The EGM2008 Global Gravitational Model

Computer Science – Performance

Scientific paper

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1214 Geopotential Theory And Determination (0903), 1219 Gravity Anomalies And Earth Structure (0920, 7205, 7240)

Scientific paper

The development of a new Earth Gravitational Model (EGM) to degree 2160 has been completed. This model, designated EGM2008, is the product of the final re-iteration of our modelling and estimation approach. Our multi-year effort has produced several Preliminary Gravitational Models (PGM) of increasingly improved performance. One of these models (PGM2007A) was provided for evaluation to an independent Evaluation Working Group, sponsored by the International Association of Geodesy (IAG). In an effort to address certain shortcomings of PGM2007A, we have considered the feedback that we received from this Working Group. As part of this effort, EGM2008 incorporates an improved version of our 5'x5' global gravity anomaly database and has benefited from the latest GRACE based satellite-only solutions (e.g., ITG- GRACE03S). EGM2008 incorporates an improved ocean-wide set of altimetry-derived gravity anomalies that were estimated using PGM2007B (a variant of PGM2007A) and its associated Dynamic Ocean Topography (DOT) model as reference models in a "Remove-Compute-Restore" fashion. For the Least Squares Collocation estimation of our final global 5'x5' area-mean gravity anomaly database, we have used consistently PGM2007B as our reference model to degree 2160. We have developed and used a formulation that predicts area-mean gravity anomalies that are effectively band-limited to degree 2160, thereby minimizing aliasing effects during the harmonic analysis process. We have also placed special emphasis on the refinement and "calibration" of the error estimates that accompany our final combination solution EGM2008. We present the main aspects of the model's development and evaluation. This evaluation was accomplished primarily through the comparison of various model derived quantities with independent data and models (e.g., geoid undulations derived from GPS positioning and spirit levelling, astronomical deflections of the vertical, etc.). We will also present comparisons of our model-implied Dynamic Ocean Topography with other contemporary estimates (e.g., from ECCO).

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