An open-source low-cost sensor for SNR-based GNSS reflectometry: design and long-term validation towards sea-level altimetry

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.

SNR-Based GNSS-R for Coastal Sea-Level Altimetry

“…The first inter-comparison campaign on geodetic GNSS-R for sea level monitoring confirmed an RMSE smaller than 5 cm between GNSS-R-derived sea levels and tide gauge records at the Onsala GNSS-R tide gauge station [11]. The authors also demonstrated that the dominant tidal constituents were well captured by geodetic GNSS-R. More recently, [12] reported a 2.9 cm RMS for daily water levels at Guaiba Lake in Rio Grande do Sul by developing an open-source low-cost sensor for SNR-based GNSS reflectometry.…”

Application of GNSS Reflectometry in Water Level Monitoring using Low-cost GNSS Antenna: A Case Study in Tam Giang Lagoon, Thua Thien Hue Province

“…Gần đây, các thiết bị GNSS chi phí thấp hơn được sử dụng để theo dõi mực nước như ăng-ten GNSS tích hợp trên máy tính bảng sử dụng phương pháp phân tích quang phổ dựa trên biểu đồ Lomb -Scargle [28]. Các ăng-ten GNSS đa tần chi phí thấp được sử dụng bởi [29,30] đã cho thấy là phù hợp hơn so với các ăng-ten tiêu chuẩn trắc địa vì các ăng ten tiêu chuẩn trắc địa được thiết kế để giảm nhiễu đa đường (tín hiệu được sử dụng để truy xuất độ cao mực nước). Mặt khác, các ăng-ten GNSS đa tần sử dụng mô hình khuếch đại đẳng hướng nên có thể sử dụng các tín hiệu từ vệ tinh GNSS ở các góc cao vệ tinh lớn trong khi các ăng-ten tiêu chuẩn trắc địa chỉ sử dụng tín hiệu ở góc cao vệ tinh thấp để thực hiện phép đo mực nước [11,12].…”

High-Rate Altimetry in SNR-Based GNSS-R: Proof-of-Concept of a Synthetic Vertical Array

“…SNR-based GNSS-R has better response at low elevation satellites, where the multiple ray paths have similar polarization and direction of arrival [6]. Furthermore, as sensing occurs at slant incidence, sea surface altimetry is feasible from a sensor installed away from the water [7] Unfortunately, SNR-based GNSS-R needs approximately one hour per altimetry retrieval, as it relies on satellite elevation angle variations. The low retrieval rate is one of the main weakness of this technique [5].…”