Monash Uni, BoM sense bushfire haze with microwave backhaul signals

Microwave backhaul links used by mobile network operators may be a useful input into air quality measurement after research led by Monash University found that signal transmission patterns could be used to identify haze or smoke pollution in an area.

Led by Dr Adrien Guyot, a research fellow in Monash University’s Department of Civil Engineering, and involving the Australian Bureau of Meteorology (BoM) and Dutch researchers, the study “analysed radio link signal fluctuations during smoke events associated with the 2019-2020 Australian bushfires.”

Radio links, as defined by the study, are “commercial microwave links (CMLs) [and] are the backbone of cellular communication networks.”

“The use of CMLs for opportunistic sensing of atmospheric variables was proposed almost two decades ago,” the research paper states.

“One CML is made of a transmitting and a receiving antenna, operating in the microwave spectrum between 2 and 90 GHz and spanning over hundreds of meters to tens of kilometers.”

The researchers observed that “high ground-level concentrations of smoke … created irregular broadcast conditions for radio links and operational weather radars” in the affected area.

“Unique signal patterns were identified and shown to be related to these specific atmospheric conditions and smoke concentrations by analysing the received signal levels of these links,” the researchers said in a statement.

“This routinely recorded data by telecommunication companies could be used to predict smoke concentrations at ground level during haze events, in collaboration with other hazard reduction technologies.”

The researchers said microwave transmission data woukld be a useful input into “a blended product combining modelling, satellite remote sensing, weather radar ground clutter, in-situ observations and mobile phone data.”

Air quality monitoring using microwave signal propagation would be particularly valuable in rural areas where other air quality monitoring methods can be expensive to run.

“I can see this data being ingested in predictive capabilities no earlier than a couple of years from now, only once the technology and the understanding of processes will have reached maturity,” Dr Guyot said in a statement.

“This essentially depends on if adequate human resources and financial support are allocated to its development.”

Microwave links have also previously been used to measure other atmospheric conditions such as rainfall and humidity.  

Rainfall intensity and the concentration of water vapour in the air are known to impact attenuation - or loss of signal strength, the researchers noted.

However, they added that similar studies around the way smoke impacted transmission signals had not “seen very few investigations” until recently.

The study took into account transmission data from over 100 radio links operating across the "larger metropolitan area of Melbourne".

The work was funded from an Australian Research Council (ARC) discovery project grant.