Airborne SAR observations of ocean surface waves penetrating floating ice

Raney, R. K.; Vachon, P.W.; Abreu, R.A. De

doi:10.1109/tgrs.1989.35932

Cited by 31 publications

(10 citation statements)

References 12 publications

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“…Lyzenga et al [1985] suggested that velocity bunching is the dominant image contrast modulation mechanism for these waves that enables the SAR imaging of waves in ice. Further study on this subject has been reported by Raney et al [1988Raney et al [ , 1989. Finally, ice motion sensor packages were deployed on ice floes in the MIZ during LIMEX '87 as reported by Eid et al [1989] which provide wave frequency spectra.…”

Section: Introductionmentioning

confidence: 99%

Wave propagation in the marginal ice zone: Model predictions and comparisons with buoy and synthetic aperture radar data

1991

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In this paper the ocean wave dispersion relation and viscous attenuation by a sea ice cover are studied for waves propagating into the marginal ice zone (MIZ). The derivation of the dispersion relation and the viscous attenuation by an ice sheet are discussed for waves under flexure and pack compression. In the MIZ, the flexure effect is important for short waves. For a fixed wave period the changes in wavelength and group velocity as a function of ice thickness are significant. In turn, the exponential wave attenuation rate shows a rollover at short wave periods, whereby the rapid increase in wave attenuation rate with decreasing wave period slows down or even turns into a decrease. The Labrador Ice Margin Experiment (LIMEX), conducted on the MIZ off the east coast of Newfoundland, Canada, in March 1987, provides us with aircraft synthetic aperture radar (SAR) imagery, wave buoy, and ice property data. On the basis of the wave number spectrum from the SAR data and the concurrent wave frequency spectrum from the ocean buoy data and accelerometer data on the ice during LIMEX '87, the dispersion relation has been estimated and compared with a model. Wave energy attenuation rates are estimated from SAR data and the ice motion package data which were deployed at the ice edge and into the ice pack, and compared with the model. The model‐data comparisons are reasonably good for the ice conditions observed during LIMEX '87. Some previously reported data of wave attenuation in the MIZ are revisited for model comparison.

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Section: Introductionmentioning

confidence: 99%

Wave propagation in the marginal ice zone: Model predictions and comparisons with buoy and synthetic aperture radar data

1991

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“…Synthetic aperture radar (SAR) has been found to be capable of detecting ocean waves and swell within a sea ice cover. Observations to date have been made using airborne Xband SAR [Lyzenga et al, 1985] and C band SAR Raney et al, 1989;Liu et al, 1991] in marginal ice zones comprising ice floes tens of meters in diameter. A very important component of the ice edge region, however, is pancake ice, which is composed of much smaller cakes and which is often associated with, or arises from, frazil ice, a suspension of small ice crystals in water.…”

Section: Introductionmentioning

confidence: 99%

Waves in frazil and pancake ice and their detection in Seasat synthetic aperture radar imagery

Wadhams¹,

Holt²

1991

J. Geophys. Res.

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A theoretical model of waves propagating into an ice cover composed of frazil and pancake ice is developed and compared with measurements of wavelength and direction derived from synthetic aperture radar (SAR) imagery obtained from Seasat in October 1978. The theoretical model is based on the concept that ice of these types, which consists of small crystals or cakes, has only a mass‐loading effect on the water surface. We derive the dispersion relation for phase and group velocities, finding that there is an upper frequency limit for propagation into the ice. From the reflection coefficient at the ice edge we derive the wave radiation pressure exerted on the ice, showing that it will cause a slick of frazil ice backed by thicker floes to become more dense or thick with increasing penetration. The implications for radar scattering enabling detection on SAR are that the Bragg resonant wavelength corresponds to waves above the frequency limit for propagation, so that a frazil slick appears dark on an SAR image. When the frazil ice becomes transformed into pancake ice, through slick compression or other means, the raised edges of the pancakes cause the ice to appear bright despite the fact that there are no waves present at the Bragg wavelength. These results are applied to a Seasat SAR image obtained from the Chukchi Sea. The appearance of the ice in the image corresponds to what we expect for frazil ice gradually transforming itself into pancake ice, backed by thicker floes. We derive directional wave number spectra outside and inside the ice cover by digital Fourier analysis of image subscenes, and we find that the change of wavelength and angle of refraction of the dominant wave entering the ice field are both characteristic of the dispersion relation derived theoretically. Mean ice thicknesses extracted from the theory correspond to thicknesses expected for such slicks. The technique offers a possible means of extracting the thickness of fields of frazil and pancake ice from SAR imagery; this may be of considerable utility when ERS 1 SAR is used to study the advancing winter ice edge in the Antarctic, which consists of vast areas of these ice types.

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“…Ka Ka G(x,'r,K)= e 2 2 (1B)_2 (7) x(IO(x, t)n(x,t)10(O,t + 'r)n(O,t + Since I0(x,t) and n(x,t) are independent variables and assuming the speckle to be white uncorrelated noise it follows that;…”

Section: Speckle Noise In Sar Image Spectramentioning

confidence: 99%

<title>Using cross-image spectra in a SAR ocean wave inversion scheme</title>

1994

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Cross-image spectra obtained by combining two sub-look SAR images are utilized in an inversion scheme for extrating the underlying ocean wave spectrum. The reasons for proposing the use of crossimage spectra instead of standard multilook spectra are twofold. First, the cross-image spectra are shown to significantly reduce the speckle noise level while preserving the spectral shape. Second, the crossimage spectra provide informations abouth the wave propagation direction. A closed form expression of the ocean-to-SAR spectral transform and its inversion is formulated for the cross-image case. The SAR cross-image spectra are shown to yield a SNR typically 5 to 8 dB higher than the corresponding standard 3 look image spectra. The noise level is typically reduced with a factor of 2 compared to the 3 look spectra and a factor of 6 compared to the single sub-look spectra. The inherent informations about the wave propagation direction are utilized in the inversion scheme to resolve the 1 80 degree ambiguity without using any external informations. The method is demonstrated on airborne C-band SAR data. O-8194-1649-5/94/$6.OO SPIE Vol. 2319 / 61 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 08/18/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

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Airborne SAR observations of ocean surface waves penetrating floating ice

Cited by 31 publications

References 12 publications

Wave propagation in the marginal ice zone: Model predictions and comparisons with buoy and synthetic aperture radar data

Wave propagation in the marginal ice zone: Model predictions and comparisons with buoy and synthetic aperture radar data

Waves in frazil and pancake ice and their detection in Seasat synthetic aperture radar imagery

<title>Using cross-image spectra in a SAR ocean wave inversion scheme</title>

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