@article{KurtenbachEickerMayerGuerretal.2012,
  author    = {Kurtenbach, E. and Eicker, A. and Mayer-Guerr, T. and Holschneider, Matthias and Hayn, M. and Fuhrmann, M. and Kusche, J.},
  title     = {Improved daily GRACE gravity field solutions using a Kalman smoother},
  series = {Journal of geodynamics},
  volume    = {59},
  journal   = {Journal of geodynamics},
  number    = {3},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0264-3707},
  doi       = {10.1016/j.jog.2012.02.006},
  pages     = {39 -- 48},
  year      = {2012},
  abstract  = {Different GRACE data analysis centers provide temporal variations of the Earth's gravity field as monthly, 10-daily or weekly solutions. These temporal mean fields cannot model the variations occurring during the respective time span. The aim of our approach is to extract as much temporal information as possible out of the given GRACE data. Therefore the temporal resolution shall be increased with the goal to derive daily snapshots. Yet, such an increase in temporal resolution is accompanied by a loss of redundancy and therefore in a reduced accuracy if the daily solutions are calculated individually. The approach presented here therefore introduces spatial and temporal correlations of the expected gravity field signal derived from geophysical models in addition to the daily observations, thus effectively constraining the spatial and temporal evolution of the GRACE solution. The GRACE data processing is then performed within the framework of a Kalman filter and smoother estimation procedure. The approach is at first investigated in a closed-loop simulation scenario and then applied to the original GRACE observations (level-1B data) to calculate daily solutions as part of the gravity field model ITG-Grace2010. Finally, the daily models are compared to vertical GPS station displacements and ocean bottom pressure observations. From these comparisons it can be concluded that particular in higher latitudes the daily solutions contain high-frequent temporal gravity field information and represent an improvement to existing geophysical models.},
  language  = {en}
}
@misc{SinghSeitzEickeretal.2016,
  author    = {Singh, Alka and Seitz, Florian and Eicker, Annette and G{\"u}ntner, Andreas},
  title     = {Water budget analysis within the surrounding of prominent lakes and reservoirs from multi-sensor earth observation data and hydrological models},
  series = {remote sensing},
  journal   = {remote sensing},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-407902},
  pages     = {21},
  year      = {2016},
  abstract  = {The hydrological budget of a region is determined based on the horizontal and vertical water fluxes acting in both inward and outward directions. These integrated water fluxes vary, altering the total water storage and consequently the gravitational force of the region. The time-dependent gravitational field can be observed through the Gravity Recovery and Climate Experiment (GRACE) gravimetric satellite mission, provided that the mass variation is above the sensitivity of GRACE. This study evaluates mass changes in prominent reservoir regions through three independent approaches viz. fluxes, storages, and gravity, by combining remote sensing products, in-situ data and hydrological model outputs using WaterGAP Global Hydrological Model (WGHM) and Global Land Data Assimilation System (GLDAS). The results show that the dynamics revealed by the GRACE signal can be better explored by a hybrid method, which combines remote sensing-based reservoir volume estimates with hydrological model outputs, than by exclusive model-based storage estimates. For the given arid/ semi-arid regions, GLDAS based storage estimations perform better than WGHM.},
  language  = {en}
}
@article{SinghSeitzEickeretal.2016,
  author    = {Singh, Alka and Seitz, Florian and Eicker, Annette and G{\"u}ntner, Andreas},
  title     = {Water Budget Analysis within the Surrounding of Prominent Lakes and Reservoirs from Multi-Sensor Earth Observation Data and Hydrological Models: Case Studies of the Aral Sea and Lake Mead},
  series = {Remote sensing},
  volume    = {8},
  journal   = {Remote sensing},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2072-4292},
  doi       = {10.3390/rs8110953},
  pages     = {21},
  year      = {2016},
  abstract  = {The hydrological budget of a region is determined based on the horizontal and vertical water fluxes acting in both inward and outward directions. These integrated water fluxes vary, altering the total water storage and consequently the gravitational force of the region. The time-dependent gravitational field can be observed through the Gravity Recovery and Climate Experiment (GRACE) gravimetric satellite mission, provided that the mass variation is above the sensitivity of GRACE. This study evaluates mass changes in prominent reservoir regions through three independent approaches viz. fluxes, storages, and gravity, by combining remote sensing products, in-situ data and hydrological model outputs using WaterGAP Global Hydrological Model (WGHM) and Global Land Data Assimilation System (GLDAS). The results show that the dynamics revealed by the GRACE signal can be better explored by a hybrid method, which combines remote sensing-based reservoir volume estimates with hydrological model outputs, than by exclusive model-based storage estimates. For the given arid/ semi-arid regions, GLDAS based storage estimations perform better than WGHM.},
  language  = {en}
}
@article{BoergensGuentnerDobslawetal.2020,
  author    = {Boergens, Eva and G{\"u}ntner, Andreas and Dobslaw, Henryk and Dahle, Christoph},
  title     = {Quantifying the Central European droughts in 2018 and 2019 with GRACE Follow-On},
  series = {Geophysical research letters : GRL},
  volume    = {47},
  journal   = {Geophysical research letters : GRL},
  number    = {14},
  publisher = {American Geophysical Union},
  address   = {Washington, DC},
  issn      = {0094-8276},
  doi       = {10.1029/2020GL087285},
  pages     = {9},
  year      = {2020},
  abstract  = {The GRACE-FO satellites launched in May 2018 are able to quantify the water mass deficit in Central Europe during the two consecutive summer droughts of 2018 and 2019. Relative to the long-term climatology, the water mass deficits were-112 +/- 10.5 Gt in 2018 and-145 +/- 12 Gt in 2019. These deficits are 73\% and 94\% of the mean amplitude of seasonal water storage variations, which is so severe that a recovery cannot be expected within 1 year. The water deficits in 2018 and 2019 are the largest in the whole GRACE and GRACE-FO time span. Globally, the data do not show an offset between the two missions, which proves the successful continuation of GRACE by GRACE-FO and thus the reliability of the observed extreme events in Central Europe. This allows for a joint assessment of the four Central European droughts in 2003, 2015, 2018, and 2019 in terms of total water storage deficits.},
  language  = {en}
}