Weather Influence and Classification with Automotive Lidar Sensors

Lidar sensors are often used in mobile robots and autonomous vehicles to complement camera, radar and ultrasonic sensors for environment perception. Typically, perception algorithms are trained to only detect moving and static objects as well as ground estimation, but intentionally ignore weather effects to reduce false detections. In this work, we present an in-depth analysis of automotive lidar performance under harsh weather conditions, i.e. heavy rain and dense fog. An extensive data set has been recorded for various fog and rain conditions, which is the basis for the conducted in-depth analysis of the point cloud under changing environmental conditions. In addition, we introduce a novel approach to detect and classify rain or fog with lidar sensors only and achieve an mean union over intersection of 97.14 % for a data set in controlled environments. The analysis of weather influences on the performance of lidar sensors and the weather detection are important steps towards improving safety levels for autonomous driving in adverse weather conditions by providing reliable information to adapt vehicle behavior.Comment: 8 pages, will be published in the IEEE IV 2019 Proceeding

Imaging through obscurants using time-correlated single-photon counting in the short-wave infrared

Single-photon time-of-flight (ToF) light detection and ranging (LiDAR) systems have emerged in recent years as a candidate technology for high-resolution depth imaging in challenging environments, such as long-range imaging and imaging in scattering media. This Thesis investigates the potential of two ToF single-photon depth imaging systems based on the time-correlated single-photon (TCSPC) technique for imaging targets in highly scattering environments. The high sensitivity and picosecond timing resolution afforded by the TCSPC technique offers high-resolution depth profiling of remote targets while maintaining low optical power levels. Both systems comprised a pulsed picosecond laser source with an operating wavelength of 1550 nm, and employed InGaAs/InP SPAD detectors. The main benefits of operating in the shortwave infrared (SWIR) band include improved atmospheric transmission, reduced solar background, as well as increased laser eye-safety thresholds over visible band sensors. Firstly, a monostatic scanning transceiver unit was used in conjunction with a single-element Peltier-cooled InGaAs/InP SPAD detector to attain sub-centimetre resolution three-dimensional images of long-range targets obscured by camouflage netting or in high levels of scattering media. Secondly, a bistatic system, which employed a 32 × 32 pixel format InGaAs/InP SPAD array was used to obtain rapid depth profiles of targets which were flood-illuminated by a higher power pulsed laser source. The performance of this system was assessed in indoor and outdoor scenarios in the presence of obscurants and high ambient background levels. Bespoke image processing algorithms were developed to reconstruct both the depth and intensity images for data with very low signal returns and short data acquisition times, illustrating the practicality of TCSPC-based LiDAR systems for real-time image acquisition in the SWIR wavelength region - even in the photon-starved regime.The Defence Science and Technology Laboratory ( Dstl) National PhD Schem

Advanced manufacturing techniques for X-ray and VHE gamma-ray astronomical mirrors.

The main theme of this thesis is on the development of the technologies for the future X-ray astronomy telescopes and specifically for the New Hard X-ray Mission and eROSITA (Spectrum-RG) missions. Other important next future X-ray missions, currently under advanced study and/or manufacturing are NuSTAR (USA), ASTRO-H (Japan) and GEMS (USA). The New Hard X-ray Mission (NHXM) is being developed in Italy as an evolution of the original HEXIT-SAT project and is now the hard x-ray project of reference for the Italian high energy community. NHXM is meant to provide a real breakthrough on a number of hot astrophysical issues, by exploiting the most advanced technology in broad-band (0.2 \u2013 80 keV) high angular resolution (<20 arc seconds HEW) grazing incidence mirrors and spectroscopic detectors, together with the use of a high efficiency imaging polarimeter. Such issues can be summarized in two main headings: \u25cf making the census of the population of black holes in the Universe and probing the physics of accretion in the most diverse conditions; \u25cf investigating the particle acceleration mechanisms at work in different contexts, and the effects of radiative transfer in highly magnetized plasmas and strong gravitational fields. These topics were identified as top priority in the study commissioned by the Italian Space Agency (ASI) in 2004 to the Italian scientific community with contracts involving Thales-Alenia Space Italy (TAS-I, Turin), the Media Lario Technologies (MLT, Lecco) company and the INAF institution. NHXM benefits from the phase A study of the canceled French-Italian-German SIMBOL-X mission (2007-2008) and has been recently subjected to a scientific phase B study financed by ASI. Media Lario Technologies company received a contract from ASI in 2009 for a Technology Development Program (ASI-TDP) aiming at improving the technology readiness level with also in-house adoption of hardware for the metrology/manufacturing of the multilayer x-ray optics. Spectrum-RG is a Russian - German x-ray astrophysical observatory scheduled for lunch in 2013. German Space Agency (DLR) is responsible for the development of the key mission instrument - the x-ray grazing incident mirror telescope eROSITA. The second experiment is ART-XC - an x-ray mirror telescope with a harder response than eROSITA, which is being developed by Russia (IKI, Moscow and VNIIEF, Sarov). The name eROSITA stands for extended Roentgen Survey with an Imaging Telescope Array. The general design of the eROSITA x-ray telescope is derived from that of ABRIXAS: a bundle of 7 mirror modules with short focal lengths make up a compact telescope which is ideal for survey observations. Similar designs had been proposed for the missions DUO and ROSITA but were not realized. Compared to those, however, the effective area in the soft x-ray band has now much increased by adding 27 additional outer mirror shells to the original 27 ones of each mirror module. The requirement on the on-axis resolution has also been confined, namely to 15 arc seconds HEW. For these reasons the prefix \u201cextended\u201d to the original name \u201cROSITA\u201d had been added. The scientific motivation for this extension is founded in the ambitious goal to detect about 100000 clusters of galaxies which trace the large scale structure of the Universe in space and time. The main scientific goals are: \u25cf to detect the hot intergalactic medium of 50-100 thousand galaxy clusters and groups and hot gas in filaments between clusters to map out the large scale structure in the Universe for the study of cosmic structure evolution; \u25cf to detect systematically all obscured accreting Black Holes in nearby galaxies and many (up to 3 Million) new, distant active galactic nuclei; \u25cf to study in detail the physics of galactic x-ray source populations, like pre-main sequence stars, supernova remnants and x-ray binaries. Max-Planck-Institute f\ufcr extraterrestrische Physik (MPE) is the scientific institute responsible for the eROSITA Payload. Media Lario Technologies (MLT) is the industrial enabler for the manufacturing of the Optical Payload for eROSITA - including the flight quality mandrels, and it is currently in the C/D Phase of the project. The research activity described in this thesis has been carried out at Media Lario Technologies company and at the Brera Astronomical Observatory under the supervision of INAF-OAB researchers Dott. Giovanni Pareschi and Dott. Gianpiero Tagliaferri. The research activity of the author of this thesis is focused on the development of an advance polishing technique for the mandrels to be used as masters in the mirrors replication by electroforming. The goal is to implement a process where the mandrels can be manufactured with a high accuracy (< 6 arc seconds HEW) and low roughness (< 0.2 nm rms) within a consistent short time. In the contest of the eROSITA and NHXM (projects currently running in MLT) the author participated as technical/scientific responsible, investigating innovative mandrels manufacturing technologies (e.g. Single Point Diamond Turning, shape corrective polishing) representing an evolution of the standard approach used so far. In this frame the author has also contributed to the adoption of a customized deterministic polishing machine and a customized 3D metrology device for the mandrel geometrical characterization. An additional research activity, performed by the author at Media Lario Technologies company and at the Brera Astronomical Observatory, is focused on the development of lightweight glass mirrors manufactured via cold-slumping technique for Imaging Atmospheric Cherenkov Telescopes (IACT). Very High Energy (VHE) gamma rays, with photon energies in the TeV range, can be detected by ground based experiments. In fact, such high energy photons interact high in the upper atmosphere and generate an air shower of secondary particles. These particles emit the so-called Cherenkov light, a faint blue light. The mirror elements here developed have a sandwich-like structure where the reflecting and backing facets are composed by glass sheets with an interposed honeycomb aluminum core. This effort found application at the world\u2019s largest IACT, the 17m MAGIC II telescope (currently operating in Roque de los Muchachos - La Palma, Canary Islands), where 112 mirrors (~ 1 squared meter each), manufactured with the newly developed cold-slumping technique here described, are installed

3D Characterisation of microcracks in concrete

The nature of microcracks that developed in concrete is not well understood. One reason for this is the lack of suitable techniques to detect and characterise the microcracks. Conventional methods include imaging polished cross sections with scanning electron microscopy and optical microscopy. However, these techniques only provide a two-dimensional representation of a three-dimensional structure, which significantly reduces the insights from such analysis. Another reason is that the development of microcracks may be associated with various complex forms of concrete deterioration during service life, e.g. due to mechanical loading, drying, thermal effects and chemical reactions. This complicates laboratory scale experiments and inducing “realistic” microcracks in concrete samples becomes very difficult. The aim of this study is to develop new techniques for three-dimensional quantitative characterisation of microcracks and to apply these to understand the properties of microcracks in concrete. A thorough literature review was conducted to identify the causes of microcracking in concrete, mechanisms of microcrack initiation and propagation, transport properties of micro-cracked concrete and methods to characterise microcracks in two dimensions (2D) and three dimensions (3D). Materials and experimental procedures for inducing different types of microcracks, sample preparation for imaging and image analysis of microcracks are discussed. The feasibility of three-dimensional techniques such as focused ion beam nanotomography (FIB-nt), broad ion beam combines with serial sectioning (BIB), X-ray microtomography (μ-CT) and laser scanning confocal microscopy (LSCM) for imaging microcracks were investigated. A new approach that combines LSCM with serial sectioning was proposed to enhance the capability of LSCM for imaging microcracks in 3D. A major focus of this thesis was dedicated to microcracks induced by autogenous shrinkage because this has been previously neglected due to the dominant role of drying shrinkage. Nonetheless, the increasing use of high strength concretes containing low water/binder ratio, complex binder systems and multiple chemical admixtures in recent years has highlighted the problem of autogenous shrinkage in these concretes. This study presents a first attempt on direct characterisation and understanding of the microcracks caused by autogenous shrinkage in 3D. Various concrete samples were produced and sealed cured to induce autogenous shrinkage. The water/binder ratio, cement type and content, and aggregate particle size distribution were varied to vary the magnitude of autogenous shrinkage and degree of microcracking. Linear deformation measurement was performed to correlate autogenous shrinkage with degree of microcracking. Samples were imaged in 2D using laser scanning confocal microscope (LSCM) and in 3D with X-ray microtomography (μ-CT). Subsequently, 2D and 3D image analysis was employed to quantify microcracks > 1 μm in width. A major challenge was to isolate the microcracks that are inherently connected to pores and air voids. Therefore, an algorithm was developed to separate microcracks from pores, and to extract quantitative data such as crack density, orientation degree, distribution of width and length, as well as connectivity and tortuosity. The results show that use of supplementary cementitious materials and low water/binder ratio can increase linear deformation and the amount of the microcracks. The thesis discusses the effect of autogenous shrinkage on the characteristics of the induced microcracking, which is critical to understanding the transport properties and long-term durability of concretes containing supplementary cementitious materials.Open Acces

Sixteenth International Laser Radar Conference, part 2

Given here are extended abstracts of papers presented at the 16th International Laser Radar Conference, held in Cambridge, Massachusetts, July 20-24, 1992. Topics discussed include the Mt. Pinatubo volcanic dust laser observations, global change, ozone measurements, Earth mesospheric measurements, wind measurements, imaging, ranging, water vapor measurements, and laser devices and technology

Physico-chemical hydrodynamics of droplets on textured surfaces with engineered micro/nanostructures

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references.Understanding physico-chemical hydrodynamics of droplets on textured surfaces is of fundamental and practical significance for designing a diverse range of engineered surfaces such as low-reflective, self-cleaning or anti-fogging glass, easy-cleaning robust inkjet printer heads, or efficient fog-harvesting surfaces. Developing such functional surfaces requires interdisciplinary considerations that have not been broadly explored and which integrate principles from capillarity, optics, nanofabrication, hydrodynamics of complex fluids, and even aerodynamics. The primary contribution of this thesis is to integrate consideration of wetting phenomena coupled with reflection of light, mechanical failure of slender structures, energy dissipation in non-Newtonian fluids, and aerodynamics of airborne droplets impacting onto permeable structures. Based on this integrative understanding, we construct design frameworks for both quantifying the performance of the desired functionalities for each application and for developing optimal functional surfaces. The first part of this thesis is focused on the development of superhydrophobic and superphotophilic surfaces that can be used for improving light-harvesting efficiency of photovoltaic cells. A design framework that combines wetting phenomena and adiabatic refractive index-matching together with a novel nanofabrication method is introduced to select slender tapered nanostructures that fulfill the multiple functionalities. The resulting nanoconetextured glass substrate exhibits highly robust superhydrophobicity and omnidirectional broadband anti-reflectivity as well as self-cleaning or anti-fogging property when conformally coated with a suitable chemical layer. Extending the nonwettability of textured surfaces to low surface tension oils is more difficult because oleophobic surfaces require a re-entrant topography. Deep reactive ion etching is used to fabricate square arrays of silicon nanopillars with wavy sidewalls that help support the superoleophobic state. The effect of the re-entrant nanotexture on the apparent contact angle, contact angle hysteresis, and sliding angle of water and hexadecane droplets is studied. We discuss numerical predictions for the critical pressure differences that cause failure of the Cassie- Baxter state that characterizes the super-repellent state for water and hexadecane droplets on the textured surfaces. In addition, dimensionless design parameters for quantifying the resistance to bending or buckling of the slender nanostructures are derived to design robust superoleophobic inkjet printer heads. Because of the natural repellency of many leaf surfaces to water, non-Newtonian fluids such as dilute polymer solutions are widely used to maximize the deposition rate of aqueous droplets sprayed onto textured liquid-repellent target surfaces. The drop impact dynamics of complex liquids on such surfaces is studied to develop a systematic understanding of the coupled effects of fluid viscoelasticity and the resulting dynamic wetting characteristics. We use hydrophobically-coated flat glass substrates, microtextured pillar surfaces, and nanocone surfaces as well as natural lotus leaves in conjunction with impacting droplets of dilute polyethylene oxide solutions to construct a drop impact dynamics diagram that can be used for understanding deposition of complex fluids on a wide range of hydrophobic textured surfaces. Lastly, the fundamental principles underlying the collection of fog droplets impacting permeable and textured structures such as woven meshes are studied. A design map predicting the theoretical collection efficiency is constructed based on two important dimensionless ratios that characterize the mesh geometry and the impacting droplet stream. Two physical limitations associated with clogging and re-entrainment are identified and potential solutions utilizing surface wettability are discussed. We use a family of physico-chemically patterned meshes with a directed stream of fog droplets to simulate a natural foggy environment and demonstrate a fivefold enhancement in the fog-collecting efficiency of a conventional polyolefin mesh. The design rules developed in this thesis can be applied to select a mesh surface with optimal topography and wetting characteristics to harvest enhanced water fluxes over a wide range of natural convected fog environments. In summary, by developing an integrative understanding of the physico-chemical hydrodynamics of droplets on textured substrates, we have been able to realize a number of novel functionalities using textured surfaces and have constructed design frameworks that can be applied for optimizing the performance of each multi-functional surface. For future work, initial steps for commercializing several of these multi-functional surfaces developed in this thesis are briefly discussed.by Kyoo Chul Park.Ph.D

Study of Microstructure and Corrosion Behavior of AH36 FSW Welds and HSLA S690 ARC Weld

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Ναυτική και Θαλάσσια Τεχνολογία και Επιστήμη