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Qian, N. (author), Chang, Guobin (author), Ditmar, P.G. (author), Gao, Jingxiang (author), Wei, Zhengqiang (author)High-frequency and correlated noise filtering is one of the important preprocessing steps for GRACE level-2 products before calculating mass anomaly. Decorrelation and denoising kernel (DDK) filters are usually considered as such optimal filters to solve this problem. In this work, a sparse DDK filter is proposed. This is achieved by...journal article 2022
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Ditmar, P.G. (author)A novel technique has been developed to assess noise levels in GRACE-based mass anomaly time-series when the true signal is not known. The technique is based on computing an optimal combination of analyzed time-series in the presence of a regularization. To find the optimal weights associated with individual time-series, variance component...journal article 2022
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Ran, Jiangjun (author), Ditmar, P.G. (author), Liu, Lin (author), Xiao, Yun (author), Klees, R. (author), Tang, Xueyuan (author)Mascon products derived from Gravity Recovery and Climate Experiment satellite gravimetry data are widely used to study the Greenland ice sheet mass balance. However, the products released by different research groups—JPL, CSR, and GSFC—show noticeable discrepancies. To understand them, we compare those mascon products with mascon solutions...journal article 2021
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Guo, Xiang (author), Ditmar, P.G. (author), Zhao, Qile (author), Xiao, Yun (author)To monitor temporal variations of the Earth’s gravity field and mass transport in the Earth’s system, data from gravity recovery and climate experiment (GRACE) satellite mission and its successor GRACE Follow-On (GFO) are used. To fill in the temporal gap between these missions, other satellites’ kinematic orbits derived from GPS-based high...journal article 2020
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Sun, Y. (author), Riva, R.E.M. (author), Ditmar, P.G. (author), Rietbroek, Roelof (author)We present a new approach to estimate time variations in J2. Those variations are represented as the sum of contributions from individual sources. This approach uses solely Gravity Recovery And Climate Experiment (GRACE) data and the geoid fingerprints of mass redistributions that take place both at the surface and in the interior of the solid...journal article 2019
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Groh, Andreas (author), Horwath, Martin (author), Horvath, Alexander (author), Meister, Rakia (author), Wouters, B. (author), Ditmar, P.G. (author), Ran, J. (author), Klees, R. (author), Schrama, Ernst (author)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...journal article 2019
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Ditmar, P.G. (author)Time-varying Stokes coefficients estimated from GRACE satellite data are routinely converted into mass anomalies at the Earth’s surface with the expression proposed for that purpose by Wahr et al. (J Geophys Res 103(B12):30,205–30,229, 1998). However, the results obtained with it represent mass transport at the spherical surface of 6378 km...journal article 2018
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Ditmar, P.G. (author), Tangdamrongsub, N. (author), Ran, J. (author), Klees, R. (author)We propose a technique to regularize a GRACE-based mass-anomaly time-series in order to (i) quantify the Standard Deviation (SD) of random noise in the data, and (ii) reduce the level of that noise. The proposed regularization functional minimizes the Month-to-month Year-to-year Double Differences (MYDD) of mass anomalies. As such, it does...journal article 2018
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Ran, J. (author), Ditmar, P.G. (author), Klees, R. (author)The mascon approach is a well-known technique to estimate mass anomalies in Greenland using GRACE satellite gravity data. It partitions the area of interest into laterally-homogeneous patches (mascons). An important aspect of the mascon approach is the chosen geometry of mascons. So far, its impact has not been fully understood. In this study,...journal article 2018
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Ditmar, P.G. (author)A methodology has been developed to estimate the accuracy of GRACE monthly solutions as functions of space or time without using independent geophysical models. An application of the methodology to several commonly-used solution time-series reveals that the ITSG-Grace2016 solutions show the highest accuracy among those considered. Furthermore,...poster 2018
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Sun, Y. (author), Riva, R.E.M. (author), Ditmar, P.G. (author), Klees, R. (author)With the launch of the Gravity Recovery and Climate Experiment (GRACE) satellite mission in 2002 (http://www.csr.utexas.edu/grace), Satellite Gravimetry has become a unique tool to estimate hydrological water balance and mass balance of ice sheets, as well as to monitor mass re-distribution in the oceans and the solid Earth. However, satellite...poster 2018
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- Ditmar, P.G. (author), Brussee, M. (author), Sun, Y. (author), Riva, R.E.M. (author) other 2018
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- Ditmar, P.G. (author), Engels, Olga (author), Klees, R. (author) other 2018
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Ran, J. (author), Vizcaino, M. (author), Ditmar, P.G. (author), van den Broeke, Michiel R. (author), Moon, Twila (author), Steger, Christian (author), Enderlin, Ellyn (author), Wouters, Bert (author), Noël, Brice (author), Reijmer, Catharina (author), Klees, R. (author), Zhong, Min (author)The Greenland Ice Sheet (GrIS) is currently losing ice mass as the result of changes in the complex ice-climate interactions that have been driven by global climate change. In order to accurately predict future sea level rise, the mechanisms driving the observed mass loss must be better understood. Here, we combine data from the satellite...journal article 2018
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Guo, Xiang (author), Zhao, Qile (author), Ditmar, P.G. (author), Sun, Yu (author), Liu, Jingnan (author)The Gravity Recovery And Climate Experiment (GRACE) mission has achieved a quantum leap in knowledge of the Earth's gravity field. However, current gravity field solutions still cannot reach the prelaunch baseline accuracy. One of the reasons for that is the presence of colored noise in GRACE data, which is typically ignored in the classical...journal article 2018
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Sun, Y. (author), Ditmar, P.G. (author), Riva, R.E.M. (author)In this study, we develop a methodology to estimate monthly variations in degree-1 andC<sub>20</sub> coefficients by combing Gravity Recovery and Climate Experiment (GRACE) data withoceanic mass anomalies (combination approach).With respect to the method by Swenson et al.,the proposed approach exploits noise covariance information of both...journal article 2017
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Tangdamrongsub, N. (author), Steele-Dunne, S.C. (author), Gunter, B.C. (author), Ditmar, P.G. (author), Sutanudjaja, Edwin H. (author), Sun, Y. (author), Xia, Ting (author), Wang, Zhongjing (author)An accurate estimation of water resources dynamics is crucial for proper management of both agriculture and the local ecology, particularly in semi-arid regions. Imperfections in model physics, uncertainties in model land parameters and meteorological data, as well as the human impact on land changes often limit the accuracy of hydrological...journal article 2017
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Guo, X. (author), Ditmar, P.G. (author), Zhao, Q (author), Klees, R. (author), Farahani, H. (author)GPS data collected by satellite gravity missions can be used for extracting the long-wavelength part of the Earth’s gravity field. We propose a new data processing method which makes use of the ‘average acceleration’ approach to gravity field modelling. In this method, satellite accelerations are directly derived from GPS carrier phase...journal article 2017
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Hashemi Farahani, H. (author), Ditmar, P.G. (author), Miragaia Gomes Inacio, P. (author), Engels, Olga (author), Gunter, B.C. (author), Klees, R. (author), Guo, X. (author), Guo, Jing (author), Sun, Y. (author), Liu, Xianglin (author), Zhao, Qile (author), Riva, R.E.M. (author)We present a high resolution model of the linear trend in the Earth’s mass variations based on DMT-2 (Delft Mass Transport model, release 2). DMT-2 was produced primarily from K-Band Ranging (KBR) data of the Gravity Recovery And Climate Experiment (GRACE). It comprises a time series of monthly solutions complete to spherical harmonic degree 120...journal article 2017
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Ran, J. (author), Ditmar, P.G. (author), Klees, R. (author), Farahani, H. (author)We present an improved mascon approach to transform monthly spherical harmonic solutions based on GRACE satellite data into mass anomaly estimates in Greenland. The GRACE-based spherical harmonic coefficients are used to synthesize gravity anomalies at satellite altitude, which are then inverted into mass anomalies per mascon. The limited...journal article 2017