Commission A2 WG Theory of Earth Rotation and Validation (IAU / IAG Joint WG)



To promote the development of theories of Earth rotation that are fully consistent and that agree with observations and provide predictions of the Earth orientation parameters (EOPs) with the accuracy required to meet the needs of the near future as recommended by, e.g., GGOS, the Global Geodetic Observing System of the International Association of Geodesy (IAG).


Recent efforts have not led to improvements in the accuracy of theoretical models of the Earth’s rotation that approach the required millimeter level, so there is a strong need to develop such theories to meet the current and future accuracy of the observations and trying to improve predictions.

Terms of Reference:

1. A main objective of the Working Group (WG) is to assess and ensure the level of consistency of EOP predictions derived from theories with the corresponding EOPs determined from analyses of the observational data provided by the various geodetic techniques. Consistency must be understood in its broader meaning, referring to models, processing standards, conventions etc.

2. Clearer definitions of polar motion and nutation are needed for both their separation in observational data analysis and for use in theoretical modeling.

3. Theoretical approaches must be consistent with IAU and IAG Resolutions concerning reference systems, frames and time scales.

4. Searching for potential sources of systematic differences between theory and observations is encouraged, including potential effects of differences in reference frame realization.

5. The derivation of comprehensive theories accounting for all relevant astronomical and geophysical effects and able to predict all EOPs is sought. In case more than one theory is needed to accomplish this, their consistency should be ensured.

6. There are no a priori preferred approaches or methods of solution, although solutions must be suitable for operational use and the simplicity of their adaptation to future improvements or changes in background models should be considered.

7. The incorporation into current models of corrections stemming from newly studied effects or improvements of existing models may be recommended by the JWG when they lead to significant accuracy enhancements, validated by comparisons with determined EOP.

Desired Outcomes:

1. Contribute to improving the accuracy of precession‐nutation and Earth rotation parameters (ERP) theoretical models by proposing both new models and additional corrections to existing ones.

2. Clarify the issue of consistency among conventional EOPs, their definitions in various theoretical approaches, and their practical determination.

3. Establish guidelines or requirements for future theoretical developments with improved accuracy.


Working Group Web Page

Working Group Members (35)


Commission A2 Rotation of the Earth

Jose Manuel Ferrándiz

Universidad de Alicante
Depto de Matematica Aplicada
Escuela Politécnica Superior
Campus de San Vicente. PO Box 99
03080 Alicante

Phone: +34 96 590 3731
Email: jmferrandizuaes
Organization website:

NCA adherence: Spain

Last updated:
July 11, 2018

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