Airborne GNSS reflectometry for coastal monitoring of sea state

2020 ◽  
Author(s):  
Mario Moreno ◽  
Maximilian Semmling ◽  
Georges Stienne ◽  
Serge Reboul ◽  
Jens Wickert
Keyword(s):  
Carrier Phase ◽  
Signal Amplitude ◽  
Navigation Systems ◽  
Sea State ◽  
Wind Retrieval ◽  
The North ◽  
Front End ◽  
The North Sea ◽  
Gnss Reflectometry ◽  
Satellite Navigation Systems

<p>Global Satellite Navigation Systems (GNSS) applications like navigation and positioning generally focus on the use of the direct radio signal broadcasted by the navigation satellites. From these signals, very highly precise coordinates can be obtained. However, there is a proportion of signals, that do not reach the receivers directly, that is, the signals that are reflected off Earth’s surface before reaching the receivers. That phenomenon gave way to one of the techniques that is taking an important role in the scope of GNSS remote sensing called GNSS-Reflectometry (GNSS-R). Due to the high reflection coefficient of the water and its importance within the climate system, the ocean is one of the surfaces with greatest interest in GNSS-R research projects. The objective of this study is to retrieve information about ocean height measured through the delay of the signal, and sea state and wind retrieval (ocean surface roughness) from the analysis of the signal amplitude.</p><p>During this study, GNSS-R measurements were executed along the North Sea coast between the cities of Calais and Boulogne, France, onboard of a gyrocopter. The setup consisted of a front-end data recorder with a right-handed circular polarization (RHCP) antenna. The campaign was conducted in July 2019 within a total of 9h 40m flight time. Each flight was performed at an altitude of about 800 m above sea level going on two legs forth and back along the coast. The legs differed in the distance from the coastline, of 700 m and 2 km, respectively.</p><p>Reflectometry signal processing involves three data levels. Level (0): The raw data samples of Syntony front-end receiver. Level (1): The Delay-Doppler Map (DDM) of the correlated reflected signal and the carrier phase, from which geophysical information can be derived. And Level (2): height estimation (from signal correlation in delay and frequency domain) and roughness estimation (from signal amplitude).</p><p>By using the DDM and the carrier phase delay the sea state shall be assessed including the achievable precision and reliability of estimates. An additional aim is also to validate the configuration in terms of the used platform, antenna setup, and flight design.</p>

scholarly journals Influence of Sea State on Sea Surface Height Oscillation from Doppler Altimeter Measurements in the North Sea

2018 ◽  
Vol 10 (7) ◽  
pp. 1100 ◽  
Author(s):  
Ferdinando Reale ◽  
Fabio Dentale ◽  
Eugenio Carratelli ◽  
Luciana Fenoglio-Marc
Keyword(s):  
North Sea ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Sea State ◽  
The North ◽  
The North Sea

scholarly journals Wave current interaction: Effect on force prediction for fixed offshore structures

2018 ◽  
Vol 203 ◽  
pp. 01011
Author(s):  
Mohamed Latheef ◽  
Nasir Abdulla ◽  
Mohd Faieez Mohd Jupri
Keyword(s):  
Vertical Structure ◽  
Offshore Structures ◽  
Base Shear ◽  
Sea State ◽  
Clear Trend ◽  
The North ◽  
Relative Water ◽  
The North Sea ◽  
Current Interaction ◽  
Typical Design

MetOcean conditions in the South China Sea (SCS) indicates that unlike other locations such as the North Sea, the magnitude of the currents can be relatively large. In addition, these currents are strongly sheared. The present study focused on the typical design problem of calculating the ultimate base shear and overturning moments for slender fixed structureswiththe inclusion of the interaction between the currents and the wave field. It has been found that the loads on average can be around 15% larger when this interaction is accounted for in the calculation of the loads, highlighting the importance. In addition, the level of these amplifications were found to be dependent on the sea state steepness and the relative water depth. While no clear trend was found (changed case by case) in the present work, incorporating the vertical structure of the current was found to change the pattern of the amplification of the loads.

Statistics of Greater Sea States

2011 ◽  
Author(s):  
Anne M. Fullerton ◽  
Thomas C. Fu
Keyword(s):  
Numerical Models ◽  
Ship Motions ◽  
Frequency Range ◽  
Sea State ◽  
The North ◽  
Spectral Models ◽  
Wave Heights ◽  
The North Sea ◽  
Computational Predictions ◽  
The Ideal

Accurate representations of seaway statistics are important for physical and computational predictions of ship motions. The spectra that are most typically used in these applications are the Pierson-Moskowitz or Bretschneider. While these spectra are useful for fully developed seas, the larger sea states (Sea State (SS) 7 and higher) are typically not fully developed. In these cases, other spectral models may be more appropriate. It is critical to ship motion prediction, for both physical and numerical models, to accurately capture the frequency range for the sea state of interest. Sea state statistics, including wave heights, periods, and spectral bandwidths from various buoys and a platform in the North Sea are collected and compared with statistics from lower sea states. The spectral data are then averaged to generate a typical spectrum under the measured conditions. These developed spectra are compared with the ideal spectra mentioned previously.

scholarly journals NEW DESIGN OF THE BALTRUM DUNE REVETMENT BASED ON HYDRAULIC MODEL TESTS

2012 ◽  
Vol 1 (33) ◽  
pp. 75
Author(s):  
Frank Thorenz ◽  
Holger Blum ◽  
Andreas Kortenhaus
Keyword(s):  
Storm Surges ◽  
Model Tests ◽  
Federal State ◽  
Lower Saxony ◽  
Sea State ◽  
Design Storm ◽  
The North ◽  
The North Sea ◽  
Run Up ◽  
North Western

The sandy barrier island of Baltrum is located in the north-western part of the German Federal State Lower Saxony in the North Sea. The north-western part of the island is protected by a dune revetment against storm surges and erosion. In order to determine the functionality and loading of the construction under design storm surge conditions and investigate planning alternatives, numerical modeling of sea state conditions in combination with hydraulical model tests for the construction were executed. Measured overtopping rates of up to 125 l/(s.m) and loads up to 150 kPa showed the necessity to strengthen and heighten the initial construction. A combination of wall elements for wave run-up and overtopping reduction in combination with a crest wall were designed in order to meet the technical demands of coastal defence as well as the touristical needs of an important recreation locality.

scholarly journals ESTIMATES OF LONG WAVES IN THE WESER ESTUARY

1984 ◽  
Vol 1 (19) ◽  
pp. 53
Author(s):  
V. Barthel ◽  
E.R. Funke
Keyword(s):  
Wave Climate ◽  
Long Waves ◽  
Sea State ◽  
Floating Structures ◽  
Weser Estuary ◽  
Model Studies ◽  
The North ◽  
Frequency Components ◽  
The North Sea ◽  
Harbour Oscillations

Long waves of small amplitudes can excite harbour oscillations as well as the motion of floating structures or vessels. Field data from the Weser Estuary, German Bight of the North Sea were analysed with respect to waves with periods greater than 8 s. After preprocessing of the mostly noisy data records, special analysis incorporated the reconstruction of incorrectly recorded frequency components below .03 Hz and bivariate distributions of heights and periods. Results suggest that long wave activity increases towards the inner estuary. Grouping properties are dependent on wind direction and on directionality of the sea state. Further investigations and model studies for the response of travelling vessels to this wave climate are recommended.

Determining Appropriate Stiffness Levels for Spudcan Foundations Using Jack-Up Case Records

2002 ◽  
Author(s):  
M. J. Cassidy ◽  
G. T. Houlsby ◽  
M. Hoyle ◽  
M. R. Marcom
Keyword(s):  
Numerical Simulation ◽  
Back Analysis ◽  
Soil Conditions ◽  
Sea State ◽  
Soil Stiffness ◽  
The North ◽  
Assessment Guidelines ◽  
The North Sea ◽  
Specific Assessment ◽  
Jack Up

The level of soil stiffness under spudcan footings is an area of intense interest and debate, with many practitioners believing that current jack-up assessment guidelines are overly conservative. In order to evaluate appropriate stiffness parameters, back-analysis of case records of jack-up platforms in the North Sea has been performed. The records relate to three different rigs at a total of eight locations, which include a variety of soil conditions, water depths and sea-state severity. For each site the horizontal deck displacements and the sea-state conditions under storm loading are available. Numerical simulation of the platforms under storm loading was undertaken with varying levels of foundation stiffness. For each set of stiffness one-hour of numerical simulation was performed, with the most severe recorded environmental loading conditions for that site used. The horizontal deck displacements of the measured data and the numerical simulation results have been compared in both the frequency domain and by the magnitude of response. On the basis of the analyses, recommendations can be made for higher stiffness factors then are currently suggested in the SNAME, 1997 Technical & Research Bulletin 5-5A, Site Specific Assessment of Mobile Jack-up Units (SNAME, 1997).

scholarly journals Towards a Topographically-Accurate Reflection Point Prediction Algorithm for Operational Spaceborne GNSS Reflectometry—Development and Verification

2021 ◽  
Vol 13 (5) ◽  
pp. 1031
Author(s):  
Lucinda King ◽  
Martin Unwin ◽  
Jonathan Rawlinson ◽  
Raffaella Guida ◽  
Craig Underwood
Keyword(s):  
Global Climate ◽  
Prediction Algorithm ◽  
Navigation Systems ◽  
Reflection Point ◽  
Digital Elevation ◽  
Data Gaps ◽  
Gnss Reflectometry ◽  
Elevation Model ◽  
Satellite Navigation Systems ◽  
Ocean Wind

GNSS Reflectometry (GNSS-R), a method of remote sensing using the reflections from satellite navigation systems, was initially envisaged for ocean wind speed sensing. In recent times there has been significant interest in the use of GNSS-R for sensing land parameters such as soil moisture, which has been identified as an Essential Climate Variable (ECV). Monitoring objectives for ECVs set by the Global Climate Observing System (GCOS) organisation include a reduction in data gaps from spaceborne sources. GNSS-R can be implemented on small, relatively cheap platforms and can enable the launch of constellations, thus reducing such data gaps in these important datasets. However in order to realise operational land sensing with GNSS-R, adaptations are required to existing instrumentation. Spaceborne GNSS-R requires the reflection points to be predicted in advance, and for land sensing this means the effect of topography must be considered. This paper presents an algorithm for on-board prediction of reflection points over the land, allowing generation of DDMs on-board as well as compression and calibration. The algorithm is tested using real satellite data from TechDemoSat-1 in a software receiver with on-board constraints being considered. Three different resolutions of Digital Elevation Model are compared. The algorithm is shown to perform better against the operational requirements of sensing land parameters than existing methods and is ready to proceed to flight testing.

scholarly journals Sea-state contributions to sea-level variability in the European Seas

2020 ◽  
Vol 70 (12) ◽  
pp. 1547-1569
Author(s):  
Antonio Bonaduce ◽  
Joanna Staneva ◽  
Sebastian Grayek ◽  
Jean-Raymond Bidlot ◽  
Øyvind Breivik
Keyword(s):  
Sea Level ◽  
North Sea ◽  
Ocean Circulation ◽  
Ocean Wave ◽  
Sea State ◽  
Sea Level Variability ◽  
The North ◽  
The North Sea ◽  
The Baltic ◽  
Wave Induced

AbstractThe contribution of sea-state-induced processes to sea-level variability is investigated through ocean-wave coupled simulations. These experiments are performed with a high-resolution configuration of the Geestacht COAstal model SysTem (GCOAST), implemented in the Northeast Atlantic, the North Sea and the Baltic Sea which are considered as connected basins. The GCOAST system accounts for wave-ocean interactions and the ocean circulation relies on the NEMO (Nucleus for European Modelling of the Ocean) ocean model, while ocean-wave simulations are performed using the spectral wave model WAM. The objective is to demonstrate the contribution of wave-induced processes to sea level at different temporal and spatial scales of variability. When comparing the ocean-wave coupled experiment with in situ data, a significant reduction of the errors (up to 40% in the North Sea) is observed, compared with the reference. Spectral analysis shows that the reduction of the errors is mainly due to an improved representation of sea-level variability at temporal scales up to 12 h. Investigating the representation of sea-level extremes in the experiments, significant contributions (> 20%) due to wave-induced processes are observed both over continental shelf areas and in the Atlantic, associated with different patterns of variability. Sensitivity experiments to the impact of the different wave-induced processes show a major impact of wave-modified surface stress over the shelf areas in the North Sea and in the Baltic Sea. In the Atlantic, the signature of wave-induced processes is driven by the interaction of wave-modified momentum flux and turbulent mixing, and it shows its impact to the occurrence of mesoscale features of the ocean circulation. Wave-induced energy fluxes also have a role (10%) in the modulation of surge at the shelf break.

scholarly journals DIRECTIONAL SEA STATE NEAR THE ISLAND OF SYLT

1988 ◽  
Vol 1 (21) ◽  
pp. 22
Author(s):  
Daniel Schade ◽  
Karl-Friedrich Daemrich
Keyword(s):  
Frequency Range ◽  
Sea State ◽  
Joint Research ◽  
Density Distributions ◽  
The North ◽  
Wave Measurements ◽  
The North Sea ◽  
Morphological Processes ◽  
Joint Research Program ◽  
Good Agreement

In the scope of a joint research program dealing with erosion problems of the island of Sylt in the North Sea, wave measurements with two pitch-and-roll buoys are carried out in order to obtain more detailed information on the sea state with regard to wave dependent morphological processes. The instrumentation is described. Results from the directional analysis of closely spaced buoys are compared, showing good agreement in significant parameters and in distributions in the frequency range. Differences between wave and wind directions are discussed. A method of separating double peak spectra by fitting theoretical shallow water spectra to the measured energy density distributions is presented.

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