北斗电离层模型改正精度分析

电离层误差是影响单频用户机定位精度的主要误差源。卫星导航系统播发电离层模型改正参数供用户使用,模型改正精度会对定位结果产生直接影响。北斗卫星导航系统根据连续监测站实测数据,计算并发播地理坐标系下8参数Klobuchar电离层模型参数,且每2 h更新一次。为了科学评估北斗电离层模型改正效果,文中基于北斗最新观测数据,首先,以CODE提供的GIM模型作为比对基准,详细分析了不同纬度地区、不同时间段内的电离层模型改正精度;其次,分别按照以下定位模式进行计算:1)北斗单频不加电离层改正,2)北斗单频+北斗K8模型,3)北斗单频+GPS K8模型,并分析了电离层改正残差对定位结果影响大小。结果表明,北斗电离层模型改正精度在北半球优于南半球,中纬度地区改正效果最好,其改正残差RMS均值在0.6 m左右,往低纬和高纬度地区呈递减趋势;北京地区北斗单频+北斗K8模型定位精度优于GPS K8模型。

Correction Accuracy Analysis on Ionospheric Model of Beidou System

The ionospheric error was the main error sources affecting positioning accuracy for single￣frequency users machines. The parameters of ionospheric model were broadcast by satellite navigation systems for users so the cor￣rection accuracy of the model had a direct impact on positioning results. Based on continuous monitoring stations Beidou system 8 parameters of Klobuchar were calculated and broadcast under the geographic coordinate system and they were updated every 2 hours. In order to scientifically evaluate the correction effect of Beidou ionospheric model firstly the ionospheric model accuracy of different time periods and different latitudes was analyzed through the basis of GIM model provided by CODE based on Beidou latest observations. Secondly the following positioning modes were calculated respectively. 1 Single￣frequency positioning without ionospheric corrections of Beidou. 2 Beidou single￣frequency +Beidou K8 model. 3 Beidou single￣frequency+GPS K8 model. The effect of residual i￣onospheric corrections was analyzed for positioning results. The results showed that the northern hemisphere was better than the southern hemisphere for the accuracy of Beidou ionospheric model. Mid￣latitudes regions could get the best correction and the RMS of correction residuals was average about 0.6 meters and it showed a decreasing trend to the low￣latitude and high￣latitude regions. Beidou K8 model was better than GPS K8 model for single fre￣quency positioning in Beijing.