Observation of Vehicle Axles Through Pass-by Noise: A Strategy of Microphone Array Design

This paper focuses on road traffic monitoring using sounds and proposes, more specifically, a microphone array design methodology for observing vehicle trajectory from acoustic-based correlation functions. In a former work, authors have shown that combining generalized cross correlation (GCC) functions and a particle filter onto the audio signals simultaneously acquired by two sensors placed near the road allows the joint estimation of the speed and the wheelbase length of road vehicles as they pass by. This is mainly due to the broadband nature of the tire/road noise, which makes their spatial dissociation possible by means of an appropriate GCC processor. At the time, nothing has been said about the best distance to chose between the sensors. A methodology is proposed here to find this optimum, which is expected to improve the observation quality and, thus, the tracking performance. Theoretical developments of this paper are partially assessed with preliminary experiments

Nondestructive fiber optic sensor system for measurement of traffic speed

Disertační práce popisuje návrh, realizaci a otestování nového způsobu detekce a měření rychlosti vozidel s primárním zaměřením na silniční provoz do rychlosti 100km/h, který lze využít v koncepci SMART Cities. Uvedené výsledky v této práci potvrzují, že podobný přístup lze využít rovněž pro monitorování tramvajového provozu, provozu metra a vlakových souprav na železnici. Popsaný měřicí systém je založen na využití interference v optických vláknech. Základem řešení je sériové zapojení senzorických jednotek na bázi Mach-Zehnderova interferometru pracujících s jednovidovými telekomunikačními optickými vlákny standardu G.652.D. a G.653, vlnovou délkou 1550nm a nároky na výkon zdroje záření v řádech jednotek mW. Řešení popsaná v této disertační práci jsou v současné době chráněna autorským osvědčením (patent číslo 306992). Základem tohoto řešení je imunita vůči elektromagnetickým interferencím (EMI) a jednoduchá implementace, protože senzorické jednotky není nutné instalovat destruktivně do vozovky nebo kolejiště. Vzhledem k masivnímu rozšíření optických kabelů podél silnic a železničních tratí, které zabezpečují telekomunikační a bezpečnostní služby, je významnou výhodou i možnost přímého napojení senzorů na stávající infrastrukturu a možnost vzdáleného vyhodnocení. Měřicí systém byl dlouhodobě testován v reálném provozu a je charakterizován chybou v toleranci ± 3km/h udávané u úsekových měřicích systémů do rychlosti 100km/h v České republice.My dissertation thesis describes a design, implementation, and testing of a new way of vehicles detection and speed measurement primarily used in the road transport with the speed limit up to 100kph, which can be utilized in the concept of SMART Cities. Results published in this thesis confirm that a similar approach can be also used for the monitoring of tram, underground and railway transport. The proposed measuring system is based on the interference in optical fibers. The key condition is that sensory units are connected in series on the basis of Mach-Zehnder interferometer working with single-mode optical fibers of G.652.D. and G.653 standards, with the wavelength of 1550nm and demands on the radiation source output in the range of mW. Solutions described in this dissertation thesis are currently protected by copyright (the patent No.306992). The basis of this solution lies in electromagnetic interference immunity (EMI) and simple implementation as the sensory units do not need to be installed destructively into the roadway or railway. With regard to a massive use of optical fibers along roads and railway tracks, which provides telecommunications and security services, the important advantage is also the possibility of direct connections of sensors to existing infrastructure and the possibility of remote evaluation. The measuring system was tested in real traffic over a long period and is characterized by an error with the tolerance of ± 3kph which is given by sectional speed measuring systems up to 100kph in the Czech Republic.440 - Katedra telekomunikační technikyvyhově

Bimodal sound source tracking applied to road traffic monitoring

The constant increase of road traffic requires closer and closer road network monitoring. The awareness of traffic characteristics in real time as well as its historical trends, facilitates decision-making for flow regulation, triggering relief operations, ensuring the motorists’ safety and contribute to optimize transport infrastructures. Today, the heterogeneity of the available data makes their processing complex and expensive (multiple sensors with different technologies, placed in different locations, with their own data format, unsynchronized, etc.). This leads metrologists to develop “smarter” monitoring devices, i.e. capable of providing all the necessary data synchronized from a single measurement point, with no impact on the flow road itself and ideally without complex installation. This work contributes to achieve such an objective through the development of a passive, compact, non-intrusive, acoustic-based system composed of a microphone array with a few number of elements placed on the roadside. The proposed signal processing techniques enable vehicle detection, the estimation of their speed as well as the estimation of their wheelbase length as they pass by. Sound sources emitted by tyre/road interactions are localized using generalized cross-correlation functions between sensor pairs. These successive correlation measurements are filtered using a sequential Monte Carlo method (particle filter) enabling, on one hand, the simultaneous tracking of multiple vehicles (that follow or pass each other) and on the other hand, a discrimination between useful sound sources and interfering noises. This document focuses on two-axle road vehicles only. The two tyre/road interactions (front and rear) observed by a microphone array on the roadside are modeled as two stochastic, zero-mean and uncorrelated processes, spatially disjoint by the wheelbase length. This bimodal sound source model defines a specific particle filter, called bimodal particle filter, which is presented here. Compared to the classical (unimodal) particle filter, a better robustness for speed estimation is achieved especially in cases of harsh observation. Moreover the proposed algorithm enables the wheelbase length estimation through purely passive acoustic measurement. An innovative microphone array design methodology, based on a mathematical expression of the observation and the tracking methodology itself is also presented. The developed algorithms are validated and assessed through in-situ measurements. Estimates provided by the acoustical signal processing are compared with standard radar measurements and confronted to video monitoring images. Although presented in a purely road-related applied context, we feel that the developed methodologies can be, at least partly, applied to rail, aerial, underwater or industrial metrology