共查询到20条相似文献,搜索用时 0 毫秒
1.
B. Tatarov T. Trifonov B. Kaprielov I. Kolev 《Applied physics. B, Lasers and optics》2000,71(4):593-600
We report an experimental study of the lidar signal depolarization as a function of the relative contribution of the multiple
scattering in case of optically dense objects in the atmospheric planetary boundary layer. Results of the observation of fog
and stratus clouds are presented, as well as those obtained by sounding of stratocumulus clouds during a snowfall. The lidar
data point to a rise of the depolarization coefficient as the influence of the multiple scattering increases in consequence
of both viewing angle enlargement and penetration into the object sounded. The variations of the depolarization coefficient
are studied as a function of the field of view. In the case of fog, this dependence is approximated by a three-parameter exponential
law; it is found that the depolarization increases steeply when the viewing angle is increased from 9 mrad to 12.5 mrad. The
relationships between the approximation parameters and the microphysical characteristics of the scattering medium are considered.
The experimentally determined size of the area where multiple scattering occurs is in good agreement with that calculated
according to the diffusion model. The results obtained on the multiple scattering effect on the depolarization can also be
employed in determining the extinction coefficient profiles in optically dense objects, as well as in evaluating the characteristic
size of the scattering particles.
Received: 6 September 1999 / Revised version: 7 February 2000 / Published online: 6 September 2000 相似文献
2.
I.A. Veselovskii H.K. Cha D.H. Kim S.C. Choi J.M. Lee 《Applied physics. B, Lasers and optics》2001,73(7):739-744
A combined elastic–Raman lidar system based on a tripled Nd:YAG laser is used for the separate detection of elastic backscatter
and Raman signals from atmospheric nitrogen, water vapor and liquid water and for their depolarization measurement. Vertical
profiles of water-vapor and liquid-water content measured under clear-sky conditions behave differently: inside the boundary
layer the ratio of liquid-water to water-vapor Raman backscatters rises with altitude. The depolarization measurements bring
additional information about atmospheric scattering. The observed depolarization ratio of the water-vapor Raman signal is
about 14%, while for liquid water this ratio varies in the 30–75% range, which exceeds the depolarization of bulk water and
is attributed to the water-aerosol effects. Raman contours of water vapor and liquid water are partially overlapped, and bleed-through
of liquid-water Raman backscatter leads to enhancement of depolarization of the water-vapor Raman signal. This parameter may
be used as a convenient indicator of liquid-water interference in water-vapor measurements.
Received: 12 December 2000 / Revised version: 27 September 2001 / Published online: 7 November 2001 相似文献
3.
K. Stelmaszczyk A. Czyzewski A. Szymanski A. Pietruczuk S. Chudzynski K. Ernst T. Stacewicz 《Applied physics. B, Lasers and optics》2000,70(2):295-299
In lidar measurements noise and fluctuations strongly affect the results. The reason is a rapid decrease of the signal-to-noise
ratio with an increase of distance. The differential absorption lidar (DIAL) is particularly sensitive to the signal instabilities.
In this paper we present a method of the signal acquisition that is suitable for registration of both large light fluxes and
single photons. We also present new method of solution of the DIAL equations. Compared to the traditional algorithm used for
signal elaboration our procedures are much more stable and they are able to increase the effective range of lidar measurements.
Received: 2 February 1999 / Revised version: 30 June 1999 / Published online: 16 September 1999 相似文献
4.
The results of statistical simulation of the spatiotemporal structure of the multiply scattered component of lidar returns
by the Monte Carlo method are discussed for the case of monostatic sensing geometry. The spatial characteristics of the region
of the medium where occurs the last scattering of photon before arriving at the reciever. This region of the medium is called
the instantaneous brightness body of multiply scattered radiation. It is demonstrated that the instantaneous brightness body
of multiply scattered radiation that propagates toward the receiver may occupy a large volume that does not necessarily coincide
with the region of formation of the singly scattered component. The main factors influencing the spatial and brightness characteristics
of this volume source are established. The effect of scattering order on the spatiotemporal structure of lidar returns is
analyzed for the case of sensing of aerosol haze and advective and radiative fogs with optical thickness 2<τ<8.
Received: 2 August 2001 / Revised version: 7 January 2002 / Published online: 25 September 2002
RID="*"
ID="*"Corresponding author. Fax: +7-38/2225-8026, E-mail: belov@iao.ru 相似文献
5.
X. Wang A. Boselli L. D’Avino R. Velotta N. Spinelli P. Bruscaglioni A. Ismaelli G. Zaccanti 《Applied physics. B, Lasers and optics》2005,80(4-5):609-615
A Monte Carlo-based evaluation of the multiple-scattering influence on ground-based Raman lidar measurements is presented.
The lidar returns from cirrus clouds are analyzed in order to evaluate vertical profiles of the extinction and backscattering
coefficients. Results show that for the typical cirrus cloud, the presence of the multiple scattering can lead to an underestimation
of the extinction coefficient by as large as 200% whereas the backscattering coefficient is almost unaffected for the Raman
lidar technique. An algorithm to select one or a set of phase functions which fit to the lidar data is also presented. It
is an iterative procedure based on Monte Carlo scattering simulation. By comparison of the experimental value of the lidar
ratio, corrected for the multiple scattering influence, and the phase function used in the Monte Carlo simulation, one can
determine a suitable phase function. The validity and sensitivity of the algorithm have been demonstrated by applying it to
simulated cases. The application to some real cases indicates that our procedure allows for the establishing of a practical
scattering model for the cirrus clouds. 相似文献
6.
The efficiencies of direct lidars operating at 355, 532, 1064 and 1540-nm radiation wavelengths for early forest fire detection
were compared. For each wavelength, the range for reliable smoke-plume detection was estimated on the basis of a computer
simulation plume using a one-dimensional “top-hat” gas dynamic model for the calculation of the backscattering and extinction-coefficient
profiles within the plume. The agreement between the predicted signal-to-noise ratio (SNR) and experimental results for 532
and 1064-nm wavelength radiation is good. The decrease of the signal-to-noise ratio with distance is maximum for 355 nm and
minimum for 1064 nm. At 1540 nm, the decay of SNR with distance is slightly faster, but the SNR is higher than for other wavelengths,
leading to the highest detection efficiency for the same energy of the probing laser pulse. For a burning rate of 2 kg/s and
a laser beam divergence of 2.5 mr, the maximum distance for reliable detection varies between 6 and 12 km, depending on the
wavelength.
Received: 15 May 2002 / Revised version: 13 September 2002 / Published online: 22 January 2003
RID="*"
ID="*"Corresponding author. Fax: +351-21/841-8120, E-mail: rui.vilar@ist.utl.pt 相似文献
7.
A deconvolution filtering model of multiple scattering in ground-based single field of view (SFOV) LIDAR returns is described.
It is based on time series deconvolution techniques. The contribution of multiply scattered photons in SFOV LIDAR returns
can be numerically modeled by processing LIDAR signals without additional information about aerosol properties and measurement
geometry. Deconvolution results are in good agreement with those performed by Monte Carlo calculations, showing that the significance
of multiply scattered photons is strongly correlated with aerosol concentration. It is found that, for ground-based LIDAR,
the contribution of multiply scattered photons to LIDAR signals is typically below 5% in a clear urban atmosphere, and up
to 14% in a very dirty urban atmosphere in Hong Kong during winter seasons.
Received: 8 October 2002 / Revised version: 29 January 2003 / Published online: 22 May 2003
RID="*"
ID="*"Corresponding author. Fax: +81-298/51-8229, E-mail: gao@proteo.gr.jp
RID="**"
ID="**"Present address: Preteomics Lab., Amakubo 1-16-1, Tsukuba 305-0005, Japan 相似文献
8.
A. Iwasaki N. Aközbek B. Ferland Q. Luo G. Roy C.M. Bowden S.L. Chin 《Applied physics. B, Lasers and optics》2003,76(3):231-236
We demonstrate a new method for measuring the length of a femtosecond laser pulse induced filament in air using a LIDAR (LIght
Detection And Ranging) technique. The LIDAR involves a detector with a fast response time. The back-scattered multiphoton
induced fluorescence from nitrogen molecules excited inside the filament is measured, from which the length of the filament
can be determined. We find good agreement between the measured filament length and the length estimated from burn patterns
on paper. In addition, good qualitative agreement between the experimental measurement and numerical simulations is obtained
for the signal features of the filament. We propose that this new method can be used to quantitatively determine filamentation
at longer distances.
Received: 11 June 2002 / Revised version: 21 October 2002 / Published online: 5 February 2003
RID="*"
ID="*"Corresponding author. Fax: +1-418/656-2623, E-mail: aiwasaki@phy.ulaval.ca 相似文献
9.
Parameters of eyesafe lidar at 1.54 μm for detection of small plumes of smoke from burning wood or oil have been evaluated.
It was assumed that a diode-pumped solid-state Er:glass laser at 1.54 μm or a Nd:YAG laser with a Raman cell or optical-parametric
oscillator is used as a light source and that detection of backscattered light is performed with an avalanche photodiode.
Ash and soot particle size distributions were taken from experiments. A backscattering coefficient at 1.54 μm for various
source of smoke was estimated. In computing the laser energy, range between lidar and smoke, receiver optics diameter, fuel
mass burned in unit time, fire source radius, laser pulse duration and visibility were varied. Results of the computations
enabled estimation of the required laser energy, which ranges from 0.05 to 1400 mJ depending on the parameters.
Received: 5 January 2000 / Revised version: 3 March 2000 / Published online: 11 May 2000 相似文献
10.
A.B. Utkin A.V. Lavrov L. Costa F. Simões R. Vilar 《Applied physics. B, Lasers and optics》2002,74(1):77-83
The possibility of detecting small forest fires with the help of a simple and cheap lidar operating at 0.532-μm wavelength
up to distances of about 6.5 km is demonstrated. The values of the signal-to-noise ratio (SNR) achieved in the experiments
are consistent with theoretical estimations obtained by computational modeling of the lidar detection process, including simulation
of the smoke-plume shape and of the laser beam–plume interaction. This model was used to assess the potential of the lidar
technique for fire surveillance in large forest areas. In particular, the upper limiting range for effective detection (SNR>5)
of small localized fires in dry- and clear-weather conditions is estimated at 7–15 km depending on operation mode, burning
rate, and observation geometry.
Received: 29 August 2001 / Published online: 29 November 2001 相似文献
11.
T. Lindström U. Holst P. Weibring H. Edner 《Applied physics. B, Lasers and optics》2002,74(2):155-165
The lidar technique is an efficient tool for remote monitoring of the distribution of a number of atmospheric species. We
study measurements of sulphur dioxide emitted from the Italian volcano Mt. Etna. This study is focused on the treatment of
data and on the procedure to evaluate range-resolved concentrations. In order to make an in-depth analysis, the lidar system
was prepared to store measurements of individual backscattered laser pulses. Utilizing these repeated measurements a comparison
of three different methods to average the returned signals is made. In the evaluation process we use local polynomial regression
to estimate the range-resolved concentrations. Here we calculate optimal bandwidths based on the empirical-bias bandwidth
selector. We also compare two different variance estimators for the path-integrated curves: local polynomial variance estimation
and variance estimation based on Taylor approximations. Results show that the method performs well. An advantage compared
to previous methods for evaluation of lidar measurements is that an estimate of the mean squared error of the estimated concentration
can be calculated.
Received: 9 July 2001 / Revised version: 15 November 2001 / Published online: 17 January 2002 相似文献
12.
It is the intention of this paper to report on the currently used methods to solve the different LIDAR signal inversion problems for molecular atmospheres, aerosols and clouds. Apart from more traditional approaches, we shall present a recent one using multiple scattering effects rather than avoiding them, which is useful especially for dense clouds. 相似文献
13.
T. Gasmi H.A. Zeaiter G. Ropero A. González Urena 《Applied physics. B, Lasers and optics》2000,71(2):169-175
This paper presents the construction, use and characterisation of a laser-induced sealed plasma shutter to clip off the nitrogen
pulse tail of a CO2-TEA laser-based lidar dial system. Investigation of the optimum gas filling pressure, temporal profile of the clipped pulse,
and the laser threshold power intensities to achieve ionisation growth and breakdown in helium, argon, and nitrogen are also
presented. Values of these power density thresholds lie between 3×1011 W cm-2–5×1012 W cm-2, 2×1011 W cm-2–2×1012 W cm-2 and 3×1013 W cm-2–2×1014 W cm-2 for helium, argon, and nitrogen, respectively. The range resolution attainable with the present clipped pulses is 15 m, which
is 30 times better than that readily obtained with the nitrogen-tailed pulses. Field measurements of the lidar returns with
the clipped pulse from a co-operative target are presented.
Received: 27 December 1999 / Revised version: 11 February 2000 / Published online: 27 April 2000 相似文献
14.
V. Cuomo P. Di Girolamo F. Esposito G. Pappalardo C. Serio N. Spinelli M. Armenante B. Bartoli V. Berardi R. Bruzzese C. Bellecci G.E. Caputi F. De Donato P. Gaudio M. Valentini H. Melfi M.P. McCormick 《Applied physics. B, Lasers and optics》1997,64(5):553-559
A,355 and RA,532); the two data sets appearing to be highly correlated. LITE vs. Potenza LIDAR measurements of RA,355 and RA,532 display a correlation coefficient of 0.72 and 0.86, respectively. Stratospheric aerosol dimensional characteristics are determined
starting from the measured values of the ?ngstrom coefficient.
Received: 24 May 1996/Revised version: 8 October 1996 相似文献
15.
Measurement of filament length generated by an intense femtosecond laser pulse using electromagnetic radiation detection 总被引:4,自引:0,他引:4
We present a new method to measure the length of a filament induced by the propagation of intense femtosecond laser pulses
in air. We used an antenna to detect electromagnetic pulses radiated from multipole moments inside the filament oscillating
at the plasma frequency. The results are compared with the values detected from the backscattered fluorescence induced by
multiphoton ionization of nitrogen molecules excited inside the filament. The values are found to be in good agreement.
Received: 6 November 2002 / Revised version: 27 January 2003 / Published online: 24 April 2003
RID="*"
ID="*"Corresponding author. Fax: +1-418/656-2623, E-mail: shosseini@phy.ulaval.ca 相似文献
16.
We study the quantification of signal strength in wavelength-modulation spectroscopy, and present algorithms which allow for
the quantitative analysis of second-harmonic spectra for arbitrary combinations of line width and modulation depth. The algorithms
are validated through measurements on CO lines in the 0 ? 3 overtone band. They can be used for measuring the line strength
of lines that are too weak to allow direct absorbance measurements, and for quantifying the response from monitors applying
wavelength-modulation under conditions where calibration with certified gases is not feasible.
Received: 20 August 1999 / Revised version: 2 September 1999 / Published online: 30 November 1999 相似文献
17.
G. Ehret A. Fix V. Weiss G. Poberaj T. Baumert 《Applied physics. B, Lasers and optics》1998,67(4):427-431
Received: 4 May 1998/Revised version: 17 July 1998 相似文献
18.
N.V. Didenko E.M. Kim D.A. Muzychenko A.A. Nikulin O.A. Aktsipetrov 《Applied physics. B, Lasers and optics》2002,74(7-8):647-651
Incoherent second-harmonic generation, or hyper-Rayleigh scattering (HRS), and atomic force microscopy (AFM) are proposed
as a combined probe of nonlinear optical and structural properties of silver-island films. HRS and linear (Rayleigh) scattering
indicatrices are measured. The correlation function, deduced from the HRS indicatrices and characterising spatial fluctuations
of the total polarisation at second-harmonic frequency, has a length scale significantly larger than that of the correlation
functions that are obtained from the AFM data and characterise spatial fluctuations of quadratic optical susceptibilities
of the dipole and quadrupole types. This difference is interpreted as indicating that the HRS indicatrix shape is determined
by the long-range fluctuations of the local-field factors.
Received: 16 October 2001 / Revised version: 16 April 2002 / Published online: 6 June 2002 相似文献
19.
T.J. Kulp S.E. Bisson R.P. Bambha T.A. Reichardt U.-B. Goers K.W. Aniolek D.A.V. Kliner B.A. Richman K.M. Armstrong R. Sommers R. Schmitt P.E. Powers O. Levi T. Pinguet M. Fejer J.P. Koplow L. Goldberg T.G. McRae 《Applied physics. B, Lasers and optics》2002,75(2-3):317-327
Quasi-phase-matched (QPM) materials allow the generation of spectroscopically useful infrared radiation in an efficient and
broadly tunable format. Here, we describe several applications of QPM-based light sources to remote and local chemical sensing.
The remote systems are gas imagers that employ a fiber-pumped continuous-wave optical parametric oscillator or a microlaser-pumped,
diode-seeded optical parametric amplifier as the illumination source. Technology described for local sensing includes a cavity
ring down spectrometer that employs a novel optical parametric generator–amplifier to achieve ≥350 cm-1 of contiguous tuning and a long-wave infrared light source based on QPM GaAs. In each case the use of QPM materials in conjunction
with effective pump sources instills simplicity and ruggedness into the sensing systems.
Received: 15 April 2002 / Revised version: 6 June 2002 / Published online: 12 September 2002
RID="*"
ID="*"Corresponding author. Fax: +1-925/294-2595, E-mail: tjkulp@sandia.gov
RID="**"
ID="**"Present address: Corning Inc., Corning, NY 14831, USA
RID="*"
ID="*"Present address: Corning Inc., Corning, NY 14831, USA
RID="**"
ID="**"Present address: Blue Leaf Networks, Sunnyvale, CA 94086, USA
RID="***"
ID="***"Present address: Sandia National Laboratories, Albuquerque, NM 87185, USA 相似文献
20.
A. Thomasson S. Geffroy E. Frejafon D. Weidauer R. Fabian Y. Godet M. Nominé T. Ménard P. Rairoux D. Moeller J.P. Wolf 《Applied physics. B, Lasers and optics》2002,74(4-5):453-459
Continuous mapping of an ozone episode in Paris in June 1999 has been performed using a differential absorption lidar system.
The 2D ozone concentration vertical maps recorded over 33 h at the Champ de Mars are compiled in a video clip that gives access
to local photochemical dynamics with unprecedented precision. The lidar data are compared over the whole period with point
monitors located at 0-, 50-, and 300-m altitudes on the Eiffel Tower. Very good agreement is found when spatial resolution,
acquisition time, and required concentration accuracy are optimized. Sensitivity to these parameters for successful intercomparison
in urban areas is discussed.
Received: 11 February 2002 / Published online: 14 March 2002 相似文献