scholarly journals Improving the Accuracy of Krill Target Strength Using a Shape Catalog

2021 ◽  
Vol 8 ◽  
Author(s):  
Fiona Bairstow ◽  
Sven Gastauer ◽  
Luke Finley ◽  
Tom Edwards ◽  
C. Tom A. Brown ◽  
...  
Keyword(s):  
Antarctic Krill ◽  
Length Distribution ◽  
Practical Method ◽  
Orientation Distribution ◽  
Mie Scattering ◽  
Target Strength ◽  
Limiting Factor ◽  
Backscattering Cross Section ◽  
Orientation Distributions ◽  
Strength Models

Antarctic krill are subject to precautionary catch limits, based on biomass estimates, to ensure human activities do not adversely impact their important ecological role. Accurate target strength models of individual krill underpin biomass estimates. These models are scaled using measured and estimated distributions of length and orientation. However, while the length distribution of a krill swarm is accessible from net samples, there is currently limited consensus on the method for estimating krill orientation distribution. This leads to a limiting factor in biomass calculations. In this work, we consider geometric shape as a variable in target strength calculations and describe a practical method for generating a catalog of krill shapes. A catalog of shapes produces a more variable target strength response than an equivalent population of a scaled generic shape. Furthermore, using a shape catalog has the greatest impact on backscattering cross-section (linearized target strength) where the dominant scattering mechanism is mie scattering, irrespective of orientation distribution weighting. We suggest that shape distributions should be used in addition to length and orientation distributions to improve the accuracy of krill biomass estimates.

scholarly journals Improved parametrization of Antarctic krill target strength models

2006 ◽  
Vol 119 (1) ◽  
pp. 232-242 ◽  
Author(s):  
Gareth L. Lawson ◽  
Peter H. Wiebe ◽  
Carin J. Ashjian ◽  
Dezhang Chu ◽  
Timothy K. Stanton
Keyword(s):  
Antarctic Krill ◽  
Target Strength ◽  
Strength Models

scholarly journals Improved parameterization of the SDWBA for estimating krill target strength

2006 ◽  
Vol 63 (5) ◽  
pp. 928-935 ◽  
Author(s):  
Stéphane G. Conti ◽  
David A. Demer
Keyword(s):  
Antarctic Krill ◽  
Euphausia Superba ◽  
Orientation Distribution ◽  
Target Strength ◽  
Model Parameters ◽  
Distorted Wave ◽  
Acoustic Frequency ◽  
General Application ◽  
Broad Bandwidth ◽  
Phase Variability

Abstract Recently, a Stochastic Distorted Wave Born Approximation (SDWBA) model was proposed to improve target strength (TS) estimates for Antarctic krill, Euphausia superba. The krill shape is modelled by a collection of cylinders, and total sound scatter is estimated by semi-coherent summation of scatter from each element. The SDWBA model was evaluated with a generic krill shape comprising 14 cylinders and a phase variability of , and predictions were validated with empirical TS and total TS data at 120 kHz, and over a broad bandwidth, respectively. For general application, parameterization of the SDWBA model is improved to account explicitly for dependence among four of the model parameters: standard length of krill, number of cylinders used to describe its shape, amplitude of inter-element phase variability, and acoustic frequency. The model improvements are demonstrated, and the uncertainty in orientation distribution of krill beneath survey vessels and its ramifications on krill biomass estimates are highlighted.

scholarly journals Tools for Visualizing and Analyzing Fourier Space Sampling in Cryo-EM

2020 ◽  
Author(s):  
Philip R. Baldwin ◽  
Dmitry Lyumkis
Keyword(s):  
Graphical User Interface ◽  
Signal To Noise Ratio ◽  
Orientation Distribution ◽  
Geometrical Factor ◽  
Fourier Space ◽  
Complete Understanding ◽  
Spherical Surfaces ◽  
Compensation Factor ◽  
Spectral Signal ◽  
Orientation Distributions

AbstractA complete understanding of how an orientation distribution contributes to a cryo-EM reconstruction remains lacking. It is necessary to begin critically assessing the set of views to gain an understanding of its effect on experimental reconstructions. Toward that end, we recently suggested that the type of orientation distribution may alter resolution measures in a systematic manner. We introduced the sampling compensation factor (SCF), which incorporates how the collection geometry might change the spectral signal-to-noise ratio (SSNR), irrespective of the other experimental aspects. We show here that knowledge of the sampling restricted to spherical surfaces of sufficiently large radii in Fourier space is equivalent to knowledge of the set of projection views. Moreover, the SCF geometrical factor may be calculated from one such surface. To aid cryo-EM researchers, we developed a graphical user interface (GUI) tool that evaluates experimental orientation distributions. The GUI returns plots of projection directions, sampling constrained to the surface of a sphere, the SCF value, the fraction of the empty region of Fourier space, and a histogram of the sampling values over the points on a sphere. Finally, a fixed tilt angle may be incorporated to determine how tilting the grid during collection may improve the distribution of views and Fourier space sampling. We advocate this simple conception of sampling and the use of such tools as a complement to the distribution of views to capture the different aspects of the effect of projection directions on cryo-EM reconstructions.

Reliability criteria in quantitative texture analysis with experimental and simulated orientation distributions

2005 ◽  
Vol 38 (4) ◽  
pp. 603-611 ◽  
Author(s):  
Daniel Chateigner
Keyword(s):  
Texture Analysis ◽  
Orientation Distribution ◽  
Point Of View ◽  
Real Sample ◽  
Experimental Point ◽  
Orientation Distributions ◽  
Counting Statistics ◽  
New Criterion

Quantitative texture analysis reliability factors are examined from an experimental point of view, using real-sample and modelled orientation distribution refinements. The classicalRPfactors of texture analysis are shown to depend on the texture strength, and their representation of the various textures is not homogeneous. The surface-weightedRPwhomologues exhibit lower texture strength dependency and better homogeneities, but still do not allow for comparison of refinements operated on samples with different textures. New factors,Rw, weighted by the counting statistics, show the lowest dependency and best homogeneity. FromRw1(Rw0) curves a new criterion is established, which allows the detection of poorly refined orientation distributions. This study highlights a unique entropy-to-texture index relationship, which also gives a new criterion for testing refinement reliability, and proposes two different ranges in which to apply the texture index and the entropy factors.

scholarly journals Multifrequency target strength of northern krill (Meganyctiphanes norvegica) swimming horizontally

2011 ◽  
Vol 69 (1) ◽  
pp. 119-130 ◽  
Author(s):  
Lucio Calise ◽  
Tor Knutsen
Keyword(s):  
Length Distribution ◽  
Ex Situ ◽  
Target Strength ◽  
Acoustic Backscatter ◽  
Acoustic Measurements ◽  
Acoustic Beams ◽  
Meganyctiphanes Norvegica ◽  
Acoustic Identification ◽  
Made In

Abstract Calise, L., and Knutsen, T. 2012. Multifrequency target strength of northern krill (Meganyctiphanes norvegica) swimming horizontally. – ICES Journal of Marine Science, 69: 119–130. Multifrequency acoustic measurements on ex situ horizontally swimming krill were made in a novel experimental setting. An ensemble of northern krill (Meganyctiphanes norvegica) was introduced to a large enclosure (a mesocosm), and acoustic backscatter was sampled using a multifrequency (70, 120, and 200 kHz) echosounder (Simrad EK60). Two submerged lamps were placed at opposite sides of the mesocosm and switched on and off to induce the krill, by light attraction, to swim horizontally through the acoustic beams. By tracking echoes, animal displacement, swimming speed, and target strength (TS) by frequency were estimated. The dominant and secondary modes of the total-length distribution were 21.8 ± 3.0 and 27.8 ± 2.7 mm, respectively. Although krill orientation was assumed stable and the ping rate was high, the range and inter-ping variability of the average TS values were large, decreasing and increasing with frequency, respectively. The overall TS frequency response observed and concurrent measurements at 120 and 200 kHz confirm the theoretical expectation that the acoustic backscatter from the investigated organisms were confined to the Rayleigh and Geometric scattering regions, a finding that might both aid acoustic identification and size-group separation of in situ northern krill.

Memory impairment in flowing suspensions. II. Experimental results

1978 ◽  
Vol 56 (22) ◽  
pp. 2824-2832 ◽  
Author(s):  
G. J. Ennis ◽  
A. Okagawa ◽  
S. G. Mason
Keyword(s):  
Memory Loss ◽  
Orientation Distribution ◽  
Particle Orientation ◽  
Light Transmittance ◽  
Particle Interactions ◽  
Electrical Shock ◽  
Cyclic Shear ◽  
Rigid Rods ◽  
Gradual Loss ◽  
Orientation Distributions

Experiments on the reversibility of particle orientation distributions in suspensions of nearly monodisperse rigid rods and hardened red blood cells (HRBC) subjected to cyclic shearing are described.The orientation distributions of initially aligned rods measured by direct observation exhibited a gradual loss in memory as flow was reversed back and forth which was attributed mainly to non-reversible particle interactions. When an electric field was applied continuously during cyclic shear flow, the rate of memory loss was increased. However, if an electrical shock was applied momentarily between each reversal of flow, the suspension maintained some memory. These results are generally in agreement with the theory presented in the preceding paper.With suspensions of HRBC, the particles were initially randomly oriented and the light transmittance across the planes of shear was used to measure changes in orientation distribution. Since HRBC are small enough to exhibit appreciable rotary Brownian motion, memory loss was inevitable and increased with the duration of each shear cycle and the cell concentration.Memory loss was also observed for rods and HRBC in non-Newtonian media and was attributed to drift in the rotational orbit constants of the particles.

Estimation of Fish Length from Acoustic Target Strengths

1987 ◽  
Vol 44 (10) ◽  
pp. 1782-1785 ◽  
Author(s):  
U. Buerkle
Keyword(s):  
Gadus Morhua ◽  
Statistical Significance ◽  
Orientation Distribution ◽  
Target Strength ◽  
Fish Length ◽  
Fish Sample ◽  
Length Frequency ◽  
Frequency Structure ◽  
Acoustic Target

I show that fish length distributions calculated from acoustic target strengths of cod (Gadus morhua) are in error when target strength–length relationships are used that do not account for the orientation distribution of the fish. The magnitude and statistical significance of the errors vary with the length frequency structure of the fish sample and are thought to be large enough to question the value of acoustically determined lengths in fish surveys if corrections for fish orientation are not applied.

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