A new hybrid method to improve the ultra-short-term prediction of LOD

Sadegh Modiri,Robert Heinkelmann,Harald Schuh,José M Ferrándiz,Santiago Belda,Mostafa Hoseini

doi:10.1007/s00190-020-01354-y

Abstract

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 since it is largely affected by the torques associated with changes in atmospheric circulation. In this study, the combination of Copula-based analysis and singular spectrum analysis (SSA) method is introduced to improve the accuracy of the forecasted LOD. The procedure operates as follows: First, we derive the dependence structure between LOD and the Z component of the effective angular momentum (EAM) arising from atmospheric, hydrologic, and oceanic origins (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 the IERS 05 C04 time series to assess the capability of our hybrid model. The results illustrate that the proposed method can efficiently predict LOD.

Highlights

Earth orientation parameters (EOP) are a collection of parameters that describe irregularities in the rotation of the Earth
We introduce an algorithm to improve the length of day (LOD) prediction for reaching the accuracy goals pursued by the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG), i.e., 1 mm accuracy and 0.1 mm/year stability on global scales in terms of the International Terrestrial Reference Frame (ITRF) defining parameters (Plag and Pearlman 2009)
We introduce several approaches based on Copulas which were applied to bivariate frequency analysis

Summary

Introduction

Earth orientation parameters (EOP) are a collection of parameters that describe irregularities in the rotation of the Earth. EOP are classified into three groups: polar motion (PM) given by the x, y, parameters; diurnal rotation (e.g., ERA = Earth rotation angle, or UT1-UTC); and precession–nutation (PN) pair, which give the orientation of the conventional Celestial Intermediate Pole (CIP) in the geocentric celestial reference. The EOP can be observed with modern high-precision space geodetic techniques, such as very long baseline interferometry (VLBI), satellite laser ranging (SLR), and global positioning system (GPS) (Tapley et al 1985; Lichten et al.1992; Schuh and Schmitz-Hübsch 2000). The prediction of EOP from past observed data or combining with the geophysical phenomena is of great scientific and practical importance. In addition to the five EOP, the length of day (LOD) is used to model the variations in the Earth’s rotation rate. LOD is the difference between the duration of the day measured by space geodesy and nominal day of 86,400 s duration and defined as: LOD

Methods

Discussion

Conclusion