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A device for the depth penetration measurement based on the transmition of
He-Ne laser light power through samples of river water was developed.
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Differential optical absorption spectroscopy has been applied in atmospheric
ammonia monitoring. The absorption of gaseous ammonia in the UV region between
190 nm and 230 nm has been examined and compared with spectra of interfering
species and atmospheric transmission. A wavelength region around 210 nm was
utilized in measurements of atmosphric ammonia over a 265 m path in a rural
area with a detection limit of 1 ig/m
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Ammonia monitoring is needed in most schemes for denitrification of power plant emission. In the PALAMON system
we use a 500 MHz tunable, single mode, single line, CO2 laser as light source for a low pressure, high temperature,
photoacoustic cell. With this cell we can resolve the sR(5,O) line of the ammonia spectrum, and suppress the
interfering C02(9R30) absorption line down to a lppm NH3 detection limit. The validity of the measured ammonia
concentrations is strongly dependent on details of the sampling system and on the reliability of the calibration
routines. In particular calibration with certified mixtures of NH3:N2 has proved insufficient due to the multiple and
long time constants caused by adsorption of ammonia to different materials in the system. Presence of water vapor
in the gas greatly reduces these time constants. Therefore a number of methods for simple production of moist
calibration gases from macroscopic amounts of NH3 are applied. The calibrations are translated to response from
an easily managable absorber in order to allow automated recalibration of the photoacoustic response. Data from a
field test of the system, and calibration data will be presented.
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In the environmental problem of acidification, deposition of
atmospheric ammonia is an important factor in NW Europe. Background
concentrations are generally low but variations due to local sources
may be large and rapid, so a sensitive measuring instrument with a
high dynamic range and good time resolution is required. A
photoacoustic ammonia measurement system with a detection limit
for NH3 of about 1 ppbv and a time resolution of about 5 minutes
is described. The results of 'a measurement campaign in the field
during the spring of 1989, with the instrument installed in a
caravan, will be reported. Concentrations were determined at a
single position above the ground (2 m.). The instrument has since
then been adapted to measurements at four different heights from
which vertical fluxes can be derived. The encouraging first results
will be presented.
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With the passage of the 1977 Clean Air Act Amendments, the United States
Congress emphasized visibility protection for the pristine areas of the country
as a major national goal. Federal programs were implemented to estimate existing
levels of atmospheric extinction. Until recently, this has been accomplished
primarily by the use of various techniques to measure apparent target/horizon sky
contrast. While the ability of these methods to accurately determine contrast is
well proven, the estimation of extinction using the Koschmieder relationship is
usually compromised by theoretical assumptions that are typically not met in
practice. To address this problem, the United States National Park Service has
supported the development, testing, and deployment of an instrument that
accurately and reliably measures the transmission of an ambient atmospheric
optical path. The average atmospheric extinction coefficient of the path can be
calculated directly from this measurement. This transmissometer consists of a
constant output light source transmitter and a computer-controlled photometer
receiver. The irradiance at visible wavelengths from the transmitter can be
measured to a high degree of accuracy both day and night over path lengths of 0.5
to 30km. A complete description of the transmissometer will be presented.
Atmospheric optical considerations will be combined with design parameters and
experimental data to confirm the ability of this instrument to make an accurate,
precise, and reliable extinction measurement.
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A quantitative measurement of laser light extinction during
particle growth in an expansion chamber of a condensation nuclei
counter was performed. The attenuated light flux and the light flux
scattered at a chosen scattering angle are monitored simultaneously
during the particle growth process. From the transmitted light flux
vs time the light extinction during particle growth can be
determined quantitatively. The experimental scattered light flux vs
time allows a precise determination of particle sizes at various
times during particle growth. Knowing the actual particle size the
light attenuation obtained from the transmitted light flux allotis a
direct, quantitative determination of particle number concentration
without referring to any calibration of the apparatus and can be
regarded as an absolute method.
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In this paper a near-JR diode laser system for emission and process control has been designed and tested.
The system utilizes derivative spectroscopy to increase the sensitivity of the measurement due to the
low line strengths of the absorption lines in the 0.7 - 1.7 p.m wavelengths region. A minimum detectable
absorbance of 2 iO-5 was obtained at an integration time of 3 ms. Oxygen was used in the experiments
and the corresponding minimum detectable concentration was 200 ppm. No interference effects was observed
from co-existing emission gases. The system utilizes a unique modulation concept for compensation
of non'gas-related transmission variations in the measurement path. Due to the short response time
the system is very useful for on-line process control.
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Mercury is the only atmospheric pollutant that is present in the atmosphere
in atomic form. Range-resolved Hg mapping can be performed using the
differential absorption lidar (dial) technique employing the 254 nm Hg resonance
line. We have used the lidar technique both for mapping of industrial
plumes and for background concentration measurements. Our studies also include
mercury of geophysical origin. A field test has been performed in Icelandic
geothermal fields. We have also attempted studies of Hg emission from lake
surfaces.
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Optical and laser remote sensing techniques provide powerful tools for environmental monitoring in particular for determination
of concentrations of atmospheric pollutants .TheifferentiaI absorption and catteiing (DAS) lidar method is very
well suited and widely used to measure from ground conceniration of e.g. 502, NO2, NO and O316. The available systems
are mainly stationary in laboratories of research institutes and few of them are now mobile, mounted on trucks and
trailers.
ARGOS (advanced remote gaseous Qxide ensor) is based on many years experimental experience in the area of remote air
pollution measurements of the in Geesthacht, a resaerch institute located in the vincinity of Hamburg. In this
paper the objectives, specifications and realization of a vanboine air pollution measurement system will be presented based
on advanced electro-optical and computer equipment as well as on a wind profile sensor. The emphasis of the development
is to realize a mobile and operational system not to verify applied methods and techniques.
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By linking a battery operated logger unit and power supply with a submersible fluorometer we have been able to make
continuous untended measurements ofphytoplankton chlorophyll fluorescence, and hence estimate algal biomass for periods
of up to 35 days at moorings. Calibration aixi data processing procedures are described, and some examples of the results of
deployments in waters around the United Kingdom are presented.
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New, optical, approaches to automatize and to accelerate the analysis of algae
are discussed. Firstly, the application of flow cytometric analysis will be
presented. This technique is based on classification of particles in flow by
measuring several optical properties per individual particle. Characteristics of the
Optical Plankton Analyser, a flow cytometer constructed specifically for the
analysis of phytoplankton, will be presented. Two experiments that demonstrate the
suitability of this instrument for the analysis of coastal phytoplankton will be
presented. Subsequently, the applicability of flow cytometry and other optical
approaches to the measurement of phytoplankton, in particular for monitoring
purposes, will be discussed. Microscopy, as well as in-situ measurement and optical
remote sensing are approaches that each offer specific advantages for the
determination of phytoplankton. An optimal and integrated picture of the development
of the distribution of phytoplankton species in space and time can be obtained by
the combined application of these techniques.
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The exciatation light intensity 'e provided by a 6 mW He-Ne laser
is switched by a combination of an acousto-optical modulator OS and a
mechanical shutter MS. A switching-time below 0.3 s and a power
density of 10 mW/cm2 at the object are achieved. Two photoinultipliers
measure the fluorescence intensities F685(t) and F730(t) at the two
peak wavelengths (685 mu and 730 mn), the nieasuring signals are
synchronously stored by a transient recorder with a time resolution of
10 p.s and a capacity of 8000 pairs of measuring values and by a
computer with a time resolution which is decreased in steps from 200
1L5 to 200 ins within the total measuring time of 5 mm. The combined
use of OS and MS ensures the stability of 'e within 5% during the
total measuring time. In addition to the peak intensity F0 and the
steady-state intensity F5 which are commonly determined b' devices
with low time resolution, the initial intensity Fb and its time
derivative Db and intensity F1, time tj, and time derivative D of the
inflection point can accurately be determined by the device. The ratio
R(t) = F730(t)/F685(t) shows an initial value Rb which is similar to
the steady-state-value R5 and two minimum values Rml and Rm2 near 10
ms and 15, respectively.
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Three novel techniques of fiber-optic spectroscopy have been recently introduced
into research of forest decline. These include measurement of luminescence changes
and fluorescence-decay of chiorophylls (i) under continuous irradiation, and after
pulse-induction in the (ii) long-term and the (iii) picosecond time range. These changes will be correlated both with environmental factors such as air pollutants, soil,
fertilization and various experimental and physiological conditions.
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Ultraviolet fluorescence spectroscopy is now widely used in surveys and
monitoring studies for the determination of hydrocarbon concentrations in
seawater. This paper describes a high sensitivity in-situ ultraviolet
fluorimeter, discusses calibration methods and illustrates some
appl icat ions.
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The developed laboratory prototype fluorimeter is the first step to a new in-situ instrument, and
is based on a pulsed nitrogen laser (pumping a color dye laser and the laserbeam passing through a
frequency doubler) with a pulse width less than 1 nsec. With such a short excitation pulse it is
possible to measure the exponential decay of the fluorescence from the aromatic compounds and thus
determine the fluorescence lifetime-curves, which are typically in the region of 5-40 nsec.
The emitted fluorescence is collected simultaneously in 35 channels in the wavelength region 250-600
nm. If the fluorescence falls within the transmission areas of the interference filters in each channel
the light will be collected by a plastic light guide (doped PMMA) in the actual channel and transmitted to the channels photo multiplier tube (PMT). (The use of the plastic light guide improves the
sensitivity). The signal from the PMT is passed on to a 200 MHz 8-bit flash AID-converter connected to a local memory. From this local memory the digital lifetime curves from each channel are
transmitted to a computer for presentation of the 3-dimensional spectrum. This spectrum has been
obtained with a single laser shot.
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Use of UV-visibletransmitting optical fibers for real-time, remote, in situfluorescencemeasurementsof chemical
constituents in environmental samples is described. In order to improve the capability of fluorescence techniques
for resoMng complex mixtures we have deVelOped a fiber optic-based system that uses a pulsed nrogen laser to
induce fluorescence and a time-gated linear photodiode array coupled to a spectrograph for measuring resutting
emisalon spectra This permfts rapid extraction of both spectral information and temporal data (fluorescence decay
times).
The performance of the system for monftoring aromatic hydrocarbons directly in seawater over a bare-ended"
fiber optic cable is discussed. Techniques for extending the Capability to determination of metals and other
non-fluorescing compounds are presented. A system in which a fluorogenic indicator molecule for metal ions is
constantly renewed at the sensing end of the fiber is described that (1)exhibits very fast response times (1 second)
and (2)eliminates problems of reversibility common with immobilized indicators.
Presently, the pulsed-laser/photodiode fiber optic system is being adapted to a truck-mounted cone
penetrometer system for characterizing the distribution of chemical contaminants at hazardous waste sites. The
system can push a 35.7 mm diameter rod up to 50 m into the sI at a rate of approximately 2 cm/sec. The
penetrometer probe tip will be equipped with sapphire viewing windows that permft one fiber to screen for aromatic
orgarc compounds and a fluorogeruc indicator release system that can be used with a second fiber for trace metal
screening.
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Since 1988 oceanographic vehicles equipped with a variety of optical sensors
have been deployed successfully from ships-of-opportunity in the North Sea as
part of an environmental monitoring programme. The towed vehicles are deployed
and recovered by the ship's crew and the instrument packages are activated
automatically during the tow by electronic sea water switches. The vehicles
carry sensors for measuring chlorophyll fluorescence, turbidity, conductivity,
temperature, depth and upwelling and downwelling light in three wavebands; the
measurements are stored in a solid state logger. The filters used in the
irradiance sensors have wavelengths at 412, 450 and 550 nm with sensitivity at
0.1 pW cm2. The light measurements are used for the determination of the
diffuse attenuation coefficient and the reflectance of blue light (R4l2, R450)
and green light (R55O) and together with measurements of chlorophyll
fluorescence are being used for the development of an algorithm for estimation
of primary production in coastal waters and the open sea. Data are shown from a
number of fixed-depth and variable-depth vehicle deployments from selected
shipping routes in 1988/89, including a Copenhagen, Kattegat, Skagerrak, North
Sea, Harwich route. From March 1990 a nutrient sensor measuring combined
nitrite, nitrate in a continuous flow analyser will be carried by these towed
vehicles.
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In the proposed paper an empirical method has been developed for determination of nitrous oxide concentration using the absorption band 2'), in proximity
of), 3.87J4m, free from overlapping with absorption bands from other atmospheric
gases. The transmission spectra of the atmospheric air are recorded with unresolved rotation-vibration structure. The method is inexpensive, simple and efficient
It may be used for determination of enviromental pollution in homogeneous media
(laboratory or production plant conditions, ground layer of atmosphere) and of
unhomogeneous composistion mixtures when studying the contents of nitrous oxide
along slope paths in troposphere and stratosphere.
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The design and the main features of the new double pendulum type
michelson interferometer (DPI) by Kayser-Threde are presented.
The advantages of this spectrometer in comparison to conventional Fourier spectrometers are discussed. The DPI is compact in
design, mobile, insensitive to vibrations and temperature changes and, thus, well adapted to field measurements. The spectrometer was applied to emission as well as immission measurements
of air pollutants. Several molecules could be identified and
their concentrations could be estimated. The detection limit of
the DPI yields 15 - 60 ppm depending on the analyzed gas for
emission measurements, 6 - 84 ppb for immission measurements.
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The problems of the use of space photographic survey are discussed regarding exploration of the Earth natural
resources. The concrete information is presented on the successfully operated Soviet equipment system. A conclusion
is drawn on the feasibility to set up international Earth remote sensing global system with a view to enhance economy
efficiency, scientific research, environment monitoring and contribute to solving other problems pertaining to
development of the mankind habitat.
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