lecture12_rs1

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16 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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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


Radio waves


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

Electromagnetic radiation energy:

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

behaviors of light/electromagnetic radiation.

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
radiation is very destructive (sunburns)


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


Radar


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


Advanced Very High Resolution Radiometer (AVHRR)


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


Radiometric

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



Illuminates Materials in Shadows



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


Emitted EM Radiation



Nighttime Emitted EM Radiation

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.

Radiometric Resolution


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
colors are shades of gray



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