电离层TEC预报的直接法和间接法及其比较

Direct and Indirect Methods on Predicting Ionosphere and Their Compare

提出用时间序列分析理论中的ARIMA(p,d,q)模型对电离层进行预报的直接法及间接法.直接法也就是对每个网格点上的电子总含量所形成的时间序列进行直接预报.间接法为:首先对电离层电子总含量用球谐函数拟合得到拟合系数的时间序列;再用时间序列分析理论中的ARIMA(p,d,q)模型对拟合系数进行预报;然后计算出对应时刻所需点的电子总含量.利用2004年1月1日至2005年1月3l International GPS Service(IGS)所给出的电离层资料对提出的两种方法进行检验和比较,结果表明,在12天以内,上述两种方法的预报结果基本一致,长于12天的预报时,间接法的精度高于直接法.在20天时间内,预报值与已知值之差小于3个TECU的电离层点数占总点数的百分比基本上都在80%左右;随着时间的推移,这个比值的下降对直接法并不明显,而对间接法则有所下降.显然,直接法适用于区域性的电子总含量的预报;而间接法适用于全球性的电子总含量的预报.

The direct and indirect methods on predicting ionosphere are proposed in this paper. These methods are using ARIMA（p, d, q） model of the time series theory to predict ionosphere. The direct method is predicting the TEC in each node of grid forming time series. The indirect method is： Firstly, the ionospheric TEC is fitted by spherical-harmonic expansion, the fitted coefficients for different time forming time series can be obtained; and then, these time series will be analyzed by ARIMA（p, d, q） model and will be used to predict the spherical-harmonic coefficients; and finally, the ionospheric TEC will be predicted by the predicted spherical-harmonic coefficients. The TEC data in the duration of 2004 Jan 1 to 2005 Jan 31 from International GPS Service（IGS） is used to verify and compare the two methods. The results of the two methods are nearly the same in the first 12 days. In last days, the prediction of the indirect method is more accurate than the direct method. Within 20 days, the percentage of the grids number of the difference between prediction value and original value less than 3 TECU is about 80%. As time going, this percentage of the indirect method clearly descends but this percentage of the direct method descends un-conspicuously. The direct method is suitably applied to local predicting TEC while the indirect method to global predicting TEC.