scholarly journals Whitecap Observations by Microwave Radiometers: With Discussion on Surface Roughness and Foam Contributions

2020 ◽  
Vol 12 (14) ◽  
pp. 2277
Author(s):  
Paul A. Hwang
Keyword(s):  
Surface Roughness ◽  
Dielectric Properties ◽  
Surface Wave ◽  
Wave Breaking ◽  
Microwave Radiometer ◽  
Video Recording ◽  
Ocean Surface ◽  
Optical Observations ◽  
Microwave Signals ◽  
Microwave Radiometers

Ocean surface whitecaps manifest surface wave breaking. Most of the whitecap data reported in the literature are based on optical observations through photographic or video recording. The air in whitecaps modifies the dielectric properties of microwave emissions and scattering. Therefore, whitecap information is intrinsic to microwave signals. This paper discusses a method to retrieve the ocean surface whitecap coverage from microwave radiometer signals.

Field measurements and scaling of ocean surface wave-breaking statistics

2013 ◽  
Vol 40 (12) ◽  
pp. 3074-3079 ◽  
Author(s):  
Peter Sutherland ◽  
W. Kendall Melville
Keyword(s):  
Surface Wave ◽  
Wave Breaking ◽  
Field Measurements ◽  
Ocean Surface ◽  
Ocean Surface Wave

scholarly journals High-Wind Drag Coefficient and Whitecap Coverage Derived from Microwave Radiometer Observations in Tropical Cyclones

2018 ◽  
Vol 48 (10) ◽  
pp. 2221-2232 ◽  
Author(s):  
Paul A. Hwang
Keyword(s):  
Remote Sensing ◽  
Surface Roughness ◽  
Wind Speed ◽  
Drag Coefficient ◽  
Tropical Cyclones ◽  
Microwave Radiometer ◽  
Microwave Remote Sensing ◽  
Ocean Surface ◽  
Whitecap Coverage ◽  
High Winds

AbstractOcean surface roughness and whitecaps are driven by the ocean surface wind stress; thus, their values calculated from the wind speed input may vary significantly depending on the drag coefficient formula applied. Because roughness and whitecaps are critical elements of the ocean surface response in microwave remote sensing, the extensive microwave remote sensing measurements contain the information of the drag coefficient, surface roughness, and whitecap coverage. The scattering radar cross sections from global measurements under calm to tropical cyclone conditions have been used effectively to improve the formulation of the surface roughness spectrum. In this paper, the microwave radiometer measurements in tropical cyclones are exploited to extract information of the drag coefficient and whitecap coverage in high winds. The results show that when expressed as a wind speed power function, the exponent in high winds (greater than about 35 m s−1) is about −1 for the drag coefficient, 0.5 for the wind friction velocity, and 1.25 for the whitecap coverage.

scholarly journals Mapping Surface Currents and Waves with Interferometric Synthetic Aperture Radar in Coastal Waters: Observations of Wave Breaking in Swell-Dominant Conditions*

2013 ◽  
Vol 43 (3) ◽  
pp. 563-582 ◽  
Author(s):  
Paul A. Hwang ◽  
Jakov V. Toporkov ◽  
Mark A. Sletten ◽  
Steven P. Menk
Keyword(s):  
Surface Roughness ◽  
Wave Breaking ◽  
Wave Spectrum ◽  
Ocean Surface ◽  
Breaking Waves ◽  
Surface Velocity ◽  
Synthetic Aperture ◽  
Large Area ◽  
Length Scales ◽  
Spatial Coverage

Abstract Airborne and spaceborne interferometric synthetic aperture radars (InSARs) produce surface velocity measurements at very high spatial resolutions over a large area. The data allow construction of the velocity strain field for highlighting ocean surface processes such as wave breaking and rip currents. Also, coherence between signals from two interferometric channels is a descriptor of the correlation condition of the surface roughness that scatters back the radar signals and it is an indication of the ocean surface turbulence. Wave breaking is a major turbulence source causing surface roughness decorrelation, thus the coherence parameter serves as an independent means for detecting wave breaking. The results of breaking detection using roughness decorrelation and critical local acceleration are comparable. In this paper, the breaking fraction in swell-dominant mixed seas along a cross-shore transect is compared with several steepness parameters characterizing different length scales of surface waves. The highest correlation coefficient (from 0.90 to 0.99) is between the breaking fraction and windsea mean square slope contributed primarily by short waves. This result reinforces the previous field observations showing that the length scales of breaking waves are much shorter than the energetic components near the spectral peak, although dominant waves and the associated wave group modulation are important in triggering the breaking process. The large spatial coverage of airborne or spaceborne operation further offers the opportunity to investigate evolution of the surface wave spectrum in high spatial (subkilometer) resolution. This capability is very useful for monitoring the coastal wave and current environment.

Anatomy of the Ocean Surface Roughness

2002 ◽  
Author(s):  
Paul A. Hwang ◽  
David W. Wang ◽  
William J. Teague ◽  
Gregg A. Jacobs ◽  
Joel Wesson
Keyword(s):  
Surface Roughness ◽  
Ocean Surface
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