GeoWerkstatt-Projekt des Monats Juli 2026
Projekt: Combination of data from ring lasers, Lunar Laser Ranging (LLR) and Very Long Baseline Interferometry (VLBI) for optimal determination of Earth orientation Parameters (EOP) and their prediction
Forschende: Dr.-Ing Mingyue Zhang & Prof. Dr.-Ing. habil. Jürgen Müller
Projektidee: Covering the full spectrum of Earth rotation variations by combining ring laser data (high temporal resolution) with LLR and VLBI (long-term variations)
What do the GPS in our cars, space travel, and astronomy have in common? For all of this, it is important to know the Earth's exact rotation. The Earth does not always rotate in exactly the same way. For example, the Earth’s axis slowly points in different directions over time. This is called precession and nutation. The Earth Orientation Parameters (EOP) are quantities that describe how Earth is spinning with respect to “fixed” stars.
How are the Earth orientation parameters determined?
Earth Orientation Parameters are carefully measured using different techniques. In this project – as part of the new DFG research unit “RING: Rotational Movements in Physics, Geophysics, and Geodesy”, we will exploit the enhanced ring laser (RL) data for determining Earth Orientation Parameters (EOP) by combining ring laser with the complementary space geodetic techniques Very Long Baseline Interferometry (VLBI) and Lunar Laser Ranging (LLR).
- Ring Laser (RL): An enhanced ring laser is a powerful tool that helps scientists measure Earth's rotation very precisely by comparing the paths of light in a circular loop. It uses advanced technology to detect even the tiniest and fastest changes.
- Very Long Baseline Interferometry (VLBI): Huge radio telescopes in different parts of the world listen to radio waves from quasars, very bright objects that are so far away that they appear not to move at all. By comparing what each telescope “hears”, they can measure changes in the Earth’s orientation and determine the related reference systems.
- Lunar Laser Ranging (LLR): Scientists shoot lasers to special mirrors on the Moon. The laser beams bounce off the mirrors and one can measure how long it takes the laser pulse to come back, and so learn about the Earth’s and Moon’s dynamics.
What benefits are expected from combining these three techniques?
VLBI and LLR are unique in providing the full set of EOP, including the phase of Earth rotation ΔUT1 and precession-nutation. Moreover, they provide the links to the International Celestial Reference System (ICRS) – kinematically via VLBI and dynamically via the Lunar ephemeris (= precise position and rotation of the moon). The International Celestial Reference System (ICRS) is a universal sky map, which gives exact coordinates of the observed space objects. In contrast, RL enable the direct and near real-time measurement of variations of Earth rotation with high temporal resolution.
Due to the envisaged improvements of RL measurements and the advance of VLBI and LLR technologies in the Research Unit RING, we will determine a novel set of complete and consistent Earth Orientation Parameters by integrating RL, VLBI and LLR data. These unique EOP will cover the full frequency spectrum and provide a largely enhanced connection between the Earth- and space-fixed reference systems with utmost accuracy.
A further research objective is the prediction of EOP that will then also give improved values at high frequencies.
The innovative combination of the three techniques will enable also the determination of other specific VLBI and LLR parameters with higher accuracy. The three-technique combination will advance our understanding of all involved techniques and strongly support a better determination of the various physical parameters.
©
BKG / Uwe Hessels
©
Astrid Eckert / TUM
Earth rotation variations observed via space geodetic techniques like Lunar Laser Ranging, and ring lasers on ground, e.g, at the Geodetic Observatory in Wettzell.
What are the next steps?
In the first funding phase, we will quantify RL-based improvements for geodesy and fundamental physics through global scale simulations, where the focus at the Institute of Geodesy at Leibniz University Hannover is at the LLR part.
In the second phase, a sufficient number of RL data will be available to fully exploit their strength. One example is the worldwide leading tests of Einstein's relativity theory in the Earth-Moon system and beyond that can then be carried out at the next level of accuracy thanks to the RL data.
For more information see www.ringlaser.de
