Sedimentary facies characterization through CPTU profiles: An effective tool for subsurface investigation of modern alluvial and coastal plains

Cone penetration tests, a method that is typically used to determine the engineering properties of soils, can be used as an effective tool for refined subsurface stratigraphic investigations of alluvial and coastal plains, aside from the geographic location. High-resolution calibration of piezocone penetration tests (CPTU) with 20 sediment cores enabled the detailed characterization of alluvial, deltaic and coastal depositional systems of the Po Plain. Twelve cored facies associations, typical of alluvial and coastal plain environments, were characterized based on four distinct CPTU profiles: basic cone resistance (Qc), sleeve friction (Fs), water pore pressure (U) and friction ratio (FR). Sandy facies associations (fluvial/distributary channel, bay-head delta, transgressive barrier, delta-front/beach-ridge) typically have high (>4 MPa) Qc, low-to-negative U and low (<2%) FR. Muddy deposits (well-drained/poorly-drained floodplain, swamp, lagoon and prodelta) exhibit opposite trends. Heterolithic facies associations (crevasse-levee, offshore/delta-front transition) display characteristic seesaw profiles. Plotting of late Quaternary deposits onto the latest version of the cone penetration test typical soil behaviour chart (Robertson, 2010) enables the identification of distinctive facies associations reflecting distinctive grain size. CPTU interpretation leads to sedimentary facies recognition well beyond the simple lithological differentiation and, in particular, allows the refined characterization of clay-rich and silt-rich depositional units (swamp clays and peats, central-inner and outer lagoon, proximal/distal prodelta deposits) that exhibit only subtle differences in lithology. CPTU data can also serve for the accurate detection of key stratigraphic surfaces with potential engineering applications, such as the Pleistocene-Holocene boundary. This latter, a common feature of several alluvial and coastal plain successions, is commonly marked by an abrupt upward decrease of basic cone resistance and sleeve friction from Late Pleistocene, pedogenized, stiff strata to overlying Holocene, organic-rich, soft deposits. This study offers an updated CPTU-facies characterization method that could be suitable for subsurface investigations of modern alluvial and coastal plains worldwide

Timing and mechanisms of sediment accumulation and pedogenesis: Insights from the Po Plain (northern Italy)

The relationships between pedogenetic processes and fluvial-coastal dynamics in the Po Plain have been reconstructed through sedimentological analysis and correlation of ca. 170 core data chronologically constrained by 376 radiocarbon dates. Vertically stacked, weakly developed paleosols within Upper Pleistocene and Holocene mud-prone strata testify to intermittent pedogenesis, periodically interrupted by overbank sedimentation. Individual paleosols are laterally traceable for tens of km and exhibit A-Bk-Bw, A-Bk or A-Bw profiles. Strati graphically ordered 14C calibrated ages from A organo-mineral horizons testify to slow aggradation during 4-6 thousand years-long exposure periods. Burial ages, with an error of few centuries, are provided by plant debris at the top of A horizons.Millennial-scale climate oscillations and glacio-eustasy are the main drivers of the pedo-sedimentary evolution of the area during the last 50 kyr. Upper Pleistocene paleosols (P1-P3) developed in well-drained floodplain environments, during relatively warm periods.Paleosol burial occurred during colder phases. High-sediment supply during the Last Glacial Maximum hindered pedogenesis and led to the accumulation of 3-10 m-thick overbank strata. Widespread soil development (paleosol PH) occurred at the end of Last Glacial Maximum, following the retreat of Alpine glaciers and the afforestation of Apennine drainage basins. At distal locations, paleosol PH was progressively buried under estuarine sediments during the Holocene phases of post-glacial sea level rise. Beyond the area of marine influence, burial ages of paleosol PH change from a place to another without specific spatial trends and reflect upstream fluvial sedimentation dominated by avulsions and deposition of spatially restricted alluvial units. Holocene (H1-H2) paleosols show a poor correlation potential and laterally variable degree of maturity that reflect avulsive sedimentation patterns and crevassing. This paper provides insights on the timing and mechanisms of formation and burial of weakly-developed paleosols. The outcomes of this research are applicable to similar Quaternary alluvial systems, and may help interpreting ancient paleosolbearing successions

Palynological characterization of the Po delta succession (northern Italy): Holocene vegetation dynamics, stratigraphic patterns and palaeoclimate variability

The 40 m-long core EM2, recovered in the innermost portion of Po delta plain, was sampled for palynological analysis, in order to link coastal-deltaic facies architecture to vegetation dynamics and Holocene climate variability. Pollen data refine facies characterization of the 25 m-thick Holocene succession: freshwater swamp clays alternating with overbank/channel sands document millennial to centennial-scale water table oscillations that invariably peak in correspondence of peaty layers. Pollen signature allows identification of the landward equivalent of the Maximum Flooding Surface atop the 7.6 ka-dated peaty interval and furnishes new insights on the relationship between coastal facies patterns and climate events

The Pleistocene-Holocene Transition in the Po Plain (Italy): Stratigraphic Architecture and Sequence Stratigraphy from a Highly-Subsiding Basin

This work focuses on the Late Pleistocene-Holocene transition in the southern Po Basin. Five areas were investigated, with the aim of unraveling the role of different allogenic factors (climate, eustacy, sediment supply) on stratigraphic architecture in the last 45 ky. The study starts from the distal portion of the basin (the coastal plain deposits) and then moves towards increasingly internal areas: the alluvial sector characterized by the Po channel belt deposits, and the mud-prone interfluvial succession between the Apenninic margin and the Po channel belt. In the coastal sector, high-resolution facies analysis, along with a well-constrained chronostratigraphic framework, led to the accurate paleoenvironmental reconstruction of the last 45 ky BP depositional history along the 93 km-long transect. It is also provided a sequence stratigraphic interpretation for the whole sedimentary succession. In the Po channel belt sector, based on 28 radiocarbon dates, facies interpretation from high-quality core descriptions and freshly-drilled continuous cores, the contrasting stratigraphic architecture of Late Pleistocene and Holocene deposits was highlighted. Changes in lithofacies and channel stacking patterns reveal the vertical superposition of amalgamated fluvial-channel sands (Late Pleistocene) and mud-dominated deposits (Holocene), with isolated fluvial-channel bodies. We also attempted to establish the link between facies architecture, sea-level fluctuations and climate changes. The 3rd study area (interfuvial succession) was selected to test a new method for paleosol identification, on the basis of geotechnical properties generated from pocket penetrometer values. Through the reconstruction of the Biferno coastal deposits (4th study area, located ca. 300 km south of the Po Plain) we had the opportunity to document two coeval (Late Pleistocene - Holocene) coastal sedimentary successions, diverging in terms of shelf gradient and proximity to the LGM-lowstand Po Delta. The 5th study area, broadly coincides with Ferrara, was selected to show how high-resolution stratigraphic studies can be used for aquifer protection

10B4C Multi-Grid as an alternative to 3He for Large Area Neutron Detectors

Despite its present shortage, 3He continues to be the most common neutron converter for detectors in neutron scattering science. However, it is obvious that the development of large area neutron detectors based on alternative neutron converters is rapidly becoming a matter of urgency. In the technique presented, grids each comprising 30 10B4C layers (each 1 µm thick) are used to convert neutrons into ionising particles which are subsequently detected in proportional gas counters. Several prototypes, the largest with a total active area of 8 cm x 200 cm, were tested. Up to 4.6 m2 of 10B-enriched boron carbide were coated onto aluminium blades using a DC magnetron sputtering machine. Characterisation of the prototype showed neutron efficiency to be n = 53.04% for 2.5 A neutrons, which is in line with expectations from MC simulation. Gamma-sensitivity = 5 · 10-5 was measured for a broad range of energies. Long term stability measurements were also performed. These results demonstrate the potential of this technique as alternative to 3He-based position sensitive detectors

Factors controlling natural subsidence in the Po Plain

Understanding the causes and mechanisms of land subsidence is crucial, especially in densely populated coastal plains. In this work, we calculated subsidence rates (SR) in the Po coastal plain, averaged over the last 5.6 and 120 kyr, providing information about land movements on intermediate (103–105 years) time scales. The calculation of SR relied upon core-based correlation of two lagoon horizons over tens of km. Subsidence in the last 120 kyr appears to be controlled mainly by the location of buried tectonic structures, which in turn controlled sedimentation rates and location of highly compressible depositional facies. Numerical modelling shows that subsidence in the last 5.6 kyr is mainly due to compaction of the Late Pleistocene and Holocene deposits (uppermost 30 m)

Learning the surroundings: 3D scene understanding from omnidirectional images

Las redes neuronales se han extendido por todo el mundo, siendo utilizadas en una gran variedad de aplicaciones. Estos métodos son capaces de reconocer música y audio, generar textos completos a partir de ideas simples u obtener información detallada y relevante de imágenes y videos. Las posibilidades que ofrecen las redes neuronales y métodos de aprendizaje profundo son incontables, convirtiéndose en la principal herramienta de investigación y nuevas aplicaciones en nuestra vida diaria. Al mismo tiempo, las imágenes omnidireccionales se están extendiendo dentro de la industria y nuestra sociedad, causando que la visión omnidireccional gane atención. A partir de imágenes 360 capturamos toda la información que rodea a la cámara en una sola toma.La combinación del aprendizaje profundo y la visión omnidireccional ha atraído a muchos investigadores. A partir de una única imagen omnidireccional se obtiene suficiente información del entorno para que una red neuronal comprenda sus alrededores y pueda interactuar con el entorno. Para aplicaciones como navegación y conducción autónoma, el uso de cámaras omnidireccionales proporciona información en torno del robot, person o vehículo, mientras que las cámaras convencionales carecen de esta información contextual debido a su reducido campo de visión. Aunque algunas aplicaciones pueden incluir varias cámaras convencionales para aumentar el campo de visión del sistema, tareas en las que el peso es importante (P.ej. guiado de personas con discapacidad visual o navegación de drones autónomos), un número reducido de dispositivos es altamente deseable.En esta tesis nos centramos en el uso conjunto de cámaras omnidireccionales, aprendizaje profundo, geometría y fotometría. Evaluamos diferentes enfoques para tratar con imágenes omnidireccionales, adaptando métodos a los modelos de proyección omnidireccionales y proponiendo nuevas soluciones para afrontar los retos de este tipo de imágenes. Para la comprensión de entornos interiores, proponemos una nueva red neuronal que obtiene segmentación semántica y mapas de profundidad de forma conjunta a partir de un único panoramaequirectangular. Nuestra red logra, con un nuevo enfoque convolucional, aprovechar la información del entorno proporcionada por la imagen panorámica y explotar la información combinada de semántica y profundidad. En el mismo tema, combinamos aprendizaje profundo y soluciones geométricas para recuperar el diseño estructural, junto con su escala, de entornos de interior a partir de un único panorama no central. Esta combinación de métodos proporciona una implementación rápida, debido a la red neuronal, y resultados precisos, gracias a lassoluciones geométricas. Además, también proponemos varios enfoques para la adaptación de redes neuronales a la distorsión de modelos de proyección omnidireccionales para la navegación y la adaptación del dominio soluciones previas. En términos generales, esta tesis busca encontrar soluciones novedosas e innovadoras para aprovechar las ventajas de las cámaras omnidireccionales y superar los desafíos que plantean.Neural networks have become widespread all around the world and are used for many different applications. These new methods are able to recognize music and audio, generate full texts from simple ideas and obtain detailed and relevant information from images and videos. The possibilities of neural networks and deep learning methods are uncountable, becoming the main tool for research and new applications in our daily-life. At the same time, omnidirectional and 360 images are also becoming widespread in industry and in consumer society, causing omnidirectional computer vision to gain attention. From 360 images, we capture all the information surrounding the camera in a single shot. The combination of deep learning methods and omnidirectional computer vision have attracted many researchers to this new field. From a single omnidirectional image, we obtain enough information of the environment to make a neural network understand its surroundings and interact with the environment. For applications such as navigation and autonomous driving, the use of omnidirectional cameras provide information all around the robot, person or vehicle, while conventional perspective cameras lack this context information due to their narrow field of view. Even if some applications can include several conventional cameras to increase the system's field of view, tasks where weight is more important (i.e. guidance of visually impaired people or navigation of autonomous drones), the less cameras we need to include, the better. In this thesis, we focus in the joint use of omnidirectional cameras, deep learning, geometry and photometric methods. We evaluate different approaches to handle omnidirectional images, adapting previous methods to the distortion of omnidirectional projection models and also proposing new solutions to tackle the challenges of this kind of images. For indoor scene understanding, we propose a novel neural network that jointly obtains semantic segmentation and depth maps from single equirectangular panoramas. Our network manages, with a new convolutional approach, to leverage the context information provided by the panoramic image and exploit the combined information of semantics and depth. In the same topic, we combine deep learning and geometric solvers to recover the scaled structural layout of indoor environments from single non-central panoramas. This combination provides a fast implementation, thanks to the learning approach, and accurate result, due to the geometric solvers. Additionally, we also propose several approaches of network adaptation to the distortion of omnidirectional projection models for outdoor navigation and domain adaptation of previous solutions. All in all, this thesis looks for finding novel and innovative solutions to take advantage of omnidirectional cameras while overcoming the challenges they pose.<br /

Ground-based observability of Dimorphos DART impact ejecta: Photometric predictions

The Double Asteroid Redirection Test (DART) is a NASA mission intended to crash a projectile on Dimorphos, the secondary component of the binary (65803) Didymos system, to study its orbit deflection. As a consequence of the impact, a dust cloud will be be ejected from the body, potentially forming a transient coma- or comet-like tail on the hours or days following the impact, which might be observed using ground-based instrumentation. Based on the mass and speed of the impactor, and using known scaling laws, the total mass ejected can be roughly estimated. Then, with the aim to provide approximate expected brightness levels of the coma and tail extent and morphology, we have propagated the orbits of the particles ejected by integrating their equation of motion, and have used a Monte Carlo approach to study the evolution of the coma and tail brightness. For typical power-law particle size distribution of index --3.5, with radii r$_{rmin}$=1 $\mu$m and r$_{max}$=1 cm, and ejection speeds near 10 times the escape velocity of Dimorphos, we predict an increase of brightness of $\sim$3 magnitudes right after the impact, and a decay to pre-impact levels some 10 days after. That would be the case if the prevailing ejection mechanism comes from the impact-induced seismic wave. However, if most of the ejecta is released at speeds of the order of $\gtrsim$100 $\mathrm{m\; s^{-1}}$, the observability of the event would reduce to a very short time span, of the order of one day or shorter.Comment: Accepted by MNRAS, June 30, 202

Lofting of low speed ejecta produced in the DART experiment and production of a dust cloud

NASA sent the DART (Double Asteroid Redirection Test) mission to impact Dimorphos, the satellite of the asteroid binary system (65803) Didymos. DART will release LICIACube prior to impact to obtain high-resolution post-impact images. The impact will produce a crater and a large amount of material ejected at high speed (several tens of m/s), producing an ejecta cone that will quickly disperse. We analyzed an additional effect: the lofting of material at low velocity due to the generation of seismic waves that propagate inside Dimorphos, producing surface shaking far from the impact point. We divide the process into different stages: from the generation of impact-induced waves, the interaction of them with surface particles, the ejection of dust particles at velocities, and the prediction of the observability of the dust coma and trail. We anticipate the following observable effects: i) generation of a dust cloud that will produce a hazy appearance of Dimorphos' surface, detectable by LICIACube; ii) brightness increase of the binary system due to enhancement of the cross section produced by the dust cloud; iii) generation of a dust trail, similar to those observed in some Active Asteroids, which can last for several weeks after impact. Numerical prediction of the detectability of these effects depends on the amount and size distribution of ejected particles, which are largely unknown. In case these effects are observable, an inversion method can be applied to compute the amount of ejected material and its velocity distribution, and discuss the relevance of the shaking process.Comment: 12 pages, 13 figure

Idades U-Pb de zircões nas areias quaternárias do Algarve

O objectivo deste trabalho é realçar e quantificar a contribuição das variações geomorfológicas nas modificações da rede de drenagem através de datações de minerais detríticos que permitam a caracterização de fontes de sedimentos desde o Pliocénico