1,721,302 research outputs found
Multiple UAVs trajectory generation and waypoint assignment in urban environment based on DOP maps
No full textThis paper tackles strategic path planning for a multi-UAV routing problem in low altitude urban environment, where GNSS coverage challenges typically affect navigation performance and thus autonomous flight capabilities. These issues are addressed with a multi-step strategy that includes automated definition of GNSS-challenging volumes based on a georeferenced three-dimensional environment model, derivation of candidate obstacle-free paths between waypoints, waypoint assignment and definition of time-tagged trajectories for all UAVs. In all the steps, attention is paid to limiting the computational burden, thus ensuring applicability in real mission scenarios. Going beyond binary logics which consider GNSS-challenging volumes as obstacles, a discrete number of dilution of precision levels is considered, leading to different three-dimensional maps of the environment defined as “DOP layers”. Then, the basic idea to ensure that the designed trajectories are “flyable” with given positioning accuracy requirements is to take navigation performance into account at waypoint assignment level, using propagated covariance as a metric. The approach thus combines “navigation aware” planning with multi-vehicle task assignment, generating a solution that depends on the sensors embarked onboard the UAVs, and can be naturally extended to account for multi-sensor-based navigation architectures and ground-infrastructure support. The algorithm is tested in simulations based on a real world scenario, considering a wide combination of input parameters in terms of positioning error threshold, maximum UAV velocity, number of UAVs, navigation sensors performance, and mission epoch
Gathering SAR data under different bistatic angles: a new potential of COSMO/SkyMed constellation
No full textEnergy Efficiency in Buildings - Thematic Research Summary
Full text linkBuildings are the largest energy-consuming sector in the world, accounting for over one third of all carbon emissions. 75–90% of OECD building stock will still be in service by 2050. Yet the performance of most existing buildings is below current standards. Energy efficiency in buildings is a key focus in European and global climate and energy policies. This TRS aims to deliver a structured overview of research activities in this sector. Several results have arisen from R&D on cost-effectiveness and reliability of products and techniques, and from RD&D of “low-energy” and “nearly zero-energy” buildings for penetration in the market. Although progress is being made, deep renovation remains a priority if the potential for substantial savings and multiple related benefits is to be realised. A new approach to energy system integration and the extension of the research at district and community levels (taking in social, ICT, health and environmental issues) have started but still require supplementary developments. In this context storage is assuming a growing role in boosting energy efficiency, integrating renewable energy sources (RESs) and promoting interoperability between systems. The connections between individual buildings and district energy systems should be increasingly strengthened and the potential for flexibility in buildings within smart grids demonstrated, resulting in reduced energy consumption and lower CO2 emissions. Computational tools are necessary to take account of the complexity of buildings during design, assessment and operation. These should be supported by a series of targeted tools and solutions enabling better decision-making, plus education and awareness on available innovative techniques
Multi-Objective Modular Strategic Planning Framework for Low Altitude Missions Within the Urban Air Mobility Ecosystem
No full textThis paper introduces a multi-metric multi-constraint strategic path planning framework applicable to unstructured urban airspace. The planner is based on a modular and scalable approach to handle several information sources and aspects characterizing urban flight scenarios, such as risk and weather maps, landing site locations, navigation requirements, and mobile and fixed obstacle characteristics. This information is coupled with dynamic constraints and UAV specifications to derive a flyable and safe path connecting a start position and a destination. Strategies for data gathering and synthesis, used to keep a reduced computational burden, are described along with the path planner algorithm. The latter consists in three steps specifically developed to handle both static and time-varying information. A multi-objective cost function with variable weighting coefficients has been implemented so that the most relevant factors for the considered applications can be selected in an adaptive fashion. The performance of the developed algorithms is tested by investigating the planner behavior when changing its inputs as well as the cost function weighting coefficients, demonstrating the ability of the planner in returning an efficient and safe trajectory
Improving Navigation in GNSS-challenging Environments: Multi-UAS Cooperation and Generalized Dilution of Precision
Full text linkThis paper presents an approach to tackle navigation challenges for Unmanned Aircraft Systems flying under non nominal GNSS coverage. The concept used to improve navigation performance in these environments consists in using one or more cooperative platforms and relative sensing measurements (based on vision and/or ranging) to the navigation aid. The paper details the cooperative navigation filter which can exploit multiple cooperative platforms and multiple relative measurements, while also using partial GNSS information. The achievable navigation accuracy can be predicted using the concept of "generalized dilution of precision", which derives from applying the idea of dilution of precision to the mathematical structure of the cooperative navigation filter. Values and trends of generalized dilution of precision are discussed as a function of the relative geometry in common GNSS-challenging scenarios. Finally, navigation performance is assessed based on simulations and on multi-drone flight tests
Multi-drone cooperation to improve navigation integrity in low altitude urban environments
No full textThis paper uses multi-UAV cooperation to enhance the positioning performance of a swarm when GNSS measurements are affected by faults. Only pseudorange observables are accounted for and a centralized extended Kalman filter, which can deal with both cooperative and non cooperative measurements, has been developed. The filter is complemented with a fault detection and elimination strategy based on Mahalanobis distance, which removes pseudoranges that are deemed faulty. Contribution of relative sensing sources (camera or ranging devices) and formation geometry to cooperative GNSS integrity mitigation is investigated, and the concept of cooperative slope is introduced as a metric to define the best cooperative formation geometry. Results demonstrate, by simulating spoofing and multipath phenomena, that cooperation enhances the navigation performance of the UAVs in a multi vehicle formation only if the formation geometry is correctly selected with the aid of the cooperative slope metric
An Improvement of the Pivoting Strategy in the Bunch and Kaufman Decomposition, Within Truncated Newton Methods
Full text linkIn this work we consider the solution of large scale (possibly nonconvex) unconstrained optimization problems. We focus on Truncated Newton methods which represent one of the commonest methods to tackle such problems. In particular, we follow the approach detailed in Caliciotti et al. (Comput Optim Appl 77:627-651, 2020), where a modified version of the Bunch and Kaufman decomposition (Bunch and Kaufman, Math Comput 31:163-179, 1977) is proposed for solving the Newton equation. Such decomposition is used within SYMMBK routine as proposed by Chandra (Conjugate gradient methods for partial differential equations, Ph.D. thesis, Yale University, New Haven, 1978; see also Conn et al., Trust-Region Methods, MPS-SIAM Series on Optimization, Philadelphia, PA, 2000; HSL: A collection of Fortran codes for large scale scientific computation, https://www.hsl.rl.ac.uki ; Marcia, Appl Numer Math 58(4):449-458, 2008) for iteratively solving symmetric possibly indefinite linear systems. The proposal in Caliciotti et al. (Comput Optim Appl 77:627-651, 2020) enabled to overcome a relevant drawback of nonconvex problems, namely the computed search direction might not be gradient-related. Here we propose further extensions of such approach, aiming at improving the pivoting strategy of the Bunch and Kaufman decomposition and enhancing its flexibility
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