Since IGY (International Geophysical Year), through coordinated global observations, ionospheric research has been carried out by many countries. This effort primarily helped in the design and operation of HF radio wa...Since IGY (International Geophysical Year), through coordinated global observations, ionospheric research has been carried out by many countries. This effort primarily helped in the design and operation of HF radio wave communication systems. The Indian region covers a highly variable part of the equatorial electrojet and EIA (Equatorial Ionisation Anomaly) phenomena making its predictability difficult. With the advent of satellite communication and navigation, the need for accurate ionospheric TEC (Total Electron Content) models at global and regional scales has been stressed. The GAGAN (GPS Aided Geo Augmented Navigation) project jointly undertaken by the Indian Space Research Organisation (ISRO) and the Airport Authority of India (AAI) aims at effectively utilising the Global Navigational Satellite System (GNSS) to determine position coordinates accurately for aircraft precision landing applications. For this purpose the range errors are estimated by using a ground network of TEC stations spread over Indian region. The near simultaneous data collected from these dual frequency GPS stations can be used to generate the geo-referenced TEC values for various applications. The author has developed necessary algorithm and associated computer programmes for a real-time vertical TEC (VTEC) model based on TEC data collected from the GAGAN ground based network stations. The model has been tested and sample results presented here show that it adequately provides for the latitudinal resolution of 1° for the entire longitude span and also for two longitude blocks (73 - 83 & 83 - 93°E) separately. Cubic spline and bilinear interpolation techniques are used for filling up temporal and spatial data gaps. The model provides tabulated output of hourly average VTEC data with latitude for ready use, as well as graphical displays of VTEC maps and contours for monitoring purpose. The real-time model and its extensions are also being used for detailed scientific studies;examples of these show small day to day variability of VTEC without any change in solar activity and indication of the change in the shape of the VTEC diurnal curve with season. The present model will be used for further studies to derive the monthly average variation of the diurnal pattern and the relationship between VTEC peak amplitudes with changes in solar activity. The new information generated can be fed back to improve the real-time model so that eventually the dependence of such models on ground based network stations data can be minimised.展开更多
Machine learning techniques which are about the construction and study of system that can learn from data are combined with many application fields.A method on ionospheric total electron content(TEC)mapping is propose...Machine learning techniques which are about the construction and study of system that can learn from data are combined with many application fields.A method on ionospheric total electron content(TEC)mapping is proposed based on radical basis function(RBF)neural network improved by Gaussian mixture model(GMM).Due to the complicated ionospheric behavior over China,GMM is used to determine the center of basis function in the unsupervised training process.Gradient descent is performed to update the weights function on a sum of squared output error function in the supervised learning process.The TEC values from the center for orbit determination in Europe(CODE)global ionospheric maps covering the period from 2007to 2010 are used to investigate the performance of the developed network model.For independent validation,the simulated TEC values at different latitudes(20°N,30°N and 40°N)along 120°E longitude are analyzed and evaluated.The results show that the simulated TEC from the RBF network based model has good agreement with the observed CODE TEC with acceptable errors.The theoretical research indicates that RBF can offer a powerful and reliable alternative to the design of ionospheric TEC forecast technologies and thus make a significant contribution to the ionospheric modeling efforts in China.展开更多
SAMI2(Sami2 is Another Model of the Ionosphere)是美国海军实验室开发的电离层物理模型.利用该物理模型,模拟了东亚扇区不同太阳活动强度、不同纬度地区三个站的电离层电子浓度总含量(TEC).通过模拟结果与GPS观测站TEC数据的比较,检...SAMI2(Sami2 is Another Model of the Ionosphere)是美国海军实验室开发的电离层物理模型.利用该物理模型,模拟了东亚扇区不同太阳活动强度、不同纬度地区三个站的电离层电子浓度总含量(TEC).通过模拟结果与GPS观测站TEC数据的比较,检验SAMI2在此扇区的电离层TEC计算精度.结果表明,物理模型输出的电离层TEC具备与观测数据一致的周日变化、季节变化,太阳活动变化.周日分布上,上午时段SAMI2 TEC与观测数据吻合度优于午后时段;季节分布上,SAMI2 TEC在冬季与观测值偏差小于其他季节;SAMI2 TEC与GPS TEC相关系数各站均达到0.87以上,与赤道地区Guam站相关性最好;太阳活动低年计算结果优于太阳活动高年;多数情况下,SAMI2 TEC相对GPS TEC偏大.本文结果为基于SAMI2模型构建背景误差分布特征,开展该区域电离层数值预报研究可行性提供了理论支持.展开更多
文摘Since IGY (International Geophysical Year), through coordinated global observations, ionospheric research has been carried out by many countries. This effort primarily helped in the design and operation of HF radio wave communication systems. The Indian region covers a highly variable part of the equatorial electrojet and EIA (Equatorial Ionisation Anomaly) phenomena making its predictability difficult. With the advent of satellite communication and navigation, the need for accurate ionospheric TEC (Total Electron Content) models at global and regional scales has been stressed. The GAGAN (GPS Aided Geo Augmented Navigation) project jointly undertaken by the Indian Space Research Organisation (ISRO) and the Airport Authority of India (AAI) aims at effectively utilising the Global Navigational Satellite System (GNSS) to determine position coordinates accurately for aircraft precision landing applications. For this purpose the range errors are estimated by using a ground network of TEC stations spread over Indian region. The near simultaneous data collected from these dual frequency GPS stations can be used to generate the geo-referenced TEC values for various applications. The author has developed necessary algorithm and associated computer programmes for a real-time vertical TEC (VTEC) model based on TEC data collected from the GAGAN ground based network stations. The model has been tested and sample results presented here show that it adequately provides for the latitudinal resolution of 1° for the entire longitude span and also for two longitude blocks (73 - 83 & 83 - 93°E) separately. Cubic spline and bilinear interpolation techniques are used for filling up temporal and spatial data gaps. The model provides tabulated output of hourly average VTEC data with latitude for ready use, as well as graphical displays of VTEC maps and contours for monitoring purpose. The real-time model and its extensions are also being used for detailed scientific studies;examples of these show small day to day variability of VTEC without any change in solar activity and indication of the change in the shape of the VTEC diurnal curve with season. The present model will be used for further studies to derive the monthly average variation of the diurnal pattern and the relationship between VTEC peak amplitudes with changes in solar activity. The new information generated can be fed back to improve the real-time model so that eventually the dependence of such models on ground based network stations data can be minimised.
基金supported by the National Natural Science Foundation of China(Grant No.41104096)
文摘Machine learning techniques which are about the construction and study of system that can learn from data are combined with many application fields.A method on ionospheric total electron content(TEC)mapping is proposed based on radical basis function(RBF)neural network improved by Gaussian mixture model(GMM).Due to the complicated ionospheric behavior over China,GMM is used to determine the center of basis function in the unsupervised training process.Gradient descent is performed to update the weights function on a sum of squared output error function in the supervised learning process.The TEC values from the center for orbit determination in Europe(CODE)global ionospheric maps covering the period from 2007to 2010 are used to investigate the performance of the developed network model.For independent validation,the simulated TEC values at different latitudes(20°N,30°N and 40°N)along 120°E longitude are analyzed and evaluated.The results show that the simulated TEC from the RBF network based model has good agreement with the observed CODE TEC with acceptable errors.The theoretical research indicates that RBF can offer a powerful and reliable alternative to the design of ionospheric TEC forecast technologies and thus make a significant contribution to the ionospheric modeling efforts in China.
文摘SAMI2(Sami2 is Another Model of the Ionosphere)是美国海军实验室开发的电离层物理模型.利用该物理模型,模拟了东亚扇区不同太阳活动强度、不同纬度地区三个站的电离层电子浓度总含量(TEC).通过模拟结果与GPS观测站TEC数据的比较,检验SAMI2在此扇区的电离层TEC计算精度.结果表明,物理模型输出的电离层TEC具备与观测数据一致的周日变化、季节变化,太阳活动变化.周日分布上,上午时段SAMI2 TEC与观测数据吻合度优于午后时段;季节分布上,SAMI2 TEC在冬季与观测值偏差小于其他季节;SAMI2 TEC与GPS TEC相关系数各站均达到0.87以上,与赤道地区Guam站相关性最好;太阳活动低年计算结果优于太阳活动高年;多数情况下,SAMI2 TEC相对GPS TEC偏大.本文结果为基于SAMI2模型构建背景误差分布特征,开展该区域电离层数值预报研究可行性提供了理论支持.
