A challenging task in physical studies of the upper ocean using underwater sound is the interpretation of high-resolution acoustic images. This paper covers a number of basic concepts necessary for undergraduate and postgraduate students to identify the most distinctive features of the images, providing a link with the acoustic signatures of physical processes occurring simultaneously beneath the surface of the sea. Sonars are so sensitive that they detected a new acoustic signature at the breaking of surface gravity waves in deep water, which resembles oblique motion-like vortices.
Low-cost technologies are needed in developing and least-developed countries to improve monitoring capabilities to determine the dispersion characteristics of inland and coastal waters. Thus, the objective of the paper is to describe the design and construction of a low-cost saucer-shaped drifter, including its internal electronics, remote-control unit, and software. The system can operate over short timescales and distances and is thus suitable for estimating dispersion coefficients and differential kinematic properties of the fluid. The drifter was constructed primarily from readily available plastic products. The main electronic components were a global positioning receiver, microcontroller, lithium-polymer battery, wireless communication module, and activation and battery status indicators. The electronic design simplifies operation because the stored positions can be transferred to a computer via a mini-universal serial bus port without having to open the buoy. In addition, communication between the control unit and saucer-shaped drifter and its memory enhances its operational capability in the field. Water tightness tests were successful, and the operation of electronics was tested at a wetland known as Estero Topila, México, to infer dispersion characteristics using a trio of drifters. Agreement with the Richardson's 4/3 power law provides reliability of the electronics system performance and measured data.
The wave power in the Gulf of Mexico was analyzed, using 42 years (1979–2020) of simulated data, with ERA-5 winds to force the WAVEWATCH III wave model. The model was successfully validated with three NDBC buoys, 42,055, 42,001 and 42,002. Comparison of significant wave heights obtained from the Jason-2, Cryosat-2, and Saral satellites showed good mean correlation coefficients and root mean squares. The spatial distribution of wave power was studied, as well as its seasonal variability. The region studied has moderate availability of wave power with marked seasonality. A multi-criteria MCA approach, including both sea state and wave energy converters (WECs), was then applied. Nine virtual sites were selected for the study and the AAHPA device gave best results in 7 virtual sites and the Wavestar device in the remaining two. The technology of these two devices, a system of oscillating buoys, is the most viable technology for the Gulf of Mexico.
Analysis of the omnidirectional energy spectrum from storm wave measurements provides valuable parameters for understanding the specific local conditions that wave energy converters would have to withstand. Partitioning the energy spectrum also helps to identify wave groups with low directional spread propagating in the direction of the dominant waves of the more energetic wave systems. This paper analyzes the partition of the Hurricane Wilma energy spectrum using single-point measurements obtained in shallow water. Hurricane Wilma generated simultaneous crossing wave systems with different significant wave heights and steepnesses. The maximum estimated significant height among the wave groups was 5.5 m. The corresponding height of the partitions and the omnidirectional energy spectrum were 11.0 m (swell) and 12 m, respectively. While linear superposition was the main mechanism responsible for driving the wave groups, at times, modulational instability produced nonlinear wave groups. This is a new finding, since modulational instability is usually considered an open-sea phenomenon. For shorelines with multidirectional wave groups, submerged and semi-submerged devices should be designed to account for changes in wave direction and wave height, although under extreme hurricane conditions, energy harvesting might have to be sacrificed for the benefit of device integrity.
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