Tunable diode laser measurements of water vapour absorption line parameters

Tunable diode laser measurements of water vapour lines in the 5 μm region have been extended to include oxygen as well as nitrogen broadening. Positive pressure shifts of line positions have been observed for the first time in the v ₂ band. Absolute calibration of a line position using the CO laser as a reference has also been carried out.     

Intercomparison measurements of Rn concentration in water samples in Poland

The paper presents the results of intercalibration measurements of ²²²Rn concentration in water samples. The aim of the experiments was to evaluate the different measurement methods of radon determination in water samples performed by eleven laboratories in Poland and to test these methods in field work. In the years 2001-2003 three national intercomparison experiments were organized. The results allowed the participating laboratories to improve their measurement methodologies and to achieve better, i.e. more convergent results of determining radon concentration in water samples. The results show that the use of liquid-scintillation technique seems to be the best measurement method. It should be emphasized that comparative experiments are essential for all laboratories and they should be carried out as often as possible, based both on prepared samples with known concentration values of ²²²Rn and natural water samples, the most commonly used in laboratory practice.     

The water vapour content in the western European atmosphere obtained from infrared measurements

We report on measurements of the water vapour content in the western European atmosphere obtained from infrared attenuation measurements, made during a site survey for a millimetre-wave radio observatory.     

Simulating forest fire spread and fire-fighting using cellular automata

In response to the transboundary haze problem in Southeast Asia, a physical model is adopted to simulate the spread and extinguishing of fire. This study is done in the context of Dumai, Indonesia, as it is one of the areas that significantly contribute to the haze problem. This model aims to provide perspectives on the persistence of forest fires despite fire-fighting efforts. While existing models using Huygens’ principle of wave propagation allow an understanding of the natural spread of fire, our model applies cellular automata to predict and analyse the effects of fire-fighting intervention strategies, with the spatial and propagation dynamics of fire considered. Cellular automata is an active area of research among physicists, and is widely used by chemists and biologists to model many types of natural phenomena. We note similarities between our model predictions and observations of real-world phenomena. Analyses on the factors that affect the spread of fire are presented, in order to understand which ones are dominant in differing situations. This provides insights on optimum conditions for fire-fighting efforts, and suggests guidelines that may be considered for fire control in future forest fires.     

In situ measurement of CO2 and water vapour isotopic compositions at a forest site using mid-infrared laser absorption spectroscopy

We conducted continuous, high time-resolution measurements of CO₂ and water vapour isotopologues (¹⁶O¹²C¹⁶O, ¹⁶O¹³C¹⁶O and ¹⁸O¹²C¹⁶O for CO₂, and H₂¹⁸O for water vapour) in a red pine forest at the foot of Mt. Fuji for 9 days from the end of July 2010 using in situ absorption laser spectroscopy. The δ¹⁸O values in water vapour were estimated using the δ²H–δ¹⁸O relationship. At a scale of several days, the temporal variations in δ¹⁸O-CO₂ and δ¹⁸O-H₂O are similar. The orders of the daily Keeling plots are almost identical. A possible reason for the similar behaviour of δ¹⁸O-CO₂ and δ¹⁸O-H₂O is considered to be that the air masses with different water vapour isotopic ratios moved into the forest, and changed the atmosphere of the forest. A significant correlation was observed between δ¹⁸O-CO₂ and δ¹³C-CO₂ values at nighttime (r²≈0.9) due to mixing between soil (and/or leaf) respiration and tropospheric CO₂. The ratios of the discrimination coefficients (Δ_a/Δ) for oxygen (Δ_a) and carbon (Δ) isotopes during photosynthesis were estimated in the range of 0.7–1.2 from the daytime correlations between δ¹⁸O-CO₂ and δ¹³C-CO₂ values.     

Sound velocity in water vapour

The effective potential is used to calculate the sound velocity of water vapour. The agreement between theoretical and experimental values confirms the validity of the effective potential.     

Application of a CO2 dial system for infrared detection of forest fire and reduction of false alarm

Forest fires can be the cause of serious environmental and economic damages. For this reason considerable effort has been directed toward forest protection and fire fighting. The means traditionally used for early fire detection mainly consist in human observers dispersed over forest regions. A significant improvement in early warning capabilities could be obtained by using automatic detection apparatus. In order to early detect small forest fires and minimize false alarms, the use of a lidar system and dial technique will be considered. A first evaluation of the lowest detectable concentration will be estimated by numerical simulation. The theoretical model will also be used to get the capability of the dial system to control wooded areas. Fixing the burning rate for several fuels, the maximum range of detection will be evaluated. Finally results of simulations will be reported. PACS 42.68.Wt; 89.60.Ec; 92.60.Mt; 92.60.Iq     

Range-resolved gas concentration measurements using tunable semiconductor lasers

A method for range-resolved gas sensing using path-integrated optical systems is presented. The method involves dividing an absorption path into several measurement segments and extracting the gas concentration in each segment from two path-integrated measurements. We implemented the method with tunable lasers (a 1389-nm VCSEL and a 10.9-μm pulsed quantum cascade laser) and a group of retro reflectors (RRs) distributed along absorption paths. Using a rotating mirror with the VCSEL configuration, we could scan a group of seven tape RRs spaced by 10 cm in ∼ 9 ms to extract an H₂O concentration profile. Reduced H₂O concentrations were recorded in the segments purged with dry air. Hollow corner cube RRs were used in the quantum cascade laser configuration at distances up to 1.1 km from the laser. Two RRs placed at 66 m and 125 m from the laser allowed us to determine H₂O concentrations in both segments. The RRs returns were separated due to the different round trip travel time of the 200-ns laser pulse. Novel instruments for range-resolved remote sensing in the atmosphere can be developed for a variety of applications, including monitoring the fluxes of atmospheric pollutants and controlling air quality in populated areas. PACS 42.68.Wt; 42.62.Fi; 39.30.+w     

Simultaneous infrared spectral hygrometer and radiosonde measurements of the precipitable water vapour content in the atmosphere

We report on simultaneous measurements of the atmospheric precipitable water vapour content in the central part of Spain, carried out with an infrared spectral hygrometer and by radiosonde. The correlation between both types of measurements is analysed and we find a linear correlation coefficient r = 0.85. From a comparative analysis of our results with those obtained for other European sites, it appears that altitude differences up to about 1000m may not be a decisive factor in determining the amount of precipitable water vapour present at a particular intermediate altitude (∼ 1000–2000 m) site.     

Frequency-stabilized cavity ring-down spectrometer for high-sensitivity measurements of water vapor concentration

We present a portable spectrometer that uses the frequency-stabilized cavity ring-down spectroscopy technique capable of high-precision measurements of trace water vapor concentration. Measuring one of the strongest rovibrational transitions in the ν₁+ν₃ water vapor combination band near ˜ν=7181.156 cm^-1, we compare spectroscopic and thermodynamic determinations of trace water vapor in N₂, and find systematic differences attributable to water vapor background effects and/or uncertainties in line intensities. We also compare the frequency-stabilized ring-down method with other cavity ring-down approaches that are based on unstabilized probe lasers and unstabilized ring-down cavities. We show that for the determination of water vapor concentration, the frequency-stabilized cavity ring-down method has the minimum measurement uncertainty of these techniques. The minimum noise-equivalent absorption coefficient of the spectrometer was 1.2×10^-10 cm^-1 Hz^-1/2, which further corresponds to a minimum detectable water vapor mole fraction equal to 0.7×10^-9 for an absorption spectrum of 10 minutes duration. PACS 33.20.-t; 33.70.Jg; 33.70.Fd; 42.62.Fi     

Local fuel concentration measurements in internal combustion engines using spark-emission spectroscopy

Spectrally resolved visible and ultraviolet emissions are investigated as a basis for wide-range, individual-cycle measurement of the local fuel concentration in spark-ignition engines. The 388-nm CN emission intensity, normalized by the spark-discharge energy during the observation interval (typically 150 μs at the start of the glow discharge), is found to be the most useful measure of fuel concentration when data are required over a wide range. Calibration data for homogeneous propane–air and isooctane–air mixtures over a wide range of cylinder gas conditions at the time of ignition collapse to a single curve when the fuel concentration is expressed in terms of the number density of carbon atoms. The carbon number densities measured in this study correspond to fuel–air equivalence-ratios in the range 0–3 at 95% throttle conditions. Random and systematic errors are 10% or less. Applied to an engine in which liquid fuel is injected directly into the cylinder, the technique reveals substantial cyclic fluctuations in the fuel concentration at the spark gap for early fuel injection (intended to produce a homogeneous fuel–air mixture in the combustion chamber) and large fuel-concentration fluctuations for late fuel injection (which produces a highly stratified mixture). The results also show that for stratified operation with a fixed fuel-injection timing, a spark timing that is later than optimum leads to incomplete combustion in many cycles due to fuel–air ratios that are too lean for good ignition and rapid flame development. Received: 6 November 2001 / Revised version: 6 May 2002 / Published online: 25 September 2002 RID="*" ID="*"Corresponding author. Fax: +1-586/986 0176, E-mail: todd.fansler@gm.com     

Opto-thermal radiometry and condenser-chamber method for stratum corneum water concentration measurements

Opto-thermal radiometry and the condenser-chamber TEWL (trans-epidermal water loss) method are two novel technologies for in-vivo skin studies. In this paper, for the first time, we combine the measurement results of the two technologies, and study the stratum corneum water concentration distribution, water status in stratum corneum, stratum corneum thickness as well as its swelling effects, and stratum corneum water-holding capabilities. We present both the theoretical background and illustrative measurement results. PACS 87.61.Ff; 87.80.-y; 87.50.Hj     

Uranium concentration in drinking water samples using the SSNTDs

Uranium concentrations in the drinking water samples collected mainly from hand pumps along the Amritsar to Bathinda track are presented. Uranium concentration values in these samples show a wide range of variation depending upon different factors like source, location, depth and local geology etc. The observed uranium content in water samples has been found to be varying from 0.9 ± 0.08 to 63 ± 0.21 ppb and even the radon activity in ground water observed in our earlier survey carried out in this area has been found to be increasing from Amritsar towards Bathinda. The higher values were observed from the ground water samples particularly of the areas falling in belt from Zira to Maur towards the Haryana border. The values observed at certain locations are found to be higher than the highest recommended value of 15 ppb [1]. The high uranium concentration observed particularly in certain areas along this track can be attributed due to interaction of ground water with the soil formation of this region and the local subsurface geology of the region.      

Solitons in the one-dimensional forest fire model

Fires in the one-dimensional Bak-Chen-Tang forest fire model propagate as solitons, resembling shocks in Burgers turbulence. The branching of solitons, creating new fires, is balanced by the pairwise annihilation of oppositely moving solitons. Two distinct, diverging length scales appear in the limit where the growth rate of trees, p, vanishes. The width of the solitons, w, diverges as a power law, 1/p, while the average distance between solitons diverges much faster as d approximately exp(pi2/12p).     

In-cylinder gas temperature and water concentration measurements in HCCI engines using a multiplexed-wavelength diode-laser system: Sensor development and initial demonstration

A wavelength-multiplexed, fiber-optic-based, line-of-sight, diode-laser absorption sensor is developed for crank-angle-resolved measurements of temperature and water concentration in a homogeneous-charge-compression-ignition (HCCI) engine. An initial demonstration of its use on two optical HCCI engines at Sandia National Laboratories is reported. The measurements encompassed both motored- and fired-engine operation for temperatures between 300 and 1700 K and pressures between 1 and 55 bar. A spectroscopic line selection process identifies the most appropriate water absorption linepair for thermometry under these conditions. Key solutions to suppress crank-angle-dependent noise in the transmitted laser signals are reported, including careful spectroscopic design and optical engineering to accommodate beam-steering, engine vibration and polarization-related interference. Data obtained through this sensor can provide critical engine characteristics such as combustion efficiency, peak combustion temperature, and autoignition temperature. The flexibility of the wavelength-multiplexed architecture allows the straightforward addition of other wavelengths to potentially enable the simultaneous measurement of other important engine parameters such as temperature non-uniformity, and fuel, CO, and CO₂ concentrations.     

Atomic hydrogen concentration mapping in thermal plasma chemical vapour deposition

Two-dimensional maps of atomic hydrogen concentration in reactive gas layers were measured using two-photon laser-induced fluorescence. The measurements were made in conditions of diamond-film chemical vapour deposition using a thermal inductively coupled plasma. Their purpose was to investigate the influence of the atomic hydrogen concentration in the reactive gas layer on the diamond growth. Concentration maps were obtained under parametric variation of the plasma flow conditions. Axial profiles were extracted from the measured maps and compared to temperature profiles measured by Rayleigh scattering to determine the degree of chemical non-equilibrium in the reactive layer. The non-uniform quenching over the measured area was accounted for with an iterative calculation of the species concentrations. For small differences of the atomic hydrogen concentration in the reactive layer a large variation in quality of the grown diamond was observed. Received: 28 June 2000 / Revised version: 6 October 2000 / Published online: 21 February 2001     

Dynamics of forest fire under rotational constraint

A rotationally constrained forest fire model is studied on square and triangular lattices of size 400×400. The critical probabilityp _c for onset of fire propagation is determined. The scaling relationsMt ^d _r, R_gt^v andMR _g ^d _f are analysed at fire propagation probabilityp=p _c whereM is the number of burnt trees,R _g the radius of gyration andd _f the fractal dimension of the cluster of burnt trees at timet. Numerical estimates ofd _t, v andd _f have been obtained.