Accuracy assessment of the GPS-TEC calibration constants by means of a simulation technique |
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| Authors: | Juan Federico Conte Francisco Azpilicueta Claudio Brunini |
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| Institution: | (1) School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK |
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| Abstract: | During the last 2 decades, Global Positioning System (GPS) measurements have become a very important data-source for ionospheric
studies. However, it is not a direct and easy task to obtain accurate ionospheric information from these measurements because
it is necessary to perform a careful estimation of the calibration constants affecting the GPS observations, the so-called
differential code biases (DCBs). In this paper, the most common approximations used in several GPS calibration methods, e.g.
the La Plata Ionospheric Model (LPIM), are applied to a set of specially computed synthetic slant Total Electron Content datasets
to assess the accuracy of the DCB estimation in a global scale scenario. These synthetic datasets were generated using a modified
version of the NeQuick model, and have two important features: they show a realistic temporal and spatial behavior and all
a-priori DCBs are set to zero by construction. Then, after the application of the calibration method the deviations from zero
of the estimated DCBs are direct indicators of the accuracy of the method. To evaluate the effect of the solar activity radiation
level the analysis was performed for years 2001 (high solar activity) and 2006 (low solar activity). To take into account
seasonal changes of the ionosphere behavior, the analysis was repeated for three consecutive days close to each equinox and
solstice of every year. Then, a data package comprising 24 days from approximately 200 IGS permanent stations was processed.
In order to avoid unwanted geomagnetic storms effects, the selected days correspond to periods of quiet geomagnetic conditions.
The most important results of this work are: i) the estimated DCBs can be affected by errors around ±8 TECu for high solar
activity and ±3 TECu for low solar activity; and ii) DCB errors present a systematic behavior depending on the modip coordinate,
that is more evident for the positive modip region. |
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