許雪晴

(中國科學(xué)院上海天文臺(tái)上海200030)

地球定向參數(shù)高精度預(yù)報(bào)方法研究

許雪晴?

(中國科學(xué)院上海天文臺(tái)上海200030)

博士學(xué)位論文摘要選登

地球自轉(zhuǎn)表征了固體地球與大氣、海洋、地幔和地核在各種時(shí)空尺度上的耦合過程,地球的自轉(zhuǎn)運(yùn)動(dòng)可以用地球定向參數(shù)(EOP)(主要包括極移兩個(gè)分量和日長(zhǎng)變化)來描述.EOP是地球參考系和天球參考系之間的轉(zhuǎn)換參數(shù),在深空探測(cè)、衛(wèi)星精密定軌和天文地球動(dòng)力學(xué)研究等領(lǐng)域都有重要應(yīng)用.由于復(fù)雜的數(shù)據(jù)處理過程,空間大地測(cè)量技術(shù)獲取的EOP存在幾天至兩個(gè)星期的延遲.現(xiàn)代空間導(dǎo)航等對(duì)EOP預(yù)報(bào)值的需求日益增長(zhǎng),使得尋求高精度EOP預(yù)報(bào)方法成為一項(xiàng)需要深入研究的課題.本文主要從以下幾個(gè)方面展開,探討提高EOP預(yù)報(bào)精度的方法.

(1)分析基礎(chǔ)預(yù)報(bào)序列的長(zhǎng)度對(duì)EOP預(yù)報(bào)精度的影響,并應(yīng)用線性的自回歸(AR)模型和非線性的人工神經(jīng)網(wǎng)絡(luò)(ANN)模型對(duì)EOP殘差序列作預(yù)報(bào),結(jié)合最小二乘(LS)外推EOP周期項(xiàng)數(shù)據(jù),對(duì)比分析兩種方法的預(yù)報(bào)精度.結(jié)果表明,EOP預(yù)報(bào)精度與基礎(chǔ)預(yù)報(bào)序列長(zhǎng)度具有一定的聯(lián)系,預(yù)報(bào)工作中應(yīng)合理地選取基礎(chǔ)數(shù)據(jù)序列,預(yù)報(bào)跨度比較小的時(shí)候,基礎(chǔ)預(yù)報(bào)序列可以短一些,預(yù)報(bào)跨度大時(shí),則需要比較長(zhǎng)的基礎(chǔ)預(yù)報(bào)序列.對(duì)于EOP序列的不同跨度預(yù)報(bào),LS+AR模型在短期預(yù)報(bào)中精度較高,而LS+ANN模型則在中長(zhǎng)期預(yù)報(bào)中顯出優(yōu)勢(shì).

(2)研究一種AR模型與卡爾曼濾波(Kalman filter)的組合預(yù)報(bào)方法(AR+Kalman),并將此聯(lián)合方法首次運(yùn)用到EOP的短期預(yù)報(bào)中.該聯(lián)合方法是以EOP序列建立觀測(cè)方程,以AR模型自回歸系數(shù)建立狀態(tài)方程,形成卡爾曼濾波函數(shù)模型,對(duì)AR模型自回歸系數(shù)進(jìn)行濾波改正.計(jì)算結(jié)果表明,與單純的AR模型以及其他EOP預(yù)報(bào)結(jié)果相比較,AR+Kalman方法預(yù)報(bào)精度較高,表現(xiàn)更穩(wěn)定.其中,對(duì)PMX和PMY,預(yù)報(bào)呈現(xiàn)出明顯的精度優(yōu)勢(shì),對(duì)UT1-UTC和?LOD,預(yù)報(bào)也有較高的精度表現(xiàn).

(3)為了檢驗(yàn)我們的EOP預(yù)報(bào)工作,自2010年起參加了國際地球定向參數(shù)聯(lián)合預(yù)報(bào)(EOPC PPP)活動(dòng),也是我國首次參與此項(xiàng)活動(dòng).我們的預(yù)報(bào)產(chǎn)品包括PMX、PMY、UT1-UTC和?LOD的短期至中期(1～90 d)預(yù)報(bào)序列.從目前的統(tǒng)計(jì)結(jié)果來看,我們的EOP預(yù)報(bào)精度處于國際中等水平.在EOP預(yù)報(bào)方面,我們還處于起步階段,今后將進(jìn)一步拓展,開展更多的創(chuàng)新研究來提高EOP預(yù)報(bào)精度,更好地為導(dǎo)航定位等應(yīng)用需求服務(wù).

The Earth rotation reflects the coupling process among the solid Earth,atmosphere, oceans,mantle,and core of the Earth on multiple spatial and temporal scales.The Earth rotation can be described by the Earth’s orientation parameters,which are abbreviated as EOP(mainly including two polar motion components PMXand PMY,and variation in the length of day?LOD).The EOP is crucial in the transformation between the terrestrial and celestial reference systems,and has important applications in many areas such as the deep space exploration,satellite precise orbit determination,and astrogeodynamics.However, the EOP products obtained by the space geodetic technologies generally delay by several days to two weeks.The growing demands for modern space navigation make high-accuracy EOP prediction be a worthy topic.This thesis is composed of the following three aspects, for the purpose of improving the EOP forecast accuracy.

(1)We analyze the relation between the length of the basic data series and the EOP forecast accuracy,and compare the EOP prediction accuracy for the linear autoregressive (AR)model and the nonlinear artificial neural network(ANN)method by performing the least squares(LS)extrapolations.The results show that the high precision forecast of EOP can be realized by appropriate selection of the basic data series length according to the required time span of EOP prediction:for short-term prediction,the basic data series should be shorter,while for the long-term prediction,the series should be longer.The analysis also showed that the LS+AR model is more suitable for the short-term forecasts, while the LS+ANN model shows the advantages in the medium-and long-term forecasts.

(2)We develop for the first time a new method which combines the autoregressive model and Kalman filter(AR+Kalman)in short-term EOP prediction.The equations of observation and state are established using the EOP series and the autoregressive coefficients respectively,which are used to improve/re-evaluate the AR model.Comparing to the single AR model,the AR+Kalman method performs better in the prediction of UT1-UTC and?LOD,and the improvement in the prediction of the polar motion is significant.

(3)Following the successful Earth Orientation Parameter Prediction Comparison Campaign(EOP PCC),the Earth Orientation Parameter Combination of Prediction Pilot Project (EOPC PPP)was sponsored in 2010.As one of the participants from China,we update and submit the short-and medium-term(1 to 90 days)EOP predictions every day.From the current comparative statistics,our prediction accuracy is on the medium international level.We will carry out more innovative researches to improve the EOP forecast accuracy and enhance our level in EOP forecast.

Researches on High Accuracy Prediction Methods of Earth Orientation Parameters

XU Xue-qing
(Shanghai Astronomical Observatory,Chinese Academy of Sciences,Shanghai 200030)

10.15940/j.cnki.0001-5245.2015.05.012

?2013-01-06獲得博士學(xué)位,導(dǎo)師:上海天文臺(tái)周永宏研究員;xqxu@shao.ac.cn