Simple Explanation (ELI5)

Think of the Earth as a giant pillow: when the air pressure changes, the pillow slightly inflates or deflates by a millimeter. This tiny shift, known as 'tide loading', can move GPS reference points.

Key Advantages & Current Limits

🟢 Pros: Corrects systematic errors, improving GPS accuracy. 🟢 Pros: Helps meet millimeter-level requirements for the future global terrestrial reference frame. 🔴 Cons: The effect is tiny (sub-millimeter), often negligible. 🔴 Cons: Different models (GGFC vs VMF) can differ by up to 180°, introducing uncertainty.

Future Outlook & Takeaways

In the next 3-5 years, adoption of the GGFC model is expected to become standard, enhancing millimeter-level accuracy of the global terrestrial reference frame. This will lead to more reliable GPS positioning for scientific and industrial applications. Additionally, real-time integration of atmospheric data could further reduce uncertainties.

Do atmospheric tides shift GPS positions by a millimeter? Is it...

Article

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Ever thought that weather could nudge GPS reference points? When atmospheric pressure shifts, the Earth's crust deforms by a few millimetres. This "tide loading" effect is strongest with daily (S1) and semi‑daily (S2) atmospheric tides. Researchers compared two global models – the Global Geophysical Fluid Center (GGFC) and the Vienna Mapping Function (VMF) – to gauge how these tides affect GPS coordinates.

At low latitudes, the vertical (Up) displacement can reach 1.5 mm, three times larger than horizontal shifts. The biggest discrepancy between the models lies in the S2 phase for horizontal components, differing by up to 180°. To test real‑world impact, data from 108 international GPS stations were processed with and without S1‑S2 corrections. Results show RMS differences below 0.2 mm east‑west, but up to 0.5 mm upward.

In practice, part of the periodic GPS “draconitic” signals stems from unmodelled tides, with amplitudes around 0.2 mm upward. Experts recommend the GGFC model, which improves coordinate residuals for nearly half the stations. Although the effect on linear velocities is tiny, it still meets the millimetre‑level precision required for the future global terrestrial reference frame.

Bonus

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Atmospheric tides are periodic oscillations of atmospheric pressure, primarily driven by the differential solar heating between day and night. These oscillations exert loading forces on the Earth's surface, causing elastic deformation of the crust. The GGFC model employs high‑resolution global pressure data and a physical formulation based on elastic equilibrium equations, whereas VMF relies on a more simplified parametrization. The S2 phase, representing the semi‑daily component, is especially sensitive to the geographic distribution of air masses, explaining the observed phase discrepancies.

PPP (Precise Point Positioning) analyses allowed isolation of atmospheric tide effects from background noise, achieving coordinate solutions at the millimetre level. RMS (Root Mean Square) values were computed for each component (E, N, U) by comparing solutions with and without the correction. RMS reduction is more pronounced in the vertical component, consistent with larger vertical deformation amplitudes.

Draconitic harmonics, linked to Earth's orbital period around the Sun (365.25 days), appear in GPS data when loading corrections are omitted. Their amplitude of 0.2 mm in Up is significant for future Terrestrial Reference Frame (TRF) realizations, as GGOS standards demand stability at the millimetre level. Adopting the GGFC model, with its superior S2 phase representation, helps meet these requirements by reducing systematic uncertainty in global positioning products.