Sea Level Monitoring Research Articles

A Correction Method of Height Variation Error Based on One SNR Arc Applied in GNSS–IR Sea-Level Retrieval

Sea-level monitoring is important for the safety of coastal cities and analysis of ocean and climate. Sea levels can be estimated based using the global navigation satellite system–interferometry reflectometry (GNSS–IR). The frequency in a signal-to-noise ratio (SNR) arc has been found to be related to the height between the GNSS antenna and reflecting surface, which is called reflector height (RH, h). The height variation of the reflecting surface causes an error, and this error is the most significant error in the GNSS–IR sea-level retrieval. The key to the correction of height variation error lies in the determination of the RH variation rate h˙. The classical correction method determines h˙ based on tide analysis of a coarse RH series over a longer time period. Therefore, h˙ inherits errors in coarse RH series, which contains significant bias during a storm surge, and correcting this requires data accumulation. This study proposes a correction method of height variation error based on just one SNR arc based on wavelet analysis and least-square estimation. First, using wavelet analysis, instantaneous frequencies are extracted in one SNR arc; these frequencies are then converted to RH series. Second, using least-square estimation, h and h˙ are conjointly solved based on the RH series from wavelet analysis. Data of GNSS site HKQT located in Hong Kong, China, during a period of time that includes Typhoon Hato were used. The root-mean-square errors (RMSEs) of retrievals were 21.5 cm for L1, 9.5 cm for L2P, 9.3 cm for L2C, and 7.6 cm for L5 of GPS; 16.8 cm for L1C, 14.1 cm for L1P, 12.6 cm for L2C, and 10.7 cm for L2P of GLONASS; 15.7 cm for L1, 11.2 cm for L5, 12.2 cm for L7, and 9.6 cm for L8 of Galileo. Results showed this method can correct the height variation error based on just one SNR arc, can avoid the inheritance of errors, and can be used during periods of storm surge.

ANCHORS: A multi‐decadal tide gauge dataset to monitor Australian relative sea level changes

AbstractHere, we describe a new national tide gauge‐based sea level dataset for monitoring sea level changes around Australia, and the novel homogenization methodology used to develop it. Homogenization is a two‐step process that involves the detection of jumps or steps in the data (inhomogeneities) followed by a correction applied to remove the change. This new dataset is called the Australian National Collection of Homogenized Observations of Relative Sea Level (ANCHORS). ANCHORS provides coastal sea levels at hourly resolution with homogenization performed on annual means. ANCHORS is intended to be a national tide gauge‐based sea level dataset to monitor changes in mean sea level and resultant coastal flood frequency changes around Australia. Whilst sea levels are rising around Australia in response to global mean sea level changes, coastal water levels represent a notable gap in the suite of in situ high‐quality datasets available for researchers, governments and industry. Tide gauge datasets are well suited to impact‐based assessments of changes in flood frequency, duration and risk. In this regard, ANCHORS will sit alongside existing satellite‐ and numerical modelling‐based sea level datasets to provide enhanced insights into the physical impacts of sea level rise on Australian coastlines. We have adapted established homogenization techniques to develop a national collection of homogenous long tide gauge records. The dataset comprises 38 tide gauge records from around Australia, varying in length from 34 to 123 years, with an average of 57 years. Finally, we discuss limitations and potential applications for ANCHORS and how these have informed the design of this coastal sea level dataset.

Copernicus Sea Level Space Observations: A Basis for Assessing Mitigation and Developing Adaptation Strategies to Sea Level Rise

It is essential to monitor accurately current sea level changes to better understand and project future sea level rise (SLR). This is the basis to support the design of adaptation strategies to climate change. Altimeter sea level products are operationally produced and distributed by the E.U. Copernicus services dedicated to the marine environment (CMEMS) and climate change (C3S). The present article is a review paper that intends to explain why and to which extent the sea level monitoring indicators derived from these products are appropriate to develop adaptation strategies to SLR. We first present the main key scientific questions and challenges related to SLR monitoring. The different processing steps of the altimeter production system are presented including those ensuring the quality and the stability of the sea level record (starting in 1993). Due to the numerous altimeter algorithms required for the production, it is complex to ensure both the retrieval of high-resolution mesoscale signals and the stability of the large-scale wavelengths. This has led to the operational production of two different sea level datasets whose specificities are characterized. We present the corresponding indicators: the global mean sea level (GMSL) evolution and the regional map of sea level trends, with their respective uncertainties. We discuss how these products and associated indicators support adaptation to SLR, and we illustrate with an example of downstream application. The remaining gaps are analyzed and recommendations for the future are provided.

Enhancing marsh elevation using sediment augmentation: A case study from southern California, USA

Tidal marshes are an important component of estuaries that provide habitat for fish and wildlife, protection from flooding, recreation opportunities, and can improve water quality. Critical to maintaining these functions is vertical accretion, a key mechanism by which tidal marshes build elevation relative to local sea level. The beneficial use of dredged material to build marsh elevations in response to accelerating sea level rise has gained attention as a management action to prevent habitat loss over the coming decades. In January 2016, a sediment augmentation project using local dredged material was undertaken at Seal Beach National Wildlife Refuge in Anaheim Bay, California, USA, to benefit tidal marsh habitat and the listed species it supports. The application process added 12,900 cubic meters of sediment with an initial, average 22-cm gain in elevation over a 3.2-hectare site. Due to sediment characteristics and higher than anticipated elevations in some areas, vegetation colonization did not occur at the expected rate; therefore, adaptive management measures were undertaken to improve hydrology of the site and facilitate vegetation colonization. More case studies that test and monitor sea level adaptation actions are needed to assist in the planning and implementation of climate-resilient projects to prevent coastal habitat loss over the coming century.

Potential Source Analysis of Macrodebris in Untung Java Island by Using Trajectory Particle Modelling

Untung Java is one of the small islands in Thousand islands. One of the most highlighted problems on this island is the accumulation of macrodebris that occurs in the coastal and mangrove ecosystems. The purpose of this study is to determine the most potential source point for distributing debris to Untung Java Island by using a hydrodynamic model and particle trajectory model of MIKE 21. The scenario of the simulation is using pre-reclamation condition in 1999 and 2019. The estuary in Jakarta Bay is illustrated as the starting point for debris transport. Five other estuaries as potential source assumption are selected, namely Cisadane, Citarum, Muara Angke, Ciliwung and Cikeas. The validation data model used tidal data from Intergovernmental Oceanographic Commission (IOC) Sea Level Monitoring by utilizing Root Mean Square Error (RMSE) method. The RMSE is calculated up to 0.49-12.78%. The tidal current of Jakarta Bay is simulated up to 0.015-0.375 m/s. The Cisadane estuary is the most potential source as a supplier of macrodebris to Untung Java Island due to its debris movement pattern and the nearest distance to the island.

IDSL (Inexpensive Device for Sea Level) performance analysis for tews (Tsunami Early Warning System) in Sadeng fisheries port

Inexpensive Device for Sea Level Monitoring or IDSL is one of TEWS devices operating in Indonesia for more than two years, monitoring real-time on a 24/7 sea level and providing email, SMS alerts, CCTV images, and information about a potential event of a tsunami. This paper aims to analyze the device’s performance at Sadeng Fisheries Port based on critical parameters for tsunami early warning systems such as data quality, latency time, the quality of CCTV images, and the release of warning capabilities. The results show that the tidal range at spring tide is about 3.19 m, in line with BIG tidal station data. These data also indicate that the minimum tide height is 0.06 m and the maximum tide height is 3.25 m. Performance results show a total data gap of 1717 data gaps with a minimum gap of 10 seconds and a maximum gap for two days of 9 hours, with latency intervals dominated by values less than 30 seconds. However, consist eight extreme latencies in the observation period are associated with internet quotas and technical interference. For the quality of CCTV cameras, good quality images contributed to about 84,85%. Although there are many interferences from GSM signals and vessel activity below the sensors, the overall performance of this device has shown high reliability to strengthen the existing tsunami early warning system in the South of Java and Indonesia.

Design of Sea Level Monitoring System Using Accelerometer with IoT Based

Sea level is always changing, either influenced by meteorological aspects, gravitational forces, or geological effects. Monitoring the sea level is very beneficial, especially in such a big archipelago as Indonesia. This monitoring system is designed to use accelerometer sensor to sense the sea level changes vertically to obtain the level changes over time. This device is also featured by internet connection so that the data obtained from the sensor could be process on site using Arduino microcontroller and then sent to online website for remote monitoring process. This research is using experimental method, focusing on the electronic system design. The working flow of the research is started with literature studies and problem statement, then followed by system design, continued to software design, server building, and software and hardware integration. The last step is to test the device and analyze the result. After trial using simple pulley system, it is found that this device is able to sense the vertical level changes well, with an error for the sensor itself is at most 6 cm or about 2%. But there are some connection problems occurred between the device and the internet which resulted in a delay on the process, making the online monitoring system not perform as desired.

Sea-level variations from co-located tide gauge and GNSS stations using GNSS-Reflectometry in Indonesia

Sea level variation is an important key for hazard mitigation in the coastal region to study climate change. In the last decade, reflected GNSS signals have been used in many applications, such as snow, sea level, and ocean storm monitoring. In this research, we use GNSS-Reflectometry co-located with a tide gauge station to monitor sea-level variations. We use the Signal Noise to Ratio (SNR) data to derive sea-level height from GNSS. One-month comparison of sea-level variations has been made from a tide gauge and a GNSS measurement in Barus, North Sumatra Indonesia. The results have a mean bias of about 2 cm with a root mean square error of 11 cm and a correlation coefficient value of 0.90. Our result demonstrates that the GNSS-Reflectometry technique is potential to provide a new approach to monitor sea-level changes that complement the existing tide-gauge networks in Indonesia.

Accuracy analysis of ground-based GNSS-R sea level monitoring based on multi GNSS and multi SNR

With the expansion of GNSS applications, Global Navigation Satellite System Reflectometry (GNSS-R) technology has become an essential means for sea level monitoring. The development and improvement of multi-GNSS have brought new opportunities for ground-based GNSS-R sea level inversion research. More than 100 satellites in orbit are expected to improve the time resolution and the reliability of inversion results significantly. And GNSS-R technology is an SNR-based inversion technology. With the opening of different frequency channels of various GNSS systems, more signal-to-noise ratio (SNR) types are available. Therefore, the research on the multi-GNSS sea level inversion was carried out, and the multi signals inversion accuracy was analyzed. Based on the 2017–2019 observation data of the MAYG on the east coast of Africa, the SNR of the navigation satellite signal is used to invert the sea level. The results show that the time resolution of multi-GNSS inversion is significantly improved, and the average number of inversions per day reaches 51. The time interval between the two inversion results is only 18.5 min, which is 2.4 times that of GPS alone. There is a high agreement between the inversion results and the measured values. The root mean square error (RMSE) of the two is 0.36 m, and the correlation coefficient (R) is 0.93. In particular, the BDS of 2019 is monitored. It is concluded that BDS2-GEO is not suitable for coastal altimetry, the monitoring accuracy of BDS2-MEO is better than that of BDS2-IGSO and the monitoring effect of BDS3-MEO is equal to that of BDS2-MEO.

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

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]

Sea level rise exposure assessment of U.S. East Coast cargo container terminals

ABSTRACT Continuity of marine port operations and recovery in the event of disaster and flooding are dependent upon planning for acute or chronic disruptions. Ports are developing the capacity to integrate climate change adaptation with strategic planning and making capital investments in infrastructure. Geospatial risk assessments have demonstrated utility for planning marine port terminal facilities. Such assessments have tended to be coarse and comprehensive (whole port cities) or narrow, site-specific and single-hazard approaches (single terminal or site scale). This study develops a methodology for major container port terminals on the Eastern Seaboard of the United States to advance a screening approach to sea level rise, identify exposure to terminals and associated surface transportation, and enable comparative assessment. The study leverages geospatial data, elevation, imagery, transportation databases, tide gauges, and sea level rise projections. The approach extends prior methods to quantify exposure across multiple ports and terminals. Hypsographs and modelled future tidal flooding are derived for each port. Results highlight the need for port planning to develop GIS, monitor sea level rise trends, engage in integrative assessments, and optimize mitigation and adaptation actions. Results show similarities across yet also differentially increasing threats of relative sea level rise and tidal flooding at individual terminals.

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

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.

Establishing an Integrated Permanent Sea-Level Monitoring Infrastructure towards the Implementation of Maritime Spatial Planning in Cyprus

The Maritime Spatial Planning is a piece of legislation (2014/89/EU) of the European Union that must be implemented by all member countries to enable management of their waters in a more coherent way to reduce conflicts, encourage investments, increase cross-border cooperation and protect the environment. Cyprus and Greece are working together in the frame of the THALCHOR2 project to implement this directive. From the Cyprus point of view, this directive has been a unique opportunity to modernize its Hydrographic and Geodetic Infrastructure to enable and facilitate the generation of reliable marine geospatial information. Concordantly, a network of integrated state-of-the-art multi-sensor stations has been established along the shoreline of the government-controlled territories to seamlessly monitor sea level, vertical crustal motion and meteorological parameters. This research provides insight into the implementation of this infrastructure and the data processing workflow to determine tidal levels. Furthermore, the first results acquired after exploiting two years of observations are presented along with initial aspects concerning mean sea-level variability in the Southeastern Mediterranean region.

A simplification of rigorous atmospheric raytracing based on judicious rectilinear paths for near-surface GNSS reflectometry

Atmospheric delays are known to cause biases in Global Navigation Satellite System Reflectometry (GNSS-R) altimetry applications, such as for sea-level monitoring. The main quantity of interest is the reflection-minus-direct or interferometric atmospheric delay. Recently, we have presented a rigorous raytracing procedure to account for linear and angular refraction in conjunction with reflection as observed from near-surface platforms. Here, we demonstrate the feasibility of simplifying the ray trajectory by imposing a rectilinear wave propagation model. Two variants were assessed, based on the apparent or refracted satellite direction on the one hand and the geometric or vacuum conditions on the other hand. The former was shown to agree with rigorous results in terms of interferometric radio length while the latter agreed in terms of the interferometric vacuum distance. Upon a judicious combination of the best aspects of the two rectilinear cases, we have defined a mixed variant with excellent agreement with rigorous raytracing in terms of interferometric atmospheric delay. We further showed that mapping functions developed for GNSS positioning cannot be reused for GNSS-R purposes without adaptations. Otherwise, the total atmospheric delay may be underestimated by up to 50% at low elevation angles. The present work facilitates the adaptation of existing atmospheric raytracing software for GNSS-R purposes.

New Integrated Networks for Monitoring Seismic and Tsunami Activity in Morocco

A number of networks are currently being deployed for the real-time seismic and sea-level monitoring within Morocco, which has historically known several destructive earthquakes. In particular, a new seismic network that relies on satellite transmission for real-time data acquisition is being deployed in the country and consists of a hub for the management of VSAT and 48 seismic stations, all connected to a Central acquisition, processing and data storage Unit in Rabat. In addition, a seismic array consisting of 10 high-detection seismic stations is also connected by VSAT to the Rabat central recording site. A strong-motion network consisting of 70 instruments is installed for the seismic monitoring of large infrastructures. These instruments have allowed the recording, so far, of more than 40 accelerograms. A second set of 50 digital accelerographs is currently being deployed in urban centers in order to rapidly provide maps of estimated damage distribution following a significant earthquake. Moreover, a new network of seven tide-gauges for sea level monitoring is being installed along Moroccan coasts. Combined with the above-mentioned seismic network and an installed tsunami analysis system, this tide-gauges network aims at setting up in the near future, a center for early warning against tsunamis. Compared to the previous network, the new network has allowed the recording of five times more events per year and helped lower the threshold of detected magnitudes. A 24/7 surveillance has been set up for this monitoring and for providing rapid seismic warning to national authorities in charge of seismic risk management.

Developing a Pilot Operational Oceanography System for an Enclosed Basin

The first stages of the development of a pilot oceanographic observatory for an enclosed basin (Kalloni Gulf, Lesvos, Greece) are described. The focus of the present work is related to the estimation of the water exchange with the open sea, using a numerical model of the region, volume flux measurements based on current velocity, and sea-level measurements. Three different methods of assessment of the exchange are described and evaluated, in order to select a reference method to calibrate submarine telephone cable measurements. The high-resolution coastal circulation model for the enclosed sea, nested in a larger-domain model, is developed and evaluated against in situ data, focusing on the adequate representation of the exchange and the hydrographic structure in the basin. Monitoring the water level is selected as the best-suited method for estimating the water exchange in hourly-to-weekly time scales. The model reproduces adequately the tidal exchange and sea-level response, as well as the hydrographic characteristics of the basin. The cable voltage measurements exhibit tidal signals overwhelmed by low-frequency noise, possibly attributable to circuitry and ground failures; however, the most suitable method for estimating exchanges of the basin with the open sea appears to be sea-level monitoring.

Coherent GNSS Reflection Signal Processing for High-Precision and High-Resolution Spaceborne Applications

This article presents an adaptive hybrid-tracking (AHT) algorithm designed to process GNSS-R signals with a sufficient coherent component. Coherent GNSS-R signals have the potential to enable high-precision and high-resolution carrier-phase measurements for altimetry, sea-level monitoring, soil-moisture monitoring, flood mapping, snow-water equivalent measurements, and so on. The AHT algorithm incorporates the model inputs typically used in the master-slave open-loop (MS-OL) architecture into a closed-phase lock loop. Raw IF data recorded by the CYGNSS satellites over in-land water, land, and open-ocean surface are used to demonstrate the performance of the AHT. The results show that the AHT algorithm achieves comparable robustness with the MS-OL implementation while maintaining centimeter-level accuracy and excellent carrier-phase continuity that can be achieved with a fine-tuned Kalman filter (KF)-based adaptive closed-loop (ACL) system. Moreover, the AHT is suitable for real-time implementation and is applicable to other radio signals-of-opportunity.

P.224 BAD activation is involved in survival-promoting effect of NGF and BDNF dipeptide mimetics

Global sea level rise due to an increasingly warmer climate has begun to induce hazards, adversely affecting the lives and properties of people residing in low-lying coastal regions and islands. Therefore, it is important to monitor and understand variations in coastal sea level covering offshore regions. Signal-to-noise ratio (SNR) data of Global Navigation Satellite System (GNSS) have been successfully used to robustly derive sea level heights (SLHs). In Taiwan, there are a number of continuously operating GNSS stations, not originally installed for sea level monitoring. They were established in harbors or near coastal regions for monitoring land motion. This study utilizes existing SNR data from three GNSS stations (Kaohsiung, Suao, and TaiCOAST) in Taiwan to compute SLHs with two methods, namely, Lomb–Scargle Periodogram (LSP)-only, and LSP aided with tidal harmonic analysis developed in this study. The results of both methods are compared with co-located or nearby tide gauge records. Due to the poor quality of SNR data, the worst accuracy of SLHs derived from traditional LSP-only method exceeds 1 m at the TaiCOAST station. With our procedure, the standard deviations (STDs) of difference between GNSS-derived SLHs and tide gauge records in Kaohsiung and Suao stations decreased to 10 cm and the results show excellent agreement with tide gauge derived relative sea level records, with STD of differences of 7 cm and correlation coefficient of 0.96. In addition, the absolute GNSS-R sea level trend in Kaohsiung during 2006–2011 agrees well with that derived from satellite altimetry. We conclude that the coastal GNSS stations in Taiwan have the potential of monitoring absolute coastal sea level change accurately when our proposed methodology is used.

KAJIAN APLIKASI PANTULAN SINYAL GNSS UNTUK PEMANTAUAN KETINGGIAN PERMUKAAN AIR LAUT

Design and experiment of ocean current power generation system have been carried out using the Bach In Indonesia, the tsunami early warning system only applies the earthquake and hydrosphere relationship model to predict tsunamis. To date, no tsunami detector has used radar or GNSS technology. GNSS technology can be applied as an early warning system for tsunamis, provided that tsunamis are caused by earthquakes greater than 7 magnitudes, occur 70 kilometers below sea level, and are caused by normal faults. This could be an alternative to Bouy GNSS which is expensive to install and maintain, especially for countries with vast oceans such as Indonesia. In this paper, a review of the application of GNSS signal reflection was carried out using one International GNSS Service (IGS) station, JOG2, and one Continuously Operating Reference Station (CORS), CLSA, each located in Java and Sumatra to investigate the availability of sea level monitoring in Indonesia. Determination of sea level is obtained from two methods, the GNSS signal phase data analysis method and the GNSS Signal-to-Noise Ratio (SNR) data analysis method. Both methods use reflected GNSS signals or multipath effects to obtain sea level. The results of the study show that the number of satellites that pass through Indonesia every 15 minutes is enough to get sea-level data every 15 minutes to one hour. This shows that it is possible to apply the multipath effect to obtain sea level information in Indonesia to detect tides and tsunamis as part of the tsunami early warning system in Indonesia.

Satellite Altimetry Measurements of Sea Level in the Coastal Zone

Satellite radar altimetry provides a unique sea level data set that extends over more than 25 years back in time and that has an almost global coverage. However, when approaching the coasts, the extraction of correct sea level estimates is challenging due to corrupted waveforms and to errors in most of the corrections and in some auxiliary information used in the data processing. The development of methods dedicated to the improvement of altimeter data in the coastal zone dates back to the 1990s, but the major progress happened during the last decade thanks to progress in radar technology [e.g., synthetic aperture radar (SAR) mode and Ka-band frequency], improved waveform retracking algorithms, the availability of new/improved corrections (e.g., wet troposphere and tidal models) and processing workflows oriented to the coastal zone. Today, a set of techniques exists for the processing of coastal altimetry data, generally called “coastal altimetry.” They have been used to generate coastal altimetry products. Altimetry is now recognized as part of the integrated observing system devoted to coastal sea level monitoring. In this article, we review the recent technical advances in processing and the new technological capabilities of satellite radar altimetry in the coastal zone. We also illustrate the fast-growing use of coastal altimetry data sets in coastal sea level research and applications, as high-frequency (tides and storm surge) and long-term sea level change studies.