The Raspberry Pi Reflector Uses GPS Signals to Monitor Rivers for Flooding Risks

A team of scientists from the University of Bonn, the Federal University of Rio Grande do Sul, and the University of Colorado have developed a low-cost solar-powered sensor designed to provide wide-area flood warnings: the Raspberry Pi Reflector (RPR).

"The Raspberry Pi Reflector (RPR) is a prototype for tracking water levels with centimeter level accuracy," the team explains of its creation. "The core of our device is a low-cost GNSS [Global Navigation Satellite System] receiver and antenna," adds Makan Karegar, PhD and first author of the paper detailing the project. "[The] satellite signals can also be used to measure the height of the GNSS antenna above the river surface."

The method of operation is given in its name: only some of the GNSS radio signals are picked up directly from the satellites, with the remainder coming in as environmental reflections — including from the surface of the river to be monitored. By creating an interference pattern between the directly-received and the reflected signals, the Raspberry Pi can figure out the distance between the antenna and the water's surface.

"We can attach the GNSS antenna to any structure, whether it's a bridge, a building, or a tree or fence next to the river," Karegar explains. "From there, it can measure the river level around the clock without contact — to within around 1.5 centimeters [around 0.6"] on average. And yet it is less likely to be damaged during extreme flooding events."

With little more than a Raspberry Pi single-board computer, Adafruit GPS FeatherWing and Adalogger data-logging board, and either a local power source or a solar panel, the Raspberry Pi Reflector is an extremely affordable way to monitor water levels in rivers — but there is one catch: the current version only works if the river's width is at least 131 feet wide. ""This is the smallest radius from which the antenna can receive the reflected satellite signal," Karegar says. "If the watercourse is too narrow, most of the reflected signals come from the land."

Interested parties can find full instructions and source code for creating their own Raspberry Pi Reflector on Karegar's GitHub repository, under an unspecified open source license. The paper detailing the project, meanwhile, has been published in the journal Water Resources Research and is available in accepted article form under open-access terms.