Instrumentation For The High Resolution Measurement Of Ocean Surface Waves And Currents Over Km Square Areas

The objective of this project, funded by the Office of Naval Research, was to develop imaging sonar with increasingly higher resolution. With modern advancements in digital electronics, it is now feasible to digitize incoming sonar data at the carrier frequency, in this case, approximately 3 x 50 kHz. Subsequent homodying and data compression can be done using software. The sonar technology was tested on two occasions on the research platform R/V FLIP. On the first occasion it was mounted on FLIP at a depth of 20 meters and operated over a 20-day period with FLIP moored in 200 meters of deep water. In these summer experiments the mixed layer depth was very thin. The sonar was positioned in the upper thermocline, where sound is strongly downward refracted. Thus, the sonar scattered primarily from the sea surface for the first 800-meter range, and subsequently recorded a mix of surface and bottom echoes to ranges greater than 2.5 km. A second data collection opportunity occurred in Sep-Oct 2002, when FLIP was moored off the Hawaiian Island of Oahu, observing large amplitude internal waves generated by tidal flow over the Keana Ridge. Here the depth of the mixed layer was 25 meters and breaking waves, which provide subsurface bubbles as scattering targets, were common. The sonar was operated continuously for about 20 days, achieving ranges of 1.5 km from pure surface scattering. The dominant signal seen was the surface wave field, which was quite energetic during trade wind conditions. When these signals were low-pass filtered in time, images of underlying Langmuir cells emerged. Further filtering has begun to reveal the internal wave signature. The next developmental task is to create a real-time analysis and display capability to match the speed of this sonar, which digitally recorded at a rate of 100 Gigabytes per day.

This book provides a comprehensive overview of ocean electronics, energy conversion, and instrumentation. As remote (satellite) sensing becomes increasingly important, this text provides readers with a solid background of wireless sensor networks and image-processing for oceans and ocean-related energy issues. Features: * Focuses on wind energy, ocean wave, ocean tidal, and ocean thermal energy conversion * Discusses the measurements of ocean monitoring parameters such as ocean color, sediment monitoring methods, surface currents, surface wind waves, wave height and wind speed, sea surface temperature, upwelling, wave power and the ocean floor * Discusses sensors like scanner sensor systems, weather satellites sensors, synthetic aperture radar sensors, marine observation satellite(MOS) sensors, micro sensors for monitoring ocean acidification * Includes material on underwater acoustics and underwater communication * Assesses the environmental impact of generating energy from the ocean * Explores the design of applications of marine electronics and oceanographic instruments

The Norwegian coastal current originates primarily from the freshwater outflow from the Baltic and the freshwater runoff from Norway. It flows northwards along the coast of Norway as a low-salinity current. This coastal region is the spawning ground for a number of important oceanic fish stocks, and the physical environment has an impact on the recruitment, growth, and geographical distribution of these stocks. In the late 1920s and early 1930s, the Institute of Marine Research in Norway established a coastal oceanographic observation system. This continued to evolve, and its core elements are still in operation. Drawing on the results generated by this observation system, as well as by other coastal studies, this book reviews the current understanding of the physical/chemical conditions in the Norwegian coastal current in such a way as to make the material more easily accessible to non-specialists. A series of chapters introduces readers to the geography, currents, water masses, and the temporal and spatial variability of the Norwegian coastal current. Interannual fluctuations in physical conditions are most likely to be the prime cause of ecosystem variability. The editor hopes that this book will act as a point of departure for a future summary of the ecology of Norwegian coastal waters.

A bottom-mounted narrow-beam active sonar has been designed, built and operated to measure wave height in the open ocean. The experiments were carried out at a depth of 145 feet. The apparatus is capable of measuring wave height at depths ranging from 25 to 200 feet without modification, AND TO 500 FEET WITH A MINIMUM OF DEVELOPMENT. The amplitude resolution of the wave measurements was a fraction of 1 inch, and the spatial resolution on the surface of the ocean was approximately 24 inches. The wave data has been processed by digital methods, and the autocorrelation functions and power spectra of the ocean waves have been computed. The experiments have shown that it is possible to measure the statistical properties of surface waves in the ocean with great precision. It has also been shown that the instrumentation has high reliability and longevity. An induced surface wave pattern was not generated for measurement at this time due to geographic location and shallowness of water in the instrumented area. It is believed, however, that the apparatus is fully capable of making such measurements, and it is recommended that induced surface wave pattern studies be carried out in the future. (Author).

In the history of humankind, the sea has always played a key role as a privileged medium for communication, commerce and contact among population centers. It constitutes an essential ecosystem, and an invaluable reservoir and source of food for all living beings. Therefore, its heath is a critical challenge for the survival of all humanity, particularly as one the most important environmental components targeted by global warming. Measuring and monitoring techniques are key tools for managing the marine environment and for supporting the Blue Economy. With this perspective, a series of annual international events, entitled Metrology for the Sea (MetroSea for short) was begun in 2017. Their increasing success inspired this book, which provides an anthology of tutorials dealing with a representative selection of topics of concern to a broad readership. The book covers two broad application areas, marine hydrography and meteorology, and then deals with instrumentation for measurement at sea. Typical metrological issues such as calibration and traceability, are considered, for both physical and chemical quantities. Key techniques, such as underwater acoustic investigation, remote sensing, measurement of waves and monitoring networks, are treated alongside marine geology and the monitoring of animal species. Economic and legal aspects of metrology for navigation are also discussed. Such an unparalleled wide vision of measurement for the sea will be of interest to a broad audience of scientists, engineers, economists, and their students.

The chapter is devoted to the development of methods for remote measurement of spatial spectra of waves arising on marine and ocean surface. It is shown that in most natural conditions of optical image formation, a nonlinear modulation of the brightness field occurs by slopes of water surface elements. Methods for reconstructing the spectra of surface waves from optical image spectra with allowance for such modulation are proposed. The methods are based on the numerical simulation of water surface taking into account wave formation conditions and conditions of light entering the sea surface from the upper and lower hemispheres. Using the results of numerical simulation, special operators are built to retrieve wave spectra from the spectra of aerospace images. These retrieving operators are presented in the form of analytical expressions, depending on the sets of parameters, which are determined by the conditions for the formation of images. The results of experimental studies of the sea wave spectra in various water areas using satellite optical images of high spatial resolution are presented. In the experimental studies, the spatial spectral characteristics of sea waves estimated from remote sensing data were compared with the corresponding characteristics measured by contact assets under controlled conditions.