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4 1. Sun is EM Energy Source 2. Energy emitted from sun based on Stephan/Boltzman Law, Planck’s formula, and Wein Displacement Law (Lecture 2) 3. EM Energy interacts with the atmosphere 4. EM energy reflected from Earth’s Surface – Lectures 7/8 VIS/NIR Satellite EM energy 5. EM Energy interacts with the atmosphere Lecture 3

1. Key Atmospheric Constituents Gases, water, particulate matter 2. Effects of the atmosphere on EM energy Reflection, Absorption, Scattering, Transmittance 3. Atmospheric extinction and the attenuation coefficient 4. Net effects of the atmosphere on VIS/IR energy reaching the earth’s surface - atmospheric windows 5

1. Refraction 2. Reflection 3. Absorption 4. Scattering 5. Transmittance 6

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8 Constituents of the atmosphere that will interact with EM radiation Gases – CO 2, N 2 O x, CH 4, O 2, O 3 Water – –Water vapor –Water droplets –Ice particles Particulate matter – smoke, dust, other particles VIS/NIR Satellite EM energy

Nitrogen – N 2 – 78% Oxygen – O 2 – 21% Argon – Ar – 1% H 2 0 – 0 to 7% Major atmospheric trace gases (less than 0.1% each) Carbon dioxide – CO 2 Ozone – O 3 Methane – CH 4 Carbon Monoxide – CO Nitrous Oxide – N 2 O x Chlorofluorocarbons (CFCs) 9

Water is present in a variety of forms in the atmosphere Gas/vapor, droplets (liquid and frozen), ice crystals The physical state (e.g., gas, liquid, solid) and density of water determines the manner in which it reacts with EM radiation The amount of water in the atmosphere is highly variable, depending on climatic processes and earth/atmosphere interactions, particularly the hydrologic cycle 10

When water is present in the form of clouds, it totally blocks radiation in the visible/RIR region of the EM spectrum In other forms, atmospheric water affects the absorption, scattering, and transmission of visible/RIR radiation through the atmosphere 11

12 Water is continuously being added to and removed from the atmosphere in a variety of forms through the global water cycle This water strongly influences EM radiation is passing through the atmosphere – it is a very transient characteristic, e.g., it is always changing

Inorganic and organic particles that have been suspended in the atmosphere from a variety of sources 13

Natural processes Volcanic eruptions – ash and inorganic compounds (example - sulfur dioxide) Dust storms – small soil particles (sand, silt, and clay) Wildland fires – soot and ash Biological processes – emissions of complex hydrocarbons Sea mist – water in droplets blowing of the sea surface evaporates, leaving sea salts Human activities Burning of fossil fuels – soot and inorganic compounds Biomass burning – soot, ash 14

15 Dust cloud south of Iceland Observed by MODIS

16 Smoke plume over Eastern US observed by MODIS in July 2002 from Forest Fires (red dots) in Quebec

17 Landsat Image of Mt. Pinatubo Eruption

Particulate matter Highly variable both spatially and temporally, driven by the hydrologic cycle A regional phenomenon, dependent on sources Corrections must be made to account for the impacts of particulate matter Need to understand possible sources for particulate matter in the regions of interest 18

Atmospheric water Highly variable both spatially and temporally, driven by the hydrologic cycle A global phenomenon Corrections must be made to account for the impacts of atmospheric water Need to understand how hydrologic cycle is influencing atmospheric water in the regions of study 19

Trace gases CO 2 CO N 2 O x CH 4 CFC’s Generally well mixed throughout the atmosphere Change in response to physical, biological and chemical processes Except for CO 2, Spatial/temporal variations do not influence radiation in the VIS/RIR region of the EM spectrum 20

The constituents of the atmosphere are highly variable both spatially and temporally These constituents interact with EM energy To perform quantitative analyses of satellite remote sensing imagery requires an understanding of and accounting for atmospheric effects Sophisticated computer models have been developed to quantify the effects of the atmosphere and to normalize remote sensing data for its effects 21

1. Key Atmospheric Constituents Gases, water, particulate matter 2. Effects of the atmosphere on EM energy Reflection, Absorption, Scattering, Transmittance 3. Atmospheric extinction and the attenuation coefficient 4. Net effects of the atmosphere on VIS/IR energy reaching the earth’s surface - atmospheric windows 22

23 Incident EM Radiation Refraction Reflection Transmittance Absorption Scattering

Reflection Absorption Scattering Transmittance 24

25 Incoming Radiation Outgoing Radiation

Reflection of EM energy in the Visible/RIR region of the EM spectrum occurs primarily from the tops of dense clouds ~25% of incoming solar EM energy in this wavelength region is reflected by clouds When clouds of particulate matter (e.g., smoke, dust, etc.) are particularly thick or dense, the reflection from the tops of these can also occur 26

The process by which EM radiant energy is absorbed by a molecule or particle and converted to another form of energy 27

28 UV radiation

Some trace atmospheric gases are strong absorbers of EM energy, but this absorption is confined to specific wavelength regions Water is a very strong absorber of EM energy in specific wavelength regions > 0.7  m Atmospheric particles will absorb some EM energy – because they are large, they tend to absorb all wavelengths equally 29

The process whereby EM radiation is absorbed and immediately re-emitted by a particle or molecule – energy can be emitted in multiple-directions 30 Incoming EM energy Scattered energy Note: No EM energy is lost during scattering

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Rayleigh scattering Mie scattering Non-selective scattering The type of scattering is controlled by the size of the wavelength relative to the size of the particle 32

Occurs when the wavelength λ >> the particle size 33

34 Rayleigh scattering ~ 1 / 4 Rayleigh scattering occurs at a molecular level Through Rayleigh scattering, blue light (0.4 um) is scattered 5 times as much as red light (0.6 um)

35 90 km Most Rayleigh scattering occurs in the top 10 km of the stratosphere, e.g., at the ozone layer

36 For further discussion of this slide, see The clear sky appears blue because Rayleigh scattering high in the atmosphere influence short wavelength (blue) radiation the most Note UV radiation is not scattered by the upper atmosphere because it is absorbed by the OZONE Layer

Occurs at the molecular level The degree of Rayleigh scattering is inversely proportional to the fourth power of the EM wavelength Most Rayleigh scattering occurs in the upper 10 km of the stratosphere 37

Occurs when the wavelength  particle size 38

Occurs with particles that are actually 0.1 to 10 times the size of the wavelength Primary Mie scatterers are dust particles, soot from smoke Mie scatterers are found lower in the Troposphere 39

40 Where does Mie Scattering Occur? The sources of Mie scatterers are at the earth’s surface, therefore, Mie scatterers are largely confined to the lower troposphere The exception are volcanoes, whose plumes of particulate matter are lifted well above the tropopause into the lower stratosphere

41 Occurs when the wavelength << particle size

Its name derives from the fact that all wavelengths (visible/near IR) are equally affected Particles are very large, typically water droplets and ice crystals of fog banks and clouds Particles are 10 times the size of the wavelength, e.g., > 20 um in size 42

43 For further discussion of this slide, see

1. Refraction 2. Reflection 3. Absorption 4. Scattering 5. Transmittance 44

45 sun Reflected Refracted Scattered Absorbed Transmitted

The fraction or percent of a particular frequency or wavelength of electromagnetic radiation that passes through the atmosphere without being reflected, absorbed or scattered. 46

1. Key Atmospheric Constituents Gases, water, particulate matter 2. Effects of the atmosphere on EM energy Reflection, Absorption, Scattering, Transmittance 3. Atmospheric extinction and the attenuation coefficient 4. Net effects of the atmosphere on VIS/IR energy reaching the earth’s surface - atmospheric windows 47

Extinction is a term used to account for the loss or attenuation of radiant energy as light passes through the atmosphere, and includes both scattering and absorption Extinction quantifies the amount of atmospheric transmittance 48

49 I o - the unattenuated light intensity passing into the atmosphere L - the path length through the atmosphere I - attenuated light intensity

I / I o = e -  L where I is the attenuated light intensity I o is the unattenuated light intensity L is the path length through the a uniform medium such as the atmosphere  is the extinction coefficient in the units of inverse distance 50

 = b m + b p + k where b m is the Rayleigh or molecular scattering coefficient b p is the Mie scattering coefficient (due to the airborne particles) k is the absorption coefficient 51

1. Key Atmospheric Constituents Gases, water, particulate matter 2. Effects of the atmosphere on EM energy Reflection, Absorption, Scattering, Transmittance 3. Atmospheric extinction and the attenuation coefficient 4. Net effects of the atmosphere on VIS/IR energy reaching the earth’s surface - atmospheric windows 52

Those regions of the EM spectrum which are to some degree unaffected by attenuation by constituents of the atmosphere, and therefore can be used in vis/RIR instruments for remote sensing of the earth’s surface 53

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55 Visible 1 window Near IR 3 windows Shortwave IR 2 windows

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