Dual-beam ATI SAR measurements of surface currents in the nearshore ocean

Farquharson, Gordon; Deng, Huazeng; Goncharenko, Yuriy; Mower, John

doi:10.1109/igarss.2014.6947021

Cited by 19 publications

(8 citation statements)

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“…Additionally, this paper represents a rare attempt to compare airborne interferometric SAR velocities to in situ data. The compared data sample is very limited, but valuable, as only few attempts of this kind were described in previous literature [28], leaving much room for a more comprehensive validation study in the future. Other most closely related active microwave current retrieval and validation studies employed methodologies based on offshore platform or ship-based marine radars and reported successful comparisons to bottom-mounted ADCP and surface drifters in situ velocity measurements [24,44].…”

Section: Discussionmentioning

confidence: 99%

“…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%

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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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Section: Discussionmentioning

confidence: 99%

Section: Microwave Methodsmentioning

confidence: 99%

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

et al. 2018

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“…Furthermore, these gradients may cause refractive focusing of the incident waves, which might cause increased wave breaking. The dataset includes a few cases where spatial information is available in the form of surface current maps derived from airborne interferometric synthetic aperture radar (SAR) (Farquharson et al 2014). An example of buoy 5-min drift positions are shown overlaid on a SAR composite velocity map in Fig.…”

Section: Frontsmentioning

confidence: 99%

Turbulence from Breaking Surface Waves at a River Mouth

Zippel

Thomson

Farquharson

2018

Journal of Physical Oceanography

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Observations of surface waves, currents, and turbulence at the Columbia River mouth are used to investigate the source and vertical structure of turbulence in the surface boundary layer. Turbulent velocity data collected on board freely drifting Surface Wave Instrument Float with Tracking (SWIFT) buoys are corrected for platform motions to estimate turbulent kinetic energy (TKE) and TKE dissipation rates. Both of these quantities are correlated with wave steepness, which has previously been shown to determine wave breaking within the same dataset. Estimates of the turbulent length scale increase linearly with distance from the free surface, and roughness lengths estimated from velocity statistics scale with significant wave height. The vertical decay of turbulence is consistent with a balance between vertical diffusion and dissipation. Below a critical depth, a power-law scaling commonly applied in the literature works well to fit the data. Above this depth, an exponential scaling fits the data well. These results, which are in a surface-following reference frame, are reconciled with results from the literature in a fixed reference frame. A mapping between freesurface and mean-surface reference coordinates suggests 30% of the TKE is dissipated above the mean sea surface.

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“…In order to measure the high-resolution ocean current vec-tors, the ATI-SAR results of two sets of flight trajectories can be used for synthesis, but only the currents in the area where the trajectories overlap can be obtained [2]. The Dual-Beam Interferometry (DBI) technology proposed by Frasier and Camps [3] in 2001 achieved the goal of measuring the current vectors within the entire swath in a single flight.…”

Section: Introductionmentioning

confidence: 99%