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
Blackbody Radiation CurvesBlackbody Radiation Curves
Michael D. King, EOS Senior Project Scientist August 25, 20027
Spectral Characteristics of Energy Sources and Sensing Systems
Spectral Characteristics of Energy Sources and Sensing Systems
Michael D. King, EOS Senior Project Scientist August 25, 20028
Atmospheric Absorption in the Wavelength Range from 0-15 µmAtmospheric Absorption in the
Wavelength Range from 0-15 µm
Michael D. King, EOS Senior Project Scientist August 25, 20029
Basic Interactions between Electromagnetic Energy and the
Earth’s Surface
Basic Interactions between Electromagnetic Energy and the
Earth’s Surface
Michael D. King, EOS Senior Project Scientist August 25, 200210
Generalized Spectral Reflectance Envelopes for Deciduous and
Coniferous Trees
Generalized Spectral Reflectance Envelopes for Deciduous and
Coniferous Trees
Michael D. King, EOS Senior Project Scientist August 25, 200211
Typical Spectral Reflectance Curves for Vegetation, Soil, and
Water
Typical Spectral Reflectance Curves for Vegetation, Soil, and
Water
Michael D. King, EOS Senior Project Scientist August 25, 200212
Atmospheric Effects Influencing the Measurement of Reflected
Solar Energy
Atmospheric Effects Influencing the Measurement of Reflected
Solar Energy
Michael D. King, EOS Senior Project Scientist August 25, 200213
Atmospheric Transmission SpectraAtmospheric Transmission Spectra
Wavelength (µm)
0.2 250.0
0.2
0.6
0.8
0.4
1 10
1.0
Tra
nsm
issi
on
UV VNIR
SWIR
MWIR
LWIR
Michael D. King, EOS Senior Project Scientist August 25, 200214
Low Earth Orbit ConceptsLow Earth Orbit Concepts
Equator
South Pole
Ground track
Ascending node
Inclination angle
Descending node
Orbit
Perigee
Apogee
Orbit
Michael D. King, EOS Senior Project Scientist August 25, 200215
Terra Satellite in Low Earth Orbit (LEO)
Terra Satellite in Low Earth Orbit (LEO)
Michael D. King, EOS Senior Project Scientist August 25, 200216
Satellites in Geosynchronous Orbits are used as Relay Satellites
for LEO Spacecraft
Satellites in Geosynchronous Orbits are used as Relay Satellites
for LEO SpacecraftImaging
System (e.g., Terra)
Communication relay system
Communication relay
system (e.g., TDRSS)
GEO
LEOGround station
Michael D. King, EOS Senior Project Scientist August 25, 200217
Scattering of Sunlight by the Earth-Atmosphere-Surface System
Scattering of Sunlight by the Earth-Atmosphere-Surface System
A = radiation transmitted through the atmosphere and reflected by the surface
B = radiation scattered by the atmosphere and reflected by the surface
C = radiation scattered by the atmosphere and into the ‘radiometer’
G = radiation transmitted through the atmosphere, reflected by background objects, and subsequently reflected by the surface towards the ‘radiometer’
I = ‘adjacency effect’ of reflectance from a surface outside the field of view of the sensor into its field of view
Michael D. King, EOS Senior Project Scientist August 25, 200218
Thermal Emission from the Earth-Atmosphere-Surface System
Thermal Emission from the Earth-Atmosphere-Surface System
D
H
E
F
D = radiation emanating directly from the target
E = radiation emanating from the atmosphere downward and subsequently reflected by the surface towards the ‘radiometer’
F = radiation self-emitted by the atmosphere
H = radiation emitted by background objects and subsequently reflected by the target into the direction of the observer
Michael D. King, EOS Senior Project Scientist August 25, 200219
Irradiance (Flux per unit Area)Irradiance (Flux per unit Area)
E0
E = E0
cos
E0
E=irradiance = flux per unit area [Wm-2]
= ddA
Michael D. King, EOS Senior Project Scientist August 25, 200220
Element of Solid AngleElement of Solid Angle
d = [sr]dAr2
Michael D. King, EOS Senior Project Scientist August 25, 200221
d2dAcosd
dEdcos
N
I
Intensity (or Radiance)Intensity (or Radiance)
I = flux per unit area per unit solid angle normal to the direction of propagation [Wm-2sr-1]
= =
Michael D. King, EOS Senior Project Scientist August 25, 200222
Projected Area Effects on Irradiance
Projected Area Effects on Irradiance
E0
A = Au/cos
Au
Au
N
E0
E0
E = E0cosAu
N
N
Irradiance crossing area A at angle of incidence is reduced from that on a normal surface due to the growth in cross sectional area
P
P
P
Michael D. King, EOS Senior Project Scientist August 25, 200223
Solid Angle Representation on Spherical Coordinates
Solid Angle Representation on Spherical Coordinates
sin
z
d
d
d
sind
d
y
x
d
d = sindd
Michael D. King, EOS Senior Project Scientist August 25, 200224
Angular Scattering CoefficientAngular Scattering Coefficient
Propagating beam
d
Scattering center
Unit length
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
Surface at the Surface of the Earth
€
E(t ,0 ;μ0 ,μ,φ)= I(t ,0 ;μ0 ,μ,φ)μdμdφ+μ0F0 (exp−0
1
∫0
2π
∫ t / μ0 )
€
=μ0F01π
T(t ,0 ;μ0 ,μ,φ)μdμdφ+ (exp−0
1
∫0
2π
∫ t / μ0 )⎡
⎣⎢⎢
⎤
⎦⎥⎥
€
€
T(t ,0 ;μ0 ,μ,φ)=πI(t ,μ,φ)μ0F0
Michael D. King, EOS Senior Project Scientist August 25, 200237
Reflectance Properties of Idealized Surfaces
Reflectance Properties of Idealized Surfaces
Specular reflector Diffuse
Nearly diffuse
Less idealized surface
Nearly specular
‘Lambertian’
Michael D. King, EOS Senior Project Scientist August 25, 200238
Bidirectional Reflectance ConceptBidirectional Reflectance Concept
0
0
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
accuracy
Cloud Absorption RadiometerCloud Absorption Radiometer
Michael D. King, EOS Senior Project Scientist August 25, 200241
Roll: ~20° Time: ~2 min Speed: ~80 m s-1
Height: ~600 m Diameter: ~3 km Resolution
– 10 m (nadir)– 270 m ( = 80°)
Channels– 8 continuously
sampled (0.34-1.25 µm)
– 2 filter wheel channels used for BRDF measurements (1.64 & 2.20 µm)
Bidirectional Reflectance Measurements
Bidirectional Reflectance Measurements
Michael D. King, EOS Senior Project Scientist August 25, 200242
= 1.64 µm = 0.67 µm
0.0
Bidirectional Reflectance - Tundra Melt Season (0 = 81°)
Bidirectional Reflectance - Tundra Melt Season (0 = 81°)
0.2
0.4
0.6
0.8
1.0
Michael D. King, EOS Senior Project Scientist August 25, 200243
Bidirectional Reflectance - Tundra Melt Season (0 = 81°)
Bidirectional Reflectance - Tundra Melt Season (0 = 81°)
Snow Free Tundra
Michael D. King, EOS Senior Project Scientist August 25, 200244
= 1.64 µm = 0.67 µm
Bidirectional Reflectance - Atlantic Ocean
Sunglint (0 = 19°)
Bidirectional Reflectance - Atlantic Ocean
Sunglint (0 = 19°)
0.0
0.2
0.4
0.6
0.8
1.0
Michael D. King, EOS Senior Project Scientist August 25, 200245
Atlantic Ocean (sun glint)
Bidirectional Reflectance - Atlantic Ocean
Sunglint (0 = 19°)
Bidirectional Reflectance - Atlantic Ocean
Sunglint (0 = 19°)
0.0
0.1
0.2
0.3
0.4
0.5
0.472 µm0.675 µm0.869 µm1.038 µm1.219 µm1.271 µm1.643 µm2.207 µm
Opposition0
90 60 030 30 60 90
Backward ScatteringAngle Forward Scattering
SunGlint
Michael D. King, EOS Senior Project Scientist August 25, 200246
TRMM11/27/97
Terra12/18/9
9
QuikScat
6/19/99
Landsat 7
4/15/99
NASA Earth Science Spacecraft in Orbit
NASA Earth Science Spacecraft in Orbit
Michael D. King, EOS Senior Project Scientist August 25, 200247
EO-111/21/00
SAGE III
12/10/01
Jason-1
12/7/01
NASA Earth Science Spacecraft in Orbit
NASA Earth Science Spacecraft in Orbit
Aqua5/4/02
Michael D. King, EOS Senior Project Scientist August 25, 200248
Aura1/04
SORCE12/02
ICESat
12/02
EOS Spacecraft Under Development
EOS Spacecraft Under Development
Michael D. King, EOS Senior Project Scientist August 25, 200249
NASA ER-2 High Altitude Research Aircraft
NASA ER-2 High Altitude Research Aircraft
Michael D. King, EOS Senior Project Scientist August 25, 200250
ER-2 Pilot in SpacesuitER-2 Pilot in Spacesuit
Michael D. King, EOS Senior Project Scientist August 25, 200251
Skukuza, South Africa Maun, Botswana
Flux TowerFlux Tower
Photograph courtesy of Michael KingPhotograph courtesy of NASA Dryden
Michael D. King, EOS Senior Project Scientist August 25, 200252
Surface Instrumentation for Measuring Shortwave Radiation
Surface Instrumentation for Measuring Shortwave Radiation
Photograph courtesy of NASA
Michael D. King, EOS Senior Project Scientist August 25, 200253
New EOS science results published in lay terms on NASA’s award-winning Web site:
earthobservatory.nasa.gov
Michael D. King, EOS Senior Project Scientist August 25, 200254
Natural Hazards Section– Dust & Smoke– Fires– Floods– Severe Storms– Volcanoes– Unique Imagery
Timely, newsworthy imagery posted as thumbs, medium sized, and full-resolution
Weekly updates of maps showing locations & severity of hazards around the globe
Michael D. King, EOS Senior Project Scientist August 25, 200255
Severe Storm ExampleSuper Typhoon Fengshen