A Modified GPS Broadcast Ionospheric Model And Analysis Of The Spp Error Over The Polar Regions

The time delay in ionosphere is the most dominant error source in Global Navigation Satellite System.The ionosphere in polar area is changeable,which greatly damage precision of GPS.For single-frequency Global Navigation Satellite System(GNSS)users,it is necessary to select a simple and effective broadcast ionospheric model to mitigate the ionospheric delay in SPP.Compared to the observed VTEC data derived from CODE-GIM model,we compares the RMS and correction of these three correction models(two kinds of Klobuchar model adopted by GPS/BDS and Nequick model)on the ionospheric delay accuracy.In this paper,the data from 2009 to 2013 are used to analyze the accuracy of correction models.Considering the simplicity and practicability of GPS Klobuchar model,under the premise of no additional model parameters,a modified Klobuchar model is established for single-frequency GNSS users over the Polar Regions by improving the nighttime term and the amplitude of the cosine term.The performance of the new model is validated by different ionospheric correction models and their applications in single-frequency single-point positioning.This study suggests that the modified Klobuchar model is more accurate to depict the polar ionosphere and could be used to achieve better positioning accuracy for single-frequency GNSS users over the Polar Regions.The main contributions of this paper are as follows:1.The basic theory,Spatial and temporal variation of ionosphere and the merits and demerits of the existing broadcast ionospheric model are summarized.2.The correction effect of existing broadcast ionospheric models in different spatial and temporal range is compared in detail,and the following conclusions are obtained:1)In the area at latitude more than 57.5°,Klobuchar model adopted by GPS have a negative effect in most cases,but better than BDS.2)In Arctic Nequick model performs worse than middle and low latitudes;its correction effect is mostly about 40%.3)In the area at latitude more than 65°N,Klobuchar model adopted by BDS have a negative effect in most cases,even worse than GPS-Klobuchar model.3.A new broadcast ionosphere model is proposed.The new model has the following ionospheric correction accuracy:1)During different seasons and different levels of solar activities.The new model can reduce the ionospheric error by 60%over the Polar Regions,while the GPS-Klobuchar even increase the ionospheric error in many cases.2)Over the Polar Regions,the single-frequency SPP error using the new model is approximately 3m in vertical direction and lm in horizontal direction,which is superior to GPS-Klobuchar.