Remote Gas Detection Research Articles

Design Analysis of Mid IR DIAL System for Detection of Hazardous Chemical Species

Nowadays, both military and public agencies are concerned with the remote detection of toxic gases and chemical warfare agents in the atmosphere. A promising method for the remote detection of such harmful chemicals in the atmosphere is Differential Absorption Lidar (DIAL). In the current paper, system design analysis has been carried out to build a DIAL system for the detection of toxic chemical warfare agents, chemical warfare simulants, explosive precursors, and pollutants. The proposed DIAL system comprises an Optical Parametric Oscillator (OPO) based tuneable laser, a 203 mm diameter Cassegrain telescope, a TE-cooled MCT detector, suitable data acquisition hardware, etc. The DIAL output parameters like return signals, SNR, and minimum measurable concentrations have been simulated under different weather conditions such as clear sky, moderately hazy sky, and hazy atmospheric conditions for given system input parameters (pulse energy, detectivity, bandwidth, DAQ resolution, etc.). We have considered chemicals such as Sarin, Thiodiglycol (TDG), acetone, and methane to be detected using the system. Analysis has been carried out for these chemicals present at different locations with varying concentrations. Our analysis reveals that the DIAL system with a laser transmitter of 5 mJ energy and 203 mm receiver telescope is capable of detecting a few ppm concentrations of toxic chemicals present anywhere between the ranges from a few tens of meters to 2 km with topographic target present. The sensitivity of the system in terms of minimum detectable concentrations for the considered chemicals is also estimated for different atmospheric conditions. It is seen that the minimum detectable concentration of TDG is 3.2 ppm in clear weather conditions which increases to 9.2 ppm under a hazy atmosphere. A similar analysis has been carried out for other toxic chemicals and has been discussed in the paper.

Enhancing MAX-DOAS atmospheric state retrievals by multispectral polarimetry – studies using synthetic data

Abstract. Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) is a widely used measurement technique for the remote detection of atmospheric aerosol and trace gases. The technique relies on the analysis of ultra-violet and visible radiation spectra of scattered sunlight (skylight) to obtain information on different atmospheric parameters. From an appropriate set of spectra recorded under different viewing directions (typically a group of observations at different elevation angles) the retrieval of aerosol and trace gas vertical distributions is achieved through numerical inversion methods. It is well known that the polarisation state of skylight is particularly sensitive to atmospheric aerosol content as well as aerosol properties and that polarimetric measurements could therefore provide additional information for MAX-DOAS profile retrievals; however, such measurements have not yet been used for this purpose. To address this issue, we have developed the RAPSODI (Retrieval of Atmospheric Parameters from Spectroscopic Observations using DOAS Instruments) algorithm. In contrast to existing MAX-DOAS algorithms, it can process polarimetric information, and it can retrieve simultaneously profiles of aerosols and various trace gases at multiple wavelengths in a single retrieval step; a further advantage is that it contains a Mie scattering model, allowing for the retrieval of aerosol microphysical properties. The forward-model component in RAPSODI is based on a linearised vector radiative transfer model with Jacobian facilities, and we have used this model to create a database of synthetic measurements in order to carry out sensitivity analyses aimed at assessing the potential of polarimetric MAX-DOAS observations. We find that multispectral polarimetry significantly enhances the sensitivity, particularly to aerosol-related quantities. Assuming typical viewing geometries, the degrees of freedom for signal (DOFS) increase by about 50 % and 70 % for aerosol vertical distributions and aerosol properties, respectively, and by approximately 10 % for trace gas vertical profiles. For an idealised scenario with a horizontally homogeneous atmosphere, our findings predict an improvement in the inversion results' accuracy (root-mean-square deviations to the true values) of about 60 % for aerosol vertical column densities (VCDs) as well as for aerosol surface concentrations and by 40 % for aerosol properties. For trace gas VCDs, very little improvement is apparent, although the accuracy of trace gas surface concentrations improves by about 50 %.

Идентификация тринитротолуола (TNT) в дальней ИК-области с помощью параметрического лазера

Computational and experimental studies of the amplitude-time and spectroscopic characteristics of an IR parametric laser based on mercury thiogallate with frequency tuning in the range from 5 to 9 mi-crons, an output energy of 10 MJ and a spectral emission width of ≤ 0,7 cm-1 have been carried out. A multifunctional IR parametric laser complex for remote detection and identification of atmospheric gases, including explosive and chemically aggressive substances in the range of electromagnetic wave-lengths from 1,41–9,07 microns, by differential absorption and dispersing has been developed, created and tested. The paper presents the results of computational and experimental studies on remote determination of spectroscopic characteristics of the most famous explosives TNT, RDX, PETN. It shows the possibility of highly sensitive determination of the concentration (~1 ppm) of explosives using a multifunctional optical system based on an IR parametric laser.

Fiber Fabry-Perot astrophotonic correlation spectroscopy for remote gas identification and radial velocity measurements.

We present a novel, to the best of our knowledge, remote gas detection and identification technique based on correlation spectroscopy with a piezoelectric tunable fiber-optic Fabry-Perot filter. We show that the spectral correlation amplitude between the filter transmission window and gas absorption features is related to the gas absorption optical depth, and that different gases can be distinguished from one another using their correlation signal phase. Using a previously captured telluric-corrected high-resolution near-infrared spectrum of Venus, we show that the radial velocity of Venus can be extracted from the phase of higher order harmonic lock-in signals. This correlation spectroscopy technique has applications in the detection and radial velocity determination of weak spectral features in astronomy and remote sensing. We experimentally demonstrate a remote CO2 detection system using a lock-in amplifier, fiber-optic Fabry-Perot filter, and single channel avalanche photodiode.

Trace CH4 Gas Detection Based on an Integrated Spherical Photoacoustic Cell

This paper presents an integrated spherical photoacoustic cell (SPAC) for trace methane (CH4) gas detection. Theoretical analysis and analogue simulations are carried out to analyze the acoustic field distribution of the SPAC at resonant and non-resonant modes. The finite element simulation results based on COMSOL show that the first-order radial resonant frequency and second-order angular resonant frequency are 24,540 Hz and 18,250 Hz, respectively, which show good agreements with the formula analysis results. The integrated SPAC, together with a high-speed spectrometer and a distributed feedback (DFB) laser source, makes up a photoacoustic (PA) spectroscopy (PAS) system, which is employed for CH4 detection. The minimum detection limit (MDL) is measured to be 126.9 parts per billion (ppb) at an average time of 1000 s. The proposed SPAC has an integrated, miniaturized and all-optical structure, which can be used for remote and long-distance trace gas detection.

All-optical high-sensitivity resonant photoacoustic sensor for remote CH4 gas detection.

This paper presents an all-optical high-sensitivity resonant photoacoustic (PA) sensor to realize remote, long-distance and space-limited trace gas detection. The sensor is an integration of a T-type resonant PA cell and a particular cantilever-based fiber-optic acoustic sensor. The finite element simulations about the cantilever vibration mode and the PA field distributions are carried out based on COMSOL. The all-optical high-sensitivity resonant PA sensor, together with a high-speed spectrometer and a DFB laser source, makes up of a photoacoustic spectroscopy (PAS) system which is employed for CH4 detection. The measured sensitivity is 0.6 pm/ppm in the case of 1000 s average time, and the minimum detection limit (MDL) reaches 15.9 parts per billion (ppb). The detective light source and the excitation light source are all transmitted by optical fibers, therefore remote and long-distance measurement of trace gas can be realized. Furthermore, the excitation light source and the acoustic sensor are designed at the same side of the PA cell, the sensor may be used for space-limited trace gas detection.

A high-sensitive methane measuring telemetry system based on a direct optical absorption technique

In this paper, a reflective methane (CH4) gas telemetry system has been developed based on the direct optical absorption spectroscopy technique for an open light path. It can realize the real-time in-situ monitoring of CH4 gas within a range of 150 m. Considering the potential cross-interference effects of hydrocarbon gases in ambient air, a diode laser operating at a specific wavelength of 1653.7 nm is employed to target the strong CH4 absorption line in near-infrared region and therefore avoid the interference of water vapor absorption simultaneously. A measurement precision of 0.02 ppm within 40 m open optical path has been achieved over 30 h of continuous monitoring, indicating the excellent measuring sensitivity and stability of our telemetry system. Through the field test of leaked CH4 gas with a 150 m one-way open optical path, the developed CH4 telemetry system has proved to have great potential and reliability for environmental monitoring and remote gas detection in various industries.

Quartz-tuning-fork enhanced photothermal spectroscopy for ultra-high sensitive trace gas detection.

A gas sensing method based on quartz-tuning-fork enhanced photothermal spectroscopy (QEPTS) is reported in this paper. Unlike usually used thermally sensitive elements, a sharply resonant quartz-tuning-fork with the capability of enhanced mechanical resonance was used to amplify the photothermal signal level. Acetylene (C2H2) detection was used to verify the QEPTS sensor performance. The measured results indicate a minimum detection limit (MDL) of 718 ppb and a normalized noise equivalent absorption coefficient (NNEA) of 7.63 × 10-9 cm-1W/√Hz. This performance demonstrates that QEPTS can be an ultra-high sensitive technique for gas detection and shows superiority when compared to usually used methods of tunable diode laser absorption spectroscopy (TDLAS) and quartz-enhanced photoacoustic spectroscopy (QEPAS). Furthermore, when compared to an optical detector, especially a costly mercury cadmium telluride (MCT) detector with cryogenic cooling used in TDLAS, a quartz-tuning-fork is much cheap and tiny. Besides, compared to the QEPAS technique, QEPTS is a non-contact measurement technique and therefore can be used for standoff and remote trace gas detection.

Remote chemical sensing: a review of techniques and recent developments

PurposeThis paper aims to provide technical details of the techniques used for the remote detection of chemical compounds in a number of applications and also to highlight key research themes.Design/methodology/approachFollowing a short introduction, this first considers remote gas detection using the DIAL technique. Remote gas cloud imaging is then discussed, and this is followed by a review of chemical warfare agent detection technologies. A selection of research activities and product developments aimed at remotely detecting explosives are considered and, finally, brief concluding comments are drawn.FindingsRemote gas sensing is now a practical reality, and products are available which can remotely detect, identify, quantify and in some cases visualise a wide range of toxic and environmentally threatening gases. These satisfy numerous industrial, environmental and military applications. Remotely detecting explosives poses a significant technological challenge, and despite some commercialisation, it remains the topic of an extensive research effort, much involving LIBS and Raman techniques. Importantly, much of this work also has potential in non-military applications, with several developments being shown to detect various industrially important compounds.Originality/valueThis provides a technical insight into the techniques and products used in a range of remote chemical sensing applications.

Laser-Based Remote Sensing of Explosives by a Differential Absorption and Scattering Method

A multifunctional IR parametric laser system is developed and tested for remote detection and identification of atmospheric gases, including explosive and chemically aggressive substances. Calculations and experimental studies of remote determination of the spectroscopic parameters of the best known explosive substances TNT, RDX, and PETN are carried out. The feasibility of high sensitivity detection (~1 ppm) of these substances with the aid of a multifunctional IR parametric light source by differential absorption and scattering is demonstrated.

Colorimetric detection of hazardous gases using a remotely operated capturing and processing system

This paper presents an electronic system for the automatic detection of hazardous gases. The proposed system implements colorimetric sensing algorithms, thus providing a low-cost solution to the problem of gas sensing. It is remotely operated and it performs the tasks of image capturing and processing, hence obtaining colour measurements in RGB (Red–Green–Blue) space that are subsequently sent to a remote operator via the internet. A prototype of the system has been built to test its performance. Specifically, experiments have been carried out aimed at the detection of CO, CO2, NO, NO2, SO2 and formaldehyde at diverse concentrations by using a chromogenic array composed by 13 active and 2 inert compounds. Statistical analyses of the results reveal a good performance of the electronic system and the feasibility of remote hazardous gas detection using colorimetric sensor arrays.

Compact Superconducting Terahertz Source Operating in Liquid Nitrogen

Sources of terahertz radiation (between the far infrared and microwave frequencies) are in high demand for a host of applications. The authors report on what is essentially a ``T-ray flashlight'', a compact and portable source of tunable, continuous terahertz light, employing a stack of intrinsic Josephson junctions in a cuprate superconductor as the emitter. This economical and convenient device can be driven by one everyday 1.5-V battery, and should facilitate airport security, nondestructive evaluation, and remote detection of trace gases, among other applications.

User studies on teleoperation of robots for plant inspection

Purpose – To avoid harm to humans, environment, and capital goods, hazardous or explosive gases that are possibly escaping from industrial and infrastructure facilities of the gas and oil processing industry have to be detected and located quickly and reliably. Project RoboGasInspector aims at the development and evaluation of a human-robot system that applies autonomous robots equipped with remote gas detection devices to detect and locate gas leaks. This article aims to focus on the usability of telemanipulation in this context. Design/methodology/approach – This paper presents four user studies concerning human-robot interfaces for teleoperation in industrial inspection tasks. Their purpose is to resolve contradictory scientific findings regarding aspects of teleoperation and to verify functionality, usability, and technology acceptance of the designed solution in the actual context of use. Therefore, aspects concerning teleoperation that were separately examined before are evaluated in an integrated way. Considered aspects are influence of media technology on telepresence, simulator sickness and head slaved camera control, usability of different input devices for telemanipulation, and identification of intuitive gestures for teleoperation of mobile robots. Findings – In general, the implemented interaction concepts perform better compared to conventional ones used in contemporary, actually applied robot systems. Otherwise, reasons are analyzed and approaches for further improvements are discussed. Exemplary results are given for each study. Originality/value – The solution combines several technical approaches that are so far separately examined. Each approach is transferred to the innovative domain of industrial inspections and its applicability in this context is verified. New findings give design recommendations for remote workplaces of robot operators.

Remote sensing of gases by hyperspectral imaging: system performance and measurements

Remote gas detection and visualization provides vital information in scenarios involving gas leaks, environmental monitoring, chemical accidents or attacks. Imaging systems based on Fourier transform spectrometers with single detector elements have been applied for several years by emergency response forces for gas identification and quantification. In this work a hyperspectral imager employing a Michelson interferometer and an infrared focal plane array detector is characterized. The system provides spatially resolved spectral information about the measurement scene. The performance of the system is evaluated by laboratory measurements. Results of gas detection in the field are presented and discussed. The gas detection algorithm is based on a physical model for the measured radiance. In this model the atmosphere is divided into multiple homogenous layers of constant temperature. The signatures of the gases present in these layers are then compensated in the measured spectrum. No information about the signature of the background is required. Moreover an algorithm that combines spectral and spatial information is presented. This algorithm enhances the signal to noise ratio of the spectra and thus improves the detection limits. Using these algorithms it is possible to identify, visualize, and track gas clouds in real time.

Remote intelligent concentration measurement of gas dissolved in water

This thesis describes principle of remote gas detection via intelligent fiber optic sensing system. Introduction of fibre optic based systems, operating on the principle of optical spectroscopy allow remote intelligent sensing and concentration measurement of gasses dissolved in water on a great depth. Laser modulation spectroscopy is a suitable technique which can be applied to reduce the cost of water monitoring devices and provide accurate concentration measurements in water.

Application of Millimeter-Wave Radiometry for Remote Chemical Detection

Passive millimeter-wave systems have been used in the past to remotely map solid targets and to measure low-pressure spectral lines of stratospheric and interstellar gases; however, its application to pressure-broadened spectral line detection of industrial emissions is new. We developed a radiative transfer model to determine feasibility and system requirements for passive millimeter-wave spectral detection of terrestrial gases. We designed and built a Dicke-switched multispectral radiometer in the 146-154-GHz band to detect nitric oxide (NO), a prototypical gas of nuclear fuel processing operations. We first tested the spectral detection capability of the radiometer in the laboratory using a gas cell and then field tested it at the Nevada test site at a distance of 600 m from a stack that released hot plumes of NO and air. With features such as Dicke-switched integration, frequent online calibration, and spectral baseline subtraction, we demonstrated the feasibility of remote detection of terrestrial gases by a ground-based radiometer.

Airborne laser IR thermographic system for detecting gas leaks from underground pipelines

An airborne laser IR thermographic system intended for remote gas detection is described. The system involves three channels of which one is active and two are passive. The active channel includes a 15 mW tunable laser diode illuminating the ground surface with 1 ms pulses of IR radiation at the wavelength of 1650 nm. The system sensitivity by the laser channel is about 100 ppm*m at 100 m (by methane). The two passive channels allow visualizing the ground surface in both the visual and mid-IR wavelength. The system has passed on-flight testing in cooperation with some Russian gas transportation companies.

Remote detection and identification of organic remains: an assessment of archaeological potential

AbstractThis paper reviews the various methods of using natural or induced light spectra as analytical tools in forensic archaeology. Chemical identification can be made at long range and wide scale (tens of metres) down to short range and very small scale (nanometres). The identification of organic gases and materials has used either chemical capture and chromatography, induced (laser or ultraviolet) light sources or laser Raman microscope spectroscopy. The remote gas detection method relies on the identification of atmospheric gases by their characteristic light spectra. Modern spectroscopes can detect gases down to a few parts per million of an atmosphere. When the light source (wavelength) and direction is controlled, so laser‐induced spectroscopy may be used to monitor the emission of gases such methane from buried organic remains. In order to identify the location of buried organic remains, a grid of sample points must be established using a base line or global positioning system. When matched to base line or ground‐positioning systems, such data can be manipulated by geographical information system packages. This would enable pinpointing of anomalies for excavation or avoidance. Microscope‐based laser Raman spectroscopy can be used to directly analyse captured gases, swabs and surfaces without the problems of long‐path detection. Copyright © 2002 John Wiley & Sons, Ltd.

Prediction of the limits of detection of hazardous vapors by passive infrared with the use of MODTRAN

Passive infrared remote detection of hazardous gases, vapors, and aerosols is based on the difference, Δ T, between the air temperature of the threat vapor cloud and the effective radiative temperature of the background. In this paper I address the problem of detection with a low-angle-sky background. I used Modtran to predict Δ T and atmospheric transmittance for standard atmospheric models. The detection limits, at 2-cm(-1) resolution, are discussed for sulfur hexafluoride, Sarin, trichloroethylene, methyl isocyanate, mustard gas, methyl chloride, and sulfur dioxide for selected cases with the U.S. Standard, the Subarctic Winter, and the Tropical models. I used a particularly interesting case of Sarin detection with the Subarctic Winter atmospheric model to illustrate the power of Modtran to predict subtle changes in Δ T with angle of elevation (AOE).

OTIM—passive remote gas detector gas cloud‐imaging industrial development programme

Outlines a project undertaken by the Defence Research Agency [DRA] to produce a “gas cloud imaging” system based on optical transform image modulation [OTIM]. Describes the military origins of the OTIM technology and the OTIM Remote Gas Detection Technique, including the temporal coherence measurement used in the gas detector. Lists the capabilities and key features of OTIM and explains that the exploitation of the technology for civil applications has been targeted at industrial plant safety and environmental monitoring. Concludes with an outline project plan for developing the OTIM gas cloud‐imaging system.