Remote sensing a a

1
Remote sensinga a

• Geology 175

2
What is remote sensing? DDefinition  -        
Remote sensing is a wooly term broadly it
describes the collection and interpretation of
information about a target without being in
physical contact with it. It is usually implicit
that the detecting and measuring medium is
electromagnetic energy. This definition excludes
endeavors such as seismography, magnetic,
gravity, and electric surveying, which tend to
come under the label of geophysical surveying.
Remote sensing is not a scientific discipline but
rather a tool whose range in applications is
limited only by our imagination (Oppenheimer,
1996).
3
-         Definition Remote
sensing is the practice of deriving information
about the earths land and water surfaces using
images acquired from an overhead perspective,
using electromagnetic radiation in one or more
regions of the electromagnetic spectrum,
reflected or emitted from the earths surface
(Campbell, 1996).  
4
Key attributes

• Remotely sensed data are acquired from a great
  distance.
• Satellite data allow many kinds of ongoing
  studies.
• Remote sensing is safe.
• Remote sensing offers very significant cost
  benefit analysis
• Sensors can be tuned to many different
  wavelengths of the electromagnetic spectrum.
•  

5
Some examples of the applications of using remote
sensing
Mapping the rocks in a region (usually applicable
in arid areas without much vegetative cover)
This satellite thematic mapper (TM) image of the
Orocopia Mountains was created by Bob Crippen and
Ron Blom at JPL. It serves as a fantastic tool
for investigating rock relationships and serves
as the regional base map. In the portion of this
image that is outlined, note the distinct
difference in colors (rock types) across the box.
6
Some examples of the applications of using remote
sensing

• Mapping structural lineaments

7
Some examples of the applications of using remote
sensing

• Bathymetry
• Multispectral imagery can be used to map water
  depths in certain circumstances. Visible
  wavebands TM1 (blue), TM2 (green) and TM3 (red)
  penetrate water to different amounts, the shorter
  the wavelength the greater the penetration. Red
  light can penetrate up to 10m and blue light as
  much as 30m.

8
Some examples of the applications of using remote
sensing

• Imaging buried structures
• The Landsat simulated true color mosaic (left)
  shows the Selima Sand Sheet covering all but
  rocky areas of the Sahara Desert in Sudan. On the
  right, a 50-kilometer-wide strip of Shuttle
  Imaging Radar, SIR-A, is placed over the Landsat
  mosaic to reveal old stream channels and geologic
  structures like these. Structures that are
  otherwise invisible under the surface sands are
  potential sources of water, placer minerals,
  ancient artifacts, and information on changes of
  climate in arid areas (courtesy of USGS Image
  Processing Facility, Flagstaff).

9
Some examples of the applications of using remote
sensing

• Earthquake prediction
• The surface displacement associated with the
  June 1992magnitude 7.3 earthquake

10
Some examples of the applications of using remote
sensing

• Determination of the surface composition of
  terrestrial planets
• The surface of Europa is broken up into large
  plates and covered with extensive fractures. The
  plates in many regions appear to have shifted and
  rotated, and can be fit back together like pieces
  in a puzzle. The false-color image to the left
  shows Minos Linea. The long red bands are 10 to
  20 km wide and have lighter lines running through
  the centers.

11
Some examples of the applications of using remote
sensing

• Volcanism in terrestrial planets
• 1. Volcanic plume (March 4, 1999)taken by
  Voyager spacecraft
• 2. Volcanic plume (July 3, 1999)taken by Galileo
  spacecraft

12
Some examples of the applications of using remote
sensing

• MOUNT ETNA, a volcanic peak in Sicily, subsided
  as magma drained away below it. An interferogram
  produced by two radar scans made 13 months apart
  by the ERS-1 satellite displays four cycles of
  interference fringes, indicating that the top of
  the mountain settled by about 11 centimeters
  during this interval.

13
Electromagnetic spectrum

• Electromagnetic energy refers to all energy that
  moves with the velocity of light in harmonic
  motion

14
Electromagnetic spectrum

• An EM wave has two components, oscillating as
  sine waves mutually at right angles, one
  consisting of the electric field, the other the
  magnetic field.

15
Elecrtromagnetic spectrum
16
Electromagnetic energy

• Sources of electromagnetic radiation
• 1. Sun (stars)
• 2. Matter with a temperature above
  absolute zero
• 3. Artificial transmitters (radio, radar)

17
Electromagnetic energy

• The higher the frequency, the higher the energy!

18
Electromagnetic energy Interaction with
materials
19
Electromagnetic energy Interaction with
materials
Atmospheric windows
20
Broad classification of sensors

• Passive - senses the radiation that naturally
  upwell from the target, whether reflected or
  backscattered sunlight or thermal radiation
• Active systems - illuminate the target with an
  artificial source of radiation

21
Passive system

• Sunlight or thermal radiation
• Inappropriate at wavelengths at which
  insignificant amounts of radiation occur naturally

22
Active system system

• Radar
• May not be practical at wavelengths where the
  active source requires considerable power in
  order to get enough signal returned to the sensor
  (e.g. camera flash)

23
fig 3.2
24
Raster image data

• Consists of discrete picture elements called
  pixels
• Each has an associated position within the image
  and a brightness value or digital number, DN.

25
Sensor Performance and Resolution

• Researchers at the Spectroscopy Lab have measured
  the spectral reflectance of hundreds of materials
  in the lab, and have compiled a spectral library.
  The library is used as a reference for material
  identification in remote sensing images.

26
(No Transcript)
27
(No Transcript)
28

• For images with more than one spectral band, the
  various bands are co-registered
• -therefore information from each spectral
  channel is available

29
Landsat band 4
Landsat band 5
Landsat band 7
False color image
30
(No Transcript)
31
(No Transcript)
32
Satellite sensors/missions SEAWIFS
http//seawifs.gsfc.nasa.gov/SEAWIFS.html
Landsat 7 http//landsat.gsfc.nasa.gov/ Terra
(EOS AM-1) http//terra.nasa.gov/ ASTER
http//asterweb.jpl.nasa.gov/ MODIS
http//modis.gsfc.nasa.gov/ GOES
http//www.goes.noaa.gov/ SPOT
http//www.spot.com Very High Resolution
technology Commercial satellites offering up to 1
m spatial resolution are available. See the
following sites for information http//www.digita
lglobe.com http//www.orbimage.com http//spaceima
ge.com
33
Satellite Orbits
Polar
Inclined
geostationary
34
Active sensors (Radar)

• Components
• Antenna array - devices that control the
  propagation of an EM wave (wave guide)
• Recorder Records and or displays the signal as
  an image

35
(No Transcript)
36
Side-looking airborne radar

• SLAR an antenna array aimed to the side of
  sensor platforms so that it forms an image strip
  of land.
• All weather capability
• Missions can be scheduled at night
• Provides clear, crisp representations of
  topography with good positional accuracy.

37
(No Transcript)
38
Geometry of the radar image

• Depression angle
• Nadir
• Far range
• Near range
• Mid-range

39
Geometry of the radar image

• Slant range direct distance from the antenna to
  an object on the ground
• Ground range the map representation of ground
  distances

40
Geometry of the radar image

• Geometric artifacts (Radar layover)
• at near range, the top of tall objects are
  closer to the antenna than its base
• Result is the signal from the tall objects are
  sometimes received ahead of near-range signals

41
Geometry of the radar image

• Geometric artifacts (Radar foreshortening)
• Incorrect depiction of slope
• Occurs in terrain of moderate to high relief

42
Wavelength
Table 7.1
43
Radar sensors

• JERS
• ERS
• SIR-C
• ENVISAT
• AIRSAR

44
Optical remote sensing from satellites

• Multispectral vs. hyperspectral remote sensing
• Multispectral remote sensing (MRS) can be defined
  as an imaging system with 2 or more bands but
  about 12 to 15 bands is the practical maximum.
• A "band" is defined as a portion of the spectrum
  with a given spectral width, such as 10 or 50 nm.
  
• Multispectral systems are non-contiguous in their
  coverage of the spectrum.

45
Optical remote sensing from satellites

• Multispectral vs. hyperspectral remote sensing
• Multispectral remote sensing (MRS) can be defined
  as an imaging system with 2 or more bands but
  about 12 to 15 bands is the practical maximum.
• A "band" is defined as a portion of the spectrum
  with a given spectral width, such as 10 or 50 nm.
  
• Multispectral systems are non-contiguous in their
  coverage of the spectrum.

46
Optical remote sensing from satellites

• Multispectral vs hyperspectral remote sensing
• The bands can be spectrally narrow or wide.
• Many satellite systems have traditionally had
  wide (50 - 200 nm) bands while some aircraft
  systems have discrete narrow bands (around 10
  nm).

47
Optical remote sensing from satellites

• Hyperspectral remote sensing
• Hyperspectral systems are known for having dozens
  to hundreds of narrow contiguous bands.
• Most are able to collect images starting at about
  400 nm which is the edge of the blue visible part
  of the spectrum

48
(No Transcript)
49
Optical remote sensing from satellites

• Hyperspectral remote sensing
• these systems can measure energy up to 1100 or
  even 2500 nm.
• Why important? Ans for detecting fine spectral
  features that can identify specific materials

50
(No Transcript)
51
Optical remote sensing from satellites

• A hyperspectral system would reveal the subtle
  absorption features (the "valleys)
• The valleys at 1.4-1.5 um (1400-1500 nm) are the
  distinguishing features or fingerprint of alunite
  and distinguish it from other minerals.
• Wide spectral bands could not find this feature
  and the TM and MODIS sensors do not even have
  bands centered on these wavelengths.

52
end