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Earth, Planets and Space
Fig. 1 | Earth, Planets and Space

Fig. 1

From: Improving the estimation of thermospheric neutral density via two-step assimilation of in situ neutral density into a numerical model

Fig. 1

The green lines illustrate the grid of the TIE-GCM at one epoch. We call it the state grid. The blue lines show the (constant) grid at which we evaluate the NRLMSIS 2.0. We call it the data grid. The black curve illustrates the orbit of the CHAMP satellite for some revolutions. In the two-step approach we first calibrate the NRLMSIS 2.0 with the accelerometer-derived density of the CHAMP satellite, and evaluate it on the data grid. In a second step we assimilated the densities located on the data grid—in data assimilation terminology this are the observations—into the TIE-GCM. The grids appear thicker as they are in reality, since the radius of Earth is not added. Actually both grids cover the entire Earth, but we show only a subset for a clearer illustration

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