scholarly journals Is it Possible to Get a SAR Image of Ocean Waves Free of Spectral Cut-off by Direct Measurement?

2021 ◽  
Vol 4 (2) ◽  
Keyword(s):  
Direct Measurement ◽  
Ocean Surface ◽  
Ocean Waves ◽  
Wave Pattern ◽  
Matched Filtering ◽  
Sar Image ◽  
Spectral Cut ◽  
Track Line

A method of SAR sounding of the ocean surface is proposed, which is capable of providing an undistorted by spectral cut-off wave pattern. The method involves the use of two synchronized SARs, which look across the track line and illuminate the same area of the surface. Each SAR records its own backscattered signal, which are then multiplied with each other and the resulting signal is undergoing the procedure of matched filtering. Numerical estimates of the applicability conditions of the method are carried out.

scholarly journals How to Obtain a SAR Image of the Ocean Surface That Is Actually Free from The Impact of Orbital Velocities

2021 ◽  
Vol 4 (2) ◽  
Keyword(s):  
Synthetic Aperture Radar ◽  
Ocean Surface ◽  
Synthetic Aperture ◽  
Small Scale ◽  
Matched Filtering ◽  
Sar Image ◽  
Synthesis Procedure ◽  
Reflected Signal ◽  
Reflecting Surface ◽  
The Impact

As is known, the main problem in interpreting images of the ocean surface formed by microwave synthetic aperture radar (SAR) is the distortions introduced by the orbital movements of the small-scale (centimeter and decimeter) ripples in the field of large waves. The point is that the standard aperture synthesis procedure is a matched filtering operation aimed at extracting from the reflected signal a part that has a phase that changes according to a known scenario corresponding to a stationary reflecting surface.

Simulation of SAR image cross spectra from mixed ocean waves

2007 ◽  
Author(s):  
Jingsong Yang ◽  
He Wang ◽  
Qingmei Xiao ◽  
Weigen Huang
Keyword(s):  
Ocean Waves ◽  
Sar Image

Improving 3-D Variational Stereo Reconstruction of Oceanic Sea States by Camera Calibration Refinement

2013 ◽  
Author(s):  
Ping-Chang Shih ◽  
Guillermo Gallego ◽  
Anthony Yezzi ◽  
Francesco Fedele
Keyword(s):  
Error Function ◽  
Image Plane ◽  
Ocean Surface ◽  
Ocean Waves ◽  
Breaking Waves ◽  
Wave Climate ◽  
Climate Extreme ◽  
Projection Model ◽  
Refinement Procedure ◽  
Camera Parameters

Studies of wave climate, extreme ocean events, turbulence, and the energy dissipation of breaking and non-breaking waves are closely related to the measurements of the ocean surface. To gauge and analyze ocean waves on a computer, we reconstruct their 3-D model by utilizing the concepts of stereoscopic reconstruction and variational optimization. This technique requires a pair of calibrated cameras — cameras whose parameters are estimated for the mathematical projection model from space to an image plane — to take videos of the ocean surface as input. However, the accuracy of camera parameters, including the orientations and the positions of cameras as well as the internal specifications of optics elements, are subject to environmental factors and manual calibration errors. Because the errors of camera parameters magnify the errors of the 3-D reconstruction after projection, we propose a novel algorithm that refines camera parameters, thereby improving the accuracy of variational 3-D reconstruction. We design a multivariate error function that represents discrepancies between captured images and the reprojection of the reconstruction onto the images. As a result of the iteratively diminished error function, the camera parameters and the reconstruction of ocean waves evolve to optimal values. We demonstrate the success of our algorithm by comparing the reconstruction results with the refinement procedure to those without it and show improvements in the statistics and spectrum of the wave reconstruction after the refinement procedure.

scholarly journals Measuring Ocean Waves From Space: Objectives and Characteristics of the China-France Oceanography SATellite (CFOSAT)

2010 ◽  
Author(s):  
Danie`le Hauser ◽  
Ce´line Tison ◽  
Jean-Michel Lefe`vre ◽  
Juliette Lambin ◽  
Amiot Thierry ◽  
...  
Keyword(s):  
Spectral Properties ◽  
Ocean Surface ◽  
Ocean Waves ◽  
Wave Spectra ◽  
Wind Vector ◽  
Satellite Mission ◽  
Surface Ocean ◽  
Related Science ◽  
Directional Wave ◽  
Ku Band

The Chinese and French Space Agencies are jointly preparing a satellite mission devoted to the monitoring of the ocean surface and related science and applications. This is the so-called “China France Oceanography SATellite” (CFOSAT), to be launched around 2013. This mission will provide simultaneous and collocated observations of wind at the ocean surface and spectral properties of surface ocean waves using two scatterometers, both in Ku-Band: SWIM for measurements of directional wave spectra and SCAT for wind vector measurements. The SWIM instrument will use a real aperture observation technique so as to avoid limitations encountered with SAR systems. This paper describes the main objectives and characteristics of the mission with a focus on the SWIM instrument designed and developed under French responsibility to measure directional spectra of ocean waves.

Generating Power From Ocean Waves Using a Float With Excessive Buoyancy: Theory and Dynamic Model Results

2003 ◽  
Author(s):  
T. MacCready ◽  
T. Zambrano ◽  
B. D. Hibbs
Keyword(s):  
Numerical Model ◽  
Natural Frequency ◽  
Power Output ◽  
Ocean Surface ◽  
Ocean Waves ◽  
The Body ◽  
Energy Extraction ◽  
Ocean Energy ◽  
Wave Conditions ◽  
Rich Data

We are exploring a new approach to ocean energy extraction through a device that we refer to as the NAF (an acronym for Non-Archimedean Float). The NAF is a fully submerged body with excess buoyancy; i.e., the mass of the body is far less than the mass of the water it displaces. When such a float is tethered beneath the ocean surface the buoyancy yields a large force vector in the direction perpendicular to the isobaric surfaces that parallel the water/air interface. The constant shifting of the wave troughs provides the opportunity for energy extraction using turbines affixed to the float. We are exploring the NAF concept because its simplicity results in many inherent benefits. The device has few moving parts, gathers energy from waves coming in any direction, and exists as a non-obtrusive, completely submerged installation. A numerical model of the NAF has been created to determine the dynamic behavior and power output for various configurations and under various wave conditions. The numerical model is set up to calculate the various forces experienced by the NAF float, and from these it calculates the velocity and position of the float through time series steps. The model effectively demonstrates which variables are important and how power output relates to NAF dimensions. One early finding from the model result relates to tuning the natural frequency of the NAF to match the natural frequency of the waves. The NAF moves like an inverted pendulum, and its natural frequency is primarily dependent on the length of the pendulum. Regardless of the actual float buoyancy, the 6 to 12 second periods that typify average wave conditions dictate that the NAF tether should be between 30-m and 60-m long. Also, a scale version of this novel energy device consisting of a float tethered beneath the ocean surface was deployed off the coast of southern California. The deployment yielded rich data sequences that are sufficient for comparison with a dynamic numerical model.

scholarly journals High-Resolution Satellite Surface Latent Heat Fluxes in North Atlantic Hurricanes

2011 ◽  
Vol 139 (9) ◽  
pp. 2735-2747 ◽  
Author(s):  
Jiping Liu ◽  
Judith A. Curry ◽  
Carol Anne Clayson ◽  
Mark A. Bourassa
Keyword(s):  
High Resolution ◽  
Latent Heat ◽  
North Atlantic ◽  
Weather Prediction ◽  
Surface Flux ◽  
Ocean Surface ◽  
Ocean Waves ◽  
Heat Fluxes ◽  
Atlantic Hurricanes ◽  
Better Than

This study presents a new high-resolution satellite-derived ocean surface flux product, XSeaFlux, which is evaluated for its potential use in hurricane studies. The XSeaFlux employs new satellite datasets using improved retrieval methods, and uses a new bulk flux algorithm formulated for high wind conditions. The XSeaFlux latent heat flux (LHF) performs much better than the existing numerical weather prediction reanalysis and satellite-derived flux products in a comparison with measurements from the Coupled Boundary Layer Air–Sea Transfer (CBLAST) field experiment. Also, the XSeaFlux shows well-organized LHF structure and large LHF values in response to hurricane conditions relative to the other flux products. The XSeaFlux dataset is used to interpret details of the ocean surface LHF for selected North Atlantic hurricanes. Analysis of the XSeaFlux dataset suggests that ocean waves, sea spray, and cold wake have substantial impacts on LHF associated with the hurricanes.

Two Variational Stereo Methods for Space-Time Measurements of Ocean Waves

2013 ◽  
Author(s):  
Guillermo Gallego ◽  
Anthony Yezzi ◽  
Francesco Fedele ◽  
Alvise Benetazzo
Keyword(s):  
Spatial Scales ◽  
Ocean Surface ◽  
Ocean Waves ◽  
Video Data ◽  
The Black Sea ◽  
Intermediate Step ◽  
Surface Displacements ◽  
Pros And Cons ◽  
Variational Approaches ◽  
The Waves

In recent years, the study of the dynamics of ocean waves via stereo vision systems has focused on investigating sea states with wavelengths in the range of 0.01 m to 1 m. In this work, we present two modern stereo variational approaches, viz. the disparity and graph methods, for the estimation of the ocean surface displacements over larger spatial scales of 10 to 100 m. The disparity method estimates the disparity between images as an intermediate step toward retrieving the depth of the waves with respect to the cameras, and the graph method estimates the ocean surface displacements directly in 3-D space. The pros and cons of both methods are compared and their performance is evaluated using experimental video data collected at an offshore platform in the Black Sea.

Application of ERS and ENVISAT Synthetic Aperture Radar Images for Coastal Water Analysis

2005 ◽  
Author(s):  
Jose´ Carlos Nieto Borge ◽  
Tobias Schneiderhan ◽  
Johannes Schulz-Stellenfleth ◽  
Andreas Niedermeier
Keyword(s):  
Synthetic Aperture Radar ◽  
Ocean Surface ◽  
Ocean Waves ◽  
Synthetic Aperture ◽  
Incoming Wave ◽  
Wave Fields ◽  
Practical Applications ◽  
Radar Images ◽  
The North ◽  
Aperture Radar

The scientific developments carried out in the last years with spaceborne synthetic aperture radar (SAR), as well as the comparisons with in-situ sensors, have demonstrated that SAR is a reliable remote sensing tool to study wave fields on the open ocean. In their so-called SAR image mode, SAR systems on board satellites are able to scan ocean areas about 100 × 100 km2 with a spatial resolution about 20 × 20 m2. These SAR images are able to provide information about the spatial variability of wave fields, as well as other phenomena that occur on the ocean surface, such as the local wind field. This work investigates the capabilities of spaceborne SAR to extract sea state information for those areas close to coastal locations, where the incoming wave fields present high spatial inhomogeneities. For this purpose, ERS-2 SAR and ENVISAT Advanced SAR (ASAR) images acquired over the North Sea and the Bay of Biscay are used to study ocean waves in shallow waters under different climate and oceanographic conditions. In addition, the potential of ENVISAT ASAR capability to scan the ocean surface with dual polarizations (horizontal, HH, and vertical, VV) is analyzed in this work. The relevance of these investigations for different practical applications concerning the analysis of ocean waves is discussed.

Direct measurement of ocean waves velocity field from a single SPOT-5 dataset

2012 ◽  
Vol 119 ◽  
pp. 266-271 ◽  
Author(s):  
Marcello de Michele ◽  
Sébastien Leprince ◽  
Jérôme Thiébot ◽  
Daniel Raucoules ◽  
Renaud Binet
Keyword(s):  
Velocity Field ◽  
Direct Measurement ◽  
Ocean Waves ◽  
Single Spot ◽  
Spot 5
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