Investigation of the Anisotropic Patterns in the Altimeter Backscatter Measurements Over Ocean Wave Surfaces

This article attempts to analyze the influence of the anisotropic effects of the ocean wave surface on SAR altimetry backscatter coefficient (Sigma-0) measurements, which has not been intensively addressed in publications. Data of Sentinel-3A, Cryosat-2, and Jason-3 altimeters allocated by the WW3 numeric wave model were analyzed, and the patterns of Sigma-0 with respect to the wave direction were acquired under ∼2 m significant wave height. The ocean waves were classified into six categories, among which the moderate swell and short win-wave cases were analyzed intensively. Swell-dominated ocean surface shows less randomness than the wind-wave-dominated ocean surface. Clear and significant sinusoid trends are found in the Sigma-0 and SSB patterns of both operational modes (SAR mode and PLRM mode) of the Sentinel-3A altimeter for the moderate swell case, indicating the sensitivity of Sigma-0 and SSB measurements to the anisotropic features of the altimeter measurements. The anisotropic pattern in the Sentinel-3A PLRM Sigma-0 is somewhat counterintuitive, but the analysis of Jason-3 altimeter data would show similar results. Additionally, by comparing the anisotropic patterns of two orthogonally polarized SAR altimeters (Sentinel-3A and Cryosat-2), we could draw the conclusion that the Sigma-0 measurements are not sensitive to the polarization mode. As for the SSHA patterns, no clear sinusoid could be identified for the moderate swell. A possible explanation is that the SSB pattern may be overwhelmed in the complicated factors that can influence the SSHA pattern.

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Ocean Surface Modeling in Vary Wind Field

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.480-481.1452 ◽

2011 ◽

Vol 480-481 ◽

pp. 1452-1456

Author(s):

Li Bo ◽

Zhong Yi Li ◽

Yue Jin Zhang

Keyword(s):

Wind Field ◽

Wave Spectrum ◽

Wave Model ◽

Ocean Surface ◽

Ocean Waves ◽

Surface Modeling ◽

Ocean Wave ◽

Statistical Characteristics ◽

Linear Wave ◽

Wave Models

In ocean surface modeling a popular method of wave modeling is making use of ocean wave spectrum, which is a physical wave model and based on linear wave theories. The ocean waves produced in this way can reflect the statistical characteristics of the real ocean well. However, few investigations of ocean simulation have been focused on turbulent fluid under vary wind field in this way, while all ocean wave models are built with the same wind parameters. In order to resolve the problem of traditional method, we proposed a new method of dividing the ocean surface into regular grids and generating wave models with different parameters of wind in different location of view scope. The method not only preserves the fidelity of statistical characteristics, but also can be accelerated with the processing of GPU and widely used in VR applications.

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Sea State Determination from Ship-Based Geodetic GPS

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-13-00211.1 ◽

2014 ◽

Vol 31 (11) ◽

pp. 2556-2564 ◽

Cited By ~ 9

Author(s):

James Foster ◽

Ning Li ◽

Kwok Fai Cheung

Keyword(s):

Wave Height ◽

Wave Model ◽

Ocean Waves ◽

Sea Surface ◽

Wave Direction ◽

Sea State ◽

Dominant Wave ◽

Model Predictions ◽

Economic Vitality ◽

Buoy Data

AbstractOcean waves have a profound impact on navigation, offshore operations, recreation, safety, and the economic vitality of a nation’s maritime and coastal communities. This study demonstrates that ships equipped with geodetic GPS and a radar gauge can provide accurate estimates of sea state. The Research Vessel (R/V) Kilo Moana recorded 1-Hz data for the entire period of a 10-day cruise around the Hawaiian Islands. Solving for precise kinematic positions for the ship and combining these solutions with the ranges from the ship to the sea surface provided by the radar gauge, it was possible to retrieve 1-Hz estimates of the sea surface elevation along the cruise track. Converting these into estimates of significant wave height, strong agreement was found with wave buoy measurements and hindcast wave data. Comparison with buoy data indicates the estimates have errors on the order of 0.22 m, or less than 11% of the wave height. Using wave model predictions of the dominant directions, the data were processed further to correct for the Doppler shift and to estimate the dominant wave period. Although relatively noisy in locations where the predicted wave directions are expected to be poor, in general these estimates also show a good agreement with the wave buoy observations and hindcast wave estimates. A segment of the cruise that formed a circuit allowed for testing the consistency of the ship-based estimates and for determining a dominant wave direction, which was found to agree closely with model predictions.

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Seasonal fluctuations in the secondary microseism wavefield recorded offshore Ireland

10.5194/egusphere-egu2020-19154 ◽

2020 ◽

Author(s):

Florian Le Pape ◽

Christopher J. Bean

Keyword(s):

Wave Model ◽

Ocean Waves ◽

Ocean Wave ◽

Ocean Bottom ◽

Ocean Bottom Seismometer ◽

Storm Activity ◽

Directional Spectrum ◽

Sea Bottom ◽

Ocean Wave Model ◽

Obs Data

Generated in the ocean, secondary microseisms result from the interaction of opposing ocean wave fronts and represent the strongest ambient seismic noise level measured on land. The recorded noise energy will vary with seasons due to changes in storm activity and associated secondary microseism source locations. Here, ocean bottom seismometer (OBS) data collected offshore Ireland in 2016 have been processed to look into the seasonal variations of the ambient noise wavefield recorded at the seafloor. Daily cross-correlations of OBS pairs located on top of thick sediments in deep water highlight seasonal changes between Rayleigh waves fundamental mode and first overtone for winter and summer months. Comparisons with ocean wave directional spectrum data derived from ocean wave model hindcasts suggest those variations are correlated with changing patterns in ocean waves interactions and therefore microseism source locations. In order to understand those observations in detail, we use 3D numerical simulations to show how the water column but also the subsurface structure below the sea bottom will affect the recorded wavefield at the seafloor for different stations and sources locations. Compared to land stations, the secondary microseism wavefield observed in the ocean and in particular changes in the excitation of Rayleigh modes due to site effects can help characterize the microseism source locations that fluctuate through the seasons.

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Ocean Wave Information Retrieval Using Simulated Compact Polarized SAR from Radarsat-2

Journal of Sensors ◽

10.1155/2018/1738014 ◽

2018 ◽

Vol 2018 ◽

pp. 1-12 ◽

Cited By ~ 1

Author(s):

Xiaochen Wang ◽

Yun Shao ◽

Lu She ◽

Wei Tian ◽

Kun Li ◽

...

Keyword(s):

Wave Field ◽

Ocean Surface ◽

Ocean Wave ◽

Wave Direction ◽

National Data ◽

Slope Spectrum ◽

Field Information ◽

Wave Slope ◽

Good Agreement

The main objective of this paper is to demonstrate the capability of compact polarized (CP) synthetic aperture radar (SAR) to retrieve ocean wave field parameters. Souyris’ and Nord’s algorithms are used to carry out the reconstruction of CP SAR pseudo quad-polarized data for the ocean surface under both the circular transmit linear receive (CTLR) and π/4 mode. The results show that, for the CP reconstruction, Nord’s algorithm has a better convergence ability than Souyris’. In addition, the investigation of the reconstruction accuracy shows that the CTLR mode is superior to the π/4 mode, in terms of ocean surface reconstruction. It is, therefore, concluded that the reconstructed parameters of CP CTLR mode data by Nord’s algorithm adapt to retrieve ocean wave information. The ocean wave slope spectrum and other main wave parameters are also calculated from reconstructed CP data and compared with measurements from in situ National Data Buoy Center (NDBC) matched-up buoys. Comparison of CP SAR-based wave field information with buoy outputs also shows good agreement in the case of dominate wave height, wave direction, and wave period, with biases of 0.36 m, 17.96°, and 0.88 s, respectively.

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Comparison of Envisat ASAR Ocean Wave Spectra with Buoy and Altimeter Data via a Wave Model

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2008jtecho529.1 ◽

2009 ◽

Vol 26 (3) ◽

pp. 593-614 ◽

Cited By ~ 10

Author(s):

Jian-Guo Li ◽

Martin Holt

Keyword(s):

Wave Height ◽

Spectral Characteristics ◽

Wave Model ◽

Ocean Wave ◽

Global Ocean ◽

Altimeter Data ◽

Wave Spectra ◽

Envisat Asar ◽

Comparison Results ◽

Wave Heights

Abstract The Advanced Synthetic Aperture Radar (ASAR) on board the Envisat satellite is an important resource for observation of global ocean surface wave spectra. However, assessment of this valuable dataset is not straightforward as a result of a lack of other independent ocean wave spectral observations. The radar altimeter (RA-2) on board the same satellite measures ocean wave height at the same time as the ASAR but at a location about 200 km distant. A small number of moored buoys produce one-dimensional (1D) ocean wave spectra but few ASAR spectra fall on the buoy positions in a given period. Indirect comparison of the Envisat ASAR 2D wave spectra with the RA-2 wave heights and 1D spectra of three selected buoys from July 2004 to February 2006 is facilitated by a wave model, which provides coherent spatial and temporal links between these observations. In addition to the conventional significant wave height (SWH), four spectral subrange wave heights (SRWHs) are used to illustrate the spectral characteristics of these observations. A comparison of three Envisat ASAR 2D spectra with the closest model and buoy spectra is also attempted to illustrate the qualities of these different observations and to demonstrate the restrictions to their direct comparison. Results indicate that these three independent observations are in good agreement in terms of SWH, though the Envisat ASAR shows the largest variance. Comparison of SRWHs indicates that the ASAR spectra agree well with buoy and model in moderately long waves, but the ASAR instrument does not resolve high-frequency waves, especially along the satellite track.

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Accuracy Evaluation of CFOSAT SWIM L2 Products Based on NDBC Buoy and Jason-3 Altimeter Data

Remote Sensing ◽

10.3390/rs13050887 ◽

2021 ◽

Vol 13 (5) ◽

pp. 887

Author(s):

Guozhou Liang ◽

Jungang Yang ◽

Jichao Wang

Keyword(s):

Wave Height ◽

Wave Spectrum ◽

Data Accuracy ◽

Ocean Wave ◽

Global Ocean ◽

Altimeter Data ◽

Accuracy Evaluation ◽

Wave Direction ◽

Dominant Wave ◽

Better Than

Chinese-French Oceanography Satellite (CFOSAT), the first satellite which can observe global ocean wave and wind synchronously, was successfully launched On 29 October 2018. The CFOSAT carries SWIM that can observe ocean wave on a global scale. Based on National Data Buoy Center (NDBC) buoys and Jason-3 altimeter data, this study evaluated the accuracy of L2 level products of CFOSAT SWIM from August 2019 to September 2020. The results show that the accuracy of the nadir Significant Wave Height (SWH) data of the SWIM wave spectrometer is good. Compared with the data of the NDBC buoys and Jason-3 altimeter, the RMSE of the nadir box SWH were 0.39 and 0.21 m, respectively. The variation trend of SWH were first increasing and then decreasing with the increasing of the wave height. The precision of off-nadir wave spectrum SWH is not better than nadir box SWH data. Accuracy was evaluated for off-nadir data from August 2019 to June 2020 and after June 2020, respectively. After linear regression correction, the accuracy of off-nadir wave spectrum SWH was improved. The data accuracy evaluation and comparison of different time period showed that the off-nadir wave spectrum SWH accuracy was improved after the data version was updated in June 2020, especially for 6° and 8° wave spectrum. The precision of off-nadir wave spectrum SWH decreases with the increasing of wave height. The accuracy of the dominant wave direction of each wave spectrum is also not very good, and the accuracy of the dominant wave direction of 10° wave spectrum is slightly better than the others. In general, the accuracy of SWIM nadir beam SWH data reaches the high data accuracy of traditional altimeter, while the accuracy of off-nadir wave spectrum SWH is less than that of nadir beam SWH data. The off-nadir SWH data accuracy after June 2020 has been greatly improved.

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Ocean Wave Measurement Using GPS Buoys

Journal of Geodetic Science ◽

10.2478/jogs-2013-0023 ◽

2013 ◽

Vol 3 (3) ◽

pp. 163-172 ◽

Cited By ~ 8

Author(s):

G. Joodaki ◽

H. Nahavandchi ◽

K. Cheng

Keyword(s):

Ocean Surface ◽

Ocean Wave ◽

Gps Receiver ◽

Wave Direction ◽

Ocean Surface Waves ◽

Estimated Parameters ◽

Wave Parameters ◽

Measurement Wave ◽

Ocean Surface Wave ◽

High Pass

AbstractThe observation of ocean wave parameters is necessary to improve forecasts of ocean wave conditions. In this paper, we investigate the viability of using a single GPS receiver to measure ocean-surface waves, and present a method to enhance the accuracy of the estimated wave parameters. The application of high-pass filtering to GPS data in conjunction with directional wave spectral theory is a core concept in this article. Laboratory experiments were conducted to test the viability and accuracy measurements of wave parameters made by a single GPS receiver buoy. These tests identified an error of less than 1% for the rotational arm measurement (wave height) and an error of 1% in verifications of the wave direction and wave period, and showed a 0.488 s bias; this is sufficiently accurate for many specific purposes. These results are based on the best cut-off frequency value derived in this study. A moored-sea GPS buoy on the Taiwanese coast was used to estimate the GPS-derived wave parameters. Our results indicate that data from a single GPS receiver, processed with the presented method to reduce the error of the estimated parameters, can provide measurements of ocean surface wave to reasonable accuracy.

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Assessing the Performance of the Dissipation Parameterizations in WAVEWATCH III Using Collocated Altimetry Data

Journal of Physical Oceanography ◽

10.1175/2009jpo4182.1 ◽

2009 ◽

Vol 39 (11) ◽

pp. 2800-2819 ◽

Cited By ~ 13

Author(s):

Georgia D. Kalantzi ◽

Christine Gommenginger ◽

Meric Srokosz

Keyword(s):

Wave Height ◽

Wave Breaking ◽

Source Term ◽

Wave Spectrum ◽

Wave Model ◽

North Indian Ocean ◽

Altimeter Data ◽

Wave Direction ◽

Wavewatch Iii ◽

The North

Abstract Wave-breaking dissipation is one of the least understood processes implemented in contemporary wave models. Significant effort has been put in its parameterization, but it has not proven to be totally satisfactory, either theoretically or practically. In this work, the WAVEWATCH III (version 2.22; Tolman) wave model is used to evaluate the two wind input/dissipation source term packages that it includes: (i) Wave Model (WAM) cycle 3 (WAMDIG) and (ii) Tolman and Chalikov. Global model outputs were obtained under the same wind forcing for the two dissipation formulations and were collocated in space and time in the north Indian Ocean with Ocean Topography Experiment (TOPEX) altimeter data. The performance of the model was assessed by evaluating the statistical behavior of the collocated datasets. The parameters examined were significant wave height, wind speed, wind direction, wave direction, wave height for fully developed seas, and energy loss due to wave breaking. From the results, the behavior of the input/dissipation formulations in specific wind and wave conditions was identified; that is, the results give insight to the way the two source term packages “work” and how they respond to local wind sea or swell. Specifically, both of the packages were unable to perform adequately during a season when the area can be mostly affected by swell. However, the results confirmed that the examination of only integral spectral wave parameters does not give information on the inherent physical characteristics of the formulations. Further study, on the basis of point spectra, is necessary to examine the formulations’ performance across the wave spectrum.

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Directional and frequency spread of surface ocean waves from CFOSAT/SWIM satelllite measurements

10.5194/egusphere-egu21-2544 ◽

2021 ◽

Author(s):

Danièle Hauser ◽

Eva Le Merle ◽

Lotfi Aouf ◽

Charles Peureux

Keyword(s):

Wave Model ◽

Ocean Waves ◽

Global Scale ◽

Ocean Wave ◽

Wave Spectra ◽

Physical Processes ◽

Satellite Mission ◽

Sea State ◽

Surface Ocean ◽

Frequency Spread

The CFOSAT (China France Oceanography Satellite) mission launched in 2018 now routinely provides at the global scale, directional spectra of ocean waves. The principle is based on the analysis of the normalized radar cross-section measured by the instrument SWIM (Surface Waves Investigation and Monitoring), a near-nadir pointing Ku-Band real-aperture scanning radar. From the ocean wave spectra derived from SWIM, the principal parameters of ocean wave spectra as significant wave height, peak wavelength, and peak direction are now available to better characterize the sea-state. However, it is known that these principal parameters are not sufficient not fully characterize the distribution of wave energy and understand or validate the physical processes impacting its evolution during growth order decay. Here we show that the parameters characterizing the shape of the wave spectra (e.g directional and frequency spread) can be estimated at the global scale from the SWIM measurements. We also show that they can provide consistent values of the Benjamin-Feir index, an index proposed to estimate the probability of extreme waves. Similarities of differences with the shape parameters of the MFWAM numerical wave model are also discussed.

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Amplitude Malformation in the IFFT Ocean Wave Rendering under the Influence of the Fourier Coefficient

Electronics ETF ◽

10.7251/els1418089c ◽

2014 ◽

Vol 18 (2) ◽

pp. 89

Author(s):

Lining Chen ◽

Yicheng Jin ◽

Yong Yin

Keyword(s):

Fourier Coefficient ◽

Integral Domain ◽

Wave Model ◽

Ocean Waves ◽

Ocean Wave ◽

Wave Number ◽

Not Given ◽

Source Codes ◽

Wave Potential ◽

Wavenumber Spectrum

Although Tessendorf’s IFFT Gerstner wave model hasbeen widely used, the value of A, a constant of the Fouriercoefficient, is not given. A will strongly influence the shape of therendered ocean wave and even cause amplitude malformation.We study the algorithm of the IFFT Gerstner wave, and give themethod of A calculating. The method of the paper can guaranteethere is no amplitude malformation in rendered ocean waves. Theexpression of the IFFT Gerstner wave with the amplitude of thecosine wave is derived again. The definite integral of the wavenumber spectrum is discretized. Further, another expression ofthe IFFT Gerstner wave is gotten. The Fourier coefficient of theexpression contains the wave number spectrum and the area ofthe discrete integral domain. The method makes the shape of thegenerated wave stable. Comparing Tessdendorf’s method with themethod of the paper, we find that the expression of A shouldcontain the area of the discrete integral domain and the spectralconstant of the wave number spectrum. If A contains only thespectral constant, the amplitude malformation may occur. Byreading some well known open source codes, we find that the codeauthors adopted some factitious methods to suppress themalformed amplitude Obviously, the code authors have alreadynoticed the phenomenon of the malformation, but not probed thecause. The rendering results of the codes are close to that of themethod of the paper. Furthermore, the wave potential iscomputed using the Gerstner wave model directly, the author findit is quite close to that of the paper. The experimental results andcomparisons show that the method of the paper correctlycomputes the wave potential and effectively solves the problem ofamplitude malformation.

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