scholarly journals The Bistatic Radar as an Effective Tool for Detecting and Monitoring the Presence of Phytoplankton on the Ocean Surface

2021 ◽  
Vol 13 (12) ◽  
pp. 2248
Author(s):  
Nereida Rodriguez-Alvarez ◽  
Kamal Oudrhiri
Keyword(s):  
Remote Sensing ◽  
Surface Tension ◽  
Surface Roughness ◽  
Dust Storm ◽  
Ocean Surface ◽  
Bistatic Radar ◽  
Phytoplankton Blooms ◽  
Dust Clouds ◽  
Radar Measurements ◽  
Ocean Biogeochemistry

A massive dust storm formed over the Sahara Desert in June 2020. The African dust cloud, which traveled over the tropical Atlantic’s main development region for hurricanes, resulted in the highest aerosol optical thickness (AOT) for the past two decades. Dust particles contained in dust clouds are at some point deposited on the ocean surface, impacting the ocean biogeochemistry through the supply of nutrients. Although there are remote sensing systems that can map the AOT, the locations of the aerosol particles deposited on the ocean surface remain unknown quantities with remote sensing measurements. In addition, the supplied nutrients are not static and are displaced by ocean currents. Nutrients trigger the phytoplankton (algae) blooms, which form a film on the ocean surface and affect the ocean surface tension. The change in ocean surface tension causes a local decrease of ocean surface roughness over the areas covered with phytoplankton. Bistatic radar data from the CYclone Global Navigation Satellite System (CYGNSS) mission can detect changes in the ocean surface roughness, expressed as an increase in reflectivity when the surface becomes smoother. Therefore, decreased ocean surface roughness correlated with a recent dust storm represents a key indicator of the presence of phytoplankton. In this paper, we present for the first time the capability of bistatic radar measurements to provide an effective tool to map information of areas covered with phytoplankton, establishing bistatic radar as the most reliable remote sensing tool for detecting phytoplankton blooms and monitoring their presence across the ocean surface. We present the analysis of low ocean roughness signatures in the bistatic radar measurements from the CYGNSS mission observed in the Gulf of Mexico after the Sahara’s dust storm circulation from Africa to the American continent from May to July 2020. CYGNSS data offer an unprecedented spatial and temporal coverage that allows for the analysis of those signatures at time scales of 1-day, robust to the presence of clouds and dust clouds. The described capability benefits the improvement of models, promoting a better constraint of the supply of dust into the ocean surface and a better understanding of the excess of nutrients that triggers the phytoplankton blooms. This new bistatic radar application enhances our understanding on the role of dust storms on ocean biogeochemistry and the global carbon cycle.

scholarly journals Ocean Surface Roughness Spectrum in High Wind Condition for Microwave Backscatter and Emission Computations*

2013 ◽  
Vol 30 (9) ◽  
pp. 2168-2188 ◽  
Author(s):  
Paul A. Hwang ◽  
Derek M. Burrage ◽  
David W. Wang ◽  
Joel C. Wesson
Keyword(s):  
Remote Sensing ◽  
Surface Roughness ◽  
Surface Waves ◽  
Microwave Remote Sensing ◽  
Ocean Surface ◽  
Short Wave ◽  
Wind Condition ◽  
Bragg Resonance ◽  
High Wind ◽  
Radar Backscatter

Abstract Ocean surface roughness plays an important role in air–sea interaction and ocean remote sensing. Its primary contribution is from surface waves much shorter than the energetic wave components near the peak of the wave energy spectrum. Field measurements of short-scale waves are scarce. In contrast, microwave remote sensing has produced a large volume of data useful for short-wave investigation. Particularly, Bragg resonance is the primary mechanism of radar backscatter from the ocean surface and the radar serves as a spectrometer of short surface waves. The roughness spectra inverted from radar backscatter measurements expand the short-wave database to high wind conditions in which in situ sensors do not function well. Using scatterometer geophysical model functions for L-, C-, and Ku-band microwave frequencies, the inverted roughness spectra, covering Bragg resonance wavelengths from 0.012 to 0.20 m, show a convergent trend in high winds. This convergent trend is incorporated in the surface roughness spectrum model to improve the applicable wind speed range for microwave scattering and emission computations.

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.

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

Theorem for the combination of bistatic radar measurements using least squares

2003 ◽  
Vol 39 (4) ◽  
pp. 1441-1445 ◽  
Author(s):  
You He ◽  
Jian-juan Xiu ◽  
Guo-Hong Wang ◽  
Jian-Hua Xiu
Keyword(s):  
Least Squares ◽  
Bistatic Radar ◽  
Radar Measurements

Fundamental Study on Laser Interactions With Nanoparticles-Reinforced Metals—Part II: Effect of Nanoparticles on Surface Tension, Viscosity, and Laser Melting

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Chao Ma ◽  
Jingzhou Zhao ◽  
Chezheng Cao ◽  
Ting-Chiang Lin ◽  
Xiaochun Li
Keyword(s):  
Surface Tension ◽  
Surface Roughness ◽  
Thermophysical Properties ◽  
Melting Process ◽  
Laser Melting ◽  
Fundamental Study ◽  
Laser Polishing ◽  
Laser Manufacturing ◽  
Manufacturing Technologies ◽  
Laser Interactions

It is of great scientific and technical interests to conduct fundamental studies on the laser interactions with nanoparticles-reinforced metals. This part of the study presents the effects of nanoparticles on surface tension and viscosity, thus the heat transfer and fluid flow, and eventually the laser melting process. In order to determine the surface tension and viscosity of nanoparticles-reinforced metals, an innovative measurement system was developed based on the characteristics of oscillating metal melt drops after laser melting. The surface tensions of Ni/Al2O3 (4.4 vol. %) and Ni/SiC (3.6 vol. %) at ∼1500 °C were 1.39 ± 0.03 N/m and 1.57 ± 0.06 N/m, respectively, slightly lower than that of pure Ni, 1.68 ± 0.04 N/m. The viscosities of these Ni/Al2O3 and Ni/SiC MMNCs at ∼1500 °C were 13.3 ± 0.8 mPa·s and 17.3 ± 3.1 mPa·s, respectively, significantly higher than that of pure Ni, 4.8 ± 0.3 mPa·s. To understand the influences of the nanoparticles-modified thermophysical properties on laser melting, an analytical model was used to theoretically predict the melt pool flows using the newly measured material properties from both Part I and Part II. The theoretical analysis indicated that the thermocapillary flows were tremendously suppressed due to the significantly increased viscosity after the addition of nanoparticles. To test the hypothesis that laser polishing could significantly benefit from this new phenomenon, systematic laser polishing experiments at various laser pulse energies were conducted on Ni/Al2O3 (4.4 vol. %) and pure Ni for comparison. The surface roughness of the Ni/Al2O3 was reduced from 323 nm to 72 nm with optimized laser polishing parameters while that of pure Ni only from 254 nm to 107 nm. The normalized surface roughness reduced by nearly a factor of two with the help of nanoparticles, validating the feasibility to tune thermophysical properties and thus control laser-processing outcomes by nanoparticles. It is expected that the nanoparticle approach can be applied to many laser manufacturing technologies to improve the process capability and broaden the application space.

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