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Lecture 3 Remote Sensing in the Visible and Reflected IR Region of the EM spectrum - The Effects of the Atmosphere on EM Radiation February 9th 2009.

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Our atmosphere

Lecture 3 Remote Sensing in the Visible and Reflected IR Region of the EM spectrum - The Effects of the Atmosphereon EM RadiationFebruary 9th 2009


Our atmosphere

SyllabusLecture/Hourly Exam Schedule and Assigned Readings (Subject to Change)WeekDateLecture TopicReading Part I Remote Sensing Basics 126-Jan1 Introduction to Remote SensingCh 1 28-JanUniversity Closed202-Feb2 Principles of EM radiometry and basic EM TheoryCh 204-Feb Principles of EM radiometry and basic EM Theory II309-Feb3 Atmospheric Influences on EM Radiation 11-Feb4 Photographic Systems/Image InterpretationCh 3,5416-Feb5 The Digital Image ICh 4,1018-Feb The Digital Image II523-Feb6 Applications with areal and space photography 25-FebExam 126-FebLab 1 Introduction to ENVI – manipulation of digital imagery


Our atmosphere

Our atmosphere


Key components of vis rir remote sensing

Key components of VIS/RIR remote sensing

2. Energy emitted from sun based on Stephan/Boltzman Law, Planck’s formula, and Wein Displacement Law (Lecture 2)

1. Sun is EM Energy Source

VIS/NIR Satellite

EM energy

EM energy

3. EM Energy interacts with the atmosphere

5. EM Energy interacts with the atmosphere

Lecture 3

4.EM energy reflected from Earth’s Surface – Lectures 7/8


Lecture 3 topics key points

Lecture 3 Topics/Key Points

  • Key Atmospheric Constituents

    • Gases, water, particulate matter

  • Effects of the atmosphere on EM energy

    • Reflection, Absorption, Scattering, Transmittance

  • Atmospheric extinction and the attenuation coefficient

  • Net effects of the atmosphere on VIS/IR energy reaching the earth’s surface - atmospheric windows


What do gases and particles in the atmosphere do to em radiation

What do gases and particles in the atmosphere do to EM radiation?

  • Refraction

  • Reflection

  • Absorption

  • Scattering

  • Transmittance


Our atmosphere

90 km


Key components of vis nir remote sensing

Key components of VIS/NIR remote sensing

VIS/NIR Satellite

EM energy

EM energy

  • Constituents of the atmosphere that will interact with EM radiation

  • Gases – CO2, N2Ox, CH4, O2, O3

  • Water –

    • Water vapor

    • Water droplets

    • Ice particles

  • Particulate matter – smoke, dust, other particles


Atmospheric gases

Atmospheric Gases

Nitrogen – N2 – 78%

Oxygen – O2 – 21%

Argon – Ar – 1%

H20 – 0 to 7%

  • Major atmospheric trace gases (less than 0.1% each)

    Carbon dioxide – CO2

    Ozone – O3

    Methane – CH4

    Carbon Monoxide – CO

    Nitrous Oxide – N2Ox

    Chlorofluorocarbons (CFCs)


Water in the atmosphere

Water in the atmosphere

  • 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


Impacts of atmospheric water

Impacts of atmospheric water

  • 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


Our atmosphere

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


Particulate matter

Particulate Matter

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


Sources of particulate matter

Sources of particulate matter

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


Our atmosphere

Dust cloud south of Iceland Observed by MODIS


Our atmosphere

Smoke plume over

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


Our atmosphere

Landsat Image of Mt. Pinatubo Eruption


Temporal spatial variability of atmospheric constituents

Temporal/spatial variability of atmospheric constituents

  • 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


Temporal spatial variability of atmospheric constituents1

Temporal/spatial variability of atmospheric constituents

  • 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


Temporal spatial variability of atmospheric constituents2

Temporal/spatial variability of atmospheric constituents

Trace gases CO2 CO N2Ox CH4CFC’s

  • Generally well mixed throughout the atmosphere

  • Change in response to physical, biological and chemical processes

  • Except for CO2, Spatial/temporal variations do not influence radiation in the VIS/RIR region of the EM spectrum


The bottom line

The bottom line!!!

  • 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


Lecture 3 topics key points1

Lecture 3 Topics/Key Points

  • Key Atmospheric Constituents

    • Gases, water, particulate matter

  • Effects of the atmosphere on EM energy

    • Reflection, Absorption, Scattering, Transmittance

  • Atmospheric extinction and the attenuation coefficient

  • Net effects of the atmosphere on VIS/IR energy reaching the earth’s surface - atmospheric windows


Basic em energy matter interactions

Basic EM energy/matter interactions

Incident EM Radiation

Reflection

Scattering

Refraction

Absorption

Transmittance


What do gases and particles in the atmosphere do to em radiation1

What do gases and particles in the atmosphere do to EM radiation?

  • Reflection

  • Absorption

  • Scattering

  • Transmittance


Reflectance the process whereby incoming em radiation is reflected off the surface of an object

Reflectance – the process whereby incoming EM radiation is reflected off the surface of an object

Incoming

Radiation

Outgoing

Radiation


Atmospheric reflection

Atmospheric Reflection

  • 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


Absorption

Absorption

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


Our atmosphere

UV radiation


Summary of atmospheric absorption

Summary of atmospheric absorption

  • 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


Scattering

Scattering

  • The process whereby EM radiation is absorbed and immediately re-emitted by a particleor molecule – energy can be emitted in multiple-directions

Incoming EM energy

Scattered energy

Note: No EM energy is lost during scattering


Types of scattering

Types of Scattering

  • 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


Rayleigh scattering also called molecular scattering

Rayleigh Scattering(also called molecular scattering)

Occurs when the wavelength λ>> the particle size


Our atmosphere

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)


Our atmosphere

90 km

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


Our atmosphere

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

For further discussion of this slide, see

http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html#c5


Summary of rayleigh scattering

Summary of Rayleigh Scattering

  • 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


Mie scattering

Mie Scattering

Occurs when the wavelength  particle size


Mie scattering1

Mie Scattering

  • 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


Our atmosphere

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


Non selective scattering

Non-Selective Scattering

Occurs when the wavelength << particle size


Non selective scattering1

Non-Selective Scattering

  • 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


Our atmosphere

For further discussion of this slide, see

http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html#c5


What do gases and particles in the atmosphere do to em radiation2

What do gases and particles in the atmosphere do to EM radiation?

  • Refraction

  • Reflection

  • Absorption

  • Scattering

  • Transmittance


Our atmosphere

sun

Reflected

Refracted

Scattered

Absorbed

Transmitted


Atmospheric transmittance

Atmospheric Transmittance

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


Lecture 3 topics key points2

Lecture 3 Topics/Key Points

  • Key Atmospheric Constituents

    • Gases, water, particulate matter

  • Effects of the atmosphere on EM energy

    • Reflection, Absorption, Scattering, Transmittance

  • Atmospheric extinction and the attenuation coefficient

  • Net effects of the atmosphere on VIS/IR energy reaching the earth’s surface - atmospheric windows


Atmospheric extinction

Atmospheric Extinction

  • 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


Atmospheric extinction1

Atmospheric Extinction

Io - the unattenuated light intensity passing into the atmosphere

L - the path length through

the atmosphere

I - attenuated light intensity


Extinction coefficient

Extinction Coefficient - 

I / Io= e- L

where

I is the attenuated light intensity

Io 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


Extinction coefficient1

Extinction Coefficient - 

 = bm + bp + k  

where

bmis the Rayleigh or molecular scattering coefficient

bpis the Mie scattering coefficient (due to the airborne particles)

k is the absorption coefficient


Lecture 3 topics key points3

Lecture 3 Topics/Key Points

  • Key Atmospheric Constituents

    • Gases, water, particulate matter

  • Effects of the atmosphere on EM energy

    • Reflection, Absorption, Scattering, Transmittance

  • Atmospheric extinction and the attenuation coefficient

  • Net effects of the atmosphere on VIS/IR energy reaching the earth’s surface - atmospheric windows


Atmospheric window

Atmospheric Window

  • 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


Our atmosphere

Visible

1 window

Near IR

3 windows

Shortwave IR

2 windows


Our atmosphere

Our atmosphere


Our atmosphere

SyllabusLecture/Hourly Exam Schedule and Assigned Readings (Subject to Change)WeekDateLecture TopicReading Part I Remote Sensing Basics 126-Jan1 Introduction to Remote SensingCh 1 28-JanUniversity Closed202-Feb2 Principles of EM radiometry and basic EM TheoryCh 204-Feb Principles of EM radiometry and basic EM Theory II309-Feb3 Atmospheric Influences on EM Radiation 11-Feb4 Photographic Systems/Image InterpretationCh 3,5416-Feb5 The Digital Image ICh 4,1018-Feb The Digital Image II523-Feb6 Applications with areal and space photography 25-FebExam 126-FebLab 1 Introduction to ENVI – manipulation of digital imagery


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