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GNSS service may not be adversely affected by August 21 solar eclipse in US, says NASA

NASA map of the United States showing the path of totality for the August 21 total solar eclipse. Photo Credit: NASA

On Monday, August 21, all of North America will be treated to an eclipse of the sun. To cover the event and give an in-depth analysis, NASA has developed a website that will offer guidance and has issued a statement about the eclipse’s effect on GNSS users.

This path of the total solar eclipse, where the moon will completely cover the sun and the sun’s tenuous atmosphere — the corona — can be seen, which will stretch from Salem, Oregon to Charleston, South Carolina. Observers outside this path will still see a partial solar eclipse.

From the ionospheric point of view, the expected effect of solar eclipse is a significant reduction in solar EUV ionization (solar EUV radiation is blocked) and thus in the amount of ionospheric total electron content (TEC) with respect to nominal conditions along the eclipse path. Some observations also show wave-like TEC perturbations in small magnitude (~1 TECU) during. The wave-like perturbations appear to be the effect of atmospheric gravity waves or traveling ionospheric disturbances (TIDs) that might be triggered during eclipse.

The TEC decrease would reduce the ionospheric-induced delay of GPS signals. The small-magnitude TIDs won’t cause any major effects on GPS signals. These should not cause loss of GPS signals.

A solar eclipse occurs when the Moon passes between the Sun and the Earth, thereby totally or partly obscuring the image of the sun for a viewer on Earth. There is a region of Earth’s upper atmosphere, called the ionosphere which affects radio waves, including GNNS. The ionosphere consists of “ions,” a shell of electrons and electrically charged atoms and molecules. Because ions are created through sunlight interacting with the atoms and molecules in the very thin upper atmosphere, the density (thickness and consistency) of the ionosphere varies from day to night.

The ionosphere bends radio signals, similar to the way water will bend light signals. That is why you can hear AM radio broadcasts from far away at night. Also, ham radio operators rely on the ionosphere to bounce their signals from their station to the far reaches of the globe.

Since GNSS is a radio signal, its measurements are slightly impacted by ionosphere changes, resulting in small increases in position error. For all except very precise GNSS users, these changes are negligible. Note that a total eclipse of the sun is similar to our day-night cycle, only very much faster. So, while the ionosphere will be more dynamic during an eclipse, it will not cause a loss of the GNSS signal.

In summary, while any effects from the eclipse are of scientific interest, GNSS service should not be adversely affected by the Aug. 21 Solar Eclipse.

Ionospheric effects should not be confused with those from solar flares (a brief eruption of intense high-energy radiation from the sun’s surface) that can cause significant electromagnetic disturbances on the Earth, impacting radio frequency communications/transmissions (including GNSS signals) and power line transmissions. Solar flares are not produced because of an eclipse.