Outline

1
Remote Sensing

• Outline
• definition of remote sensing
• components of system
• electromagnetic radiation
• nature of an image
• light interaction with atmosphere and surface
• types of remote sensors

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Remote Sensing

• science and art of obtaining information about
  something from a distance.
• analysis of collected data to obtain information
  about the objects, areas or phenomenon under
  investigation.

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Components of System
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Components of System

• Data Analysis
• examining the data using various viewing and
  interpretation devices to analyze pictorial data
  and/or a computer to analyze digital sensor data
  (i.e. GIS).

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Electromagnetic Radiation

• Energy Sources
• energy available from sun is described by
  electromagnetic spectrum

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Electromagnetic Radiation
Wavelength - distance from one wave crest to
another. Frequency - number of wave crests
passing a fixed point in a given period of time.
Measured in hertz (1 cycle per second)
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Electromagnetic Radiation
Amplitude - height of each peak. Measured as
spectral irradiance
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Electromagnetic Radiation

• Ultraviolet Radiation - 0.4 micrometers
• not much is done with UV for remote sensing since
  these shorter wavelengths are easily scattered by
  the atmosphere

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Electromagnetic Radiation
Visible Radiation BLUE (.4-.5 micrometers) GREEN
(.5-.6 micrometers) RED (.6-.73 micrometers)
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Electromagnetic Radiation

• Infrared Radiation - .72 - 15 micrometers
• Near Infrared - reflected, can be recorded on film

• Mid Infrared - reflected, can be detected using
  electro-optical sensors.
• Thermal Infrared - emitted, can only be detected
  using electro-optical sensors

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Electromagnetic Radiation
Microwave Radiation - radar sensors, wavelengths
range from 1mm to 1m
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Electromagnetic Radiation

• most systems rely on the sun to generate all the
  EM energy needed to image terrestrial surfaces -
  passive sensors.
• other sensors generate their own energy, called
  active sensors, transmits that energy in a
  certain direction and records the portion
  reflected back by features within the signal path

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Light Interaction with Atmosphere

• atmospheric modification of incoming and outgoing
  EM radiation includes scattering, refraction and
  absorption

• Scattering
• redirection of light by particles
• can be in any direction

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Light Interaction with Atmosphere

• General Effects of Scattering
• causes skylight (allows us to see in shadow)
• forces image to record the brightness of the
  atmosphere in addition to the target.
• directs reflected light away from the sensor,
  decreasing spatial detail (fuzzy images)
• tends to make dark objects lighter and light
  objects darker (reduces contrast)

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Light Interaction with Atmosphere

• Refraction
• bending of light when it passes through two media
• degrades spectral signatures on hot- humid days

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Light Interaction with Atmosphere

• Absorption
• mostly caused by three atmospheric gases ozone,
  carbon dioxide and water vapour

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Light Interaction with Surface

• Reflection
• the bouncing of electromagnetic energy from a
  surface
• type of reflection is dependent on the size of
  the surface irregularities relative to the
  incident wavelength.

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Light Interaction with Surface

• Specular Reflectance
• light is reflected in a single direction -
  'mirror' reflection
• specular reflectance helps and hinders remote
  sensing

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Light Interaction with Surface

• Diffuse/Lambertian Reflectance
• energy is reflected equally in all directions
• many natural surfaces act as a diffuse reflector
  to some extent.

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Nature of the Image

• image model target features described through
  the use of spectral reflectance
• software and hardware specially designed to
  analyze these images give us the ability to see a
  pictorial rendition of targets.
• images that we see on a computer screen are made
  up of picture elements called pixels.

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Nature of the image

• Pixel - picture element having both spatial and
  spectral properties.
• the spatial property defines the "on ground"
  height and width.
• the spectral property defines the intensity of
  spectral response for a cell in a particular band

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Nature of the Image
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Nature of the Image

• when only one band of the EM spectrum is sensed,
  the output device (colour monitor) renders the
  pixels in shades of grey

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Nature of the Image

• multispectral sensors detect light reflectance in
  more than one or two bands of the EM spectrum.

• these bands represent different data - when
  combined into the red, green, blue guns of a
  color monitor, they form different colors

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Nature of the Image

• multispectral image is composed of 'n' rows and
  'n' columns of pixels in each of three or more
  spectral bands

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Aerial Photography/Airphoto

• most common, versatile and economic form of
  remote sensing
• spectral range 0.3 to 0.9 mm (visible portion of
  spectrum).
• photogrammetry is the science, art and technology
  of obtaining reliable measurements, maps, other
  derived products from photographs.

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ADVANTAGES OF AERIAL PHOTOGRAPHY

• Five Basic Advantages
• Improved vantage point
• Capability to stop action
• Permanent recording
• Broadened spectral sensitivity
• Increased spatial resolution and geometric
  fidelity

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Aerial Photography/Airphoto

• camera produces a large-format 23x23cm photo
• contain high precision/well calibrated lenses
  that minimize spatial distortions
• motor-driven film advances 60 overlap between
  successive exposures

• panchromatic, black-and-white, true-colour film

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Aerial Photography/Airphoto

• Grey scale step wedge
• Notes
• Altimeter
• Fiducial marks
• Clock
• Lens serial number
• Focal length
• Frame number
• Mission name and date

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Aerial Photography/Airphoto
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Aerial Photography/Airphoto

• advantages improves vantage point, capability to
  stop action, permanent recording, broadened
  spectral sensitivity, increased spatial
  resolution.
• disadvantages cant get at elevation, not
  appropriate for urban areas (tall buildings block
  information)
• applications land use/land cover mapping,
  geologic and soil mapping, agricultural
  application, forest applications, wildlife
  ecology, etc.

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Satellite Remote Sensors

• currently there are 2777 satellites orbiting the
  earth (US 878)
• multi-purpose
• scientific
• defense
• communications
• global positioning system (GPS)

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Satellite Remote Sensors

• geostationary orbiting satellites are those that
  remain stationary relative to a point on the
  surface of the earth
• i.e. communications and meteorological
  satellites

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Satellite Remote Sensors

• polar-orbiting satellites are those in which the
  position of the satellites orbital plane is kept
  constant relative to the sun.
• i.e. Landsat satellite series

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ACTIVE VS PASSIVE REMOTE SENSING

• Passive Remote Sensing
• measure natural radiation emitted by target
  or/and radiation energy from other sources
  reflected from the target
• examples passive microwave radiometers, LandSat,
  SPOT

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ACTIVE VS PASSIVE REMOTE SENSING

• Active Remote Sensing
• transmit their own signal and measure the energy
  that is reflected or scattered back from the
  target
• advantages ability to see regardless of time
  of day or season use wavelengths not part of
  solar spectrum better control of the way target
  is illuminated

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Microwave Sensors

• sensors that operate in the microwave portion of
  the spectrum
• advantages capable of penetrating atmosphere
  under virtually all conditions, different view of
  the environment.
• disadvantage radar instruments have a hard time
  identifying water bodies because the wavelength
  is much longer than the general character of the
  surface roughness
• applications sea ice and snow, geologic
  features, ocean bottom contours, other planets.

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Microwave Sensors

• Microwave radiometer narrow-beam antenna
  attached to a scanning device
• soil moisture, water content of snow, geologic
  strata
• Synthetic Aperture Radar shorter antenna that
  emits and receives returned energy from ground
  objects
• day/night, clouds/cloud free operation

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Microwave Sensors

• RADARSAT
• launched in November 1995
• developed by Canada to monitor environmental
  change and the planets natural resources
• heart is synthetic aperture radar (SAR)
  microwave instrument that sends pulsed signals to
  earth and processes the received reflected pulses.

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Microwave Sensors
First RADARSAT Image
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Microwave Sensors
European SAR
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Optical Sensors

• sensors that operate in the optical portion of
  spectrum, which extends from approximately 0.3 to
  14 mm.
• can do more with these data because it is
  numbers.
• look at differences in colors
• look at differences over time
• applications meteorological, ocean monitoring
  (i.e. chlorophyll absorption).

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Optical Sensors

• show how much energy from the sun was being
  reflected or emitted off the Earth's surface when
  the image was taken.
• clear water reflects little radiation, so it
  looks black.
• pavement and bare ground reflect a lot of
  radiation, so they look bright.
• urban areas usually look light blue-grey.
• vegetation absorbs visible light but reflects
  infrared, so it looks red

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Optical image of Montreal area during ice storm
of 1998. Ice snow and clouds appear as various
colors of white, vegetation is green.
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Optical Sensors
GOES - Geostationary Operational Environmental
Satellite (Visible to NIR, Thermal) DMSP -
Defense Meterological Satellite Program 600 m
resolution (Visible to NIR, Thermal), urban heat
island studies Nimbus - CZCS - coastal zone color
scanner, 825 m spatial resolution AVHRR -
Advanced Very High Resolution Radiometer
meteorological satellite (visible, NIR, thermal)
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AVHRR - Advanced Very High Resolution Radiometer
meteorological satellite (visible, NIR, thermal)
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AVHRR Channels
Channel Wavelength Primary Use1
0.58 - 0.68 Daytime cloud/surface
mapping 2 0.725 - 1.10
Surface water delineation, ice and snow
melt 3A 1.58 - 1.64 Snow
/ ice discrimination (NOAA K,L,M) 3
3.55 - 3.93 Sea surface temperature,
nighttime cloud mapping 4
10.30 - 11.30 Sea surface temperature,
day and night cloud mapping 5
11.50 - 12.50 Sea surface
temperature, day and night cloud
mapping
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Optical Sensors

• LANDSAT - visible, NIR spectral bands (Landsats
  1,2,3), and MIR and Thermal (Landsats 4 and 5)
• Multispectral scanner - 4 spectral bands Green,
  Red, and 2 NIR
• Thematic mapper - 7 spectral bands Blue/Green,
  Green, Red, NIR, MIR, MIR, Thermal

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LANDSAT MSS image - Grand Canyon
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LANDSAT TM image - southwestern Utah and Southern
Nevada
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SPOT Image of the WTC Fires