光学遥感图像大气校正（英文版）

遥感图像

大气校正

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CHAPTER

Atmospheric Correction of Optical

Imagery

OUTLINE

5.1. Atmospheric Effects 112

5.1.1. Atmospheric Characterization

in a

Quantitative Remote-Sensing

Model 112

5.1.2. Atmospheric Composition 112

5.1.3. Interaction between

Electromagnetic Waves and the

Atmosphere 113

5.1.4. Major Aspects of Atmospheric

Correction 114

5.2. Correcting the Aerosol Impact 114

5.2.1. Spectral Informationebased

Correction Method 115

5.2.2. Temporal Infromation-based

Correction Method 117

5.2.3. Angular Information-based

Correction Method 119

5.2.4. Spatial Information-based

Correction Method 120

5.2.5. Polarization Information-based

Correction Method 121

5.3. Correcting the Impact of Water Vapor 121

5.4. Correcting the Impacts of Other

Constituents 122

5.5. Commonly Used Models and Software 122

5.5.1. MODTRAN Model 123

5.5.2. 6S Model 123

5.5.3. FLAASH 124

5.5.4. ATCOR 124

5.5.5. ACORN 124

5.6. Conclusions 124

Abstract

This chapter introduces the subject of atmospheric

effects on the process of remote-sensing imaging and

their corrections. Section 5.1 presents the background

of atmospheric effects. Section 5.2 discusses various

algorithms for estimating the aerosol properties based

on its spectral, temporal, angular, spatial, and polari-

zation characteristics. Section 5.3 introduces the algo-

rithms for estimating atmospheric moisture content.

Finally, the inﬂuences of other atmospheric compo-

nents and the commonly used atmospheric correction

models are illustrated.

Advanced Remote Sensing : Terrestrial Information Extraction and Applications, edited by Shunlin Liang, et al., Elsevier Science & Technology, 2012. ProQuest

Ebook Central, http://ebookcentral.proquest.com/lib/jlu-ebooks/detail.action?docID=965002.

Created from jlu-ebooks on 2018-09-29 19:59:57.

5.1. ATMOSPHERIC EFFECTS

5.1.1. Atmospheric Characterization

in a Quantitative Remote-Sensing Model

An optical remote-sensing system can be

divided into ﬁve subsystems (Figure 5.1): the

scene radiative transfer model, the atmospheric

radiative transfer model, the navigation

system, the sensor system, and the mapping

and binning system. The scene radiative trans-

fer model describes the relationship between

the surface radiative signals and the surface

characteristic parameters. The atmospheric

radiative transfer model characterizes the

atmospheric impacts on the surface radiative

signals that are received by the remote sensors.

The navigation system mainly involves the

surface-imaging systems of carried satellites,

aircraft, and other sensor platforms. The sensor

system includes the sensor spectral response,

spatial response, band division, noise treat-

ment, and digital processing, and t he mapp ing

and binning system mainly involves the

projection transformation and r esampling of

imagery.

The atmospheric radiative transfer model is

a critical link that connects the surface character-

istic parameters with the signals received by the

sensors. This model is also considered to be an

important factor that inﬂuences the quantitative

retrieval of the surface parameters from remote-

sensing imagery.

5.1.2. Atmospheric Composition

The atmosphere is a mixture of various gases

and suspended liquid and solid impurities. An

atmosphere free of water vapor and impurities

is called dry-clean air. The atmosphere is

composed primarily of oxygen, nitrogen, and

several inert gases, which together account for

99.9% of the total air. Excluding carbon dioxide

and water vapor, other compositions of these

gases are stable in the troposphere. The water

vapor and carbon dioxide concentrations vary

with the region, season, and weather conditions.

In most cases, water vapor and carbon dioxide

account for 0% 4% and 0.033% of the atmo-

sphere, respectively, as shown in Table 5.1.

The large number s of solid and liquid parti-

cles suspended in the atmosphere are called

aerosols, which typically include haze, smoke,

and fog. Aerosols are mainly produced by

volcanic eruptions, ground dust, sandstorms,

forest ﬁres, various acidic particles, industry,

transportation, construction, agriculture, and

other production and living activities. The aero-

sols can be divided by particle size. Those with

a particle size between 5.0  10

3

and 0.2 mm

are called Aitken nuclei; those from 0.2 to 1 mm

are called large particles; and those greater

than 1 mm are called giant particles. In the tropo-

sphere, the aerosol concentration is subject to

exponential decay with increasing height; in

the stratosphere, the aeroso l concentration is

relatively stable.

Surface attributes

Scene radiative transfer

model

Atmospheric radiative

transfer model

Navigation

system

Sensor system

Mapping and

binning system

Remote sensing data

FIGURE 5.1 Optical remote-sensing system models. (Liang, 2004).

5. ATMOSPHERIC CORRECTION OF OPTICAL IMAGERY112

Advanced Remote Sensing : Terrestrial Information Extraction and Applications, edited by Shunlin Liang, et al., Elsevier Science & Technology, 2012. ProQuest

Ebook Central, http://ebookcentral.proquest.com/lib/jlu-ebooks/detail.action?docID=965002.

Created from jlu-ebooks on 2018-09-29 19:59:57.

5.1.3. Interaction between

Electromagnetic Waves and the

Atmosphere

If polarization effects are disregarded and the

particles can be considered to be isotropic, then

the one-dimensional radiative transfer equati on

can be expressed as follows:

dLðs; m; fÞ

¼ Lðs; m; fÞ

1

Lðs; m

; f

 Pðm; f; m

; f

Þdm

(5.1)

where L is the radiance; ðm; 4Þ are the observa-

tion angle coordinates; q is the zenith angle; f

is the relative azimuth between the solar direc-

tion and the observation direction, m ¼ cosðqÞ;

s is the aerosol optical thickness (AOT), deﬁned

by s ¼

ðzÞdz where s

ðzÞ is the extinction

coefﬁcient; u is the single scattering albedo,

which describes the probability that scattering

will occur in a photonic collision with particles

of the medium; and Pðm; 4; m

; 4

Þis the scattering

phase function describing the probability of

photon scattering from other directions.

Molecular absorption refers to the conversion

of radiant energy into molecular excited oscilla-

tion energy. Scattering refers to the redistribution

of incident energy to other directions, and the

total effect shifts incident energy away from the

scatter. The atmospheric molecules that absorb

electromagnetic waves mainly include O

O, CO

,CH

,andN

O. Of these molecules,

ozone, carbon dioxide, and water vapor absorb

solar radiation energy the most effectively. Ozone

has a strong absorption band in the ultraviolet

region (0.22 to 0.32 mm) and in the 0.6 mm, 4.7

mm, 9.6 mmand14mm spectral regions as well.

Carbon dioxide is mainly distributed in the lower

atmosphere, with absorption bands in the 1.4 mm,

1.6 mm, 2.0 mm, 2.7 mm, 4.3 mm, 4.8 mm, 5.2 mm,

and 15.0 mm spectral regions, of which the bands

at 2.7 mm, 4.3 mm, and 15 mm are strong absorp-

tion bands. Water vapor has absorption bands

at 0.94 mm, 1.1 mm, 1.38 mm, 1.87 mm, 2.7 mm,

3.2 mm, and 6.3 mm, which cover almost the entire

infrared band.

The atmospheric scattering of electromagnetic

waves is mainly divided into two categories:

selective scattering, which is further divided

into Rayleigh scattering and Mie scattering, and

nonselective scattering. When the diameter of

an atmospheric particle causing scattering is far

smaller than the wavelength of the incident elec-

tromagnetic waves, Rayleigh scattering occurs.

The scattering of visible light by oxygen,

nitrogen, and other gas molecules in the atmo-

sphere belongs to this category. The Rayleigh

scattering intensity is inversely proportional to

the fourth power of the wavelength, and the

forward scattering has equal intensity to

the backscattering. Rayleigh scattering is one of

the main causes of radiometric distortion and

TABLE 5.1 Major Atmospheric Constituents

Stable compositions Variable compositions

Composition

Volume

ratio (%) Composition

Volume

ratio (%)

78.084 H

O 0.04

20.948 O

12  10

-4

Ar 0.934 SO

0.001  10

-4

0.033 NO

0.001  10

-4

Ne 18.18  10

-4

0.001  10

-4

He 5.24  10

-4

NO 0.0005  10

-4

Kr 1.14  10

-4

S 0.00005  10

-4

Xe 0.089  10

-4

Nitric acid

vapor

Trace

0.5  10

-4

1.5  10

-4

O 0.27  10

-4

CO 0.19  10

-4

5.1. ATMOSPHERIC EFFECTS 113

Advanced Remote Sensing : Terrestrial Information Extraction and Applications, edited by Shunlin Liang, et al., Elsevier Science & Technology, 2012. ProQuest

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blurring of remote-sensing short-wave imagery.

When the diameter of the atmospheric particle

causing scattering is equal to the wavelength of

the incident waves, Mie scattering occurs. Scat-

tering by small particles and other aerosols sus-

pended in the atmosphere belongs to this

category. Forward Mie scattering is usually far

greater than its backscattering. Under general

atmospheric conditions, Rayleigh scattering plays

a dominant role; however, when Mie scattering is

superimposed on Rayleigh scattering, the sky

becomes gloomy. When the diameter of the atmo-

spheric particle causing scattering is much larger

than the wavelength of the incident waves, nonse-

lective scattering occurs, and its scattering inten-

sity is not related to the wavelength. Scattering

by clouds, fog, water droplets and dust in the

atmosphere falls into this category.

The physical matter in the atmosphere attenu-

ates electromagnetic signals due to absorption,

refraction and other phenomena. Atmospheric

effects are among the key issues in quantitative

remote sensing and they can interfere with the

quantitative application of remote sensing. The

removal of this interference is necessary in order

to quantitatively use remotely sensed data.

5.1.4. Major Aspects of Atmospheric

Correction

Atmospheric correction consists of two parts:

the estimation of atmospheric parameters and

the retrieval of surface reﬂectance. If the surface

is Lambertian and all of the atmospheric param-

eters are known, then remote-sensing imagery

can be calcul ated to directly retrieve the surfa ce

reﬂectance. Based on radiative transfer theory

and assuming that the target is a uniform

Lambertian surface, the radiance received by

a sensor at the top of the atmosphere (TOA) can

be expressed as follows:

L ¼ L

1  sr

(5.2)

where L

is the atmospheric radiation path in the

case of no surface reﬂection, T is the

transmittance from the surface to the sensor, s is

the atmospheric spherical reﬂectance, r is the

surface target reﬂectance, and F

is the down-

ward radiat ion ﬂux reaching the surface. Accord-

ing to the equation, the radiance received by the

sensors that is given by L, L

, s, and TF

/p can

be calculated by the radiative transfer model

and used to calculate the surface reﬂectance.

As shown in Figure 5.2, MODTRAN (see

Section 5.5.1) is used to simulate the apparent

radiance within the wavelength range of

0.4e2.5 mm. For the simulation, vegetation is

used for the surface reﬂectance, the atmosphere

is set as a midlatitude summer, the aerosol type

is set to the rural type, the water vapor content

remains constant, and the visibility varies from

2 to 60 km. As indicated in the ﬁgure, the visi-

bility has the greatest impact on the visible spec-

trum. The radiance of the visible band gradually

decreases with the increase in visibility.

Besides particle scattering, the main absorbers

include wate r vapor, ozone, oxygen, and aero-

sols. Molecular scattering and absorption by

ozone, oxygen, and other gases are relative ly

easy to correct because the concentrations of

these elem ents are relatively stable in time and

space; however, estimating the aerosol and

water vapor parameters is rather difﬁcult. There-

fore, removal of the impacts of aerosols and

water vapor is the main component of atmo-

spheric correction.

5.2. CORRECTING THE AEROSOL

IMPACT

Atmospheric aerosol refers to multidispersed

bodies consisting of small particles suspended

in the atmosphere, whose scale ranges between

0.001 and 10 mm. Atmospheric aerosols have

a considerable impact on the global climate.

Through their absorption and scattering of solar

and infrared radiation, they change the radiation

budget of the Eartheatmosphere system. By

absorbing and scattering radiation, aerosols can

directly interfere with the signal reception of

5. ATMOSPHERIC CORRECTION OF OPTICAL IMAGERY114

Advanced Remote Sensing : Terrestrial Information Extraction and Applications, edited by Shunlin Liang, et al., Elsevier Science & Technology, 2012. ProQuest

Ebook Central, http://ebookcentral.proquest.com/lib/jlu-ebooks/detail.action?docID=965002.

Created from jlu-ebooks on 2018-09-29 19:59:57.

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