Evaluation of Nominal Klobuchar Model Performance

Abstract

Ionospheric delay is a major source of error for GNSS positioning, which is a vital tool in various industries. In particular, for single-frequency users, ionospheric delay presents a major issue.

This paper analyzes the nominal accuracy of the Klobuchar model, an ionospheric correction model for single-frequency GPS users based on a half-cosine function with varying amplitude and period with a fixed nighttime delay, at various latitudes. The delay derived from the IGS GIM (International GNSS Service Global Ionosphere Maps), which is assumed to be accurate in this paper, is compared to the ionospheric delay calculated using the Klobuchar model at 0°N, 30°N, and 60°N. From the experiments, it is seen that at low-latitudes, the Klobuchar model estimates ionospheric delay well and GPS L1 users can expect an average percent error of approximately 20%. At mid-latitudes, the Klobuchar model performs reasonably well, but tends to overestimate the delay by as much as 0.8 meters. Meanwhile, at high-latitudes, the model drastically overestimates ionospheric delay and is highly inaccurate compared to other regions. Our findings show that GPS L1 users can generally expect accurate positioning data at low-latitudes, however at higher-latitudes, the Klobuchar model is not reliable and requires improvement.