engleski

Extension of Standard GPS Ionospheric Model for Quiet Space Weather Conditions

The GPS ionospheric delay is by far the major source of the GPS positioning error. Standard GPS service provides the global ionospheric error correction model (known as Klobuchar model, after its developer), which is reportedly capable of tackling up to 70% positioning error caused by the GPS ionospheric delay. Klobuchar model assumes composition of two components in modelling daily GPS ionospheric delay distribution for a given location: a constant error representing night values, and a variable component expressed by cosine function representing the daily dynamics of the GPS ionospheric error. Klobuchar model achieves the best results in periods of quiet space weather and ionospheric conditions. However, even in the ideal conditions, Klobuchar model cannot describe daily GPS ionospheric dynamics completely, as it is evident in a certain amount of residual GPS ionospheric delay error remaining after deployment of Klobuchar model corrections. Here an extension of the Klobuchar model for quiet space weather conditions is proposed, based on the additive model of a time series. In an attempt to improve the performance of the standard Klobuchar model, an additional random component is introduced, which is to be added to the previously established night-time (monotonous) and day-time (short-term cosine) components. The random component used in the extended Klobuchar model has a specific statistical profile, determined by previous measurements of GPS positioning performance. Proposed three-component Klobuchar model is validated through the comparison with real GPS ionospheric delay data obtained from GPS pseudorange measurements taken at the reference station in Croatia in a period of quiet space weather conditions. The analysis shows improvement in modelling the GPS ionospheric delay with the three-component model, compared with the standard Klobuchar model. Finally, the importance of continued work on GPS ionospheric delay anomalies identification and statistical description is emphasised, and will form a core of the future research work.

ionospheric delay; space weather; Klobuchar model

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