A new echosounder that exploits the resonance frequency of swimbladder-bearing fish is described. The system is a custom configuration of a commercial device originally developed for studying the ...seafloor and adapted for studying fish. The frequencies span the range 1.7 kHz to 100 kHz, with some gaps, with the lower portion of that range corresponding to the resonance frequency of common adult fish. Through pulse-compression processing of the broadband signals, the range resolution is greatly improved to about 20 cm at the lowest frequencies and about 3 cm at the highest frequencies. As a result of the resonance classification at these low frequencies, significant ambiguities that are normally associated with interpretation of high frequency echosounder data are eliminated. Summarized in this paper are the design and calibration of the system, as well as results from using the system to study schools of fish in the ocean.
The overall goal of the ONR STRATAFORM program is to advance our understanding of the formation of stratigraphic sequences on continental shelves and slopes. The primary objectives of this project ...are to conduct observations to determine the mechanisms of cross-shore sediment transport on the Eel river shelf and to relate the transport to the source of sediments in the Eel river plume.
See also ADM002006. Published in the Proceedings of the MTS/IEEE OCEANS 2006 Boston Conference and Exhibition held in Boston, MA on September 15-21, 2006. Grant No. NAO3NMF4270183. The original ...document contains color images.
An extensive field study was conducted to investigate the current velocities and mooring system tensions in a 20-unit net pen fish farm located in Eastport Maine, USA, near the Bay of Fundy where extreme tides create strong currents loading fish farm components. To understand the flow characteristics at the site, currents meters were deployed at external and internal farm locations during three distinct operational conditions: (1) clean nets for smolts, (2) clean nets for standard grow out and (3) nets for standard grow out at the end of the stocking schedule, when the gear is fouled with biological material. Also, several load cells were deployed at the same time on important anchor leg and net pen attachment components to measure system loads. The current meter data sets provided evidence of velocity flow reduction through the farm by examining the current meter statistics and tidal harmonic constituents. Tidal analysis also showed substantial tidal harmonics or shallow water tides. The load cells measured maximum loads of 104 kN for anchor leg and 11 kN for net pen lines. The results are significant because few extensive fish farm engineering data sets exist, especially for different combinations of nets and levels of biological fouling. These results are being used in complementary studies to quantify flow reduction, to validate Morison equation type numerical models and as a baseline for specifying offshore fish farm gear.
For sediment transport studies, one describes the transport on a size class by size class basis as a function of vertical height. This requires the suspended sediment size spectrum as a function of ...depth and time. No in-situ instrumentation determines the full particle size spectrum, but the LISST (Laser In-Situ Sizing and Transmissometry) particle sizer, appeared to meet some of our observational needs. Three LlSSTs were purchased and two mounted on our bottom boundary layer tripods. The third was retrofitted with a settling tube to make it a "LISST-ST." These LISSTs have been deployed at the LEO-IS site off New Jersey in the fall of 1995, and in STRATAFORM in the winter 1996 on the Northern California shelf. Finally, we studied the LISST's response to real sediments from various sites. The sediment was sieved to obtain various sized sediments and the LISST's response to each size class was observed. Also, quantitative calibrations were made to see if the LlSST would integrate the total suspended sediment properly, and these results are currently being written into a paper.
Funding was provided by the Gulf of Maine Ocean Observing System(GoMOOS under ONR grant N0014-01-1-0999),NOAA-UNH CINEMAR (NOAA Grant Number NA16RP1718), andGLOBEC (NSF OCE93-13670 and OCE02-27679).
...Compliance must be supplied to any surface mooring to allow the buoy to move with the waves and currents,and remain moored in position. This can be supplied with a traditional chain catenary or newer compliantelastic tether or stretch hose technologies. Some applications of each of these three techniques are shown,with the emphasis placed on the use of compliant elastic tethers. For modeling and designing thesemoorings, the elastic modulus of the tether material must be known. Therefore, a new and used piece ofelastic material was terminated, tested for the stretch-strain relationship under set conditions, and theelastic modulus calculated. For these tests, the elastic tether was stretched out to a mean elongationbetween 100 and 250%, then cycled about that stretch by ±25 and ±50% to duplicate a moored application.The resultant elastic modulus is presented to aid in mooring design. At low elongations, the elastic modulusis constant at about 125 PSI, but as the mean elongation increases the modulus increases, and as the cycletension increase the modulus also increases, reaching a maximum of 900 PSI at 275% stretch.
To measure oceanographic parameters such as currents, temperature, conductivity, pressure, and suspended sediment concentrations, two film-recording current meters were upgraded with ...microprocessor-controlled data recorders and additional sensors. Two telemetry links relay data and allow the in situ operation of the remote instrument to be checked. In one configuration, the bottom-mounted current meter communicated by a 35-m-long wire to a small surface spar buoy, and then by a packet radio link to a nearby ship. In another development, the current meter relays data to a controller and buoyant data capsule on the bottom instrument package. The controller collects and processes the data from the current meter and periodically transfers these processed data to a data capsule and releases it. When released, the capsule rises to the surface and transmits its data to shore via the ARGOS satellite, while acting as a satellite tracked drifter.< >
A statistical description of the deep ocean internal wave field is presented using measurements from the Midocean Acoustic Transmission Experiment, conducted near Cobb Seamount in the NE Pacific ...(46°46′N, 130°47′W) during June–July 1977. The unique feature of this experiment is the variety of data obtained simultaneously from the same location: time series of temperature and velocity, and vertical and horizontal profiles of temperature. A generalized form of the Garrett‐Munk (GM) internal wave spectrum is developed and used to interpret the data. This spectral model is specified by three parameters,
E˜
, t, and p (energy level, wave number bandwidth, and frequency spectral slope, respectively). The variety of measurement types permit these three model parameters to be estimated from more than one measurement. The overall best fit values to the MATE data were p = 2.7 (GM use p = 3), t = 3.1 m−1 s (equivalent to j* = 6, twice the GM value), and
E˜=8×10−4 j/kg
(within 20% of the GM level). Although significant differences were found in the values of the bandwidth (t) and spectral slope (p) from those specified by Garrett‐Munk, the deviations are consistent with the behavior expected in a random internal wave field.
