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Author: Eng-Chong Ha
Publisher:
ISBN:
Category : Ocean currents
Languages : en
Pages : 158
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Book Description
The Doppler spectrum of radar return from the sea at HF contains two narrow lines displaced upward and downward from the carrier frequency, resulting from backscatter off ocean surface waves moving toward and away from the radar, respectively. These Bragg lines indicate resonant backscatter which occurs for the ocean waves of length one-half the radio wavelength. The phase velocity of these gravity waves consists of two components; the first is determined by the wavelength and the second by the current component in the direction of wave propagation averaged over depth with an exponential weighting function that has a characteristic scale proportional to the wavelength. The Doppler shift of the radar carrier is determined by the wave phase velocity. Its variation with carrier frequency is thus related to the vertical profile of the current component in the radar direction by a Laplace transform; therein lies the principle of radio measurement of ocean current and its vertical shear. Radio backscatter experiments to verify the feasibility of such measurements were conducted using the radar operating at four frequencies covering the range from 3 to 30 MHz. The depth-averaged radial current deduced from the centroid of the Doppler-shifted sea echo experiments at 6.8, 13.3, 21.7, and 29.8 MHz showed fluctuations on the order of 1 cm/sec superimposed on temporal trends that reached maximum values of about 40 cm/sec. It is concluded that multifrequency backscatter ground-wave radar at HF constitutes a powerful technique for mapping current and its vertical profile in the top few meters of the ocean.
Author: Eng-Chong Ha
Publisher:
ISBN:
Category : Ocean currents
Languages : en
Pages : 158
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Book Description
The Doppler spectrum of radar return from the sea at HF contains two narrow lines displaced upward and downward from the carrier frequency, resulting from backscatter off ocean surface waves moving toward and away from the radar, respectively. These Bragg lines indicate resonant backscatter which occurs for the ocean waves of length one-half the radio wavelength. The phase velocity of these gravity waves consists of two components; the first is determined by the wavelength and the second by the current component in the direction of wave propagation averaged over depth with an exponential weighting function that has a characteristic scale proportional to the wavelength. The Doppler shift of the radar carrier is determined by the wave phase velocity. Its variation with carrier frequency is thus related to the vertical profile of the current component in the radar direction by a Laplace transform; therein lies the principle of radio measurement of ocean current and its vertical shear. Radio backscatter experiments to verify the feasibility of such measurements were conducted using the radar operating at four frequencies covering the range from 3 to 30 MHz. The depth-averaged radial current deduced from the centroid of the Doppler-shifted sea echo experiments at 6.8, 13.3, 21.7, and 29.8 MHz showed fluctuations on the order of 1 cm/sec superimposed on temporal trends that reached maximum values of about 40 cm/sec. It is concluded that multifrequency backscatter ground-wave radar at HF constitutes a powerful technique for mapping current and its vertical profile in the top few meters of the ocean.
Author: Weimin Huang
Publisher: IET
ISBN: 1839531614
Category : Technology & Engineering
Languages : en
Pages : 654
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Book Description
The book provides a systematic introduction to the principles, state-of-the-art methods and applications of high frequency surface/sky wave radar and microwave marine radar, as well as an exploration of ongoing challenges in the field. It is a valuable resource for the radar and remote sensing communities.
Author: J. P. Matthews
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Antony Joseph
Publisher: Newnes
ISBN: 0123914280
Category : Science
Languages : en
Pages : 447
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Book Description
Measuring Ocean Currents: Tools, Technologies, and Data covers all major aspects of ocean current measurements in view of the implications of ocean currents on changing climate, increasing pollution levels, and offshore engineering activities. Although more than 70% of the Earth is covered by ocean, there is limited information on the countless fine- to large-scale water motions taking place within them. This book fills that information gap as the first work that summarizes the state-of-the-art methods and instruments used for surface, subsurface, and abyssal ocean current measurements. Readers of this book will find a wealth of information on Lagrangian measurements, horizontal mapping, imaging, Eulerian measurements, and vertical profiling techniques. In addition, the book describes modern technologies for remote measurement of ocean currents and their signatures, including HF Doppler radar systems, satellite-borne sensors, ocean acoustic tomography, and more. Crucial aspects of ocean currents are described in detail as well, including dispersion of effluents discharged into the sea and transport of beneficial materials—as well as environmentally hazardous materials—from one region to another. The book highlights several important practical applications, showing how measurements relate to climate change and pollution levels, how they affect coastal and offshore engineering activities, and how they can aid in tsunami detection. Coverage of measurement, mapping and profiling techniques Descriptions of technologies for remote measurement of ocean currents and their signatures Reviews crucial aspects of ocean currents, including special emphasis on the planet-spanning thermohaline circulation, known as the ocean's "conveyor belt," and its crucial role in climate change
Author: Abdelrahman M. Elabdalla
Publisher:
ISBN:
Category : Ocean waves
Languages : en
Pages : 114
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 3
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Book Description
Over the past decade, high-frequency ground wave Doppler radar has emerged as a powerful tool in the remote sensing of ocean surface phenomena, particularly in coastal regions. This paper examines how a four-element square array, now used for mapping surface currents, could be used to extract ocean wave parameters.
Author: Darryl C. Melton
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Radial current data from the CODAR HF radar network around Monterey Bay, California, were analyzed for the period of August-December 1994. Previous studies in Monterey Bay used total vector current data. Long-term percent coverage maps showed that coverage decreased radially, vice range, from the site. Through statistical exarnination of radial current data from the Santa Crux and Point Piiios SeaSonde sites and the Moss Landing CODAR site, comparisons along and around the baseline between systems were used to assess system performance. Significant discrepancies were discovered in the directional information from the Point Pinos and Moss Landing sites. Point Pinos' error was approximately 10 counterclockwise and Moss Landing's error was approximately 5 counterclockwise. RMS differences among even the best correlated baseline pairs were approximately 15 cm/s. Data from the baseline was used to select vector currents when the baseline difference was less than 10 cm/s for comparisons with independent nearby moored current observations. This subsampled data did not show significantly better correlation with the moored data than the full data set. Analysis of the radial error estimates provided by the system algorithms determined that no correlation exists between absolute value difference of the radial velocities along the baselines between systems and these built in error estimates.
Author: Darryl C. Melton
Publisher:
ISBN:
Category :
Languages : en
Pages : 65
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Book Description
Radial current data from the CODAR HF radar network around Monterey Bay, California, were analyzed for the period of August-December 1994. Previous studies in Monterey Bay used total vector current data. Long-term percent coverage maps showed that coverage decreased radially, vice range, from the site. Through statistical exarnination of radial current data from the Santa Crux and Point Piiios SeaSonde sites and the Moss Landing CODAR site, comparisons along and around the baseline between systems were used to assess system performance. Significant discrepancies were discovered in the directional information from the Point Pinos and Moss Landing sites. Point Pinos' error was approximately 10 counterclockwise and Moss Landing's error was approximately 5 counterclockwise. RMS differences among even the best correlated baseline pairs were approximately 15 cm/s. Data from the baseline was used to select vector currents when the baseline difference was less than 10 cm/s for comparisons with independent nearby moored current observations. This subsampled data did not show significantly better correlation with the moored data than the full data set. Analysis of the radial error estimates provided by the system algorithms determined that no correlation exists between absolute value difference of the radial velocities along the baselines between systems and these built in error estimates.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 892
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Book Description
Author: Thomas Martin Georges
Publisher:
ISBN:
Category : Ocean currents
Languages : en
Pages : 352
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Book Description
