Transcript Remote Sensing • • • • • Introduction to light and color. What is remote sensing? Introduction to satellite imagery. 5 resolutions of satellite imagery. Satellite image display.

Remote Sensing
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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:
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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.
amplitude
An electromagnetic Wave
Physical location
Imagine you’re here
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.
Electromagnetic radiation energy: Wave-particle duality
Light has properties that behave as waves and properties that behave
as particles.
wave
particle
For remote sensing purposes we are primarily concerned with the wave
behaviors of light/electromagnetic radiation.
Electromagnetic Waves
Wavelength ()
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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)]
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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)
ers)
One micrometer = one millionth (10-6) of a meter
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
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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
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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.
Spatial resolution
AVHRR
English Channel
Spatial resolution
Landsat Thematic Mapper
Greenville, NC
Spatial resolution
SPOT
Palm Springs, CA
Spatial resolution
IKONOS
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
Landsat TM:
Wavelength (in
micrometers)
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
Description
Blue-green
Green
Red
Near-IR
IR
Thermal
Mid-IR
Spectral Regions – Landsat MSS
BAND 1 (Visible Blue)
PANCHROMATIC
BLUE
0.4
0.5
GREEN
0.6
NEAR IR
RED
0.7
SHORT
WAVE IR
1.1
MIDWAVE IR
3.0
LONGWAVE IR
5.0
0.4 - 0.5 mm
• Illuminates Materials in Shadows
• Water Penetration for Bathymetry
• Soil / Vegetation Differentiation
• Deciduous / Coniferous Differentiation
14.0
Band 1
Spectral Regions – Landsat MSS
BAND 2 (Visible Green)
PANCHROMATIC
BLUE
0.4
0.5
GREEN
0.6
NEAR IR
RED
0.7
SHORT
WAVE IR
1.1
MIDWAVE IR
3.0
LONGWAVE IR
5.0
0.5 - 0.6 mm
• Water Penetration for Bathymetry
• Clear and Turbid Water Contrast
• Discrimination of Oil on Water
• Green Reflectance Peak of
Healthy Vegetation
14.0
Band 2
Spectral Regions – Landsat MSS
BAND 3 (Visible Red)
PANCHROMATIC
BLUE
0.4
0.5
GREEN
0.6
NEAR IR
RED
0.7
SHORT
WAVE IR
1.1
MIDWAVE IR
3.0
5.0
0.6 - 0.7mm
• Vegetation Differentiation
• Chlorophyll Absorption
• Limited Water Penetration for
Bathymetry
LONGWAVE IR
14.0
Band 3
Spectral Regions – Landsat MSS
BAND 4 (Near Infrared)
PANCHROMATIC
BLUE
0.4
0.5
GREEN
NEAR IR
RED
0.6
0.7
SHORT
WAVE IR
1.1
MIDWAVE IR
3.0
5.0
0.7 - 1.1mm
• Vegetation Analysis
• Shoreline Mapping
• Landcover Discrimination
LONGWAVE IR
14.0
Band 4
Spectral Regions – Landsat MSS
BAND 5 (Short-wave Infrared)
PANCHROMATIC
BLUE
0.4
0.5
GREEN
0.6
NEAR IR
RED
0.7
SHORT
WAVE IR
1.1
MIDWAVE IR
3.0
5.0
1.1 - 3.0mm
• Fire Mapping
• Discrimination of Oil on Water
• Moisture Content of Soil and
Vegetation
• Snow / Cloud Differentiation
• Vegetation Analysis
LONGWAVE IR
14.0
Band 5
Spectral Regions – Landsat MSS
BAND 7 (Mid-wave Infrared)
PANCHROMATIC
BLUE
0.4
0.5
GREEN
0.6
NEAR IR
RED
0.7
SHORT
WAVE IR
1.1
MIDWAVE IR
3.0
5.0
3.0 - 5.0mm
• Solar Reflectance From Specular
Metal Roofs
• Smoke Penetration
• Daytime Reflectance Mixed With
Emitted EM Radiation
• Nighttime Emitted EM Radiation
LONGWAVE IR
14.0
Band 7
Spectral Regions – Landsat MSS
BAND 6 (Long-wave Infrared)
PANCHROMATIC
BLUE
0.4
0.5
GREEN
0.6
NEAR IR
RED
0.7
SHORT
WAVE IR
1.1
MIDWAVE IR
3.0
5.0 - 14.0mm
• Thermal Analysis
• Vegetation Density
• Urban Heat Islands
5.0
LONGWAVE IR
14.0
Band 6
Landsat Bands
BLUE
GREEN
RED
Band 1
Band 2
Band 3
NEAR IR
Band 4
SHORT
WAVE IR
MIDWAVE IR
Band 5
Band 7
LONGWAVE IR
Band 6
Spectral Resolution of Landsat TM
These bands provide a coarse summary of spectral signatures.
TM Band: 1
2
3
4
5
7
Radiometric Resolution
• Number of possible data values reported by the sensor
• Range is expressed as a power (2n )
– 8-bit resolution has 28 values, or 256 values
Range is 0-255
– 12-bit resolution has 216 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
Band 1
Red color gun
Band 1
Band 1
Green color gun
Blue color gun
• All three colors display the same value, so the
colors are shades of gray
Landsat Image of Idaho
Band 1
Band 2
Band 3
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)
True Color
Composite
Red color gun
Green (2)
Green color gun
Blue (1)
Blue color gun
(321)
Near Infrared (4)
False Color
Composite
(432)
Red color gun
Red (3)
Green color gun
Green (2)
Blue color gun
Multispectral Imagery
Display
Band Composite Output =
Color Guns =
Landsat TM Band =
2
4
7
Band Combination =
BLUE
GREEN
RED
1
2
3
NEAR IR
4
SHORT
WAVE IR
5
MIDWAVE IR
7
LONGWAVE IR
6
Color Composite Image
Color composite image
Band A
Blue color gun
Band B
Band C
Green color gun
Red color gun
Landsat TM Image of
Idaho
321
432
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