共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
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
3.
4.
The technology and applications of the differential absorption lidar (DIAL) technique have progressed significantly since
the first DIAL measurements of Schotland [1], and airborne DIAL measurements of ozone and water vapor are frequently being
made in a wide range of field experiments. In addition, plans are underway to develop DIAL systems for use on satellites for
continuous global measurements. This paper will highlight the history of airborne lidar and DIAL systems, summarize the major
accomplishments of the NASA Langley DIAL program, and discuss specifications and goals for DIAL systems in space.
Received: 2 April 1998 相似文献
5.
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
6.
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
7.
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
8.
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
9.
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
10.
Using the Colorado State Na Lidar, surges of stratospheric aerosols caused by the eruption of Mt. Pinatubo have been observed from August to December 1991 over Fort Collins, CO (40.6° N, 105° W), showing a clear increasing trend in stratospheric aerosol activities. These aerosol layers are characterized by the backscatter-ratio profile at 589 nm for altitudes from 12 km to 40 km.On leave from: Department of Radioelectronics, Peking University, Beijing, P.R. China 相似文献
11.
R. Agishev B. Gross F. Moshary S. Ahmed A. Gilerson 《Applied physics. B, Lasers and optics》2005,80(6):765-776
We present a general methodology for evaluating the capabilities of a general lidar system encompassing both backscatter (elastic and Raman lidar) and topographic targets. By introducing a well-defined atmospheric reference medium and by individually examining and decomposing the contributions of lidar system parameters including lidar transmitter power, field of view, receiver noise, atmospheric conditions, and sky background on the signal-to-noise ratio, we obtain a simple dimensionless parameterization of the lidar system. Using this parameterization, numerical simulations are carried out to determine achievable lidar performance including operation range, minimum detectable gas concentration, and so on.This revised version was published online in August 2005 with a corrected cover date. 相似文献
12.
13.
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
14.
High-spectral-resolution rayleigh-mie lidar measurement of vertical aerosol and atmospheric profiles 总被引:1,自引:0,他引:1
C. Y. She R. J. Alvarez II L. M. Caldwell D. A. Krueger 《Applied physics. B, Lasers and optics》1992,55(2):154-158
A new two-channel ground-based high-spectral-resolution Rayleigh-Mie lidar and its operation is described. Upon the inversion of data collected during the night of August 14–15, 1990, with this unique lidar system (553.7 nm), vertical profiles of atmospheric parameters including temperature, potential temperature, pressure and density, as well as aerosol parameters including backscatter-ratio, extinction coefficient and backscatter phase function are determined. 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 present results of experimental investigations of the signal-polarization characteristics in the case of lidar sounding
during precipitation. We show and discuss the lidar signals and the depolarization profiles along the sounding path for liquid-
and solid-phase precipitation. In the former case we compare the signal characteristics at different degrees of precipitation
rate. In the latter situation, we consider snowfall with particle shape close to that of Chebyshev particles. We also follow
the lidar-signal changes depending on the field-of-view of the receiving optics. The experimental data are compared with results
of theoretical estimates and models concerning the optical and microphysical characteristics of the rain and snow particles.
In the case of liquid-phase precipitation – rain – the observed dependence of the lidar’s signal-polarization structure on
the precipitation intensity has two aspects: on the one hand, the change of the raindrops’ shape, and, on the other, the multiple-scattering
effects. The lidar data demonstrate that the signal depolarization, and, more specifically, its behavior along the sounding
path, can be used as a criterion for the presence of multiple scattering. In the case of a snowfall consisting of Chebyshev
particles, the simultaneous role is evident of two factors influencing the lidar-signal depolarization, namely, the non-spherical
shape of the particles and the multiple-scattering effects. When the scattering takes place off particles with a large size
and a shape strongly differing from spherical, we observed the predominant role of the non-sphericity of the scattering centers
in the signal depolarization.
Received: 6 December 2000 / Revised version: 11 July 2001 / Published online: 19 September 2001 相似文献
17.
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
18.
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
19.
I.A. Veselovskii H.K. Cha D.H. Kim S.C. Choi J.M. Lee 《Applied physics. B, Lasers and optics》2000,71(1):113-117
A Raman lidar system based on a tripled Nd:YAG laser is used for profiling of water vapor and liquid water in the troposphere.
The Raman signals from water in the gas and liquid state are separated by interference filters and their relative intensities
are studied for different atmospheric conditions. For clean weather or immediately after the rain the Raman signal from liquid
water inside PBL is about one order of magnitude lower than the signal from water vapor. But during cloud measurements both
Raman signals become comparable and the results of water vapor measurements must be corrected for the interference of liquid
water Raman scattering. The obtained results are used for the estimation of liquid water content in the atmosphere.
Received: 4 October 1999 / Revised version: 18 February 2000 / Published online: 11 May 2000 相似文献
20.
Lidar is an efficient tool for remotely measuring physical quantities or detecting targets. To improve the range resolution in long pulse lidars, such as lidar systems based on TEA-CO2 lasers, deconvolution methods were used by previous investigators. Deconvolution is a noise sensitive process. In order to avoid noise amplification during the deconvolution process, the Fourier-wavelet regularized deconvolution method is used to deconvolve and denoise the back-scattered lidar signal simultaneously. This method is applied to lidar systems based on the TEA-CO2 laser and the results are compared to nitrogen tail clipping method. Numerical simulation shows, in comparison to the clipping nitrogen tail technique, by using the ForWaRD method; the range resolution and working distance of the lidar is improved and the clipping tail apparatus is also eliminated. 相似文献