117,587 research outputs found
A Review of Distributed Fibre Optic Sensors for Geo-Hydrological Applications
No full textDistributed optical fibre sensing, employing either Rayleigh, Raman, or Brillouin scattering, is the only physical-contact sensor technology capable of accurately estimating physical fields with spatial continuity along the fibre. This unique feature and the other features of standard optical fibre sensors (e.g., minimal invasiveness and lightweight, remote powering/interrogating capabilities) have for many years promoted the technology to be a promising candidate for geo-hydrological monitoring. Relentless research efforts are being undertaken to bring the technology to complete maturity through laboratory, physical models, and in-situ tests. The application of distributed optical fibre sensors to geo-hydrological monitoring is here reviewed and discussed, along with basic principles and main acquisition techniques. Among the many existing geo-hydrological processes, the emphasis is placed on those related to soil levees, slopes/landslide, and ground subsidence that constitute a significant percentage of current geohazards
Distributed Sensing in Geotechnical and Hydrological Applications
No full textDistributed Sensing is a disruptive technology in many geotechnical and geo-hydrological applications and, among the different sensing techniques, Optical Frequency Domain Reflectometry can be effectively used at different scales, in laboratory setups, physical models, and in-situ applications
Fiber-optic sensors for geo-hydrological applications: Basic concepts and applications
No full textIn this short note, basic concepts about fiber-optic sensors are presented, with respect to applications in geology and hydrology. Fiber-Bragg gratings and distributed fiber-optic sensors are then discussed more in detail. © Società Geologica Italiana, Roma 2014
Heavy-tails in Kalman filtering with packet losses: Confidence bounds vs second moment stability
No full textIn this paper, we study the existence of a steady state
distribution and its tail behaviour for the estimation error arising
from Kalman filtering for unstable scalar systems. Although a
large body of literature has studied the problem of Kalman
filtering with packet losses in terms of analysis of the second
moment, no study has addressed the actual distribution of the
estimation error. By drawing results from Renewal Theory, in
this work we show that under the assumption that packet loss
probability is smaller than unity, and the system is on average
contractive, a stationary distribution always exists and is heavytailed, i.e. its absolute moments beyond a certain order do not
exist. We also show that under additional technical assumptions,
the steady state distribution of the Kalman prediction error has
an asymptotic power-law tail, i.e. P[|e| > s] ∼ s
−α
, as s → ∞,
where α can be explicitly computed. We further explore how to
optimally select the sampling period assuming exponential decay
of packet loss probability with respect to the sampling period. In
order to minimize the expected value of second moment or the
confidence bounds, we illustrate that in general a larger sampling
period will need to be chosen in the latter case as a result of the
heavy tail behaviour
To Zero or to Hold Control Inputs With Lossy Links?
No full textThis technical note studies the linear quadratic (LQ) performance of networked control systems where control packets are subject to loss. In particular we explore the two simplest compensation strategies commonly found in the literature: the zero-input strategy, in which the input to the plant is set to zero if a packet is dropped, and the hold-input strategy, in which the previous control input is used if packet is lost. We derive expressions for computing the optimal static gain for both strategies and we compare their performance on some numerical examples. Interestingly, none of the two can be claimed superior to the other, even for simple scalar systems, since there are scenarios where one strategy performs better then the other and scenarios where the converse occurs
Single-Pump Parametric Amplification in Randomly Birefringent Unidirectionally Spun Fibers
No full textA systematic study of the effects of polarization-mode dispersion (PMD) on broadband and narrowband single-pump fiber parametric amplifiers is realized through numerical solutions of the equations governing the interaction. The nonlinear polarization rotation is shown to be a relevant effect that can increase gain randomness when it mixes with PMD. In unidirectionally spun fibers, the signal-pump alignment, and hence the gain, can be highly enhanced, and nonlinear polarization rotation effects appear for larger PMD values. In spite of the enhanced alignment, for large PMD, the interaction becomes inefficient and the gain decreases to zero
On the Use of Optical Fiber Sensors for Debris Flow Monitoring: A Review of Recent Achievements
No full textDebris flows are among the most common and dangerous types of landslides on the planet, often occurring in mountainous areas. Because of their tremendous speeds and the sheer destructive power of their flow, they are extremely hazardous to life and property. Geotechnical instrumentation is critical for monitoring and warning debris flows. However, traditional monitoring systems are hampered by limitations, such as limited spatial resolution and sensitivity, reduced robustness, and powering and cabling issues. These limitations can be surpassed using optical fiber sensors, which are gaining increasing interest by the scientific and stakeholders community. In this paper, we have selected and review some of the most significant achievements and trends on this topic
Disaster Risk Reduction in Italy: A Case History of a High-Risk Landslide
No full textThe aim of the paper is to provide a short commentary on the risk reduction approach in Italy with special emphasis on landslides, floods and extreme rainfall events. In dealing with this topic, it’s very important to preliminary defined a clear conceptual framework as well as a commonly accepted terminology to adopt in order to avoid misinterpretation and promote a culture of sharing data and experiences among researchers, professionals, stakeholders and any other actors involved in decision making. Therefore, the most important documents on risk reduction and adaptation strategies so far accepted at the international level will be introduced along with some basic concepts on hazard and risk assessment and management. The Italian system of Civil Protection will be then discussed, providing some data on the national meteorological monitoring system, moreover, an outline of the administrative and management structure which copes with risk situations and emergency procedures will be illustrated. The Italian law provides for risk reduction to be achieved by means of the Civil Protection Plan at the municipality level. This document considers all different types of risk affecting the territory and defines the main actions to be taken in order to reduce their impact on the natural, economic and social environment. One of the first attempts to adopt and test this plan in a very high-risk condition due to landslide hazard was carried out in the north-eastern Italian Alps several years ago; therefore, a short description of such experience will be reported in the final section of the paper
Consensus-based source-seeking with a circular formation of agents
No full textThis paper deals with the source-seeking problem in which a group of autonomous vehicles must locate and follow the source of some signal based on measurements of the signal strength at different positions. As recently suggested, the gradient of the signal strength can be approximated by a circular formation of agents via a simple weighted average of the signal measured by the agents. Using this result, we propose a distributed source-seeking algorithm based on a consensus method which is guaranteed to steer the circular formation towards the source location using the estimated gradient direction. The proposed algorithm is provided with two tunable parameters that allow for a tradeoff between speed of convergence, noise filtering and formation stability. The benefit of using consensus-based algorithms resides in a more realist discrete time control of the agents and in asynchronous communication resilient to delays which is particularly relevant for underwater applications. The analytic results are finally complemented with numerical simulations
Optimal network topology of multi-agent systems subject to computation and communication latency
No full textWe study minimum-variance feedback-control design for a networked control system with retarded dynamics, where inter-agent information exchange is subject to latency. We prove that such a control design can be solved efficiently for circular formations and compute near-optimal control gains in closed form. Also, we show that the centralized control is in general a poor design choice when adding communication links to the network increases the latency, and propose a control-driven optimization of the network topology
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