Rayleigh-scattering calculations for the terrestrial atmosphere
TL;DR: The dispersion of the depolarization factor is shown to affect the Rayleigh phase function slightly, by approximately 1% in the forward, backscattered, and 90° scattering-angle directions.
Abstract: Rayleigh-scattering cross sections and volume-scattering coefficients are computed for standard air; they incorporate the variation of the depolarization factor with wavelength. Rayleigh optical depths are then calculated for the 1962 U.S. Standard Atmosphere and for five supplementary models. Analytic formulas are derived for each of the parameters listed. The new optical depths can be 1.3% lower to 3% higher at midvisible wavelengths and up to 10% higher in the UV region compared with previous calculations, in which a constant or incorrect depolarization factor was used. The dispersion of the depolarization factor is also shown to affect the Rayleigh phase function slightly, by approximately 1% in the forward, backscattered, and 90° scattering-angle directions.
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TL;DR: The operation and philosophy of the monitoring system, the precision and accuracy of the measuring radiometers, a brief description of the processing system, and access to the database are discussed.
6,535 citations
Cites background from "Rayleigh-scattering calculations fo..."
...Climatology, sky Size dist.. phase function g Basic Computations Penndorf, 1957 Edlen, 1966 Young, 1980 Burcholtz, 1995 Michalsky, 1988 Iqbal, 1983 London et al., 1976 Kasten and Young, 1989 Kasten and Young, 1989 Komhyr et al., 1989 Harnamatsu Inc. and Lab measurements Kneizys et al.,…...
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TL;DR: In this article, the first principles of Rayleigh scattering theory are used to calculate Rayleigh optical depth in the atmosphere, rather than the variety of curve-fitting techniques currently in use.
Abstract: Many different techniques are used for the calculation of Rayleigh optical depth in the atmosphere. In some cases differences among these techniques can be important, especially in the UV region of the spectrum and under clean atmospheric conditions. The authors recommend that the calculation of Rayleigh optical depth be approached by going back to the first principles of Rayleigh scattering theory rather than the variety of curve-fitting techniques currently in use. A survey of the literature was conducted in order to determine the latest values of the physical constants necessary and to review the methods available for the calculation of Rayleigh optical depth. The recommended approach requires the accurate calculation of the refractive index of air based on the latest published measurements. Calculations estimating Rayleigh optical depth should be done as accurately as possible because the inaccuracies that arise can equal or even exceed other quantities being estimated, such as aerosol optica...
608 citations
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...Bates (1984) and Bucholtz (1995) discussed the depolarization in detail....
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...However, since ( 2 1)/2ns ( 1 2) is proportional to Ns, the resulting expression2ns for s is independent of temperature and pressure (McCartney 1976; Bucholtz 1995)....
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...…(n 1 2) 6 2 7rs s where s is the scattering cross section per molecule; Ns is molecular density; the term (6 1 3r)/(6 2 7r) is called the depolarization term, F(air), or the King factor; and r is the depolarization factor or depolarization ratio, which describes the effect of molecular anisotropy....
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...Using the above equations we now present example calculations to show new values for the scattering cross section (as a function of wavelength) of dry air containing 360 ppm CO2, similar to the presentations of Penndorf (1957) and Bucholtz (1995)....
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...Equation (4) is specified for standard air but at the beginning of their paper, Peck and Reeder (1972) specify standard air as having 330 ppm CO2....
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TL;DR: In this paper, the spectral properties of Rayleigh scattering are discussed and a review of the new advances in flow field imaging that have been achieved using the new filter approaches is presented.
Abstract: Rayleigh scattering is a powerful diagnostic tool for the study of gases and is particularly useful for aiding in the understanding of complex flow fields and combustion phenomena. Although the mechanism associated with the scattering, induced electric dipole radiation, is conceptually straightforward, the features of the scattering are complex because of the anisotropy of molecules, collective scattering from many molecules and inelastic scattering associated with rotational and vibrational transitions. These effects cause the scattered signal to be depolarized and to have spectral features that reflect the pressure, temperature and internal energy states of the gas. The very small scattering cross section makes molecular Rayleigh scattering particularly susceptible to background interference. Scattering from very small particles also falls into the Rayleigh range and may dominate the scattering from molecules if the particle density is high. This particle scattering can be used to enhance flow visualization and velocity measurements, or it may be removed by spectral filtering. New approaches to spectral filtering are now being applied to both Rayleigh molecular scattering and Rayleigh particle scattering to extract quantitative information about complex gas flow fields. This paper outlines the classical properties of Rayleigh scattering and reviews some of the new advances in flow field imaging that have been achieved using the new filter approaches.
508 citations
TL;DR: The design of the airborne HSRL, the internal calibration and accuracy of the instrument, data products produced, and observations and calibration data from the first two field missions are discussed.
Abstract: A compact, highly robust airborne High Spectral Resolution Lidar (HSRL) that provides measurements of aerosol backscatter and extinction coefficients and aerosol depolarization at two wavelengths has been developed, tested, and deployed on nine field experiments (over 650 flight hours). A unique and advantageous design element of the HSRL system is the ability to radiometrically calibrate the instrument internally, eliminating any reliance on vicarious calibration from atmospheric targets for which aerosol loading must be estimated. This paper discusses the design of the airborne HSRL, the internal calibration and accuracy of the instrument, data products produced, and observations and calibration data from the first two field missions: the Joint Intercontinental Chemical Transport Experiment--Phase B (INTEX-B)/Megacity Aerosol Experiment--Mexico City (MAX-Mex)/Megacities Impacts on Regional and Global Environment (MILAGRO) field mission (hereafter MILAGRO) and the Gulf of Mexico Atmospheric Composition and Climate Study/Texas Air Quality Study II (hereafter GoMACCS/TexAQS II).
426 citations
Cites methods from "Rayleigh-scattering calculations fo..."
...The molecular extinction coefficient is calculated from the modeled or sonde-derived molecular density profile, N, and the total molecular cross section, σ 1⁄4 5:168 × 10−31 m2 (3:1247 × 10−32 m2) for 532nm (1064nm) from Bucholtz [36]....
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...The molecular extinction coefficient is calculated from the modeled or sonde-derived molecular density profile, N, and the total molecular cross section, σ ¼ 5:168 × 10−31 m2 (3:1247 × 10−32 m2) for 532nm (1064nm) from Bucholtz [36]....
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...The molecular backscatter coefficient (Cabannes scattering only) [22,36], βm 1⁄4 Ndσπ=dΩ, where dσπ=dΩ 1⁄4 5:931 × 10−32 m2 sr−1 (3:592 × 10−33 m2 sr−1) at 532nm (1064nm) in Eq....
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TL;DR: A modified time-of-flight three-dimensional imaging system, which can use compressed sensing techniques to reduce acquisition times, whilst distributing the optical illumination over the full field of view, is shown.
Abstract: A three-dimensional imaging system which distributes the optical illumination over the full field-of-view is sought after. Here, the authors demonstrate the capability of reconstructing 128 × 128 pixel resolution three-dimensional scenes to an accuracy of 3 mm as well as real-time video with a frame-rate up to 12 Hz.
409 citations
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...The potential application of 3D imaging in the infrared could provide enhanced visibility at long-range, due to reduced atmospheric scattering [27]....
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References
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TL;DR: In this article, the authors presented an improved dispersion formula for standard air, (n − 1)s × 108 = 8342, where σ is the vacuum wave-number in μm-1.
Abstract: Present knowledge of the refractive index of air is reviewed. Regarding the absolute values there are as yet no definite indications that the standard adopted in 1953 on the basis of Barrell and Sears' measurements should be changed, but new experiments aiming at reducing the present uncertainty of about ± 5 × 10-8 would be desirable. Several recent investigations have contributed important new information on the dispersion of air, which has made it possible to derive an improved dispersion formula for standard air, (n − 1)s × 108 = 8342.13 + 2406030 (130 − σ2)-1 + 15997 (38.9 − σ2)−1, where σ is the vacuum wave-number in μm-1. The deviations from the 1953 formula are small and practically negligible in most spectroscopic work. An equation for the dependence of refractivity on temperature and pressure based on theoretical considerations has been derived. For the range of atmospheric conditions normally found in a laboratory the equation can be approximated by the formula (n − 1)tp = (n − 1)s × 0.00138823 p/(1 + 0.003671 t), with p in torr, t in °C, and (n − 1)s given by the dispersion formula for standard air. The effect of carbon dioxide and water vapour is discussed. From Erickson's dispersion data for water vapour, combined with Barrell and Sears' absolute measurements, one obtains the equation ntpf – ntp = −f (5.722 − 0.0457 σ2) × 10-8 for the difference in refractive index of moist air, containing f torr of water vapour, and dry air at equal temperature and total pressure. The equation is valid for visible radiations and normal atmospheric conditions.
1,229 citations
TL;DR: In this article, the optical properties of the atmosphere have been investigated and the authors propose a method to estimate the distance from the Earth to the Sun in terms of the distance to the Earth's surface.
Abstract: (1979). Optical Properties of the Atmosphere. Optica Acta: International Journal of Optics: Vol. 26, No. 4, pp. 420-421.
967 citations
615 citations
21 Feb 1980
TL;DR: In this paper, a computer code for predicting atmospheric transmittance and the thermal radiation emitted by the atmosphere and earth from 350 to 40,000 per cm at a spectral resolution of 20 per cm is described.
Abstract: : This report describes a computer code for predicting atmospheric transmittance and the thermal radiation emitted by the atmosphere and earth from 350 to 40,000 per cm at a spectral resolution of 20 per cm. The program is based on the LOWTRAN 4 (1978) computer code. New altitude and relative-humidity dependent aerosol models and new fog models are included in the code. In addition, the new code structure consists of a main program and 19 subroutines. The computer code contains representative (geographical and seasonal) atmospheric models and representative aerosol models with an option to replace them with user-derived or measured values. The program can be run in one of two modes, namely, to compute only atmospheric transmittance or both atmospheric transmittance and radiance for any given slant path geometry.
571 citations