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Modulation of Ka-Band Doppler Radar Signals Backscattered From the Sea Surface ArchiMer
Yurovsky, Yury Yu.; Kudryavtsev, Vladimir N.; Chapron, Bertrand; Grodsky, Semyon A..
This paper presents dual copolarized (VV and HH) Ka-band radar measurements of joint modulation of normalized radar crass section (NRCS) and Doppler velocity (DV) performed from a sea research platform. NRCS and DV modulations are well correlated. NRCS modulations exhibit a spiky structure. HH modulations are stronger than VV ones leading to modulations of the polarization ratio. This suggests that an important portion of NRCS modulations is produced by nonpolarized radar returns from modulated wave breaking facets. DV modulations reveal that at incidence angles <50 degrees, NRCS spikes are attributable to rather slow moving facets, which may he interpreted as short wave breaking disturbances embedded in the water at crests of modulating waves. Using...
Tipo: Text Palavras-chave: Doppler shift; Modulation transfer function (MTF); Radar backscattering; Sea surface; Spikes; Wave breaking.
Ano: 2018 URL: http://archimer.ifremer.fr/doc/00440/55156/56750.pdf
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Low-Frequency Sea Surface Radar Doppler Echo ArchiMer
Yurovsky, Yury Yu.; Kudryavtsev, Vladimir N.; Grodsky, Semyon A.; Chapron, Bertrand.
The sea surface normalized radar backscatter cross-section (NRCS) and Doppler velocity (DV) exhibit energy at low frequencies (LF) below the surface wave peak. These NRCS and DV variations are coherent and thus may produce a bias in the DV averaged over large footprints, which is important for interpretation of Doppler scatterometer measurements. To understand the origin of LF variations, the platform-borne Ka-band radar measurements with well-pronounced LF variations at frequencies below wave peak (0.19 Hz) are analyzed. These data show that the LF NRCS is coherent with wind speed at 21 m height while the LF DV is not. The NRCS-wind correlation is significant only at frequencies below 0.01 Hz indicating either differences between near-surface wind...
Tipo: Text Palavras-chave: Radar; Ocean; Backscatter; Doppler shift; Wave groups; Non-linearity; Modulation.
Ano: 2018 URL: http://archimer.ifremer.fr/doc/00445/55646/57298.pdf
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Sea Surface Ka-Band Doppler Measurements: Analysis and Model Development ArchiMer
Yurovsky, Yury; Kudryavtsev, Vladimir; Grodsky, Semyon; Chapron, Bertrand.
Multi-year field measurements of sea surface Ka-band dual-co-polarized (vertical transmit–receive polarization (VV) and horizontal transmit–receive polarization (HH)) radar Doppler characteristics from an oceanographic platform in the Black Sea are presented. The Doppler centroid (DC) estimated using the first moment of 5 min averaged spectrum, corrected for measured sea surface current, ranges between 0 and ≈1 m/s for incidence angles increasing from 0 to 70∘ . Besides the known wind-to-radar azimuth dependence, the DC can also depend on wind-to-dominant wave direction. For co-aligned wind and waves, a negative crosswind DC residual is found, ≈−0.1 m/s, at ≈20 ∘ incidence angle, becoming negligible at ≈ 60 ∘ , and raising to, ≈+0.5 m/s, at 70∘ . For our...
Tipo: Text Palavras-chave: Radar; Scatterometer; Ocean; Backscatter; Doppler shift; Doppler centroid; Sea surface current; Wind drift; Modulation; Transfer function; Empirical model.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00489/60077/63399.pdf
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