The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Philipp A Lange - One of the best experts on this subject based on the ideXlab platform.
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wind wave tank measurements of wave damping and Radar Cross Sections in the presence of monomolecular surface films
Journal of Geophysical Research, 1998Co-Authors: Martin Gade, Werner Alpers, Heinrich Hühnerfuss, Philipp A LangeAbstract:Measurements of the damping of small gravity and gravity-capillary water surface waves covered with monomolecular organic films of different viscoelastic properties were performed in the wind wave tank facility of the University of Hamburg. The wind speed dependence of the Radar Cross Sections for X and Ka band was measured with upwind looking microwave antennas. It is shown that Marangoni damping theory, which describes the damping of water surface waves by viscoelastic surface films, is not the only damping mechanism in wind wave tank experiments where the wind sea is not fully developed. The other source terms of the action balance equation, i.e., the energy input into the water waves from the wind, the nonlinear wave-wave interaction, and the dissipation by wave breaking, are affected differently by the various substances. It is hypothesized that this difference is caused by the different viscoelastic properties of the substances, i.e., by the different intermolecular interactions of the film molecules. A slight dip in the wind dependence of the Radar Cross section at Ka band at wind speeds of 8-9 m/s was measured, which corresponds to comparable reductions of the mean squared wave height and wave slope. Polarization ratios (i.e., the ratios of the Radar backscatter at vertical and horizontal polarization) higher than those predicted by simple Bragg scattering theory for X band at low wind speeds and different incidence angles are explained within a (three-scale) composite-surface model. At higher wind speeds, where the polarization ratio decreases rapidly, breaking by wedges and spilling breakers is hypothesized to become more dominant. The dependence of the polarization ratio on the coverage of the water surface with a slick is explained qualitatively by means of the composite-surface model. Finally, it is stated that wind wave tank measurements in the presence of monomolecular surface films are useful for the verification of theories concerning Radar backscattering, wave damping, and wind-wave and wave-wave interactions.
Chengxi Shen - One of the best experts on this subject based on the ideXlab platform.
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high frequency Radar Cross Sections of swell contaminated seas for a pulsed waveform
Iet Radar Sonar and Navigation, 2014Co-Authors: Chengxi Shen, Eric W Gill, Weimin HuangAbstract:The first- and second-order monostatic Cross-Sections of swell-contaminated seas for high-frequency ground wave pulsed Radar operation are derived from the fundamental electric field equations. In this case, the ocean surface, a mixture of both swell and wind wave components, is first represented with a Fourier series. In one of the two approaches used, the total Fourier coefficient is expanded as a linear sum of the contribution from swell and wind waves without considering the possible interaction between the two regimes; whereas in a second, more general situation, the analysis includes coupling effects between the wind waves and swell. Then, the corresponding electric fields received from the swell-contaminated sea surface are obtained. A Fourier transform of the autocorrelation of the electric fields gives the Doppler power spectral density (PSD), and a comparison between this PSD and monostatic Radar range equation yields the Radar Cross-Sections. Simulation shows that the assumption incorporating the coupling effects leads to results that better agree with historical field observations. Overall, the model proposed here not only lays a solid foundation for the development of future swell inversion algorithms, but also reveals the existence of non-linear energy transfer between swell and wind waves from a new perspective
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the derivation of high frequency Radar Cross Sections for swell contaminated seas
International Geoscience and Remote Sensing Symposium, 2013Co-Authors: Chengxi Shen, Weimin Huang, Eric W GillAbstract:The first- and second-order monostatic Cross Sections of swell contaminated seas for high-frequency ground wave pulsed Radar operation are derived based on the fundamental electric field equations. The ocean surface, a mixture of both swell and wind wave components, is first represented with a Fourier series. The corresponding equations of the received electric field are then obtained. Fourier transformation of the autocorrelations of the electric field gives the Doppler power spectral density, which ultimately leads to the Radar Cross Sections. Simulated results are also provided and are observed to be highly consistent with real Doppler spectra.
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the shallow water hf Radar Cross Sections for swell contaminated seas
NECEC 2012., 2012Co-Authors: Chengxi ShenAbstract:Based on the previously developed monostatic HF Radar Cross section model for swell contaminated seas, some modifications are presented to account for the effects of shallow water on long period swell. The full dispersion relationship and the shallow water hydrodynamic coupling coefficient are first employed to modify the original deep water Cross Sections. Then, the proposed model is simulated and compared with its counterpart in deep water cases. Results show that the amplitudes and positions of swell peaks can be significantly altered when the water depth decreases, which suggests that the development of a modified swell inversion routine is necessary.
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simulation of hf Radar Cross Sections for swell contaminated seas
OCEANS Conference, 2012Co-Authors: Chengxi Shen, Eric W Gill, Weimin HuangAbstract:Based on HF bistatic models for the first- and second-order ocean Cross Sections developed earlier, a new monostatic Cross section model for swell contaminated seas is proposed. The methodology of modelling is to incorporate a Wallop wave spectrum to represent the swell portion while describing the wind wave part with a typical Pierson-Moskowitz spectrum. Then, it is assumed that the total ocean surface is zero-mean Gaussian, and the general expression for the monostatic Radar Cross section still holds for the combined swell-wind wave spectrum. Simulated results are provided and are seen to be highly consistent with real Doppler spectra. This suggests the contamination of the swell component could be removed with refined inversion algorithms.
H Leong - One of the best experts on this subject based on the ideXlab platform.
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an estimation of Radar Cross Sections of small vessels at hf
IEEE International Radar Conference, 2007Co-Authors: H LeongAbstract:In this paper, we estimate the Radar Cross Sections (RCS) of ships with Gross Registered Tonnage (GRT) of about 1000 tons ("small vessels") for HF Radar operating between 3 and 5 MHz. The estimation is focused on the RCS of ships at aspects close to the end-on (rear- or bow-on) directions. The conclusion of the estimation is that the RCS of the small vessels at aspect angles of up to 25° from the end-on directions are about 25-30 dBm2. (4 pages)
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an estimation and verification of vessel Radar Cross Sections for high frequency surface wave Radar
IEEE Antennas and Propagation Magazine, 2006Co-Authors: H Leong, H WilsonAbstract:The Radar Cross Sections of both small and large ships for high-frequency surface-wave Radar (HFSWR) were studied by using the numerical electromagnetics code, and by using measurements from an HFSWR system at Cape Race, Newfoundland, Canada. The results of the study indicated that Teleost, a 2405-ton Canadian Coast Guard ship, and large cargo container vessels (-36000 ton) have comparable RCS values at 3.1 and 4.1 MHz. This was verified by comparing Teleost signals with the reflections of seven cargo-container vessels, identified during an operational evaluation of the HFSWR. The conclusion of the study was that Teleost and the large cargo container vessels had an angle-averaged Radar Cross section (RCS) of -40 dBm/sup 2/, while small vessels (-1000 tons) could reasonably be characterized by an angle-averaged RCS of -30 dBm/sup 2/, in the lower end of the HF band (3-5 MHz).
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an estimation and verification of vessel Radar Cross Sections for hf surface wave Radar
IEEE International Radar Conference, 2003Co-Authors: H Wilson, H LeongAbstract:The Radar Cross Sections (RCS) of both small and large ships for High Frequency Surface Wave Radar (HFSWR) were studied by using Numerical Electromagnetics Code and by using measurements from a HFSWR system at Cape Race, Newfoundland, Canada. The results of the study indicate that Teleost, a 2405-ton Canadian Coast Guard ship, and large cargo-container vessels (/spl sim/36000 ton) have comparable RCS values at 3.1 and 4.1 MHz. This was verified by comparing Teleost signals with the reflections of seven cargo-container vessels identified during an operational evaluation of the HFSWR. The conclusion of the study is that Teleost and the large cargo-container vessels have an angle-averaged RCS of /spl sim/40dBm/sup 2/, while small vessels (/spl sim/1000 tons) could reasonably be characterized by an angle-averaged RCS of /spl sim/30 dBm/sup 2/, in the lower end of the HF band (3-5 MHz).
Weimin Huang - One of the best experts on this subject based on the ideXlab platform.
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high frequency Radar Cross Sections of the ocean surface incorporating pitch and roll motions of a floating platform
OCEANS Conference, 2018Co-Authors: Eric W Gill, Weimin HuangAbstract:The first- and second-order high frequency Radar Cross Sections of the ocean surface incorporating pitch and roll motion of a floating platform are derived. Based on these newly derived Radar Cross Sections, simulations are conducted to show the effect of the pitch and roll motion on the Radar Doppler spectra. Compared to the conclusions made from the existing work, the Radar Cross section models proposed in this paper are reasonably validated. Results show that pitch and roll motion bring a frequency modulation to the Radar signal. These cause motion-induced peaks to appear symmetrically in the Doppler frequency. The effect of pitch and roll motion on the Radar Doppler spectra is seen to be similar to that caused by horizontal motion of the platform. Increasing the amplitudes of the pitch and roll motion is seen to produce a greater modulation effect on the Doppler spectra.
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high frequency Radar Cross Sections of swell contaminated seas for a pulsed waveform
Iet Radar Sonar and Navigation, 2014Co-Authors: Chengxi Shen, Eric W Gill, Weimin HuangAbstract:The first- and second-order monostatic Cross-Sections of swell-contaminated seas for high-frequency ground wave pulsed Radar operation are derived from the fundamental electric field equations. In this case, the ocean surface, a mixture of both swell and wind wave components, is first represented with a Fourier series. In one of the two approaches used, the total Fourier coefficient is expanded as a linear sum of the contribution from swell and wind waves without considering the possible interaction between the two regimes; whereas in a second, more general situation, the analysis includes coupling effects between the wind waves and swell. Then, the corresponding electric fields received from the swell-contaminated sea surface are obtained. A Fourier transform of the autocorrelation of the electric fields gives the Doppler power spectral density (PSD), and a comparison between this PSD and monostatic Radar range equation yields the Radar Cross-Sections. Simulation shows that the assumption incorporating the coupling effects leads to results that better agree with historical field observations. Overall, the model proposed here not only lays a solid foundation for the development of future swell inversion algorithms, but also reveals the existence of non-linear energy transfer between swell and wind waves from a new perspective
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the derivation of high frequency Radar Cross Sections for swell contaminated seas
International Geoscience and Remote Sensing Symposium, 2013Co-Authors: Chengxi Shen, Weimin Huang, Eric W GillAbstract:The first- and second-order monostatic Cross Sections of swell contaminated seas for high-frequency ground wave pulsed Radar operation are derived based on the fundamental electric field equations. The ocean surface, a mixture of both swell and wind wave components, is first represented with a Fourier series. The corresponding equations of the received electric field are then obtained. Fourier transformation of the autocorrelations of the electric field gives the Doppler power spectral density, which ultimately leads to the Radar Cross Sections. Simulated results are also provided and are observed to be highly consistent with real Doppler spectra.
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simulation of hf Radar Cross Sections for swell contaminated seas
OCEANS Conference, 2012Co-Authors: Chengxi Shen, Eric W Gill, Weimin HuangAbstract:Based on HF bistatic models for the first- and second-order ocean Cross Sections developed earlier, a new monostatic Cross section model for swell contaminated seas is proposed. The methodology of modelling is to incorporate a Wallop wave spectrum to represent the swell portion while describing the wind wave part with a typical Pierson-Moskowitz spectrum. Then, it is assumed that the total ocean surface is zero-mean Gaussian, and the general expression for the monostatic Radar Cross section still holds for the combined swell-wind wave spectrum. Simulated results are provided and are seen to be highly consistent with real Doppler spectra. This suggests the contamination of the swell component could be removed with refined inversion algorithms.
H Wilson - One of the best experts on this subject based on the ideXlab platform.
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an estimation and verification of vessel Radar Cross Sections for high frequency surface wave Radar
IEEE Antennas and Propagation Magazine, 2006Co-Authors: H Leong, H WilsonAbstract:The Radar Cross Sections of both small and large ships for high-frequency surface-wave Radar (HFSWR) were studied by using the numerical electromagnetics code, and by using measurements from an HFSWR system at Cape Race, Newfoundland, Canada. The results of the study indicated that Teleost, a 2405-ton Canadian Coast Guard ship, and large cargo container vessels (-36000 ton) have comparable RCS values at 3.1 and 4.1 MHz. This was verified by comparing Teleost signals with the reflections of seven cargo-container vessels, identified during an operational evaluation of the HFSWR. The conclusion of the study was that Teleost and the large cargo container vessels had an angle-averaged Radar Cross section (RCS) of -40 dBm/sup 2/, while small vessels (-1000 tons) could reasonably be characterized by an angle-averaged RCS of -30 dBm/sup 2/, in the lower end of the HF band (3-5 MHz).
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2006Co-Authors: Hank Leong, H WilsonAbstract:The Radar Cross sectio ns of both small and large ships for high-frequency surface-wave Radar (HFSWR) were studied by using the Numerical Electromagnetics Code, and by using measurements from an HFSWR system at Cape Race, Newfoundland, Canada. The results of the study indicated that Teleost, a 2405-lon Canadian Coast Guard ship, and large cargo container vessels (-36000 ton) have comparable RCS values at 3.1 and 4.1 MHz. This was verified by comparing Teleost signals with the reflections of seven cargo-container vessels, identified during an operational evaluation of the HFSWR. The conclusion of the study was that Teleost and the large cargo container vessels had an angle-averaged Radar Cross section (RCS) of -40 dBm2, while small vessels (-1000 tons) could reasonably be characterized by an angle-averaged RCS of -30 dBm2, in the lower end of the HF band (3-5 MHz).
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an estimation and verification of vessel Radar Cross Sections for hf surface wave Radar
IEEE International Radar Conference, 2003Co-Authors: H Wilson, H LeongAbstract:The Radar Cross Sections (RCS) of both small and large ships for High Frequency Surface Wave Radar (HFSWR) were studied by using Numerical Electromagnetics Code and by using measurements from a HFSWR system at Cape Race, Newfoundland, Canada. The results of the study indicate that Teleost, a 2405-ton Canadian Coast Guard ship, and large cargo-container vessels (/spl sim/36000 ton) have comparable RCS values at 3.1 and 4.1 MHz. This was verified by comparing Teleost signals with the reflections of seven cargo-container vessels identified during an operational evaluation of the HFSWR. The conclusion of the study is that Teleost and the large cargo-container vessels have an angle-averaged RCS of /spl sim/40dBm/sup 2/, while small vessels (/spl sim/1000 tons) could reasonably be characterized by an angle-averaged RCS of /spl sim/30 dBm/sup 2/, in the lower end of the HF band (3-5 MHz).
