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Author: Publisher: ISBN: Category : Languages : en Pages : 20
Book Description
The capability of phased-array HF radar systems to sample the spatial distribution of wave energy is investigated in different storm scenarios and coastal configurations. First, a formulation introduced by D.E. Barrick to extract significant wave height Hs from backscatter Doppler spectra was calibrated and subsequently tested (to assess bias and uncertainty) with data from seven different buoy/gauge stations collected during three different field experiments. Afterward, Hs observations were obtained for selected sampling locations within the radar effective domain (in all experiments), and a filtering technique based on wavelet transform characterization and decomposition was applied. The accuracy of the filtered radar-derived observations was assessed by comparing these estimates to results from independently calibrated wave propagation models. It was found that the HF radar accurately measured the energy field induced by different storm events. The filtering technique minimized the contribution of unrealistic features introduced by the presence of defective sampling, which is intrinsic to radar remote sensing at this frequency, and it proved to be central for the use of the HF radar as a tool to identify wave energy trends and potential zones of wave energy concentration in coastal areas. These findings show that the sampling capabilities of radar systems may be greatly enhanced because reliable wave energy estimates can be obtained in addition to conventional surface current measurements. This is particularly important in locations such as harbor entrances where in situ measuring devices cannot be deployed.
Author: Publisher: ISBN: Category : Languages : en Pages : 20
Book Description
The capability of phased-array HF radar systems to sample the spatial distribution of wave energy is investigated in different storm scenarios and coastal configurations. First, a formulation introduced by D.E. Barrick to extract significant wave height Hs from backscatter Doppler spectra was calibrated and subsequently tested (to assess bias and uncertainty) with data from seven different buoy/gauge stations collected during three different field experiments. Afterward, Hs observations were obtained for selected sampling locations within the radar effective domain (in all experiments), and a filtering technique based on wavelet transform characterization and decomposition was applied. The accuracy of the filtered radar-derived observations was assessed by comparing these estimates to results from independently calibrated wave propagation models. It was found that the HF radar accurately measured the energy field induced by different storm events. The filtering technique minimized the contribution of unrealistic features introduced by the presence of defective sampling, which is intrinsic to radar remote sensing at this frequency, and it proved to be central for the use of the HF radar as a tool to identify wave energy trends and potential zones of wave energy concentration in coastal areas. These findings show that the sampling capabilities of radar systems may be greatly enhanced because reliable wave energy estimates can be obtained in addition to conventional surface current measurements. This is particularly important in locations such as harbor entrances where in situ measuring devices cannot be deployed.
Author: Larry Atkinson Publisher: ISBN: Category : Languages : en Pages : 77
Book Description
Partial contents include: (1) HF Radar Instruments, Past to Present; (2) Mapping Surface Currents in Monterey Bay with CODAR-type HF Radar; (3) The Coastal Jet: Observations of Surface Currents over the Oregon Continental Shelf from HF Radar; (4) Tidal and Wind-driven Currents from OSCR; (5) Larval Transport and Coastal Upwelling: an Application of HF Radar in Ecological Research; (6) Evolution of Bearing Determination in HF Current Mapping Radars; (7) Shipboard Deployment of a VHF OSCR System for Measuring Offshore Currents; and (8) Experience with Shipborne Measurements of Surface Current Fields by Radar.
Author: Publisher: ISBN: Category : Languages : en Pages : 6
Book Description
The National High Frequency Surface Current Mapping Radar Network is being developed as a backbone system within the Integrated Ocean Observing System (IOOS). Of the core variables recognized in the IOOS Development Plan, two can be measured by High Frequency Radar (HFR): ocean surface currents and ocean surface waves. Rutgers University operates a nested multi-frequency network of HF Radar systems along the coast of New Jersey. The network provides near real-time current observations with varying coverage from the coast to the shelf break. This is a subset of the larger regional coverage of the 26 site Mid-Atlantic HF Radar Consortium. The primary goal of this consortium is to operate the regional system in a coordinated way to guarantee the delivery of quality ocean current and wave data. In this paper we present the validation of both wave and current observations measured with this nested network. Particular emphasis is placed on surface current comparisons with Coast Guard deployed surface drifters (SLDMBs) and nearshore wave comparisons with moorings. The Coast Guard comparisons have a specific focus on quantifying the uncertainty in the HF radar surface current estimates as applied to search and rescue operations. These metrics will be used to ensure that quality data is going to the Coast Guard and that this information is properly incorporated into existing search planning tools. The nearshore measurements focus on algorithm development projects to incorporate shallow water effects into the estimates of nearshore waves.
Author: Yonggang Liu Publisher: Academic Press ISBN: 012802061X Category : Science Languages : en Pages : 491
Book Description
Coastal Ocean Observing Systems provides state-of-the-art scientific and technological knowledge in coastal ocean observing systems, along with guidance on establishing, restructuring, and improving similar systems. The book is intended to help oceanographers understand, identify, and recognize how oceanographic research feeds into the various designs of ocean observing systems. In addition, readers will learn how ocean observing systems are defined and how each system operates in relation to its geographical, environmental, and political region. The book provides further insights into all of these problem areas, offering lessons learned and results from the types of research sponsored and utilized by ocean observing systems and the types of research design and experiments conducted by professionals specializing in ocean research and affiliated with observing systems. Includes international contributions from individuals working in academia, management, and industry Showcases the application of science and technology in coastal observing systems Highlights lessons learned on partnerships, governance structure, data management, and stakeholder relationships required for successful implementation Provides insight into how ocean research transfers to application and societal benefit
Author: Publisher: ISBN: Category : Languages : en Pages : 6
Book Description
The objectives of this project began with the construction and deployment of two and later three multifrequency HF radar instruments (called MCR for Multifrequency Coastal Radar) to Monterey Bay, California. Further experiment deployments were to the Virginia coast and to Lake Michigan for fresh water experiments (NSF sponsorship). The data collected at these sites is reduced, analyzed and interpreted to achieve the specific research objectives listed below: 1. Improvement of radar performance by upgrading hardware and software and developing improved transmit antennas, signal processing and flexible use of multiple frequencies 2. Improvement of HF radar estimates of surface currents, vertical shear, winds, friction velocity and waves by improved estimation algorithms that use knowledge of air-sea interaction physics 3. Estimate surface wind speed and direction using multifrequency HF radar measurements by exploiting air-sea interaction physics and HF radar measurements of vertical current shear 4. Ocean science investigations, including assimilation of HF radar data into coastal ocean models for circulation, chemical and biological properties as well as air-sea interaction studies 5. Use of continuing HF radar observations on Monterey Bay in observing ships to assess the usefulness of multiple frequency HF radar in ship detection and tracking.
Author: G.J. Komen Publisher: Springer Science & Business Media ISBN: 9400923090 Category : Science Languages : en Pages : 265
Book Description
Ten years ago, de Loor and co-workers at TNO, The Netherlands, were the first to report bottom topography patterns in real aperture radar (RAR) images of the southern North Sea. At that time, this was a real puzzle. The skin depth of microwaves for sea water is only of the order of centimeters while the sea bottom is about 20 meters below the surface. Electromagnetic radiation therefore cannot probe the bottom directly. Similar phenomena were found in radar imagery from SEASAT and SIR-AlB synthetic aperture radars (SAR's) of Nantucket Shoals, the English Channel and many other coastal areas. Since then theory and ocean field experiments (Le., Phelps Bank, Georgia Straits, SARSEX, TOWARD, FASINEX, etc.) have advanced our understanding considerably. We now know that these surface signatures are the results of surface currents, perturbed by the bottom topography, which refract the propagation and modulate the energy of (short) surface waves so as to cause microwave backscatter power variations. Hence, any large scale ocean features containing nonuniform surface currents (i.e. internal waves, eddies, fronts, etc.) will cause similar manifestations in the radar imagery by means of current-wave-microwave interactions. Observations confirm this.
Author: Weili Wang Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Nearshore marine environment contains many complex processes, but the lack of high-resolution data over a large area during a long time is often the primary obstacle to further research. High-frequency (HF) radar is a mean of remote sensing which obtains continuous near-real time sea surface information over a large area. Thus the study of inversion of marine parameters from HF radar data is very meaningful. Thisthesis makes use of a 13-month-long dataset collected by two phased array HF radar to investigate the characteristics of the sea echo signals, study the data processing and inversion methods, compute sea surface parameters and evaluate the accuracy of radarinversion of swell parameters.The thesis refers to the ground wave HF radar, whose radio waves interact with ocean by Bragg resonance scattering. The development history and applications of HF radar is introduced. The basic theory of electromagnetic wave is reviewed. The principles of inversion of sea surface current, wind direction and swell parameters are described. The feasibility of the swell parameter inversion is investigated. Based on theoretical analysis and statistical studies of a large number of samples, the thesis proposes a series of methods on raw signal processing and quality control, including the determination of the noise level, data averaging in space and time, the proper identification of spectral peaks, the peak width threshold, etc. Respecting the characteristics of different physical processes, inversions of current and wind use spectra collected every 20 min; inversion of swell parameters uses one-hour averaged spectra. The statistics of qualified spectra for swell parameter calculations are presented for both stations. A set of efficient, with a reduced computational cost, automatic computing programs are developed to do the processing and derive marine parameters. Radial current velocities are derived from single radar station. Current vector fields are obtained by combination of both stations. One-year mean flow field in the Iroise Sea is shown, together with the computation of vorticity and divergence. A one-month SeaSonde radar dataset off Qingdao is studied. One-month mean flow pattern together with vorticity and divergence are presented.Relative wind direction with respect to radar look direction is measured through ratio of Bragg peaks amplitudes. Different empirical models are employed to derive radar-inverted relative wind direction. Results show reasonable agreement with model estimations. Different directional distribution models are used to measure the spreading factor for the Iroise Sea. The thesis focuses on the study of swell parameters. Results are validated by buoy and wave model (WAVEWATCH III) data. The assessments show that the accuracy of swell frequency is very good, the accuracy of swell significant waveheight is reasonable, and the accuracy of relative swell direction is low.Consistency of measurements by both radar stations is verified by comparison between the two. This also supports the use of double samples to do the inversion. Use of two radars not only further improves the accuracy but also solves the ambiguity of relative swell direction from single station and gives the absolute wave direction to a certain precision. The thesis proposes a constant relative directionmethod to derive swell significant waveheight, based on the studies of radar integral equation and the inverted results of relative swell direction. This proposal is demonstrated to improve the agreement of radar inversion and buoy/model provided significant waveheight and increases significantly the number of samples. The thesis investigates the accuracy of swell parameters obtained by HF radar. Contributions of random errors in radar observations are quantified. Comparing the differences between radar and buoy/model estimations gives assessments of the contribution of radar intrinsic uncertainty and contribution of other factors.
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Author: Sheila O'Keefe
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Author: Larry Atkinson
Author: Thomas Martin Georges
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Author: Yonggang Liu
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Author: G.J. Komen
Author: Weili Wang