A Low-Cost Flood-Proof Water Level Measurement System, Using GNSS Reflectrometry

Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) is a well-established technology to determine water heights in reservoirs, rivers, and lakes. A big advantage of GNSS-IR over traditional level measurements is that it is a non-contact flood-proof method. So far, GNSS-IR has been applied through off-site processing, necessitating a good internet connection for near-real-time monitoring. In Africa, where the TEMBO project seeks to develop in situ monitoring of weather and water, such connections are often not available, especially in more remote river valleys. Although a live satellite uplink would be possible, these tend to be costly and very energy-hungry. For this reason, equipment was developed that allowed local processing (edge processing). The advantage is that only water levels and some system information need to be communicated, which can be done with a simple satellite modem at very moderate costs. Existing gnssrefl code (https://gnssrefl.readthedocs.io/), written in Python, was rewritten in Rust to facilitate running the code on a PICO 2.  By reducing unneeded lines of code, the runtime was reduced from three minutes with the original Python code to less than three seconds. In all, energy use was minimized to avoid the need for large solar panels. With power cycling and uploads four times per day, the average power consumption was 44mW, which translates into a small solar panel of 1.2 W (66mm x 113mm). Water level measurement accuracy depended on integration time or, better, the number of satellites captured and was about 8cm when five or more satellites were captured. Total material costs, excluding the satellite modem, were about EU 50. The satellite modem and antenna were, at EU 360, the most expensive parts.

TEMBO Africa: The work leading to these results has received funding from the European Horizon Europe Programme (2021-2027) under grant agreement n° 101086209. The opinions expressed in the document are of the authors only and in no way reflect the European Commission’s opinions. The European Union is not liable for any use that may be made of the information.