The Southern Ocean Waves Experiment. Part III: Sea Surface Slope Statistics and Near-Nadir Remote Sensing

2008 ◽  
Vol 38 (3) ◽  
pp. 670-685 ◽  
Author(s):  
E. J. Walsh ◽  
C. W. Wright ◽  
M. L. Banner ◽  
D. C. Vandemark ◽  
B. Chapron ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Incidence Angle ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Sea Surface ◽  
Radar Altimeter ◽  
Ka Band ◽  
Wide Range ◽  
Non Gaussian

Abstract During the Southern Ocean Waves Experiment (SOWEX), registered ocean wave topography and backscattered power data at Ka band (36 GHz) were collected with the NASA Scanning Radar Altimeter (SRA) off the coast of Tasmania under a wide range of wind and sea conditions, from quiescent to gale-force winds with 9-m significant wave height. Collection altitude varied from 35 m to over 1 km, allowing determination of the sea surface mean square slope (mss), the directional wave spectrum, and the detailed variation of backscattered power with incidence angle, which deviated from a simple Gaussian scattering model. The non-Gaussian characteristics of the backscatter increased systematically with the mss, suggesting that a global model to characterize Ka-band radar backscatter from the sea surface within 25° of nadir might be possible.

Semi-Empirical Model for the Ka-band Sea Surface Doppler Centroid

2020 ◽  
Author(s):  
Yury Yurovsky ◽  
Vladimir Kudryavtsev ◽  
Semyon Grodsky ◽  
Bertrand Chapron
Keyword(s):  
Wind Speed ◽  
Large Scale ◽  
Incidence Angle ◽  
Wave Spectrum ◽  
Sea Surface ◽  
Doppler Spectrum ◽  
The Black Sea ◽  
Small Scale ◽  
Ka Band ◽  
Semi Empirical

<p>The sea surface Doppler spectrum centroid is a principal parameter for the sea surface current retrieval from Doppler radar measurements. Satellite Doppler scatterometers are proposed to operate in the Ka-band (SKIM, DopplerScatt/WaCM, SEASTAR) in order to achieve sufficient measurement accuracy. Todays documentation of the Ka-band sea surface backscattering parameters is poor, thus this work is aimed at presenting a model for the sea surface Doppler spectrum centroid (DC) deducted from field data collected from the Black Sea research platform. The model relies on the well-known two-scale surface separation approach. Within this framework, the small-scale waves are the scatterers moving at their inherent speed (Bragg wave phase velocity or specular point velocity), which, in turn, are advected by the large-scale wave orbital velocities. These modulations lead to correlated variations of local scatterer cross-section and speed. The inherent scatterer velocity is computed theoretically, while the modulation term is described by the empirical modulation transfer function (MTF) which naturally involves both tilt and hydrodynamics components as a function of look geometry and sea state. The proposed semi-empirical DC model is in good agreement with measurements if in situ wave gauge directional spectrum is used as a wave input. Based on this finding, we extrapolate the semi-empirical DC model on the arbitrary surface described by the physical model of the wind wave spectrum. The resulting DC model is compared to the published empirical models and measurements (SAXON-FPN, DopplerScatt, AirSWOT, Wavemill field campaigns, and CDOP Envisat ASAR model). The model DC dependencies on incidence angle and wind speed are consistent with Ku-band<br>SAXON-FPN, Ka-band AirSWOT, and DopplerScatt datasets, but differs from C-band CDOP model and X-band Wavemill dataset, which generally have higher DC magnitude (besides longer operating radar wavelength, the difference can be attributed to swell dominated sea observed in the CDOP and Wavemill cases). The model predicts that the DC rises with wind speed at small incidence angles, 20–30<sup>o</sup>, but the DC level is almost independent of wind at larger incidence angles, 50–55<sup>o</sup>. Such behavior is explained by the balance between opposing wind dependencies of the MTF magnitude and the magnitude of modulating wave orbital velocities.</p><p>The work is supported by the Russian Science Foundation under grant No. 17-77-30019.</p>

scholarly journals Semiempirical Dissipation Source Functions for Ocean Waves. Part I: Definition, Calibration, and Validation

2010 ◽  
Vol 40 (9) ◽  
pp. 1917-1941 ◽  
Author(s):  
Fabrice Ardhuin ◽  
Erick Rogers ◽  
Alexander V. Babanin ◽  
Jean-François Filipot ◽  
Rudy Magne ◽  
...  
Keyword(s):  
Wind Speed ◽  
Wave Height ◽  
Wave Breaking ◽  
Wave Spectrum ◽  
Remote Sensing Data ◽  
Ocean Waves ◽  
Breaking Waves ◽  
Global Ocean ◽  
Short Waves ◽  
Wide Range

Abstract New parameterizations for the spectral dissipation of wind-generated waves are proposed. The rates of dissipation have no predetermined spectral shapes and are functions of the wave spectrum and wind speed and direction, in a way consistent with observations of wave breaking and swell dissipation properties. Namely, the swell dissipation is nonlinear and proportional to the swell steepness, and dissipation due to wave breaking is nonzero only when a nondimensional spectrum exceeds the threshold at which waves are observed to start breaking. An additional source of short-wave dissipation is introduced to represent the dissipation of short waves due to longer breaking waves. A reduction of the wind-wave generation of short waves is meant to account for the momentum flux absorbed by longer waves. These parameterizations are combined and calibrated with the discrete interaction approximation for the nonlinear interactions. Parameters are adjusted to reproduce observed shapes of directional wave spectra, and the variability of spectral moments with wind speed and wave height. The wave energy balance is verified in a wide range of conditions and scales, from the global ocean to coastal settings. Wave height, peak and mean periods, and spectral data are validated using in situ and remote sensing data. Some systematic defects are still present, but, overall, the parameterizations probably yield the most accurate estimates of wave parameters to date. Perspectives for further improvement are also given.

The directional spectrum of ocean waves, and processes of wave generation

1962 ◽  
Vol 265 (1322) ◽  
pp. 286-315 ◽  
Keyword(s):  
Pressure Fluctuations ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Wave Generation ◽  
Air Pressure ◽  
Sea Surface ◽  
Shear Instability ◽  
Main Stage ◽  
Sea Waves ◽  
Directional Spectrum

This paper describes some recent observations of the directional spectrum of sea waves and of air pressure fluctuations at the sea surface, and discusses their implications for theories of wave generation. The angular spread of the wave energy in the generating area is found to be comparable with the ‘resonance angle’ sec -1 ( σU/g ) ( σ = wave frequency, U = wind speed) but lies slightly below it in the middle range of frequencies. The best fit to the directional spectrum F ( σ, ɸ ) is shown to be a cosine-power law: F ( σ, ɸ ) ∝ cos 2s (1/2 ɸ ), where s decreases as σ in ­ creases. At the higher frequencies the total spectrum satisfies the equilibrium law: F ( σ ) ∝ σ -5 . The initial stages of wave generation are attributed to turbulence in the air stream, and the main stage of growth to the shear instability mechanism described by Miles. At the highest frequencies the form of the spectrum suggests that wave breaking plays a predominant part, as proposed by Phillips. The broadening of the angular distribution at the highest frequencies may also be due partly to third-order ‘resonant’ interactions among components of the wave spectrum . The air-pressure fluctuations are nearly in phase with the vertical displacement of the sea surface (over most of the frequency range) and are consistent with the shear-flow model proposed by Miles. The turbulent component of the air pressure is much smaller than was previously supposed.

scholarly journals Analysis of Ku- and Ka-Band Sea Surface Backscattering Characteristics at Low-Incidence Angles Based on the GPM Dual-Frequency Precipitation Radar Measurements

2019 ◽  
Vol 11 (7) ◽  
pp. 754 ◽  
Author(s):  
Qiushuang Yan ◽  
Jie Zhang ◽  
Chenqing Fan ◽  
Junmin Meng
Keyword(s):  
Wind Direction ◽  
Incidence Angle ◽  
Surface Wind ◽  
Sea Surface ◽  
Dual Frequency ◽  
Precipitation Radar ◽  
Ka Band ◽  
Surface Conditions ◽  
Wave Parameters ◽  
Low Incidence

The co-located normalized radar backscatter cross section measurements from the Global Precipitation Measurement (GPM) Ku/Ka-band dual-frequency precipitation radar (DPR) and sea surface wind; wave and temperature observations from the National Data Buoy Center (NDBC) moored buoys are used to analyze the dependence and sensitivity of Ku- and Ka-band backscatter on surface conditions at low-incidence angles. Then the potential for inverting wind and wave parameters directly from low-incidence σ0 measurements is discussed. The results show that the KaPR σ0 is more sensitive to surface conditions than the KuPR σ0 overall. Nevertheless; both the KuPR σ0 and KaPR σ0 are strongly correlated with wind speed (U10) and average wave steepness (δa) with the exception of specific transitional incidence angles. Moreover, U10 and δa could be retrieved from pointwise σ0 near nadir and near 18°. Near 18°; wind direction information is needed as the effect of wind direction on σ0 becomes increasingly significant with incidence angle. To improve the performance of U10 retrieval; especially for low U10; auxiliary δa information would be most helpful; and sea surface temperature is better taken into account. Other wave parameters; such as significant wave height; wave period and wave age; are partly correlated with σ0. It is generally more difficult to retrieve those parameters directly from pointwise σ0. For the retrieval of those wave parameters; various auxiliary information is needed. Wind direction and wave direction cannot be retrieved from pointwise σ0.

scholarly journals Surface-based Ku- and Ka-band polarimetric radar for sea ice studies

2020 ◽  
Vol 14 (12) ◽  
pp. 4405-4426
Author(s):  
Julienne Stroeve ◽  
Vishnu Nandan ◽  
Rosemary Willatt ◽  
Rasmus Tonboe ◽  
Stefan Hendricks ◽  
...  
Keyword(s):  
Sea Ice ◽  
Snow Depth ◽  
Ice Thickness ◽  
Polarimetric Radar ◽  
Radar Altimeter ◽  
Radar Backscatter ◽  
Sea Ice Thickness ◽  
Ka Band ◽  
Snow Properties ◽  
Wide Range

Abstract. To improve our understanding of how snow properties influence sea ice thickness retrievals from presently operational and upcoming satellite radar altimeter missions, as well as to investigate the potential for combining dual frequencies to simultaneously map snow depth and sea ice thickness, a new, surface-based, fully polarimetric Ku- and Ka-band radar (KuKa radar) was built and deployed during the 2019–2020 year-long MOSAiC international Arctic drift expedition. This instrument, built to operate both as an altimeter (stare mode) and as a scatterometer (scan mode), provided the first in situ Ku- and Ka-band dual-frequency radar observations from autumn freeze-up through midwinter and covering newly formed ice in leads and first-year and second-year ice floes. Data gathered in the altimeter mode will be used to investigate the potential for estimating snow depth as the difference between dominant radar scattering horizons in the Ka- and Ku-band data. In the scatterometer mode, the Ku- and Ka-band radars operated under a wide range of azimuth and incidence angles, continuously assessing changes in the polarimetric radar backscatter and derived polarimetric parameters, as snow properties varied under varying atmospheric conditions. These observations allow for characterizing radar backscatter responses to changes in atmospheric and surface geophysical conditions. In this paper, we describe the KuKa radar, illustrate examples of its data and demonstrate their potential for these investigations.

scholarly journals Sea Surface Ka-Band Doppler Measurements: Analysis and Model Development

2019 ◽  
Vol 11 (7) ◽  
pp. 839 ◽  
Author(s):  
Yury Yurovsky ◽  
Vladimir Kudryavtsev ◽  
Semyon Grodsky ◽  
Bertrand Chapron
Keyword(s):  
Incidence Angle ◽  
Wave Length ◽  
Sea Surface ◽  
Scale Model ◽  
The Black Sea ◽  
Modulation Transfer ◽  
Data Set ◽  
Ka Band ◽  
Dominant Wave ◽  
Wave Induced

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 observations, with a rather constant dominant wave length, the DC is almost wind independent. Yet, results confirm that, besides surface currents, the DC encodes an expected wave-induced contribution. To help the interpretation, a two-scale model (KaDOP) is proposed to fit the observed DC, based on the radar modulation transfer function (MTF) previously developed for the same data set. Assuming universal spectral shape of energy containing sea surface waves, the wave-induced DC contribution is then expressed as a function of MTF, significant wave height, and wave peak frequency. The resulting KaDOP agrees well with independent DC data, except for swell-dominated cases. The swell impact is estimated using the KaDOP with a modified empirical MTF.

Sign in / Sign up

Export Citation Format

Share Document