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3. The International DORIS Service after 20 years: Achievements and Look to the Future

Author

Lemoine, F., Moreaux, G., Stepanek, P., Capdeville, H., Otten, M., Dettmering, D., Soudarin, L., Saunier, J., Schrama, E., Sellé, A., and Ferrage, P.

Abstract

Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) is one of the four techniques of Space Geodesy that contributes to the International Terrestrial Reference Frame (ITRF).DORIS as an operational geodetic method began with the SPOT-2 satellite in 1990.Following the lead of the other techniques of space geodesy, the International DORIS Service (IDS) was accepted as a service of the International Association of Geodesy (IAG) in 2003.As with the other techniques, the goal of the IDS is to coordinate the analyses of DORIS data in a systematic way, organize the contributions of the technique to the development of different realizations of the ITRF,and work to continue to improve the quality of the data and products that are available. In this paper we review the development of scientific products that are provided by the DORIS technique. We highlight thecontributions to precise orbit determination (POD) for altimetric satellites, including its current performance with respect to the Sentinel-3A/B and Sentinel-6Asatellites.We review the improvements in the quality of the geodetic parameters, both in positioning and in the Earth Orientation Parameters with the successive ITRF realizations, as different technical and modelling improvements were implemented. We also discuss the continued challenges with respect to DORIS including the sensitivity of the DORIS USO to the South Atlantic Anomaly (SAA), the modelling strategies that have been developed to deal with this effect.Finallywe highlight also recent developments including a new focus on near-real-time products developed from DORIS data., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Published
2023
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4. Ocean mass change and its uncertainty from GRACE and GRACE-FO GSM data

Author

Schrama, E.

Abstract

The GRACE GRACE-FO project provides several science data products from which we use the monthly potential coefficient solutions release 6 and release 6.1 from the Center of Space Research at the University of Texas in Austin for a level-2 mascon method to estimate rates of mass change and uncertainties by selected area. Coefficient corrections for geo-center motions, low degree and order coefficients, glacial isostatic adjustment and hydrological corrections are applied to obtain water levels by mascon element since 2002. There are 10242 nodes in the solution in which case we use a direct in core solver, there is also a higher resolution set with 40962 nodes in which case a pre-conjugate gradient solver is used. Since mass conservation is ensured we can infer an ocean mass change from the mascon solutions. Our experience is that all GRACE and GRACE-FO GSM coefficient solutions exhibit leakage effects and that a compensation algorithm in the mascon method is effective in recovering the rates of mass loss over land. For the ocean domain we find that the rate of mass change should probably be around 750 +/- 60 Gt/yr for instance depending on the GIA model that is used. We discuss an update in the level-2 mascon method to compensate the ca 10% correction of ocean mass change., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Published
2023
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15. 605P Dutch LGMD registry: real-world data to facilitate trial readiness.

Author

Schrama, E., Hoek, R., Bongers, J., Straathof, C., Badrising, U., van Reenen, R., van der Kooi, A., van Duyvenvoorde, H., Krom, Y., and Niks, E.

Subjects
*LIMB-girdle muscular dystrophy, *MUSCLE weakness, *MUSCLE fatigue, *CARDIOVASCULAR agents, *GENETIC disorder diagnosis
Abstract

Limb-girdle muscular dystrophies (LGMD) are a heterogenic group of genetic conditions characterized by progressive proximal muscle weakness. The Dutch LGMD registry was established to gain insight in the epidemiology and disease course of the subtypes. Registration by written informed consent opened in July 2022. In 2024 it became possible to register via e-consent. The registry collects clinician- and patient-reported real-world data in accordance with the TREAT-NMD core dataset. Patient reported data are collected through yearly online questionnaires on diagnosis, first and current symptoms, disease milestones, cardiac and respiratory involvement, and medication use. On 29-03-2024, 111 participants (51% male) were included, with a mean age of 48.3y (range 11-81). Most common diagnoses were LGMD R12 (anoctamin 5, 22%), R1 (calpain 3, 17%) and R3 (α-sarcoglycan, 9%). Questionnaires were returned by 89 (81%). Mean reported age of onset was 24.9y (range 0-67). Mean age of clinical diagnoses was 33.5y (range 5-71). Muscle weakness was most frequently reported as first symptom (77%), followed by muscle fatigue (47%), myalgia (32%) and falls (27%). Current symptoms overlapped with initial symptoms: muscle weakness (88%), muscle fatigue (78%), myalgia (46%) and falls (39%). By contrast, 16% reported respiratory complaints as a current symptom and 11% reported swallowing difficulties, while this was uncommon as first symptom (0% and 1%, respectively). Invasive respiratory support was used by 2%, non-invasive by 8%. Cardiac medication was used by 26%. The majority of respondents were ambulant (68%), defined as the ability to walk 5 steps without support. Distribution of LGMD-subtypes in the registry is in accordance with previous data on genetic diagnoses in Netherlands suggesting representative sampling. The registry will serve as a tool to provide continuous data on natural history and epidemiology in Netherlands and facilitate treatment development. [ABSTRACT FROM AUTHOR]

Published
2024
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16. 648P MRI demonstrates altered skeletal muscle membrane permeability in Becker muscular dystrophy, representing a potential biomarker for disease activity.

Author

Schrama, E., Hooijmans, M., Niks, E., Kan, H., and Cameron, D.

Subjects
*BECKER muscular dystrophy, *NUCLEAR magnetic resonance spectroscopy, *MUSCULAR dystrophy, *MAGNETIC resonance imaging, *LEG muscles
Abstract

Magnetic resonance imaging (MRI)-derived fat fraction is widely used as a marker for disease progression in muscular dystrophies, including Becker muscular dystrophy (BMD), but reflects end-stage disease progression. We evaluated phosphorus magnetic resonance spectroscopy (31P-MRS) and multi-diffusion-time diffusion-tensor-(DT)-MRI as markers for disease activity. Thirteen BMD patients (20-59y) and 9 male controls (23-65y) underwent 31P-MRS and DT-MRI in the left lower-leg. Metabolite ratios of phosphocreatine to adenosine-triphosphate (ATP) and phosphodiesters (PDE) to ATP, weighted pH, and ionised magnesium ([Mg2+]) were calculated. In the DT-MRI data, regions of interest were drawn on fat-water images, and radial diffusivities per diffusion time were fitted with the random permeable barrier model (RPBM), producing membrane permeabilities and fibre diameters. Groups were compared via t-tests or Mann-Whitney U-tests, correlations were assessed via Pearson's r, and p<0.05 was considered statistically significant. Results are presented for the tibialis anterior muscle; analyses of other muscles are pending. Notably, 31P-MRS-derived [Mg2+] was lower in BMD versus controls: mean (SD)=0.63 (0.17) vs 0.86 (0.22) mM, respectively; p=0.022. PDE/γ-ATP was larger in patients versus controls: mean (SD)=0.36 (0.17) vs 0.22 (0.09), respectively; p=0.029. RPBM-DT-MRI showed similar permeabilities in patients versus controls—0.042 (0.033) vs 0.032 (0.021) μm/ms, respectively, p=0.410. RPBM fibre diameters were larger in patients, as reported previously. The reduced intramuscular [Mg2+] is likely due to membrane leakiness, and the increased PDE/ATP may reflect membrane phospholipid breakdown. Together, these results suggest greater membrane permeability in BMD and potential for 31P-MRS metrics as biomarkers of disease activity. Ongoing analysis will include the other lower leg muscles, relation to fat fraction, and 2-year follow-up data in this cohort of BMD patients. [ABSTRACT FROM AUTHOR]

Published
2024
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17. Total Land Water Storage Change over 2003 - 2013 Estimated from a Global Mass Budget Approach

Author

Dieng, H. B, Champollion, N, Cazenave, A, Wada, Y, Schrama, E, and Meyssignac, B

Subjects
Meteorology And Climatology
Abstract

We estimate the total land water storage (LWS) change between 2003 and 2013 using a global water mass budget approach. Hereby we compare the ocean mass change (estimated from GRACE space gravimetry on the one hand, and from the satellite altimetry-based global mean sea level corrected for steric effects on the other hand) to the sum of the main water mass components of the climate system: glaciers, Greenland and Antarctica ice sheets, atmospheric water and LWS (the latter being the unknown quantity to be estimated). For glaciers and ice sheets, we use published estimates of ice mass trends based on various types of observations covering different time spans between 2003 and 2013. From the mass budget equation, we derive a net LWS trend over the study period. The mean trend amounts to +0.30 +/- 0.18 mm/yr in sea level equivalent. This corresponds to a net decrease of −108 +/- 64 cu km/yr in LWS over the 2003-2013 decade. We also estimate the rate of change in LWS and find no significant acceleration over the study period. The computed mean global LWS trend over the study period is shown to be explained mainly by direct anthropogenic effects on land hydrology, i.e. the net effect of groundwater depletion and impoundment of water in man-made reservoirs, and to a lesser extent the effect of naturally-forced land hydrology variability. Our results compare well with independent estimates of human-induced changes in global land hydrology.

Published
2015
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18. DMD/BMD – OUTCOME MEASURES

Author

Schrama, E., primary, Koeks, Z., additional, van de Velde, N., additional, Kan, H., additional, Krom, Y., additional, van Duyvenvoorde, H., additional, and Niks, E., additional

Published
2021
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28. Evaluating GRACE mass change time series for the antarctic and Greenland ice sheet-methods and results

Author

Groh, A, Horwath, M, Horvath, A, Meister, R, Sørensen, LS, Barletta, VR, Forsberg, R, Wouters, B, Ditmar, P, Ran, J, Klees, R, Su, X, Shang, K, Guo, J, Shum, CK, Schrama, E, Shepherd, A, Sub Dynamics Meteorology, and Marine and Atmospheric Research

Subjects
grace, lcsh:QE1-996.5, Greenland, antarctica, ice mass change, methods, lcsh:Geology, GRACE, greenland, Methods, SDG 13 - Climate Action, Antarctica, Ice mass change
Abstract

Satellite gravimetry data acquired by the Gravity Recovery and Climate Experiment (GRACE) allows to derive the temporal evolution in ice mass for both the Antarctic Ice Sheet (AIS) and the Greenland Ice Sheet (GIS). Various algorithms have been used in a wide range of studies to generate Gravimetric Mass Balance (GMB) products. Results from different studies may be affected by substantial differences in the processing, including the applied algorithm, the utilised background models and the time period under consideration. This study gives a detailed description of an assessment of the performance of GMB algorithms using actual GRACE monthly solutions for a prescribed period as well as synthetic data sets. The inter-comparison exercise was conducted in the scope of the European Space Agency&rsquo, s Climate Change Initiative (CCI) project for the AIS and GIS, and was, for the first time, open to everyone. GMB products generated by different groups could be evaluated and directly compared against each other. For the period from 2003-02 to 2013-12, estimated linear trends in ice mass vary between &minus, 99 Gt/yr and &minus, 108 Gt/yr for the AIS and between &minus, 252 Gt/yr and &minus, 274 Gt/yr for the GIS, respectively. The spread between the solutions is larger if smaller drainage basins or gridded GMB products are considered. Finally, findings from the exercise formed the basis to select the algorithms used for the GMB product generation within the AIS and GIS CCI project.

Published
2019
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34. Global sea-level budget 1993-present

Author

Cazenave, Anny, Meyssignac, Benoit, Ablain, Michael, Balmaseda, Magdalena, Bamber, Jonathan, Barletta, Valentina, Beckley, Brian, Benveniste, Jerome, Berthier, Etienne, Blazquez, Alejandro, Boyer, Tim, Caceres, Denise, Chambers, Don, Champollion, Nicolas, Chao, Ben, Chen, Jianli, Cheng, Lijing, Church, John A., Chuter, Stephen, Cogley, J. Graham, Dangendorf, Soenke, Desbruyeres, Damien, Doell, Petra, Domingues, Catia, Falk, Ulrike, Famiglietti, James, Fenoglio-marc, Luciana, Forsberg, Rene, Galassi, Gaia, Gardner, Alex, Groh, Andreas, Hamlington, Benjamin, Hogg, Anna, Horwath, Martin, Humphrey, Vincent, Husson, Laurent, Ishii, Masayoshi, Jaeggi, Adrian, Jevrejeva, Svetlana, Johnson, Gregory, Kolodziejczyk, Nicolas, Kusche, Juergen, Lambeck, Kurt, Landerer, Felix, Leclercq, Paul, Legresy, Benoit, Leuliette, Eric, Llovel, William, Longuevergne, Laurent, Loomis, Bryant D., Luthcke, Scott B., Marcos, Marta, Marzeion, Ben, Merchant, Chris, Merrifield, Mark, Milne, Glenn, Mitchum, Gary, Mohajerani, Yara, Monier, Maeva, Monselesan, Didier, Nerem, Steve, Palanisamy, Hindumathi, Paul, Frank, Perez, Begona, Piecuch, Christopher G., Ponte, Rui M., Purkey, Sarah G., Reager, John T., Rietbroek, Roelof, Rignot, Eric, Riva, Riccardo, Roemmich, Dean H., Sorensen, Louise Sandberg, Sasgen, Ingo, Schrama, E. J. O., Seneviratne, Sonia I., Shum, C. K., Spada, Giorgio, Stammer, Detlef, Van De Wal, Roderic, Velicogna, Isabella, Von Schuckmann, Karina, Wada, Yoshihide, Wang, Yiguo, Watson, Christopher, Wiese, David, Wijffels, Susan, Westaway, Richard, Woppelmann, Guy, Wouters, Bert, Cazenave, Anny, Meyssignac, Benoit, Ablain, Michael, Balmaseda, Magdalena, Bamber, Jonathan, Barletta, Valentina, Beckley, Brian, Benveniste, Jerome, Berthier, Etienne, Blazquez, Alejandro, Boyer, Tim, Caceres, Denise, Chambers, Don, Champollion, Nicolas, Chao, Ben, Chen, Jianli, Cheng, Lijing, Church, John A., Chuter, Stephen, Cogley, J. Graham, Dangendorf, Soenke, Desbruyeres, Damien, Doell, Petra, Domingues, Catia, Falk, Ulrike, Famiglietti, James, Fenoglio-marc, Luciana, Forsberg, Rene, Galassi, Gaia, Gardner, Alex, Groh, Andreas, Hamlington, Benjamin, Hogg, Anna, Horwath, Martin, Humphrey, Vincent, Husson, Laurent, Ishii, Masayoshi, Jaeggi, Adrian, Jevrejeva, Svetlana, Johnson, Gregory, Kolodziejczyk, Nicolas, Kusche, Juergen, Lambeck, Kurt, Landerer, Felix, Leclercq, Paul, Legresy, Benoit, Leuliette, Eric, Llovel, William, Longuevergne, Laurent, Loomis, Bryant D., Luthcke, Scott B., Marcos, Marta, Marzeion, Ben, Merchant, Chris, Merrifield, Mark, Milne, Glenn, Mitchum, Gary, Mohajerani, Yara, Monier, Maeva, Monselesan, Didier, Nerem, Steve, Palanisamy, Hindumathi, Paul, Frank, Perez, Begona, Piecuch, Christopher G., Ponte, Rui M., Purkey, Sarah G., Reager, John T., Rietbroek, Roelof, Rignot, Eric, Riva, Riccardo, Roemmich, Dean H., Sorensen, Louise Sandberg, Sasgen, Ingo, Schrama, E. J. O., Seneviratne, Sonia I., Shum, C. K., Spada, Giorgio, Stammer, Detlef, Van De Wal, Roderic, Velicogna, Isabella, Von Schuckmann, Karina, Wada, Yoshihide, Wang, Yiguo, Watson, Christopher, Wiese, David, Wijffels, Susan, Westaway, Richard, Woppelmann, Guy, and Wouters, Bert

Abstract

Global mean sea level is an integral of changes occurring in the climate system in response to unforced climate variability as well as natural and anthropogenic forcing factors. Its temporal evolution allows changes (e.g.,acceleration) to be detected in one or more components. Study of the sea-level budget provides constraints on missing or poorly known contributions, such as the unsurveyed deep ocean or the still uncertain land water component. In the context of the World Climate Research Programme Grand Challenge entitled "Regional Sea Level and Coastal Impacts", an international effort involving the sea-level community worldwide has been recently initiated with the objective of assessing the various datasets used to estimate components of the sea-level budget during the altimetry era (1993 to present). These datasets are based on the combination of a broad range of space-based and in situ observations, model estimates, and algorithms. Evaluating their quality, quantifying uncertainties and identifying sources of discrepancies between component estimates is extremely useful for various applications in climate research. This effort involves several tens of scientists from about 50 research teams/institutions worldwide (www.wcrp-climate.org/grand-challenges/gc-sea-level, last access: 22 August 2018). The results presented in this paper are a synthesis of the first assessment performed during 2017-2018. We present estimates of the altimetry-based global mean sea level (average rate of 3.1 +/- 0.3mm yr(-1) and acceleration of 0.1 mm yr(-2) over 1993-present), as well as of the different components of the sea-level budget (http://doi.org/10.17882/54854, last access: 22 August 2018). We further examine closure of the sea-level budget, comparing the observed global mean sea level with the sum of components. Ocean thermal expansion, glaciers, Greenland and Antarctica contribute 42%, 21%, 15% and 8% to the global mean sea level over the 1993-present period. We also study t

Published
2018
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36. A preliminary evaluation of ocean topography from the TOPEX/POSEIDON mission

Author

Nerem, R. S, Schrama, E. J, Koblinsky, C. J, and Beckley, B

Subjects
Oceanography
Abstract

We have analyzed 50 ten-day cycles of TOPEX/POSEIDON (T/P) altimeter data to evaluate the ocean dynamic topography and its temporal variations. We have employed data from both the U.S. and French altimeters along with the NASA precision orbits in this analysis. Errors in the diurnal and semidiurnal components of the Cartwright-Ray tide model have been significantly reduced using a correction developed from a combination of JGM-2 and OSU91A was employed, as well as a geoid model based solely on OSU91A. The long wavelengths of the comparisons to historical data, although geoid error still corrupts the dynamic topography for wavelengths shorter than 2500 km. The root mean square (RMS) variability is similar to previous results from Geosat, with bakground 'noise' approaching 3 cm RMS. The computed annual and semiannual variations are also similar to previous Geosat results, although the hemispheric distribution of the annual heating cycle is much better presented in the T/P results. They also compare reasonably well with the Levitus hydrographic compilation in the northern hemisphere, although the T/P variations generally have larger amplitudes. Ten-day average maps of variations in sea level compare well with simulations measurements at ocean tide gauges, with RMS differences of less than 4 cm and correlations greater than 0.6 for most of the island gauges. Time-longitude plots of these sea level variations at different latitudes in the Pacific clearly show the presence of equatorial Kelvin waves and Rossby waves, with the wave speeds agreeing well with theoretical and observed values. Measurement of variations in global sea level over cycles 2-51 have an RMS variability of 6.3 mm and a rate of change of -3.5 +/- 8 mm/yr, the uncertainty primarily due to insufficient averaging of the interannual and periodic sea level variations. These results show that the accuracy of the T/P measurements of sea level has dramatically improved over previous missions, with estimated time variable errors of 4 cm or less. Although geographically correlated orbit errors have also been reduced to the few centimeter level, further improvement in determinations of the mean dynamic topography will be difficult to obtain until a more accurate model of the marine geoid is available.

Published
1994
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37. A preliminary tidal analysis of TOPEX/POSEIDON altimetry

Author

Schrama, E. J. O and Ray, R. D

Subjects
Oceanography
Abstract

Approximately 12 months of data from the TOPEX/POSEIDON satellite altimeter mission are analyzed for the major short-period oceanic tides. A harmonic analysis is performed on data captured within bins defined on a deep-ocean grid, which, owing to tidal aliasing considerations, must have a relatively coarse spatial resolution. Our analysis is in terms of corrections to the Schwiderski and Cartwright-Ray models, and it confirms many of the Schwiderski differences previously reported by Cartwright and Ray. Our differences with respect to the Geosat-based Cartwright and Ray model form a sectorial pattern in M(sub 2) with high/low differences separated roughly 180 deg in longitude. We suggest that these sectorial errors were most likely induced by Geosat's relatively large orbit error. Comparisons to independent data validate the improved TOPEX/POSEIDON solutions; in-situ 'ground truth' shows M(sub 2) root mean square (RMS) differences of 4.10 cm (Schwiderski), 3.86 cm (cartwright and Ray), 2.63 cm (this paper). Global rates of energy dissipation confirm earlier estimates for M(sub 2), and show improved agreement with satellite tracking studies for K(sub 1) and S(sub 2). These preliminary exercises confirm that TOPEX/POSEIDON should results in a new generation of improved global tidal models.

Published
1994
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38. Gravity field error analysis: Applications of GPS receivers and gradiometers on low orbiting platforms

Author

Schrama, E

Subjects
Geosciences (General)
Abstract

The concept of a Global Positioning System (GPS) receiver as a tracking facility and a gradiometer as a separate instrument on a low orbiting platform offers a unique tool to map the Earth's gravitational field with unprecedented accuracies. The former technique allows determination of the spacecraft's ephemeris at any epoch to within 3 to 10 cm, the latter permits the measurement of the tensor of second order derivatives of the gravity field to within 0.01 to 0.0001 Eotvos units depending on the type of gradiometer. First, a variety of error sources in gradiometry where emphasis is placed on the rotational problem pursuing as well a static as a dynamic approach is described. Next, an analytical technique is described and applied for an error analysis of gravity field parameters from gradiometer and GPS observation types. Results are discussed for various configurations proposed on Topex/Poseidon, Gravity Probe-B, and Aristoteles, indicating that GPS only solutions may be computed up to degree and order 35, 55, and 85 respectively, whereas a combined GPS/gradiometer experiment on Aristoteles may result in an acceptable solution up to degree and order 240.

Published
1990

39. CryoSat Land Ice Product Validation within the CryoVal-LI project

Author

Sandberg Sørensen, L., Baker, S., Csatho, B., Forsberg, R., Gourmelen, N., Helm, Veit, Langley, K., Martinez, B., Nienow, P., Schrama, E., Shepherd, A., Davidson, M., Simonsen, S. B., Sandberg Sørensen, L., Baker, S., Csatho, B., Forsberg, R., Gourmelen, N., Helm, Veit, Langley, K., Martinez, B., Nienow, P., Schrama, E., Shepherd, A., Davidson, M., and Simonsen, S. B.

Abstract

The main objective of the ESA funded CryoVal-LI project has been to identify and quantify the error sources for the CryoSat-2 mission over land ice. This has been undertaken through the careful documentation of the possible error sources, the identification of suitable validation sites and the creation of a public database containing validation data for these areas from recent ground and airborne field campaigns. These sites also offer considerable potential as sites on which to focus future validation efforts. Through the utilization of these observational datasets, an extensive comparative analysis has been carried out in which Cryosat-2 data has been evaluated against airborne and in-situ data. A number of different Cryosat-2 data sets have been included in this analysis with the goal of testing the performance of different processing and retracking algorithms. A similar, but smaller validation analysis has also been carried out for ICESat data. Here, we present the results of these analyses and outline the conclusions reached. Based on the findings from the project, a set of recommendations for the design of future land-ice/satellite validation campaigns will be given. Furthermore, the outcome of the re-tracker inter-comparison will be used to advocate a set of optimal re-tracking algorithms for Cryosat-2 in the next generation of L2 products.

Published
2016

41. Total land water storage change over 2003-2013 estimated from a global mass budget approach

Author

Dieng, H. B., Champollion, N., Cazenave, A., Wada, Y., Schrama, E., Meyssignac, B., Dieng, H. B., Champollion, N., Cazenave, A., Wada, Y., Schrama, E., and Meyssignac, B.

Abstract

We estimate the total land water storage (LWS) change between 2003 and 2013 using a global water mass budget approach. Hereby we compare the ocean mass change (estimated from GRACE space gravimetry on the one hand, and from the satellite altimetry-based global mean sea level corrected for steric effects on the other hand) to the sum of the main water mass components of the climate system: glaciers, Greenland and Antarctica ice sheets, atmospheric water and LWS (the latter being the unknown quantity to be estimated). For glaciers and ice sheets, we use published estimates of ice mass trends based on various types of observations covering different time spans between 2003 and 2013. From the mass budget equation, we derive a net LWS trend over the study period. The mean trend amounts to +0.30 ± 0.18 mm yr-1 in sea level equivalent. This corresponds to a net decrease of -108 ± 64 km3 yr-1 in LWS over the 2003-2013 decade. We also estimate the rate of change in LWS and find no significant acceleration over the study period. The computed mean global LWS trend over the study period is shown to be explained mainly by direct anthropogenic effects on land hydrology, i.e. the net effect of groundwater depletion and impoundment of water in man-made reservoirs, and to a lesser extent the effect of naturally-forced land hydrology variability. Our results compare well with independent estimates of human-induced changes in global land hydrology.

Published
2015

43. Antarctic contribution to sea level rise observed by GRACE with improved GIA correction

Author

Ivins, E., James, T., Wahr, J., O. Schrama, E., Landerer, F., and Simon, K.

Subjects
GRACE, sea level rise, ice sheet mass balance, Antarctica, GIA models, mantle viscosity
Abstract

Antarctic volume changes during the past 21 thousand years are smaller than previously thought, and here we construct an ice sheet history that drives a forward model prediction of the glacial isostatic adjustment (GIA) gravity signal. The new model, in turn, should give predictions that are constrained with recent uplift data. The impact of the GIA signal on a Gravity Recovery and Climate Experiment (GRACE) Antarctic mass balance estimate depends on the specific GRACE analysis method used. For the method described in this paper, the GIA contribution to the apparent surface mass change is re-evaluated to be +55±13 Gt/yr by considering a revised ice history model and a parameter search for vertical motion predictions that best fit the GPS observations at 18 high-quality stations. Although the GIA model spans a range of possible Earth rheological structure values, the data are not yet sufficient for solving for a preferred value of upper and lower mantle viscosity nor for a preferred lithospheric thickness. GRACE monthly solutions from the Center for Space Research Release 04 (CSR-RL04) release time series from January 2003 to the beginning of January 2012, uncorrected for GIA, yield an ice mass rate of +2.9± 29 Gt/yr. The new GIA correction increases the solved-for ice mass imbalance of Antarctica to ?57±34 Gt/yr. The revised GIA correction is smaller than past GRACE estimates by about 50 to 90 Gt/yr. The new upper bound to the sea level rise from the Antarctic ice sheet, averaged over the time span 2003.0–2012.0, is about 0.16±0.09 mm/yr.

Published
2013

49. Improved accuracy of GRACE gravity solutions through empirical orthogonal function filtering of spherical harmonics

Author

Wouters, B. and Schrama, E.

Subjects
GRACE, EOF, filtering
Abstract

One of the major problems one has to deal with when working with Gravity Recovery and Climate Experiment (GRACE) data is the increasing error spectrum at higher degrees in the provided Stokes coefficients, appearing as unphysical North?South striping patterns in the maps of equivalent water height (EWH). This phenomenon is commonly suppressed by application of a Gaussian smoothing filter, which unfortunately causes loss of signal and leakage between basins. In this paper we show how a significant amount of the striping can be removed by making use of the temporal characteristics of the error spectrum. The Stokes coefficients are decomposed using empirical orthogonal function analysis and the individual modes are tested for temporal noisiness. After filtering, maps of EWH are largely free of striping. Tests on simulated EWH estimates show that our filtering technique has a marginal effect on the predicted geophysical signal.

Published
2007

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