Flow Measurements in a Tidal Channel Using an Acoustic Current Profiler


Book Description

An acoustic Doppler current profiler (ADCP) was applied to measure the three-dimensional flow field in a tidal channel along the coast of Vancouver Island, British Columbia. The ADCP was rigidly mounted to the bottom in the center of the channel, and rapidly sampled the velocity profiles along its inclined beams. The data were directly read by a computer on shore. This method of deployment allows for an explicit estimate of the uncertainty of mean velocity due to turbulence, and obtains the weak signal of vertical velocity. The mean flow vector is derived from the measured beam velocities under the assumption that the flow is statistically homogeneous in the horizontal plane over the distance separating the inclined beams of the ADCP. It is argued that sufficient averaging is required for flow measurements in a highly turbulent environment. The depth-time variations of velocity and shear in this natural channel are more complex than is found in idealized one-dimensional channel flow, which seldom occurs in nature. The channel contains strong secondary circulation, intense up- and down-welling intervals, frequent shear reversals and a substantial amount of transverse velocity shear.







Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat


Book Description

The mission of the U.S. Geological Survey (USGS) Water Resources Discipline is to provide the information and understanding needed for wise management of the Nation's water resources. Inherent in this mission is the responsibility of collecting data that accurately describe the physical, chemical, and biological attributes of water systems. These data are used for environmental and resource assessments by the USGS, other government agencies and scientific organizations, and the general public. Reliable and quality-assured data are essential to the credibility and impartiality of the water-resources appraisals carried out by the USGS.




Use of Ship-mounted Acoustic Doppler Current Profiler Data to Study Mesoscale Oceanic Circulation Patterns in the Archipielago de Colon (Galapagos Islands) and the Gulf of the Farallones


Book Description

Ship-mounted acoustic Doppler current profiler (ADCP) data are used to study regional ocean patterns around the biologically rich regions of the Archipielago de Colon (Galapagos Islands) and the Gulf of the Farallones to test our assumptions about the circulation derived primarily from hydrographic samples. West of the Galapagos, an equatorial undercurrent transporting 7 Sv was present in November 1993, which decelerated within 30 km of the archipelago, shoaled, and diverged with a strong deflection to the southwest. A method of removing tidal velocities from ADCP measurements by creating an empirical model of the tides and using it to predict and subtract the tides is described. It is shown that in the Gulf of the Farallones, a large number of observations, typically more than acquired on one cruise, are necessary to reduce tidal model error. Detided ADCP data are used to describe the circulation in the Gulf under various wind conditions. Over the continental slope, Surface-to-depth poleward flow is present throughout the year. During wind relaxations, poleward flow strengthens and warmer, fresher water is transported onshore.




Air-Sea Interaction


Book Description

During the past decade, man's centuries-old interest in marine me teorology and oceanography has broadened. Ocean and atmosphere are now treated as coupled parts of one system; the resulting interest in air-sea interaction problems has led to a rapid growth in the sophistication of instruments and measurement techniques. This book has been designed as a reference text which describes, albng with the instruments themselves, the accumulated practical experi ence of experts engaged in field observations of air-sea interac tions. It is meant to supplement rather than replace manuals on standard routine observations or instnunentation handbooks. At the inception a textbook was planned, which would contain only well tested methods and instruments. It was quickly discovered that for the book to be useful many devices and techniques would have to be included which are still evolving rapidly. The reader is therefore cautioned to take nothing in these pages for granted. Certainly, every contributor is an expert, but while some are back ed up by generations of published work, others are pioneers. The choice of topics, of course, is debatable. The types of observa tions included are not exhaustive and topics such as marine aero sols and radio-tracers are omitted, as was the general subject of remote sensing, which was felt to be too broad and evol ving too rapidly. The guideline adopted in limiting size was maximum use fulness to 'a trained experimentalist new to the field'.










Coastal Acoustic Tomography


Book Description

Coastal Acoustic Tomography begins with the specifics required for designing a Coastal Acoustic Tomography (CAT) experiment and operating the CAT system in coastal seas. Following sections discuss the procedure for data analyses and various application examples of CAT to coastal/shallow seas (obtained in various locations). These sections are broken down into four kinds of methods: horizontal-slice inversion, vertical-slice inversion, modal expansion method and data assimilation. This book emphasizes how dynamic phenomena occurring in coastal/shallow seas can be analyzed using the standard method of inversion and data assimilation. The book is relevant for physical oceanographers, ocean environmentalists and ocean dynamists, focusing on the event being observed rather than the intrinsic details of observational processes. Application examples of successful dynamic phenomena measured by coastal acoustic tomography are also included. Provides the information needed for researchers and graduate students in physical oceanography, ocean-fluid dynamics and ocean environments to apply Ocean Acoustic Tomography (OAT) to their own fields Presents the benefits of using acoustic tomography, including less disturbance to aquatic environments vs. other monitoring methods Includes the assimilation of CAT data into a coastal sea circulation model, a powerful tool to predict coastal-sea environmental changes