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Most published Xplore authors for Sea State

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Xplore Articles related to Sea State

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Incidence of Fourier transform parameters on sea spectrum resampling from wave time history

2018 IEEE International Workshop on Metrology for the Sea; Learning to Measure Sea Health Parameters (MetroSea), 2018

The aim of the work is to analyse the incidence of Fourier transform parameters on sea spectrum resampling from wave time history, investigating how the selection of different parameters influences the rebuilt of the spectrum. Several cases have been examined to obtain a correlation between the recording time and the amplitude of the embodied window, useful to correctly resemble the ...


Robust Control System for Vessel Descent-Rise Device with Heave Compensation Capability

2018 International Conference on Industrial Engineering, Applications and Manufacturing (ICIEAM), 2018

The deviation of the underwater towed vehicle's immersion depth is caused by vessel heave. To gain more efficiency of underwater operations, it is offered to realize a heave motion compensation system as a descent-rise device with a nodding boom. There is uncertainty in the models of the system “vessel - cable - underwater vehicle” and input disturbances. That is why ...


High resolution wind and wave measurements from TerraSAR-X and Tandem-X satellites in comparison to marine forecast

2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 2015

Remote sensing Synthetic Aperture Radar (SAR) data from TerraSAR-X and Tandem-X (TS-X and TD-X) satellites have been used for validation and verification of newly developed coastal forecast models in the German Bight of the North Sea. The empirical XWAVE algorithm for estimation of significant wave height from X-band satellite data has been adopted for coastal application. All available TS-X images ...


GA optimized signal based mixed sensitivity controller design for ship heading changing

2015 Chinese Automation Congress (CAC), 2015

A signal based S/KS/T mixed sensitivity robust control algorithm is designed with two degrees-of-freedom control structure for ship heading changing control with plant model perturbation and environmental disturbances. Weight function parameters are optimized with genetic algorithm in the worst conditions by closed-loop simulation optimization. Simulation demonstrates the closed-loop system is robust stable and good robust performance is achieved under various ...


Impact of the elevation angle in the coherence time as a function of the sea wave height

2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 2015

For a given geometry, the coherence time of a GNSS-R waveform can be initially related to the significant wave height. However, when the coherence time is analyzed, several issues shall be considered, such as the geometry (i.e altitude, elevation angle). This work presents a review of the coherence time and its dependence on the geometry. In addition, the impact that ...


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Educational Resources on Sea State

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IEEE-USA E-Books

  • Incidence of Fourier transform parameters on sea spectrum resampling from wave time history

    The aim of the work is to analyse the incidence of Fourier transform parameters on sea spectrum resampling from wave time history, investigating how the selection of different parameters influences the rebuilt of the spectrum. Several cases have been examined to obtain a correlation between the recording time and the amplitude of the embodied window, useful to correctly resemble the input spectrum.

  • Robust Control System for Vessel Descent-Rise Device with Heave Compensation Capability

    The deviation of the underwater towed vehicle's immersion depth is caused by vessel heave. To gain more efficiency of underwater operations, it is offered to realize a heave motion compensation system as a descent-rise device with a nodding boom. There is uncertainty in the models of the system “vessel - cable - underwater vehicle” and input disturbances. That is why there are difficulties in the design of control systems of underwater vehicle immerging depth. This control system has been stable and highly effective for heave compensation of any sea states and different parameters of the vehicle and cable. It is offered to use the robust theory but without traditional methods of optimization at control system synthesis.

  • High resolution wind and wave measurements from TerraSAR-X and Tandem-X satellites in comparison to marine forecast

    Remote sensing Synthetic Aperture Radar (SAR) data from TerraSAR-X and Tandem-X (TS-X and TD-X) satellites have been used for validation and verification of newly developed coastal forecast models in the German Bight of the North Sea. The empirical XWAVE algorithm for estimation of significant wave height from X-band satellite data has been adopted for coastal application. All available TS-X images in the German Bight collocated with measurements of 6 buoys since 2013 were processed and analysed (53 passages with 196 StripMap images). One TS-X overflight covers strips with length of ~200km and width of 30km over the German Bight from East-Frisian Islands to the Danish coast with a sequence of 3-6 StripMap images. The comparisons with results of wave prediction model show a number of local variations due to variety in bathymetry and wind fronts. The developed Sea State Processor SSP includes XWAVE, pre-filtering of ships and other artefacts and checking results was implemented for NRT services. The comparison with in-situ buoy measurements results in Scatter Index of 20% and RMSE of 0.25m.

  • GA optimized signal based mixed sensitivity controller design for ship heading changing

    A signal based S/KS/T mixed sensitivity robust control algorithm is designed with two degrees-of-freedom control structure for ship heading changing control with plant model perturbation and environmental disturbances. Weight function parameters are optimized with genetic algorithm in the worst conditions by closed-loop simulation optimization. Simulation demonstrates the closed-loop system is robust stable and good robust performance is achieved under various speed and sea conditions.

  • Impact of the elevation angle in the coherence time as a function of the sea wave height

    For a given geometry, the coherence time of a GNSS-R waveform can be initially related to the significant wave height. However, when the coherence time is analyzed, several issues shall be considered, such as the geometry (i.e altitude, elevation angle). This work presents a review of the coherence time and its dependence on the geometry. In addition, the impact that the SWH has on both the coherence time and elevation angles is analyzed. Real data from different scenarios (spaceborne, airborne, and ground based) are used in this study.

  • Synthetic metocean time series generation for offshore operability and design based on multivariate Markov model

    Probabilistic assessment of expected time for occurrence of operative weather windows for critical Installation analysis, when only a short time series is available, would largely benefit from a methodology to generate additional sea state time series given the observed one. Additional time series should have not only the same statistical properties but also a different but consistent temporal sequence of weather windows. In the present paper, a first order multivariate Markov chain model is developed. The model is demonstrated to be effective to generate synthetic time series with the same statistical properties of the original one. More notably, this procedure is demonstrated to correctly represent persistence and autocovariance properties of the original time series. This feature is particularly relevant not only for Installation purpose, but also for other Ocean Engineering applications, like pipe-soil interaction, sediment transport, coastal erosion and free-span analysis.

  • A global distribution of crossing swell from Envisat ASAR Wave Mode data based on swell propagation

    Crossing swell, is a complicated sea state characterized by the co-existence of swell systems generating from different sources. Although many investigations have focused on the global swell climatology, our understanding of global statistical distribution for the crossing swell is still limited so far. In this paper, we present a global view of crossing swell using 10-years Synthetic Aperture Radar (SAR) derived directional swell spectra from Envisat ASAR in Wave Mode from 2003 to 2011. In contrast to analyze the directly but occasionally SAR captured sea state of crossing swell, we employ an approach of propagating observed swell taking advantage of the internal consistency of swells. Results indicate three dominated crossing swell areas termed “crossing swell pools”, in Pacific, Atlantic and Indian Oceans. The pool in Atlantic Ocean shows a relative stable behavior for all seasons, in contrast to the one in Indian Ocean with seasonal occurrence and the one in Pacific Ocean shrinking during boreal summer. Forming and seasonal variation of the crossing swells are interpreted using the swell origins derived from ASAR Wave Mode.

  • Accuracy of wave direction estimation from directional wave rider buoy time series

    The directionality of single-wave events measured with a directional waverider buoy is analyzed. The method used for directionality analysis is presented and an estimation of the achievable accuracy, based on the bootstrap method is given.

  • The impact of multipath effect on jamming of active decoy outboard

    Multipath effect of sea surface has an impact on jamming of active decoy outboard. Firstly, the model of multipath effect of sea surface has been determined. Study of multipath effect is based on the simplest model of mirror reflection, in which it is assumed that mirror target is just below real target and that flat ground surface achieves good electrical conductivity. In the case of mirror reflection, it can be solved by studying the relation with reflection of flat ground surface. Secondly, CCIR mathematical model of active jamming under multipath effect has been presented. Plural permittivity of electromagnetism characteristic and reflection characteristic over the ocean are researched. Varying rule of the seawater relative Permittivity, the sea water conductivity, reflection coefficient over slick offing and modified factor over crude offing are analyzed through stimulation. Sea state is used as wave height partitioning adopted by Douglas. Main factor that influence their change is gained. Lastly, impact of multipath effect on active decoy jamming under typical conditions has been analyzed by simulation. It is pointed out that under high level of sea state when roughness of sea surface increases multipath effect will decrease, while under low level of sea state when roughness of sea surface decreases multipath effect will increase. Also when height of active decoy jamming outboard increases energy fluctuation of jamming signal will decrease.

  • Improving the accuracy of sea surface salinity retrieval using GNSS-R data to correct the sea state effect

    Reflectometry using GNSS signals of opportunity (GNSS-R) has stood as a powerful technique for ocean remote sensing. Particularly, the use of these techniques has been proposed to retrieve sea state information (i.e. sea surface roughness) among other applications. Precise knowledge of the sea state is a key issue to process L-band radiometric measurements for sea surface salinity retrieval. It has been recently shown that GNSS-R data can be directly linked to the brightness temperature variations caused by the sea state effect, without the use of emission/scattering models or sea spectra models. In this study, this approach is applied to CoSMOS 2007 flights data. Firstly, the radiometric and GNSS-R data sets are presented. Secondly, measured brightness temperature is corrected using the collocated GNSS-R data. In particular, the area under the normalized waveforms is used to directly compute the required brightness temperature correction. Thirdly, the salinity retrievals are presented (achieving an error reduction from 2.8 psu for the raw measurements down to 0.51 psu). Finally, the obtained results are compared with the WISE correction approach, based on the wind speed correction, and the conclusions of this work are presented.



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