Luis M. Fuentes

People tracking in surveillance applications

Abstract This paper presents a real-time algorithm that allows robust tracking of multiple objects in complex environments. Foreground pixels are detected using luminance contrast and grouped into blobs. Blobs from two consecutive frames are matched creating the matching matrices. Tracking is performed using direct and inverse matching matrices. This method successfully solves blobs merging and splitting. Some application in automatic surveillance systems are suggested by linking trajectories and blob position information with the events to be detected.

Electric field strengths in a hollow cathode measured by Doppler-free two-photon optogalvanic spectroscopy via Stark splitting of the 2S level of deuterium

We present, in this work, Doppler-free two-photon optogalvanic spectroscopy as a tool to measure the electric field strength in the cathode fall region of a hollow cathode discharge via the Stark splitting of the 2S level of atomic deuterium. The strong electric field strength (1 to 4 kV cm−1) present in the hollow cathode is determined for various discharge conditions (currents from 50 to 200 mA and pressures from 400 to 1350 Pa), which allows investigation of the corresponding variations of the cathode fall and its changes with discharge operation time.

Tracking people for automatic surveillance applications

The authors present a simple but robust real-time algorithm that allows tracking of multiple objects in complex environments. As the first stage, the foreground segmentation uses luminance contrast, reducing computation time avoiding the use colour information at this stage. Foreground pixels are then grouped into blobs analysing X-Y histograms. Tracking is achieved by matching blobs from two consecutive frames using overlapping information from bounding boxes and a linear prediction for the centroid’s position. This method successfully solves blobs merging into groups and tracking them until they split again. Application in automatic surveillance is suggested by linking blob’s information, in terms of trajectories and positions, with the events to be detected. Some examples in transport environments are outlined.

Calculation of the spatial resolution in two-photon absorption spectroscopy applied to plasma diagnosis

We report a detailed characterization of the spatial resolution provided by two-photon absorption spectroscopy suited for plasma diagnosis via the 1S-2S transition of atomic hydrogen for optogalvanic detection and laser induced fluorescence (LIF). A precise knowledge of the spatial resolution is crucial for a correct interpretation of measurements, if the plasma parameters to be analysed undergo strong spatial variations. The present study is based on a novel approach which provides a reliable and realistic determination of the spatial resolution. Measured irradiance distribution of laser beam waists in the overlap volume, provided by a high resolution UV camera, are employed to resolve coupled rate equations accounting for two-photon excitation, fluorescence decay and ionization. The resulting three-dimensional yield distributions reveal in detail the spatial resolution for optogalvanic and LIF detection and related saturation due to depletion. Two-photon absorption profiles broader than the Fourier transform-limited laser bandwidth are also incorporated in the calculations. The approach allows an accurate analysis of the spatial resolution present in recent and future measurements.

Mobile Voronoi Diagrams for Traffic Monitoring under Bad Visibility Conditions

A semiautomatic management of traffic scenes displays a large diversity of mobile data arising from usual Computer Vision techniques. The mobile nature of inputs requires the combination of different techniques for filtering, tracking, and clustering features along a video sequence. These problems are considerably harder in presence of low visibility conditions arising from rain, fog or dazzling conditions. It is necessary a robust coarse-to-fine approach for supporting early alert in presence of conflict or dangerous situation at road intersections. Currently, there is no a general solution developed for low visibility conditions, and what there is, has been developed following particular strategies involving a specific combination of filters for extracting and analyzing the situation. Under low visibility conditions, mobile features are clustered as blobs with similar motion patterns and labelled in terms of a mobile Voronoi site which represents the centroid of a coloured region with similar kinematic pattern. For a fixed camera, and in absence of information about relative velocities of vehicles, kinematic involves the relative variation of colour and shape. With low visibility conditions and for real-time response, it is not necessary to work with a large palette of colours, and a reduction of bits per pixel is performed in the preprocessing stage. We illustrate our results with some scenes where reflections in water (rainy weather) or discontinuities linked to fog, can produce hallucinations for which our approach provides a robust kinematic method justifying the application of mobile Voronoi diagrams for mobile blobs as unifying principle.

Optogalvanic spectroscopy measurements of the electric field strength in a hydrogen glow discharge

A high-resolution spectroscopy method is used in order to measure the electric field distribution in a hollow cathode glow discharge in hydrogen.

Analysis of the measured 1S-2S Stark spectra of hydrogen isotopes used for E-field strength determination in a hollow cathode discharge

This paper is dedicated to analyse in detail the Stark splitting spectra of the 1S – 2S transition of hydrogen isotopes, used to determine the local electric field strength in the cathode fall of a hollow cathode discharge, by measuring the Doppler free two-photon absorption via optogalvanic detection. The measured irradiance distribution in the overlap volume of the two laser beams is used to integrate the rate equations, which give the ion yield distribution with high spatial resolution. Inserting the local ion yield in the local electric field strength of the cathode fall allows reconstructing and analysing the Stark splitting spectra.

Characterization of the spatial resolution in two-photon spectroscopic techniques used for plasma diagnostics

We report a detailed characterization of the spatial resolution provided by different two-photon absorption spectroscopy techniques used in plasma diagnostics: two-photon absorption laser induced fluorescence (TALIF) and two-photon optogalvanic spectroscopy. Well-understood and characterized spatial resolution has especial importance for a precise control of experimental conditions, and absolute measurements. Beam profiles recorded with high resolution allow calculating the beam propagation and irradiance distribution in the beams overlap, the resulting fluorescence and ionization yield, and the corresponding spatial resolution.

Measurements of two-photon absorption cross-section of Xe for laser spectroscopic techniques calibration

Two-photon transition cross section for one xenon transition (5p6 1S0-5p56p[1/2]0) will be measured with very low uncertainty by two-photon polarization spectroscopy. The method, which is explained in this paper, is based on a comparison of direct measurements of the two-photon absorption in xenon gas at two closed wavelengths (resonant and no resonant).

Research areas of the Optics Department at University of Valladolid

In this article we present the different groups of investigation which work at the Department of Optics and Applied Physics of the University of Valladolid (Spain). The areas covered by these groups are the following: (1) optical diagnostic techniques in plasmas, (2) calculation of spectral line shapes, (3) atmospheric optics, (4) radiometry and photometry, and (5) history of science and techniques.