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Bernese GPS Software Version 5.0 - Bernese GNSS Software

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12. Ionosphere Modeling and Estimation<br />

Figure 12.14: Parameter setup and pre-elimination (2).<br />

In panel “<strong>GPS</strong>EST 5.1: Setup of Parameters and Pre-Elimination 1” you have to set up “Global ionosphere<br />

parameters”, and, exclusively in the zero-difference case, you have to set up “Differential<br />

code biases” in panel “<strong>GPS</strong>EST 5.2: Setup of Parameters and Pre-Elimination 2”.<br />

In panel “<strong>GPS</strong>EST 6.4.1: Global Ionosphere Parameters 1” (cf. Figure 12.15), you may enter the<br />

requests specific to the TEC modeling. The “Parameter spacing/interval” should be set to 24<br />

00 00 for regional – or station-specific – models assuming a (maximum) session length of<br />

24 hours. A larger number of coefficient sets (models) and, therefore, a shorter parameter<br />

spacing may be appropriate for the global application.<br />

“Maximum degree of spherical harmonics” and “Maximum order of spherical harmonics” correspond<br />

to nmax and mmax(≤ nmax) of the TEC model, Eqn. (12.13). For regional models, a<br />

smaller maximum degree than given in the above panel should be specified (e. g., nmax = 6,<br />

mmax = 6), depending on the extent of the network processed. Assuming mmax = nmax,<br />

you have to reckon with (nmax + 1) 2 GIM parameters per session.<br />

Modeling characteristics may be set in panel “<strong>GPS</strong>EST 6.4.2: Global Ionosphere Parameters 2” (cf.<br />

Figure 12.16). Select STATIC to create ionosphere models representing static (or “frozen”)<br />

TEC structures in the sun-fixed frame. They refer to specific time intervals. DYNAMIC<br />

models the TEC coefficients as piece-wise linear functions anm(t) and bnm(t) representing<br />

a (low-)dynamic ionosphere E(β,s,t). If you select DYNAMIC, the TEC coefficients are<br />

always referred to particular reference epochs. With the option “Reference frame definition”,<br />

you may decide in which reference frame the TEC should be modeled, a GEOGRAPHIC or<br />

a GEOMAGNETIC frame. With the setting MEAN or TRUE for the “Longitude of the Sun”, the<br />

argument s is computed according to the right-hand or left-hand side of Eqn. (12.12). The<br />

“Mapping function” should be COSZ to be in accordance with Eqn. (12.8).<br />

It is recommended to set the “A priori height of single layer” to H = 450 km. The fields “Latitude<br />

of geomagnetic pole” and “Longitude of geomagnetic pole” expect the coordinates of the Earthcentered<br />

dipole axis, if you chose GEOMAGNETIC as reference frame. Finally, you have the<br />

possibility to define “Absolute” as well as “Relative sigma for coefficients”. An absolute sigma<br />

of, e. g, 10 TECU is recommended to produce regional or station-specific models.<br />

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