Study of aerosols and molecular extinction effects in ultraviolet DIAL remote sensing in the lower atmosphere

Light passing through the atmosphere is scattered and absorbed by the molecules and particles in the atmosphere. This can adversely restrict and limit not only the signal-to-noise ratio (SNR) but also the accuracy and sensitivity of measurements, especially in long-path remote sensing. Usually, in differential absorption lidar (DIAL) techniques, errors are increased mainly because of the different extinction and backscattering properties of the atmosphere at the DIAL probe wavelengths. In this work we have investigated the effects of background aerosol and molecular extinction in DIAL remote sensing in the lower atmosphere for several visibilities at ultraviolet (UV) wavelengths by taking into account the dependence of refraction on the air temperature and pressure. For simplicity, we neglected the spatial inhomogeneity of aerosols in the lower atmosphere. Because of the weak attenuation produced by oxygen and other gaseous atmospheric constituents in this region compared with that from ozone, only ozone is considered as significant among the expected errors. Values for the total attenuation (km^?1) at wavelengths 200–400 nm are tabulated for several values of visibility. The acquired results show that the absorption and scattering by the molecules and aerosols vary with wavelength and visibility. The aerosol attenuation in the UV region varies smoothly and thereby errors caused by aerosol scattering can be neglected in remote sensing by UV-DIAL. In addition, aerosols play a very important role in lidar remote sensing in the lower atmosphere by scattering and absorption of radiation, which is considered as a significant factor. At high altitudes, the aerosol concentration is lower than at the ground; the molecular scattering is important, especially for wavelengths greater than 310 nm, where ozone attenuation is not important. The obtained results are important for accurate UV-DIAL measurements of concentration as well as when real-world signals are not available, for example when designing lidar and simulating or when access to real-world signals is not possible.     

The iodine molecules in the near-earth atmospheric layer fluorescence lidar sensing from space orbit

The iodine molecules radioactive isotopes in the atmosphere upper the atomic energy station can be the indicator of the air radioactive pollutant. These molecules emission into the atmosphere sensing by the space platform fluorescence lidar is the new perspective in the global environmental monitoring. The fluorescence lidar potential possibilities estimation for the iodine molecules lidar sensing from the outer space in the near-Earth atmospheric layer at the height range 100–600 km at the concentration level of 10¹⁰ cm⁻³ and above is the present paper goal. These fluorescence lidar equation simulation results analysis shows that optimal variant for the iodine molecules lidar sensing from the 600 km height and lower is the laser radiation wavelength λ₀ = 532 nm for the given molecules concentration level and fluorescence emission energy of 1 photon and the time detection values at this laser radiation wavelength for the height range 100–600 km are equal to 0.11–3.85 s.     

The hydrocarbon molecules concentration remote measurement by lidar with the diode lasers

Lidar systems for the pollution molecules concentration remote measurements in the atmosphere can become a basis for the atmospheric air quality controlling systems and the emergency pollution emissions prediction in the atmosphere under the industrial enterprises. The Raman lidar potential possibilities estimation with the diode lasers for the hydrocarbons molecules sensing in atmosphere for such molecules concentration level detection in atmosphere over industrial region and above is the present paper goal. The Raman lidar equation computer simulation results show the possibility of the optimal laser radiation wavelength choosing for the hydrocarbon molecules sensing in atmosphere in the photon-counting regime and these molecules concentration level exceeding over the given level in the distance range from 10 m up to 1 km. The 405 nm diode laser radiation was the best result wavelength with the minimal detection time value of 180 ms for the pentane molecule at the ranging distance of 1 km in the photon-counting Raman lidar regime.     

Alkane hydrocarbons molecules Raman lidar sensing from space orbit

The pollutants emergency emission in the atmosphere sensing by the space platform lidar is the new perspective in the global environmental monitoring. The Raman lidar potential possibilities theoretical estimation for the alkane hydrocarbon molecules emission in the near-Earth atmospheric layer at the concentration level of the limit admitted level and above detection from the space orbit presents this paper task. These Raman lidar equation computer simulations results show that optimal lidar variant for the given molecules concentration level, Raman pulse energy is equal to 1 photon, the methane molecules sensing from the 600 km height and lower is the laser radiation wavelength λ₀ = 532 nm that the recording time for this wavelength and height range 100–600 km will change from 11 ms up to 385 ms.     

HF molecules laser sensing in gaseous flows

The lidar monitoring are widely used for the gaseous molecules ultra low concentration levels in atmosphere and technological gaseous flows. It demands the detail studies of the atmospheric optics basics and computer simulation of the laser sensing possibility in such a molecules detection by the laser radiation with pulse energy up to 35 mJ at the wavelength of 532 nm. The lidar signal of the HF molecule versus the sensing distance have been a subject of the simulation studies of this signal molecules concentration dependence. It has been taken into account the Sun background radiation as the minimal lidar HF signal. The HF concentration versus distance dependences for this molecules ultra low concentration level in atmosphere simulation results show the HF molecules Raman and DAS lidar sensing efficiency for low concentration in the distance range from 1 to 1000 m by chosen laser wavelength and pulse energy in the daytime ranging regime. The text was submitted by the authors in English.     

Optical parametric oscillators in lidar sounding of trace atmospheric gases in the 3–4 μm spectral range

Applicability of a KTA crystal-based laser system with optical parametric generation to lidar sounding of the atmosphere in the spectral range 3–4 μm is studied in this work. A technique developed for lidar sounding of trace atmospheric gases is based on differential absorption lidar (DIAL) technique and differential optical absorption spectroscopy (DOAS). The DIAL-DOAS technique is tested to estimate its efficiency for lidar sounding of atmospheric trace gases.     

Low concentration iodine molecules lidar sensing

Lidar monitoring of the gaseous molecules in atmosphere can be used for concentration measurements of the toxic pollutants in the air of the urban and industrial regions. Such a concentration studies in the multi-components gaseous mixture essentially by lidar technique is a complex problem in atmospheric pollution monitoring. There are the fluorescence lidar and differential absorption lidar the most preferable for the detection of iodine molecules at very low concentration levels. Laboratory lidar studies and lidar equation simulation in these lidar variants gave the iodine molecules fluorescence differential cross section and iodine molecules absorption cross section in good agreement with earlier data. The experimental results confirm the possibility of the molecular iodine lidar sensing at low pressure and the measuring results treatment allows to get iodine molecules parameters. The text was submitted by the authors in English.     

Optical properties of inorganic suspended solids and their influence on ocean colour remote sensing in highly turbid coastal waters

The influence of the optical properties of inorganic suspended solids (ISS) on in-water algorithms was evaluated using an optical model in highly turbid coastal water, whose ISS concentration reached several hundred grams per cubic metre. The measurements were conducted in the upper Gulf of Thailand. The backscattering coefficient of the ISS was calculated using the Lorenz–Mie scattering theory. On the basis of the measurement, the ISS size distribution was parameterized as a function of ISS concentration, and both the spherical and non-spherical particle shape models were evaluated. For ISS concentrations of 10 g m^?3, an estimate of the chlorophyll-a (chl-a) concentration within a factor of 2 on a logarithmic scale is possible in a [chl-a] range of 4–30 mg m^?3. The differential coefficient of remote sensing reflectance was calculated to evaluate its respective sensitivities for chl-a and ISS concentrations. The use of radiometric data at 670 nm (700–900 nm) is valid for in-water algorithms used to estimate chl-a (ISS) concentration in highly turbid coastal waters.     

Remote measurement of chemical warfare agents by differential absorption CO<Subscript>2</Subscript> lidar

The possibilities of remote sensing of chemical warfare agents by the differential absorption method are analyzed. The CO₂ laser emission lines suitable for sensing chemical warfare agents with accounting for disturbing absorption by water vapor were chosen. The detection range of chemical warfare agents is obtained for a lidar based on CO₂ laser. Factors influencing upon the sensing range have been analyzed.     

The influence of a south Asian dust storm on aerosol radiative forcing at a high-altitude station in central Himalayas

The impact of long-range transported dust aerosols, originating from the Thar Desert region, to a high-altitude station in the central Himalayas was studied with the help of micro-pulse lidar (MPL) observations. A drastic change in lidar back-scatter profile was observed on a dust day as compared with that on a pre-dust day. The back-scatter coefficient on a dust day revealed that the dust layer peaked at an altitude ～1300 m above ground level (AGL) and extended up to ～3000 m AGL, with maximum value ～3?×?10^–5 m^–1 sr^–1. Aerosol Index (AI) and air mass back-trajectory analysis substantiate the transport of dust aerosols from the far-off Thar Desert region to the experimental site. A significant effect of dust aerosols was also observed over the station on the spectral aerosol optical depths (AODs), measured using a Microtops-II Sunphotometer. It showed significantly different spectral behaviour of AOD on a dust day as compared with that on a pre-dust day. The Ångström exponent (α) showed a marked decrease from 0.42 to 0.04 from the pre-dust day to the dust day. The aerosol radiative forcing estimated using the Santa Barbara DISORT (discrete ordinate radiative transfer) atmospheric radiative transfer (SBDART) model, in conjunction with the optical properties of aerosol and cloud (OPAC) model, showed values of about –30, –45 and?+15 W m^–2, respectively, at top-of-atmosphere (TOA), surface and in the atmosphere on the dust day. The positive atmosphere forcing caused an estimated heating of the lower atmosphere by ～0.4 K day^–1.     

Laser remote measurements of atmospheric gas components by dial: Modeling and experiments

This paper reports the development of LIDAS (LIdar Differential Absorption Sensing) program-algorithmic system for laser remote sensing of minor gas constituents (MGCs) of the atmosphere by the differential absorption method. The system includes modules for the search of wave-lengths informative for laser gas analysis by the differential absorption method, for numerical simulation of lidar sensing of atmospheric MGCs, and for calculation of errors of methodical, atmospheric, spectral, and instrumental origin. Lidar sensing of gas constituents by the differential absorption method as applied to problems of sensing of atmospheric MGCs is simulated numerically. Results of experiments on remote sensing of gas constituents of the atmosphere with the use of CO laser are presented.     

DIAL,a system for atmospheric methane measurement over Guwahati: development and results

The article discusses the development and operational details of Differential Absorption LiDAR (DIAL) for the measurement of methane concentration in the semi-urban environment of Gauhati University. The system comprises two specifically selected wavelengths in 3 μm range: one is an absorbing wavelength (λ_on) and the other is non-absorbed (λ_off) by methane molecules. Pulses of 10 ns for the two wavelengths are transmitted alternately for interleaved sampling of differential absorption. The pulse repetition rate is variable between 1 and 20 Hz. The slope and integrated target approaches are adopted to calculate the methane concentration, and observed figures are compared with globally reported values.     

Non-intrusive measurement of microscale temperature distribution by spontaneous Raman imaging

A non-intrusive and spatially resolved temperature measurement technique based on spontaneous Raman imaging was developed to measure two-dimensional temperature distributions in microfluidic systems. Raman scattering arising from OH stretching vibrations of H₂O molecules was used to measure the local channel flow temperature because of its high sensitivity to temperature. The OH stretching band has two parts with contrasting temperature dependences: hydrogen-bonded (HB) and non-hydrogen-bonded (NHB) modes. Raman images of HB and NHB modes were separately captured by an electron-multiplying charge-coupled device camera using two bandpass filters with center wavelengths of 642 and 660 nm, respectively. The two-dimensional temperature distributions were obtained from the intensity ratio of the two images by applying a calibration curve, which showed that there was a linear relationship between the temperature and the intensity ratio of HB to NHB modes for temperatures in the range 293–333 K. Temperature distribution measurements were demonstrated in the mixing flow field in the junction area of a T-shaped channel composed of a poly(dimethylsiloxane) chip and borosilicate glass slides. Non-uniform temperature distributions were quantitatively visualized at a spatial resolution of 12.8 × 12.8 μm² for three different heating conditions.     

Airborne DIAL lidar gas analysis of the atmosphere by middle IR gas lasers: Numerical modeling

The subject of this paper is an estimation of possibility of gas analysis by differential absorption lidars (DIAL) based on gas lasers of the middle IR spectrum range. The potential of lidar systems based on CO₂ laser with radiation frequency converter for ground and onboard sensing of atmospheric water vapor and carbonic oxide concentration profiles is analyzed. Possibilities of NO and NO₂ emission detection in ground atmospheric layers using converted frequencies of CO and CO₂ laser radiation in onboard DIAL are discussed. Absorption lines for methane and ammonia sensing by lidar system based on tunable TEA CO₂ laser with frequency converter has chosen. The results of an estimation of methane leakage detection from pipelines by onboard lidar are submitted. Applicability of the DF laser in onboard DIAL for a control of atmospheric gases is reported. The text was submitted by the author in English.     

Measuring forest structure and biomass in New England forest stands using Echidna ground-based lidar

A ground-based, upward-scanning, near-infrared lidar, the Echidna® validation instrument (EVI), built by CSIRO Australia, retrieves forest stand structural parameters, including mean diameter at breast height (DBH), stem count density (stems/area), basal area, and above-ground woody biomass with very good accuracy in six New England hardwood and conifer forest stands. Comparing forest structural parameters retrieved using EVI data with extensive ground measurements, we found excellent agreement at the site level using five EVI scans (plots) per site (R² = 0.94-0.99); very good agreement at the plot level for stem count density and biomass (R² = 0.90-0.85); and good agreement at the plot level for mean DBH and basal area (R² = 0.48-0.66). The observed variance at site and plot levels suggest that a sample area of at least 1 ha (10⁴ m²) is required to estimate these parameters accurately at the stand level using either lidar-based or conventional methods. The algorithms and procedures used to retrieve these structural parameters are dependent on the unique ability of the Echidna® lidar to digitize the full waveform of the scattered lidar pulse as it returns to the instrument, which allows consistent separation of scattering by trunks and large branches from scattering by leaves. This successful application of ground-based lidar technology opens the door to rapid and accurate measurement of biomass and timber volume in areal sampling scenarios and as a calibration and validation tool for mapping biomass using airborne or spaceborne remotely sensed data.     

Lidar profiling of aerosol scavenging parameters at a tropical station,Pune, India

In this study, we deal with observations of aerosol column content (height integration of vertical distribution of aerosol number density) that have been carried out using an Ar⁺ lidar for three different measurement cycles (each cycle consisting of three experimental days associated with non-rain, rain, and non-rain, respectively) of weekly spaced observations for pre-monsoon (March/April 1994), monsoon (September 1991), and post-monsoon (October 1998). Based on these observed profiles of aerosol number concentration on rainy days with respect to those on non-rainy days, vertical distributions of scavenging collection efficiencies (SCEs) are computed and discussed in this article. The SCE is found to decrease from 0.3 to 0.01 between the heights, 100 and 800 m for thunderstorm rain in April 1994, and during monsoon, it increases from 0.1 to 0.7. In the October 1998 episode, SCE was found to increase initially from 0.35 to 0.75 for heights between 40 and 200 m and thereafter decrease to 0.35 in the height interval of 200–800 m. For the rainfall intensity increase from 1 to 10 mm hour^?1, the corresponding scavenging coefficient (SC) for atmospheric layer 50–100 m varies from 4 × 10^?6 to 4 × 10^?5 s^?1 for thunderstorm in April 1994 and between 5 × 10^?6 and 5 × 10^?5 s^?1 in October 1998, respectively. During monsoon, these values vary from 3 × 10^?5 to 5 × 10^?4 s^?1. They lie in the range of those observed in the earlier field studies. The results are found useful to establish links between aerosols and cloud properties, and the influence of such interactions on weather and climate.     

An effective PDMS microfluidic chip for chemiluminescence detection of cobalt (II) in water

A microfluidic chip for the chemiluminescence detection of cobalt (II) in water samples, based on the measurement of light emitted from the cobalt (II) catalysed oxidation of luminol by hydrogen peroxide in basic aqueous solution, is presented. The microfluidic chip was designed and fabricated from polydimethylsiloxane using micro-molding method. Optimized reagents conditions were found to be 5.0 × 10^?4 mol/L luminol, 1.0 × 10^?2 mol/L hydrogen peroxide, and 8.0 × 10^?2 mol/L sodium hydroxide. The system can perform fully automated detection with a reagent consumption of only 2.4 μL each time. The linear range of the cobalt (II) ions concentration was 1.0 × 10^?10–1.0 × 10^?3 mol/L and the detection limit was 5.6 × 10^?11 mol/L with the S/N ratio of 3. The relative standard deviation was 4.6 % for 1.0 × 10^?5 mol/L cobalt (II) ions (n = 10).     

Selective and in-situ determination of carbonate and oxide particles in aqueous solution using laser-induced breakdown spectroscopy (LIBS) for wearable information equipment

Laser-induced breakdown spectroscopy (LIBS) has been applied for quantitative analysis of Al₂O₃, CaCO₃ and MgO particles suspended in water. In the single elemental system, the plasma emission intensities of Al, Ca and Mg were linearly increased with concentration of elements in the range of 1.0×10^?5–1.0×10^?3  M, 1.0×10^?4–2.0×10^?3 M and 8.0×10^?5 –4.0×10^?3 M, respectively. We also investigated the concentration dependence of breakdown spectra for suspended mixtures of Al₂O₃, CaCO₃ and MgO particles. The emission lines, such as Al I, Ca I, Ca II and Mg I, were appeared in the LIBS spectrum simultaneously, and each emission peak could be deconvoluted. The plasma emission intensities of Al, Ca and Mg in the multielemental system were also linearly increased with their concentrations in the range of 1.0×10^?5–1.0×10^?3 M, 1.0×10^?4–2.0×10^?3 M and 4.0×10^?4–2.0×10^?3 M, respectively. LIBS was found to be available for quantitative and qualitative measurement of the concentrations of Al₂O₃, CaCO₃ and MgO particles suspended in water. The present results suggest that LIBS is a potentially useful tool for in-situ analysis on particles composition and concentrations for environmental monitoring by the wearable information equipments.     

Performance evaluation of copper ion selective electrode based on cyanocopolymers

A copper(II) ion selective electrode based on copper(II) salicylaniline Schiff's base complex in styrene-co-acrylonitrile copolymer (SAN) has been developed. The SAN-based membrane electrode containing copper(II)–Schiff's base complex, dioctylphthalate as plasticizer and sodium tetraphenylborate as an anion excluder exhibited a linear response with a Nerstian slope of 30 mV decade⁻¹ within the concentration range of 10⁻⁶–10⁻² mol dm⁻³ of Cu²⁺ ions. The prepared electrode has an average response time of 15 s to achieve 95% steady potential for Cu²⁺ concentration ranging from 10⁻⁴ to 10⁻² mol dm⁻³. The electrode has shown a detection limit of 10⁻⁷ mol dm⁻³ of Cu²⁺ ion with an average lifetime of 6 months. The selectivity of electrode for Cu²⁺ ion has been found to be better in comparison to other various interfering ions. The electrode is suitable for use within the pH range of 2.0–7.0 at 1.0×10⁻³ mol dm⁻³ of Cu²⁺ ion. The prepared electrode can be used successfully as an indicator electrode for the potentiometric titration of the Cu²⁺ ion using EDTA.     

Detecting very small quantity of molecular probes in solution using nano-mechanically made Au-cavities array with SERS-active effect

Well-ordered nano-mechanically made Au-cavities array (nAu) is tailored as a functional surface with high density tip-to-tip cavities, adjustable indentation depths, and a number of edges within the nanostructures. In this study, the nAu was fabricated by a physical way and utilized as a characterization tool with the advantage of preventing samples from chemical or residual contaminations. Two types of molecular probe solutions: 5,5′-dithio-bis-(2-nitrobenzoic acid) (DTNB) and Rhodamine 6G (R6G) were evaluated. For DTNB solution, the chemically adsorbed monolayer was formed upon the nAu, which resulted in the effect of surface enhanced Raman scattering (SERS), mainly induced by the combined chemical and electromagnetic effects. Within the range of 1 × 10⁻²³ to 3.2 × 10⁻²² mole, Raman intensity and the quantity of DTNB molecules exhibited a sharp exponential relationship. For R6G solution within the equivalent nAu and the identical range, the relationship exhibited nearly linear; however, within an extended range of 1 × 10⁻²³ to 3.2 × 10⁻²¹ mole, a moderate exponential relationship was obtained. The enhancement factors for detecting DTNB and R6G solutions using the nAu could be optimized to 1.62 × 10⁸ and 4.60 × 10⁷, respectively.