GNSS reflectometry measurements improved with COVID-19 pandemic

Parked cars near ground station decreased accuracy from 2 to 4 centimeters

A new study shows that the quality of GNSS reflectometry measurements may have improved significantly during the pandemic because of the lack of cars parked near the ground station, according to Science Daily. GNSS reflectometry is used for earthquake early warning systems, determining flood risks, and many other geodesy applications.

The study, carried out by geodesists from the University of Bonn, investigated the location of a precise GNSS antenna in Boston, Massachusetts.

GNSS reflectometry works well if the surrounding ground is flat, like the surface of a mirror, study author Jürgen Kusche explained to Science Daily. “But many GNSS receivers are mounted on buildings in cities or in industrial zones. They are often surrounded by large parking lots — as is the case with the antenna we investigated in Boston.”

The researchers show that parked cars significantly reduced the quality of the elevation data by scattering the GNSS signals, causing them to be reflected several times before they reached the antenna, like a cracked mirror. This reduces signal intensity and provides “noisy” data — hard to correct with pattern recognition because the parked cars change positions every day.

“Before the pandemic, measurements of antenna height had an average accuracy of about 4 centimeters due to the higher level of noise,” Makan Karegar told Science Daily. “During the lockdown, however, there were almost no vehicles parked in the vicinity of the antenna; this improved the accuracy to about 2 centimeters.”

While GNSS stations were historically installed in sparsely populated regions, recent installations have been in urban areas to support engineering and surveying work.

“Our study recommends that we should try to avoid installation of GNSS sensors next to parking lots,” Karegar said.

Citation. Makan A. Karegar, Jürgen Kusche. Imprints of COVID‐19 lockdown on GNSS observations: An initial demonstration using GNSS interferometric reflectometry. Geophysical Research Letters, 2020; DOI: 10.1029/2020GL089647

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