The main advantage of filament-induced fluorescence spectroscopy is the simultaneous detection of multiple species. The possibility of this interpretation is reported on an approach for simultaneous monitoring of multi-gases pollutants based on fluorescence emission of trace gases, induced by the filamentation of intense femtosecond laser pulses in air. This method is illustrated by the simultaneous detection and identification of similar atmospheric trace gases, methane and acetylene. The spectra of an "unknown" mixture are analyzed with a genetic algorithm, showing good concentrations agreements with the experimental results within an error of 25%.

Aquifer formations along the northern shore of the Saint-Lawrence River in Quebec (Canada) mainly consist of glacial and coastal deposits of variable thickness overlying Precambrian bedrock. These deposits are important because they provide the main water supply for many communities. As part of a continuing project aimed at developing an inventory of the groundwater resources in the Charlevoix and Haute-Côte-Nord (CHCN) regions of the province of Quebec in Canada, the central loop transient electromagnetic (TEM) method was used to map the principal hydrogeological environments in these regions. One-dimensional smooth inversion models of the TEM soundings have been used to construct two-dimensional electrical resistivity sections, which provided images for hydrogeological validation. Electrical contour lines of aquifer environments were compared against available well logs and Quaternary surface maps in order to interpret TEM soundings. A calibration table was achieved to represent common deposits and basements. The calibration table was then exported throughout the CHCN region. This paper presents three case studies; one in the Forestville site, another in the Les Escoumins site and the other in the Saint-Urbain site. These sites were selected as targets for geophysical surveys because of the general lack of local direct hydrogeological data related to them.

We demonstrate the feasibility of filament-induced breakdown spectroscopy (FIBS) for remote sensing of solid samples in a polar environment. FIBS spectra from an aluminum target induced by 800-nm laser pulses propagating in air were probed. The air visibility in an open winter field was as low as 3.2 km fluctuating with precipitation, pressure and relative humidity. Under such polar condition, clean spectral Al I lines from an aluminum target located at a distance of 60 m were obtained. This shows the technique FIBS could be potentially useful for sensing remote targets in a variety of polar environments.

PreviousNext No AccessSEG Technical Program Expanded Abstracts 2011Multiple‐scale porosity simulation using wavelet decomposition of GPR tomographic dataAuthors: P. SimardE. GloaguenP. RuggeriC. DubreuilB. GirouxP. SimardInstitut National de la Recherche Scientifique, G1K 9A9, Québec, Qc, CanadaSearch for more papers by this author, E. GloaguenInstitut National de la Recherche Scientifique, G1K 9A9, Québec, Qc, CanadaSearch for more papers by this author, P. RuggeriInstitut de géophysique, Université Lausanne, SwitzerlandSearch for more papers by this author, C. DubreuilInstitut National de la Recherche Scientifique, G1K 9A9, Québec, Qc, CanadaSearch for more papers by this author, and B. GirouxInstitut National de la Recherche Scientifique, G1K 9A9, Québec, Qc, CanadaSearch for more papers by this authorhttps://doi.org/10.1190/1.3627983 SectionsSupplemental MaterialAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract In Earth sciences, it is common to image a target property using indirect low‐resolution geophysical data. Downscaling low‐resolution indirect data to the appropriate target resolution is a major issue in imaging. In this paper, we use a wavelet‐based methodology to downscale the low‐resolution geophysical images to high‐resolution geological model through the use of a hydrogeophysical analog. First, all available images are wavelet transformed. Bayesian sequential simulation is used to translate the measured geophysical wavelet approximation coefficients into target wavelet approximation coefficients. High‐resolution porosity textures are reproduced by means of a simulated annealing optimizing the target detail wavelet coefficients statistics with the analog detail wavelet coefficient statistics at each scale. The approach is tested on a synthetic porosity model. Resulting porosity realizations reproduce the large scale features of the target porosity field supported by the geophysical data as well as the high‐frequency textures extracted from the analog porosity field.Permalink: https://doi.org/10.1190/1.3627983FiguresReferencesRelatedDetails SEG Technical Program Expanded Abstracts 2011ISSN (print):1052-3812 ISSN (online):1949-4645Copyright: 2011 Pages: 4424 Publisher:Society of Exploration Geophysicists HistoryPublished: 25 May 2012 CITATION INFORMATION P. Simard, E. Gloaguen, P. Ruggeri, C. Dubreuil, and B. Giroux, (2011), "Multiple‐scale porosity simulation using wavelet decomposition of GPR tomographic data," SEG Technical Program Expanded Abstracts : 3740-3744. https://doi.org/10.1190/1.3627983 Plain-Language Summary PDF DownloadLoading ...

Introduction: Patient-specific evaluation of bone mechanical properties usually relies on the apparent density using clinical Quantitative Computed Tomography (QCT). However, evidence has been reported that bone microarchitecture has an important effect on its mechanical properties.

In this paper, we present a novel approach to simulate porosity fields constrained by borehole radar tomography images. The cornerstone of the method is the bayesian analysis of the approximation wavelet coefficients of a petro-physical analogue. The method is tested with a two-dimensional porosity field generated from a digital picture of a real sand deposit. The porosity field is translated into electrical properties and a cross-hole tomography synthetic survey is modeled using a finite-difference modeling algorithm. In parallel, an analogue deposit is created based on the geological knowledge of the area under study. The analogue porosity field is converted into electrical property fields using the same equations as previously. A synthetic GPR tomography is also computed from the latter. Wavelet decomposition of both measured and analogue tomograms and porosity analogue fields is then calculated. Based on the assumption that geophysical data carry only the large-scale information about the geological model, statistical analysis of the approximation coefficients of each variable is carried out. From the measured tomogram approximation coefficients and the cross statistics evaluated on the analogues, the approximation of the real porosity field is inferred using bayesian inference. Finally, based on the geostatistical relationships between wavelet coefficients across the different scales, all the porosity wavelet detail coefficients are simulated using a standard geostatistical simulation algorithm. The wavelet coefficients are then back transformed in the porosity space. The final simulated porosity fields contain the large wavelengths of the measured radar tomogram and the texture of the analogue porosity field.

All matters in the path of filaments induced by an intense femtosecond laser pulse propagating in air could be fragmented and result in the emission of characteristic fluorescence spectra from the excited fragments. The fluorescence spectra exhibit specific signatures (fingerprints) that can be used for the identification of various substances including chemical and biological species. In this paper, we present an overview of the recent progress in our laboratory concerning the "remote" sensing of chemical and biological agents/pollutants in air using filamentation-induced nonlinear fluorescence techniques.

The mobile femtosecond laser facility T&T (terawatt & terahertz) of DRDC-Valcartier was used to detect trace methane gas remotely in an open field atmosphere during daytime (with strong sun light) using filament-induced fluorescence spectroscopy. Comparison of the results obtained in the laboratory and in the field validates the long range extrapolations of short distance results taken in our laboratory in the past. This could be considered a breakthrough for remote sensing based on filamentation.

The critical power for self-focussing of a femtosecond laser pulse in helium has been measured using the moving focus method. The experimental value is Pcritexp(1 atm) ∼268 GW. Using this value, the nonlinear refractive index is inferred to be n2exp(1atm) ∼ 3.6 × 10-21 cm2/W. In addition, the plots of the electron densities versus energy and pressure have also been used to determine the critical power of helium, based on the intensity clamping of the filamentation process. The value agrees well with the one by the moving focus method.

Remote filament-induced breakdown spectroscopy (R-FIBS) is a novel technique that could be applied at long distance up to a few kilometers. Our work demonstrates that by creating short and strong filaments in the atmosphere with a telescopic beam delivering system, continuum background in R-FIBS spectrum will be significantly reduced. This allows for a non-gated R-FIBS configuration for identifying solid targets. As an example, we used an aluminum plate located 50 in away from our detection system. The obtained fingerprint spectrum is so strong that the detection limit could reach 1.9 kin in distance and ppm level in terms of minor element concentration. (c) 2007 Elsevier B.V. All rights reserved.

The authors report on an approach for simultaneous monitoring of multigas pollutants based on fluorescence emission of trace gases, induced by the filamentation of intense femtosecond laser pulses in air. The high intensity inside a filament can dissociate the gas molecules into small fragments which emit characteristic fluorescence. This method is illustrated for simultaneously sensing atmospheric trace gases, methane and acetylene. The spectra of an “unknown” mixture were analyzed by using a genetic algorithm, showing good concentration agreement with the experimental results within an error of 25%.

Our experiment shows that external focusing strongly influences the plasma density and the diameter of femtosecond Ti-sapphire laser filaments generated in air. The control of plasma filament parameters is suitable for many applications such as remote spectroscopy, laser induced electrical discharge, and femtosecond laser material interactions. The measurements of the filament showed the plasma density increases from 10(15)cm(-3) to 2 x 10(18)cm(-3) when the focal length decreases from 380 cm to 10 cm while the diameter of the plasma column varies from 30 microm to 90 microm. The experimental results are in good qualitative agreement with the results of numerical simulations.

The unavoidable hot spots in a practical terawatt level laser pulse will self-focus in air at a short distance. The short distance cannot be changed significantly by only controlling the chirp or divergence. We overcome such early self-focusing by using a telescope, which enlarges the diameter of the beam, thus that of the hot spots. The telescope's effective focal length is much shorter than the self-focusing distance of both the enlarged beam and the hot spots. Then, the resulting filaments merge into the geometrical focus whose position is controllable by the telescope. This technique also minimizes the generation of white light.

We demonstrated the feasibility of remote detection and differentiation of some very similar agricultural-activity related bioaerosols, namely barley, corn, and wheat grain dusts, through nonlinear fluorescence of fragments induced by the high-intensity inside filaments of femtosecond laser pulses in air. The signals were detected in Lidar configuration with targets located at 4.7 m away from the detection system. All the species showed identical spectra, namely those from molecular C 2 and CN bands, as well as atomic Si, C, Mg, Al, Na, Ca, Mn, Fe, Sr and K lines. These identical spectral bands and lines reveal similar chemical compositions; however, the relative intensities of the spectra are different showing different element abundances from these three bio-targets. The intensity ratios of different elemental lines were used to distinguish these three samples. Good reproducibility was obtained. We expect that this technique could be used at long distance and thus played as a sensor of similar biological hazards for public and defense security.