Coastal embayment rotation; morphological response to bi-directional wave climates and atmospheric forcing

Work from Chapter 2 is published in: Wiggins, M.; Scott, T.; Masselink, G.; Russell, P.; McCarroll, R.J., 2019, Coastal embayment rotation: Response to extreme events and climate control, using full embayment surveys. Geomorphology, 327, 385–403. DOI: https://doi.org/10.1016/j.geomorph.2018.11.014 Work from Chapter 3 is published in: Wiggins, M.; Scott, T.; Masselink, G.; Russell, P., Valiente N. G., 2019, Regionally-Coherent Embayment Rotation: Behavioural Response to Bi-Directional Waves and Atmospheric Forcing. Journal of Marine Science and Engineering, 7(4), 116. DOI: https://doi.org/10.3390/jmse7040116 Work from Chapter 4 is published in: Wiggins, M., Scott, T., Masselink, G., McCarroll, R. J., Russell, P., 2020, Predicting beach rotation using multiple atmospheric indices, Marine Geology, 426, 106207. DOI: https://doi.org/10.1016/j.margeo.2020.106207Beach rotation through longshore sediment transport can alter shoreline orientation, increasing erosional risks for coastal communities at short-term (storm events) and decadal to centurial time scales (long-term evolution). Identifying, predicting and planning for embayed beach rotation requires understanding of the morphological response to changes in directional wave climates driven by atmospheric forcing. Through assessment of annual to centurial datasets, this thesis aims to improve understanding of beach rotation at local (embayment) to regional (coastline) extents. The multi-annual rotational response of a 12-km, longshore-dominated gravel embayment (Start Bay, Devon, UK) to a set of extreme and contrasting bi-directional winter wave conditions was assessed using multi-method topo-bathymetric surveys. Previously, the limited extent of intertidal measurements constrained insights into sediment pathways during rotational events; however, this study found that accounting for measurement uncertainty was critical in the calculation of robust total sediment budgets (sub-aerial to sub-tidal), allowing identification of full-embayment rotation. Application of this new methodology revealed that under extreme directional wave energy (>1:50 year southerly winter season), full-embayment rotation (6.5 x 105 m3 transport) is possible through headland bypassing (50% of total) and sub-tidal change (33% of total), providing new insights into sediment transport pathways for gravel beaches. Retrieval of beach volumes after rotational events requires sustained or equal extreme wave energy from opposing directions; however, only sub-embayment rotation was observed (under opposing easterly conditions), proposing that headland bypassing is asymmetrical, extending previously understood timescales of recovery. Analysis of hindcast modelled wave data and a 10-year record of 36 intertidal beach profiles located across the full embayment of Start Bay, revealed that interannual to decadal scale beach rotation may be predicted by a new index of the normalized wave power directional balance (WDI), suggesting that subtle variations in bi-directional wave climate drive sustained changes in beach planform, increasing erosional risk at embayment extremities. Assessment of the modelled wave climate (1980 - 2018) highlighted that the two dominant wave directions (southerly and easterly) are correlated with winter averages of two key climate indices, the North Atlantic Oscillation (NAO) and West Europe Pressure Anomaly (WEPA). This is the first robust demonstration of the relationship between negative NAO and easterly wave power, indicating that atmospheric variability significantly explains the WDI and beach rotation at this location. Spatial expansion of this analysis revealed that bi-directional wave climates are regionally comparable, extending throughout the length of the South coast of England. Similar correlations with both climate indices were exhibited, showing other rotational sites are controlled by the atmospheric influence of bi-directional wave climates. Examination of 10-15 years of intertidal beach profiles at 22 embayed South coast locations identified 11 sites exhibiting significant rotational responses, with regionally coherent common factors, including oblique shoreline orientation to bi-directional wave approach, steep slopes and coarser sediment. Beach rotation was shown to be correlated with the WDI for most sites, and significant direct correlations between beach rotation and WEPA at a number of locations, indicates the future potential skilful forecasts of atmospheric indices may have in predicting seasonal rotation at regional to basin-wide scales. To explore the significance of recent (10-year) beach rotational behaviour in Start Bay within centurial timescales, a stepwise multi-linear regression model was developed to hindcast the WDI using long-term (1906-present) sea-level pressure records of the NAO and WEPA. It was found that combining the two indices vastly improved the predictive skill of the regression model when compared to using individual indices (R2 of 0.66 between model data and index predicted values of the WDI). Qualitative validation of beach rotation in response to the >100-yr hindcast WDI timeseries was achieved from proxy records of oblique photography and topographic maps, finding that low frequency (~60 years) phases of clockwise/anticlockwise beach rotation followed positive/negative phases of the detrended cumulative hindcast WDI record, over the period 1906 to 2018. This variability reflects observed multi-decadal fluctuations in phases of NAO (~60-80 year) and WEPA (~50-60 year), demonstrating atmospheric control of directional wave climate and beach rotation over centurial timescales, explaining historical accounts of coastal settlement relocation. When examined in the context of millennial-scale proxy NAO reconstructions, the recent centurial-scale analysis does not capture the much greater magnitude and duration of past detrended cumulative variability observed over the last 3000 years, indicating that previously inferred phases of extreme coastal realignment may recur in the future, presenting a significant long-term issue for locations affected by beach rotation. This work contributes new insights into embayment rotation at different spatial and temporal scales. Application of a new total sediment budget approach improves knowledge of full embayment rotation and recovery, whilst bi-directional waves are shown to predict beach rotation, driven by atmospheric forcing at medium to longer timescales. This thesis directly contributes towards new understanding of the past and future timescales of beach rotation, as well as proposing a mechanism for season ahead forecasting based on atmospheric variability

AmbiFreeVerb 2—Development of a 3D ambisonic reverb with spatial warping and variable scattering

In this paper the development of a three dimensional Ambisonic reverb based on the open source FreeVerb algorithm will be presented and discussed. This model is then extended to include processing in over-specified A-format, rather than B-format, variable scattering between channels along with controls for warping the distribution of the reflections to implement a reverb that is able to react to the source position in a spatially coherent way with an acoustical analysis of its performance

Exploring Musical Expression on the Web: Deforming, Exaggerating, and Blending Decomposed Recordings

We introduce a prototype of an educational web application for comparative performance analysis based on source separation and object-based audio techniques. The underlying system decomposes recordings of classical music performances into note events using score-informed source separation and represents the decomposed material using semantic web technologies. In a visual and interactive way, users can explore individual performances by highlighting specific musical aspects directly within the audio and by altering the temporal characteristics to obtain versions in which the micro-timing is exaggerated or suppressed. Multiple performances of the same work can be compared by juxtaposing and blending between the corresponding recordings. Finally, by adjusting the timing of events, users can generate intermediates of multiple performances to investigate their commonalities and differences

Unaffiliated Lay Vincentians\u27 Informal Engagement with the Vincentian Mission

In winter 2013, DePaul University’s Office of Mission and Values (OMV) commissioned the Center for Applied Research in the Apostolate (CARA) at Georgetown University to conduct a survey of “unaffiliated lay Vincentians,” that is young adults between the ages of 18 to 35 who have had a formative experience in the Vincentian mission either as a student or as a post-graduate volunteer at a Vincentian institution. The central purpose of this research is to help OMV explore these unaffiliated lay Vincentians’ understanding of their experiences with the Vincentian mission, their commitment to that mission, and their desire for more formation in the Vincentian charism. In collaboration with OMV, CARA designed an online survey with 72 closed-ended and four open-ended questions. The survey asked respondents about their past and current engagement with the Vincentian mission, their understanding of the dimensions of the Vincentian mission, the importance they give to Vincentian values, their interest in learning more about the Vincentian charism, their past and current religiosity and spirituality, and their demographic characteristics. Between February 2014 and May 2014, CARA and OMV distributed a link to the survey to a total of 1,737 men and women that OVM identified as unaffiliated lay Vincentians. A total of 351 men and women (or 20 percent of those who had been sent the survey) completed the questionnaire.https://via.library.depaul.edu/vincentian_ebooks/1022/thumbnail.jp

Note: femtosecond laser micromachining of straight and linearly tapered capillary discharge waveguides

Gas-filled capillary discharge waveguides are important structures in laser-plasma interaction applications, such as the laser wakefield accelerator. We present the methodology for applying femtosecond laser micromachining in the production of capillary channels (typically 200–300 μm in diameter and 30–40 mm in length), including the formalism for capillaries with a linearly tapered diameter. The latter is demonstrated to possess a smooth variation in diameter along the length of the capillary (tunable with the micromachining trajectories). This would lead to a longitudinal plasma density gradient in the waveguide that may dramatically improve the laser-plasma interaction efficiency in applications

WHAM: To Asymmetry and Beyond!

Auralisation of acoustic spaces is a tool used in many industries. To provide a truly representative result, the systems used must capture and deliver critical, dynamic, psychoacoustic cues that react to the listeners head position. The WHAM (Webcam Head-tracked Ambisonics) website (www.brucewiggins.co.uk/WHAM) utilises webcams to provide auralisation that reacts to head rotation via the browser using standard HRTF data; visitors to the site can experience very high order horizontal only Ambisonic to binaural presentation of room responses. In its initial inception, orders were limited to 7th order asymmetry for the final binaural presentation, which previous research has shown to fall below a transparent perceptual threshold compared to orders up to 31st. This paper documents the developments to deliver beyond 7th order and improvements in functionality made to the WHAM website and open-source JS Ambisonics software library, that continue to make it a useful remote resource for acoustic auralisation purposes.N/

The transparency of binaural auralisation using very high order circular harmonics

Ambisonics to binaural rendering has become the de facto format for processing and reproducing spatial sound scenes, but direct capture and software generated output is limited to low orders; limiting the accuracy of psycho-acoustic cues and therefore the illusion of a ‘real-world’ experience. Applying a practical method through the use of acoustic modelling software, this study examines the potential of using very high horizontal only Ambisonic orders (up to 31st) to binaural rendering. A novel approach to the scene capturing process is implemented to realise these very high orders for a reverberant space with head-tracking capabilities. A headphone based subjective test is conducted, evaluating specific attributes of a presented auditory scene to determine when a limit to the perceived auditory differences of varying orders has been reached.N/

WHAM - Webcam Head-tracked AMbisonics

This paper describes the development and implementation of a real-time head-tracked auralisation platform using Higher Order Ambisonics (HOA) decoded binaurally based on open-source and freely available web technologies without the need for specialist head-tracking hardware. An example implementation of this work can be found at https://brucewiggins.co.uk/WHAM/.N/

Room acoustics and virtual reality: An implementation of auralisation and 360 degree image techniques to create virtual representations of spaces

There has been a huge increase in enthusiasm for virtual reality in recent years. Spatial audio is of significant importance when creating virtual reality content if the experience is to be perceptually congruent. This project aims to intersect the worlds of virtual acoustic auralisation and virtual reality, creating a novel method of demonstrating room acoustic environments with maximal audio visual impact in a user friendly fashion. An open source library of 3D impulse responses together with 360° image/video capture using a variety of techniques will be created in different spaces (and positions within). Various spaces will be measured and analysed including classrooms, music venues, buildings of historical interest and theatres. As well as impulse response (IR) measurements, 360° images will be recorded using photospheres, captured on android smart phones [1] and the Ricoh theta S [2]. Future applications for these impulse responses will be the development of a virtual mixing tool, where the user will be able to experience mixing live performances within an auralised virtual environment, a method of allowing audiences to view and hear auralisations of different seating positions within a space for ticketing and marketing purposes, and the possibility of a real time auralised virtual concert.N/

What can an echocardiographer see in briefly presented stimuli? : perceptual expertise in dynamic search

Background: Experts in medical image perception are able to detect abnormalities rapidly from medical images. This ability is likely due to enhanced pattern recognition on a global scale. However, the bulk of research in this domain has focused on static rather than dynamic images, so it remains unclear what level of information that can be extracted from these displays. This study was designed to examine the visual capabilities of echocardiographers—practitioners who provide information regarding cardiac integrity and functionality. In three experiments, echocardiographers and naïve participants completed an abnormality detection task that comprised movies presented on a range of durations, where half were abnormal. This was followed by an abnormality categorization task. Results: Across all durations, the results showed that performance was high for detection, but less so for categorization, indicating that categorization was a more challenging task. Not surprisingly, echocardiographers outperformed naïve participants. Conclusions: Together, this suggests that echocardiographers have a finely tuned capability for cardiac dysfunction, and a great deal of visual information can be extracted during a global assessment, within a brief glance. No relationship was evident between experience and performance which suggests that other factors such as individual differences need to be considered for future studies