Spatial Coherence of Nonlinear, Nonstationary, Non-Gaussian Ocean Waves on a One-Mile Scale from Scanning Radar Altimeter

1999 ◽  
Author(s):  
Leon E. Borgman ◽  
Ronald W. Marrs ◽  
Edward J. Walsh
Keyword(s):  
Spatial Coherence ◽  
Ocean Waves ◽  
Radar Altimeter ◽  
Non Gaussian

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 Surface Wave Breaking Caused by Internal Solitary Waves: Effects on Radar Backscattering Measured by SAR and Radar Altimeter

Oceanography ◽  
2021 ◽  
Vol 34 (2) ◽  
Author(s):  
Jorge Magalhães ◽  
Werner Alpers ◽  
Adriana Santos-Ferreira ◽  
José da Silva
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Solitary Waves ◽  
Wave Energy ◽  
Wave Breaking ◽  
Ocean Waves ◽  
Altimeter Data ◽  
Internal Solitary Waves ◽  
Radar Altimeter ◽  
Wind Speeds

Breaking surface waves play a key role in the exchange of momentum, heat, and gases between the atmosphere and the ocean. Waves break at the ocean’s surface at high or medium wind speeds or in the absence of wind due to shoaling of the seafloor. However, surface waves also break due to interactions with internal solitary waves (ISWs). In this paper, we revisit surface wave breaking caused by ISWs and how ISWs are manifested in synthetic aperture radar (SAR) images acquired by the TerraSAR-X and Sentinel-1 satellites and in high-resolution radar altimeter data acquired by the SAR altimeter (SRAL) onboard the Sentinel-3A satellite. X-band TerraSAR-X images acquired at low wind speeds suggest that meter-scale surface breaking waves resulting from large-scale ISWs are associated with large modulations in backscatter at HH and VV polarizations that cannot be explained by present theories. Furthermore, Sentinel-1 C-band SAR satellite images acquired at moderate to high wind speeds also exhibit large radar signatures from surface wave breaking at VV and VH cross-polarizations. Finally, new observations from the Sentinel-3 SRAL altimeter show clear evidence of significant wave height (SWH) variations along the propagation paths of ISWs. The SWH signatures are unique in showing that the surface wave energy does not return to its unperturbed level after an ISW passes, most likely because intense meter-scale wave breaking results in surface wave energy dissipation. In summary, these results show that surface wave breaking contributes significantly to radar remote sensing of ISWs.

Approximation of Crossing Intensities for Non Linear Responses Subjected to Non Gaussian Loadings

2010 ◽  
Author(s):  
Thomas Galtier ◽  
Sayan Gupta ◽  
Igor Rychlik
Keyword(s):  
Heavy Tails ◽  
Moving Average ◽  
Ocean Waves ◽  
Response Characteristic ◽  
Second Order ◽  
Computationally Efficient ◽  
Marine Structures ◽  
Efficient Manner ◽  
New Class ◽  
Non Gaussian

Crossing intensity constitute an important response characteristic for randomly vibrating structures, especially if one is interested in estimating the risk against failures. This paper focusses on developing approximations by which estimates of the crossing intensities for response of marine structures can be obtained in a computationally efficient manner, when the loads are modeled as a special class of non-Gaussian processes, namely as LMA processes. Ocean waves exhibit considerable non-Gaussianity as marked by their skewed marginal distributions and heavy tails. Here, a new class of processes-the Laplace driven Moving Average (LMA) processes are used to model the ocean waves. LMA processes are non-Gaussian, strictly stationary, can model in principle any spectrum and have the additional flexibility to model the skewness and the kurtosis of the marginal distribution. The structure behavior assumed is limited to quadratic systems characterized by second order kernels, which is common for marine structures. Thus, an estimation of the crossing intensities of the response involves studying the crossing characteristics of a LMA process passing through a second order filter. A new computationally efficient hybrid method, which uses the saddle point approximations along with limited Monte Carlo simulations, is developed to compute crossing intensity of the response. The proposed method is illustrated through numerical examples.

scholarly journals David Edgar Cartwright. 21 October 1926 — 2 December 2015

2017 ◽  
Vol 63 ◽  
pp. 99-115
Author(s):  
David J. Webb
Keyword(s):  
Deep Ocean ◽  
Ocean Waves ◽  
Wave Climate ◽  
Internal Tides ◽  
Altimeter Data ◽  
Ship Motions ◽  
Ocean Tides ◽  
Radar Altimeter ◽  
Directional Spectrum ◽  
The Uk

David Cartwright was one of the world's leading authorities on the tides. However, when reflecting on his life, Cartwright made the point that his early scientific career was not a success. Indeed in 1953, at the age of 27, he had virtually despaired of any creative scientific future. At the time he was being pressurized to stop his work on the statistics of ship motions but his prospects rapidly changed when he was invited to apply for a post at the new National Institute of Oceanography (NIO) being set up by George Deacon. At NIO he soon made important contributions to the study of ocean waves, especially the calculation of directional spectrum and wave climate. His earlier involvement with ship motions also culminated in a successful joint study with Louis Rydill on the response of ships to the spectrum of waves. Following this, his use of computer methods for time-series analysis led to an invitation to the Scripps Institution of Oceanography where, with Walter Munk, he developed the response method of analysing tides making use of the very long tidal records collected from Hawaii and Newlyn. He was also made aware of the significant lack of good tidal data from the deep ocean. Returning to the UK, he continued these interests, studying the deep-ocean tides of the Atlantic and leading an international collaboration that measured deep-ocean tides. He also investigated the effect of tides on storm surges around the UK. He became assistant director in charge of the Institute of Oceanographic Sciences (IOS) Bidston laboratory, where he continued these activities and started research on estimating the tides using data from the Seasat radar altimeter. After retirement he successfully extended this work with Richard Ray at the Goddard Space Flight Center. Using Geosat altimeter data they generated accurate global maps of the tides in a set of papers that Cartwright considered to be his best work. He wrote a successful book titled ‘ Tides: a scientific history ’, and later published further work with Ray on the internal tides of the ocean.

Measuring Global Ocean Wave Skewness by Retracking RA-2 Envisat Waveforms

2007 ◽  
Vol 24 (6) ◽  
pp. 1102-1116 ◽  
Author(s):  
J. Gómez-Enri ◽  
C. P. Gommenginger ◽  
M. A. Srokosz ◽  
P. G. Challenor ◽  
J. Benveniste
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Likelihood Estimation ◽  
Ocean Waves ◽  
Ocean Wave ◽  
Global Ocean ◽  
Radar Altimeter ◽  
Significant Wave ◽  
Linear And Nonlinear ◽  
The Impact

For early satellite altimeters, the retrieval of geophysical information (e.g., range, significant wave height) from altimeter ocean waveforms was performed on board the satellite, but this was restricted by computational constraints that limited how much processing could be performed. Today, ground-based retracking of averaged waveforms transmitted to the earth is less restrictive, especially with respect to assumptions about the statistics of ocean waves. In this paper, a theoretical maximum likelihood estimation (MLE) ocean waveform retracker is applied tothe Envisat Radar Altimeter system (RA-2) 18-Hz averaged waveforms under both linear (Gaussian) and nonlinear ocean wave statistics assumptions, to determine whether ocean wave skewness can be sensibly retrieved from Envisat RA-2 waveforms. Results from the MLE retracker used in nonlinear mode provide the first estimates of global ocean wave skewness based on RA-2 Envisat averaged waveforms. These results show for the first time geographically coherent skewness fields and confirm the notion that large values of skewness occur primarily in regions of large significant wave height. Results from the MLE retracker run in linear and nonlinear modes are compared with each other and with the RA-2 Level 2 Sensor Geophysical Data Records (SGDR) products to evaluate the impact of retrieving skewness on other geophysical parameters. Good agreement is obtained between the linear and nonlinear MLE results for both significant wave height and epoch (range), except in areas of high-wave-height conditions.

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