Space Technology and Applications Remote Sensing Missions

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Space Technology and ApplicationsRemote
Sensing Missions
Week 11 Sellers, Chapter 11, pp 382-393
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Remote Sensing Missions(examples)

• Environmental Monitoring
• Intelligence
• Reconnaissance -- SIGINT
• Surveillance -- IMINT
• Visible, Infrared, Microwave, Radar

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Remote Sensing Missions
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Electromagnetic (EM) radiation
The radiation of energy as transverse waves
that is produced by moving charges. A
charge can radiate electromagnetic radiation only
if it is undergoing accelerated motion.
Electromagnetic radiation is also known as an
electromagnetic wave, and consists of
oscillating electric and magnetic fields at
right angles to one another and to the
propagation direction. Electromagnetic
radiation comes in discrete packets known as
photons.  Light is a general term referring to
electromagnetic radiation in the visible part
of the spectrum. Like all electromagnetic
radiation, light comes in discrete packets
known as photons.
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EM Radiation Interacting witha Solid Surface
a
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EM radiation sources
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Black Body Radiation Curve
Solar Radiation
The hotter the object, the more EM Radiation it
emits at shorter wave- Lengths. Black
Body -- a,e 1
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Wiens Displacement Law
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Emitted Radiation (contd)
Emitted Radiant Energy -- as object heats
up, it radiates energy back into space
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Remote Sensing Payloads
Look at Target -- move sensor to point at
subject See the Target -- collect EM radiation
from subject Conversion -- Transform sensed EM
radiation to useable data Processing --
analyze data to produce useable information
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Remote Sensing Design Parameters

• Coverage, Revisit Time
• Field of View, Magnification, Resolution

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Coverage and Revisit
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Telescopes
All remote sensors are basically one of two
variations on a Telescope
Reflecting telescope (Hale (Mt. Palomar),
Radar, Radio telescopes, DSS)
Primary Mirror
Eyepiece
Refracting telescope (very cumbersome and
expensive)
Objective lens
Eyepiece
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Telescopes (contd)
Hubble Space Telescope
Catadioptric Telescope (hybrid)
Convex lens
Secondary Mirror
Convex Mirror
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Hubble Space Telescope
2.4 m
Catadioptric Design
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Field of View
rd radius of detector fl focal length
of Optics h sensor height Rg ground
swath radius
h
Rg
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Magnification
Magnification is the increase (or decrease) in
size of an image produced by an optical system
compared to the true size.
l
l
Virtual Image
di-f
M
l
l
l
d0-f
Parabolic Mirror focuses all rays to a single
point Virtual Image is Compared to Original
Image
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Magnification (contd)
Virtual Image is Magnified by the Eyepiece
Total Magnification
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Magnification (concluded)
Example 1 meter focal length mirror, 10 mm eye
piece
Theoretically All telescopes are capable of
nearly infinite magnification Practically
telescopes are resolution limited by the size of
their Primary optics
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Resolution
Rayleigh Limit
Minimum Angular Arc which an Optical System can
resolve Bigger the mirror or Lens the better
the Resolution no matter what the
magnification Optical Light Gives better
Image resolution infrared of radar (why?)
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Example
HST Best resolution of earth 2.4-meter
telescope
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Example
HST Best resolution of Alpha-Centarii 4.2
light Years
Still cant see the stars surface!!!!
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Resolution Comparison
10-cm resolution permits the description of
vehicles. 25-cm resolution permits the
identification of vehicles. 50-cm resolution is
marginally adequate for identification of
vehicles. 1-meter resolution permits recognition
but not identification of vehicles.
10 25
50
100
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Slant Range
Image is not always seen from nadir angle
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Interpretability More than Resolution
Sharpness Noise in Image Viewing Angle Image
Processing Image Display Tech Weather
National Imagery Interpretability Rating
Scale (NIIRS)
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Synthesized Aperture
Combined aperture radar
Formation Flight allows Satellites to act As
one giant radar antenna
Techsat 21
SIGNAL Processing does the rest
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Techsat 21 Design
Techsat 21
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Techsat 21 Orbital Mechanics