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

GPS Solutions ◽  
2021 ◽  
Vol 25 (2) ◽  
Author(s):  
M. A. R. Fagundes ◽  
I. Mendonça-Tinti ◽  
A. L. Iescheck ◽  
D. M. Akos ◽  
F. Geremia-Nievinski
Keyword(s):  
Open Source ◽  
Sea Level ◽  
Tide Gauge ◽  
Signal To Noise Ratio ◽  
Low Cost ◽  
Satellite System ◽  
Open Science ◽  
Coastal Sea ◽  
Commercial Off The Shelf ◽  
Global Navigation Satellite

AbstractMonitoring 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.

Performance Assessment of GNSS-R Polarimetric Observations for Sea Level Monitoring

2021 ◽  
Author(s):  
Mahmoud Rajabi ◽  
Mstafa Hoseini ◽  
Hossein Nahavandchi ◽  
Maximilian Semmling ◽  
Markus Ramatschi ◽  
...  
Keyword(s):  
Time Series ◽  
Circular Polarization ◽  
Sea Level ◽  
Tide Gauge ◽  
Satellite System ◽  
Sea Surface ◽  
Analysis Tool ◽  
Lower Accuracy ◽  
Coastal Sea ◽  
Global Navigation Satellite

<p>Determination and monitoring of the mean sea level especially in the coastal areas are essential, environmentally, and as a vertical datum. Ground-based Global Navigation Satellite System Reflectometry (GNSS-R) is an innovative way which is becoming a reliable alternative for coastal sea-level altimetry. Comparing to traditional tide gauges, GNSS-R can offer different parameters of sea surface, one of which is the sea level. The measurements derived from this technique can cover wider areas of the sea surface in contrast to point-wise observations of a tide gauge.  </p><p>We use long-term ground-based GNSS-R observations to estimate sea level. The dataset includes one-year data from January to December 2016. The data was collected by a coastal GNSS-R experiment at the Onsala space observatory in Sweden. The experiment utilizes three antennas with different polarization designs and orientations. The setup has one up-looking, and two sea-looking antennas at about 3 meters above the sea surface level. The up-looking antenna is Right-Handed Circular Polarization (RHCP). The sea-looking antennas with RHCP and Left-Handed Circular Polarization (LHCP) are used for capturing sea reflected Global Positioning System (GPS) signals. A dedicated reflectometry receiver (GORS type) provides In-phase and Quadrature (I/Q) correlation sums for each antenna based on the captured interferometric signal. The generated time series of I/Q samples from different satellites are analyzed using the Least Squares Harmonic Estimation (LSHE) method. This method is a multivariate analysis tool which can flexibly retrieve the frequencies of a time series regardless of possible gaps or unevenly spaced sampling. The interferometric frequency, which is related to the reflection geometry and sea level, is obtained by LSHE with a temporal resolution of 15 minutes. The sea level is calculated based on this frequency in six modes from the three antennas in GPS L1 and L2 signals.</p><p>Our investigation shows that the sea-looking antennas perform better compared to the up-looking antenna. The highest accuracy is achieved using the sea-looking LHCP antenna and GPS L1 signal. The annual Root Mean Square Error (RMSE) of 15-min GNSS-R water level time series compared to tide gauge observations is 3.7 (L1) and 5.2 (L2) cm for sea-looking LHCP, 5.8 (L1) and 9.1 (L2) cm for sea-looking RHCP, 6.2 (L1) and 8.5 (L2) cm for up-looking RHCP. It is worth noting that the GPS IIR block satellites show lower accuracy due to the lack of L2C code. Therefore, the L2 observations from this block are eliminated.</p>

Further validation of an open-source low-cost GNSS-R remote sensor for coastal sea level altimetry

2021 ◽  
Author(s):  
Manuella Fagundes ◽  
Felipe Geremia-Nievinski
Keyword(s):  
Open Source ◽  
Sea Level ◽  
Tide Gauge ◽  
Low Cost ◽  
Superposition Principle ◽  
Weather Conditions ◽  
Breaking Waves ◽  
Mitigation Strategies ◽  
Destructive Interference ◽  
Coastal Sea

<p>Contemporary sea level rise renders tide gauging essential in support of adaptation and mitigation strategies and to minimize its economic and societal impacts. Global Navigation Satellite System Reflectometry (GNSS-R) has been widely demonstrated for coastal sea level monitoring. One particular configuration of GNSS-R, called GNSS multipath reflectometry (GNSS-MR), is based on the combined tracking of direct and reflected radio waves against a single signal replica. The most common observable in GNSS-MR is the signal-to-noise ratio (SNR), which records the constructive/destructive interference pattern arising from the superposition of the two coherent ray paths. Recently we reported the development of a complete hardware and software system for SNR-based GNSS-R. We made it freely available as open-source based on low-cost commercial off-the-shelf components. We have deployed multiple working units of the sensor in the field, where they have operated uninterruptedly 24/7 for years, having resisted severe weather conditions. Initial validation was done by a lake (30.0277° S, 51.2287° W) for 317 days by comparison to a co-located radar-type tide gauge. Statistics confirmed that the sensor can retrieve water level with a very high correlation (0.989) and centimeter-level RMSE (2.9 cm). Here we report further coastal validation results of our GNSS-R sensor. The experiment was setup in a port (28.232019° S, 48.651064° W) with several co-located tide gauges within 100-m distance, including a radar sensor with 5-minute update interval and millimeter numerical resolution. We analyzed the time series of one week (June 19-25, 2019), and found a correlation of 0.885 and RMSE of 8.0 cm. We should emphasize this is the instantaneous sea level results and results for daily mean sea level would be improved. Although the location is sheltered from breaking waves, wind-driven waves are much greater, compared to the initial lake experiment. The increased surface roughness affects the coherence of radio wave reflections, which may eventually hamper the interferometric superposition principle, essential in GNSS-MR. This is part of ongoing validation efforts to quantity how correlation and RMSE in sea level altimetry are degraded due to the above error sources.</p>

Beach Deployment of a Low-Cost GNSS Buoy for Determining Sea-Level and Wave Characteristics

Geosciences ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 494
Author(s):  
Philip J. Knight ◽  
Cai O. Bird ◽  
Alex Sinclair ◽  
Jonathan Higham ◽  
Andrew J. Plater
Keyword(s):  
Sea Level ◽  
Tide Gauge ◽  
Low Cost ◽  
Satellite System ◽  
Mooring Line ◽  
Level Data ◽  
Elevation Data ◽  
Satellite Signal ◽  
Global Navigation Satellite ◽  
Spatially Explicit Data

Spatially explicit data on tidal and waves are required as part of coastal monitoring applications (e.g., radar monitoring of coastal change) for the design of interventions to mitigate the impacts of climate change. A deployment over two tidal cycles of a low-cost Global Navigation Satellite System (GNSS) buoy at Rossall (near Fleetwood), UK demonstrated the potential to record good quality sea level and wave data within the intertidal zone. During each slack water and the following ebb tide, the sea level data were of good quality and comparable with data from nearby tide gauges on the national tide gauge network. Moreover, the GNSS receiver was able to capture wave information and these compared well with data from a commercial wave buoy situated 9.5 km offshore. Discontinuities were observed in the elevation data during flood tide, coincident with high accelerations and losing satellite signal lock. These were probably due to strong tidal currents, which, combined with spilling waves, would put the mooring line under tension and allow white water to spill over the antenna resulting in the periodic loss of GNSS signals, hence degrading the vertical solutions.

scholarly journals High-rate altimetry in SNR-based GNSS-R: Proof-of-concept of a synthetic vertical array

2021 ◽  
Author(s):  
Mauricio Kenji Yamawaki ◽  
Felipe Geremia-Nievinski ◽  
João Francisco Monico
Keyword(s):  
Sea Level ◽  
Signal To Noise Ratio ◽  
Satellite System ◽  
High Rate ◽  
Proof Of Concept ◽  
Radio Waves ◽  
Vertical Array ◽  
Remote Sensing Technique ◽  
Single Antenna ◽  
Global Navigation Satellite

Global Navigation Satellite System Reflectometry (GNSS-R) has emerged as a promising remote sensing technique for coastal sea level monitoring. The GNSS-R based on signal-to-noise ratio (SNR) observations employs a single antenna and a conventional receiver. It performs best for low elevation satellites, where direct and reflected radio waves are very similar in polarization and direction of arrival. One of the disadvantages of SNR-based GNSS-R for sea level altimetry is its low temporal resolution, which is of the order of one hour for each independent satellite pass. Here we present a proof-of-concept based on a synthetic vertical array. It exploits the mechanical movement of a single antenna at high rate (about 1 Hz). SNR observations can then be fit to a known modulation, of the order of the antenna sweeping rate. We demonstrate that centimetric altimetry precision can be achieved in a 5-minute session. [©2021 IEEE]

scholarly journals Precise water level measurements using low-cost GNSS antenna arrays

2021 ◽  
Author(s):  
David J. Purnell ◽  
Natalya Gomez ◽  
William Minarik ◽  
David Porter ◽  
Gregory Langston
Keyword(s):  
Antenna Arrays ◽  
Tide Gauge ◽  
Signal To Noise Ratio ◽  
Low Cost ◽  
Satellite System ◽  
Water Levels ◽  
Optimum Number ◽  
Tide Gauges ◽  
Single Antenna ◽  
Wide Range

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 because they are much less expensive (even when using multiple antennas in the same location) and 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 0.7–1.2 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 degrees) and elevation angles (at least 30 degrees).

scholarly journals Coastal sea level rise at Senetosa (Corsica) during the Jason altimetry missions

Ocean Science ◽  
2020 ◽  
Vol 16 (5) ◽  
pp. 1165-1182 ◽  
Author(s):  
Yvan Gouzenes ◽  
Fabien Léger ◽  
Anny Cazenave ◽  
Florence Birol ◽  
Pascal Bonnefond ◽  
...  
Keyword(s):  
High Resolution ◽  
Sea Level Rise ◽  
Sea Level ◽  
Leading Edge ◽  
Satellite System ◽  
Careful Examination ◽  
Coastal Zones ◽  
Coastal Sea ◽  
Potential Contributor ◽  
Global Navigation Satellite

Abstract. In the context of the ESA Climate Change Initiative project, we are engaged in a regional reprocessing of high-resolution (20 Hz) altimetry data of the classical missions in a number of the world's coastal zones. It is done using the ALES (Adaptive Leading Edge Subwaveform) retracker combined with the X-TRACK system dedicated to improve geophysical corrections at the coast. Using the Jason-1 and Jason-2 satellite data, high-resolution, along-track sea level time series have been generated, and coastal sea level trends have been computed over a 14-year time span (from July 2002 to June 2016). In this paper, we focus on a particular coastal site where the Jason track crosses land, Senetosa, located south of Corsica in the Mediterranean Sea, for two reasons: (1) the rate of sea level rise estimated in this project increases significantly in the last 4–5 km to the coast compared to what is observed further offshore, and (2) Senetosa is the calibration site for the TOPEX/Poseidon and Jason altimetry missions, which are equipped for that purpose with in situ instrumentation, in particular tide gauges and a Global Navigation Satellite System (GNSS) antenna. A careful examination of all the potential errors that could explain the increased rate of sea level rise close to the coast (e.g., spurious trends in the geophysical corrections, imperfect inter-mission bias estimate, decrease of valid data close to the coast and errors in waveform retracking) has been carried out, but none of these effects appear able to explain the trend increase. We further explored the possibility that it results from real physical processes. Change in wave conditions was investigated, but wave setup was excluded as a potential contributor because the magnitude was too low and too localized in the immediate vicinity of the shoreline. A preliminary model-based investigation about the contribution of coastal currents indicates that it could be a plausible explanation of the observed change in sea level trend close to the coast.

scholarly journals A comparison of methods to estimate vertical land motion trends from GNSS and altimetry at tide gauge stations

Ocean Science ◽  
2018 ◽  
Vol 14 (2) ◽  
pp. 187-204 ◽  
Author(s):  
Marcel Kleinherenbrink ◽  
Riccardo Riva ◽  
Thomas Frederikse
Keyword(s):  
Time Series ◽  
Sea Level ◽  
Tide Gauge ◽  
Satellite System ◽  
Vertical Land Motion ◽  
Correlation Threshold ◽  
The Mean ◽  
Highly Correlated ◽  
Global Navigation Satellite ◽  
Along Track

Abstract. Tide gauge (TG) records are affected by vertical land motion (VLM), causing them to observe relative instead of geocentric sea level. VLM can be estimated from global navigation satellite system (GNSS) time series, but only a few TGs are equipped with a GNSS receiver. Hence, (multiple) neighboring GNSS stations can be used to estimate VLM at the TG. This study compares eight approaches to estimate VLM trends at 570 TG stations using GNSS by taking into account all GNSS trends with an uncertainty smaller than 1 mm yr−1 within 50 km. The range between the methods is comparable with the formal uncertainties of the GNSS trends. Taking the median of the surrounding GNSS trends shows the best agreement with differenced altimetry–tide gauge (ALT–TG) trends. An attempt is also made to improve VLM trends from ALT–TG time series. Only using highly correlated along-track altimetry and TG time series reduces the SD of ALT–TG time series by up to 10 %. As a result, there are spatially coherent changes in the trends, but the reduction in the root mean square (RMS) of differences between ALT–TG and GNSS trends is insignificant. However, setting correlation thresholds also acts like a filter to remove problematic TG time series. This results in sets of ALT–TG VLM trends at 344–663 TG locations, depending on the correlation threshold. Compared to other studies, we decrease the RMS of differences between GNSS and ALT–TG trends (from 1.47 to 1.22 mm yr−1), while we increase the number of locations (from 109 to 155), Depending on the methods the mean of differences between ALT–TG and GNSS trends vary between 0.1 and 0.2 mm yr−1. We reduce the mean of the differences by taking into account the effect of elastic deformation due to present-day mass redistribution. At varying ALT–TG correlation thresholds, we provide new sets of trends for 759 to 939 different TG stations. If both GNSS and ALT–TG trend estimates are available, we recommend using the GNSS trend estimates because residual ocean signals might correlate over long distances. However, if large discrepancies ( > 3 mm yr−1) between the two methods are present, local VLM differences between the TG and the GNSS station are likely the culprit and therefore it is better to take the ALT–TG trend estimate. GNSS estimates for which only a single GNSS station and no ALT–TG estimate are available might still require some inspection before they are used in sea level studies.

scholarly journals High-rate altimetry in SNR-based GNSS-R: Proof-of-concept of a synthetic vertical array

2021 ◽  
Author(s):  
Mauricio Kenji Yamawaki ◽  
Felipe Geremia-Nievinski ◽  
João Francisco Monico
Keyword(s):  
Sea Level ◽  
Signal To Noise Ratio ◽  
Satellite System ◽  
High Rate ◽  
Proof Of Concept ◽  
Radio Waves ◽  
Vertical Array ◽  
Remote Sensing Technique ◽  
Single Antenna ◽  
Global Navigation Satellite

Global Navigation Satellite System Reflectometry (GNSS-R) has emerged as a promising remote sensing technique for coastal sea level monitoring. The GNSS-R based on signal-to-noise ratio (SNR) observations employs a single antenna and a conventional receiver. It performs best for low elevation satellites, where direct and reflected radio waves are very similar in polarization and direction of arrival. One of the disadvantages of SNR-based GNSS-R for sea level altimetry is its low temporal resolution, which is of the order of one hour for each independent satellite pass. Here we present a proof-of-concept based on a synthetic vertical array. It exploits the mechanical movement of a single antenna at high rate (about 1 Hz). SNR observations can then be fit to a known modulation, of the order of the antenna sweeping rate. We demonstrate that centimetric altimetry precision can be achieved in a 5-minute session. [©2021 IEEE]

scholarly journals Testing an “IoT” Tide Gauge Network for Coastal Monitoring

IoT ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 17-32
Author(s):  
Philip Knight ◽  
Cai Bird ◽  
Alex Sinclair ◽  
Jonathan Higham ◽  
Andy Plater
Keyword(s):  
Sea Level ◽  
Morphological Changes ◽  
Tide Gauge ◽  
Low Cost ◽  
Pressure Sensors ◽  
Wave Activity ◽  
Tide Gauges ◽  
Coastal Monitoring ◽  
Level Data ◽  
Operational Constraints

A low-cost “Internet of Things” (IoT) tide gauge network was developed to provide real-time and “delayed mode” sea-level data to support monitoring of spatial and temporal coastal morphological changes. It is based on the Arduino Sigfox MKR 1200 micro-controller platform with a Measurement Specialties pressure sensor (MS5837). Experiments at two sites colocated with established tide gauges show that these inexpensive pressure sensors can make accurate sea-level measurements. While these pressure sensors are capable of ~1 cm accuracy, as with other comparable gauges, the effect of significant wave activity can distort the overall sea-level measurements. Various off-the-shelf hardware and software configurations were tested to provide complementary data as part of a localized network and to overcome operational constraints, such as lack of suitable infrastructure for mounting the tide gauges and for exposed beach locations.

scholarly journals Design of a Multiband Global Navigation Satellite System Radio Frequency Interference Monitoring Front-End with Synchronized Secondary Sensors

Sensors ◽  
2018 ◽  
Vol 18 (8) ◽  
pp. 2594
Author(s):  
Aiden Morrison ◽  
Nadezda Sokolova ◽  
James Curran
Keyword(s):  
Radio Frequency ◽  
Global Navigation Satellite System ◽  
Low Cost ◽  
Satellite System ◽  
Radio Frequency Interference ◽  
Navigation Satellite ◽  
Inertial Measurement ◽  
Front End ◽  
Global Navigation ◽  
Global Navigation Satellite

This paper investigates the challenges of developing a multi-frequency radio frequency interference (RFI) monitoring and characterization system that is optimized for ease of deployment and operation as well as low per unit cost. To achieve this, we explore the design and development of a multiband global navigation satellite system (GNSS) front-end which is intrinsically capable of synchronizing side channel information from non-RF sensors, such as inertial measurement units and integrated power meters, to allow the simultaneous production of substantial amounts of sampled spectrum while also allowing low-cost, real-time monitoring and logging of detected RFI events. While the inertial measurement unit and barometer are not used in the RFI investigation discussed, the design features that provide for their precise synchronization with the RF sample stream are presented as design elements worth consideration. The designed system, referred to as Four Independent Tuners with Data-packing (FITWD), was utilized in a data collection campaign over multiple European and Scandinavian countries in support of the determination of the relative occurrence rates of L1/E1 and L5/E5a interference events and intensities where it proved itself a successful alternative to larger and more expensive commercial solutions. The dual conclusions reached were that it was possible to develop a compact low-cost, multi-channel radio frequency (RF) front-end that implicitly supported external data source synchronization, and that such monitoring systems or similar capabilities integrated within receivers are likely to be needed in the future due to the increasing occurrence rates of GNSS RFI events.

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