The Experts below are selected from a list of 7401 Experts worldwide ranked by ideXlab platform
Guillaume Ramillien - One of the best experts on this subject based on the ideXlab platform.
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the spatio temporal variability of groundwater storage in the amazon river basin
2019Co-Authors: Frederic Frappart, Andreas Güntner, Guillaume Ramillien, Thaise Emilio, J. Pfeffer, Javier Tomasella, Fabrice Papa, Juliana SchiettiAbstract:Abstract In large Tropical River basins such as the Amazon, groundwater plays a major role in the water and ecological cycles with large influences on the rainforest ecosystems and climate variability. However, due to the lack of monitoring networks, Amazon groundwater storage and its variability remain poorly known. Here, we provide an unprecedented direct estimate of the spatio-temporal variations of the anomaly of groundwater storage over the period January 2003 -September 2010 in the Amazon Basin by decomposing the total terrestrial water storage measured by the Gravity Recovery and Climate Experiment (GRACE) Mission into the individual contributions of other hydrological reservoirs, using multi-satellite data for the surface waters and floodplains and models outputs for the soil moisture. We show that the seasonal variations of groundwater storage represent between 20 and 35% of the terrestrial water storage seasonal volume variations of the Amazon. Larger seasonal amplitudes of groundwater storage (>450 mm) are found in the Alter do Chao and Ica aquifers in the central part of the Amazon Basin. Anomalies of groundwater storage exhibit a strong interannual variability (STD reaching 120 mm along the central corridor) during the study period in response to hydrologic variability and climatic events such as the extreme drought that occurred in 2005.
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application of the regional water mass variations from GRACE satellite gravimetry to large scale water management in africa
2014Co-Authors: Guillaume Ramillien, Frederic Frappart, Lucia SeoaneAbstract:Time series of regional 2° × 2° Gravity Recovery and Climate Experiment (GRACE) solutions of surface water mass change have been computed over Africa from 2003 to 2012 with a 10-day resolution by using a new regional approach. These regional maps are used to describe and quantify water mass change. The contribution of African hydrology to actual sea level rise is negative and small in magnitude (i.e., −0.1 mm/y of equivalent sea level (ESL)) mainly explained by the water retained in the Zambezi River basin. Analysis of the regional water mass maps is used to distinguish different zones of important water mass variations, with the exception of the dominant seasonal cycle of the African monsoon in the Sahel and Central Africa. The analysis of the regional solutions reveals the accumulation in the Okavango swamp and South Niger. It confirms the continuous depletion of water in the North Sahara aquifer at the rate of −2.3 km3/y, with a decrease in early 2008. Synergistic use of altimetry-based lake water volume with total water storage (TWS) from GRACE permits a continuous monitoring of sub-surface water storage for large lake drainage areas. These different applications demonstrate the potential of the GRACE Mission for the management of water resources at the regional scale.
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Evolution of high-latitude snow mass derived from the GRACE gravimetry Mission (2002-2004)
2013Co-Authors: Guillaume Ramillien, Sylvain Biancamaria, Nelly MognardAbstract:1 Abstract: Since March 2002, the GRACE Mission provides monthly global maps of geoid time-variations. These new data carry information on the continental water storage, including snow mass variations, with a ground resolution of ~600-700 km. We have computed monthly snow mass solutions from the inversion of the 22 GRACE geoids (04/2002- 05/2004). The inverse approach developed here allows to separate the soil waters from snow signal. These snow mass solutions are further compared to predictions from three global land surface models and snow depths derived from satellite microwave data. We find that the GRACE solutions correlate well with the high-latitude zones of strong accumulation of snow. Regional means computed for four large boreal basins (Yenisey, Ob, Mac Kenzie and Yukon) show
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time variations of equivalent water heights from GRACE Mission and in situ river stages in the amazon basin
2012Co-Authors: Flavio Vaz G De Almeida, Guillaume Ramillien, Stephane Calmant, Frederique Seyler, Denizar Blitzkow, Ana Cristina Oliveira Cancoro De Matos, Joecila Santos Da SilvaAbstract:Gravity Recovery and Climate Experiment (GRACE) Mission is dedicated to measuring temporal variations of the Earth's gravity field. In this study, the Stokes coefficients made available by Groupe de Recherche en Geodesie Spatiale (GRGS) at a 10-day interval were converted into equivalent water height (EWH) for a ~4-year period in the Amazon basin (from July-2002 to May-2006). The seasonal amplitudes of EWH signal are the largest on the surface of Earth and reach ~ 1250mm at that basin's center. Error budget represents ~130 mm of EWH, including formal errors on Stokes coefficient, leakage errors (12 ~ 21 mm) and spectrum truncation (10 ~ 15 mm). Comparison between in situ river level time series measured at 233 ground-based hydrometric stations (HS) in the Amazon basin and vertically-integrated EWH derived from GRACE is carried out in this paper. Although EWH and HS measure different water bodies, in most of the cases a high correlation (up to ~80%) is detected between the HS series and EWH series at the same site. This correlation allows adjusting linear relationships between in situ and GRACE-based series for the major tributaries of the Amazon river. The regression coefficients decrease from up to down stream along the rivers reaching the theoretical value 1 at the Amazon's mouth in the Atlantic Ocean. The variation of the regression coefficients versus the distance from estuary is analysed for the largest rivers in the basin. In a second step, a classification of the proportionality between in situ and GRACE time-series is proposed.
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GRACE estimates of sea surface height anomalies in the gulf of carpentaria australia
2008Co-Authors: Paul Tregoning, Kurt Lambeck, Guillaume RamillienAbstract:Abstract The Gulf of Carpentaria in northern Australia has a weather-driven annual periodic amplitude in sea surface height of ~ 0.4 m. Such a signal generates a mass variation that is readily detected by the GRACE Mission. We used this naturally occurring phenomenon over a region of ~ 2.6 × 10 5 km 2 to evaluate the accuracy of the GRACE estimates of temporal mass variation. Comparison of the Groupe de Recherche de Geodesie Spatiale 10-day GRACE solutions and observations from a nearby tide gauge show a correlation of 0.93, indicating that the GRGS GRACE solutions capture well the regional signal. On the other hand, the MOG2D-G barotropic model accounts for only ~ 50% of the non-gravitational annual signal, suggesting either deficiencies in the model or that some other non-barotropic process is occurring.
Frederic Frappart - One of the best experts on this subject based on the ideXlab platform.
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the spatio temporal variability of groundwater storage in the amazon river basin
2019Co-Authors: Frederic Frappart, Andreas Güntner, Guillaume Ramillien, Thaise Emilio, J. Pfeffer, Javier Tomasella, Fabrice Papa, Juliana SchiettiAbstract:Abstract In large Tropical River basins such as the Amazon, groundwater plays a major role in the water and ecological cycles with large influences on the rainforest ecosystems and climate variability. However, due to the lack of monitoring networks, Amazon groundwater storage and its variability remain poorly known. Here, we provide an unprecedented direct estimate of the spatio-temporal variations of the anomaly of groundwater storage over the period January 2003 -September 2010 in the Amazon Basin by decomposing the total terrestrial water storage measured by the Gravity Recovery and Climate Experiment (GRACE) Mission into the individual contributions of other hydrological reservoirs, using multi-satellite data for the surface waters and floodplains and models outputs for the soil moisture. We show that the seasonal variations of groundwater storage represent between 20 and 35% of the terrestrial water storage seasonal volume variations of the Amazon. Larger seasonal amplitudes of groundwater storage (>450 mm) are found in the Alter do Chao and Ica aquifers in the central part of the Amazon Basin. Anomalies of groundwater storage exhibit a strong interannual variability (STD reaching 120 mm along the central corridor) during the study period in response to hydrologic variability and climatic events such as the extreme drought that occurred in 2005.
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application of the regional water mass variations from GRACE satellite gravimetry to large scale water management in africa
2014Co-Authors: Guillaume Ramillien, Frederic Frappart, Lucia SeoaneAbstract:Time series of regional 2° × 2° Gravity Recovery and Climate Experiment (GRACE) solutions of surface water mass change have been computed over Africa from 2003 to 2012 with a 10-day resolution by using a new regional approach. These regional maps are used to describe and quantify water mass change. The contribution of African hydrology to actual sea level rise is negative and small in magnitude (i.e., −0.1 mm/y of equivalent sea level (ESL)) mainly explained by the water retained in the Zambezi River basin. Analysis of the regional water mass maps is used to distinguish different zones of important water mass variations, with the exception of the dominant seasonal cycle of the African monsoon in the Sahel and Central Africa. The analysis of the regional solutions reveals the accumulation in the Okavango swamp and South Niger. It confirms the continuous depletion of water in the North Sahara aquifer at the rate of −2.3 km3/y, with a decrease in early 2008. Synergistic use of altimetry-based lake water volume with total water storage (TWS) from GRACE permits a continuous monitoring of sub-surface water storage for large lake drainage areas. These different applications demonstrate the potential of the GRACE Mission for the management of water resources at the regional scale.
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time variations of the regional evapotranspiration rate from gravity recovery and climate experiment GRACE satellite gravimetry
2006Co-Authors: Guillaume Ramillien, Andreas Güntner, Frederic Frappart, Anny Cazenave, Thanh Ngoduc, K LavalAbstract:Since its launch in March 2002, the GRACE Mission is measuring the global time variations of the Earth's gravity field with a current resolution of ~500 km. Especially over the continents, these measurements represent the integrated land water mass including surface waters (lakes, wetlands and rivers), soil moisture, groundwater and snow cover. In this study, we use the GRACE land water solutions computed by Ramillien et al. (2005a) through an iterative inversion of monthly geoids from April 2002 to May 2004, to estimate time-series of basin-scale regional evapotranspiration rate -and associated uncertainties-. Evapotranspiration is determined by integrating and solving the water mass balance equation, which relates land water storage (from GRACE), precipitation data (from the Global Precipitation Climatology Centre), runoff (from a global land surface model) and evapotranspiration (the unknown). We further examine the sensibility of the computation when using different model runoff. Evapotranspiration results are compared to outputs of four different global land surface models. The overall satisfactory agreement between GRACE-derived and model-based evapotranspiration prove the ability of GRACE to provide realistic estimates of this parameter.
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Evolution of high-latitude snow mass derived from the GRACE gravimetry Mission (2002-2004)
2006Co-Authors: Frederic Frappart, Guillaume Ramillien, Sylvain Biancamaria, Nelly Mognard-campbell, Anny CazenaveAbstract:Since March 2002, the GRACE Mission provides monthly global maps of geoid time-variations. These new data carry information on the continental water storage, including snow mass variations, with a ground resolution of ~600-700 km. We have computed monthly snow mass solutions from the inversion of the 22 GRACE geoids (04/2002 - 05/2004). The inverse approach developed here allows to separate the soil waters from snow signal. These snow mass solutions are further compared to predictions from three global land surface models and snow depths derived from satellite microwave data. We find that the GRACE solutions correlate well with the high-latitude zones of strong accumulation of snow. Regional means computed for four large boreal basins (Yenisey, Ob, Mac Kenzie and Yukon) show a good agreement at seasonal scale between the snow mass solutions and model predictions (global rms ~30-40 mm of equivalent-water height and ~10-20 mm regionally).
Sylvain Biancamaria - One of the best experts on this subject based on the ideXlab platform.
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Total water storage variability from GRACE Mission and hydrological models for a 50,000 km2 temperate watershed: the Garonne River basin (France)
2019Co-Authors: Sylvain Biancamaria, Moussa Mballo, Patrick Le Moigne, Jose-miguel Sanchez-perez, Grégory Espitalier-noël, Youen Grusson, Roxelane Cakir, Vincent Häfliger, Florian Barathieu, Marhiu TrasmonteAbstract:Study Region Garonne Basin, France. Study Focus This study analyses water mass variations for the whole Garonne basin (50,000 km2 drainage area). To do so, Total Water Storage Anomalies (TWSA) from seven global solutions based on the Gravity Recovery And Climate Experiment (GRACE) satellite Mission measurements (˜300 km spatial resolution) are inter-compared with TWSA from two hydrological models, SAFRAN-ISBA-MODCOU (SIM) and Soil and Water Assessment Tool (SWAT), between January 2003 and December 2010. New Hydrological Insights for the Region Despite the small size of the Garonne basin compared to GRACE spatial resolution, good agreement between GRACE solutions and hydrological model TWSA has been found (maximum correlation coefficient ˜0.9 and Nash-Sutcliffe Efficiency, NSE, ˜0.7). These datasets showed that TWSA in the Garonne basin is mainly due to water stored in the first dozen meters of soil and in the shallow aquifer. To a smaller extent, snow also influences Garonne TWSA. Open surface water TWSA is quite small and TWSA from deep aquifer is negligible. The most important drought period occurred in 2011/2012, due to low precipitation during the two hydrological years and ETR close to previous years. Important precipitation in 2013/2014 helps to refill the water stocks. This study also showed that GRACE and models mismatches should be due to GRACE poor spatial resolution, but also to its monthly time resolution (rarely shown in previous studies).
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Evolution of high-latitude snow mass derived from the GRACE gravimetry Mission (2002-2004)
2013Co-Authors: Guillaume Ramillien, Sylvain Biancamaria, Nelly MognardAbstract:1 Abstract: Since March 2002, the GRACE Mission provides monthly global maps of geoid time-variations. These new data carry information on the continental water storage, including snow mass variations, with a ground resolution of ~600-700 km. We have computed monthly snow mass solutions from the inversion of the 22 GRACE geoids (04/2002- 05/2004). The inverse approach developed here allows to separate the soil waters from snow signal. These snow mass solutions are further compared to predictions from three global land surface models and snow depths derived from satellite microwave data. We find that the GRACE solutions correlate well with the high-latitude zones of strong accumulation of snow. Regional means computed for four large boreal basins (Yenisey, Ob, Mac Kenzie and Yukon) show
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Evolution of high-latitude snow mass derived from the GRACE gravimetry Mission (2002-2004)
2006Co-Authors: Frederic Frappart, Guillaume Ramillien, Sylvain Biancamaria, Nelly Mognard-campbell, Anny CazenaveAbstract:Since March 2002, the GRACE Mission provides monthly global maps of geoid time-variations. These new data carry information on the continental water storage, including snow mass variations, with a ground resolution of ~600-700 km. We have computed monthly snow mass solutions from the inversion of the 22 GRACE geoids (04/2002 - 05/2004). The inverse approach developed here allows to separate the soil waters from snow signal. These snow mass solutions are further compared to predictions from three global land surface models and snow depths derived from satellite microwave data. We find that the GRACE solutions correlate well with the high-latitude zones of strong accumulation of snow. Regional means computed for four large boreal basins (Yenisey, Ob, Mac Kenzie and Yukon) show a good agreement at seasonal scale between the snow mass solutions and model predictions (global rms ~30-40 mm of equivalent-water height and ~10-20 mm regionally).
Jurgen Kusche - One of the best experts on this subject based on the ideXlab platform.
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a hybrid approach for recovering high resolution temporal gravity fields from satellite laser ranging
2021Co-Authors: Anno Locher, Jurgen KuscheAbstract:A new approach to recover time-variable gravity fields from satellite laser ranging (SLR) is presented. It takes up the concept of lumped coefficients by representing the temporal changes of the Earth’s gravity field by spatial patterns via combinations of spherical harmonics. These patterns are derived from the GRACE Mission by decomposing the series of monthly gravity field solutions into empirical orthogonal functions (EOFs). The basic idea of the approach is then to use the leading EOFs as base functions in the gravity field modelling and to adjust the respective scaling factors straightforward within the dynamic orbit computation; only for the lowest degrees, the spherical harmonic coefficients are estimated separately. As a result, the estimated gravity fields have formally the same spatial resolution as GRACE. It is shown that, within the GRACE time frame, both the secular and the seasonal signals in the GRACE time series are reproduced with high accuracy. In the period prior to GRACE, the SLR solutions are in good agreement with other techniques and models and confirm, for instance, that the Greenland ice sheet was stable until the late 1990s. Further validation is done with the first monthly fields from GRACE Follow-On, showing a similar agreement as with GRACE itself. Significant differences to the reference data only emerge occasionally when zooming into smaller river basins with strong interannual mass variations. In such cases, the approach reaches its limits which are set by the low spectral sensitivity of the SLR satellites and the strong constraints exerted by the EOFs. The benefit achieved by the enhanced spatial resolution has to be seen, therefore, primarily in the proper capturing of the mass signal in medium or large areas rather than in the opportunity to focus on isolated spatial details.
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mapping probabilities of extreme continental water storage changes from space gravimetry
2016Co-Authors: Jurgen Kusche, Annette Eicker, Ehsan Forootan, Anne Springer, Laurent LonguevergneAbstract:Using data from the Gravity Recovery And Climate Experiment (GRACE) Mission, we derive statistically robust “hot spot” regions of high probability of peak anomalous—i.e., with respect to the seasonal cycle—water storage (of up to 0.7 m one-in-five-year return level) and flux (up to 0.14 m/month). Analysis of, and comparison with, up to 32 years of ERA-Interim reanalysis fields reveals generally good agreement of these hot spot regions to GRACE results and that most exceptions are located in the tropics. However, a simulation experiment reveals that differences observed by GRACE are statistically significant, and further error analysis suggests that by around the year 2020, it will be possible to detect temporal changes in the frequency of extreme total fluxes (i.e., combined effects of mainly precipitation and floods) for at least 10–20% of the continental area, assuming that we have a continuation of GRACE by its follow-up GRACE Follow-On (GRACE-FO) Mission.
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Can GPS-Derived Surface Loading Bridge a GRACE Mission Gap?
2014Co-Authors: Roelof Rietbroek, Jurgen Kusche, Frank Flechtner, Mathias Fritsche, Christoph Dahle, Sandra-esther Brunnabend, Madlen Behnisch, Jens Schröter, Reinhard DietrichAbstract:We investigated two ‘gap-filler’ methods based on GPS-derived low-degree surface loading variations (GPS-I and GPS-C) and a more simple method (REF-S) which extends a seasonal harmonic variation into the expected Gravity Recovery and Climate Experiment (GRACE) Mission gap. We simulated two Mission gaps in a reference solution (REF), which is derived from a joint inversion of GRACE (RL05) data, GPS-derived surface loading and simulated ocean bottom pressure. The GPS-I and GPS-C methods both have a new type of constraint applied to mitigate the lack of GPS station network coverage over the ocean. To obtain the GPS-C solution, the GPS-I method is adjusted such that it fits the reference solution better in a 1.5 year overlapping period outside of the gap. As can be expected, the GPS-I and GPS-C solutions contain larger errors compared to the reference solution, which is heavily constrained by GRACE. Within the simulated gaps, the GPS-C solution generally fits the reference solution better compared to the GPS-I method, both in terms of spherical harmonic loading coefficients and in terms of selected basin-averaged hydrological mass variations. Depending on the basin, the RMS-error of the water storage variations (scaled for leakage effects) ranges between 1.6 cm (Yukon) and 15.3 cm (Orinoco). In terms of noise level, the seasonal gap-filler method (REF-S) even outperforms the GPS-I and GPS-C methods, which are still affected by spatial aliasing problems. However, it must be noted that the REF-S method cannot be used beyond the study of simple harmonic seasonal variations.
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surface mass redistribution inversion from global gps deformation and gravity recovery and climate experiment GRACE gravity data
2005Co-Authors: Jurgen Kusche, E J O SchramaAbstract:Monitoring hydrological redistributions through their integrated gravitational effect is the primary aim of the Gravity Recovery and Climate Experiment (GRACE) Mission. Time?variable gravity data from GRACE can be uniquely inverted to hydrology, since mass transfers located at or near the Earth's surface are much larger on shorter timescales than those taking place within the deeper Earth and because one can remove the contribution of atmospheric masses from air pressure data. Yet it has been proposed that at larger scales this may be achieved independently by measuring and inverting the elastic loading associated with redistributing masses, e.g., with the global network of the International GPS Service (IGS). This is particularly interesting as long as GRACE monthly gravity solutions do not (yet) match the targeted baseline accuracies at the lower spherical harmonic degrees. In this contribution (1) we describe and investigate an inversion technique which can deal jointly with GPS data and monthly GRACE solutions. (2) Previous studies with GPS data have used least squares estimators and impose solution constraints through low?degree spherical harmonic series truncation. Here we introduce a physically motivated regularization method that guarantees a stable inversion up to higher degrees, while seeking to avoid spatial aliasing. (3) We apply this technique to GPS data provided by the IGS service covering recent years. We can show that after removing the contribution ascribed to atmospheric pressure loading, estimated annual variations of continental?scale mass redistribution exhibit pattern similar to those observed with GRACE and predicted by a global hydrology model, although systematic differences appear to be present. (4) We compute what the relative contribution of GRACE and GPS would be in a joint inversion: Using current error estimates, GPS could contribute with up to 60% to degree 2 till 4 spherical harmonic coefficients and up to 30% for higher?degree coefficients.
Isabella Velicogna - One of the best experts on this subject based on the ideXlab platform.
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detection of sea level fingerprints derived from GRACE gravity data
2017Co-Authors: Chiawei Hsu, Isabella VelicognaAbstract:Mass changes of ice sheets, glaciers, ice caps, land water hydrology, atmosphere, and ocean cause a non-uniform sea level rise due to the gravitational and self-attraction and loading effects, called sea level fingerprints (SLF). SLF have been previously derived from a combination of modeled and observed mass fluxes from the continents into the ocean. Here, we derive improved SLF from time series of time-variable gravity data from the GRACE Mission for April 2002-October 2014. We evaluate the GRACE-derived SLF using Ocean Bottom Pressure (OBP) data from stations in the tropics, where OBP errors are the lowest. We detect the annual phase of the SLF in the OBP signal and separate it unambiguously from the barystatic sea level (BSL) at two stations. At the basin scale, the SLF explain a larger fraction of the variance in steric-corrected altimetry than the BSL, which has implications for evaluating mass transport between ocean basins.
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time variable gravity observations of ice sheet mass balance precision and limitations of the GRACE satellite data
2013Co-Authors: Isabella Velicogna, John WahrAbstract:Time-variable gravity data from the Gravity Recovery and Climate Experiment (GRACE) Mission have been available since 2002 to estimate the mass balance of the Greenland and Antarctic Ice Sheets. We analyze current progress and uncertainties in GRACE estimates of ice sheet mass balance. We discuss the impacts of errors associated with spherical harmonic truncation, spatial averaging, temporal sampling, and leakage from other time-dependent signals (e.g., glacial isostatic adjustment (GIA)). The largest sources of error for Antarctica are the GIA correction, the oMission of l=1 terms, nontidal changes in ocean mass, and measurement errors. For Greenland, the errors come mostly from the uncertainty in the scaling factor. Using Release 5.0 (RL05) GRACE fields for January 2003 through November 2012, we find a mass change of −258 ± 41 Gt/yr for Greenland, with an acceleration of −31 ± 6 Gt/yr2, and a loss that migrated clockwise around the ice sheet margin to progressively affect the entire periphery. For Antarctica, we report changes of −83 ± 49 and −147 ± 80 Gt/yr for two GIA models, with an acceleration of −12 ± 9 Gt/yr2 and a dominance from the southeast pacific sector of West Antarctica and the Antarctic Peninsula.
