The comparison of different spectrum analysis methods for LOD time series

Abstract

The variations in the Earth’s rotation are important to space dynamic theory and natural disasters because they affect the length-of-day (LOD) and consequently human lives. We use maximum entropy method (MEM), Lomb method (LOMB), and phase dispersion minimization (PDM) to determine the natural periods of equally spaced LOD time series. We transform the observational monthly LOD time series (LODM) to unequally sampled series (LODMD) by removing every fourth, third, and half of the total samples. We also apply spline interpolation to LODMD to yield equally spaced time series (LODMDN). The results suggest that regardless of the time series, the MEM frequency is 0.1660 month−1 and 0.0840 month−1, whereas LOMB and PDM yield 0.166 month−1 and 0.083 month−1, respectively. Furthermore, missing data that are less than half of the total data or spline interpolation do not affect the analysis. For the amplitude, neither missing data nor spline interpolation affect the analysis.