Ultra-short LOD prediction from EAM using Copula-based analysis + SSA method

Accurate, short-term predictions of Earth orientation parameters (EOP) are needed for many real-time applications including precise tracking and navigation of interplanetary spacecraft, climate forecasting, and disaster prevention. Out of the EOP, the LOD (length of day), which represents the changes in the Earth's rotation rate, is the most challenging to predict due to torques associated with changes in atmospheric circulation. In this study, the combination of Copula-based analysis and SSA method is employed to improve the accuracy of the forecasted LOD for the first time. There is a well-introduced method called Copula, and we want to combine it with the singular spectrum analysis (SSA) method for LOD prediction. First, we derive the dependence structure between LOD and the Z component of effective angular momentum (AAM+HAM+OAM). Based on the fitted theoretical Copula, we then simulate LOD from the Z component of EAM data. Next, the difference between LOD time series and its Copula-based estimation is modeled using SSA. Multiple sets of short-term LOD prediction have been done based on IERS 08 C04 time series to assess the capability of our hybrid model. The preliminary results illustrate that the proposed method can efficiently predict LOD.