A comparison of underwater visual distance estimates made by scuba divers and a stereo-video system: Implications for underwater visual census of reef fish abundance

Underwater visual census of reef fish by scuba divers is a widely used and useful technique for assessing the composition and abundance of reef fish assemblages, but suffers from several biases and errors. We compare the accuracy of underwater visual estimates of distance made by novice and experienced scientific divers and an underwater stereo-video system. We demonstrate the potential implications that distance errors may have on underwater visual census assessments of reef fish abundance. We also investigate how the accuracy and precision of scuba diver length estimates of fish is affected as distance increases. Distance was underestimated by both experienced ( mean relative error = -11.7%, s.d. = 21.4%) and novice scientific divers (mean relative error = -5.0%, s. d. =17.9%). For experienced scientific divers this error may potentially result in an 82% underestimate or 194% overestimate of the actual area censused, which will affect estimates of fish density. The stereo-video system also underestimated distance but to a much lesser degree (mean relative error = -0.9%, s.d. = 2.6%) and with less variability than the divers. There was no correlation between the relative error of length estimates and the distance of the fish away from the observer

Optimised multi-camera systems for dimensional control in factory environments

As part of the United Kingdom’s Light Controlled Factory project, University College London aims to develop a large-scale multi-camera system for dimensional control tasks in manufacturing, such as part assembly and tracking. Accuracy requirements in manufacturing are demanding, and improvements in the modelling and analysis of both camera imaging and the measurement environment are essential. A major aspect to improved camera modelling is the use of monochromatic imaging of retro-reflective target points, together with a camera model designed for a particular illumination wavelength. A small-scale system for laboratory testing has been constructed using eight low-cost monochrome cameras with C-mount lenses on a rigid metal framework. Red, green and blue monochromatic light-emitting diode ring illumination has been tested, with a broadband white illumination for comparison. Potentially, accuracy may be further enhanced by the reduction in refraction errors caused by a non-homogeneous factory environment, typically manifest in varying temperatures in the workspace. A refraction modelling tool under development in the parallel European Union LUMINAR project is being used to simulate refraction in order to test methods which may be able to reduce or eliminate this effect in practice

Towards automating underwater measurement of fish length: a comparison of semi-automatic and manual stereo–video measurements

Underwater stereo–video systems are widely used for counting and measuring fish in aquaculture, fisheries, and conservation management. Length measurements are generated from stereo–video recordings by a software operator using a mouse to locate the head and tail of a fish in synchronized pairs of images. This data can be used to compare spatial and temporal changes in the mean length and biomass or frequency distributions of populations of fishes. Since the early 1990s stereo–video has also been used for measuring the lengths of fish in aquaculture for quota and farm management. However, the costs of the equipment, software, the time, and salary costs involved in post processing imagery manually and the subsequent delays in the availability of length information inhibit the adoption of this technology. We present a semi-automatic method for capturing stereo–video measurements to estimate the lengths of fish. We compare the time taken to make measurements of the same fish measured manually from stereo–video imagery to that measured semi-automatically. Using imagery recorded during transfers of Southern Bluefin Tuna (SBT) from tow cages to grow out cages, we demonstrate that the semi-automatic algorithm developed can obtain fork length measurements with an error of less than 1% of the true length and with at least a sixfold reduction in operator time in comparison to manual measurements. Of the 22 138 SBT recorded we were able to measure 52.6% (11 647) manually and 11.8% (2614) semi-automatically. For seven of the eight cage transfers recorde,d there were no statistical differences in the mean length, weight, or length frequency between manual and semi-automatic measurements. When the data were pooled across the eight cage transfers, there was no statistical difference in mean length or weight between the stereo–video-based manual and semi-automated measurements. Hence, the presented semi-automatic system can be deployed to significantly reduce the cost involved in adoption of stereo–video technology

Drug cryptomarket futures:Structure, function and evolution in response to law enforcement actions

Since cryptomarkets came into public purview in 2011, they have provided some excellent lessons for how the disruptive potential of technology can interact with the drugs trade. Over the last eight years, cryptomarkets have evolved quickly in the face of internal threats posed by malicious actors within their community and the external threat of law enforcement action. Current policy approaches favour disrupting the cryptomarket trade in much the same way as offline drugs markets to further prohibitionist objectives, yet such action seems premature given that the emerging body of evidence suggests differentials in harms and benefits unique to cryptomarkets in comparison to real-world drug markets. This chapter provides an over- view of cryptomarkets and how they have evolved since their inception, as well as how law enforcement tactics have changed over time. We shall consider whether cryptomarkets have the potential to change the global drug markets, and what impacts, if any, they might have on violence, pricing and drug purity. We will also examine the possibilities of harms and benefits that cryptomarkets bring to the global trade in drugs, and these will be shown to be ambiguous and interconnected. We conclude with some concerns about the trajectory of current policy responses to cryptomarkets, and the uncertain and possibly harmful outcomes that may result

Orthographic practices in SMS text messaging as a case signifying diachronic change in linguistic and semiotic resources

From 1998, SMS text messaging diffused in the UK from an innovation associated with a small minority, mainly adolescents, to a method of written communication practised routinely by people of all ages and social profiles. From its earliest use, and continuing to the time of writing in 2015, SMS texting has attracted strong evaluation in public sphere commentary, often focused on its spelling. This thesis presents analysis of SMS orthographic choice as practised by a sample of adolescents and young adults in England, with data collected between 2000 and 2012. A threelevel analytical framework attends to the textual evidence of SMS orthographic practices in situated use; respondents’ accounts of their choices of spelling in text messaging as a literacy practice; and the metadiscursive evaluation of text messaging spelling in situated interaction and in the public sphere. I present analysis of a variety of representations of SMS orthographic choice, including facsimile texts, electronic corpus data, questionnaire survey responses and transcripts of recorded interviews. This mixed methods empirical approach enables a cross-verified, longitudinal perspective on respondents’ practices, and on the wider significance of SMS orthographic choice, as expressed in private and public commentary. I argue that the spelling used in SMS exemplifies features, patterns, and behaviours, which are found in other forms of digitally-mediated interaction, and in previous and concurrent vernacular literacy practices. I present SMS text messaging as one of the intertextually-related forms of self-published written interaction which mark a diachronic shift towards re-regulated forms of orthographic convention, so disrupting attitudes to standard English spelling. I consider some implications represented by SMS spelling choice for the future of written conventions in standardised English, and for teaching and learning about spelling and literacy in formal educational settings