Showing papers by "University of Aberdeen published in 2023"

Hierarchical Variation in Phenotypic Flexibility across Timescales and Associated Survival Selection Shape the Dynamics of Partial Seasonal Migration

Abstract: AbstractPopulation responses to environmental variation ultimately depend on within-individual and among-individual variation in labile phenotypic traits that affect fitness and resulting episodes of selection. Yet complex patterns of individual phenotypic variation arising within and between time periods, as well as associated variation in selection, have not been fully conceptualized or quantified. We highlight how structured patterns of phenotypic variation in dichotomous threshold traits can theoretically arise and experience varying forms of selection, shaping overall phenotypic dynamics. We then fit novel multistate models to 10 years of band-resighting data from European shags to quantify phenotypic variation and selection in a key threshold trait underlying spatioseasonal population dynamics: seasonal migration versus residence. First, we demonstrate substantial among-individual variation alongside substantial between-year individual repeatability in within-year phenotypic variation ("flexibility"), with weak sexual dimorphism. Second, we demonstrate that between-year individual variation in within-year phenotypes ("supraflexibility") is structured and directional, consistent with the threshold trait model. Third, we demonstrate strong survival selection on within-year phenotypes-and hence on flexibility-that varies across years and sexes, including episodes of disruptive selection representing costs of flexibility. By quantitatively combining these results, we show how supraflexibility and survival selection on migratory flexibility jointly shape population-wide phenotypic dynamics of seasonal movement.

AI and the Bomb

Abstract: Abstract Will AI make accidental nuclear war more likely? If so, how might these risks be reduced? AI and the Bomb provides a coherent, innovative, and multidisciplinary examination of the potential effects of AI technology on nuclear strategy and escalation risk. The book addresses a gap in the international relations and strategic studies literature that considers how AI might influence nuclear security and future warfare. Its findings have significant theoretical and policy ramifications for using AI technology in the nuclear enterprise. AI and the Bomb advances an innovative theoretical framework to consider AI technology and atomic risk, drawing on insights from political psychology, neuroscience, computer science, and strategic studies. This multidisciplinary study unpacks the seminal cognitive-psychological features of the Cold War-era scholarship, offering a novel explanation for why these matter for AI applications and nuclear strategic thinking; thus ensuring the research’s policy relevance and contribution to the literature that considers the impact of military force and technological change.

Performance‐related pay, mental and physiological health

Abstract: Much of the literature on performance-related pay (PRP) and poor health relies on self-reported data, and the relationship is difficult to examine due to confounding variables. We examine the relationship between PRP and three groups of health measures using data from the UKHLS: blood pressure, inflammation markers in blood, and self-reported health. Regressions correcting for self-selection bias and socio-demographic covariates find that PRP contracts are associated with poorer mental health, higher systolic blood pressure, and higher levels of fibrinogen. These findings suggest that firms that use PRP may need to implement policies to mitigate against PRP-related stress.

Inferring the distributions of fitness effects and proportions of strongly deleterious mutations

Abstract: The distribution of fitness effects is a key property in evolutionary genetics as it has implications for several evolutionary phenomena including the evolution of sex and mating systems, the rate of adaptive evolution, and the prevalence of deleterious mutations. Despite the distribution of fitness effects being extensively studied, the effects of strongly deleterious mutations are difficult to infer since such mutations are unlikely to be present in a sample of haplotypes, so genetic data may contain very little information about them. Recent work has attempted to correct for this issue by expanding the classic gamma-distributed model to explicitly account for strongly deleterious mutations. Here, we use simulations to investigate one such method, adding a parameter (plth) to capture the proportion of strongly deleterious mutations. We show that plth can improve the model fit when applied to individual species but underestimates the true proportion of strongly deleterious mutations. The parameter can also artificially maximize the likelihood when used to jointly infer a distribution of fitness effects from multiple species. As plth and related parameters are used in current inference algorithms, our results are relevant with respect to avoiding model artifacts and improving future tools for inferring the distribution of fitness effects.

Modelling CH4 emission from rice ecosystem: A comparison between existing empirical models

Abstract: Rice is a staple food for more than three billion people and accounts for up to 11% of the global methane (CH 4 ) emissions from anthropogenic sources. With increasing populations, particularly in less developed countries where rice is a major cereal crop, production continues to increase to meet demand. Implementing site-specific mitigation measures to reduce greenhouse gas emissions from rice is important to minimise climate change. Measuring greenhouse gases is costly and time-consuming; therefore, many farmers, supply chains, and scientists rely on greenhouse gas accounting tools or internationally acceptable methodologies (e.g., Intergovernmental Panel on Climate Change) to estimate emissions and explore mitigation options. In this paper, existing empirical models that are widely used have been evaluated against measured CH 4 emission data. CH 4 emission data and management information were collected from 70 peer-reviewed scientific papers. Model input variables such as soil organic carbon (SOC), pH, water management during crop season and pre-season, and organic amendment application were collected and used for estimation of CH 4 emission. The performance of the models was evaluated by comparing the predicted emission values against measured emissions with the result showing that the models capture the impact of different management on emissions, but either under- or overestimate the emission value, and therefore are unable to capture the magnitude of emissions. Estimated emission values are much lower than observed for most of the rice-producing countries, with R correlation coefficient values varying from −0.49 to 0.87 across the models. In conclusion, current models are adequate for predicting emission trends and the directional effects of management, but are not adequate for estimating the magnitude of emissions. The existing models do not consider key site-specific variables such as soil texture, planting method, cultivar type, or growing season, which all influence emissions, and thus, the models lack sensitivity to key site variables to reliably predict emissions.

Being Agile in the Software Engineering Classroom: Using Agile Approaches Instead of Plan-driven Approaches

Abstract: We had an outdated, unsuitable pair of courses covering software engineering over an academic year, which were rewritten last summer. Out went the plan-driven project approach of GANNT charts, and a belief that 'better estimates' would save the day. In came a lightweight focus on a mix of extreme programming and scrum to incrementally, and iteratively build products.

Should Prisoners’ Participation in Neuroscientific Research Always Be Disregarded When Making Decisions About Early Release?

Abstract: This chapter will discuss ethical issues connected with neuroscientific research on prisoners, focusing specifically on whether participating in such research should always be disregarded when making decisions about early release from prison. It was once routine in some jurisdictions for a prisoner’s participation in medical research to count as “good behaviour”, which could be given weight in decisions about early release. However, medical ethicists now widely regard this practice as ethically problematic, because prisoners might feel pressurised to participate in medical research programmes by the desire to escape a coercive and harsh prison environment, and thus their agreement to take part in the programme might not satisfy the freedom requirement for valid consent. Yet, there may be a tension between traditional medical ethics and theories of punishment (a tension which also arises in other contexts at the interface between medicine and punishment). From the perspective of retributive or communication/reform-based theories of punishment, it might seem unfair for parole boards to disregard willingness to participate in medical research, if the prisoner were motivated by altruistic considerations. This altruism might indicate that the prisoner “deserves” a shorter sentence or may be a sign that the prisoner has reformed. This chapter will consider whether/how this tension between traditional medical ethics and penal theories can be resolved. For example, if the medical research involves relatively safe interventions such as fish oil pills or transcranial direct current stimulation (tDCS), then the above-mentioned worries about prisoners’ ability to provide free consent may be less pressing than if the risks of side-effects were greater. Furthermore, the validity of consent also seems to depend partly on whether the prison conditions are humane or excessively harsh. In addition, problems also arise in this context from within penal theories. Ironically, transparency about what factors will be taken into account in decisions about early release, which would presumably be encouraged by communication/reform theories, could raise the possibility that the prisoner was motivated to participate in the research programme by a desire for early release rather than altruism, thus making it harder to determine whether participation is a genuine sign of reform.

Insurgency and national security: a perspective from Cameroon’s separatist conflict

Abstract: This study examines the nature and factors associated with the onset of the conflict in Cameroon’s North West and South West regions to contribute to conceptual, theoretical and methodological debates in war/conflict studies. It used an explorative approach, examining the immediate political tensions prior to hostilities and major government policy areas. It shows that teachers’ and lawyers’ protests (beginning in 2016) and strategic miscalculations by the government and rebels are the immediate factors associated with the onset of the conflict. The underlying factors include greed, colonial heritage, a history of insurgencies, an internal geography conducive to group conflict and guerrilla warfare, poor macroeconomic performance, the ability to finance authoritarianism without relying on taxes, political decay, slow political development, a turbulent regional neighbourhood and unfavourable international relations. The results enable four main contributions to longstanding debates in war/conflict studies. First, an insurgency is a distinct type of war. Second, insurgencies occur due to several immediate and underlying factors unique to each case. Third, studying insurgencies requires a holistic approach, examining immediate and underlying factors. Finally, although rebel victory is impossible in an insurgency, multiple and widespread insurgencies can nullify the essence of a state, making insurgencies important national security threats.

Christian Ethics

Abstract: Abstract The De officiis of Ambrose of Milan (c. 339–397) represents a significant landmark in early Christian ethics for its self-conscious adaptation of Cicero’s De officiis. This chapter considers what Ambrose was seeking to do in evoking Roman moral philosophy, and the relationship between continuity and change in his reconstruction of Ciceronian-Stoic ideals. Ambrose was a natural admirer of Cicero, deeply formed by his legacy. He also aspired to represent Christian virtue as not only matching but exceeding classical standards. In picking up the structure, style, themes, and reasoning of Cicero’s text while suffusing his own approach with biblical and Christian idiom, Ambrose ventured strategic imitation by way of a sustained contrast, seeking to annex but also to replace Ciceronian-Stoic ethics as a practical guide for public figures in a different cultural world. The attempt to supersede was mixed in its results; Roman philosophy inevitably endured in and beyond its creative Christian reception.

New Insights into Underlying Mechanisms of CO2 Wettability and Residual Saturation from Laboratory Measurements of Multi-Phase Zeta Potential in Supercritical CO2-Rock-Brine Systems

Abstract: Measurements of the zeta potential using streaming potential method are frequently used to characterise flows in subsurface settings owing to a broad range of applications of this petrophysical property; examples include CO2 geological storage, hydrocarbon reservoirs, geothermal sources and freshwater aquifers. Many experimental studies of the zeta potential have been carried out covering a wide range of parameters including different rock mineralogy, brine concentration and composition, and temperature to understand the impact of each parameter. The capability of the streaming potential method to be used on intact rock samples, single-/ and multi-phase flows, wide range of salinity, pressure and temperature makes the method suitable for representation of typical subsurface conditions. However, none of previous studies reported high multi-phase measurements at high pressure conditions typical for deep reservoirs. To adequately represent subsurface conditions of carbon geological storage sites, the minimum experimental pressure of 7.38 MPa and minimum temperature of 31 °C, consistent with the supercritical-CO2 (scCO2), need to be used. Obtaining stable measurements of the streaming potential under these conditions is extremely challenging. We report a detailed design of a high-pressure experimental system and experimental protocol for multi-phase streaming potential measurements that were carried out on scCO2-sandstone-brine systems at temperature of 40 °C, pressures ≤10 MPa and with a variety of aqueous solutions.The obtained results demonstrate for the first time that the multi-phase zeta potential correlates with the measured scCO2 residual saturation and rock’s wetting state interpreted from other parameters. Moreover, our results unambiguously identify for the first time the polarity and likely magnitude of the scCO2-brine interfacial zeta potential. Our findings improve the current understanding of the complex wetting behaviour of scCO2 and provide important experimental data for numerical (surface complexation, molecular dynamics), analytical (DLVO) or combined models.

Using modelling and tools for advice on improved agricultural management to achieve climate neutrality in croplands

Abstract: Cropland soils show large potential to sequester carbon to achieve climate neutrality. Changes in management can affect an increase of carbon sequestration or reducing carbon losses in form of emissions or leaching. However, the impact of management changes on the sequestration and other processes needs to be quantified to provide advice to farmers. Experiments to analyse impacts of management changes are costly and labour intensive. Additionally, these experiments take time and cover only a small range of environmental conditions. Therefore, modelling is widely used to over-come these limitations. Model results allow the estimation of all relevant fluxes for the overall greenhouse gas emission balance or, depending on the model, for some parts. This is a fast and efficient method to quantify soil organic carbon (SOC) changes due to modifications in agricultural management. Even though, models proved their quality of simulating SOC changes, there are some restrictions in the use of models for actual advice based on model results. In the here presented study, three key points will be analysed: First, the additional impacts beside the SOC changes. Carbon sequestration can be offset by emission of other greenhouse gases or management changes affect yield, which needs to be included in the analysis. While these two variables are well covered by usual model approaches, other aspects like food quality are more difficult to include. Second, how does the complexity of the model affect the result. The simple assumption that more complex models are potentially more accurate, but also require more input data is in most cases realistic (this is a generic assumption which is not always true). More input data and more complexity are also associated with potentially increased uncertainty. Third, who is running the model. While research-based advice using more complex models might be potentially more accurate, models used by farmers might be more specific and direct in providing key information. Additionally, the impact of the increased data demand and required data can affect an increased error. These points are analysed on examples and case studies. This includes an analysis beyond the carbon sequestration and how to include these aspects in the analysis. Further, results of a tool developed for stakeholders/farmers is compared with results of a biogeochemical model for selected sites. Finally, an analysis of the limitations of the models due to data demand and data availability. The analysis of wheat yields shows mainly positive impacts on the SOC change, but mainly reduced yield. The comparison of the two models indicates the impracticability of the more complex option, as the data demand is not orientated on the data availability. The decision based on model results requires a careful use of models and a good understanding of the results.

Swell ways to measure how plant roots, biological exudates and temporal weathering impact soil structure and infiltration characteristics

Abstract: Time results in large changes to soil infiltration characteristics due to weather, mechanical stability and the action of biology.  Even as the water status changes in a wetting soil, swelling may alter infiltration characteristics. Our laboratory has developed several novel approaches to measure how soil water infiltration characteristics vary over time and are influenced by biological processes or weathering stresses.  The measurements are often combined with an assessment of mechanical properties and pore structure so that underlying processes driving soil structure dynamics can be disentangled. An overview and a discussion of the benefits and challenges of the approaches will be provided.A small-scale infiltrometer (sub-mm size) was adapted to allow for measurements of water infiltration and repellency at aggregate or rhizosphere scale.  It has been applied in numerous studies exploring the impacts of biological exudates, plant roots and weathering.  More recent research has compared results from this infiltrometer with X-Ray CT imaging to determine the impacts of soil pore structure on infiltration characteristics.  A challenge with a small-scale infiltrometer is experimental error caused by tip contact with the soil and the shape of the wetting front.  This has been demonstrated from repeated tests on repacked sands and sieved soils.If soil aggregates, spatial variability or hot spots like the rhizosphere are not of interest, conventional infiltration measurements with flow across the entire surface of a soil core offer less laboratory experimental error.  We used this approach to explore the dynamics of soil wetting and swelling as affected by a range of biological exudates.  Repacked soil discs were wetted by a sintered disc attached to a weighed water reservoir, with swelling measured dynamically in horizontal and vertical directions using infra-red sensors.  Whereas polygalacturonic acid (PGA) had no affect on sorptivity, increasing concentrations of lecithin and actigum decreased sorptivity, likely due to different mechanisms of surface tension and viscosity respectively.  Total swelling was positively correlated with water sorptivity for both lecithin and actigum, suggesting that an expanding pore structure in the unconfined soil discs may enhance water uptake rates.  Biological exudates therefore have dual impacts on decreasing wetting and swelling rates, which will affect soil structural stability.Current research is exploring soil structural stability impacts on soil hydrological properties over time.  This includes field studies exploring the impacts of soil amendments and management practices, and laboratory studies with controlled structural changes from wetting/drying and mechanical stresses.  In this work, changes in water infiltration due to stresses are explained from pore structure analysis with X-Ray CT imaging and mechanical stability tests.

Preliminary results of a thermal maturity modelling study as a tool for understanding a structural setting – the case of the Fold and Thrust Belt of Western Greece.

Abstract: The Hellenides Fold and Thrust Belt (HFTB) is an arcuate shaped belt whose rocks were deposited in a series of platforms and basins that formed the southern rifted margin of the Apulian microcontinent. Despite a renew interest in the last years due to an international licensing round for the exploration and production of hydrocarbons in Greece, still little is published about its geometry, thermal maturity and hydrocarbon generation timing of the main source rocks hosted in the Mesozoic section. The External-most exposed part of the HFTB consists of the pre-Apulian and the Ionian geotectonic zones from West to East. Being part of the southern passive margin of Tethys from Triassic to Late Cretaceous, the Ionian zone represents a sedimentary basin which was differentiated from the adjacent platforms during the Jurassic rifting and consists of Triassic evaporites, Triassic-Eocene carbonates, and Oligocene-Early Miocene turbidites. The Pre-Apulian zone, as part of the slope of the Apulian platform to the Ionian basin, is made up of Triassic evaporites and up to Miocene carbonates. Organic rich layers are found across the Pre-Apulian and Ionian zones, and chiefly within Mesozoic. Present-day geometries have resulted from the mainly thin-skinned Miocene compressional deformation developed after the collision of the Apulian and Eurasian continental paleomargins. To understand the amount of overburden thickness across the chain, we performed Rock-Eval 6 pyrolysis, Gas Chromatography-Mass Spectrometry, MicroRaman spectroscopy and transmitted light petrography on Mesozoic-Cenozoic source rocks across an ENE-WSW transect in Western Greece where westward migrating intra-Ionian imbricate thrusts are evident. Overall, the data suggest that Cenozoic samples are immature, while Lower Cretaceous and Mid-Upper Jurassic thermal maturity reaches the onset of the oil window and further increases in Lower Jurassic and Triassic successions. Maturity data were used as input parameters to 1D thermal maturity modelling of wells and pseudo-wells across this transect. Model calibration by using present-day heat flow values and a Mesozoic rifting model, suggests that the eroded thickness at each studied location exceeds 1.5km. These erosion estimates better constrain our understanding of the geometry of the belt and the timing of maximum burial.

Habits and Reflective Processes in COVID-19 Transmission-reducing Behaviors: Examining Theoretical Predictions in a Representative Sample of the Population of Scotland

Abstract: Abstract Background Based on theory, COVID-19 transmission-reducing behaviors (TRBs) should become habitual because of their frequent performance. Habits have been hypothesized to develop through reflective processes and, to act in conjunction with them. Purpose We investigated the existence, development, and consequences of TRB habits, for physical distancing, handwashing, and wearing face coverings. Methods A representative sample of the Scottish population (N = 1,003) was interviewed by a commercial polling company in August–October 2020 and half were re-interviewed later. Measures included adherence, habit, personal routine tendency, reflective processes, and action control for three TRBs. Data were analyzed using general linear modeling, regression, and mediation analyses. Results Handwashing was most habitual; only face covering became more habitual over time. Routine tendencies predicted TRB habits, and adherence to handwashing and physical distancing. Those reporting greater habits reported better adherence, for physical distancing and handwashing, and this remained true after controlling for previous adherence. Reflective and habit processes independently predicted adherence for physical distancing and handwashing; only reflective processes were independently predictive for face covering. The relationship between planning and forgetting and adherence was partly direct, and partly mediated by habit. Conclusions The results confirm hypotheses from habit theory including the role of repetition and of personal routine tendency in developing habits. They are consistent with dual processing theory in finding that both reflective and habit processes predict adherence to TRBs. Action planning partly mediated the relation between reflective processes and adherence. The COVID-19 pandemic has enabled the testing and confirmation of several theoretical hypotheses about habit processes in the enactment of TRBs.

Contrasting biopore production by deep and shallow rooting rice cultivars in compacted paddy soils and the impacts on subsequent rice growth

Abstract: Rice is often grown as multiple crops in one year, with reduced tillage upland cropping following flooded cropping gaining prominence due to water use, soil degradation and labour demands.  This study explored whether a deep rather than shallow rooting rice cultivar grown in a flooded cropping cycle, benefited deeper root growth of follow-on rice in an upland, reduced tillage cropping cycle. In a greenhouse study, a simulated flooded paddy was planted with deep (Black Gora) and shallow (IR64) root cultivars and a plant-free control.  Artificial plough pans were made in between the topsoil and subsoil to form different treatments with no plough pan (0.35 MPa), soft plough pan (1.03 MPa) and hard plough pan (1.70 MPa). After harvest of this ‘first season’ rice, the soil was drained and undisturbed to simulate zero-tillage upland, with a photoperiod insensitive variety (BRRI Dhan 28) planted. Root length, root surface area, root volume, root diameter, number of root tips and branches were measured.  The number of roots penetrating the plough pan was measured from camera images and X-ray CT. The overall root length density (RLD), root surface area, number of root tips and branching of BRRI Dhan 28 did not vary between plough pan and no plough pan treatments.  Compared to the shallow rooting rice genotype,  the deep rooting rice genotype as a ‘first season’ crop promoted 19 % greater RLD, 34 % greater surface area and 29 % more branching of BRRI Dhan 28 in the subsoil. In the topsoil, however, BRRI Dhan 28 had 28 % greater RLD, 35 % greater surface area and 43 % more branching for the shallow rather deep rooting genotype planted in the ‘first season’.  The results suggest that rice cultivar selection for a paddy cycle affects root growth of a follow-on rice crop grown under no-till, with benefits to subsoil access from deep rooting cultivars and topsoil proliferation for shallow rooting cultivars.

DC-DC Converters for DC Transmission Grids

Abstract: This chapter describes DC-DC converters which are expected to become important components in large DC transmission grids. Similarly as with AC transformers in AC transmission systems, DC-DC converters enable interconnection between two DC systems with different voltage levels. However, some DC-DC converter topologies will provide a range of other functions including breaking DC circuits, power flow control and galvanic isolation. While the description of the DC-DC systems includes many design details, the application of DC-DC converters is still a concept, and the detailed design of these systems needs further in depth studies. The information provided in the chapter focuses on the functional requirements of the DC-DC systems, which are described in significant detail in this chapter. There are two families of DC-DC converters: Non-isolated DC-DC and Isolated DC-DC. Non-Isolated DC-DC is the lowest-cost topology, with the costs and losses expected to be 1.1–1.3 pu relative to a similarly rated single MMC VSC converter. The design, modeling and control of Non-Isolated DC-DC systems are decribed. The responses during DC faults are also analysed in some depth and DC fault simulation results are presented using a typical 600 MW DC-DC test system. The isolated DC-DC will have an internal AC transformer which provides galvanic isolation between two DC systems, while costs and losses are expected to be around 2 pu compared with a similarly rated MMC VSC converter. The design, modeling and control of this DC-DC topology is described based on the application of CIGRE’s DC grid test system. DC fault responses are also analysed and illustrated using simulation responses with a typical 600 MW test system. The DC-DC converter applications for interconnecting high voltage with medium voltage DC systems are also described. This application requires higher voltage step ratio and some specific DC-DC converter topologies are found to be more suitable than others. Typical applications would include interconnection to existing medium voltage DC systems like those with renewable energy plants.

Anhydrous Superprotonic Conductivity in the Zirconium Acid Triphosphate ZrH ₅ (PO ₄ ) ₃ **

Abstract: The development of solid-state proton conductors with high proton conductivity at low temperatures is crucial for the implementation of hydrogen-based technologies for portable and automotive applications. Here, we report on the discovery of a new crystalline metal acid triphosphate, ZrH5(PO4)3 (ZP3), which exhibits record-high proton conductivity of 0.5–3.1×10−2 S cm−1 in the range 25–110 °C in anhydrous conditions. This is the highest anhydrous proton conductivity ever reported in a crystalline solid proton conductor in the range 25–110 °C. Superprotonic conductivity in ZP3 is enabled by extended defective frustrated hydrogen bond chains, where the protons are dynamically disordered over two oxygen centers. The high proton conductivity and stability in anhydrous conditions make ZP3 an excellent candidate for innovative applications in fuel cells without the need for complex water management systems, and in other energy technologies requiring fast proton transfer.

Postscript

Abstract: Abstract What does phenomenology entail for the practice of field research? Is the anthropological method of participant observation, in taking the world as a milieu of study, rather than its object, intrinsically phenomenological? To answer these questions, I describe how in my work as an ecological anthropologist, starting from a perspective rooted in the natural sciences, I eventually found myself, after a detour through ecological psychology, dipping into the writings of first Heidegger and then Merleau-Ponty. Revisiting my fieldnotes, they turn out to serve less as a repository of qualitative data that as an aid to memory, making it possible to relive past experience in the here and now. Rarely had I captured this experience in my notes, which are largely confined to what I had observed or what people had told me. It rather wells up through the cracks in the factual record. But it is not so much in participant observation and writing fieldnotes as in their subsequent writing up as ethnography, that anthropology finally parts company with phenomenology. Truly phenomenological writing, I conclude, differs from conventional ethnography in that it is a writing ‘with’ rather than ‘about’. This means joining our own lines with the writing of the world, so that the minds of readers can, in turn, mingle with ours.

Characterising faults in geothermal fields using surface waves: a numerical study

Abstract: Subsurface characterisation of geothermal fields is important for the expansion of geothermal energy as a low-carbon resource. Faults and fractures provide secondary permeability, thus, their characteristics are crucial parameters in deep geothermal fields. Analysis of ambient seismic noise provides a relatively cheap and widely accessible method for constraining faults and fractures in geothermal settings. Three-component (3C) beamforming is an array-based method that extracts the polarizations, azimuths, and phase velocities of coherent waves as a function of frequency from ambient seismic noise, offering a comprehensive understanding of the seismic wavefield. 3C beamforming can be used to determine surface wave velocities as a function of depth and the direction of propagation of waves. It is assumed that anisotropic velocities relate to the presence of faults, giving an indication of the maximum depth of the permeability essential for fluid circulation and heat flow throughout a geothermal field. Previous results suggests that some structures have a stronger effect on surface wave velocities than others. Numerical models are essential to study these relationships in more detail. Here we present a numerical simulation of wave propagation through a model of the subsurface, with anisotropy depicted as faults. This is employed by a rotated staggered grid (RSG) finite-difference (FD) scheme. We model a homogeneous half-space with a fault-like structure (40 m width), changing fault parameters, such as depth, width, velocities and internal conditions of the fault (“fill”). We generate surface waves from a single source as well as multiple sources emulating an ambient noise wavefield. We then use 3C beamforming on the synthetic data to characterise the modelled wavefield and observe the types of waves present. The polarisation and beam power of the synthetic data denote the composition of the synthetic wavefield and what percentage are retro- and prograde Rayleigh waves and Love waves. To investigate the strength of anisotropy introduced by a single fault we propagate surface waves across the fault in different directions, estimating velocities from array recordings using the beamformer. We are further able to assess the sensitivity of Rayleigh waves towards anisotropy at depth by considering Rayleigh waves at different frequencies sampling different depths.

Ocean color through satellite lidars: the COLOR project

Abstract: During the last decade, new applications exploiting data from satellite borne lidar measurements demonstrated that these sensors can give valuable information about ocean optical properties [1,2,3]. Within this framework, COLOR (CDOM-proxy retrieval from aeOLus ObseRvations) consisted in a 18-month feasibility study approved by ESA within the Aeolus+ Innovation program. COLOR had the objective to evaluate and document the feasibility of deriving an in-water prototype product from the analysis of the signal acquired by the ESA Earth Explorer Wind Mission ADM-Aeolus (Atmospheric Dynamics Mission). In particular, COLOR project focused on the AEOLUS potential retrieval of the diffuse attenuation coefficient for downwelling irradiance (Kd [m-1]) from the ocean sub-surface backscattered component of the 355 nm received lidar signal.The core activity of the project was the characterization of the signal from the AEOLUS ground bin through two parallel and strongly interacting activities: a) Radiative transfer numerical modelling; b) AEOLUS data analysis. The main result of the project will be presented together with the discussion of the perspectives of the satellite lidar missions dedicated to ocean color. [1]  M. J. Behrenfeld et al. (2019). Global satellite-observed daily vertical migrations of ocean animals», Nature, vol. 576, n. 7786, Art. n. 7786, dic. 2019, doi: 10.1038/s41586-019-1796-9.[2] Jamet, C., Ibrahim, A., Ahmad, Z., Angelini, F., Babin, M., Behrenfeld, M. J., et al. (2019). Going beyond standard ocean color observations: lidar and polarimetry. Front. Mar. Sci. 6:251. doi: 10.3389/fmars.2019.00251[3]  D. Dionisi, V. E. Brando, G. Volpe, S. Colella, e R. Santoleri (2020). Seasonal distributions of ocean particulate optical properties from spaceborne lidar measurements in Mediterranean and Black sea», Remote Sens. Environ., vol. 247, pag. 111889, set. 2020, doi: 10.1016/j.rse.2020.111889.