Handbook of Optics(Third Edition)ATMOSPHERIC OPTICS.pdf
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1、 PART 2 ATMOSPHERIC OPTICS This page intentionally left blank ATMOSPHERIC OPTICS Dennis K. Killinger Department of Physics Center for Laser Atmospheric Sensing University of South Florida Tampa, Florida James H. Churnside National Oceanic and Atmospheric Administration Earth System Research Laborato
2、ry Boulder, Colorado Laurence S. Rothman Harvard-Smithsonian Center for Astrophysics Atomic and Molecular Physics Division Cambridge, Massachusetts 3.1 GLOSSARY c speed of light Cn 2 atmospheric turbulence strength parameter D beam diameter F hypergeometric function g(n) optical absorption lineshape
3、 function H height above sea level h Plancks constant I Irradiance (intensity) of optical beam (W/m2) k optical wave number K turbulent wave number L propagation path length L0outer scale size of atmospheric turbulence l0inner scale size of atmospheric turbulence N density or concentration of molecu
4、les p(I) probability density function of irradiance fl uctuations PvPlanck radiation function R gas constant 3.3 3 3.4 ATMOSPHERIC OPTICS S molecular absorption line intensity T temperature v wind speed b backscatter coeffi cient of the atmosphere gppressure-broadened half-width of absorption line k
5、optical attenuation l wavelength noptical frequency (wave numbers) r0phase coherence length l2 variance of irradiance fl uctuations sR Rayleigh scattering cross section 3.2 INTRODUCTION Atmospheric optics involves the transmission, absorption, emission, refraction, and reflection of light by the atm
6、osphere and is probably one of the most widely observed of all optical phenomena.15 The atmosphere interacts with light due to the composition of the atmosphere, which under normal conditions, consists of a variety of different molecular species and small particles like aerosols, water droplets, and
7、 ice particles. This interaction of the atmosphere with light is observed to produce a wide variety of optical phenomena including the blue color of the sky, the red sunset, the optical absorption of specific wavelengths due to atmospheric molecules, the twinkling of stars at night, the greenish tin
8、t sometimes observed during a severe storm due to the high density of particles in the atmosphere, and is critical in determining the balance between incoming sunlight and outgoing infrared (IR) radiation and thus influencing the earths climate. One of the most basic optical phenomena of the atmosph
9、ere is the absorption of light. This absorp- tion process can be depicted as in Fig. 1 which shows the transmission spectrum of the atmosphere as FIGURE 1 Transmittance through the earths atmosphere as a function of wavelength taken with low spec- tral resolution (path length 1800 m). (From Measures
10、, Ref. 5.) ATMOSPHERIC OPTICS 3.5 a function of wavelength.5 The transmission of the atmosphere is highly dependent upon the wave- length of the spectral radiation, and, as will be covered later in this chapter, upon the composition and specific optical properties of the constituents in the atmosphe
11、re. The prominent spectral features in the transmission spectrum in Fig. 1 are primarily due to absorption bands and individual absorption lines of the molecular gases in the atmosphere, while a portion of the slowly varying background transmission is due to aerosol extinction and continuum absorpti
12、on. This chapter presents a tutorial overview of some of the basic optical properties of the atmo- sphere, with an emphasis on those properties associated with optical propagation and transmission of light through the earths atmosphere. The physical phenomena of optical absorption, scattering, emiss
13、ion, and refractive properties of the atmosphere will be covered for optical wavelengths from the ultraviolet (UV) to the far-infrared. The primary focus of this chapter is on linear optical properties associated with the transmission of light through the atmosphere. Historically, the study of atmos
14、pheric optics has centered on the radiance transfer function of the atmosphere, and the linear transmission spectrum and blackbody emission spectrum of the atmosphere. This emphasis was due to the large body of research associated with passive, electro-optical sensors which primarily use the transmi
15、ssion of ambient optical light or light from selected emission sources. During the past few decades, however, the use of lasers has added a new dimension to the study of atmospheric optics. In this case, not only is one interested in the transmission of light through the atmosphere, but also informa
16、tion regarding the optical properties of the backscat- tered optical radiation. In this chapter, the standard linear optical interactions of an optical or laser beam with the atmo- sphere will be covered, with an emphasis placed on linear absorption and scattering interactions. It should be mentione
17、d that the first edition of the OSA Handbook of Optics chapter on “Atmospheric Optics” had considerable nomographs and computational charts to aid the user in numerically cal- culating the transmission of the atmosphere.2 Because of the present availability of a wide range of spectral databases and
18、computer programs (such as the HITRAN Spectroscopy Database, LOWTRAN, MODTRAN, and FASCODE atmospheric transmission computer programs) that model and calculate the transmission of light through the atmosphere, these nomographs, while still useful, are not as vital. As a result, the emphasis on this
19、edition of the “Atmospheric Optics” chapter is on the basic theory of the optical interactions, how this theory is used to model the optics of the atmosphere, the use of available computer programs and databases to calculate the optical properties of the atmosphere, and examples of instruments and m
20、eteorological phenomena related to optical or visual remote sensing of the atmosphere. The overall organization of this chapter begins with a description of the natural, homogeneous atmosphere and the representation of its physical and chemical composition as a function of altitude. A brief survey i
21、s then made of the major linear optical interactions that can occur between a propa- gating optical beam and the naturally occurring constituents in the atmosphere. The next section covers several major computational programs (HITRAN, LOWTRAN, MODTRAN, and FASCODE) and U.S. Standard Atmospheric Mode
22、ls which are used to compute the optical transmission, scatter- ing, and absorption properties of the atmosphere. The next major technical section presents an over- view of the influence of atmospheric refractive turbulence on the statistical propagation of an optical beam or wavefront through the a
23、tmosphere. Finally, the last few sections of the chapter include a brief introduction to some optical and laser remote sensing experiments of the atmosphere, a brief introduction to the visually important field of meteorological optics, and references to the critical influence of atmospheric optics
24、on global climate change. It should be noted that the material contained within this chapter has been compiled from several recent overview/summary publications on the optical transmission and atmospheric composition of the atmosphere, as well as from a large number of technical reports and journal
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