Sound travels with greater efficiency in water than does light, which is quickly absorbed and scattered. As a consequence, a wide variety of marine taxa use sound for communication, foraging and generally sensing their environment. Since the 1970s there has been increasing concern about the potential impacts of underwater anthropogenic noise on marine animals. Sources range from short-term coas...

The control of underwater robots presents a number of unique and formidable challenges. Underwater robot dynamics are highly nonlinear, coupled, and timevarying, and subject to hydrodynamic uncertainties and external disturbances such as current. Unlike land mobile robots, underwater robots cannot use GPS (Global Positioning System). Most popular underwater positioning sensors are sonar-based, ...

This paper describes a detection method that adapts to unknown characteristics of the underlying transient signal, such as location, length, and time-frequency content. It applies a set of embedded detectors tuned to a number of signal partitions. The detectors are based on the general wavelet theory whereby two different techniques are examined, (1) the local Fourier transform (LFT) and (2) th...

The underlying approach combines field observations of wave-induced bubbles and ambient noise in the top meter of the marine boundary layer with models for wave noise generation. The field studies are organized around a bubble plume sensing system, consisting of an optical bubble counter, a depth sensor, a hydrophone and an underwater video camera. The plume sensing system is mounted on a surfa...

Several recent studies have shown that some larval fishes will approach underwater speakers that broadcast reef noise, leading to the hypothesis that larval fishes use acoustic cues to locate reefs for settlement. The purpose of the present study was to examine existing hearing data of fishes in relation to ambient sound levels around reefs to estimate the distance over which reef fish might de...

Mapping the wind over vast ocean areas is a very important practical problem, especially at high winds. Satellite measurements using scattering of electromagnetic waves from the rough ocean surface are extremely useful; however, the cross section for this scattering saturates at high winds, when wind speed measurements are most valuable. On the other hand, the same mechanism that precludes use ...

Floods can completely submerge some rice (Oryza sativa L.) fields. Leaves of rice have gas films that aid O2 and CO2 exchange under water. The present study explored the relationship between gas film persistence and underwater net photosynthesis (PN) as influenced by genotype and submergence duration. Four contrasting genotypes (FR13A, IR42, Swarna, and Swarna-Sub1) were submerged for 13 days i...

Autonomous underwater vehicles (AUV) are usually equipped with vision sensors. However, the underwater images captured by AUV often suffer from effects such as diffusion, scatter and caustics. So image enhancement methods are necessary to increase visual quality. A Median filter de-noising approach based on multi-wavelet transform was proposed to remove the impulse noise viewed as random noise ...

© 2010 American Institute of Physics, S-0031-9228-1009-030-7 Recent developments in seismology, ultrasonics, and underwater acoustics have led to a radical change in the way scientists think about ambient noise—the diffuse waves generated by pressure fluctuations in the atmosphere, the scattering of water waves in the ocean, and any number of other sources that pervade our world. Because diffus...