On C-Band Quad-Polarized Synthetic Aperture Radar Properties of Ocean Surface Currents

Fan, Shengren; Kudryavtsev, V. N.; Zhang, Biao; Perrie, William; Chapron, Bertrand; Mouche, Alexis

doi:10.3390/rs11192321

Cited by 10 publications

(8 citation statements)

References 36 publications

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“…Further work is required to clarify this issue as it pertains to MABL roll process studies using S-1 data. Future investigations may also take advantage of these findings to focus on radar measurements under highly unstable atmospheric conditions, possibly using dual-and quad-polarized SAR measurements (Kudryavtsev et al, 2014(Kudryavtsev et al, , 2019Fan et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

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An assessment of marine atmospheric boundary layer roll detection using Sentinel-1 SAR data

Wang

Vandemark

Mouche

et al. 2020

Remote Sensing of Environment

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The ability of high-resolution synthetic aperture radar (SAR) to detect marine atmospheric boundary layer (MABL) roll-induced roughness modulation of the sea surface wave field is well known. This study presents SAR measurements of MABL rolls using global coverage data collected by the European Space Agency's C-band Sentinel-1A satellite in 2016-2017. An automated classifier is used to identify likely roll events from more than 1.3 million images that were acquired at two incidence angles of 23° and 36.5° in either VV or HH polarization. Characteristics of the detected rolls are examined for different wind speeds, polarizations, incidence and relative azimuth angles. Roll detection counts are much higher at the higher incidence angle and nearly equivalent for VV and HH polarizations. Detection depends strongly on the relative azimuth with roll detection rates at crosswind being 3-10 times lower than for up-or downwind. All data show a low wind speed threshold near 2 m s−1 and that rolls are most commonly observed at wind speeds near 9 m s−1. For all viewing configurations, we find that rolls induce a wide range of mean surface wind speed modulation with the most frequent value being 8% (±3.5%). Roll detection at crosswind is associated with stronger roll-induced surface wind enhancement. Dependencies of roll detection on the incidence and relative azimuth angles are consistent with rapid short-scale wind-wave adjustments to the roll-induced surface wind gusts. These cm-scale waves are highly directional and provide limited crosswind backscatter at shallower incidence angles. The same roll-induced surface forcing is thus not equally detectable at all viewing geometries or polarizaions. Stronger and possibly longer-duration wind forcing is likely needed to produce detectable roll-induced modulations at crosswind. Highlights► First global statistics of SAR response to MABL rolls using new S-1 WV data. ► Data show 50% greater sensitivity to rolls for 36° vs. 23° SAR incidence angle. ► Crosswind (relative to SAR look direction) shows weakest sensitivity to roll imprints. ► Rolls observed at 23° and crosswind are more stationary, in more unstable conditions. ► SAR-estimated surface wind perturbations due to roll impacts are 8 ± 3.5%.

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Section: Discussionmentioning

confidence: 99%

“…This may lead to new approaches for identifying unstable conditions, and Ri B retrieval methods. In that context, dual-and quad-polarized SAR observations(Fan et al, 2019), might be favored. In particular, short-scale polarized scatter contributions can beisolated to more precisely analyze local roll signatures.…”

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confidence: 99%

An assessment of marine atmospheric boundary layer roll detection using Sentinel-1 SAR data

Wang

Vandemark

Mouche

et al. 2020

Remote Sensing of Environment

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“…A significant underestimation of the model contrasts of the manifestation of various nature currents in X-and C-band SAR images, as compared with observations, was noted in previous works [5,12]. As shown in [13] (see also [14,15]), the main reason for this discrepancy is the Bragg theory imperfection for describing the normalized radar cross section (NRCS) of the sea surface, radar reflections from breaking waves significantly contributing to backscatter and being the determining mechanism in the formation of the manifestation of currents in SAR images. At that, the anomalies of the breaking and the corresponding SAR signal contrasts are tied to the divergence zones of the currents.…”

Section: Introductionmentioning

confidence: 67%

SAR Imaging Features of Shallow Water Bathymetry

Pivaev¹,

Kudryavtsev²,

Balashova³

et al. 2020

PhO

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Purpose. The aim of the article is to study manifestations of the underwater topography features in the northern part of the White Sea in the images made by the spaceborn synthetic aperture radars (SAR) Sentinel-1A, Sentinel-1B. Methods and Results. In the SAR images, the bottom features are revealed as bright and dark brightness anomalies. The anomalies were observed at the wind speed ranging from 2.6 to 10.8 m/s, and became reverse (bright anomalies turned dark and vice versa), when a tidal current changed its direction. It is shown that the observed SAR imagery contrasts correlate to divergence of a current formed by interaction of a tidal flow with the bottom topography inhomogeneities. The simulated SAR contrasts agree with the observations, and confirm the relation between the observed SAR contrasts and the current divergence. Together with modeling the SAR contrasts, the contribution of different mechanisms to formation of the observed modulations of the normalized radar cross section was qualitatively estimated. The wave breaking effect was especially accentuated. The method for retrieving the underwater bottom topography based on the relationship between the bottom gradient and the SAR imagery contrasts is proposed. Conclusions. Location of the bottom inhomogeneities in the shallow water region on the whole coincides with that of the tidal current divergence and convergence zones, which are observed as brightness anomalies in the SAR images. Breaking of surface waves is the main contributor to the observed SAR contrasts. The bottom topography reconstructed from the SAR contrasts, and the actual one resulted from the bathymetry maps are in good agreement. Some discrepancies are interpreted as possible changes in depth and shape of the bottom topography features induced by action of strong currents and waves.

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“…where S pool is the spectrum of the seawater surface in the pool. This assumption is usually made to interpret the ocean features in SAR data [22,23] and here, the non-polarized radar returns from breaking waves are considered negligible. This NRCS can be compared with the NRCS in an ocean context σ ocean such as…”

Section: Pool To Ocean Transpositionmentioning

confidence: 99%

Surface Film Characterization From X-to-K-Band Radar Signal Inversion, a Wind-Wave-Pool Experiment

Mainvis¹,

Fabbro²,

Bourlier³

et al. 2020

PIER B

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This paper describes an experiment in a wind-wave pool in Brest, France, to characterize surface films when observed at moderate incidence from X-to-K radar bands. Measurements of the radar backscattered field were carried out for various seawater surface states and incidence angles. From this meaningful database (mainly lying in simultaneous acquisitions in X-, Ku-, and K-bands), an inversion method is proposed to characterize the elasticity modulus of the surface film. This process is based on the minimization of the cost function correlating the values given by a physical model of the damping ratio and the measured ones. The resulting oil parameters are found in overall good agreement-but still qualitative-with the various released oils. Nonetheless, the inversion method does not work properly for the rapeseed oil slick when higher wind speeds are considered, and this failure is explained. In addition, it can be seen that the results can be applied in an ocean context by comparing the modeled normalized radar cross section (NRCS) in an ocean context (given by the Bragg scattering and the Elfouhaily spectrum) and the measured NRCS.

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On C-Band Quad-Polarized Synthetic Aperture Radar Properties of Ocean Surface Currents

Cited by 10 publications

References 36 publications

An assessment of marine atmospheric boundary layer roll detection using Sentinel-1 SAR data

An assessment of marine atmospheric boundary layer roll detection using Sentinel-1 SAR data

SAR Imaging Features of Shallow Water Bathymetry

Surface Film Characterization From X-to-K-Band Radar Signal Inversion, a Wind-Wave-Pool Experiment

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