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H. Medwin

Bio: H. Medwin is an academic researcher. The author has contributed to research in topics: Acoustical oceanography. The author has an hindex of 1, co-authored 1 publications receiving 521 citations.

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Journal ArticleDOI
TL;DR: In this article, the accuracy of the acoustic Doppler velocimeter (ADV) is evaluated in a 17m flume using an ADV and a laser DOF.
Abstract: Accuracy of the acoustic Doppler velocimeter (ADV) is evaluated in this paper. Simultaneous measurements of open-channel flow were undertaken in a 17-m flume using an ADV and a laser Doppler velocimeter. Flow velocity records obtained by both instruments are used for estimating the true (“ground truth”) flow characteristics and the noise variances encountered during the experimental runs. The measured values are compared with estimates of the true flow characteristics and values of variance (〈u′2〉, 〈w′2〉) and covariance (〈u′w′〉) predicted by semiempirical models for open-channel flow. The analysis showed that the ADV sensor can measure mean velocity and Reynolds stress within 1% of the estimated true value. Mean velocities can be obtained at distances less than 1 cm from the boundary, whereas Reynolds stress values obtained at elevations greater than 3 cm above the bottom exhibit a variation that is in agreement with the predictions of the semiempirical models. Closer to the boundary, the measure...

566 citations

Journal ArticleDOI
TL;DR: Modelling and a sensitivity analysis of the acoustic observations from the Malaspina 2010 Circumnavigation Expedition show that the previous estimate of mesopelagic fishes biomass needs to be revised to at least one order of magnitude higher, and there is a close relationship between the open ocean fishes biomass and primary production.
Abstract: With a current estimate of ~1,000 million tons, mesopelagic fishes likely dominate the world total fishes biomass. However, recent acoustic observations show that mesopelagic fishes biomass could be significantly larger than the current estimate. Here we combine modelling and a sensitivity analysis of the acoustic observations from the Malaspina 2010 Circumnavigation Expedition to show that the previous estimate needs to be revised to at least one order of magnitude higher. We show that there is a close relationship between the open ocean fishes biomass and primary production, and that the energy transfer efficiency from phytoplankton to mesopelagic fishes in the open ocean is higher than what is typically assumed. Our results indicate that the role of mesopelagic fishes in oceanic ecosystems and global ocean biogeochemical cycles needs to be revised as they may be respiring ~10% of the primary production in deep waters. Mesopelagic fishes dominate the global fishes biomass, yet there exist major uncertainties regarding their global biomass. Irigoien et al.analyse acoustic data collected during a circumglobal cruise and show that biomass estimates should be raised by an order of magnitude.

545 citations

Journal ArticleDOI
01 Dec 1986-Nature
TL;DR: In this article, the authors show that the material in the layer is highly porous and is saturated with water at high pore pressure, and they conclude that the layer deforms and that the ice stream probably moves principally by such deformation.
Abstract: Seismic reflection studies recently conducted on ice stream B, part of the marine ice sheet of West Antarctica, show a metres-thick layer immediately beneath the ice in which both compressional (P) and shear (S) wave speeds are very low. These low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure. From this, and from arguments presented in an accompanying paper1 to the effect that the layer would be too weak to support the shear stress exerted by the overlying ice, we conclude that the layer is deforming and that the ice stream probably moves principally by such deformation.

353 citations

Book ChapterDOI
01 Jan 1988
TL;DR: The ability of sound speed gradients in the ocean to channel sound so that it can propagate without interaction with the surface or bottom has been studied in this paper, where sound allows long-range transmission of information underwater.
Abstract: Of all the sensory stimuli discussed in this volume, only sound allows longrange transmission of information underwater. This is a consequence of the extraordinarily low attenuation of sound in water and the ability of sound speed gradients in the ocean to channel sound so that it can propagate without interaction with the surface or bottom.

307 citations

Journal ArticleDOI
TL;DR: Theoretical treatments of the dynamics of a single bubble in a pressure field have been undertaken for many decades as mentioned in this paper, and there now exists a solid theoretical basis for the dynamic dynamics of the single bubble.

249 citations