IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing | 2015

On the Investigation of the Sea-Level Variability in Coastal Zones Using SWOT Satellite Mission: Example of the Eastern English Channel (Western France)

Imen Turki; Benoit Laignel; Laetitia Chevalier; Stéphane Costa; Nicolas Massei

The future mission of surface water and ocean topography (SWOT), launched in 2020 over a period of 3-5 years, will be designated to address the issue of combining surface water hydrology with physical oceanography aiming to present new perspectives of applications for coastal areas. The extent to which the synthetic SWOT measurements can reproduce the temporal variability of the sea level was investigated. The eastern English Channel (NW France) was considered as a case of application. The hourly sea-level records were filtered from the aliased harmonic tides by classic harmonic analyses to obtain the nontidal residual. This residual was used to simulate synthetically the satellite samples based on the number of overpasses per repeat cycle at each geographical station. Both real and synthetic SWOT measurements were compared by the use of different approaches of inference statistics and wavelets. The statistical behavior, deduced from the functions of probability density (pdf) and cumulative distribution (cdf), shows correlations between 65% and 75% for hourly measurements, which increase to 85% for monthly average ones. The frequency of positive and negative extreme values is under-estimated with an order less than 25%. The potential use of SWOT depends on the number of measurements and the sampling interval between SWOT overpasses per repeat orbit. In the time- frequency domain, the wavelet multiresolution analysis of the nontidal sea level displays four components: 1) 1 year; 2) ~4-7 month; 3) ~2-3 month; and 4) <;2 month bands. Such modes seem to be well manifested by SWOT samples with a mean explained variance more than 75%. The aliasing frequency of the altimeter generates a dispersion and an overexpression of the energy spectrum, which increases with the number of overpasses per repeat orbit and the high frequency (~2-3 and <;2 month bands). The reconstructed wavelet components evidence the capacity of SWOT to estimate the annual and the seasonal variability of the nontidal sea level. In particular, SWOT is able to reproduce the most of extreme storm surges in the English Channel. The main finding of this research clearly shows the utility of SWOT satellite altimetry in observing and understanding the sea-level variability and storm surges, complementing tide-gauge observations for the validation and improvement of coastal models.


Remote Sensing | 2018

Monitoring Sea Level and Topography of Coastal Lagoons Using Satellite Radar Altimetry: The Example of the Arcachon Bay in the Bay of Biscay

Edward Salameh; Frédéric Frappart; Vincent Marieu; Alexandra Spodar; Jean-Paul Parisot; Vincent Hanquiez; Imen Turki; Benoit Laignel

Radar altimetry was initially designed to measure the marine geoid. Thanks to the improvement in the orbit determination from the meter to the centimeter level, this technique has been providing accurate measurements of the sea surface topography over the open ocean since the launch of Topex/Poseidon in 1992. In spite of a decrease in the performance over land and coastal areas, it is now commonly used over these surfaces. This study presents a semi-automatic method that allows us to discriminate between acquisitions performed at high tides and low tides. The performances of four radar altimetry missions (ERS-2, ENVISAT, SARAL, and CryoSat-2) were analyzed for the retrieval of sea surface height and, for the very first time, of the intertidal zone topography in a coastal lagoon. The study area is the Arcachon Bay located in the Bay of Biscay. The sea level variability of the Arcachon Bay is characterized by a standard deviation of 1.05 m for the records used in this study (2001–2017). Sea surface heights are very well retrieved for SARAL (R~0.99 and RMSE 0.93 and RMSE 0.82 but with a higher RMSE >0.92 m). For the topography of the intertidal zone, very good estimates were also obtained using SARAL (R~0.71) and CryoSat-2 (R~0.79) with RMSE lower than 0.44 m for both missions.


Journal of Applied Remote Sensing | 2018

Time variability of hydrodynamics and potential use of surface water and ocean topography mission in estuarine macrotidal system: example of Seine estuary

Laetitia Chevalier; Benoit Laignel; Imen Turki; Florent Lyard; Christine Lion

Abstract. This work was supported by the National Center for Space Studies in the framework of the future mission surface water and ocean topography (SWOT). The estuarine zones with their complex hydrodynamics represent a great challenge for the future SWOT mission. The Seine estuary was selected by the SWOT Science Definition Team for the calibration/validation of the mission. Thus the aim of this study is to investigate the temporal hydrodynamic variability in the Seine estuary and the SWOT ability to reproduce this variability and hydrodynamic phenomena. For this, we used several statistical techniques and frequency analyses applied on the tide-gauge measurements of the Seine estuary and on SWOT simulated data. SWOT samples (SWOT simulated data) have been extracted synthetically from observations using the number of overpasses per repeat cycle [21 days (d)] in order to study the ability of SWOT to reproduce the time variability of the hydrodynamics. Results have demonstrated similar frequencies of multiyear, annual, and intraannual along the estuary from the Seine discharge to the Cherbourg sea level. The 11- to 22-d frequency has been only observed for estuarine and coastal time series suggesting the tide effect in these contexts. The distribution of levels has shown a high influence of tides and discharges at the downstream and the upstream, respectively. Low frequencies of water level are explained by the climate patterns of North Atlantic Oscillation with a mean range of 65%, whereas the high frequencies are associated to the periods of flooding and stormy events. Finally, simulated SWOT samples of water level show a better restitution of observations for high overpasses number. The results have shown a better restitution of hydrodynamic variability by SWOT in the river and upstream of estuary than in the downstream of estuary and coastal zone: in the estuary downstream and the coast, the annual mode is underexpressed while the 3-month (m) mode is overexpressed, which means the annual mode is underestimated and the 3-m mode is amplified by SWOT.


Physio-Géo. Géographie physique et environnement | 2013

Changements climatiques au Maghreb : vers des conditions plus humides et plus chaudes sur le littoral algérien ?

Zeineddine Nouaceur; Benoit Laignel; Imen Turki


Atmosphere | 2016

Characterization of the Interannual Variability of Precipitation and Streamflow in Tensift and Ksob Basins (Morocco) and Links with the NAO

Zineb Zamrane; Imen Turki; Benoit Laignel; Gil Mahé; Nour-Eddine Laftouhi


Arabian Journal of Geosciences | 2016

Investigating possible links between the North Atlantic Oscillation and rainfall variability in Marrakech (Morocco)

Imen Turki; Benoit Laignel; Nour-Eddine Laftouhi; Zeneddine Nouaceur; Zineb Zamrane


Arabian Journal of Geosciences | 2016

Hydrological variability of the Soummam watershed (Northeastern Algeria) and the possible links to climate fluctuations

Imen Turki; Benoit Laignel; Nicolas Massei; Zeneddine Nouaceur; Nadir Benhamiche; Khodir Madani


Ocean Dynamics | 2015

A new hybrid model for filling gaps and forecast in sea level: application to the eastern English Channel and the North Atlantic Sea (western France)

Imen Turki; Benoit Laignel; Nabil Kakeh; Laetitia Chevalier; Stéphane Costa


Archive | 2015

On the Investigation of the Sea-Level Variability in Coastal Zones Using SWOT Satellite Mission: Example of the Eastern English Channel

Imen Turki; Benoit Laignel; Laetitia Chevalier; Stéphane Costa; Nicolas Massei

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Nabil Kakeh

Polytechnic University of Catalonia

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A. Cazenave

University of Toulouse

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A. Coynel

University of Bordeaux

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