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.

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 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 Enhancing temporal correlations in EOF expansions for the reconstruction of missing data using DINEOF

2009 ◽  
Vol 6 (2) ◽  
pp. 1547-1568 ◽  
Author(s):  
A. Alvera-Azcárate ◽  
A. Barth ◽  
D. Sirjacobs ◽  
J.-M. Beckers
Keyword(s):  
Missing Data ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Empirical Orthogonal Functions ◽  
Sea Surface ◽  
The Black Sea ◽  
Time Variability ◽  
Orthogonal Functions ◽  
Data Set ◽  
Temporal Correlations

Abstract. DINEOF (Data Interpolating Empirical Orthogonal Functions) is an EOF-based technique for the reconstruction of missing data in geophysical fields, such as those produced by clouds in sea surface temperature satellite images. A technique to reduce spurious time variability in DINEOF reconstructions is presented. The reconstruction of these images within a long time series using DINEOF can lead to large discontinuities in the reconstruction. Filtering the temporal covariance matrix allows to reduce this spurious variability and therefore more realistic reconstructions are obtained. The approach is tested in a three years sea surface temperature data set over the Black Sea. The effect of the filter in the temporal EOFs is presented, as well as some examples of the improvement achieved with the filtering in the SST reconstruction, both compared to the DINEOF approach without filtering.

scholarly journals Enhancing temporal correlations in EOF expansions for the reconstruction of missing data using DINEOF

Ocean Science ◽  
2009 ◽  
Vol 5 (4) ◽  
pp. 475-485 ◽  
Author(s):  
A. Alvera-Azcárate ◽  
A. Barth ◽  
D. Sirjacobs ◽  
J.-M. Beckers
Keyword(s):  
Missing Data ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Empirical Orthogonal Functions ◽  
Sea Surface ◽  
The Black Sea ◽  
Time Variability ◽  
Orthogonal Functions ◽  
Data Set ◽  
Temporal Correlations

Abstract. DINEOF (Data Interpolating Empirical Orthogonal Functions) is an EOF-based technique for the reconstruction of missing data in geophysical fields, such as those produced by clouds in sea surface temperature satellite images. A technique to reduce spurious time variability in DINEOF reconstructions is presented. The reconstruction of these images within a long time series using DINEOF can lead to large discontinuities in the reconstruction. Filtering the temporal covariance matrix allows to reduce this spurious variability and therefore more realistic reconstructions are obtained. The approach is tested in a three years sea surface temperature data set over the Black Sea. The effect of the filter in the temporal EOFs is presented, as well as some examples of the improvement achieved with the filtering in the SST reconstruction, both compared to the DINEOF approach without filtering.

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.

scholarly journals Modulation of Wind–Wave Breaking by Long Surface Waves

2021 ◽  
Vol 13 (14) ◽  
pp. 2825
Author(s):  
Vladimir A. Dulov ◽  
Aleksandr E. Korinenko ◽  
Vladimir N. Kudryavtsev ◽  
Vladimir V. Malinovsky
Keyword(s):  
Surface Waves ◽  
Wave Breaking ◽  
Field Measurements ◽  
Quantitative Agreement ◽  
Sea Surface ◽  
The Black Sea ◽  
Modulation Transfer ◽  
S Wave ◽  
Wind Speeds ◽  
Video Recordings

This paper reports the results of field measurements of wave breaking modulations by dominant surface waves, taken from the Black Sea research platform at wind speeds ranging from 10 to 20 m/s. Wave breaking events were detected by video recordings of the sea surface synchronized and collocated with the wave gauge measurements. As observed, the main contribution to the fraction of the sea surface covered by whitecaps comes from the breaking of short gravity waves, with phase velocities exceeding 1.25 m/s. Averaging of the wave breaking over the same phases of the dominant long surface waves (LWs, with wavelengths in the range from 32 to 69 m) revealed strong modulation of whitecaps. Wave breaking occurs mainly on the crests of LWs and disappears in their troughs. Data analysis in terms of the modulation transfer function (MTF) shows that the magnitude of the MTF is about 20, it is weakly wind-dependent, and the maximum of whitecapping is windward-shifted from the LW-crest by 15 deg. A simple model of whitecaps modulations by the long waves is suggested. This model is in quantitative agreement with the measurements and correctly reproduces the modulations’ magnitude, phase, and non-sinusoidal shape.

EXTREME VALUES OF SEA SURFACE TEMPERATURE ASSOCIATED WITH LONG-PERIOD PHENOMENA OCCURRED DURING 1960-2015 IN THE COLOMBIAN PACIFIC OCEAN

2017 ◽  
Author(s):  
Diaz Juan Navia ◽  
Diaz Juan Navia ◽  
Bolaños Nancy Villegas ◽  
Bolaños Nancy Villegas ◽  
Igor Malikov ◽  
...  
Keyword(s):  
Time Series ◽  
Pacific Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Extreme Values ◽  
Sea Surface ◽  
Absolute Maximum ◽  
Data Set ◽  
Arctic Oscillation Index ◽  
Colombian Pacific

Sea Surface Temperature Anomalies (SSTA), in four coastal hydrographic stations of Colombian Pacific Ocean, were analyzed. The selected hydrographic stations were: Tumaco (1°48'N-78°45'W), Gorgona island (2°58'N-78°11'W), Solano Bay (6°13'N-77°24'W) and Malpelo island (4°0'N-81°36'W). SSTA time series for 1960-2015 were calculated from monthly Sea Surface Temperature obtained from International Comprehensive Ocean Atmosphere Data Set (ICOADS). SSTA time series, Oceanic Nino Index (ONI), Pacific Decadal Oscillation index (PDO), Arctic Oscillation index (AO) and sunspots number (associated to solar activity), were compared. It was found that the SSTA absolute minimum has occurred in Tumaco (-3.93°C) in March 2009, in Gorgona (-3.71°C) in October 2007, in Solano Bay (-4.23°C) in April 2014 and Malpelo (-4.21°C) in December 2005. The SSTA absolute maximum was observed in Tumaco (3.45°C) in January 2002, in Gorgona (5.01°C) in July 1978, in Solano Bay (5.27°C) in March 1998 and Malpelo (3.64°C) in July 2015. A high correlation between SST and ONI in large part of study period, followed by a good correlation with PDO, was identified. The AO and SSTA have showed an inverse relationship in some periods. Solar Cycle has showed to be a modulator of behavior of SSTA in the selected stations. It was determined that extreme values of SST are related to the analyzed large scale oscillations.

Role of suspended matter in controlling beryllium-7 (7Be) in the Black Sea surface layer

2021 ◽  
pp. 103513
Author(s):  
Dmitrii A. Kremenchutskii ◽  
Gennady F. Batrakov ◽  
Illarion I. Dovhyi ◽  
Yury A. Sapozhnikov
Keyword(s):  
Surface Layer ◽  
Black Sea ◽  
Suspended Matter ◽  
Sea Surface ◽  
The Black Sea
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