首先介绍了非差非组合精密单点定位(precise point positioning,PPP)算法,分析了它与传统PPP的差异;处理了300个IGS跟踪站连续7d的数据,分析了接收机伪距硬件延迟偏差(difference code bias,DCB)和先验电离层精度对非差非组合PPP收敛速...首先介绍了非差非组合精密单点定位(precise point positioning,PPP)算法,分析了它与传统PPP的差异;处理了300个IGS跟踪站连续7d的数据,分析了接收机伪距硬件延迟偏差(difference code bias,DCB)和先验电离层精度对非差非组合PPP收敛速度的影响。统计结果表明,对于非差非组合PPP,利用IGS提供的全球电离层延迟模型GIM,静态定位精度N/E方向均收敛到10cm以内,估计接收机DCB的PPP平均收敛速度为13.12min,比不估计接收机DCB的PPP快5.36min,与传统的LC PPP相当。在获得高精度电离层先验数据的条件下,估计接收机DCB的非差非组合PPP平面精度收敛10cm的速度约为8.67min,比传统PPP收敛速度平均快约3.26min。展开更多
利用全球电离层地图（global ionosphere map,GIM）提供的垂直电子含量（vertical total electron content,VTEC）观测值,采用滑动四分位距法分析了芦山地震前后的电离层异常。为了探讨异常现象与地震之间的相关性,进一步确定了震中附...利用全球电离层地图（global ionosphere map,GIM）提供的垂直电子含量（vertical total electron content,VTEC）观测值,采用滑动四分位距法分析了芦山地震前后的电离层异常。为了探讨异常现象与地震之间的相关性,进一步确定了震中附近上空VTEC东向及北向梯度变化,并比较分析了2008-2012年相同时间段的VTEC变化。结果表明,2013年4月18-20日的负异常现象很可能与地震相关。通过分析震中附近电离层赤道异常的变化,发现赤道异常峰值在震前5d内明显减小,且峰值的位置向磁赤道方向移动。结合电离层负异常现象及赤道异常的变化,本文认为芦山地震孕震区内异常电场可能是引起电离层异常的主要原因之一。展开更多
The responses of Equatorial Ionosphere Anomaly（EIA） to the storm occurred on 17 March 2015 were studied using Global Ionosphere Map（GIM）. The variations of Total Electron Content（TEC）, latitudinal TEC gradients ...The responses of Equatorial Ionosphere Anomaly（EIA） to the storm occurred on 17 March 2015 were studied using Global Ionosphere Map（GIM）. The variations of Total Electron Content（TEC）, latitudinal TEC gradients and the rate of latitudinal TEC gradients in EIA regions were investigated in 75？E, 110？E and-60？E longitudinal sectors. The results from the GIM data showed that the distributions of the latitudinal gradient of TEC became monotonous in three longitudes on 18 March（the first day of the recovery phase）, but the variations were different. On 18 March, the magnitudes of latitudinal gradients decreased in spatial and temporal in 75？E and 110？E, which means the EIA was suppressed during the recovery phase of the storm, especially in 110？E. The magnitudes of latitudinal TEC gradients showed an obvious increase in spatial and temporal in-60？E. The SAMI2 reproduced the suppression of EIA with a disturbance dynamo electric field, which indicated that the physical process controlled the behaviors of the plasma during the recovery phase of the storm.展开更多
The Klobuchar model has been widely used to correct the ionospheric delay in applications. However, the NVTEC(Nighttime Vertical Total Electron Content) of the Klobuchar model employs an empirical constant of 9 TECU(T...The Klobuchar model has been widely used to correct the ionospheric delay in applications. However, the NVTEC(Nighttime Vertical Total Electron Content) of the Klobuchar model employs an empirical constant of 9 TECU(Total Electron Content Unit) at L1 frequency. In this paper, the rationality and reliability of the nighttime constant setting are investigated using the GIM(Global Ionosphere Map) product of the IGS(International GNSS Service) from 1998 to 2015. Our study indicates that the suitable time span of NVTEC average in nighttime should be between 20:00 and 06:00 LT(local time). The NVTEC is highly correlated with seasons, having positive extremes in spring and autumn and negative extremes in summer through the mean values in all latitudes. In addition to seasonal dependence, solar activity in the solar cycle 23 strongly influences NVTEC as well and leads to its variation within a range between 25 and30 TECU in spring and autumn at solar maximum, which is about 1.5 times greater than that in summer and winter. The NVTEC also has a dependence on the latitude at solar maximum, with the mean value from 30 TECU in low latitudinal regions to 15 TECU in high latitudinal regions. Therefore, these results demonstrate that the nighttime VTEC has much greater deviations from the imperial constant in the Klobuchar model, and the newly estimated constant is expected to bring improvement to the predictability of the Klobuchar ionospheric delay model in nighttime.展开更多
Single frequency GNSS receivers are the most widely used tools for tracking, navigation and geo-referencing around the world. It is estimated that over 75% of all GNSS receivers used globally are single frequency rece...Single frequency GNSS receivers are the most widely used tools for tracking, navigation and geo-referencing around the world. It is estimated that over 75% of all GNSS receivers used globally are single frequency receivers and users experience positioning error due to the ionosphere. To enable GNSS Single Frequency Precise Point Positioning (SFPPP), accurate a-prior information about the ionosphere is needed. The variation of the ionosphere is larger around the magnetic equator and therefore depends on latitude. It will be expected that SFPPP works better on latitude further from the magnetic equator. This present study aims to investigate the accuracy of some ionospheric error mitigation approaches used in single frequency precise point positioning (SFPPP) at several GNSS station in the new Nigerian GNSS Network (NIGNet) and two IGS sites in the low equatorial African region. This study covers two epochs of observation. The first consists of observation from three consecutive days (GPS week 1638;days 0, 1 and 2) that belongs to a period of low solar activities. The second epoch consists of observation from three consecutive days (GPS week 1647;days 2, 3 and 4) that belongs to a high solar activity and intense geomagnetic conditions. The estimated position for the GNSS stations from dual frequency measurement and their known ITRF solutions were used as a benchmark to assess the accuracy of SFPPP under four conditions i.e., SFPPP without ionospheric correction, SFPPP using final GIM models from the Centre for Orbit Determination in Europe( CODE), SFPPP with Klobuchar model, and SFPPP with a computed (local) model at each station. All computation was done using Leica Geo-office software. The result of the study clearly demonstrates the significance of removing or correcting for the effect of the ionosphere, which can result in up to 7 m displacement. It was recommended that GIMs from different organization should be investigated and also efforts should be towards improvement in algorithms and clock error modeling.展开更多
文摘利用全球电离层地图（global ionosphere map,GIM）提供的垂直电子含量（vertical total electron content,VTEC）观测值,采用滑动四分位距法分析了芦山地震前后的电离层异常。为了探讨异常现象与地震之间的相关性,进一步确定了震中附近上空VTEC东向及北向梯度变化,并比较分析了2008-2012年相同时间段的VTEC变化。结果表明,2013年4月18-20日的负异常现象很可能与地震相关。通过分析震中附近电离层赤道异常的变化,发现赤道异常峰值在震前5d内明显减小,且峰值的位置向磁赤道方向移动。结合电离层负异常现象及赤道异常的变化,本文认为芦山地震孕震区内异常电场可能是引起电离层异常的主要原因之一。
基金Supported by the National Natural Science Foundation of China(41474134,41474135)
文摘The responses of Equatorial Ionosphere Anomaly（EIA） to the storm occurred on 17 March 2015 were studied using Global Ionosphere Map（GIM）. The variations of Total Electron Content（TEC）, latitudinal TEC gradients and the rate of latitudinal TEC gradients in EIA regions were investigated in 75？E, 110？E and-60？E longitudinal sectors. The results from the GIM data showed that the distributions of the latitudinal gradient of TEC became monotonous in three longitudes on 18 March（the first day of the recovery phase）, but the variations were different. On 18 March, the magnitudes of latitudinal gradients decreased in spatial and temporal in 75？E and 110？E, which means the EIA was suppressed during the recovery phase of the storm, especially in 110？E. The magnitudes of latitudinal TEC gradients showed an obvious increase in spatial and temporal in-60？E. The SAMI2 reproduced the suppression of EIA with a disturbance dynamo electric field, which indicated that the physical process controlled the behaviors of the plasma during the recovery phase of the storm.
基金supported by National Key R&D Program of China (2016YFB0501503-3)the key project of National Natural Science Fund (41730108)the National Natural Science Fund (11103068)
文摘The Klobuchar model has been widely used to correct the ionospheric delay in applications. However, the NVTEC(Nighttime Vertical Total Electron Content) of the Klobuchar model employs an empirical constant of 9 TECU(Total Electron Content Unit) at L1 frequency. In this paper, the rationality and reliability of the nighttime constant setting are investigated using the GIM(Global Ionosphere Map) product of the IGS(International GNSS Service) from 1998 to 2015. Our study indicates that the suitable time span of NVTEC average in nighttime should be between 20:00 and 06:00 LT(local time). The NVTEC is highly correlated with seasons, having positive extremes in spring and autumn and negative extremes in summer through the mean values in all latitudes. In addition to seasonal dependence, solar activity in the solar cycle 23 strongly influences NVTEC as well and leads to its variation within a range between 25 and30 TECU in spring and autumn at solar maximum, which is about 1.5 times greater than that in summer and winter. The NVTEC also has a dependence on the latitude at solar maximum, with the mean value from 30 TECU in low latitudinal regions to 15 TECU in high latitudinal regions. Therefore, these results demonstrate that the nighttime VTEC has much greater deviations from the imperial constant in the Klobuchar model, and the newly estimated constant is expected to bring improvement to the predictability of the Klobuchar ionospheric delay model in nighttime.
文摘Single frequency GNSS receivers are the most widely used tools for tracking, navigation and geo-referencing around the world. It is estimated that over 75% of all GNSS receivers used globally are single frequency receivers and users experience positioning error due to the ionosphere. To enable GNSS Single Frequency Precise Point Positioning (SFPPP), accurate a-prior information about the ionosphere is needed. The variation of the ionosphere is larger around the magnetic equator and therefore depends on latitude. It will be expected that SFPPP works better on latitude further from the magnetic equator. This present study aims to investigate the accuracy of some ionospheric error mitigation approaches used in single frequency precise point positioning (SFPPP) at several GNSS station in the new Nigerian GNSS Network (NIGNet) and two IGS sites in the low equatorial African region. This study covers two epochs of observation. The first consists of observation from three consecutive days (GPS week 1638;days 0, 1 and 2) that belongs to a period of low solar activities. The second epoch consists of observation from three consecutive days (GPS week 1647;days 2, 3 and 4) that belongs to a high solar activity and intense geomagnetic conditions. The estimated position for the GNSS stations from dual frequency measurement and their known ITRF solutions were used as a benchmark to assess the accuracy of SFPPP under four conditions i.e., SFPPP without ionospheric correction, SFPPP using final GIM models from the Centre for Orbit Determination in Europe( CODE), SFPPP with Klobuchar model, and SFPPP with a computed (local) model at each station. All computation was done using Leica Geo-office software. The result of the study clearly demonstrates the significance of removing or correcting for the effect of the ionosphere, which can result in up to 7 m displacement. It was recommended that GIMs from different organization should be investigated and also efforts should be towards improvement in algorithms and clock error modeling.
