Precise water level measurements using low-cost GNSS antenna arrays

Abstract

Abstract. We have developed a ground-based Global Navigation Satellite System Reflectometry (GNSS-R) technique for monitoring water levels with a comparable precision to standard tide gauges (e.g. pressure transducers) but at a fraction of the cost and using commercial products that are straightforward to assemble. As opposed to using geodetic-standard antennas that have been used in previous GNSS-R literature, we use multiple co-located low-cost antennas to retrieve water levels via inverse modelling of signal-to-noise ratio data. The low-cost antennas are advantageous over geodetic-standard antennas not only because they are much less expensive (even when using multiple antennas in the same location) but also because they can be used for GNSS-R analysis over a greater range of satellite elevation angles. We validate our technique using arrays of four antennas at three test sites with variable tidal forcing and co-located operational tide gauges. The root mean square error between the GNSS-R and tide gauge measurements ranges from 0.69–1.16 cm when using all four antennas at each site. We find that using four antennas instead of a single antenna improves the precision by 30 %–50 % and preliminary analysis suggests that four appears to be the optimum number of co-located antennas. In order to obtain precise measurements, we find that it is important for the antennas to track GPS, GLONASS and Galileo satellites over a wide range of azimuth angles (at least 140∘) and elevation angles (at least 30∘). We also provide software for analysing low-cost GNSS data and obtaining GNSS-R water level measurements.

Raspberry Pi Reflector (RPR): A Low‐Cost Water‐Level Monitoring System Based on GNSS Interferometric Reflectometry

“…Their unit total cost, including solar power, was ∼ $200 U.S. dollars. Purnell et al (2021) employed a stack of side-facing low-cost antenna and receivers (total cost ∼ $200-300 U.S. dollars including solar panel and battery) to track the L1 frequency of multiple GNSS constellations. The water surface reflections extended more than 140° in azimuth and over a range of elevation angles up to 50°.…”

“…Such installations have far superior reflection characteristics at the cost of poor positioning capabilities. GNSS‐IR also benefits from using an inexpensive GNSS antenna which does not mitigate reflections to the same extent as larger geodetic antenna (Fagundes et al., 2021; Purnell et al., 2021; Williams et al., 2020).…”

Real‐Time Water Levels Using GNSS‐IR: A Potential Tool for Flood Monitoring

“…Recently it has become clear that compact, low‐cost (or mass‐market) GNSS antennas and receivers, such as those that are embedded in mobile devices, may be better suited for GNSS‐IR water level monitoring than geodetic‐standard antennas (Fagundes et al., 2021; Karegar et al., 2022; D. J. Purnell et al., 2021; Williams et al., 2020). Geodetic‐standard antennas are designed to reduce the interference from reflected GNSS signals, while the low‐cost antennas are not (it should be noted that the low‐cost antennas do not perform as well as geodetic‐standard antennas for positioning applications).…”

“…In D. J. Purnell et al. (2021) (henceforth DP21), the authors found that using multiple co‐located low‐cost antennas was an effective way to reduce the effect of random noise—a key source of uncertainty in GNSS‐IR water levels (D. Purnell et al., 2020)—and hence improve the precision of water levels.…”

“…Recently it has become clear that compact, low-cost (or mass-market) GNSS antennas and receivers, such as those that are embedded in mobile devices, may be better suited for GNSS-IR water level monitoring than geodetic-standard antennas (Fagundes et al, 2021;Karegar et al, 2022;D. J. Purnell et al, 2021;Williams et al, 2020).…”