Researchers at the Institute of Geodesy and Geoinformation at the University of Bonn, led by Dr. Makan Karegar, have transferred water -level monitoring technology from the Rhine to Africa, Australia, and the Philippines as part of ESA projects. Originally developed in the DFG Collaborative Research Center SFB 1502 (DETECT), the technology enables continuous, freely accessible monitoring of inland and coastal waters in data-poor regions worldwide.
Developed in Bonn, active today on three continents
The technological centerpiece is the Raspberry Pi Reflector (RPR), a compact, solar-powered sensor developed at the University of Bonn. Using Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR), it measures water levels with centimeter-level accuracy (https://www.uni-bonn.de/en/news/272-2022).
Only a portion of the signals emitted by the GNSS satellites is directly captured by the antenna. The rest is reflected by the water surface and reaches the receiver via this detour. When superimposed with the directly received signal, it forms specific patterns known as interference patterns. These can be used to calculate the distance from the antenna to the water surface.
Each unit costs less than about 800 euros, is powered by solar energy, and transmits data daily via mobile networks. “Modern gauge stations are prohibitively expensive, and conventional ones are highly vulnerable to flood damage. These two factors together have left many countries in the Global South with little to no ground-based water-level monitoring. The low-cost GNSS-IR sensor was developed precisely to address this gap,” says Karegar.
CAMEO-WAGST Project
The CAMEO-WAGST project (“Cameroon Advanced Measurements for Enhanced Observations of Water levels using Affordable GNSS-IR and Sentinel-3 & 6 Technology”) has established the first dedicated GNSS-IR network for monitoring water levels along coasts and rivers in Camroon and was funded by the European Space Agency (ESA). Between May and June 2025, researchers, in collaboration with Dr. Loudi Yap, director of the Research Laboratory in Geodesy at the National Institute of Cartography, installed eight RPR sensors in Cameroon—two on the Sanaga River and six along the coast. “A lack of infrastructure for reliable hydrological and coastal monitoring in Cameroon has so far hindered effective flood risk management and early warning systems,” said Yap.
This collaboration, under the umbrella of the EO Africa Research and Development Facility, is already bearing fruit, says Dr. Roelof Rietbroek, research coordinator at ESA’s EO Africa R&D Facility. “We hope this paves the way for more reliable monitoring of flood-prone regions in Africa.”
St3TART-FO Project
Building on this success, the follow-up project St3TART-FO was launched in collaboration with the European Space Agency. A total of 17 RPR sensors will be installed in seven countries, including West Africa, Australia, and the Philippines. “The goal is to create a freely accessible reference measurement network for calibrating satellite data,” says Karegar. For the first time, the network will provide continuous water-level data at previously unmonitored locations.
The collaboration is based on years of scientific exchange between Africa and Europe. Partners include the International Institute for Water and Environmental Engineering (2iE) in Burkina Faso, the National Institute of Cartography in Cameroon, Ghana's Environmental Protection Authority (EPA), the Nigeria Hydrological Services Agency (NiHSA) and the University of Maiduguri in Nigeria, Assane Seck University of Ziguinchor in Senegal, the University of Southern Queensland in Australia, and the University of the Philippines Diliman.
Focus on Technology Transfer and Capacity Building
Both projects promote technology transfer and local capacity building through training, workshops, and mentoring, enabling partner institutions to operate RPR networks independently. “We want to leave behind a sustainable monitoring capacity that is operated by local scientists and institutions, openly shared with the world, and maintained well into the future,” says Dr. Makan Karegar, project manager for both initiatives.
With financial support from the Transdisciplinary Research Area (TRA) “Sustainable Futures” at the University of Bonn, Dr. Makan Karegar developed the open-access data platform gnss4surfacewater.com, which provides an independent, ground-based service for monitoring current and historical water levels using GNSS-IR.
Further information:
Open data platform: gnss4surfacewater.com
CAMEO-WAGST GitHub (code & field photos): github.com/MakanAKaregar/ESA_CAMEO_WGAST
