1. 2 3 4 1. Sun is EM Energy Source 2. Energy emitted from sun based on Stephan/Boltzman Law,...

1

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

2

SyllabusLecture/Hourly Exam Schedule and Assigned Readings (Subject to Change)

Week Date Lecture Topic Reading Part I Remote Sensing Basics

1 26-Jan 1 Introduction to Remote Sensing Ch 1 28-Jan University Closed

2 02-Feb 2 Principles of EM radiometry and basic EM Theory Ch 204-Feb Principles of EM radiometry and basic EM Theory II

3 09-Feb 3 Atmospheric Influences on EM Radiation 11-Feb 4 Photographic Systems/Image Interpretation Ch 3,5

4 16-Feb 5 The Digital Image I Ch 4,1018-Feb The Digital Image II

5 23-Feb 6 Applications with areal and space photography 25-Feb Exam 126-FebLab 1 Introduction to ENVI – manipulation of digital imagery

3

Our atmosphere

4

Key components of VIS/RIR remote sensing 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 SatelliteEM energy

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

Lecture 3 Topics/Key Points

1. Refraction2. Reflection3. Absorption4. Scattering5. Transmittance

6

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

7

90 km

8

Key components of VIS/NIR remote sensing

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

VIS/NIR SatelliteEM energy

EM energy

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 – CONitrous Oxide – N2Ox Chlorofluorocarbons (CFCs)

9

Atmospheric Gases

Water is present in a variety of forms in the atmosphereGas/vapor, droplets (liquid and frozen), ice

crystalsThe 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

Water in the atmosphere

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

Impacts of atmospheric water

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

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

14

Sources of particulate matter

15

Dust cloud south of Iceland Observed by

MODIS

16

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

17

Landsat Image of Mt.

Pinatubo Eruption

Particulate matterHighly variable both spatially and temporally,

driven by the hydrologic cycleA regional phenomenon, dependent on sourcesCorrections must be made to account for the

impacts of particulate matterNeed to understand possible sources for

particulate matter in the regions of interest

18

Temporal/spatial variability of atmospheric constituents

Atmospheric waterHighly variable both spatially and temporally,

driven by the hydrologic cycleA global phenomenonCorrections must be made to account for the

impacts of atmospheric waterNeed to understand how hydrologic cycle is

influencing atmospheric water in the regions of study

19


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

20


The constituents of the atmosphere are highly variable both spatially and temporally

These constituents interact with EM energyTo 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

The bottom line!!!






22


23

Basic EM energy/matter interactionsIncident EM Radiation

Refraction

Reflection

Transmittance

AbsorptionScattering

Reflection Absorption Scattering Transmittance

24


25

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

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

Atmospheric Reflection

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

27

Absorption

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

Summary of atmospheric absorption

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

30

Scattering

Incoming EM energyScattered energy

Note: No EM energy is lost during scattering

Rayleigh scatteringMie scattering Non-selective scattering

The type of scattering is controlled by the size of the wavelength relative to the size of the particle

32

Types of Scattering

Rayleigh Scattering(also called molecular scattering)

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

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 levelThe 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

Summary of Rayleigh Scattering

Mie Scattering

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

Mie Scattering

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

Non-Selective Scattering

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

Non-Selective Scattering

43

For further discussion of this slide, seehttp://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html#c5

1. Refraction2. Reflection3. Absorption4. Scattering5. Transmittance

44


45

sunReflected

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

Atmospheric Transmittance






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

Atmospheric Extinction

49

Atmospheric Extinction

Io - the unattenuated light intensity passing into the atmosphere

L - the path length through the atmosphere

I - attenuated light intensity

I / Io= e- L

where I is the attenuated light intensityIo 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

Extinction Coefficient -

= bm + bp + k where

bm is the Rayleigh or molecular scattering coefficient

bp is the Mie scattering coefficient (due to the airborne particles)

k is the absorption coefficient

51

Extinction Coefficient -






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

Atmospheric Window

55Visible

1 window Near IR3 windows

Shortwave IR2 windows

56

Our atmosphere

57

SyllabusLecture/Hourly Exam Schedule and Assigned Readings (Subject to Change)

Week Date Lecture Topic Reading Part I Remote Sensing Basics

1 26-Jan 1 Introduction to Remote Sensing Ch 1 28-Jan University Closed

2 02-Feb 2 Principles of EM radiometry and basic EM Theory Ch 204-Feb Principles of EM radiometry and basic EM Theory II

3 09-Feb 3 Atmospheric Influences on EM Radiation 11-Feb 4 Photographic Systems/Image Interpretation Ch 3,5

4 16-Feb 5 The Digital Image I Ch 4,1018-Feb The Digital Image II

5 23-Feb 6 Applications with areal and space photography 25-Feb Exam 126-FebLab 1 Introduction to ENVI – manipulation of digital imagery

1. 2 3 4 1. Sun is EM Energy Source 2. Energy emitted from sun based on Stephan/Boltzman Law,...

Documents

Transcript of 1. 2 3 4 1. Sun is EM Energy Source 2. Energy emitted from sun based on Stephan/Boltzman Law,...