Measurements of the effects of surface winds on ocean currents with a stepped‐frequency Δ<i>K</i> radar system

PopStefanija, Ivan; McIntosh, R.

doi:10.1029/92jc00349

Cited by 5 publications

(1 citation statement)

References 10 publications

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“…That the harmonics In contrast to measurement of mean surface current through the temporally or spatially averaged Doppler shift of the radar backscatter, this spectrum distortion can be used to estimate both the current speed and direction at a mean depth that scales with the wavelength of the waves being distorted. This is the same mechanism by which HF and microwave Delta-K radars sense ocean currents [Stewart and Joy, 1974;Plant and Schuler, 1980;Popstefanija and Mcintosh, 1992]. Young et al [1985] also used this method to estimate currents from digitized images of a marine radar's PPI display.…”

Section: Trum the Coherence Between Power And Doppler Modulations Hamentioning

confidence: 99%

Observed wavenumber‐frequency properties of microwave backscatter from the ocean surface at near‐grazing angles

Frasier¹,

McIntosh²

1996

J. Geophys. Res.

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This paper presents microwave observations of the ocean surface obtained with a high‐resolution X band imaging Doppler radar during March 1994. Besides providing time‐series imagery of the ocean surface, the radar has sufficient spatial resolution to produce wave vector‐frequency (three‐dimensional) spectra of observed power and Doppler frequency modulations due to the wind waves. The wave vector‐frequency spectra provide a complete representation of the mean spatio‐temporal properties of vertically polarized X band ocean backscatter at near‐grazing incidence. Evident in the spectra are the expected contributions from linear gravity waves exhibiting high coherences between power and Doppler (orbital) velocity and consistent with the composite‐surface‐model view of sea surface microwave backscatter. Occasionally, gravity wave harmonics possibly indicative of wave nonlinearities are observed. Also readily identified in the spectra are spatially broadband modulations due to localized scattering sources which are influenced by young gravity waves and the wind. Contributions from these apparently “non‐Bragg” scattering sources account for a significant part of the observed coherent modulations. The propagation velocity of this modulation is consistent with scattering from short gravity waves well beyond the spectral peak.

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Section: Trum the Coherence Between Power And Doppler Modulations Hamentioning

confidence: 99%

Observed wavenumber‐frequency properties of microwave backscatter from the ocean surface at near‐grazing angles

Frasier¹,

McIntosh²

1996

J. Geophys. Res.

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Mixing and transport

Mossman¹,

Jensen²,

Blancett³

1993

Water Environment Research

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Radar‐derived interferometric surface currents and their relationship to subsurface current structure

Möller¹,

Frasier²,

Porter³

et al. 1998

J. Geophys. Res.

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Abstract. Radar-derived ocean surface currents are analyzed in conjunction with in situ acoustic Doppler current profiler (ADCP) measurements. The interferometric measurements were collected by an X-band imaging Doppler radar in a manner analogous to those of along-track interferometric synthetic aperture radar (ATI-SAR). While the advent of ATI-SAR has provided a new, potentially powerful technique for current mapping, the relationship between surface currents and interferometric velocity measurements is not yet clearly understood. This paper presents comparisons between radar-derived and in situ current measurements. To develop a precise method for estimating the surface current from interferometric measurements, the influence of long wave orbital velocities and the influence of Bragg resonant waves are studied. We find that coupling between the orbital velocity and backscattered power (i.e., the modulation transfer function) can bias surface current estimates, potentially by up to 20 cm s -• in an upwind viewing orientation. Furthermore, experimental observations verify a cos 2n (0/2) analytical model for the directional spreading of Bragg resonant waves. Extending our analysis to include subsurface currents, case studies are presented under varying environmental conditions for which the vertical current structure changes considerably. Analysis of radar imagery yields both radial surface currents and vector subsurface current estimates derived from long wave dispersion characteristics. Combining these with coincident ADCP measurements yields a vertical profile of current. Using these measurement techniques, we make several observations within the upper meter of the ocean. These profiles reveal the sensitivity of X-band interferometric measurements to wind-drift and the near-surface current structure.

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Measurements of the effects of surface winds on ocean currents with a stepped‐frequency ΔK radar system

Cited by 5 publications

References 10 publications

Observed wavenumber‐frequency properties of microwave backscatter from the ocean surface at near‐grazing angles

Observed wavenumber‐frequency properties of microwave backscatter from the ocean surface at near‐grazing angles

Mixing and transport

Radar‐derived interferometric surface currents and their relationship to subsurface current structure

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