Simple relation between lidar multiple scattering and depolarization for water clouds

An empirical relationship is derived between the multiple-scattering fraction and the linear depolarization ratio by using Monte Carlo simulations of water clouds measured by backscatter lidar. This relationship is shown to hold for clouds having a wide range of extinction coefficients, mean droplet sizes, and droplet size distribution widths. The relationship is also shown to persist for various instrument fields of view and for measurements made within broken cloud fields. The results obtained from the Monte Carlo simulations are verified by using multiple-field-of-view lidar measurements. For space-based lidars equipped to measure linear depolarization ratios, this new relationship can be used to accurately assess signal perturbations due to multiple scattering within nonprecipitating water clouds.     

Optical depth and multiple scattering depolarization in liquid clouds

In this paper, we calculate multiply scattered lidar signals with Monte Carlo method for measuring optical depth (extinction coefficient), effective size of water droplets, and liquid water content of clouds, and present algorithms that implement our method. We calculated multiply scattered lidar signals for various water droplet sizes and liquid water contents using a Monte Carlo method. A simple correspondence between water droplet optical depth and the degree of polarization in a modified gamma size distribution (C₁ cloud) is found. We also calculated the degree of polarization of a lidar signal for a given liquid water content, finding that the degree of polarization is only dependent on optical depth. Since the Raman lidar signal of liquid water depends on the total volume of the water droplet, the effective radius of the water droplet can thus be recovered from the degree of polarization of the lidar signal and the Raman signal of the liquid water.     

An improved algorithm for cloud multiple scattering

Clouds' radiation characteristics are very important in clouds scene simulation, weather forecasting, pattern recognition, and other fields. Radiation of a cloud mainly comes from its multiple scattering. A new algorithm to calculate multiple scattering, called build-up factor algorithm, is proposed in this paper. In this algorithm, a modified gamma distribution is assumed to describe droplets distribution inside a cloud, then the radiation transport equation is calculated to get the solution of single scattering, and finally, a build-up factor is defined to estimate the multiple scattering contributions. This algorithm considers both single scattered radiance and multiple scattered radiance and needs shorter computing time. It can be used in real time simulations.     

Time reversal versus phase conjugation in a multiple scattering environment

We present experimental results on the reversibility of ultrasound in a multiple scattering medium. An ultrasonic pulsed wave is transmitted from a point source to a 128-element receiving array through 2D samples with various thickness. The samples consist of random collections of parallel steel rods immersed in water. The scattered waves are recorded, time reversed and sent back into the medium. The time-reversed waves are converging back to their source and the quality of spatial and temporal focusing on the source is related to the second-order moments of the scattered wave (correlation) in time and in space. Experimental results show that it is possible to obtain a robust estimation of the correlations on a single realisation of disorder, taking advantage of the wide frequency bandwidth. The spatial resolution of the system is only limited by the correlation length of the scattered field, and no longer by diffraction. Moreover, successful time-reversal focusing using a single element instead of an array is possible, whereas a one-channel monochromatic phase conjugation fails. The efficiency of broad-band time reversal compared to monochromatic phase conjugation lies in the number of 'information grains' in the frequency bandwidth.     

Lidar model with parameterized multiple scattering for retrieving cloud optical properties

Cirrus clouds play an important role in the climate through their optical and microphysical properties. The problem with measuring optical properties of these clouds can be partially addressed by using lidar systems. This paper presents a new model for describing the multiple scattering contribution to the backscatter signal measured by the lidar system. The new lidar equation introduced this way, expresses the backscatter signal in terms of a polynomial function of the cloud scattering coefficient. Cloud optical properties such as the extinction coefficient and lidar ratio can be deduced from the new proposed lidar equation. Moreover, some cloud microphysical properties can also be inferred from these optical properties. The method is applied to lidar data collected by the micropulsed lidar operating at Nauru under the auspices of the US Department of Energy ARM program.     

Single scattering profile from small-angle scattering data affected by multiple scattering: use of a basis function set

Present work involves extraction of single-scattering profile from small-angle scattering data, affected by multiple scattering, using an existing model-independent algorithm [Mazumder et al., Physica B 241–243, 1222 (1998), Mazumder et al., J. Appl. Crystallogr. 36, 840 (2003)]. It is shown that implementation of the algorithm becomes effective by representing the multiple scattering profiles in terms of a set of basis function whose form of Hankel transformed pair is known analytically. In the present paper, the methodology has been presented by introducing a Gaussian basis set and has been tested for various simulated profiles. The performance of this methodology has also been tested for scattering profiles having complex internal features and moderate statistical noise. Subsequently, the same has been applied for experimental small-angle neutron scattering data.     

Compensation of the thermally induced depolarization in a double-pass Nd:YAG rod amplifier with a stimulated Brillouin scattering phase conjugate mirror

Stimulated Brillouin scattering phase conjugate mirrors (SBS-PCMs) are extensively used to compensate the phase distortion of active media in a high-energy laser system with double-pass amplification. However, the depolarization loss from the thermally induced birefringence of the active medium by a photoelastic effect cannot be avoided despite the uses of phase conjugate mirrors. In this work, the depolarization loss in a double-pass Nd:YAG rod amplifier with a SBS-PCM has been studied with Jones matrix calculations. In addition, the depolarization ratios and the leak beam patterns are obtained experimentally and theoretically for four possible optical schemes. Both experiment and theoretical results show that depolarization is effectively compensated when a Faraday rotator is located after the amplifier.     

A diode-pumped Nd: YAG lidar for airborne cloud measurements

A new diode-pumped Nd: YAG laser with a high repetition rate, for applications in small-size lidars, has been developed. In this paper first results from airborne measurements are presented. Together with a sophisticated receiver set-up for detection of multiple scattering and depolarization effects, this new laser offers a unique possibility for airborne remote sensing of clouds.     

Seasonal variability of cirrus depolarization properties derived from CALIPSO lidar measurements over Beijing in China

<正>The seasonal variability of cirrus depolarization ratio and its altitude at the region of Beijing(39.93°N, 116.43°E,the capital of China) are presented.From the results obtained from the cloud aerosol lidar and infrared pathfinder satellite observations lidar measurements,it appears that the values of depolarization ratio and altitude of cirrus are generally higher in autumn and summer than those in spring and winter, and the cirrus altitude is modulated by the height of tropopause.Additionally,the depolarization ratio tends to linearly vary with the increase of altitude and the decrease of temperature.     

Seasonal variability of cirrus derived from CALIPSO over Beijing depolarization properties lidar measurements in China

The seasonal variability of cirrus depolarization ratio and its altitude at the region of Beijing （39.93°N, 116.43°E, the capital of China） are presented. From the results obtained from the cloud aerosol lidar and infrared pathfinder satellite observations lidar measurements, it appears that the values of depolarization ratio and altitude of cirrus are generally higher in autumn and summer than those in spring and winter, and the cirrus altitude is modulated by the height of tropopause. Additionally, the depolarization ratio tends to linearly vary with the increase of altitude and the decrease of temperature.     

LIDAR multiple scattering from clouds

Multiple-scattering LIDAR return calculations obtained by seven different models for the same specified numerical experiment are compared. This work results from an international joint effort stimulated by the workshop group called MUSCLE for MUltiple SCattering Lidar Experiments. The models include approximations to the radiative-transfer theory, Monte-Carlo calculations, a stochastic model of the process of multiple scattering, and an extension of Mie theory for particles illuminated by direct and scattered light. The model solutions are similar in form but differ by up to a factor of 5 in the strength of the multiple-scattering contributions. Various reasons for the observed differences are explored and their practical significance is discussed.     

Gamma holography from multiple scattering

Since the introduction of heterodyne methods for synchrotron radiation (Cousesement et al. in Phys. Rev. B 54:16003, 1996; Callens et al. in Phys. Rev. 67:104423, 2003) one observes interferences between two scattering amplitudes; the scattering amplitude of resonant nuclei in a reference sample and the scattering amplitude of nuclei in the sample under investigation. Theses interferences can easily been observed as resonances in velocity spectra when one uses a time integrated method. They can also been observed as quantum beats, when one would use the time differential method. For both methods it is important that one uses a reference sample and therefore both methods disserved the name “heterodyne methods.” As theses interferences are a product of two scattering amplitudes, the amplitude of a wave scattered form the investigated sample can be known with its phase. But it is assumed that the reference wave is known in advance by a proper choice of the reference sample. At first sight it is very likely that multiple scattering would add more complexity but in this paper it is claimed that on the contrary it provide a bonus, especially for single crystals. It provokes only a line broadening and a line shift of the resonances in the velocity spectra (or a change in the damping and frequency of the quantum beats when the time spectra are registered). Moreover these changes in the line shapes can easily be measured and they provide all the information needed to reconstruct a 3-D picture of the atomic arrangement of resonant nuclei and moreover they distinguish between different hyperfine sites. The method may be more practical for measurements on synchrotron radiation but it does also apply to velocity spectra obtained from resonant scattering with strong sources. The use of radioactive sources suffer from the disadvantage of poorer statistics or much longer accumulation times but they enjoy the advantage to be table-top and at-home experiments. As strong sources are now commercially available this possibility to measure not only the hyperfine fields but also the corresponding crystal structure could give a renewed impetus to the investigations with Moessbauer spectrometry, with “at home and table top” instrumentation.     

A three-parameter analytic phase function for multiple scattering calculations

A very simple procedure has been developed to fit the first three moments of an actual phase function with a three parameter analytic phase function. The exact Legendre Polynomial decomposition of this function is known which makes it quite suitable for multiple scattering calculations. The use of this function can be expected to yield excellent flux values at all depths within a medium. Since it is capable of reproducing the glory, it can be used in synthetic spectra computations from planetary atmospheres. Accurate asymptotic radiance values can also be achieved as long as the single scattering albedo ω₀ ?0.9.     

Measurement of water cloud particle size with a dual-polarization pulsed bistatic lidar

A new bistatic lidar was developed for measuring water cloud particle size at the base of lower clouds. The lidar uses a pulsed Nd:YAG laser at 532 nm and a receiver having a polarization analyzer located at a suitable scattering angle. Cloud particle size (mode radius of the assumed size distribution) was derived from the ratio of the polarization components of the scattered light based on the single scattering Mie theory. The experiment was performed on board the research vessel Mirai in the northwestern Pacific. Particle size at the bottom of maritime cumulus and stratus was measured, and the difference between the internal structures of cumulus and stratus was observed. The effect of multiple scattering was studied by changing the observing scattering angle. The effect was not significant when the penetration depth was less than 50 m.     

Rlationship between the aerosol scattering ratio and temperature of atmosphere and the sensitivity of a Doppler wind lidar with iodine filter

The sensitivity of Doppler wind lidar is an important parameter which affects the performance of Doppler wind lidar. Aerosol scattering ratio, atmospheric temperature, and wind speed obviously affect the mea- surement of Doppler wind lidar with iodine filter. We discuss about the relationship between the measurement sensitivity and the above atmospheric parameters. The numerical relationship between them is given through the theoretical simulation and calculation.     

Emulsification processes: on-line study by multiple light scattering measurements

The use of ultrasound in various processes of the chemical industry has been a subject of research and development for many years. As regards in emulsification, apart from formulation variables, power is the most important parameter. Efficiency of emulsification processes may be followed and evaluated by measuring particle size distribution, which mainly governs the kinetic stability of such dispersions. Unfortunately, this kind of measurement must be performed at high dilution (low volume fraction of dispersed phase). The present work is devoted to the on-line study of ultrasound emulsification by means of a newly developed apparatus based on multiple light scattering, which allows us to determine average droplet diameter and its variations directly on concentrated media. The model system was an oil (kerosene)-in-water emulsion stabilized by a polyethoxylated sorbitan monostearate.     

Polarization resolved stimulated raman scattering: probing depolarization ratios of liquids

Polarization resolved stimulated Raman scattering (SRS) signal is described in the case of isotropic media and linearly polarized incident fields. The model gives simple expressions for the two perpendicularly polarized SRS signals I_X and I_Y, detected along the X and Y directions, respectively, as a function of the incident pump and Stokes polarization angles. We find that Raman depolarization ratio can be simply obtained from the ratio of the SRS intensities detected along the X and Y axis. These theoretical findings are supported by polarization resolved SRS measurements performed on polarized and depolarized bands of cyclohexane. Copyright © 2011 John Wiley & Sons, Ltd.