Methods in Oceanography最新文献

A new autonomous multiple codend opening/closing system was constructed to be attached to a midwater trawl net, and the layer discrimination ability of this new system attached to the Matsuda–Oozeki–Hu Trawl (MOHT, mouth area 5 m2) was demonstrated through comparison with the Multiple layer Opening/Closing MOHT (MOC–MOHT), which was equipped with a mouth opening/closing net control system. The new multiple codend opening/closing system was 1.28 m high and 0.75 m wide and has five pyramid-shaped codend nets, with an autonomous control mechanism identical to the MOC–MOHT. Field comparison between the new system and MOC–MOHT demonstrated the accurate layer discrimination ability of the new system and the new codend opening/closing system sufficiently allowed for avoidance of contamination of specimens before the codend frame, after improvement of the main net shape with the cylindrical part before the codend frame. The new autonomous codend opening/closing system attached to MOHT (COC–MOHT) is a reliable multi-layer sampling gear, and the new system itself has the potential of transforming a traditional midwater trawl to an effective multi-layer sampling system, by adding the modification of the net shape before the codend.

Seismic oceanography is based on the passage of a regularly repeating acoustic impulsive source and an acquisition streamer along the surface of the ocean, and on summing together all signals reflected from temperature and salinity interfaces in the ocean (where there are acoustic impedance contrasts). Due to the inherent redundancy of the method, random noise is attenuated, while signal is preserved; however, if the original signal-to-noise ratio is large enough, one need not use data from the entire streamer to create a 2D profile. A processing scheme is here devised to obtain consecutive images, known as stacks, of the structure of the water column. The scheme, named Seismic Offset Groups (SOG), consists in splitting the data from the whole streamer at a given geographical position into data produced by different streamer subsets. The method is illustrated by partitioning data from a 5-km long streamer into 7 offset groups separated by 3.5 min in time, thereby imaging the same seafloor-referenced location over a period of 21 min. As the streamer passes over a fixed geographical point, motions within the water column are observed. Each stack, created with a subset of the complete streamer, can therefore be considered an image of the water column at a particular time step (animation frame). In this way each image shows a different thermohaline fabric and the animation allows us to visualize internal ocean motions.

This paper is a chronicle of three decades of my career in developing instrumentation for ocean observations. It opens with challenges of making current measurements in the upper ocean, where off-axis flow is important, using electromagnetic and acoustic Doppler instruments. A by-product of acoustic Doppler instruments, quantitative backscatter measurements, led to my contributions on the behaviour and abundance of zooplankton, especially in relation to ocean physics. What worked, and what did not, are discussed, and lessons on project initiation are set out. The Autosub autonomous underwater vehicle programmes have been a major part of my career since 1993, and the initiation and motivation for the programmes are described, together with the challenges in management and technology. Summaries of the outcomes of the Autosub Science Missions programme of 1999–2001 demonstrate the effectiveness of a focused approach to the early adoption of new technology for ocean measurements.

Body size constrains prey–predator interactions and physiology, therefore plankton size spectra have been appointed as synthetic descriptors of plankton community structure and functioning. Recently developed imaging systems and supervised classification tools provide size measurements of any object in situ or in net samples and automatically classify them into previously defined categories. But because the nature of objects detected by these imaging systems is diverse, from non-living detritus to organisms of different plankton taxa, and because the steps in the analysis could introduce specific biases, a careful analysis of such plankton size spectra is needed before going deeper into ecological considerations. Using a WP2 net time series, we propose a general framework to analyze and validate zooplankton size spectra collected with nets and analyzed with the ZooScan integrated system that includes supervised classification. Size spectra were controlled, at each step of the procedure, to assess the modification of their shape due to several possible biases: (i) the effect of objects touching each other during the image acquisition, (ii) the error of the automatic classification differing among size classes and (iii) the choice of model to estimate body biovolume.

The area of active bioacoustics involves the use of sound to study distributions of fish and zooplankton in aquatic environments. There have been significant advances in this area over the past 30 years, covering many categories, spanning technology and modeling. These advances, as witnessed throughout my career, are reviewed. Issues with past and current approaches are discussed as well as projections into the future.