A turbidity measurement system based on single photon detection technology has been developed to measure the turbidity of high turbidity water in industrial wastewater. The transmitted light measurement based on the Beer-Lambert principle is used to expand the measurement range. The avalanche photodiode (APD) based highly sensitive single photon detection technology is used to obtain the total intensity of transmitted light and quantize it to the corresponding photon number, which can improve the sensitivity and response speed of the proposed system. In order to maximize the turbidity measurement range and improve accuracy, different incident optical powers are used for the measurement of low turbidity and high turbidity respectively. It has been experimentally verified that the turbidity in the range of 100 NTU to 4000 NTU can be effectively measured when the incident optical power is 10 mw. When the low turbidity is measured, the incident light power should be set as low as 0.3mw, which is suitable for the turbidity measure between 10NTU to 100NTU.The proposed turbidity measurement system has a strong applicability and can be applied to industrial water turbidity measurement.
Detection distance is an important index of infrared imaging system, and meteorological parameters are one of the main factors affecting the detection distance. The calculation model based on the detection distance of infrared detector point source is calculated by using MODTRAN software. Peel off the factors associated with the environment. Selecting typical weather conditions to calculate the detection distance of infrared detector's point source target. The detection distance under different atmospheric parameters is obtained, and the sensitivity analysis is carried out between the detection distance of infrared detector and the parameters of the meteorological environment. The results show that the detection distance is influenced by the parameters such as temperature, humidity, pressure, visibility, wind speed and so on, and is linearly related to these meteorological parameters.
A high-resolution fiber turbidity sensor has been developed to measure the wide dynamic range of turbidity. To improve the accuracy of measurements, the high sensitive single-photon detection technique is adopted in the sensor by using an avalanche photodiode (APD) to detect the total intensity of transmitted light and quantize it to the corresponding number of photons. A theoretical model for turbidity measurement is proposed by combining the B-L transmission law with the single photon counting theory. In order to cover a wide dynamic range measurement based on only one measurement system, an optimal optical power for the sensor must be chosen. Therefore, an experiment is designed to measures the different turbidity solutions by gradually changing the power of incident light. The test results show that, with the increasement of light intensity, the measured data fit better with the theoretical one when the measured turbidity is lower than 0.1NTU. However, the light intensity cannot be increased without limit in high turbidity region, especially when the turbidity is high than 1NTU, since there is a corresponding upper limit for the detection of avalanche photodiode (APD). After the processing and analysis of test data, the test results indicated the sensor can obtain the best measurement accuracy when the optical power of incident light at 11mW. The measured turbidity range is as wide as 50dB from 0.01 to 1000NTU. The proposed fiber sensor is robust and can be used for the wide dynamic turbidity detection for drinking water or some remote monitoring of water pollution.
Typical natural backgrounds include land, sea, desert, sky and so on, and experimental measurement is an effective means to obtain background radiation data. Because the background infrared radiation is affected by season, weather and the angle of solar radiation, it is necessary to collect environmental parameters at the same time during testing. The screening and collection of major environmental parameters is crucial for subsequent radiation data processing. In view of this problem, first of all, the influence of environmental reference on background infrared radiation was theoretically calculated by MODTRAN software, and the main parameters were screened out. A test program for radiation measurement of natural background is formed, which is used as a reference for the design of background infrared radiation measurement.
An all-fiber structure detection system based on single photon detection technique(SPDT) has been developed to measure the ultra-low turbidity ofliquids. To assure the measurement accuracy,the total intensity of transmission light has been detected and quantified as number of photons by avalanche photodiode (APD) which has the advantage of high sensitivity.A fresh all-fiber structure optical fiber probe based on SPDT is applied in the system to reduce the volume and fluctuation of traditional transmission-light measurement system,in which the all-fiber structure probe is used to delivery and collection of transmission light.On the basis of Beer-Lambert (B-L) transmission law,a test system has been established and carried out a series of experiments.By combining B-Llaw with the principle of SPDT,a novel model for detecting turbidity has been proposed to explain the experimental results.The results have shown a well exponential relationship over the range of 0.01–1NTU (Nephelometric Turbidity Units).It also has showna good linear relationship with a resolution as high as 0.01NTUin the range of 0.01-0.09 NTU.When it is 1 secondofthe sampling time,the mean error of measurement result can be controlled within 5% of full scale.In addition,the new detection structure proposed in this paper, which makes the system more compact and more suitable in the small special space.
In this paper, the reconstruction of axisymmetric temperature and H2O concentration distributions in a flat flame burner is realized by tunable diode laser absorption spectroscopy (TDLAS) and filtered back-projection (FBP) algorithm. Two H2O absorption transitions (7154.354/7154.353 cm-1 and 7467.769 cm-1) are selected as line pair for temperature measurement, and time division multiplexing technology is adopted to scan this two H2O absorption transitions simultaneously at 1 kHz repetition rate. In the experiment, FBP algorithm can be used for reconstructing axisymmetric distributions of flow field parameters with only single view parallel-beam TDLAS measurements, and the same data sets from the given parallel beam are used for other virtual projection angles and beams scattered between 0° and 180°. The real-time online measurements of projection data, i.e., integrated absorbance both for pre-selected transitions on CH4/air flat flame burner are realized by Voigt on-line fitting, and the fitting residuals are less than 0.2%. By analyzing the projection data from different views based on FBP algorithm, the distributions of temperature and concentration along radial direction can be known instantly. The results demonstrate that the system and the proposed innovative FBP algorithm are capable for accurate reconstruction of axisymmetric temperature and H2O concentration distribution in combustion systems and facilities.
The main ingredient of mash gas is alkenes, and methane is the most parts of mash gas and ethane is a small portion of it. Fast, accurate, real-time measurement of methane and ethane concentration is an important task for preventing coal mining disaster. In this research, a monitoring system with tunable diode laser absorption spectroscopy (TDLAS) technology has been set up for simultaneous measurement of methane and ethane, and a DFB laser at wavelength of 1.653μm was used as the laser source. The absorption spectroscopy information of methane and ethane, especially the characteristic of the spectrum peak positions and relative intensity were determined by available spectral structures from previous study and available database. Then, the concentration inversion algorithm method based on the spectral resolution and feature extraction was designed for methane and ethane synchronous detection. At last, the continuously experimental results obtained by different concentration of methane and ethane sample gases with the multiple reflection cell and the standard distribution system. In this experiment, the standard distribution system made with the standard gas and two high precision mass flow meters of D07 Sevenstar series whose flow velocity is 1l/min and 5l/min respectively. When the multiple reflection cell work stably, the biggest detection error of methane concentration inversion was 3.7%, and the biggest detection error of ethane was 4.8%. So it is verified that this concentration inversion algorithm works stably and reliably. Thus, this technology could realize the real-time, fast and continuous measurement requirement of mash gas and it will provide the effective technical support to coal mining production in safety for our country.
Ground-based observations of the middle atmospheric density, pressure and temperature profiles can be obtained by lidar. A single-wavelength Rayleigh lidar system based at Hefei (31°N,117°E) has been used to measure the atmospheric density, pressure and temperature in the middle atmosphere in night in the altitude range from about 25 to 40 km. The structure of Rayleigh lidar system, principles of middle atmospheric density, pressure and temperature measurement which is based on the Rayleigh scattering theory and method to retrieve atmospheric density, pressure and temperature profiles were described respectively. This instrument combined a 500mW Nd:YAG laser transmitter with a 0.4 m receiver mirror to observe returns from altitudes between 25km and 40km.The lidar observed atmosphere density, pressure and temperature profiles are validated through comparison with the measure data provided by sounding balloon. According to the data from actual measurement, the inversion of the vertical distribution of middle atmosphere density, pressure and temperature are in good agreement with the result of sounding balloon. Generally, in the altitude range 25 to 40 km, the density ratio profile of Rayleigh lidar to the sounding balloon density fluctuates between 0.98 and 1.10, the pressure ratio profile of Rayleigh lidar to the sounding balloon is between 0.99 and 1.06 and the deviation of the temperature is less than 6 k.
A diode laser sensor based on absorption spectroscopy has been developed for the measurement of spectroscopic parameters of the R(50) line at 5007.787cm-1 (20012<-00001 band) of CO2. Survey spectra of the CO2 R(50) line of CO2 - CO mixture gas with 49.82% CO2 were recorded at different temperatures and pressures through a high temperature measurement system using tunable diode laser absorption spectroscopy. High-resolution measurements of the CO2 R(50) line shape were used to determine collisional broadening full-width of CO2 by CO as a function of pressure and temperature. The collisional broadening coefficients were obtained at temperatures between 323K and 1873K, and the temperature dependent coefficient of the collisional broadening full-width of CO2 by CO was calculated. These parameters are supplement and improvement to the existing database. They are helpful for the detection of CO2 concentration in combustion diagnosis to ensure the accurate inversion of CO2 concentration in the combustion process.
Signal de-noising remains an important problem in lidar signal processing. This paper presents a de-noising method based on singular value decomposition. Experimental results on lidar simulated signal and real signal show that the proposed algorithm not only improves the signal-to-noise ratio effectively, but also preserves more detail information.
To meet the need of long distance transmission in low turbidity measurement system for low-loss, a new optical structure with wavelength 1310nm and 1550nm as the incident light is employed. In this research, experiments have been done for different optical length of the two wavelength light sources. The results show that: first, the transmitted light intensity has big difference under the circumstance of same concentration and optical length, though the loss has no remarkable difference transmitted in optical fiber between 1310nm and 1550nm. Second, the optimized optical length for better absorbance has been determined for 1310nm and 1550nm and it is irrelevant to the incident intensity. Third, the intensity of the two transmitted light decreases exponentially with the increase of optical length. For example, when the range of the optical length of 1310nm is 0.5mm-2mm, the transmitted intensity is about 60%-79% and the absorbance is 0.12-0.42. The transmitted intensity is about 5%-44%. When the range of the optical length of 1550nm is 0.5mm-2mm and the absorbance is still 0.12-0.42. Our experimental data provides the basis both for the optical length selection of these two light sources in water and the near-infrared spectral wavelength selection.
Because of its aerodynamic diameter of the aerosol particles are stranded in different parts of different human respiratory system, thus affecting human health. Therefore, how to continue to effectively monitor the aerosol particles become increasingly concerned about. Use flight time of aerosol particle beam spectroscopy of atmospheric aerosol particle size distribution is the typical method for monitoring atmospheric aerosol particle size and particle concentration measurement , and it is the key point to accurate measurement of aerosol particle size spectra that measurement of aerosol particle flight time. In order to achieve accurate measurements of aerosol particles in time-of-flight, this paper design an ECL-TTL high-speed timer with ECL counter and TTL counter. The high-speed timer includes a clock generation, high-speed timer and the control module. Clock Generation Module using a crystal plus multiplier design ideas, take advantage of the stability of the crystal to provide a stable 500MHz clock signal is high counter. High count module design using ECL and TTL counter mix design, timing accuracy while effectively maintaining , expanding the timing range, and simplifies circuit design . High-speed counter control module controls high-speed counter start, stop and reset timely based on aerosol particles time-of-flight, is a key part of the high-speed counting. The high-speed counting resolution of 4ns, the full scale of 4096ns, has been successfully applied Aerodynamic Particle Sizer, to meet the precise measurement of aerosol particles time-of-flight.
Passive Fourier-transform infrared (Passive-FTIR) spectroscopy allows rapidly identification of the air pollution. However, for the localization of a leak and a complete assessment of the situation in the case of the release of a hazardous chemical gas or biological cloud, information about the position and the spatial distribution of a cloud is very important. In this work, a scanning imaging passive FTIR system, which composed of an interferometer, a data acquisition and processing software, a scanning system, a video system, and a laptop has been developed. The concentration retrieval algorithm for the passive FTIR remote measurement of gas cloud is presented, which involves the infrared radiative transfer model, radiometric calibration and absorption coefficient calculation. The concentration of the object gas is retrieved by using the
nonlinear least squares method. And no background spectra are required. The remote sensing experiment of SF6 was carried out. The measuring result shows that, the column densities of all directions in which a target compound has been identified may be retrieved by a nonlinear least squares fitting algorithm and algorithm of radiation transfer, a false color image is displayed. The results are visualized by a video image, overlaid by false color concentration distribution image. The system has a high selectivity, and it allows visualization and quantification of pollutant clouds. The system allows mobile, real-time and fast measurements of chemical gas and biological clouds.
The laser-induced breakdown spectroscopy emission characteristics of trace heavy metal lead in water is studied based
on graphite conch method, with a 1064nm wavelength Nd: YAG laser as excitation source, the echelle spectrometer and
ICCD detector are used for spectral separation and high sensitive detection with high resolution and wide spectral range.
The delay time 900ns and gate time 1600ns are determined in the experiment. The calibration curve of Pb is plotted
based on the different concentration measurement results, and a limit of detection of 0.0138mg / L is obtained for Pb in
water. Graphite conch method effectively overcomes the current problems on laser-induced breakdown spectroscopy
detection of heavy metal in water. The detection limits and stability are improved. The reference data is provided for
further study on the fast measurement of trace heavy metals in water by laser induced breakdown spectroscopy
technique.
Laser indued breakdown spectroscopy(LIBS) system was used for analysis of heavy metals (Cr, Pb,
Cu, Ni, Cd, Zn) in soil. And neuro-genetic method was applied to optimize the system parameters in
order to maximize the signal-background ratio of all heavy metals simultaneously. LIBS system
equipped with an Andor Echelle spectrometer, coupled to an ICCD detector. A Q-switched Nd:YAG
laser was used to induced plazma. Delay time, integration time, scan times of laser pluse, frequency of
laser were optimized. The optimized parameters were obtained: 1μs delay time, 4.5μs integration
time, 48 scan times, and 11Hz frequency of laser.
The tropospheric SO2 in Pearl River delta region was firstly measured by airborne Multi Axis
Differential Optical Absorption Spectroscopy in China on 10 December, 2008. The SO2 slant columns
were derived with DOAS method in the wavelength from 310~ 325nm and the vertical columns were
retrieved by radiative transfer model SCIATRAN. High values were observed near power plant regions
with the vertical column density values higher than 8x1016molec./cm2 in the measurement. Combining
with the meteorological data from local station the SO2 flux from the power plant was calculated, the
emission flux of SO2 was about 2.59x1025molec./s. Over the city of Zhuhai, the observed SO2 vertical column density was 2.46x1016molec./cm2. This is in good agreement with ground-based MAX-DOAS
of 2.62x1016molec./cm2 if the same aerosol parameter settings and a well mixed boundary layer of 1000 m is assumed.
Knowing the quantity of pollutants that the vehicle fleet is emitting to the air has become a vital question in almost every major city in China. Finding and fixing gross polluters is therefore very important to control the urban air quality and protect the human health and the environment. Remote sensing is an important advance in the technology of on-road vehicle emissions testing because it is fast, mobile, and unobtrusive. This on-road vehicle emissions remote system is designed to measure the carbon monoxide, carbon dioxide and opacity from the vehicles's tailpipe based on the Tuneable Diode Laser Absorption Spectroscopy (TDLAS). There are several advantages of this system such as compact design and ease of use. The measurement principle and optical layout of the instrument has been described in this paper. Field testing at Beijing and Hefei were conducted over one year, more than 6000 vehicles were tested. This vehicle emissions remote system has been shown to be able to measure CO,CO2 and opacity from individual at highway speeds. In parallel, the plate license, speed, acceleration and length of vehicle are recognised by computer so that the owners of vehicles exceeding the permissible level of emissions can be identified.
The field experiment of Dongpu reservoir has been carried out from April 11 to 20 in 2005, and the concentrations of dissolved organic matter (DOM) are measured and analyzed in combination with laser-induced fluorescence (LIF) measurements. The aim of the field investigations was to determine the concentration of DOM in water and evaluate the performance of fluorescence remote sensing system. In experiment, we obtained interesting data of DOM at 49.35m distance by changing the angle of excitation laser incidence to water. The concentration of the DOM is 3.325mg/l and the relative standard deviation is 2.65%. It has been shown that the measurement of water quality in real time and on line can be done using LIF technique with high sensitivity and high precision.
The Tibet plateau is characterized with its own special highland climate environment. In this paper, the temporal vertical profiles of aerosol extinction/backscattering coefficients, the boundary layer height (BLH) and cloud height during the CAMP-Tibet 2003 autumn and 2004 spring session observations at Naqu BJ site, Tibet are determined with ancillary meteorological parameters, and compared with data at Bejing site.
In the past decade interest has focused on the remote analysis of emissions from motor vehicles using spectrometric techniques, driven by recognition of the fact that a very large proportion of the environmental damage done in this way originates with a small percentage of vehicles. Several instrumentation manufacturers now market such devices, and others are developing new technologies that will offer opportunities for enhanced performance and lower cost.
In this paper we demonstrate the prototype design of vehicle emission remote sensing system by differential optical absorption spectroscopy (DOAS) and tunable diode laser absorption spectroscopy (TDLAS). In this design, vehicle emissions will be measured when they past a on road remote sensing station while driving along a road. The concentrations of hydrocarbons (HC) and Oxides of Nitrogen (NOx) are measured by DOAS, and the concentrations of Carbon Monoxide (CO) and Carbon Dioxide (CO2) are measured by TDLAS. The measurement precisions for CO and CO2 are ±0.25%, and the detection limits for HC and NO are ±250ppm.
In the past decade interest has focused on the remote analysis of emissions from motor vehicle using spectrometric techniques driven by recognition of the fact that a very proportion of the environmental damage done in this way originates with a small percentage of vehicles. In this paper a remote sensing system designed to measure air-pollutant emission from on-road motor vehicles is described. The system uses a tunable infrared laser differential absorption spectrometer and a technique of UV DOAS. It has been shown to be able to measure CO, C02 NO, HC and the dust emissions from on-road individual vehicles. Excellent detection sensitivity is obtained with measure precision.
On-road motor vehicle emissions have been estimated being the single largest contributor of major atmospheric pollutants worldwide. The amount of motor vehicles in Beijing has rapidly grown in the past few years and will increase even more noticeably in the near future. It is therefore clearly required that a targeted approach to identifying the grossly polluting vehicles will have maximum impact on reducing the detrimental effects of the emissions. In this paper we will introduce an on-road motor vehicle exhaust emission monitor built by our group. This monitor was fabricated with tunable diode laser absorption spectroscopy (TDLAS) technique. On-road remote sensing of CO and CO2 of the motor vehicle exhaust emissions on Xueyuan road and at Dayangfang motorway toll station in Beijing were performed with this monitor. Analysis of the results shows that only 73.4% on-road motor vehicles are clean. Among the rest more than 15% are heavy gross polluters which should be warn for repair or removed from service.
Sulfur dioxide is a highly toxic air contaminant that harms human health and damages the environment. It is easily converted to sulfuric acid which is the major component in acid rain and to sulfate particles. Coal-burning power plants are the main sources of SO2 pollution. It is necessary to evaluate the emissions from industry for emission reduction strategies. Passive DOAS method has been successfully applied in volcanic plume and atmosphere monitoring because of its advantage of relative simple system with no light source. Here we report the measurement of SO2 total flux from a chimney in plant area in Hefei city (China) with a compact passive DOAS system. The system consists of a small telescope pointing zenith direction and a fibre-coupled OceanOptics USB2000 spectrometer. In the measurement the system was mounted on a mobile platform moving under the plume approximately perpendicular to the plume transport direction and the spectra of the zenith direction were recorded. By combining the integrated gas concentration over the plume cross section with wind velocity data SO2 flux was estimated.
MODIS a moderate-resolution imaging spectroradiometer instrument on board EOS-AM1 and PM1 has 36 spectral bands amongst which only 9.6 μm band sensitively traces atmospheric ozone. To produce total ozone inversion one requirement is via temperature and pressure profiles a popular requirement of mass-calculation which could now be argued not a literally convenient idea. Thus in this paper I try my hand at a new method through firstly overall bands' correlative statistics and analysis based on MODIS high-precision data source in spectral radiation to materialize "similar TRIPLET" spectral data combination method. Then it comes to us a need to attain a solid cooperative optimization and thirdly with forgoing output a process is introduced here of spectrum differential calculation leading to final total ozone inversion.
KEYWORDS: Sensors, Personal digital assistants, Stray light, Spectroscopy, Absorption, Photodiodes, Lamps, Signal processing, Digital signal processing, Light sources
DOAS technique provides a more representative picture of air quality and typical urban exposures over traditional point monitoring equipments it has been widely used for urban air quality monitoring in China. Most commercial DOAS instruments presently used for air quality monitoring adopt photomultiplier and scanning slit as detector which is called slotted disk (SD) detector. In contrast with the SD detector Photodiode Array can overcome the problem of scintillation noise caused by atmospheric turbulence and reduce photon noise. We report here a new type UV-visible DOAS system based on photodiode array. The properties of the system including offset dark current noise linearity of the detector and resolution stray light ofthe spectrometer are described. Field observations of a number of pollutants (e.g. S02, NO2, 03 and HCHO) were performed in the urban area of Beijing City during August 2004. The measurement results show that the system fulfils automatic ambient air monitoring with high time resolution and sufficient sensitivity.
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