An extension to the wide swath ocean altimeter concept

Buck, Christopher

doi:10.1109/igarss.2005.1525970

Cited by 13 publications

(11 citation statements)

References 4 publications

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“…The Wavemill airborne system was developed and deployed by Astrium UK (now Airbus Defence and Space UK) as a prototype demonstrator of the Wavemill satellite mission concept presented in Buck [] in the context of a project funded by the European Space Agency. Only the main system characteristics are summarized here, with full details provided in the Wavemill proof‐of‐concept final report [ Wavemill PoC Team , ].…”

Section: Experimental Datamentioning

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: Experimental Datamentioning

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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“…Those include across-track altimetry, with the upcoming Surface Water and Ocean Topography (SWOT) mission (Fu et al, 2012) in 2021, high-frequency (e.g. Ka-band) real aperture radar techniques, like the proposed Sea Surface KInematics Multiscale monitoring (SKIM) concepts (Ardhuin et al, 2017a) and the Doppler scatterometer concept (Rodríguez et al, 2018), and multi-antenna Synthetic Aperture Radar (SAR) as proposed with the Wavemill concept (Buck, 2005;Martin and Gommenginger, 2017). Noise and viewing geometry of these instruments will generally require spatial averaging of the retrieved currents at about 20 km.…”

Section: Future Surface Current Missionsmentioning

confidence: 99%

“…Ambitious field experiments have recently been undertaken to do so (Özgökmen et al, 2014;Shcherbina et al, 2015;D'Asaro et al, 2018), but there is still a lack of more systematic means of observing the ocean dynamics at these fine horizontal scales. Efforts to remedy this situation using satellite observations are under way, with the upcoming Surface Water and Ocean Topography (SWOT) mission (Fu et al, 2012) and with the proposed Wavemill (Buck, 2005;Martin and Gommenginger, 2017) and/or Sea Surface KInematics Multiscale monitoring (SKIM) concepts (Ardhuin et al, 2017a) using radar Doppler information (Chapron et al, 2005;Johannessen et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Sunglint images of current gradients at high resolution: Critical angle and directional observing strategy

Rascle

Nouguier

Chapron

et al. 2018

Remote Sensing of Environment

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High-resolution satellite images of the ocean surface in and around the sunglint often provide unique observations of sub-mesoscale upper ocean surface processes. Local anomalies of wind, waves, currents or surfactants appear on the images as local anomalies of brightness. A quantitative interpretation of those brightness anomalies must relate them to slope properties of the wave field, which are to the lowest order described by the mean square slope (mss). The prevailing paradigm for such interpretation is that of the critical zenith angle. It states that, for subcritical zenith view angle, brightness and mss anomalies have opposite signs, and this defines the socalled inversion region. This prevailing paradigm implicitly builds on the assumption that the mss decomposition between upwind and crosswind components is conserved. The mss anomalies are then isotropic and can be reduced to a scalar (i.e. one-dimensional) quantity. In such a case, one single sunglint image would be sufficient to retrieve the mss anomaly. This isotropic case likely applies for surface wave changes induced by varying wind speed or by surfactants. Yet, satellite and airborne observations at multiple view angles recently revealed anisotropic mss anomalies, e.g. with mss increase in the upwind direction and decrease in the crosswind direction. This anisotropic behavior likely characterizes wave modulations by anisotropic surface current gradients. This paper details the expected properties of such anisotropic mss modulations. It is shown that: 1) The classical concept of critical angle does not systematically hold, neither for frontal current shear nor for internal wave divergence. 2) At least two sunglint images at different zenith and azimuth angles are needed to retrieve the mss anomalies, and a single observation is not sufficient. 3) A satellite with radiometers looking at multiple zenith angles is capable of providing a geometry favorable to retrieve mss anomalies. An illustration is discussed with internal waves observed by the Multi-angle Imaging SpectroRadiometer (MISR), where the upwind and crosswind components of the retrieved mss anomalies are anisotropic. Those results provide guidelines to interpret available observations and to Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. help refine strategy for future satellite missions. Highlights ► Sunglint images can provide wind and current variations at very high resolution. ► The concept of critical angle usually relates brightness to wave slopes. ► The concept does not systematically hold for all surface current variations. ► The use of multi-angle observations is often necessary to quantify current gradients. ► A strategy for future satellite sunglint missions is proposed.

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“…The most prominent example is the "Wavemill" project of the European Space Agency (ESA) [21], [22], which may lead to the first satellite providing high-quality vector current fields within a wide swath on a routine basis.…”

Section: Discussionmentioning

confidence: 99%

Surface current measurements by spaceborne along-track inSAR - terraSAR-X, tanDEM-X, and future systems

Romeiser

2015

2015 IEEE/OES Eleveth Current, Waves and Turbulence Measurement (CWTM)

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Within 28 years since the first demonstration of ocean current measurements by along-track interferometric synthetic aperture radar (along-track InSAR) and almost eight years since the launch of TerraSAR-X, the first satellite with experimental along-track interferometry (ATI) capabilities, a number of interesting ATI experiments and theoretical studies have been carried out, and we have learned a lot about properties of ATI data, optimal processing techniques, and the dependence of the quality of ATI-derived current fields on instrument parameters such as InSAR time lag and incidence angle. This paper gives an overview of some ATI achievements of TerraSAR-X and the twosatellite formation TanDEM-X and discusses the potential capabilities of dedicated InSAR satellites for ocean applications that may be launched within the coming years.

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An extension to the wide swath ocean altimeter concept

Cited by 13 publications

References 4 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

Sunglint images of current gradients at high resolution: Critical angle and directional observing strategy

Surface current measurements by spaceborne along-track inSAR - terraSAR-X, tanDEM-X, and future systems

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