Wave orbital velocity, fade, and SAR response to azimuth waves

1981 ◽  
Vol 6 (4) ◽  
pp. 140-146 ◽  
Author(s):  
R. Raney
2015 ◽  
Vol 120 (11) ◽  
pp. 7616-7634 ◽  
Author(s):  
Justin E. Stopa ◽  
Fabrice Ardhuin ◽  
Bertrand Chapron ◽  
Fabrice Collard

2020 ◽  
Author(s):  
Laura Brakenhoff ◽  
Reinier Schrijvershof ◽  
Bart Grasmeijer ◽  
Jebbe van der Werf ◽  
Gerben Ruessink ◽  
...  

<p>To contribute to solving scientific and practice-inspired questions, the morphological development of coastal systems is predicted using numerical morphodynamic models like Delft3D. In such models, many of the processes are parameterized, for which various assumptions have to be made. One of the estimated variables is the bedform-related hydraulic roughness, which affects the magnitude and vertical structure of the flow and consequently also the magnitude of the sediment transport. A comparison is missing between model-predicted and observed hydraulic roughness values and it is unknown how this affects the hydrodynamics and sediment transport. Furthermore, the roughness is often used as a calibration parameter. The calibrated value might be very different from observed values and models might possibly do a good job for the wrong reasons.</p><p>The aim of this study is to determine the effect of the roughness caused by small-scale ripples (length ≈ 10 cm, height ≈ 1.5 cm) on hydrodynamics and sediment transport computed by a high-resolution, fully-coupled Delft3D model that is forced by waves, tides, wind, and atmospheric pressure. The study site is the wave-current dominated environment of the Ameland ebb-tidal delta in the north of the Netherlands. In 2017, a six-week field campaign was executed here, in which bedform heights and lengths, water levels, wave orbital velocity and direction, and current velocity and direction were measured.</p><p>The model was run for the duration of the field campaign with various bedform roughness scenarios, in which the roughness was either coupled to the hydrodynamics (thus varying over space and time), or it was set to a constant and spatially uniform value based on the observed mean ripple heights. Of all scenarios, we compared the predicted ripple heights, wave orbital velocities, depth-averaged current velocities and sediment transport magnitudes and directions. In addition, we compared the modelled and observed ripple heights, wave heights and flow velocities.</p><p>A previous study focused on the field campaign showed that observed ripple heights were much more constant than the ones computed by the default ripple predictor in Delft3D. Ripple heights were found to be related to orbital velocity and no other relations between ripple characteristics and hydrodynamics were found. However, first results of the present study indicate that the predicted roughness used to calibrate Delft3D to the water levels and currents is quite similar to the measured roughness. The main difference is that the predicted roughness is highly variable through time, which is not observed in the field. The simulations also show that the ripple-related roughness especially affects the magnitude of the depth-averaged current velocity, while its effect on the wave-orbital velocity is negligible. This also affects the sediment transport magnitude, while its direction is not affected. The cumulative suspended load transport magnitude can increase with more than 50% when a constant roughness is used instead of a spatio-temporally variable roughness.</p>


2016 ◽  
Vol 110 ◽  
pp. 42-49 ◽  
Author(s):  
Alberto Alberello ◽  
Amin Chabchoub ◽  
Odin Gramstad ◽  
Alexander V. Babanin ◽  
Alessandro Toffoli

2019 ◽  
Vol 11 (1) ◽  
pp. 71 ◽  
Author(s):  
Andrew J. Kammerer ◽  
Erin E. Hackett

The wavenumber-frequency spectra of many radar measurements of the sea surface contain a linear feature at frequencies lower than the first order dispersion relationship commonly referred to as the “group line”. Plant and Farquharson, showed numerically that the group line is at least partially caused by wave interference-induced breaking of steep short gravity waves. This paper uses two wave retrieval techniques, proper orthogonal decomposition (POD) and FFT-based dispersion curve filtering, to examine two X-band radar datasets, and compare wave orbital velocity reconstructions to ground truth wave buoy measurements within the field of view of the radar. POD allows group line energy to be retained in the reconstruction, while dispersion curve filtering removes all energy not associated with the first order dispersion relationship. Results show that when group line energy is higher or comparable to dispersion curve energy, the inclusion of this group line energy in phase-resolved orbital velocity reconstructions increases the accuracy of the reconstruction. This increased accuracy is demonstrated by higher correlations between POD reconstructed time series with buoy ground truth measurements than dispersion curve filtered reconstructions. When energy lying on the dispersion relationship is much higher than the group line energy, the FFT and POD reconstruction methods perform comparably.


1980 ◽  
Vol 7 (12) ◽  
pp. 1049-1052 ◽  
Author(s):  
B. M. Lesht ◽  
T. L. Clarke ◽  
R. A. Young ◽  
D. J. P. Swift ◽  
G. L. Freeland

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