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Title An ensemble solution for the Earth's time-varying gravitational field from the NASA/DLR GRACE mission
URL
Publication Date
Date Accessioned
Degree MSin Engineering
Discipline/Department Aerospace Engineering
Degree Level masters
University/Publisher University of Texas – Austin
Abstract Several groups produce estimates of the Earth's time-varying gravitational field with data provided by the NASA/DLR Gravity Recovery and Climate Experiment (GRACE) mission. These unprecedented highly accurate global data sets track the time-variable transport of mass across and underneath the surface of the Earth and give insight into secular, seasonal, and sub seasonal variations in the global water supply. Knowledge gained from these products can inform and be incorporated into ocean and hydrological models and advise environmental policy planning. Therefore, a complete understanding of the accuracy and variations between these different fields is necessary, and the most accurate possible solutions desired. While the various gravity fields are similar, differences in processing strategies and tuning parameters result in solutions with regionally specific variations and error patterns. This study analyzed the spatial, temporal, and spectral variations between four different gravity field products. The knowledge gained in this analysis was used to develop an ensemble solution that harnesses the best characteristics of each individual field to create an optimal model. Multiple methods were used to combine and analyze the individual and ensemble solutions. First a simple mean model was created; then the different solutions were weighted based on the formal error estimates as well as the monthly deviation from the arithmetic mean ensemble. These ensemble models as well as the four individual data center solutions were analyzed for bias, long term trend, and regional variations between the solutions, evaluated statistically to assess the noise and scatter within the solutions, and compared to independent hydrological models. Therefore, the form and cause of the deviations between the models, as well as the impact of these variations, is characterized. The three ensemble solutions constructed in this analysis were all effective at reducing noise in the models and better correlate to hydrological processes than any individual solution. However, the scale of these improvements is constrained by the relative variation between the individual solutions as the deviation of these individual data products from the hydrological model output is much larger than the variations between the individual and ensemble solutions.
Subjects/Keywords GRACE; Gravity; Geodesy; Ensemble modeling
Contributors Bettadpur, Srinivas Viswanath, 1963- (advisor)
Language en
Country of Publication us
Record ID handle:2152/22498
Repository texas
Date Retrieved
Date Indexed 2019-09-12
Grantor The University of Texas at Austin
Note [] text; [department] Aerospace Engineering;

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…93 95 99 100 Chapter 6. Conclusion 102 6.1 Ensemble Model Creation . . . . . . . . . . . . . . . . . . . . . 102 6.2 Comparison and Validation of Gravity Field Solutions . . . . . 104 Appendices 108 Appendix A. River Basin Information 109 A.1 Basin…

…Elastic Love Numbers . . . . . . . . . . . . . . . . . . . . . . . 9 15 3.1 3.2 Data Used in Processing . . . . . . . . . . . . . . . . . . . . . EWH Grid statistics for the four GRACE gravity models, April 2005…

…Time-Averaged EWH Grid statistics for the four GRACE gravity models (mm EWH) . . . . . . . . . . . . . . . . . . . . . . EWH Grid statistics for the four GRACE gravity models . . . 20 GRACE Gravity Field Data Used in Ensemble Models…

…EWH Grid statistics for the four GRACE gravity models (mm) Basin RMS Statistics . . . . . . . . . . . . . . . . . . . . . . . EWH Grid statistics for the four GRACE gravity models . . . Mean Correlation Coefficients of the Ensemble and…

…91 94 95 97 98 99 A.1 Global River Basin Map . . . . . . . . . . . . . . . . . . . . . 111 xi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 1 Introduction The Gravity Recovery and Climate Experiment (…

…in March 2002 with an original five-year mission plan to track and model the Earth’s static and time-varying gravitational field on an unprecedented scale. Gravity at the most basic level is simply a measure of the attractive force between physical…

…satellites track this inter-satellite range with extremely high precision and these observations are used to determine the distribution and progression of perturbations in the Earth’s gravity field that cause this range variation. The satellites are equipped…

…are removed from the signal. Two primary models are resolved from the GRACE data. A mean or static gravity field can be determined to a much higher resolution than previously possible from a combination of many of these measurements. This mean gravity

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