中文摘要：

采用由国际地球自转及参考服务组织（IERS）提供的1990—2015年的EOP 08C04序列,分别利用小波变换和最小二乘法对极移（PM）和日长（LOD）的周期性变化进行了研究。小波分析结果表明,PM和LOD都存在明显的季节性和年际变化,但是,无法区分周年变化和钱德勒变化,可能是因为两者的频率太接近。在最小二乘意义上,对PM和LOD的趋势变化和周期变化进行了解算,结果发现LOD具有明显的半年和周年变化,同时探测了PM的半年和周年变化。1990—2015年间,LOD的趋势变化率为（-0.066 7±0.001 6）ms/a,PM在X和Y方向的趋势变化率分别为（2.898 0±0.131 0）mas/a和（0.957 0±0.152 0）mas/a,说明北极点相对地壳向18.3°E的方向移动。此外,对PM的X分量、PM的Y分量以及LOD两两之间进行了交叉小波变换,对三者之间的相关性进行了分析。

英文摘要：

The EOP 08C04 from 1990 to 2015 provided by international earth rotation and reference service organizations （IERS） are used to analyze periodic variation of polar motion （PM） and length of day （LOD）, by the wavelet power spectrum and the least square spectral analysis respectively. The Wavelet analysis shows obvious seasonal and interannual variations of LOD and PM; however, the annual variation can not be distinguished from the Chandler variation because the two frequencies are very close. The trends and periodic variations of LOD and PM are obtained in the least squares sense, and PM shows semi-annual, annual, and Chandler periods. Semi-annual and annual cycles for LOD are also detected. The trend rate of the LOD change is -0.066 7 ms per year. The trend rates of PM in the X and Y directions are 2.898 and 0.957 mas per year respectively, and the North Pole moves to 18.3°E relative to the crust during 1990-2015. In addition, the cross wavelet transform are used to analyze the relationships between PM in the X and Y directions and LOD.