利用LS+AR模型对UT1-UTC进行中长期预报

Medium/long-term prediction of UT1-UTC via LS+AR model

采用最小二乘（LS）与自回归（AR）模型相结合的方法,建立适合UT1-UTC预报的LS＋AR模型。首先扣除UT1-UTC序列中的闰秒和固体地球带谐潮汐项,并对处理后的UT1-UTC序列作一次差分,然后对差分序列进行LS拟合,再用AR模型对LS拟合残差建模,最后将AR模型预测值和LS外推值相加,得到差分序列预测值,再将预报的一次差还原,同时恢复闰秒和潮汐项,得到UT1-UTC预报值。通过与地球定向参数预报比较竞赛（EOP PCC）结果的对比表明,该方法的超短期（1-10 d）、短期（1-30 d）和中长期（1-500 d）预报精度均接近国际先进水平。同时以中国科学院国家授时中心（NTSC）每日例行预报的UT1-UTC为例进行了试验验证,进一步验证了LS＋AR模型的有效性。

The combination of least squares（LS） and autoregressive（AR） models is proposed as a prediction model to forecast UT1-UTC in this paper.The main idea is as follows.An UT1-UTC time-series are first corrected for the tidal terms and leap seconds,and then the corrected UT1-UTC time-series are differenced once between adjacent epochs to obtain a one-order differenced sequence.Secondly,the differenced sequence is fitted by using an LS model.Next,an AR model is used to model and extrapolate the LS fitting residuals.Thirdly,the predictions of the LS and AR models are added together to yield the predictions of the differenced sequence.Finally,to obtain the UT1-UTC forecasts,the predictions of the differenced sequence are recovered and the tidal terms and leap seconds are contributed to the predictions of the differenced sequence.The predicted results are analyzed and compared with those from the Earth Orientation Parameters Prediction Comparison Campaign（EOP PCC）.The results show that the accuracy of the ultra short-（1 to 10 days）,short-（1 to 30 days）,mediumand long-term（1 to 500 days） predictions approaches the advanced world level.The validity of the LS＋AR model is further validated by the real routine predictions at National Time Service Center（NTSC）.