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.

由于多年来观察到的气候变化，监测海平面至关重要。全球导航卫星系统反射法（GNSS-R）已被广泛证明用于沿海海平面监测。使用地面站的信噪比（SNR）观测结果对于测高应用特别有用。SNR记录了一个干涉图，其振荡频率允许检索未知的反射器高度。在这里，我们报告了基于SNR的GNSS-R完整硬件和软件系统的开发和验证。我们基于Arduino平台将其作为开源提供。它的价格约为200美元（包括太阳能电源），并且需要最少的组装商业现货组件。作为对沿海地区应用的初步验证，我们已经在巴西的瓜伊巴湖对系统进行了大约1年的评估。我们已经将水位测高仪的检索结果与同一地点的雷达潮汐仪（10 m以内）的独立测量结果进行了比较。GNSS-R设备几乎不间断运行，而参考雷达仪表则经历了两个故障时期，导致间隙持续了44天和38天。GNSS-R测高仪结果的稳定性使得能够在对雷达仪表进行维护后无意中引入了失调台阶（10 cm和15 cm）。排除雷达间隙及其故障周期（将时间序列的持续时间从317天减少到147天），我们发现每天的平均相关系数为0.989，RMSE为2.9 cm。为了促进开放科学并降低基于SNR的GNSS-R研究和应用的进入壁垒，