scholarly journals Reconciling theoretical versus empirical target strengths of krill: effects of phase variability on the distorted-wave Born approximation

2003 ◽  
Vol 60 (2) ◽  
pp. 429-434 ◽  
Author(s):  
David A. Demer ◽  
Stephane G. Conti
Keyword(s):  
Born Approximation ◽  
Antarctic Krill ◽  
Incidence Angle ◽  
Euphausia Superba ◽  
Side Lobe ◽  
Distorted Wave ◽  
Distorted Wave Born Approximation ◽  
Model Predictions ◽  
Practical Tool ◽  
Phase Variability

Abstract A model was recently proposed to predict the target strengths (TS) of Antarctic krill, Euphausia superba, versus incidence angle (θ) (Deep Sea Res. II 45(7) (1998) 1273). Based on the distorted-wave Born approximation (DWBA), the model depends on the coherent summation of scattering from elements of a discretized-bent cylinder. It was empirically validated at 120 kHz near-broadside incidence (θ≈90°), but large discrepancies were observed at other angles away from the main lobe. As the side-lobe measurements were both higher than the model predictions and above the noise floor, the authors noted that the differences were not entirely due to noise. In this study, the accuracy of the DWBA model is further explored. Results indicate that phase variability in the scatter from elements of a discretized-bent cylinder (krill model) causes a dramatic flattening in the side-lobe regions of TS(θ), while negligibly affecting the main scattering lobe. These results are consistent with the krill TS measurements reported by McGehee et al. Thus, by accounting for phase variability in the solution of the DWBA model, a more accurate and thus practical tool is developed for predicting krill TS.

scholarly journals Validation of the stochastic distorted-wave Born approximation model with broad bandwidth total target strength measurements of Antarctic krill

2003 ◽  
Vol 60 (3) ◽  
pp. 625-635 ◽  
Author(s):  
David A. Demer ◽  
Stéphane G. Conti
Keyword(s):  
Born Approximation ◽  
Antarctic Krill ◽  
Target Strength ◽  
Biomass Estimation ◽  
Distorted Wave ◽  
Distorted Wave Born Approximation ◽  
Sound Scattering ◽  
Important Species ◽  
Field Station ◽  
Broad Bandwidth

Abstract Total-scattering cross-sections (σt) of Antarctic krill (Euphausia superba) were measured over a broad bandwidth (36–202 kHz) using a new technique based on acoustical reverberation in a cavity. From 18 February to 9 March 2002, mean total target strengths (TTS = 10 log(σt/4π)), were measured from groups of 57–1169 krill (average standard length=31.6 mm; standard deviation=6.6 mm) at the Cape Shirreff field station, Livingston Island, Antarctica, and aboard RV “Yuzhmorgeologiya”. Chirp pulses were transmitted sequentially by an omni-directional emitter into one of three glass carboys containing groups of krill swimming in 9.3, 19.3, or 45.9 liters of seawater (0.6°C≤temperature≤4.0°C). Between each pulse the krill moved within the fixed-boundary tank and the modulated reverberations were sensed bi-statically with three omni-directional receivers. At each center frequency (fc), the coherent energy in 200-pulse ensembles identified sound scattered by the tank. The incoherent energy described total sound scattering from the krill. Thus, the TTS at each fc was extracted from a correlation analysis of energy reverberated in the tank. Measurement bias was determined to be ±0.4 dB from an experiment using metal sphere reference targets, and the precision was estimated as ±0.8 dB from the variability in the krill TTS (fc) measurements. The empirical estimates of mean σt corroborated a krill-scattering model based on the distorted-wave Born approximation (DWBA), enhanced by the authors to account for the stochastic nature of sound scattering (SDWBA), integrated over all scattering angles and averaged over all incident angles (SDWBATTS). The SDWBA, solved for target strength of Antarctic krill, may be the best predictor of backscatter for this important species and may also provide backscattering spectra for improving their acoustic identification. These advances may help to reduce uncertainty in krill-biomass estimation using multi-frequency echosounder data and echo-integration methods.

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 The target strength of Antarctic krill (Euphausia superba) measured by the split-beam method in a small tank at 70 kHz

2006 ◽  
Vol 63 (1) ◽  
pp. 36-45 ◽  
Author(s):  
Kazuo Amakasu ◽  
Masahiko Furusawa
Keyword(s):  
Antarctic Krill ◽  
Incident Angle ◽  
Euphausia Superba ◽  
Side Lobe ◽  
Target Strength ◽  
Model Predictions ◽  
And Training ◽  
Small Tank ◽  
Antarctic Krill Euphausia Superba ◽  
Good Agreement

Abstract The target strengths (TS) of Antarctic krill (Euphausia superba) were measured at 70 kHz aboard the research and training vessel “Umitaka-maru” of Tokyo University of Marine Science and Technology in February 2003 during a Southern Ocean survey. The systematic variations of TS vs. the incident angle of the ensonified wave, henceforth called TS-patterns, were successfully measured for 12 live Antarctic krill. These measurements were compared with the theoretical TS-patterns predicted by the Distorted-Wave Born Approximation-based deformed-cylinder model (DWBA model). While there was good agreement near the main lobe, the measurements were higher than the model predictions in the side-lobe regions; this is consistent with the observations of others. Several possible causes of this discrepancy such as the bending of abdomen and scattering from pleopods were examined, but no single factor was identified as the cause. Rather, it is likely that the discrepancy is a result of a combination of several factors.

NUCLEAR STRUCTURE OF 99Mo FROM THE (t,p) REACTION

2009 ◽  
Vol 18 (07) ◽  
pp. 1483-1496 ◽  
Author(s):  
M. A. RAHMAN ◽  
M. S. CHOWDHURY
Keyword(s):  
Cross Sections ◽  
Differential Cross ◽  
Born Approximation ◽  
Beam Energy ◽  
Nuclear Emulsion ◽  
Angular Distributions ◽  
Distorted Wave ◽  
Distorted Wave Born Approximation ◽  
Model Predictions ◽  
Atomic Weapon

The 97 Mo (t,p)99 Mo reaction has been studied with the triton beam energy of 12 MeV obtained from tandem Van de Graaff accelerator at the Atomic Weapon Research Establishment, Aldermaston. Proton spectra were obtained at 12 different angles from 5° to 87.5° at an interval of 7.5° and were detected in nuclear emulsion plates. Angular distributions for transitions to 46 levels in the energy range from 0 to 2.054 MeV have been measured. Absolute differential cross-sections for the levels have been measured. The experimental angular distributions are compared with the distorted-wave Born approximation calculations (DWBA) to determine L and Jπ values. The present results are compared with the previous experimental results and model predictions.

scholarly journals Broad-bandwidth, sound scattering, and absorption from krill (Meganyctiphanes norvegica), mysids (Praunus flexuosus and Neomysis integer), and shrimp (Crangon crangon)

2005 ◽  
Vol 62 (5) ◽  
pp. 956-965 ◽  
Author(s):  
Stéphane G. Conti ◽  
David A. Demer ◽  
Andrew S. Brierley
Keyword(s):  
Antarctic Krill ◽  
Euphausia Superba ◽  
Target Strength ◽  
Distorted Wave ◽  
Crangon Crangon ◽  
Distorted Wave Born Approximation ◽  
Sound Scattering ◽  
Broad Bandwidth ◽  
Different Shapes ◽  
Meganyctiphanes Norvegica

Abstract Sound scattering and absorption by Northern krill (Meganyctiphanes norvegica) were measured over the acoustic bandwidth of 30–210 kHz and compared with similar scattering measurements for Antarctic krill (Euphausia superba). The measurements of total target strength (TTS; energy scattered in all directions, averaged over all angles of incidence) match the SDWBA model (stochastic distorted-wave Born approximation) recently developed for Antarctic krill, indicating its validity for other euphausiid species with similar size and shape. However, the TTS of crustaceans with markedly different shapes are not well predicted by SDWBA derived with the generic krill shape and scaled to animal length (L). Therefore, crustacean target strength (TS) may not be estimated accurately by a linear function of log10(L), irrespective of shape, questioning the validity of the current TS relationship used for Antarctic krill derived from data measured from multiple crustaceans. TTS and TS are dependent upon both L and shape, and different crustaceans have significantly different shapes and width-to-length relationships. In contrast, modelled TTS and TS spectra for gravid and non-gravid krill appear to have differing amplitudes, but similar shapes. Additionally, measurements of absorption spectra from decapods indicate that the absorption cross-section increases with the volume of the animal.

A STUDY OF 97Mo FROM THE (t, p) REACTION

2008 ◽  
Vol 17 (06) ◽  
pp. 1141-1156 ◽  
Author(s):  
M. A. RAHMAN ◽  
M. S. CHOWDHURY
Keyword(s):  
Energy Range ◽  
Cross Sections ◽  
Differential Cross ◽  
Born Approximation ◽  
Nuclear Emulsion ◽  
Angular Distributions ◽  
Distorted Wave ◽  
Distorted Wave Born Approximation ◽  
Model Predictions ◽  
Atomic Weapon

The 97 Mo nucleus has been studied with the reaction 95 Mo (t, p) 97 Mo using a multichannel magnetic spectrograph. The isotopically enriched thin target 95 Mo was bombarded with the 12 MeV triton beam obtained from the tandem Van de Graaff accelerator at the Atomic Weapon Research Establishment, Aldermaston. Proton spectra are obtained at 12 different angles from 5° to 87.5° at an interval of 7.5° and are detected in nuclear emulsion plates. Forty-eight levels in the energy range from 0.000 to 3.189 MeV have been observed. Absolute differential cross-sections for these levels have been measured. The angular distributions are compared with the theoretical distorted-wave Born approximation calculations to determine L and Jπ values. The nuclear properties of 97 Mo are compared with previous experimental results and model predictions.

Multi-channel distorted-wave Born approximation for rovibrational transition rates in molecular collisions

2021 ◽  
Vol 155 (3) ◽  
pp. 034105
Author(s):  
Taha Selim ◽  
Arthur Christianen ◽  
Ad van der Avoird ◽  
Gerrit C. Groenenboom
Keyword(s):  
Born Approximation ◽  
Transition Rates ◽  
Distorted Wave ◽  
Distorted Wave Born Approximation ◽  
Molecular Collisions
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