Characterisation of structured surfaces and assessment of associated measurement uncertainty

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonRecently, structured surfaces, consisting of deterministic features designed to produce a particular effect, have shown promise in providing superior functional performance for a range of applications including: low friction surfaces, hydrophobic surfaces and optical effects. Methods have been developed to characterise such structured surfaces. The most widely used characterisation methods are based on segmenting the surface in feature and background regions and then determining the geometrical properties of those features. However, further work is needed to refine these characterisation techniques and provide associated uncertainties. This thesis considers the effect of various segmentation control parameters such as thresholds on the final geometric parameters. The effect of varying filter size is also considered. These considerations should help in selecting a suitable characterisation method for future projects. Additionally, uncertainty in the characterisation should be estimated in order to give an indication of the accuracy of the assessment. However, no previous work has assessed uncertainty in the dimensional properties of structured surfaces. Therefore, this thesis presents two methods to characterise the uncertainty in the geometric characteristics of structured surfaces. First, the measurement reproducibility is used, which can be determined by repeated measurement of a feature. However, measurement reproducibility cannot account for all sources of uncertainty and cannot assess any bias in the measurements. Therefore, a second method based on assessment of the metrological characteristics of the instrument is considered. The metrological characteristics estimate errors produced by the instrument in a way that can easily be measured. Monte Carlo techniques are then used to propagate the effects of the metrological characteristics and their uncertainties into the final measurement uncertainty. For the example used, it was found that the results using the metrological characteristics were in good agreement with the reproducibility results. From these results, it is concluded that the choice of segmentation method, control parameters and filtering can all significantly effect the characterisation of features on a structured surface, often in unexpected ways. Therefore, care must be taken when selecting these values for a specific application. Additionally, two methods of determining the uncertainty of the structured surfaces were considered. Both methods are valid and produce similar results. Using the measurement reproducibility is simple to perform, but requires many measurements and cannot account for some uncertainty sources such as those due to the instrument amplification factors. On the other hand, the use of metrological characteristics can account for all significant sources of uncertainty in a measurement, but is mathematically more complex, requiring Monte Carlo simulations to propagate the uncertainties into the final characteristics. Additionally, other artefacts than the sample being measured are required to determine the metrological characteristics, which may be an issue in some cases

Remote sizing of fish-like targets using broadband acoustics

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Nonlinear crosstalk in broadband multi-channel echosounders

Distortion of acoustic wave caused by nonlinear propagation transfers acoustic energy into higher harmonics of the transmitted signal. When operating several broadband echosounders with non-overlapping frequency bands to cover a wide frequency range, higher harmonics generated by one band may interfere with the fundamental band of others. This interference (i.e., crosstalk) can adversely affect the measured backscattered amplitude frequency response and in some circumstances, appears as spurious targets above and/or below the main target in pulse-compressed echograms. The nonlinear propagation of frequency-modulated acoustic waves in a directional beam was modeled and used to assess methods to reduce the deleterious effects of harmonic components in the signal, and was also compared to field experiments using the seabed echo and a metallic target sphere, with good agreement. Two methods are shown to materially reduce crosstalk: (1) reduction in transmit power, which reduces crosstalk amplitude by a larger amount than the associated reduction in transmit power, and (2) selection of a proper Fourier window length in the processing stage. The effect of crosstalk was small (<0.4 dB or 10%) for area backscattering measurements, but could be several dB for target strength measurements at different frequencies, depending on the transmit signals and processing parameters.acceptedVersio

Study of manufacturing and measurement reproducibility on a laser textured structured surface

In recent years there has been increasing interest in the use of structured surfaces to provide specific functional performance. Such surfaces often consist of localised micro-scale surface features with predetermined geometries. The performance of the feature manufacturing process affects the functional performance of the surface, and can be assessed by measurement of the resulting surface features. Measurement of the resulting micromanufactured surface features necessitates use of areal optical surface topography instruments. However, conventional characterisation methods, based on areal surface texture parameters, often prove inadequate, and may fail to capture the relevant geometric properties needed for an effective dimensional verification. This paper investigates an alternative route to verification, based on the determination of geometric attributes of the microfabricated features. This approach allows for direct assessment of manufacturing process performance, by comparison of the geometric attributes with their nominal values. An example application is shown in which a micromachining process (laser texturing) is used to fabricate a periodic pattern of dimples, which provide a low friction bearing surface. In this paper, manufacturing process performance is assessed by characterisation of the diameter and out-of-roundness. Sources of uncertainty associated with these geometric parameters are also considered

Antarctic krill (Euphausia superba) catch weight estimated with a trawl-mounted echosounder during fishing

Reporting reliable catch weight estimates is important for all fisheries management. This study explores the potential for precise and direct estimation of catch weight (green weight) for the Antarctic krill (Euphausia superba) fishery by employing a high frequency acoustic sensor in the trawl. Trials were performed off the coast of the South Orkney Islands during February 2020 using a scientific macroplankton trawl and echosounder providing a 18° beam pointing downwards across the fishing circle at the trawl mouth. The acoustically estimated catch weight and the observed catch weight had a linear relationship (R2 = 0.87, F(1,10) = 69.6, p < 0.000) where the acoustically estimated catch weight significantly predicted actual catch weight (β = 1.20, p = 0.000). The acoustic vertical densities of krill increased toward the center of the trawl opening suggesting that krill were herded during fishing. The current study demonstrates that acoustically based catch weight monitoring has the potential to be used for reporting total krill catch weight in each trawl, potentially in real-time, and that similar methods could also be employed in similar types of trawl fisheries.publishedVersio

Acoustic manual for the krill synoptic survey in 2019

The previously presented document at the 2018 ASAM WG meeting (ASAM-18-07) described a design and plans for a synoptic krill acoustic survey in CCAMLR area 48 in 2019. The survey involves the collaborative efforts of Norway, Association of Responsible Krill fishing companies (ARK: companies from Norway, Korea, China and Chile), the United Kingdom, Ukraine, Korea and China, all of whom have confirmed a commitment of survey ship time. With these commitments it is feasible to implement all transects occupied during the 2000 survey. This document is a draft survey manual, produced at the recommendation of the 2018 ASAM meeting, and describes acoustic procedures, acoustic reporting - analysis procedures and contingency plans.Acoustic manual for the krill synoptic survey in 2019publishedVersio

Multinational large scale krill synoptic survey in CCAMLR Area 48 in 2019-survey plan and protocol for consideration by SG-ASAM 2018

The objective for the Multinational Large-Scale Krill Synoptic Survey in CCAMLR area 48 3 in 2019 is to provide an updated estimate of the biomass of Antarctic krill (Euphausia 4 superba) used in models to estimate sustainable yield. The planned survey follows, as close 5 as possible, the design of the CCAMLR 2000 survey, that was undertaken in the year 2000. 6 The basis for comparisons will depend on the degree of coverage and methodology and 7 equipment available. The survey will involve the collaborative efforts of Norway, 8 Association of Responsible Krill fishing companies (ARK: companies from Norway, Korea, 9 China and Chile), United Kingdom, Ukraine, Korea and China, and hopefully also other 10 nations that still needs to confirm their participation. 11 The current survey plan organization is presented for consideration by SG-ASAM. Norway 12 has volunteered to co-ordinate the survey with other members dedicating personnel to 13 specific tasks. It is requested that members who has already made commitments on ship time, 14 also allocate contact personnel as proposed. 15 This paper has been developed after a wider consultation extending beyond the authors list. It 16 discusses some specific organizational and technical challenges to be considered by SG17 ASAM. We request advice from ASAM on “minimum requirements” regarding acoustic 18 instrumentation and sampling gear to achieve approximate consistency with the CCAMLR 19 B0 data collection protocol.Multinational large scale krill synoptic survey in CCAMLR Area 48 in 2019-survey plan and protocol for consideration by SG-ASAM 2018publishedVersio

An acoustic method to observe the distribution and behaviour of mesopelagic organisms in front of a trawl

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Akustisk fangstovervåking i not – Utfordringer og løsningsforslag til bedre metodikk

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Estimating target strength and physical characteristics of gas-bearing mesopelagic fish from wideband in situ echoes using a viscous-elastic scattering model

Wideband (38 and 50–260 kHz) target strength of organisms were measured in situ using a towed platform in mesopelagic (200–1000 m depth) layers. Organisms with a gas-inclusion are strong scatterers of sound and acoustically distinct from organisms lacking one. In the mesopelagic zone, some of the fish species and physonect siphonophores have a gas-inclusion. Trawl and multinet biological sampling as well as photographic evidence indicate that in the study area (eastern mid-Atlantic Ocean) the majority of the gas-bearing organisms were fish. Subsequently, using a two-layer viscous-elastic spherical gas backscattering model, physical characteristics such as gas-bladder features and body flesh properties were deduced from the measured backscattering signal of individual gas-bearing fish. Acoustic techniques are non-extractive, can be used for the monitoring and quantification of marine organisms in a time- and cost-effective manner, and suit studies of the mesopelagic zone, which is logistically challenging. Vessel-mounted acoustics, widely used for epipelagic studies, has limitations for mesopelagic studies as the deep organisms are inaccessible to high-frequency (≳100 kHz) acoustic pulses transmitted from the surface due to absorption. Therefore, a towed platform equipped with wideband acoustics has several features that can be utilized for monitoring the mesopelagic dense scattering layers containing mixed species.publishedVersio