Temperature measurement in flames is a challenging problem. Recently, hyperspectral imaging has demonstrated to be able to provide accurate temperature maps in a standard flame. However, hyperspectral imagers are expensive instruments, and the data analysis is laborious. Thus, a more simple approach to temperature imaging would be advisable. Since important and systematic differences exist in the low-resolution spectra of flames as a function of their temperature and chemical composition, it is in principle possible to retrieve these parameters by means of multispectral imaging. In this work, a standard flame, whose temperature and CO2 concentration are known, is studied with an infrared camera in the MIR band (3 to 5 μm), provided with a six interference filter wheel. High- resolution emission spectra are calculated, using the HITEMP2010 database, as a function of flame temperature (T) and CO2 column density (QCO2 , measured in ppm·m), and integrated over the spectral transmittance profile of the selected interference filters. Measured radiances in each channel are compared to these simulated values and the absolute error is minimized at each pixel to retrieve values of T and Q, obtaining temperature and column density maps for the flame. Results are compared to the known values of the standard flame. First estimations of errors are found to be ΔT< 100 K and ΔQCO2 < 400 ppm·m for flames with T∼2200 K and QCO2 ∼3500 ppm·m. The possibility of reducing the number of filters and their effect on accuracy is studied.
The objective of the Infrared Laboratory-LIR has been the design and development of simple and low-cost IR systems for the resolution of specific problems in real time. The study of clouds in the IR region is a problem studied since the first on-board measurement systems. Nowadays imaging systems are multispectral instruments that provide accurate information on clouds. These systems are generally large in size, weight and cost. However, in many situations, the goal is simply to get auxiliary information about the clouds. Then, the low-cost approach of LIR is ideal for designing simple cloud characterization systems. In this work, a methodology is presented to determine the emissivity and temperature of the clouds based on the brightness temperature measured from space by a bi-spectral camera in the 10 and 12 microns bands. In addition, we provide quantitative information on the capabilities of the methodology based on real data provided by MODIS instrument.
In the last decades, composite materials, particularly thermosetting carbon fiber reinforced polymers, have become the main structural material for the aerospace industry. Recently, interest has grown in thermoplastic composites, since they are chemically more stable, faster to process, fatigue-resistant and recyclable. Nevertheless, when submitted to high temperatures these materials may degrade in ways not presently well known. Therefore, the study of the thermo-mechanical properties of thermoplastic composites when exposed to fire or high-temperature events is of primary interest. In particular, a good knowledge of its behavior could improve physical modeling to the point of reducing the number of prescribed fire tests by virtualizing some of them. The first step is to measure the thermal parameters of real samples in a practical way. We have established a methodology that extends the classical flash method to obtain the effective thermal parameters (diffusivity, specific heat, heat conductivity, and Biot number) of thermoplastic composite materials by a non-contact method based on IR imaging. Values obtained have been used to simulate thermal behavior with a FEM-based solver, from room temperature up to 900°C, with an agreement with experimental data better than 1% in temperature (K) for temperatures below ∼ 260°C and better than 3% up to ∼ 850°C.
KEYWORDS: Thermography, Glasses, Modulation, Signal to noise ratio, Infrared cameras, Solar cells, Signal detection, Visualization, Infrared radiation, Infrared imaging
Infrared (IR) lock-in thermography (LIT) has been successfully used for defect detection in solar cells. Depending on the experimental setup, defects such as shunts, series resistances, pre-breakdown regions, etc., can be qualitatively visualized or quantitatively measured. IR-LIT results improve the spatial resolution (SR) in defect visualization and the signal-tonoise ratio (SNR) between defects and sound regions compared to classic DC thermography. The same results have been accomplished on solar modules, considered as an ensemble of solar cells electrically connected. The main problem that arises in IR-LIT technique is encapsulated modules/cells measurement, because most glasses used for encapsulation are opaque in the IR region. In this research, IR opacity of encapsulating glass is treated from a thermal point of view. Solar cells have been considered as a heat source with a heating frequency actively generated by a modulated forward polarization. The encapsulation behaves as a thermal low pass filter, whose cutoff frequency has been calculated. In the experiments, a modulated forward electrical polarization has been applied to a solar module in the dark. The tested sample has been a standard solar module of 36 cells connected in series. Thermal images have been acquired from the side of the external glass surface by an IR camera. A large improvement of SR and SNR has been demonstrated for shunt detection when the modulation frequency is below the cutoff.
Martian atmosphere contains two main mechanisms leading the heat transfer process: CO2 and suspended dust. The flight model (FM) of the current Dust Sensor (DS) of the Mars MetNet Mission has already been fabricated providing only with the ability for measuring the particle size distribution. The optimized DS proposed in this work includes two sub-instruments more for measuring both, CO2 concentration and ground temperature. This DS will allow correlate the
particle size distribution of the airborne dust, the CO2 concentration and the ground temperature, in a specific location on the Martian surface. All of these parameters will be measured as an in-situ parameter, giving very valuable information
about the Martian Planetary Boundary Layer (PBL). The scope of the Mars MetNet Mission is to deploy, in successive flights, several tens of mini atmospheric stations on the Martian surface. Infrared Lab in University Carlos III (LIR-
UC3M) is in charge of the design and development of the DS, a micro-sensor (mass <100 g and mean power <1W) which scope is the characterization of airborne dust and other parameters of interest in the heat transfer process. The DS detection principle is of MIE scattering wavelength dependence when particle size is similar to that., so the sensor is provided with spectral resolution,. The optimized DS incorporates angular dependence, so the data retrieval algorithm takes both spectral and angular information making the algorithm most robust. The incorporation of new parameters such as CO2 and ground temperature is possible thanks to the addition of new sensor elements, properly spectrally tuned. As in the previous DS each parameter is also measured within the MWIR range and the spectral resolution is provided by a
interference filter, specifically designed for.
Infrared cameras are well established as a useful tool for fire detection, but their use for quantitative forest fire measurements faces difficulties, due to the complex spatial and spectral structure of fires. In this work it is shown that some of these difficulties can be overcome by applying classification techniques, a standard tool for the analysis of satellite multispectral images, to bi-spectral images of fires. Images were acquired by two cameras that operate in the medium infrared (MIR) and thermal infrared (TIR) bands. They provide simultaneous and co-registered images, calibrated in brightness temperatures. The MIR-TIR scatterplot of these images can be used to classify the scene into different fire regions (background, ashes, and several ember and flame regions). It is shown that classification makes possible to obtain quantitative measurements of physical fire parameters like rate of spread, embers temperature, and radiated power in the MIR and TIR bands. An estimation of total radiated power and heat release per unit area is also made and compared with values derived from heat of combustion and fuel consumption.
The new generation of dedicated satellites for remote sensing of forest fires now in advanced development demands validation measurements from airborne platforms. A digital image acquisition system in the medium infrared (MIR) and thermal infrared (TIR) bands has been set up specifically for imaging of fires. The system provides simultaneous, co- registered and radiometrically calibrated MIR and TIR images. This makes it possible to use image processing techniques based on pixel-by-pixel comparison of MIR and TIR brightness temperatures. Analysis of a laboratory flame and a wood bonfire shows that the MIR-TIR scatterplot can be used to classify the scene into different fire regions (cold background, hot nonflaming soil, hot flaming soil and pure flame). This technique has been applied also to observations of forest fires realized from a helicopter at distance of more than 1 Km, revealing that several fire regions can be demarcated, including a fire front in which flame emission makes a large contribution.
Early remote sensing of forest fires from specifically dedicated low cost satellites has recently been proposed as one of the most promising techniques for the improvement in the efficiency of forest fire fighting on a global basis. Efficient forest fire remote sensing requires a high probability of detection for small fires combined to a low' false alarm rate. In this paper, a very simple algorithm based on the so-called fire index (FI) has been implemented in an acquisition system developed within the framework of the UE-DGXII Project FUEG02. This system is composed by tw;o infrared cameras operating in the mid and thermal infrared spectral regions and acquire simultaneous digital images of the scene that are calibrated in radiometric units. An image of the FI is then computed improving greatly the discrimination of false alarms. A new approach using only the mid infrared band is also suggested, and spectral intraband processing is studied as a basis for this approach.
An IR absorption system for real-time measurement of pollutants in exhaust gases from moving vehicles is proposed. The system consists of an IR source at one side of the road, and a wheel with specific IR filters and a detector at the other side. We have, firstly, simulated the expected exhaust gases concentrations at different inspection conditions. The well-known HITRAN database has been used in order to estimate intensities, signal-to-noise ratio and threshold concentration levels. These results have then been verified by open-path Fourier transform IR (FTIR) spectroradiometry of the exhaust gases from both gasoline and Diesel vehicles. This confirms the feasibility of such a device by using some conventional filters -those of CO, CO2 and NO2 for example - some ultra-narrow sold state Fabry-Perot filters - that of NO for example. As the proposed system monitors all kinds of oxides and hydrocarbons in exhaust gases the stoichiometry of the combustion or 'lambda coefficient' may be also deduced and it is fully applicable for 'ministry of transport' test of vehicles.
Radiometric characterization of the infrared emission of forest fires has been performed for different primary carriers (grass, shrub, and slash) and different ambient conditions in a combustion tunnel (temperature, relative humidity and wind speed). Fourier Transform-based FTIR spectroradiometer (2.2 - 18 micrometer range) as well as a thermal camera have been used in the study. Also a 'classical' characterization, based on the fuel weight before and after the burn, and the measurement of soil and fire temperatures, has been made. Temperature profiles at different heights in different points of the heating zone have been measured by using an automatically controlled thermocouple network. The thermocouples measure the temperatures each 5 seconds in the 0 - 1200 degrees Celsius range. Parameters defining the fire behavior, mainly determined by the fuel consumption ratio, rate of spread, angle and length of flames, and the fire lineal intensity, are obtained from this characterization. Comparison between these results and the radiometric measurements has been done. Information from the camera is used to obtain infrared emissivities of the fires.
This paper describes some of the work performed in the course of the design and development of a new IR sensor system for early detection of forest fires. The proposed device is a non- imaging sensor that would discriminate angular position by means of a simple IR array, working in the 3 - 5 microns wavelength region, placed at the focal plane of the optical system. In order to accomplish low cost requirements, a system with a sole IR lens has been designed. In this work, a study of the spot shape, size and optical IR power on the detector has been performed. From the analysis of the influence of lens-detector distance and incidence angle, we have derived an optimum pixel size and optical configuration. The use of TE- cooled PbSe detectors is proposed, as well as a simplified cell array.
In this work, a new spectral selection system for imaging of CO infrared emission in combustion environments is proposed. The CO and CO2 medium infrared emission bands are spectrally overlapped, so cross-talk effects would appear when trying to image CO using a IR camera equipped with a conventional band-pass filter. The system proposed belongs to a new family of infrared multilayer filters, called solid state Fabry-Perot (SSFP) filters. The transmittance of such filters can be spectrally matched to the CO fine structure emission band. Thus, it is possible to discriminate the CO emitted IR radiation from that which comes from CO2 in combustion environments. With a Fourier Transform Infrared spectroradiometer, we have studied and spectrally characterized the IR emission from hydrocarbon flames, varying the O2 inlet, i.e. the CO generated. Using these experimental data and the theoretical spectral transmission for both band-pass filter and the SSFP filter, we have demonstrated the uselessness of the former and the suitability of the latter, in order to discriminate CO and CO2. A silicon wafer, both sides covered by a reflecting multilayer, is proposed as a SSFP. The design and spectral parameters of such a filter are developed on the basis of the optical properties of the multilayers and substrate, and specific designs for CO imaging are presented.
Commercial Fourier transform based FTIR spectroradiometers can be used in an easy way as ground-based remote sensing systems. Information of the ozone column can be obtained from the spectral IR radiance in the 900-1200 cm-1 range. Tropospheric and stratospheric ozone are sounded by an appropriate selection of the experimental conditions. A theoretical study of the best choice for the wavenumbers of zenith angles for the direction of view is presented. The problem of the superimposed water emission is analyzed for the selected wavenumbers. Finally, some experimental results are presented, with a fast method to obtain the water and ozone columns from a spectral radiance spectrum.
A new Fabry-Perot filter based on a silicon wafer spacer is proposed in this work. IR gas sensors based on these filters would combine excellent selectivity and signal-to-noise ratio with an overall scheme similar to that of the simplest non-dispersive IR sensors. The filter can be fitted to the fine structure of different gases, in particular those diatomic with unlike atoms as carbon monoxide among others. The spacer of the filter is a silicon wafer of defined thickness. Fine tuning to gas absorption peaks can be reached by coupling it to other multilayers. In this work the properties of silicon wafers as spacers of the proposed filters are studied. From the study it derives that the most determining factor of the filter properties is the loss of coherence caused by surface roughness. However, as we demonstrate in this work, surface roughness limitations are not very severe and easily obtained by standard polishing procedures.
A new sensor is proposed combining arrays of interference filters with resonant cavities of high interference order (Fabry-Perot resonators) using both, high capabilities of accurate thickness control in silicon substrates derived from microelectronics and thin-film optics techniques. The interest of this type of device would be the fabrication of high resolution multigas sensors, compact, with no moving parts, for accurate measurement of low concentration gases.
The integration of different infrared interference filters on a single substrate to obtain filter arrays is discussed. These arrays, when coupled in the focal plane to linear photodetector arrays, form the so-called `spectral retinae' which permit spectral and spatial resolution with no moving parts. Its application to new multigas sensors based on infrared absorption spectroscopy is also discussed. The different aspects emerging in the integration of specific interference filters are discussed in this paper. Special attention is paid to the problems of compatibility of the different processes involved in the obtention of the integrated filter. The improvement of detection limits for gases of great environmental interest as sulfur dioxide, and nitrogen dioxide is also discussed. Aspects related to the whole conception of the sensor are studied too, mainly those related to the improvement of signal to noise ratio by means of the optimization of the optical parameters. Finally, a new concept for using spectrally selective mirrors in long path optical cells, is proposed. In this way a considerable improvement in simplicity and performance of the spectral retinae can be obtained.
GaP/InP strained-layer superlattices (SLS) grown on GaAs substrates are a novel structure with a large lattice mismatch symmetrically shared (+ 3 . 7 (GaP) -3 . 6 (InP)). We present growth and characterization of two types of GaP/InP based heterostructures: i) isolated SLSs and ii) a SLS based QW confined by A1GaAs barriers. Growth by Atomic Layer MBE has allowed to combine P- and As-containing materials in a controllable way preserving flat interfaces at low substrate temperatures. Optical characterization oftheheterostructures ispresented and correlated with akp model obtaining the first estimation for the conduction band offset at the GaP/InP heteroj unction. All superlattices studied have been found to be spatially direct (type I) being this feature very promising for their use as active layer in a semiconductor QW laser. I.
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