Carrier-to-Noise-Threshold Filtering on Off-Shore Wind Lidar Measurements

Wind lidar observations are characterized by a Carrier-to-Noise-Ratio that is often used to filter the observations. The choice of the Carrier-to-Noise-Ratio threshold value for the wind lidar observations is found to have an effect on the climatological wind speed distribution in such a way that when the Carrier-to-Noise-Ratio (CNR) threshold value is increased the wind speed distribution is shifted to higher values. Based on one year of observations carried out with a wind lidar from 126 m to 626 m height at the FINO3 (Forschungsplattform in Nord- und Ostsee Nr. 3) research platform in the North Sea, the effect that the choice of the Carrier-to-Noise threshold value has on the climatology of the wind speed and direction as well as the wind power density in relation to wind energy is illustrated and discussed. In the one-year data set considered here it is found that for thresholds larger than −29 dB, the mean wind speed and wind rose measured by the wind lidar become a function of the threshold value, and for values smaller than ~ −29 dB further decrease of the Carrier-to-Noise-Ratio threshold has a minor effect on the estimated mean wind speed and wind rose. The analysis of the data set from the North Sea shows that the limit for the Carrier-to-Noise-Ratio of the observations should be −29 dB or less to obtain a threshold independent estimate of the mean wind speed and wind rose. Alternatively, all valid observations should be used for the analysis. Although this study is specific for the conditions in the North Sea, we suggest that for a representative estimation of the wind resource with wind lidars, the effect of the CNR threshold filtering on the wind distribution should be studied when the recovery rate is less than 100%.

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Further Investigation upon the Water Movements in the English Channel. Drift-Bottle Experiments in the Summers of 1927, 1928 and 1929, with Critical Notes on Drift-Bottle Experiments in General.

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315400051869 ◽

1930 ◽

Vol 17 (1) ◽

pp. 241-275 ◽

Cited By ~ 15

Author(s):

J. N. Carruthers

Keyword(s):

Wind Speed ◽

North Sea ◽

English Channel ◽

The North ◽

Different Types ◽

The North Sea ◽

The Common ◽

Relationship Of ◽

Great Simplicity ◽

Simple Surface

In July–August of three different years common surface-floating bottles were set adrift at International Station E2 (49° 27' N.—4° 42' W.). With them, various types of drag-fitted bottles were also put out. The journeys accomplished are discussed, and the striking differences as between year and year in the case of the common surface floaters, and as between the different types in the same year, are commented upon in the light of the prevailing winds. An inter-relationship of great simplicity is deduced between wind speed and the rate of travel of simple surface floating bottles up-Channel and across the North Sea from the results of experiments carried out in four different summers.

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What can idealized storm surge simulations tell us about worst case scenarios?

10.5194/egusphere-egu21-12284 ◽

2021 ◽

Author(s):

Elin Andrée ◽

Jian Su ◽

Martin Drews ◽

Morten Andreas Dahl Larsen ◽

Asger Bendix Hansen ◽

...

Keyword(s):

Wind Speed ◽

Sea Level ◽

North Sea ◽

Wind Direction ◽

Water Levels ◽

Sea Levels ◽

The North ◽

The North Sea ◽

Sea Coast ◽

North Sea Coast

The potential impacts of extreme sea level events are becoming more apparent to the public and policy makers alike. As the magnitude of these events are expected to increase due to climate change, and increased coastal urbanization results in ever increasing stakes in the coastal zones, the need for risk assessments is growing too.The physical conditions that generate extreme sea levels are highly dependent on site specific conditions, such as bathymetry, tidal regime, wind fetch and the shape of the coastline. For a low-lying country like Denmark, which consists of a peninsula and islands that partition off the semi-enclosed Baltic Sea from the North Sea, a better understanding of how the local sea level responds to wind forcing is urgently called for.We here present a map for Denmark that shows the most efficient wind directions for generating extreme sea levels, for a total of 70 locations distributed all over the country&#8217;s coastlines. The maps are produced by conducting simulations with a high resolution, 3D-ocean model, which is used for operational storm surge modelling at the Danish Meteorological Institute. We force the model with idealized wind fields that maintain a fixed wind speed and wind direction over the entire model domain. Simulations are conducted for one wind speed and one wind direction at a time, generating ensembles of a set of wind directions for a fixed wind speed, as well as a set of wind speeds for a fixed wind direction, respectively.For each wind direction, we find that the maximum water level at a given location increases linearly with the wind speed, and the slope values show clear spatial patterns, for example distinguishing the Danish southern North Sea coast from the central or northern North Sea Coast. The slope values are highest along the southwestern North Sea coast, where the passage of North Atlantic low pressure systems over the shallow North Sea, as well as the large tidal range, result in a much larger range of variability than in the more sheltered Inner Danish Waters. However, in our simulations the large fetch of the Baltic Sea, in combination with the funneling effect of the Danish Straits, result in almost as high water levels as along the North Sea coast.Although the wind forcing is completely synthetic with no spatial and temporal structure of a real storm, this idealized approach allows us to systematically investigate the sea level response at the boundaries of what is physically plausible. We evaluate the results from these simulations by comparison to peak water levels from a 58 year long, high resolution ocean hindcast, with promising agreement.

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Shear‐wave velocity and density estimation from PS-wave AVO analysis: Application to an OBS dataset from the North Sea

Geophysics ◽

10.1190/1.1444833 ◽

2000 ◽

Vol 65 (5) ◽

pp. 1446-1454 ◽

Cited By ~ 33

Author(s):

Side Jin ◽

G. Cambois ◽

C. Vuillermoz

Keyword(s):

Wave Velocity ◽

North Sea ◽

Random Noise ◽

P Wave ◽

S Wave ◽

Data Set ◽

Avo Analysis ◽

The North ◽

Avo Inversion ◽

The North Sea

S-wave velocity and density information is crucial for hydrocarbon detection, because they help in the discrimination of pore filling fluids. Unfortunately, these two parameters cannot be accurately resolved from conventional P-wave marine data. Recent developments in ocean‐bottom seismic (OBS) technology make it possible to acquire high quality S-wave data in marine environments. The use of (S)-waves for amplitude variation with offset (AVO) analysis can give better estimates of S-wave velocity and density contrasts. Like P-wave AVO, S-wave AVO is sensitive to various types of noise. We investigate numerically and analytically the sensitivity of AVO inversion to random noise and errors in angles of incidence. Synthetic examples show that random noise and angle errors can strongly bias the parameter estimation. The use of singular value decomposition offers a simple stabilization scheme to solve for the elastic parameters. The AVO inversion is applied to an OBS data set from the North Sea. Special prestack processing techniques are required for the success of S-wave AVO inversion. The derived S-wave velocity and density contrasts help in detecting the fluid contacts and delineating the extent of the reservoir sand.

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DISPERSANT EFFECTIVENESS IN FIELD TRIALS AND IN OPERATIONAL RESPONSE

International Oil Spill Conference Proceedings ◽

10.7901/2169-3358-1997-1-923 ◽

1997 ◽

Vol 1997 (1) ◽

pp. 923-923

Author(s):

Tim Lunel ◽

Peter Wood ◽

Louise Davies

Keyword(s):

North Sea ◽

Quantitative Data ◽

Field Tests ◽

Field Trials ◽

Data Set ◽

Oil Droplet ◽

The North ◽

The North Sea ◽

Dispersant Effectiveness ◽

Oil Droplet Size

ABSTRACT The North Sea field tests described in the paper have provided a quantitative data set on dispersant efficiency that can be used to calibrate laboratory dispersant tests. Comparisons of efficiency figures from the EXDET, IFP, Swirling Flask, and WSL tests with the field dispersant efficiency figures indicate that the WSL test comes closest to replicating the observed dispersion, in terms of both the percentage of oil dispersed and the oil droplet size of the dispersion. This paper, with the accompanying presentation in the Sea Empress session of the conference, demonstrates that a combination of quantitative field tests and the WSL test can be used to guide responders in decisions of whether to use dispersants in response to an oil spill. The WSL test and the field trials indicated that dispersants were likely to be effective against both the Forties Blend crude oil and the weathered oil. These predictions were confirmed by the successful dispersant operation at the Sea Empress incident.

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On the correlation of spatial wind speed and solar irradiance variability above the North Sea

Advances in Science and Research ◽

10.5194/asr-13-57-2016 ◽

2016 ◽

Vol 13 ◽

pp. 57-61 ◽

Cited By ~ 1

Author(s):

Anna Rieke Mehrens ◽

Lueder von Bremen

Keyword(s):

Wind Speed ◽

Wind Power ◽

North Sea ◽

Time Scale ◽

Solar Irradiance ◽

High Wind ◽

Cold Air ◽

Wind Variability ◽

The North ◽

The North Sea

Abstract. Mesoscale wind fluctuations on a time scale of tens of minutes to several hours lead to high wind power fluctuations. Enhanced mesoscale wind variability emerges during cold air outbreaks and resulting cellular convection. The study investigates spatial wind and solar variability and their correlation during cellular convection. Cellular convection leads to simultaneous high solar and wind variability, but the highest solar or wind variability occurs due to other meteorological phenomena.

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Relative Motion During Single Blade Installation: Measurements From the North Sea

Volume 9: Ocean Renewable Energy ◽

10.1115/omae2020-18935 ◽

2020 ◽

Author(s):

Aljoscha Sander ◽

Andreas F. Haselsteiner ◽

Kader Barat ◽

Michael Janssen ◽

Stephan Oelker ◽

...

Keyword(s):

Wind Speed ◽

Wave Height ◽

North Sea ◽

Relative Motion ◽

Significant Wave Height ◽

Offshore Wind ◽

Wave Excitation ◽

Significant Wave ◽

The North ◽

The North Sea

Abstract During single blade installation in offshore wind farms, relative motion between nacelle and blade root due to wind and wave excitation pose a significant challenge. Wave excitation can be modelled considerably well by employing state-of-the-art simulation tools and can, therefore, be included in installation planning. Other phenomena, such as flow-induced vibrations are hard to capture and hence challenging to account for when defining installation procedures and limitations. Here, we present measurements conducted during the installation of an offshore wind farm consisting of multi-megawatt turbines installed on monopile foundations in the North Sea. A custom-built sensor capturing linear & angular acceleration and GPS-data was deployed atop the nacelle. Both partially and fully assembled turbines displayed complex oscillation orbits, swiftly changing amplitude and direction. Mean nacelle deflection correlated strongly with significant wave height as well as mean wind speed. As wind speed and significant wave height showed a strong correlation as well, it is difficult to discern which load drives the observed relative motions. While wind loads are significantly smaller than wave loads on partially assembled turbines under installation conditions, additional momentum induced by vortex shedding may prove sufficient to cause the observed effects.

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Evaluation of stability corrections in wind speed profiles over the North Sea

Journal of Wind Engineering and Industrial Aerodynamics ◽

10.1016/0167-6105(90)90007-y ◽

1990 ◽

Vol 33 (3) ◽

pp. 551-566 ◽

Cited By ~ 41

Author(s):

A.J.M. Van Wijk ◽

A.C.M. Beljaars ◽

A.A.M. Holtslag ◽

W.C. Turkenburg

Keyword(s):

Wind Speed ◽

North Sea ◽

The North ◽

The North Sea

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Extreme Values of Wind Speed and Wave Height in the North Sea for Defining Design Criteria of Offshore Installations

Seismicity and Seismic Risk in the Offshore North Sea Area ◽

10.1007/978-94-009-7046-5_15 ◽

1983 ◽

pp. 143-148

Author(s):

E. Bouws ◽

J. J. E. Pöttgens

Keyword(s):

Wind Speed ◽

Wave Height ◽

North Sea ◽

Extreme Values ◽

Design Criteria ◽

The North ◽

Offshore Installations ◽

The North Sea

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Model-based hydrodynamic leveling; a power full tool to enhance the quality of the geodetic networks

10.5194/egusphere-egu2020-19292 ◽

2020 ◽

Author(s):

Yosra Afrasteh ◽

Cornelis Slobbe ◽

Martin Verlaan ◽

Martina Sacher ◽

Roland Klees

Keyword(s):

North Sea ◽

Water Levels ◽

Offshore Platforms ◽

Tide Gauges ◽

Data Set ◽

Model Based ◽

The North ◽

Height System ◽

The North Sea ◽

The Impact

Model-based hydrodynamic leveling is an efficient and flexible alternative method to connect islands and offshore tide gauges with the height system on land. The method uses a regional, high-resolution hydrodynamic model that provides total water levels. From the model, we obtain the differences in mean water level (MWL) between tide gauges at the mainland and at the islands or offshore platforms, respectively. Adding them to the MWL relative to the national height system at the mainland&#8217;s tide gauges realizes a connection of the island and offshore platforms with the height system on the mainland. Usually, the geodetic leveling networks are based on spirit leveling. So, as we can not make the direct connections between coastal countries, due to the inability of the spirit leveling method to cross the water bodies, they are weak in these regions. In this study, we assessed the impact of using model-based hydrodynamic leveling connections among the North Sea countries on the quality at which the European Vertical Reference System can be realized. In doing so, we combined the model-based hydrodynamic leveling data with synthetic geopotential differences among the height markers of the Unified European Leveling Network (UELN) used to realize the European Vertical Reference Frame 2019. The uncertainties of the latter data set were provided by the BKG. The impact is assessed in terms of both precision and reliability. We will show that adding model-based hydrodynamic leveling connections lowers the standard deviations of the estimated heights in the North Sea countries significantly. In terms of reliability, no significant improvements are observed.

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