Investigation on Doppler Spectral Characteristics of Electromagnetic Backscattered Echoes From Dynamic Nonlinear Surfaces of Finite-Depth Sea

Nie, Ding; Min, Zhang; Geng, Xupu; Ping, Zhou

doi:10.2528/pier12062509

Cited by 9 publications

(7 citation statements)

References 30 publications

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“…This effect is clearly observed in Figure 6 where the corresponding Doppler spectra bandwidths are shown. These are similar with the results of stochastic wave sea surfaces in [27,40]. In Figure 6, if the largest incident angle, for example θ i = 80 • , is considered, it can be seen that the bandwidths of nonlinear surfaces can reach as large as 2.4 Hz while the bandwidths of linear surfaces are just about 1.0 Hz.…”

Section: Doppler Analysissupporting

confidence: 76%

Investigation on the Scattering From One-Dimensional Nonlinear Fractal Sea Surface by Second-Order Small-Slope Approximation

Luo¹,

Min²

2013

PIER

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Abstract-In this paper, a one-dimensional nonlinear fractal sea surface model has been established based on the narrow-band Lagrange model, which takes into account the vertical and horizontal skewnesses for the sea surface. By using the method of second-order small-slope approximation (SSA-II), the normalized radar cross section (NRCS) and Doppler spectrum of linear and nonlinear fractal sea surface are calculated. The calculated NRCS of the nonlinear fractal sea surface is larger than the linear surface for backscattering, especially for large incidence angles, which indicates the nonlinear surface has stronger scattering echoes. And the result of nonlinear fractal sea surface is also larger than the linear fractal sea surface for bistatic case, which is characterized as the discrepancies being small near specular direction, while the discrepancies becoming larger as the scattering angles departing from the specular direction. For the Doppler spectrum of sea surface, the nonlinearity of sea surface effects greatly enhances the Doppler shift and the Doppler spectrum bandwidth at large incidence angles, which are attributed the fact that the nonlinear-wave components propagate faster than the linear-wave components and the nonlinear fractal sea surface corrects the phase velocities by adding the horizontal and vertical skewness. And also, all the results can indicate the validity of this nonlinear model.

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Section: Doppler Analysissupporting

confidence: 76%

Investigation on the Scattering From One-Dimensional Nonlinear Fractal Sea Surface by Second-Order Small-Slope Approximation

Luo¹,

Min²

2013

PIER

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“…During the experiment, the sea surface evaporation waveguide is used as the long-distance channel [16][17][18]. It is a special channel formed by seawater evaporation at a very low altitude on the sea.…”

Section: Experiments and Their Results Analysismentioning

confidence: 99%

A Synchronous Wideband Frequency-Domain Method for Long-Distance Channel Measurement

Hu¹,

Zhou²,

Guo³

2013

PIER

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Abstract-This paper proposes a novel synchronous wideband frequency domain method for measuring time domain response of longdistance channel. Its core consists of: (1) baseband signal generators at the transmission terminal and the reception terminal respectively are used to generate the wideband signal of the same frequency; (2) the two GPS clock frequency reference sources locked on the same satellite are used to yield the high-stability 10 MHz signal as the external reference source of the baseband signal generator so that the initial phases of the wideband signals are basically the same; (3) the pulse per second (PPS) signal generated by the GPS clock frequency reference source is used as trigger signal to ensure that the baseband signal generator and the vector network analyzer (VNA) can transmit and receive signals synchronously; (4) the time domain response of the channel is indirectly obtained through the inverse Fourier transform of amplitude and phase of the frequency domain response. To verify the measurement method, experiments were performed, in which the sea surface evaporation waveguide which is tens of kilometers apart from each other was selected as the channel. The experimental results, given in Figs. 4 and 5, and their analysis show that the measurement method can obtain amplitude and phase of the signal whose band is hundreds of MHz and whose equivalent pulse width reaches 5 ns. The measurement method is used to obtain the time domain response of the long-distance channel, verifying that the measurement method is effective.

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“…Thus, the study on Doppler spectrum is of practical importance in a number of research areas such as sea surface wind retrieving, sea waves monitoring and oceanic surface current measuring. In recent years, the properties of microwave Doppler spectrum from sea surface have been the subject of extensive investigations, both experimentally and theoretically [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Over 40 years ago, experiment results showed a significant difference between the co-polarized Doppler shifts at moderate to high incidence angles, with the Doppler shifts of horizontally polarized (HH-polarization) signals being larger than the results corresponding to vertically polarized (V V -polarization) signals [18,19].…”

Section: Introductionmentioning

confidence: 99%

Microwave Doppler Spectra of Sea Echoes at High Incidence Angles: Influences of Large-Scale Waves

Wang¹,

Zhang²,

Guo³

2013

PIER B

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Abstract-Within the framework of the composite surface scattering model, analytical formulas for Doppler shift and bandwidth of radar echoes backscattered from time-varying sea surface are derived in the forms of three-dimensional integrals. In our derivations, the influences of the tilt modulation (TM), the hydrodynamic modulation (HM), the shadow and the curvature of large-scale undulating waves are all taken into account for achieving more reasonable results. Comparisons between our theoretical curves and the results obtained directly by exact numerical method demonstrate that our formulas can improve the simulated results. On the other hand, the simulations by our formulas can also help to estimate the effects of the TM, the HM, and the shadow of large-scale waves on Doppler behaviors individually. We find that the predicted Doppler shifts are always larger in HHpolarization than in V V -polarization due to the TM. Meanwhile, the simulations also show that the predicted Doppler shifts for both HHand V V -polarizations would become larger when the HM is considered. In addition, at low-grazing angles (LGA), the shadow effect results in a rapid increase in the predicted Doppler shift, and on the contrary makes the bandwidth narrower.

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Investigation on Doppler Spectral Characteristics of Electromagnetic Backscattered Echoes From Dynamic Nonlinear Surfaces of Finite-Depth Sea

Cited by 9 publications

References 30 publications

Investigation on the Scattering From One-Dimensional Nonlinear Fractal Sea Surface by Second-Order Small-Slope Approximation

Investigation on the Scattering From One-Dimensional Nonlinear Fractal Sea Surface by Second-Order Small-Slope Approximation

A Synchronous Wideband Frequency-Domain Method for Long-Distance Channel Measurement

Microwave Doppler Spectra of Sea Echoes at High Incidence Angles: Influences of Large-Scale Waves

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