scholarly journals Study on the Nearshore Evolution of Regular Waves under Steady Wind

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 686 ◽  
Author(s):  
Changbo Jiang ◽  
Yang Yang ◽  
Bin Deng
Keyword(s):  
Wind Speed ◽  
Numerical Model ◽  
Turbulent Flow ◽  
Wave Breaking ◽  
Surface Wind ◽  
Average Level ◽  
Hydrodynamic Characteristics ◽  
Turbulent Dissipation ◽  
Cross Spectrum ◽  
The Cross

We present a study on regular wave propagation on a sloping bed under the action of steady wind, which is of a great significance to complement and replenish the interaction mechanisms of nearshore wave and wind. Physical experiments were conducted in a wind-wave flume, and the corresponding numerical model was constructed based on the solver Waves2FOAM in OpenFOAM, with large-eddy simulation (LES) used to investigate the turbulent flow. The comparisons between the measured and calculated results of the free surface elevation and flow velocity indicated that the numerical model could predict the associated hydrodynamic characteristics of a nearshore wave regardless of the presence or absence of wind. The results showed that wind had a significant impact on nearshore wave evolution. It was found that under the same wind speed coverage constraint, wave breaking occurred ahead of time. The smaller the surf similarity ξ 0 was, the higher the dispersion degree of wave breaking locations would be, and the breaker index of H b / h b increased with wind speed under the same incident wave height. The main components of analysis for turbulent flow were the results of the cross-spectrum, the TKE (turbulent kinetic energy), and TDR (turbulent dissipation rate). The cross-spectrum illustrated that wind enhanced the degree of coherence of the residual velocity components and aggravated turbulence. The TKE indicated that in regions near the water surface, wind speed made it considerably larger and the average level rapidly decreased with depth. The TDR exhibited that the significant effect of wind was merely imposed after breaking, wherein the turbulence penetrated the deeper flow and the average level generally rose. The velocity profile on the slope showed that the wind accelerated the undertow, and the moment statistics indicated that the velocity distribution deviated gradually from the Gaussian distribution to the right.

scholarly journals Understanding Ku-Band Ocean Radar Backscatter at Low Incidence Angles under Weak to Severe Wind Conditions by Comparison of Measurements and Models

2020 ◽  
Vol 12 (20) ◽  
pp. 3445
Author(s):  
Qiushuang Yan ◽  
Chenqing Fan ◽  
Jie Zhang ◽  
Junmin Meng
Keyword(s):  
Wind Speed ◽  
Wave Breaking ◽  
Scattering Theory ◽  
Specular Reflection ◽  
Incidence Angle ◽  
Surface Wind ◽  
Specular Scattering ◽  
Low Incidence ◽  
The Impact ◽  
Ku Band

The rain-free normalized radar cross-section (NRCS) measurements from the Ku-band precipitation radars (PRs) aboard the tropical rainfall measuring mission (TRMM) and the global precipitation measurement (GPM) mission, along with simultaneous sea surface wind truth from buoy observations, stepped-frequency microwave radiometer (SFMR) measurements, and H*Wind analyses, are used to investigate the abilities of the quasi-specular scattering models, i.e., the physical optics model (PO) and the classical and improved geometrical optics models (GO and GO4), to reproduce the Ku-band NRCS at low incidence angles of 0–18° over the wind speed range of 0–45 m/s. On this basis, the limitations of the quasi-specular scattering theory and the effects of wave breaking are discussed. The results show that the return caused by quasi-specular reflection is affected significantly by the presence of background swell waves at low winds. At moderate wind speeds of 5–15 m/s, the NRCS is still dominated by the quasi-specular reflection, and the wave breaking starts to work but its contribution is very small, thus, the models are found in excellent agreement with the measurements. With wind speed increasing, the impact of wave breaking increases, whereas the role of standard quasi-specular reflection decreases. The wave breaking impact on NRCS is first visible at incidence angles near 18° as wind speed exceeds about 20 m/s, then it becomes dominant when wind speed exceeds about 37 m/s where the NRCS is insensitive to wind speed and depends linearly on incidence angle, which cannot be explained by the standard quasi-specular scattering theory.

scholarly journals Preliminary Analysis of Wind Retrieval Based on GF-3 Wave Mode Images

2018 ◽  
Author(s):  
Lei Wang ◽  
Bing Han ◽  
Xinzhe Yuan ◽  
Bin Lei ◽  
Chibiao Ding ◽  
...  
Keyword(s):  
Wind Speed ◽  
Incidence Angle ◽  
Surface Wind ◽  
Wave Mode ◽  
Azimuth Angle ◽  
Calibration Constant ◽  
Wind Fields ◽  
Wind Retrieval ◽  
Geophysical Model ◽  
The Cross

In this paper, we analyze the measurements of the normalized radar cross-section(NRCS) in Wave Mode for Chinese C-band Gaofen-3(GF-3) synthetic aperture radar (SAR). Based on 2779 images from GF-3 quad-polarization SAR in Wave Mode and collocated wind vectors from ERA-Interim, we verify the feasibility of using ocean surface wind fields and VV-polarized NRCS to perform normalized calibration. The method uses well-validated empirical C-band geophysical model function (CMOD4) to estimate the calibration constant for each beam. The Amazon rainforest experiment results show that the accuracy of obtained calibration constant meets the requirements. In addition, the relationship between cross-pol NRCS and wind vectors is discussed. The cross-pol NRCS increases linearly with wind speed and it has an approximate cosine modulation with the wind direction when the wind speed is greater than 8m/s. The cross-polarized system noise floor is low enough to ignore it in wind retrieval. Furthermore, we also investigate the properties of the polarization ratio, denoted PR, and show that it is dependent on incidence angle and azimuth angle. Two empirical models of the PR are fitted, one as a function of incidence angle only, the other with additional dependence on azimuth angle. Assessments show that the σ_VV^0 retrieved from new PR models as well as σ_HH^0 is in good agreement with σ_VV^0 extracted from SAR images directly. And it is also shown that considering the azimuth angle can improve polarization conversion accuracy.

scholarly journals The Statistical Theory of Breaking Entrainment Depth and Surface Whitecap Coverage of Real Sea Waves

2009 ◽  
Vol 39 (1) ◽  
pp. 143-161 ◽  
Author(s):  
Yeli Yuan ◽  
Lei Han ◽  
Feng Hua ◽  
Shuwen Zhang ◽  
Fangli Qiao ◽  
...  
Keyword(s):  
Statistical Theory ◽  
Wind Speed ◽  
Wave Breaking ◽  
Surface Wind ◽  
Sea Waves ◽  
Formation Model ◽  
Wave Characteristics ◽  
Whitecap Coverage ◽  
Analytic Expressions ◽  
Sea Wave

Abstract Some basic statistics for wave breaking have been derived based on the statistical model of real sea waves. The analytic expressions of breaking entrainment depth and surface whitecap coverage involved with both sea wave characteristics and surface wind velocity have been derived on the basis of the whitecap formation model. The concept of the upper envelope for all the whitecap coverage data versus wind speed has been proposed, and it is assumed to correspond to the whitecap coverage in the case of the infinite wind duration and fetch to determine the model constants. The analytic expressions of breaking entrainment depth and whitecap coverage have been compared with the observations in several ways, and consistently favorable agreement can be found for most observations.

scholarly journals Preliminary Analysis of Wind Retrieval Based on GF-3 Wave Mode Images

2018 ◽  
Author(s):  
Lei Wang ◽  
Bing Han ◽  
xinzhe yuan ◽  
Bin Lei ◽  
Chibiao Ding ◽  
...  
Keyword(s):  
Wind Speed ◽  
Incidence Angle ◽  
Surface Wind ◽  
Wave Mode ◽  
Azimuth Angle ◽  
Calibration Constant ◽  
Wind Fields ◽  
Wind Retrieval ◽  
Geophysical Model ◽  
The Cross

In this paper, we analyze the measurements of the normalized radar cross-section(NRCS) in Wave Mode for Chinese C-band Gaofen-3(GF-3) synthetic aperture radar (SAR). Based on 2779 images from GF-3 quad-polarization SAR in Wave Mode and collocated wind vectors from ERA-Interim, we verify the feasibility of using ocean surface wind fields and VV-polarized NRCS to perform normalized calibration. The method uses well-validated empirical C-band geophysical model function (CMOD4) to estimate the calibration constant for each beam. The Amazon rainforest experiment results show that the accuracy of obtained calibration constant meets the requirements. In addition, the relationship between cross-pol NRCS and wind vectors is discussed. The cross-pol NRCS increases linearly with wind speed and it has an approximate cosine modulation with the wind direction when the wind speed is greater than 8m/s. The cross-polarized system noise floor is low enough to ignore it in wind retrieval. Furthermore, we also investigate the properties of the polarization ratio, denoted PR, and show that it is dependent on incidence angle and azimuth angle. Two empirical models of the PR are fitted, one as a function of incidence angle only, the other with additional dependence on azimuth angle. Assessments show that the σ_VV^0 retrieved from new PR models as well as σ_HH^0 is in good agreement with σ_VV^0 extracted from SAR images directly. And it is also shown that considering the azimuth angle can improve polarization conversion accuracy.

scholarly journals Preliminary Analysis of Wind Retrieval Based on GF-3 Wave Mode Images

2018 ◽  
Author(s):  
Lei Wang ◽  
Bin Han ◽  
Xinzhe Yuan ◽  
Bin Lei ◽  
Chibiao Ding ◽  
...  
Keyword(s):  
Wind Speed ◽  
Incidence Angle ◽  
Surface Wind ◽  
Wave Mode ◽  
Azimuth Angle ◽  
Calibration Constant ◽  
Wind Fields ◽  
Wind Retrieval ◽  
Geophysical Model ◽  
The Cross

In this paper, we analyze the measurements of the normalized radar cross-section(NRCS) in Wave Mode for Chinese C-band Gaofen-3(GF-3) synthetic aperture radar (SAR). Based on 2779 images from GF-3 quad-polarization SAR in Wave Mode and collocated wind vectors from ERA-Interim, we verify the feasibility of using ocean surface wind fields and VV-polarized NRCS to perform normalized calibration. The method uses well-validated empirical C-band geophysical model function (CMOD4) to estimate the calibration constant for each beam. The Amazon rainforest experiment results show that the accuracy of obtained calibration constant meets the requirements. In addition, the relationship between cross-pol NRCS and wind vectors is discussed. The cross-pol NRCS increases linearly with wind speed and it has an approximate cosine modulation with the wind direction when the wind speed is greater than 8m/s. The cross-polarized system noise floor is low enough to ignore it in wind retrieval. Furthermore, we also investigate the properties of the polarization ratio, denoted PR, and show that it is dependent on incidence angle and azimuth angle. Two empirical models of the PR are fitted, one as a function of incidence angle only, the other with additional dependence on azimuth angle. Assessments show that the σ_VV^0 retrieved from new PR models as well as σ_HH^0 is in good agreement with σ_VV^0 extracted from SAR images directly. And it is also shown that considering the azimuth angle can improve polarization conversion accuracy.

Off-Nadir SFMR Brightness Temperature Measurements in High-Wind Conditions

2018 ◽  
Vol 35 (9) ◽  
pp. 1865-1879 ◽  
Author(s):  
Heather M. Holbach ◽  
Eric W. Uhlhorn ◽  
Mark A. Bourassa
Keyword(s):  
Wind Speed ◽  
Brightness Temperature ◽  
Wind Direction ◽  
Wave Breaking ◽  
Surface Brightness ◽  
Surface Wind ◽  
Ocean Surface ◽  
Temperature Measurements ◽  
High Wind ◽  
Wide Range

AbstractWind and wave-breaking directions are investigated as potential sources of an asymmetry identified in off-nadir remotely sensed measurements of ocean surface brightness temperatures obtained by the Stepped Frequency Microwave Radiometer (SFMR) in high-wind conditions, including in tropical cyclones. Surface wind speed, which dynamically couples the atmosphere and ocean, can be inferred from SFMR ocean surface brightness temperature measurements using a radiative transfer model and an inversion algorithm. The accuracy of the ocean surface brightness temperature to wind speed calibration relies on accurate knowledge of the surface variables that are influencing the ocean surface brightness temperature. Previous studies have identified wind direction signals in horizontally polarized radiometer measurements in low to moderate (0–20 m s−1) wind conditions over a wide range of incidence angles. This study finds that the azimuthal asymmetry in the off-nadir SFMR brightness temperature measurements is also likely a function of wind direction and extends the results of these previous studies to high-wind conditions. The off-nadir measurements from the SFMR provide critical data for improving the understanding of the relationships between brightness temperature, surface wave–breaking direction, and surface wind vectors at various incidence angles, which is extremely useful for the development of geophysical model functions for instruments like the Hurricane Imaging Radiometer (HIRAD).

scholarly journals Error Estimates for Ocean Surface Winds: Applying Desroziers Diagnostics to the Cross-Calibrated, Multiplatform Analysis of Wind Speed

2013 ◽  
Vol 30 (11) ◽  
pp. 2596-2603 ◽  
Author(s):  
Ross N. Hoffman ◽  
Joseph V. Ardizzone ◽  
S. Mark Leidner ◽  
Deborah K. Smith ◽  
Robert Atlas
Keyword(s):  
Wind Speed ◽  
Surface Wind ◽  
Ocean Surface ◽  
Surface Wind Speed ◽  
Wind Speeds ◽  
Speed Error ◽  
Ocean Surface Winds ◽  
Remote Sensing Systems ◽  
Standard Deviations ◽  
The Cross

Abstract The Desroziers diagnostics (DD) are applied to the cross-calibrated, multiplatform (CCMP) ocean surface wind datasets to estimate wind speed errors of the ECMWF background, the microwave satellite observations, and the resulting CCMP analysis. The DD confirm that the ECMWF operational surface wind speed error standard deviations vary with latitude in the range 0.8–1.3 m s−1 and that the cross-calibrated Remote Sensing Systems (RSS) wind speed retrievals’ standard deviations are in the range 0.5–0.7 m s−1. Further, the estimated CCMP analysis wind speed standard deviations are in the range 0.2–0.3 m s−1. The results suggest the need to revise the parameterization of the errors of the first guess at appropriate time (FGAT) procedure. Errors for wind speeds <16 m s−1 are homogeneous; however, for the relatively rare but critical higher wind speed situations, errors are much larger.

Recurrence Characteristics Analysis of Near-Surface Wind Speed Signal with Different Sampling Frequencies

2014 ◽  
Vol 599-601 ◽  
pp. 1605-1609 ◽  
Author(s):  
Ming Zeng ◽  
Zhan Xie Wu ◽  
Qing Hao Meng ◽  
Jing Hai Li ◽  
Shu Gen Ma
Keyword(s):  
Wind Speed ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Recurrence Plot ◽  
Sampling Frequency ◽  
Near Surface ◽  
Gas Leakage ◽  
Time Period ◽  
Characteristics Analysis ◽  
Quantification Analysis

The wind is the main factor to influence the propagation of gas in the atmosphere. Therefore, the wind signal obtained by anemometer will provide us valuable clues for searching gas leakage sources. In this paper, the Recurrence Plot (RP) and Recurrence Quantification Analysis (RQA) are applied to analyze the influence of recurrence characteristics of the wind speed time series under the condition of the same place, the same time period and with the sampling frequency of 1hz, 2hz, 4.2hz, 5hz, 8.3hz, 12.5hz and 16.7hz respectively. Research results show that when the sampling frequency is higher than 5hz, the trends of recurrence nature of different groups are basically unchanged. However, when the sampling frequency is set below 5hz, the original trend of recurrence nature is destroyed, because the recurrence characteristic curves obtained using different sampling frequencies appear cross or overlapping phenomena. The above results indicate that the anemometer will not be able to fully capture the detailed information in wind field when its sampling frequency is lower than 5hz. The recurrence characteristics analysis of the wind speed signals provides an important basis for the optimal selection of anemometer.

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