ON THE INTERPRETATION OF MAXIMUM-ENTROPY POWER SPECTRUM AND CROSS-POWER SPECTRUM IN EARTH ROTATION INVESTIGATIONS

The maximum entropy method (MEM) of spectral analysis is frequently ap plied for an interpretation of the earth rotation data. We discuss her e some important properties of the MEM power spectrum estimate, which have not been exploited so far. A basic conclusion is that the estimat ion of the MEM power spectrum should always be followed by the derivat ion of the integrated power spectrum which provides realistic informat ion about power content in the detected spectral peaks, thus about the amplitude of the corresponding oscillations. We describe how it can b e achieved numerically and demonstrate the application for an analysis of the homogeneous International Latitude Service polar motion series . An interesting new result having important theoretical and practical implications is that from the integration of the Burg's (1968) MEM po wer spectrum estimate over the Nyquist frequency interval we recover e xactly a total sample power of the input series. It is also described and illustrated on a numerical example how the algorithms for the MEM spectral analysis can be utilized to estimate the MEM cross-power spec trum which can be useful in comparative analysis of the observational time series which are either real-valued, of the type of the universal time UT1, or complex-valued, of the type of polar motion.