Michael D. King, EOS Senior Project Scientist August 25, 2002 1 Introduction to the Course & Principles of Radiative Transfer, Scattering & Orbits Michael D. King NASA Goddard Space Flight Center Outline Physical principles behind the remote sensing of atmosphere, land, and ocean properties from Terra Light scattering and emission of the Earth-atmosphere- surface system – Spacecraft, spatial resolution, swath width, and sensor characteristics Satellite orbits and repeat coverage required for global observations Fundamental concepts and terminology of radiative transfer – Atmospheric absorption and transmission characteristics – Radiance & irradiance – Scattering phase function – Optical thickness – Single and multiple scattering
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Introduction to the Course & Principles of Radiative Transfer, Scattering & Orbits
Introduction to the Course & Principles of Radiative Transfer, Scattering & Orbits. Michael D. King NASA Goddard Space Flight Center Outline Physical principles behind the remote sensing of atmosphere, land, and ocean properties from Terra - PowerPoint PPT Presentation
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Michael D. King, EOS Senior Project Scientist August 25, 20021
Introduction to the Course & Principles of Radiative Transfer,
Scattering & Orbits
Introduction to the Course & Principles of Radiative Transfer,
Scattering & OrbitsMichael D. King
NASA Goddard Space Flight Center
Outline Physical principles behind the remote sensing of atmosphere,
land, and ocean properties from Terra Light scattering and emission of the Earth-atmosphere-surface
system– Spacecraft, spatial resolution, swath width, and sensor
characteristics Satellite orbits and repeat coverage required for global
observations Fundamental concepts and terminology of radiative transfer
– Atmospheric absorption and transmission characteristics– Radiance & irradiance– Scattering phase function– Optical thickness– Single and multiple scattering
Michael D. King, EOS Senior Project Scientist August 25, 20022
Remote Sensing OverviewRemote Sensing Overview
What is “remote sensing”?– Using artificial devices, rather than our eyes, to observe or
measure things from a distance without disturbing the intervening medium» It enables us to observe & measure things on spatial,
spectral, & temporal scales that otherwise would not be possible
» It allows us to observe our environment using a consistent set of measurements throughout the globe, without prejudice associated with national boundaries and accuracy of datasets or timeliness of reporting
How is remote sensing done?– Electromagnetic spectrum
» Passive sensors from the ultraviolet to the microwave» Active sensors such as radars and lidars
– Satellite, airborne, and surface sensors– Training and validation sites
Michael D. King, EOS Senior Project Scientist August 25, 20023
Remote Sensing Applications to be Covered in this Course
Remote Sensing Applications to be Covered in this Course
History of remote sensing & global change Remote sensing of land surface properties
– Spectral and angular reflectance, land cover & land cover change
– Fire monitoring and burn scars– Leaf area index & flux of photosynthetically active radiation– Temperature & emissivity separation of terrestrial surfaces
Remote sensing of atmospheric properties– Cloud cover, cloud optical properties, and cloud top properties– Aerosol properties– Water vapor– Atmospheric chemistry (carbon monoxide and methane)– Earth radiation budget and cloud radiative forcing
Remote sensing of the oceans from space– Chlorophyll concentration and biological productivity of the
oceans – Sea surface temperature using thermal methods
Angular directional models of the Earth-atmosphere-ocean system
Michael D. King, EOS Senior Project Scientist August 25, 20024
Remote sensing uses the radiant energy that is reflected and emitted from Earth at various “wavelengths” of the electromagnetic spectrum
Our eyes are only sensitive to the “visible light” portion of the EM spectrum
Why do we use nonvisible wavelengths?
The Electromagnetic SpectrumThe Electromagnetic Spectrum
Michael D. King, EOS Senior Project Scientist August 25, 20025
Visible Spectrum
Wavelength (µm)
0.4 0.5 0.6 0.7
Schematic Wave of RadiationSchematic Wave of Radiation
From Parkinson, C. L., 1997: Earth from Above
Michael D. King, EOS Senior Project Scientist August 25, 20026
Angular scattering coefficient [()]– Fractional amount of energy scattered into the direction
per unit solid angle per unit length of transit [m-1 sr-1]
Michael D. King, EOS Senior Project Scientist August 25, 200225
Volume Scattering and Extinction Coefficient
Volume Scattering and Extinction Coefficient
Volume scattering coefficient [sca]
– Fractional amount of energy scattered in all directions per unit length of transit [m-1]
sca =
=
Volume absorption coefficient [abs]
– Fractional amount of energy absorbed per unit length of transit [m-1]
Volume extinction coefficient [ext]
– Fractional amount of energy attenuated per unit length of transit [m-1]
ext= sca + abs
Single scattering albedo [0]
– Fraction of energy scattered to that attenuated
0 = sca/(sca + abs)
€
()d∫
€
()sinddφ0
π
∫0
2π
∫
Michael D. King, EOS Senior Project Scientist August 25, 200226
Optical depth []– Total attenuation along a path length, generally a function
of wavelength [dimensionless]
Total optical thickness of the atmosphere [t]
– Total attenuation in a vertical path from the top of the atmosphere down to the surface
Transmission of the direct solar beam
Optical ThicknessOptical Thickness
t =exp[-t()]
t =exp[-t()/µ0]
0
µ0 = cos0
€
()= extdx0
X
∫
€
t()= extdz0
∞
∫
Michael D. King, EOS Senior Project Scientist August 25, 200227
Scattering phase function is defined as the ratio of the energy scattering per unit solid angle into a particular direction to the average energy scattered per unit solid angle into all directions
with this definition, the phase function obeys the following normalization
Rayleigh (molecular) scattering phase function
Scattering Phase FunctionScattering Phase Function
€
(cos)= ()()d∫
4π
=4π()sca
€
1= 14π
(cos)d0
1
∫0
2π
∫
€
=12
(cos)dcos−1
1
∫
€
(cos)=34
(1+cos2 )
Michael D. King, EOS Senior Project Scientist August 25, 200228
Shapes of Scattering Phase Function
Shapes of Scattering Phase Function
Rayleigh (molecular)Composite
180°
90°
270°
0°
45°135°
225° 315°
Michael D. King, EOS Senior Project Scientist August 25, 200229
Shapes of Scattering Phase Function
Shapes of Scattering Phase Function
Nonselective scattering
Mie scattering
180°
90°
270°
0°
45°135°
225° 315°
Michael D. King, EOS Senior Project Scientist August 25, 200230
Composition of Atmospheric Transmission
Composition of Atmospheric Transmission
Exoatmospheric solar irradiance
Exitance (300 K)
Atmospheric
transmission
Wavelength (µm)
0.2 2510
-2 1 10
Irra
dia
nce (
Wm
-2µ
m-
1)
10-1
100
101
102
103
104
0.0
0.5
1.0
Tra
nsm
ission
Michael D. King, EOS Senior Project Scientist August 25, 200231
Absorption Properties of the Earth’s Atmosphere
Absorption Properties of the Earth’s Atmosphere
0
50
100
0
50
100
0
50
100
0
50
1000 2 4 6 8 1
012
14Wavelength (µm)
0
50100
0
50100
0
50100
0
50100
H2O
Ab
sorp
tion
O3
CO
CO2
Michael D. King, EOS Senior Project Scientist August 25, 200232
Absorption Properties of the Earth’s Atmosphere
Absorption Properties of the Earth’s Atmosphere
0
50
100
0
50
100
0
50
100
0
50
1000 2 4 6 8 1
012
14Wavelength (µm)
0
50100
0
50100
0
50100
0
50100
CH4
Ab
sorp
tion
N2O
O2
Total
Michael D. King, EOS Senior Project Scientist August 25, 200233
Scattering of Sunlight by the Earth-Atmosphere-Surface System
Scattering of Sunlight by the Earth-Atmosphere-Surface System
Exoatmospheric solar irradiance F0()
Solar irradiance reaching the surface F()
0 21Wavelength (µm)
3
2000
Irra
dia
nce (
W m
-2 µ
m-1)
1500
1000
500
0
Michael D. King, EOS Senior Project Scientist August 25, 200234
Definition of Solar Zenith, View Zenith, and Relative Azimuth
Angle
Definition of Solar Zenith, View Zenith, and Relative Azimuth
Angle
0
N
E
W
S
0
Michael D. King, EOS Senior Project Scientist August 25, 200235
The reflection function is defined by
R(t, 0; µ, µ0, ) =where
t = total optical thickness
0 = the single scattering albedo (ratio of scattering to total extinction)
µ = absolute value of the cosine of the zenith angle |cos|µ0 = cosine of the solar zenith angle cos0
= relative azimuth angle between the direction of propagation of the emerging radiation and the incident solar direction
I = reflected intensity (radiance) in the outward (–µ) directionF0 = incident solar flux (irradiance) in W m-2 µm-1
Note: R, t, 0, F0 and I are all functions of wavelength
Definition of Reflection FunctionDefinition of Reflection Function
πI(0, –µ, )µ0F0
Michael D. King, EOS Senior Project Scientist August 25, 200236
The transmitted flux (irradiance) at the Earth’s surface can be calculated as:
where the transmission function is defined in an analogous manner to reflection function
Flux (Irradiance) on a Horizontal Surface at the Surface of the EarthFlux (Irradiance) on a Horizontal
Michael D. King, EOS Senior Project Scientist August 25, 200239
University of Washington CV-580University of Washington CV-580
Solar Spectral Flux
Radiometer (SSFR)
Ames Airborne Tracking
Sunphotometer (AATS)
Cloud Absorption Radiometer
(CAR)
Michael D. King, EOS Senior Project Scientist August 25, 200240
Goddard Space Flight Center– developed in 1982-1983
University of Washington– integrated & flown in 1984 (B-23)– principal data from 1987-97 (C-
131A)– flights after 1998 (CV-580)
Sensor Characteristics– 14 spectral bands ranging from
0.34 to 2.29 µm– scan ±95° from horizon on right-
hand side of aircraft– field of view 17.5 mrad (1°)– scan rate 1.67 Hz (100 rpm)– data system 9 channels @ 16 bit– 395 pixels in scan line– 4% reflectance calibration