Narrow-beam Transducer Research Articles

To: “Numerical modeling of 3D zero-offset laboratory data by a discretized Kirchhoff integral method,” Anastasiya Tantsereva, Bjørn Ursin, Nathalie Favretto-Cristini, Paul Cristini, and Arkady M. Aizenberg, Geophysics, 79, no. 2, T77–T90, doi: 10.1190/geo2013-0034.1.

Due to a production error, the captions for Figures 8–13 do not accurately reflect the figures. The corrected captions for Figures 8–13 are below. Figure 8: Time-frequency representation of the misfits for source positions NB1 (a, d, g), NB2 (b, e, h), and NB3 (c, f, i) for the narrow-beam transducer along the line Y150. (a, b, c) Time-frequency envelope misfit TFEM ( t , f ), time envelope misfit TEM ( t ), and frequency envelope misfit FEM ( f ) for NB1, NB2, and NB3. (d, e, f) Time-frequency phase misfit TFPM ( t , f ), time phase misfit TPM ( t ), and frequency phase misfit FPM ( f ) for NB1, NB2, and NB3. (g, h, i) Comparison of the laboratory (red) and numerical (blue) seismograms. Figure 9: Time-frequency representation of the misfits for source positions NB1 (a, d, g), NB2 (b, e, h), and NB3 (c, f, i) for the narrow-beam transducer along the line Y200. (a, b, c) Time-frequency envelope misfit TFEM ( t , f ), time envelope misfit TEM ( t ), and frequency envelope misfit FEM ( f ) for NB1, NB2, and NB3. (d, e, f) Time-frequency phase misfit TFPM ( t , f ), time phase misfit TPM …

Inferring the acoustic dead-zone volume by split-beam echo sounder with narrow-beam transducer on a noninertial platform

Acoustic measurement of near-bottom fish with a directional transducer is generally problematical because the powerful bottom echo interferes with weaker echoes from fish within the main lobe but at greater ranges than that of the bottom. The volume that is obscured is called the dead zone. This has already been estimated for the special case of a flat horizontal bottom when observed by an echo sounder with a stable vertical transducer beam [Ona, E., and Mitson, R. B. (1996). ICES J. Mar. Sci. 53, 677-690]. The more general case of observation by a split-beam echo sounder with a transducer mounted on a noninertial platform is addressed here. This exploits the capability of a split-beam echo sounder to measure the bottom slope relative to the beam axis and thence to allow the dead-zone volume over a flat but sloping bottom to be estimated analytically. The method is established for the Simrad EK60 scientific echo sounder, with split-beam transducers operating at 18, 38, 70, 120, and 200 kHz. It is validated by comparing their estimates of seafloor slope near the Lofoten Islands, N67-70, with simultaneous measurements made by two hydrographic multibeam sonars, the Simrad EM100295 kHz and EM30030 kHz systems working in tandem.

Review on monitoring adult salmonid ( Oncorhynchus and Salmo spp.) escapement using fixed-location split-beam hydroacoustics

Since 1992, split-beam hydroacoustic techniques have been used to monitor adult salmonid escapement ( Oncorhynchus and Salmo spp.) in 14 rivers in North America and Europe. Monitoring in rivers is one of the more challenging applications for fisheries acoustics. Rivers typically have a high reverberation level, uneven bottom bathymetry, and nonlaminar hydraulics, requiring sophisticated equipment and careful deployment, calibration, and testing. The major issues that were addressed in order to obtain estimates of adult salmon escapement included hydroacoustic equipment and techniques, site selection, transducer deployment, and fish behavior. Fixed-location hydroacoustic techniques were employed, utilizing narrow-beam transducers aimed horizontally, monitoring migrating fish in side-aspect. Fish were tracked in three dimensions as they passed through the acoustic beam. A bottom substrate of low acoustic reflectivity enabled the acoustic beam to be aimed close to the bottom. Sites were selected where fish were actively migrating, not holding or milling. In most cases, migrating salmonids were strongly shore- and bottom-oriented, where water velocities were slowest. Diel distributions of fish passage were weighted toward nighttime. Other results included fish size and velocity. Potential improvements in riverine monitoring capabilities include quadrature demodulation and FM Slide/Chirp signals.

Simulations of an adaptive equalizer applied to high-speed ocean acoustic data transmission'

Computer simulations are carried out to study the feasibility of an adaptive equalizer applied to an hydroacoustic data-transmission channel. The channel is examined with a comprehensive acoustical model to acquire worst-case examples of the ocean acoustic transmission channel. The equalizer performance is investigated by simulations with a computer-generated channel response. Equalizer behavior in a mobile time-variant environment is also studied by use of a simplified, time-discrete multipath channel model. A stochastic gradient lattice equalizer is simulated for a channel which varies due to movement of the transmitter platform. The equalizer was able to track a velocity of up to 0.4 m/s for a favorable transmission geometry, using a transmitter beamwidth of 10 degrees . The results demonstrate the feasibility of coherent modulation schemes for medium-distance ocean acoustic telemetry. It was found that small beamwidths are imperative in maintaining signal coherence and in facilitating adaptive equalization. In particular, narrow-beam transducers will reduce equalizer complexity as well as the frequency spread.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Near-surface Doppler Sonar measurements in the Indian Ocean

A ship-mounted Doppler Sonar has been used to estimate near-surface current profiles in the Somali Current region of the Indian Ocean. The system was deployed on R.R.S. Discovery in May and June 1979. Four 75-kHz, narrow beam transducers were mounted on the ship in the so-called ‘Janus configuration’. Acoustic pulses of 50 or 100 ms duration were transmitted, and echoes due to volume scattering were converted using a Fast Fourier Transform processor to a series of power spectra corresponding to successive range gates. The spectra were averaged over typical sets of 256 pulses, and the Doppler shift observed for each beam and at each depth was used to calculate the velocity of the scatterers with respect to the ship. Two sets of sample data are presented with derived current profiles, which are compared to those produced with a conventional profiling current meter. The problems with the data are discussed, in particular that of poor vertical resolution, and the effects of short-period (e.g., wave-induced)_motion of the ship on such measurements.