An experimental investigation of wave measurements using a dual‐beam interferometer: Gulf Stream as a surface wave guide

Hwang, Paul A.; Toporkov, Jakov V.; Sletten, Mark A.; Lamb, D. G. S.; Perkovic, Dragana

doi:10.1029/2006jc003482

Cited by 14 publications

(5 citation statements)

References 32 publications

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“…The oscillations observed in the interferograms are due to residual uncorrected attitude effects to which the Wavemill system is very sensitive (as reported also by e.g., Hwang et al . []). The along‐track variability in the interferograms differs between runs and is smaller at near range (by about half) than at far range.…”

Section: Resultsmentioning

confidence: 99%

Wind‐wave‐induced velocity in ATI SAR ocean surface currents: First experimental evidence from an airborne campaign

et al. 2016

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Conventional and along-track interferometric (ATI) Synthetic Aperture Radar (SAR) senses the motion of the ocean surface by measuring the Doppler shift of reflected signals. Measurements are affected by a Wind-wave-induced Artifact Surface Velocity (WASV) which was modeled theoretically in past studies and has been estimated empirically only once before with Envisat ASAR by Mouche et al. (2012). An airborne campaign in the tidally dominated Irish Sea served to evaluate this effect and the current retrieval capabilities of a dual-beam SAR interferometer known as Wavemill. A comprehensive collection of Wavemill airborne data acquired in a star pattern over a well-instrumented validation site made it possible for the first time to estimate the magnitude of the WASV, and its dependence on azimuth and incidence angle from data alone. In light wind (5.5 m/s) and moderate current (0.7 m/s) conditions, the wind-wave-induced contribution to the measured ocean surface motion reaches up to 1.6 m/s upwind, with a well-defined secondorder harmonic dependence on direction to the wind. The magnitude of the WASV is found to be larger at lower incidence angles. The airborne WASV results show excellent consistency with the empirical WASV estimated from Envisat ASAR. These results confirm that SAR and ATI surface velocity estimates are strongly affected by WASV and that the WASV can be well characterized with knowledge of the wind knowledge and of the geometry. These airborne results provide the first independent validation of Mouche et al. (2012) and confirm that the empirical model they propose provides the means to correct airborne and spaceborne SAR and ATI SAR data for WASV to obtain accurate ocean surface current measurements. After removing the WASV, the airborne Wavemill-retrieved currents show very good agreement against ADCP measurements with a root-mean-square error (RMSE) typically around 0.1 m/s in velocity and 108 in direction.

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Section: Resultsmentioning

confidence: 99%

Wind‐wave‐induced velocity in ATI SAR ocean surface currents: First experimental evidence from an airborne campaign

et al. 2016

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“…Several antenna configurations and sampling principles have been employed over the past three decades, ranging from the first demonstration of along-track interferometric (ATI) SAR [26], to the first spaceborne mission TerraSAR-X launched in 2007. The possibility of full current vector retrieval using dual-beam ATI SAR was demonstrated by [27,28], and directional wave spectrum retrieval by [29].…”

Section: Microwave Methodsmentioning

confidence: 99%

Airborne Remote Sensing of the Upper Ocean Turbulence during CASPER-East

et al. 2018

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This study takes on the challenge of resolving upper ocean surface currents with a suite of airborne remote sensing methodologies, simultaneously imaging the ocean surface in visible, infrared, and microwave bands. A series of flights were conducted over an air-sea interaction supersite established 63 km offshore by a large multi-platform CASPER-East experiment. The supersite was equipped with a range of in situ instruments resolving air-sea interface and underwater properties, of which a bottom-mounted acoustic Doppler current profiler was used extensively in this paper for the purposes of airborne current retrieval validation and interpretation. A series of water-tracing dye releases took place in coordination with aircraft overpasses, enabling dye plume velocimetry over 100 m to 10 km spatial scales. Similar scales were resolved by a Multichannel Synthetic Aperture Radar, which resolved a swath of instantaneous surface velocities (wave and current) with 10 m resolution and 5 cm/s accuracy. Details of the skin temperature variability imprinted by the upper ocean turbulence were revealed in 1-14,000 m range of spatial scales by a mid-wave infrared camera. Combined, these methodologies provide a unique insight into the complex spatial structure of the upper ocean turbulence on a previously under-resolved range of spatial scales from meters to kilometers. However, much attention in this paper is dedicated to quantifying and understanding uncertainties and ambiguities associated with these remote sensing methodologies, especially regarding the smallest resolvable turbulent scales and reference depths of retrieved currents.Keywords: airborne remote sensing; ocean surface currents; upper ocean turbulence BackgroundCapabilities for spatial measurements of ocean surface turbulence are highly desirable for a wide variety of needs ranging from basic studies of upper ocean mixing processes to data assimilation into high-resolution coastal and ocean circulation models. On the global scale, presently available observations of the ocean currents are provided by satellite altimeters, which are limited to mesoscales and resolve only the geostrophic component of the surface current. Much anticipated launches of the

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“…One reason for the choice of study site was to test the along‐track INSAR system on the large change in current across the inshore Gulf Stream front. Indeed, analysis of the interferometric phase data did show an abrupt change in current across the front of about 1.2 m/s [ Hwang et al , 2006]. Naturally we examined the INSAR phase data for current variations associated with slicks and related small‐scale features in this data set.…”

Section: Methodsmentioning

confidence: 99%

Evolution of ocean slicks under a rising wind

et al. 2008

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[1] Airborne synthetic aperture radar and high-resolution infrared imagery are used to examine the evolution of natural ocean slicks during a period of freshening wind. Initially the slicks are of the order of 50 m in width and have radar and thermal contrasts of the order of 10 dB and several 0.1°C. While there can be over time a transient reorganization of surface film material by internal waves, the slicks are observed to disperse and are no longer detectible after 5 h. The dispersion occurs through the action of Langmuir circulation, which results in along-wind streaks or ''windrows'', as well as other effects. Prominent streaks occur preferentially along a slick's upwind side, the downwind side resembling more of a ''leading edge'', at least early on. Over time, the leading edge develops a corrugated shape, and gaps begin to develop within the slicks. The formation of gaps is compared with a conceptual model by Dysthe (2006) for the tearing of a surface film in the region of positive surface straining. Eventually, the slicks break into elongated patches that co-exist with windrows, which is consistent with the effects of advective dispersion.

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An experimental investigation of wave measurements using a dual‐beam interferometer: Gulf Stream as a surface wave guide

Cited by 14 publications

References 32 publications

Wind‐wave‐induced velocity in ATI SAR ocean surface currents: First experimental evidence from an airborne campaign

Wind‐wave‐induced velocity in ATI SAR ocean surface currents: First experimental evidence from an airborne campaign

Airborne Remote Sensing of the Upper Ocean Turbulence during CASPER-East

Evolution of ocean slicks under a rising wind

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