How GPS Now Helps Us Forecast Rain More Accurately

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Scientists are using GPS signals to measure air moisture for better weather predictions.

The RMIT University, Geoscience Australia and Bureau of Meteorology (BoM) collaboration has harnessed the growing network of GPS receivers to provide more accurate, real time weather forecasts.

GPS signals can be slightly delayed on their journey from satellites to Earth by moisture in the troposphere, causing what’s known as a zenith total delay. Scientists now know how to use precise measurements of this delay to accurately calculate air moisture and likely rainfall.

Following successful trials across Australia, the method is now part of BoM's weather forecast models. RMIT Adjunct Professor and BoM Senior Principal Research Scientist, John Le Marshall, said it was an exciting new capability for real-time weather measurements and forecasting.

“Atmospheric water vapour is highly variable yet vital to accurate analysis and weather forecasting,” Le Marshall said. “The development of a GPS-based system to improve moisture analysis and forecasting over Australia is therefore an exciting step towards improved humidity and rainfall forecasting.”

GPS signals can be delayed on their journey from satellite to Earth by moisture in the troposphere, so measuring delays helps us calculate humidity and rainfall. GPS is proving increasingly useful to meteorologists, with another completed project using the bending of GPS signals through the atmosphere to determine temperature at various altitudes.

Le Marshall said while the technology could be applied almost anywhere, it was particularly valuable in a sparsely populated country like Australia with its lack of ground-based meteorological observation stations. “Weather forecasting is dependent on accurate atmospheric observations, but the limited stations we can draw measurements from across our vast continent has always been an issue,” he said. “With this technology we were able to tap into an Australia-wide network of 256 GPS receiving stations, and that number of stations is set to continue increasing over coming years.”

A study of the latest system was recently been published in Journal of Southern Hemisphere Earth Systems Science. Study co-author from RMIT University's School of Science, Dr Robert Norman, said the decade-long collaboration between RMIT and BoM had massive value for both partners. "Working closely with an end user like BoM enables us to apply our world-leading research in this field to solve real-world problems," Norman said. "Untimately, the improvement in BoM weather forecasting benefits Australian industry and the wider community as well."

RMIT was recently named Geospatial Research Institute of the Year for 2019 by the Geospatial World Forum.