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Bernese GPS Software Version 5.0 - Bernese GNSS Software

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12.5 Stochastic Ionosphere Modeling Technique<br />

12.5.1 Estimation of Stochastic Ionosphere Parameters<br />

12.5 Stochastic Ionosphere Modeling Technique<br />

Stochastic Ionosphere Parameters (SIPs), representing the term Ii k in Eqn. (12.14), may<br />

be set up in panel “<strong>GPS</strong>EST 5.1: Setup of Parameters and Pre-Elimination 1”. In the same panel<br />

a special parameter pre-elimination algorithm working epoch by epoch may be activated<br />

(select EACH EPOCH as pre-elimination method). This is recommended because of the huge<br />

number of SIPs usually involved.<br />

Panel “<strong>GPS</strong>EST 6.7: Stochastic Ionosphere Parameters” offers several options concerning SIPs<br />

(see Figure 12.20).<br />

“Elimination of reference ionosphere parameters” is the option where you decide whether to estimate<br />

SIPs on a double-difference or a quasi-single-difference level. The estimation on the<br />

quasi-single-difference level should be used when defining so-called relative a priori sigma<br />

at “Relative a priori sigma of ionospheric random walk”. If you eliminate reference ionosphere parameters,<br />

the resulting SIPs are estimated with respect to a reference satellite, actually the<br />

satellite closest to the zenith. The consideration of “Elevation-dependent parameter constraining”<br />

is recommended in particular when processing low-elevation data.<br />

An absolute a priori sigma must be specified in the field “Absolute a priori sigma on single<br />

difference level” to get “hybrid” dual-band observations. By entering 0.00, no SIP constraints<br />

are introduced. When using the General-Search ambiguity resolution strategy in conjunction<br />

with the stochastic ionosphere modeling, we recommend to specify an absolute a priori sigma<br />

between, let us say, 0.01 and 0.1 meters, and between 0.1 and 1 meters when using the Quasi-<br />

Ionosphere-Free (QIF) strategy (see also Figure 12.4). Relative a priori constraints between<br />

consecutive SIPs of the same satellite may be defined to model the correlation in time of the<br />

ionospheric signal. This option may be used only if you do not eliminate reference ionosphere<br />

parameters (option “Elimination of reference ionosphere parameters”). Such a “SIP smoothing”<br />

might be useful, e.g., for kinematic applications under moderate ionospheric conditions.<br />

Figure 12.20: Options for stochastic ionosphere parameters in <strong>GPS</strong>EST.<br />

<strong>Bernese</strong> <strong>GPS</strong> <strong>Software</strong> <strong>Version</strong> <strong>5.0</strong> Page 275

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