scholarly journals Acoustic backscatter by schools of adult Atlantic mackerel

2007 ◽  
Vol 64 (6) ◽  
pp. 1145-1151 ◽  
Author(s):  
Natalia Gorska ◽  
Rolf J. Korneliussen ◽  
Egil Ona
Keyword(s):  
Cross Sections ◽  
Relative Frequency ◽  
Acoustic Properties ◽  
Acoustic Backscatter ◽  
High Frequencies ◽  
Fish Size ◽  
Atlantic Mackerel ◽  
Scomber Scombrus ◽  
Scattering Spectra

Abstract Gorska, N., Korneliussen, R. J., and Ona, E. 2007. Acoustic backscatter by schools of adult Atlantic mackerel. – ICES Journal of Marine Science, 64: 1145–1151. The extent of acoustic backscatter by schools of adult Atlantic mackerel (Scomber scombrus) is investigated to improve biomass estimates. Previous studies involving modelled scattering from individual mackerel showed that backscattering at high frequencies is dominated by the contribution from the backbone. Accurate predictions of the scattering spectra require consideration of backscattering from the entire skeleton, including details of the bone shapes and their acoustic properties. Here, the backscattering cross-sections from mackerel flesh and backbone are estimated theoretically from 18 to 364 kHz and averaged over fish size and tilt angle, then compared with in situ measurements of volume backscattering from mackerel schools. Based on the comparisons, some gross features of the observed relative frequency response are explained, and recommendations for further studies suggested.

scholarly journals The acoustic identification of Atlantic mackerel

2010 ◽  
Vol 67 (8) ◽  
pp. 1749-1758 ◽  
Author(s):  
Rolf J. Korneliussen
Keyword(s):  
Frequency Response ◽  
Relative Frequency ◽  
Marine Science ◽  
Acoustic Feature ◽  
Atlantic Mackerel ◽  
Scomber Scombrus ◽  
Acoustic Beams ◽  
Frequency Independent ◽  
Acoustic Identification ◽  
Trawl Catches

Abstract Korneliussen, R. J. 2010. The acoustic identification of Atlantic mackerel. – ICES Journal of Marine Science, 67: 1749–1758. Calibrated, digitized data from multifrequency echosounders working simultaneously with nearly identical and overlapping acoustic beams were used to generate new, synthetic echograms which allow Atlantic mackerel (Scomber scombrus) to be identified acoustically. The raw echosounder data were processed stepwise in a modular sequence of analyses to improve categorization of the acoustic targets. The relative frequency response measured over as many as six operating frequencies, 18, 38, 70, 120, 200, and 364 kHz, was the main acoustic feature used to characterize the backscatter. Mackerel seemed to have a frequency-independent backscatter below ∼100 kHz, but significantly higher levels of backscattered energy at 200 kHz. Synthetic echograms containing targets identified acoustically as mackerel are presented and evaluated against trawl catches. Although catching fast-swimming mackerel is difficult, trawl catches from three Norwegian research vessels confirmed that the targets identified acoustically as mackerel were indeed that species. Separate experiments performed on mackerel in pens support the findings.

scholarly journals The relative frequency response derived from individually separated targets of northeast Arctic cod (Gadus morhua), saithe (Pollachius virens), and Norway pout (Trisopterus esmarkii)

2009 ◽  
Vol 66 (6) ◽  
pp. 1149-1154 ◽  
Author(s):  
Geir Pedersen ◽  
Rolf J. Korneliussen
Keyword(s):  
Frequency Response ◽  
Relative Frequency ◽  
Gadus Morhua ◽  
Target Strength ◽  
Reference Frequency ◽  
Acoustic Measurements ◽  
Arctic Cod ◽  
High Frequencies ◽  
Specific Frequency

Abstract Pedersen, G., and Korneliussen, R. J. 2009. The relative frequency response derived from individually separated targets of northeast Arctic cod (Gadus morhua), saithe (Pollachius virens), and Norway pout (Trisopterus esmarkii). – ICES Journal of Marine Science, 66: 1149–1154. The concept of relative frequency response r(f) of fish is an important feature used to characterize acoustic targets. It is defined as the volume-backscattering coefficient at a specific frequency f relative to that of a reference frequency. When based on volume backscattering, r(f) reliably distinguishes several acoustic categories if the insonified volumes are reasonably comparable between the frequencies, and that enough samples and targets are measured to constrain stochastic variations in the data within acceptable limits. Therefore, r(f) distinguishes different fish species with swimbladders poorly if they appear as single targets. Using target-strength (TS) data, the acoustic measurements are more spatially comparable, and averaging the TS over an echotrace of a single fish improves the ability to distinguish between different species. Frequency response was estimated using TS data from in situ measurements, collected using Simrad EK60 echosounders with split-beam transducers transmitting simultaneously at 18, 38, 70, 120, and 200 kHz. Selected series with nearly pure catches of northeast Arctic cod (Gadus morhua), saithe (Pollachius virens), and Norway pout (Trisopterus esmarkii) were analysed using a target-tracking algorithm. The frequency response of northeast Arctic cod and saithe did not differ significantly, but at high frequencies, the response of both northeast Arctic cod and saithe differed from that of Norway pout. However, in the latter case, northeast Arctic cod and saithe could be separated, because of their different TS magnitudes.

scholarly journals Measurements of acoustic-scattering spectra from the whole and parts of Atlantic mackerel

2009 ◽  
Vol 66 (6) ◽  
pp. 1169-1175 ◽  
Author(s):  
Tonje Lexau Nesse ◽  
Halvor Hobæk ◽  
Rolf J. Korneliussen
Keyword(s):  
Frequency Response ◽  
Acoustic Scattering ◽  
Ex Situ ◽  
Target Strength ◽  
Model Parameters ◽  
Acoustic Frequency ◽  
Atlantic Mackerel ◽  
Scattering Spectra ◽  
Laboratory Tank

Abstract Nesse, T. L., Hobæk, H., and Korneliussen, R. J. 2009. Measurements of acoustic-scattering spectra from the whole and parts of Atlantic mackerel. – ICES Journal of Marine Science, 66: 1169–1175. Atlantic mackerel (Scomber scombrus) are weak sound scatterers compared with fish that have swimbladders. Accurate acoustic estimates of mackerel abundance require estimates of target strength. Different parts of mackerel may dominate the backscattering spectra. Mackerel schools are acoustically recognized mainly by backscatter four times stronger at 200 kHz than at 38 kHz. Simulations have established that backscatter from only the flesh and the backbone could explain this frequency response, although there are uncertainties in the model parameters and simplifications. In this paper, experiments conducted in a laboratory tank to investigate the complexity of mackerel backscatter are discussed. Acoustic backscatter was measured over the frequency range 65–470 kHz from individual dead mackerel, and their backbones, heads, and skulls. Backscatter from the backbones was measured at several angles of incidence. Grating lobes (Bragg scattering) appeared at different angles, depending on the acoustic frequency and the spacing of the vertebrae. These lobes were evident in backbone backscatter after propagating through the flesh and can be used, in principle, to determine mackerel size acoustically. The frequency response of individual, ex situ Atlantic mackerel estimated from these measurements did not match that from the measurements of in situ mackerel schools. Further investigation is warranted.

In situ acoustic observation of food consumption in caged Atlantic mackerel (Scomber scombrus)

1996 ◽  
Vol 27 (1-3) ◽  
pp. 131-135 ◽  
Author(s):  
Jon-Erik Juell ◽  
Jens Christian Holm ◽  
Arvid K. Beltestad
Keyword(s):  
Food Consumption ◽  
Atlantic Mackerel ◽  
Scomber Scombrus ◽  
Acoustic Observation

scholarly journals Ultraviolet Absorption Cross-Sections of Ammonia at Elevated Temperatures for Nonintrusive Quantitative Detection in Combustion Environments

2021 ◽  
pp. 000370282199044
Author(s):  
Wubin Weng ◽  
Shen Li ◽  
Marcus Aldén ◽  
Zhongshan Li
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Absorption Cross Section ◽  
Elevated Temperatures ◽  
Uv Absorption ◽  
Energy Utilization ◽  
Quantitative Detection ◽  
Absorption Cross ◽  
Hot Gas

Ammonia (NH3) is regarded as an important nitrogen oxides (NOx) precursor and also as an effective reductant for NOx removal in energy utilization through combustion, and it has recently become an attractive non-carbon alternative fuel. To have a better understanding of thermochemical properties of NH3, accurate in situ detection of NH3 in high temperature environments is desirable. Ultraviolet (UV) absorption spectroscopy is a feasible technique. To achieve quantitative measurements, spectrally resolved UV absorption cross-sections of NH3 in hot gas environments at different temperatures from 295 K to 590 K were experimentally measured for the first time. Based on the experimental results, vibrational constants of NH3 were determined and used for the calculation of the absorption cross-section of NH3 at high temperatures above 590 K using the PGOPHER software. The investigated UV spectra covered the range of wavelengths from 190 nm to 230 nm, where spectral structures of the [Formula: see text] transition of NH3 in the umbrella bending mode, v2, were recognized. The absorption cross-section was found to decrease at higher temperatures. For example, the absorption cross-section peak of the (6, 0) vibrational band of NH3 decreases from ∼2 × 10−17 to ∼0.5 × 10−17 cm2/molecule with the increase of temperature from 295 K to 1570 K. Using the obtained absorption cross-section, in situ nonintrusive quantification of NH3 in different hot gas environments was achieved with a detection limit varying from below 10 parts per million (ppm) to around 200 ppm as temperature increased from 295 K to 1570 K. The quantitative measurement was applied to an experimental investigation of NH3 combustion process. The concentrations of NH3 and nitric oxide (NO) in the post flame zone of NH3–methane (CH4)–air premixed flames at different equivalence ratios were measured.

Selectivity of square mesh codends of pelagic trawls for Atlantic mackerel (Scomber scombrus L.)

1992 ◽  
Vol 13 (3) ◽  
pp. 267-279 ◽  
Author(s):  
J. Casey ◽  
M.D. Nicholson ◽  
S. Warnes
Keyword(s):  
Atlantic Mackerel ◽  
Scomber Scombrus

scholarly journals In-situ observation of trapped carriers in organic metal halide perovskite films with ultra-fast temporal and ultra-high energetic resolutions

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kanishka Kobbekaduwa ◽  
Shreetu Shrestha ◽  
Pan Adhikari ◽  
Exian Liu ◽  
Lawrence Coleman ◽  
...  
Keyword(s):  
Cross Sections ◽  
High Energy ◽  
High Energy Resolution ◽  
In Situ Observation ◽  
Trap States ◽  
Tunneling Mechanism ◽  
Photocurrent Spectroscopy ◽  
Metal Halide Perovskite ◽  
Halide Perovskite

AbstractWe in-situ observe the ultrafast dynamics of trapped carriers in organic methyl ammonium lead halide perovskite thin films by ultrafast photocurrent spectroscopy with a sub-25 picosecond time resolution. Upon ultrafast laser excitation, trapped carriers follow a phonon assisted tunneling mechanism and a hopping transport mechanism along ultra-shallow to shallow trap states ranging from 1.72–11.51 millielectronvolts and is demonstrated by time-dependent and independent activation energies. Using temperature as an energetic ruler, we map trap states with ultra-high energy resolution down to < 0.01 millielectronvolt. In addition to carrier mobility of ~4 cm2V−1s−1 and lifetime of ~1 nanosecond, we validate the above transport mechanisms by highlighting trap state dynamics, including trapping rates, de-trapping rates and trap properties, such as trap density, trap levels, and capture-cross sections. In this work we establish a foundation for trap dynamics in high defect-tolerant perovskites with ultra-fast temporal and ultra-high energetic resolution.

Diamond film nucleation and interface characterization

1992 ◽  
Vol 7 (8) ◽  
pp. 2151-2159 ◽  
Author(s):  
P. Bou ◽  
L. Vandenbulcke ◽  
R. Herbin ◽  
F. Hillion
Keyword(s):  
Cross Sections ◽  
Deposition Time ◽  
Sample Surface ◽  
Simultaneous Recording ◽  
Carbon Activity ◽  
Nucleation Density ◽  
Carbide Formation ◽  
Interface Characterization ◽  
Film Nucleation

A powerful micro SIMS technique coupled to a computer driven acquisition system has allowed the simultaneous recording of C−, MoO−, and Si− images of the sample surfaces, or of the transverse cross sections of the Mo-diamond interface. Diamond deposition has been shown to take place on a Mo2C layer, and the influence on the nucleation process of Si contamination, coming from the quartz tube etched by H atoms, has been investigated. Contamination can in fact occur during the shutdown procedures or during the whole experiment. This last contamination can be avoided by using suitable pressure ranges or gas combinations. Moreover, the deposition time necessary to obtain well-crystallized diamond films and the nucleation density could be optimized by an in situ pretreatment stage. This treatment reduces the delay observed before nucleation (which would correspond to the carbide formation), and increases the carbon activity at the sample surface.

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