Abstract
Time-variable gravity field models derived from observations of the Gravity Recovery and Climate Experiment (GRACE) mission, whose science operations phase ended in June 2017 after more than 15 years, enabled a multitude of studies of Earth’s surface mass transport processes and climate change. The German Research Centre for Geosciences (GFZ), routinely processing such monthly gravity fields as part of the GRACE Science Data System, has reprocessed the complete GRACE mission and released an improved GFZ GRACE RL06 monthly gravity field time series. This study provides an insight into the processing strategy of GFZ RL06 which has been considerably changed with respect to previous GFZ GRACE releases, and modifications relative to the precursor GFZ RL05a are described. The quality of the RL06 gravity field models is analyzed and discussed both in the spectral and spatial domain in comparison to the RL05a time series. All results indicate significant improvements of about 40% in terms of reduced noise. It is also shown that the GFZ RL06 time series is a step forward in terms of consistency, and that errors of the gravity field coefficients are more realistic. These findings are confirmed as well by independent validation of the monthly GRACE models, as done in this work by means of ocean bottom pressure in situ observations and orbit tests with the GOCE satellite. Thus, the GFZ GRACE RL06 time series allows for a better quantification of mass changes in the Earth system.
Highlights
During more than 15 years (April 2002 through June 2017) of successful science operations phase, the Gravity Recovery and Climate Experiment (GRACE) mission enabled breakthroughs in monitoring the terrestrial water cycle (e.g., [1,2]), ice sheet and glacier mass balances (e.g., [3,4]), sea-level change (e.g., [5,6]) and ocean bottom pressure variations (e.g., [7,8])
Most of the results shown are relative to a climatology model which has been estimated as follows: The dominating signal content of the time series is approximated by fitting a proper parameter model coefficient-wise to the monthly solutions
GFZ has reprocessed an improved monthly gravity field time series for the complete GRACE mission consisting of 163 gravity field models (Level-2 products) in the period from April 2002 through June 2017
Summary
During more than 15 years (April 2002 through June 2017) of successful science operations phase, the Gravity Recovery and Climate Experiment (GRACE) mission enabled breakthroughs in monitoring the terrestrial water cycle (e.g., [1,2]), ice sheet and glacier mass balances (e.g., [3,4]), sea-level change (e.g., [5,6]) and ocean bottom pressure variations (e.g., [7,8]). A comprehensive overview of numerous other GRACE-related studies and their contributions to understanding changes in the global climate system is reviewed by Tapley et al [9] These results are based on time-variable, in general monthly, global gravity field models. To provide consistent long-term gravity field time series of highest possible quality to the user community the SDS has recently reprocessed its gravity field solutions over the complete GRACE mission duration. Gravity variations caused by solid Earth and pole tides, atmosphere and ocean tides or short-term non-tidal atmospheric and oceanic mass variations are not supposed to be included in the gravity field solutions and are taken into account during the data processing via background models. EIGEN-6C [25] (up to d/o 200) Trend, annual and semi-annual coefficients of EIGEN-6C (up to d/o 50) EOT11a [27]
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