Bernese GPS Software Version 5.0 - Bernese GNSS Software

12. Ionosphere Modeling and Estimation
Figure 12.14: Parameter setup and pre-elimination (2).
In panel “GPSEST 5.1: Setup of Parameters and Pre-Elimination 1” you have to set up “Global ionosphere
parameters”, and, exclusively in the zero-difference case, you have to set up “Differential
code biases” in panel “GPSEST 5.2: Setup of Parameters and Pre-Elimination 2”.
In panel “GPSEST 6.4.1: Global Ionosphere Parameters 1” (cf. Figure 12.15), you may enter the
requests specific to the TEC modeling. The “Parameter spacing/interval” should be set to 24
00 00 for regional – or station-specific – models assuming a (maximum) session length of
24 hours. A larger number of coefficient sets (models) and, therefore, a shorter parameter
spacing may be appropriate for the global application.
“Maximum degree of spherical harmonics” and “Maximum order of spherical harmonics” correspond
to nmax and mmax(≤ nmax) of the TEC model, Eqn. (12.13). For regional models, a
smaller maximum degree than given in the above panel should be specified (e. g., nmax = 6,
mmax = 6), depending on the extent of the network processed. Assuming mmax = nmax,
you have to reckon with (nmax + 1) 2 GIM parameters per session.
Modeling characteristics may be set in panel “GPSEST 6.4.2: Global Ionosphere Parameters 2” (cf.
Figure 12.16). Select STATIC to create ionosphere models representing static (or “frozen”)
TEC structures in the sun-fixed frame. They refer to specific time intervals. DYNAMIC
models the TEC coefficients as piece-wise linear functions anm(t) and bnm(t) representing
a (low-)dynamic ionosphere E(β,s,t). If you select DYNAMIC, the TEC coefficients are
always referred to particular reference epochs. With the option “Reference frame definition”,
you may decide in which reference frame the TEC should be modeled, a GEOGRAPHIC or
a GEOMAGNETIC frame. With the setting MEAN or TRUE for the “Longitude of the Sun”, the
argument s is computed according to the right-hand or left-hand side of Eqn. (12.12). The
“Mapping function” should be COSZ to be in accordance with Eqn. (12.8).
It is recommended to set the “A priori height of single layer” to H = 450 km. The fields “Latitude
of geomagnetic pole” and “Longitude of geomagnetic pole” expect the coordinates of the Earthcentered
dipole axis, if you chose GEOMAGNETIC as reference frame. Finally, you have the
possibility to define “Absolute” as well as “Relative sigma for coefficients”. An absolute sigma
of, e. g, 10 TECU is recommended to produce regional or station-specific models.
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