1. 2 Definition 1 – Remote sensing is the acquiring of information about an object or scene without touching it through using electromagnetic energy a

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GEOG 372

February 4 2009

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What is remote sensing?Definition 1 – Remote sensing is the

acquiring of information about an object or scene without touching it through using electromagnetic energy

a. RS deals with systems whose data can be used to recreate images

b. RS deals with detection of the atmosphere, oceans, or land surface

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Lecture 2 Continued

The Basics of Electromagnetic Radiation (EM)

February 4th 2009

EM Radiation Particle Model -Radiation from Atomic Structures

Wave TheorySpeed of light c = 3*108 m/secWavelength =Frequency= v

c = *vv = c/l = c/v

M = T4

The amount of EM radiation (M) emitted from a body in Watts m-2 can be calculated as

Stefan-Boltzmann Law*

Wien Displacement Law* The wavelength

with the highest level of emitted radiation (max) for an object of temperature T can be calculated as

max = k / T

Types of thermal energy transfer Models of EM radiation/energy

Particle Model Photon absorption, excitation, de-excitation

Wave Model Characteristics of EM waves

Polarization, speed of light, wavelength, frequency Laws governing EM radiation

Stephan-Boltzman Law Planck’s Formula Wien Displacement Law

Remote sensing in the visible and reflected infrared region of the EM spectrum Maximum Solar Output Wavelengths λ Examples of Visible & RIR λ Images Basic Interactions of EM energy & the earths surface

Descriptors of EM radiation Radiant flux Radiant flux density – irradiance and exitance

Radiation budget equation Reflection Absorption Transmission

Remote Detection of Exitance Radiance

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Lecture Topics

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Wavelength region for VI/ reflected IR remote sensing is between 0.4

and 2.6 m

Visible λ

Reflected near and SW infrared

Figure 1

Reflected IR λ

Incoming/Outgoing

max = 2898/5880 = 0.49 mm

max = 9.7 mm

92%

Expand Information

Express it Visually










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Lecture Topics

0.7 to 1.3 m – Near infrared1.3 to 2.8 m – Reflected Middle or Shortwave

(SW) IR region

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Reflected IR Region of EM Spectrum

True Color

False Color

Air Photo:Visible λ

color film, 1-2 m detailTimothyLake, OR

Landsat 30 m

Columbia River

Mt. St. Helens

Mt. Adams

RIR λ

AVHRR 1 km

Columbia River

Olympic Pen.

Yellowstone N.P.

Mt. St. Helens

RIR λ

Landsat 30mFalse Color Composite

Space Shuttle 70 mm photo 5 m resolution

Coral Reefs Bahamas

Landsat 30mTrue Color λ










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Lecture Topics

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Key components of VIS/RIR remote sensing 1. Sun is EM

Energy Source

2. Energy emitted from sun based on Stephan/Boltzmann Law, Planck’s

formula, and Wein Displacement Law

3. EM Energy interacts with the

atmosphere

4. EM energy interacts with the Earth’s Surface

VIS/NIR Satellite

EM energy

6. EM energy detected by a

remote sensing system

5. EM Energy interacts with the

atmosphere










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Lecture Topics

The fundamental unit to measure electromagnetic radiation is radiant flux -

is defined as the amount of energy that passes into, through, or off of a surface per unit time

Radiant flux () is measured in Watts (W)

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Radiant Flux -

Newton - force required to cause the mass of one kilogram to accelerate at a rate of one meter per second squared

Joule - the amount of energy exerted when a force of one newton is applied over a displacement of one meter

Watt – one joule / second

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Definition of a Watt (FYI – I won’t ask about these definitions on exams)

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Radiant Flux Density

Radiant flux density is simply the amount of radiant flux per unit area

Radiant flux density represents the amount of EM energy coming from the area represented by a pixel

Radiant flux density = /area

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Irradiance and Exitance

Irradiance is the radiant flux energy

that strikes a surface

Exitance is the radiant flux density coming from

a surface

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Irradiance - I Irradiance is the amount of incident

radiant flux per unit area to strike a plane surface in Watts/square meter (W m –2 )

Fig 2-20 in Jensen

I

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Exitance - M Exitance is the amount of radiant flux per

unit area leaving a plane surface in Watts per square meter (W m –2 )

Fig 2-20 in Jensen










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Lecture Topics

Three things can happen to incident EM energy [i] when it interacts with a feature

1. Reflected2. Absorbed3. Transmitted

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Radiation Budget Equation

i

The degree to which EM energy is reflected, transmitted, and absorbed is dependent on the wavelength of the EM

energy & the characteristics of the material the EM energy is interacting with

Reflectance (r) is the ratio of incident EM radiation that is directly reflected from a surface of an object: r = r / i

Absorption () is the ratio of incident EM that is absorbed by the object: = a / i

Transmittance () is the ratio of incident EM radiation that is transmitted through an object: = t / i

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Reflectance, Absorption, & Transmittance

Reflectance r

Absorption α

Transmittance τ

i (λ)= r (λ)+ t (λ) + a (λ)

i (λ)= Incident Energy

r (λ)= Reflected Energy

a (λ)= Absorbed Energy t (λ)= Transmitted Energy

i = r + t + a

r is the amount of energy reflected from the surface

a is the amount of energy absorbed by the surface

t is the amount of energy transmitted through the surface

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Radiation Budget Equation*










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Lecture Topics

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VIS/RIR Remote Sensor

For a VIS/RIR remote sensing system, the surface

characteristic being detected is the result of reflectance from the earth’s surface

The sensors only detect reflected EM radiation from a certain direction and in certain wavelength regions

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In remote sensing, we are not interested in all exitance, but only that exitance in the direction of the satellite system

Because of diffuse scattering, there is exitance in all directions from a surface

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Detection of Exitance by a remote sensing system

θ – Sensor viewing angle

Area as seen by the sensor (projected area) = A cos θ

Satellite Radiometer

A = area on ground being sensed

Radiance Solid angle of the sensor

Flux from a surface is actually being emitted or reflected in all directions equally, i.e., it is being distributed into a hemisphere

The radiometer intercepts a fraction of the exitance from a surface, this fraction is defined by the solid angle, Ω, of the sensing system, which can defined by the area of the detector surface (a) and the distance to the target area (d)Ω = a/d

d

a

Space Shuttle Limb Photographs

Before Mt. Pinatubo Eruption

After Mt. Pinatubo Eruption

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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

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1. 2 Definition 1 – Remote sensing is the acquiring of information about an object or scene without touching it through using electromagnetic energy a