Abstract
Monitoring sea level is critical due to climate change observed over the years. Global Navigation Satellite System Reflectometry (GNSS-R) has been widely demonstrated for coastal sea-level monitoring. The use of signal-to-noise ratio (SNR) observations from ground-based stations has been especially productive for altimetry applications. SNR records an interference pattern whose oscillation frequency allows retrieving the unknown reflector height. Here we report the development and validation of a complete hardware and software system for SNR-based GNSS-R. We make it available as open source based on the Arduino platform. It costs about US$200 (including solar power supply) and requires minimal assembly of commercial off-the-shelf components. As an initial validation towards applications in coastal regions, we have evaluated the system over approximately 1 year by the Guaíba Lake in Brazil. We have compared water-level altimetry retrievals with independent measurements from a co-located radar tide gauge (within 10 m). The GNSS-R device ran practically uninterruptedly, while the reference radar gauge suffered two malfunctioning periods, resulting in gaps lasting for 44 and 38 days. The stability of GNSS-R altimetry results enabled the detection of miscalibration steps (10 cm and 15 cm) inadvertently introduced in the radar gauge after it underwent maintenance. Excluding the radar gaps and its malfunctioning periods (reducing the time series duration from 317 to 147 days), we have found a correlation of 0.989 and RMSE of 2.9 cm in daily means. To foster open science and lower the barriers for entry in SNR-based GNSS-R research and applications, we make a complete bill of materials and build tutorials freely available on the Internet so that interested researchers can replicate the system.
Highlights
Monitoring sea level is fundamental to assess climate change observed over the years
We report the design of a complete hardware and software system for a signal-to-noise ratio (SNR)-based Global Navigation Satellite System Reflectometry (GNSS-R) sensor and demonstrate its validation for measuring water level
The 2.9 cm root-mean-square error (RMSE) statistic found in the present study is a bit higher than that of state of art in water-level sensing, it is comparable to previous GNSS-R studies, reporting centimeter-level RMSE
Summary
Extended author information available on the last page of the article having anthropic influence or not (Cazenave and Nerem 2004). Oceanography and geodesy have become of great importance for monitoring sea level (Tamisiea et al 2014), to help to predict future situations and in planning for mitigation and adaptation (Nicholls 2011; Elsharouny 2016). The determination of mean sea level and its temporal evolution remains a challenge due to the many variables involved. Observational gaps persist both in time and in space (Cazenave and Nerem 2004). Devices with different working principles have been used to measure sea level (Cipollini et al 2017). Monostatic satellite altimeters are the main instrument in the open oceans. Though, satellite altimetry confounds land and ocean, and tide gauges remain the instrument of choice. We are close to almost two centuries of experience with automatic tide gauges (Matthäus 1972); the traditional
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