# lecture12_rs1

Urban and Civil

Nov 16, 2013 (4 years and 7 months ago)

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Remote Sensing

Introduction to light and color.

What is remote sensing?

Introduction to satellite imagery.

5 resolutions of satellite imagery.

Satellite image display.

Electromagnetic Waves

Examples of electromagnetic waves:

Red light

Green light

X rays

Gamma rays

Electromagnetic waves are moving ‘altered fields
of space’ that exert a physical force on electrically
charged objects in the field.

An electromagnetic Wave

amplitude

The
amplitude

is the strength of the force the field exerts
on a charged object.

When the sine wave is below the line, it shows a force
acting in the negative direction.

Physical location

Imagine you’re here

Wave
-
particle duality

particle

wave

Light has properties that behave as waves and properties that behave

as particles.

For remote sensing purposes we are primarily concerned with the wave

Electromagnetic Waves

Wavelength (

)

EMR energy moves at the
speed of light (c)
:

c = f

f
= frequency
: The number of waves passing through a point within
a unit time (usually expressed per second)

Energy

(

carried by a photon:

=
h f

[
h=
Planck constant (6.626

10
-
34

Joules*seconds)]

The shorter the wavelength, the higher the frequency, and the
more
energy

a photon carries. Therefore, short wave ultraviolet solar

One micrometer = one millionth (10
-
6
) of a meter

ers)

What makes objects a certain color?

The color of an object is determined by how
much light it
reflects

of each wavelength
in
the visible light portion of the EM spectrum
.

Some objects emit light as well, greatly
affecting their color.

Objects reflect some wavelengths.

Objects absorb some wavelengths.

Spectral Signatures

Remote Sensing

Remote sensors are devices that sense
energy from a remote location (i.e., a device
not in physical contact with what it is
sensing)

Remote sensing

is the science of acquiring,
processing and interpreting information/data
collected by remote sensors.

Remote Sensing

Active

emit energy and detect reflections

Sonar

Lidar

Passive

-

detect emitted/reflected energy from
other sources

Satellite sensors

Air photos

Cameras

Video recorders

Satellite Imagery

Digital data is obtained by sensors on satellite platforms.

Satellite Imagery

Described by five resolutions

Spatial

resolution
: area on ground represented by each pixel

1 km

Landsat
-

30m

SPOT

2.5m
-

20m / 2.5m
-

10m

IKONOS
-

1m/4m

Temporal

resolution
: how often a satellite obtains imagery of a particular
area

Spectral

resolution
: specific wavelength intervals in the electromagnetic
spectrum captured by each sensor

Resolution
: number of possible data values reportable by
each sensor (how sensitive the sensor is to changes in brightness of objects
that it views)

View angle

resolution
: the number of angles at which the ground objects
are recorded by the sensor.

AVHRR

Spatial resolution

English Channel

Landsat Thematic Mapper

Spatial resolution

Greenville, NC

SPOT

Spatial resolution

Palm Springs, CA

IKONOS

Spatial resolution

Sydney Olympic Park

Temporal Resolution

Number of days between overhead passes at the same location

Landsat
-

16 days

AVHRR
-

daily

IKONOS
-

1 to 3 days

Spectral Resolution

Number, spacing and width of sampled wavelength bands

Higher resolution results in more precision in
representation of
spectral signatures

Review: Electromagnetic Spectrum

A continuum of all possible energies that radiate through
space

In remote sensing, we mainly focus on visible, infrared and
microwave

Landsat spectral resolution

Wavelength (in
micrometers)

Description

1

2

3

4

5

6

7

0.45
-

0.52

0.52
-

0.60

0.63
-

0.69

0.76
-

0.90

1.55
-

1.75

10.4
-

12.5

2.08
-

2.35

Blue
-
green

Green

Red

Near
-
IR

IR

Thermal

Mid
-
IR

Landsat TM:

Spectral Regions

Landsat MSS

0.4
-

0.5
m
m

Water Penetration for Bathymetry

Soil / Vegetation Differentiation

Deciduous / Coniferous Differentiation

BLUE

GREEN

RED

NEAR IR

SHORT

WAVE IR

MID
-

WAVE IR

LONGWAVE IR

14.0

5.0

3.0

1.1

0.7

0.6

0.5

0.4

PANCHROMATIC

BAND 1 (Visible Blue)

Band 1

0.5
-

0.6
m
m

Water Penetration for Bathymetry

Clear and Turbid Water Contrast

Discrimination of Oil on Water

Green Reflectance Peak of

Healthy Vegetation

BLUE

GREEN

RED

NEAR IR

SHORT

WAVE IR

MID
-

WAVE IR

LONGWAVE IR

14.0

5.0

3.0

1.1

0.7

0.6

0.5

0.4

PANCHROMATIC

BAND 2 (Visible Green)

Spectral Regions

Landsat MSS

Band 2

0.6
-

0.7
m
m

Vegetation Differentiation

Chlorophyll Absorption

Limited Water Penetration for

Bathymetry

BLUE

GREEN

RED

NEAR IR

SHORT

WAVE IR

MID
-

WAVE IR

LONGWAVE IR

14.0

5.0

3.0

1.1

0.7

0.6

0.5

0.4

PANCHROMATIC

BAND 3 (Visible Red)

Spectral Regions

Landsat MSS

Band 3

Vegetation Analysis

Shoreline Mapping

Landcover Discrimination

0.7
-

1.1
m
m

BLUE

GREEN

RED

NEAR IR

SHORT

WAVE IR

MID
-

WAVE IR

LONGWAVE IR

14.0

5.0

3.0

1.1

0.7

0.6

0.5

0.4

PANCHROMATIC

BAND 4 (Near Infrared)

Spectral Regions

Landsat MSS

Band 4

1.1
-

3.0
m
m

Fire Mapping

Discrimination of Oil on Water

Moisture Content of Soil and

Vegetation

Snow / Cloud Differentiation

Vegetation Analysis

BLUE

GREEN

RED

NEAR IR

SHORT

WAVE IR

MID
-

WAVE IR

LONGWAVE IR

14.0

5.0

3.0

1.1

0.7

0.6

0.5

0.4

PANCHROMATIC

BAND 5 (Short
-
wave Infrared)

Spectral Regions

Landsat MSS

Band 5

3.0
-

5.0
m
m

Solar Reflectance From Specular

Metal Roofs

Smoke Penetration

Daytime Reflectance Mixed With

BLUE

GREEN

RED

NEAR IR

SHORT

WAVE IR

MID
-

WAVE IR

LONGWAVE IR

14.0

5.0

3.0

1.1

0.7

0.6

0.5

0.4

PANCHROMATIC

BAND 7 (Mid
-
wave Infrared)

Spectral Regions

Landsat MSS

Band 7

5.0
-

14.0
m
m

Thermal Analysis

Vegetation Density

Urban Heat Islands

BLUE

GREEN

RED

NEAR IR

SHORT

WAVE IR

MID
-

WAVE IR

LONGWAVE IR

14.0

5.0

3.0

1.1

0.7

0.6

0.5

0.4

PANCHROMATIC

BAND 6 (Long
-
wave Infrared)

Spectral Regions

Landsat MSS

Band 6

Landsat Bands

Band 1

Band 2

Band 3

Band 4

Band 5

Band 7

Band 6

BLUE

GREEN

RED

NEAR IR

SHORT

WAVE IR

MID
-

WAVE IR

LONGWAVE IR

Spectral Resolution of Landsat TM

TM Band:

1

2

3

4

5

7

These bands provide a coarse summary of spectral signatures.

Number of possible data values reported by the sensor

Range is expressed as a power (2
n
)

8
-
bit resolution has 2
8

values, or 256 values

Range is 0
-
255

12
-
bit resolution has 2
16
values, or 65,536 values

Range is 0
-
65535

The value in each pixel is called the

Digital Number (DN)

Brightness Value (BV)

Image Display

Graphics display devices use three
color guns

Red, Green, Blue

All colors can be formed from various combinations of these 3
colors (which is why they’re used in computer/TV screens)

The brightness values (BV) to be displayed will often have
an 8
-
bit range

0 to 255

In remote sensing, we assign one band to each color gun to
give color to the image

Image Display

For a single band, the resultant color will be
grayscale

All three colors display the same value, so the

Band 1

Band 1

Band 1

Red color gun

Green color gun

Blue color gun

Landsat Image of Idaho

Band 1

Band 3

Band 2

Band 4

Landsat Image of Idaho

Band 5

Band 7

Band 6

Image Display

For a multi
-
band image, the resultant color will depend on
which bands are assigned to which color guns

Red (3)

Green (2)

Blue (1)

Near Infrared (4)

Red (3)

Green (2)

True Color
Composite

(321)

False Color
Composite

(432)

Red color gun

Green color gun

Blue color gun

Red color gun

Green color gun

Blue color gun

Multispectral Imagery
Display

BLUE

GREEN

RED

NEAR IR

SHORT

WAVE IR

MID
-

WAVE IR

LONGWAVE IR

1

Landsat TM Band =

2

3

4

5

7

6

Band Combination =

7

4

2

Color Guns =

Band Composite Output =

Color composite image

Color Composite Image

Band A

Band B

Band C

Blue color gun

Green color gun

Red color gun

Landsat TM Image of
Idaho

321

432

543