GRACE Gravity Modeling Using the Integrated Approach
Monthly gravity field solutions up to d/o 60 are derived by applying the Integrated (one-step) Approach of space geodesy, i.e. by simultaneously processing of the GPS constellation and the twin GRACE satellites. The results are based on latest GRACE RL05
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GRACE Gravity Modeling Using the Integrated Approach Daniel König and Christoph Dahle
Abstract Monthly gravity field solutions up to d/o 60 are derived by applying the Integrated (one-step) Approach of space geodesy, i.e. by simultaneously processing of the GPS constellation and the twin GRACE satellites. The results are based on latest GRACE RL05 standards (without constraining L3-ambiguities), and consists of 24-h arcs covering the test month April 2008 where the monthly solution was obtained by accumulation of the daily normal equations. The alternative gravity model is compared with the corresponding two-step solution derived by standard two-step GFZ RL05 GRACE processing (including constrained L3-ambiguities). It is shown, that difference degree amplitudes with respect to the static satellite-only model ITG-GRACE2010s for both the Integrated Approach and the two-step solution only differ significantly beyond d/o 17 where the two-step approach still performs slightly better. A great advantage of the Integrated Approach is the largely reduced formal errors indicating higher stochastic significance. Keywords GRACE · Integrated processing · Gravity field determination
5.1 Introduction The integrated approach (Zhu et al. 2004) for deriving GRACE gravity field models follows the idea to process GPS ground data as well as the GRACE on-board data in a single step using an updated version of the GFZ Earth Parameter and Orbit System (EPOS) software. König et al. (2005) already gave a dim hint of a possible improvement of the gravity field coefficients (GFCs) of d/o two. The current integrated solution was derived for April 2008 with GFCs solved up to d/o 60 and D. König (B) · C. Dahle GFZ German Research Centre for Geosciences, Department 1, Geodesy and Remote Sensing,Münchner Str. 20, 82234 Oberpfaffenhofen, Germany e-mail: [email protected]
F. Flechtner et al. (eds.), Observation of the System Earth from Space - CHAMP, GRACE, GOCE and Future Missions, Advanced Technologies in Earth Sciences, DOI: 10.1007/978-3-642-32135-1_5, © Springer-Verlag Berlin Heidelberg 2014
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compared with the latest RL05 “standard” two-step solution (Dahle et al. 2012 this book). Specifications of the processing as well as the results of the comparison are presented here.
5.2 Specifications The specifications chosen for the processing are as follows: • satellites: GPS constellation, GRACE • observations: GPS-ground (L3), GRACE High-low GPS-SST (L3), GRACE lowlow K-band range-rate (KBRR), measured accelerations (ACC) and attitude • standards and models: GFZ RL05 (Dahle et al. 2012; except constraining of L3-ambiguities for GPS-ground) • arc length: 24 h • estimated parameters: – – – – – – –
ground stations coordinates, gravity field coefficients, initial elements, solar radiation pressure model (ROCK4) scale and y-bias for GPS satellites, empirical forces (amplitudes of periodic model), KBRR empirical coefficients and ACC calibration coefficients.
• constraints: 0.1-mm NN (No Net) conditions (translation in t
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