Ocean Wave Detection and Direction Measurements with Microwave Radars

Teleki, Paul G.; Shuchman, Robert A.; Brown, W. E.; McLeish, William; Ross, Duncan B.; Mattie, M.

doi:10.1109/oceans.1978.1151082

Cited by 16 publications

(6 citation statements)

References 10 publications

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“…A Fourier analysis of (25) contains a spectral peak at the dominant wave number K and additional smaller peaks at higher harmonics of K because of amplitude and phase image distortion. This is an analytical confLrmation of experimental work showing that a Fourier analysis of ocean wave images reproduces the shape of the ocean wave spectrum near the peak of the spectrum [Shemdin et al, 1978;Teleki et al, 1978] . Another thing to notice is that for larger R/V ratios a second harmonic peak will be introduced by the phase distortion mechanism in agreement with the prediction by Swift and Wilson [1979].…”

Section: > 2psupporting

confidence: 53%

An asymptotic formulation for SAR images of the dynamical ocean surface

Valenzuela¹

1980

Radio Science

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An analytical framework to aid in the interpretation and prediction of synthetic aperture radar (SAR) images of the ocean is developed. Using stationary phase integration, explicit results are derived for high‐resolution images including the cross‐section modulation on the ocean and the weighting by the curvature of the phase distortion introduced by the wave motion into the backscattered fields. The general formulation demonstrates that SAR images of the ocean are a ‘map’ of the stationary points on the surface as interpreted by SAR. The general formulation is applied to predict the SAR image of a simple two‐scale ocean model using Bragg scattering. This work suggests that image formation of the ocean is due to the amplitude process for light winds (large modulations) and by the phase distortion process for high wind speeds (small modulations). Numerical results are obtained for the stationary points of our simple ocean model, and for the first time an actual SAR image of the ocean is predicted. Inherent in this formulation also is the wave number distortion of the dominant wave of the ocean if its phase speed is not negligible compared to the radar platform velocity.

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Section: > 2psupporting

confidence: 53%

An asymptotic formulation for SAR images of the dynamical ocean surface

Valenzuela¹

1980

Radio Science

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“…In contrast to SLAR, synthetic aperture radar is capable of imaging azimuthally traveling swell. This has been demonstrated by airborne SAR's [see Ross et al, 1974;Teleki et al, 1978], as well as by the SEASAT-SAR. Good examples of azimuthally traveling swell imaged by SEASAT-SAR exist from revolution 308 on July 18, 1978, in the Pacific Ocean (32øN, 118øW) and from revolution 1044 on September 8, 1978, in the North Atlantic (area between Scotland and Iceland).…”

Section: Azimuthal Dependencementioning

confidence: 84%

On the detectability of ocean surface waves by real and synthetic aperture radar

Alpers¹,

Ross²,

Rufenach³

1981

J. Geophys. Res.

598

295

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Real and synthetic aperture radars have been used in recent years to image ocean surface waves. Though wavelike patterns are often discernible on radar images, it is still not fully understood how they relate to the actual wave field. The present paper reviews and extends current models on the imaging mechanism. Linear transfer functions that relate the two‐dimensional wave field to the real aperture radar (SLAR) image are calculated by using the two‐scale wave model. It is noted that a description of the imaging process by these transfer functions can only be adequate for low to moderate sea states. Possible other mechanisms that contribute to the visibility of waves by real aperture radar at higher sea states, such as Bragg scattering from spontaneously generated short waves at peaked crests or in wave breaking regions, and Rayleigh scattering from air bubbles entrained in the water and from water droplets thrown into the air by breaking waves, are discussed in a qualitative way. The imaging mechanism for synthetic aperture radars (SAR's) is strongly influenced by wave motions (i.e., by the orbital velocity and acceleration associated with the long waves). The phase velocity of the long waves does not enter into the imaging process. Focusing of ocean wave imagery is attributed to orbital acceleration effects. The orbital motions lead to a degradation in resolution which causes image smear as well as a SAR inherent imaging mechanism called velocity bunching. The parameter range for which velocity bunching is a linear mapping process is calculated. It is shown that linearity holds only for a relative small range of ocean wave parameters: The likelihood that the transfer function is linear increases as the direction of wave propagation approaches the range direction, as the wavelength increases, and as the wave height decreases. Linearity is required for applying simple linear system theory for calculating the ocean wave spectrum from the gray level intensity spectrum of the image. Although, in general, the full ocean wave spectrum cannot be recovered from the SAR image by applying simple linear inversion techniques, it is concluded that for many cases in which the ocean wave spectrum is relatively narrow the dominant wavelength and direction can still be retrieved from the image even when the mapping transfer function is nonlinear. Finally, we compare our theoretical models for the imaging mechanisms with existing SLAR and SAR imagery of ocean waves and conclude that our theoretical models are in agreement with experimental data. In particular, our theory predicts that swell traveling in flight (azimuthal) direction is not detectable by SLAR but is detectable by SAR.

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“…The PBR's from the enhancement tests consistently showed highest wave contrast resulting from SAR images of range-traveling waves and lower values resulting from azimuth waves. It has been previously reported [Teleki et al, 1978] that SAR's, particularly when operating at L band, will image range-traveling waves more clearly than azimuth waves. Using line 7 data, PBR measurements were obtained from subswath A in the same general location around the Nordsee Tower for each of the five passes.…”

Section: Several Points Should Be Made About Figures 11 and 12mentioning

confidence: 99%

Analysis of MARSEN X band SAR ocean wave data

et al. 1983

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Analysis of X band SAR imagery collected during the MARSEN experiment indicates that the APD‐10 SAR system imaged both range‐ and azimuth‐traveling gravity waves. However, only the near‐edge portion of the APD‐10 imagery provided reliable spectral wave estimates. Numerous motion artifacts, which manifest themselves as azimuth‐oriented streaks, are visible on the data and are believed to be caused by breaking waves. Because of the large platform velocity, the APD‐10 SAR data are relatively insensitive to wave enhancement adjustments performed during the processing of SAR signal histories. A modulation transfer function to relate SAR‐derived spectra to in situ measurements has been developed. The transfer function is smaller and falls off more rapidly with wave number for azimuth‐traveling waves than for range‐traveling waves. This is a consequence of the smaller inherent modulation for azimuth‐traveling waves and the degraded resolution in the azimuth direction as a result of motion effects and agrees, at least qualitatively, with theoretical predictions

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Ocean Wave Detection and Direction Measurements with Microwave Radars

Cited by 16 publications

References 10 publications

An asymptotic formulation for SAR images of the dynamical ocean surface

An asymptotic formulation for SAR images of the dynamical ocean surface

On the detectability of ocean surface waves by real and synthetic aperture radar

Analysis of MARSEN X band SAR ocean wave data

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