Remote Sensing Methods

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Remote Sensing Methods

• Two types of remote sensing instruments passive
  and active
• By Lambert (AJ) Hartle

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Passive

• Passive instruments detect natural energy that is
  reflected or emitted
• Sense only radiation emitted or reflected by the
  object under observation
• The most common external source of radiation
  sensed by passive instruments is the sunlight
  reflected by the Sun

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Types of passive remote sensing

• Radiometer an instrument that measures the
  intensity of the electromagnetic radiation in
  some wavelength
• Usually further identified by the portion of the
  spectrum it covers visible, infrared (IR),
  ultraviolet (UV) lights, and microwave

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Types of passive remote sensing contd

• Imaging Radiometer a radiometer that includes a
  scanning capability which provides a
  two-dimensional array of pixels
• Scanning can be done electronically or
  mechanically

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Types of passive remote sensing contd

• Spectrometer an instrument or device used to
  detect, measure, and analyze the spectral content
  of the incident electromagnetic radiation
• Conventional methods include using gratings or
  prisms to disperse the radiation for spectral
  discrimination

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Types of passive remote sensing contd

• Spectroradiometer radiometer using multiple
  wavelength bands (ex multispectral) to measure
  the intensity of the radiation
• Usually of a high spectral resolution which is
  extremely helpful when looking at more specific
  parameters ex sea surface temperature, contd

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Types of passive remote sensing contd

• cloud characteristics, ocean colors, vegetation,
  trace chemicals in the atmosphere, etc.

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Types of active remote sensing

• Radar (Radio Detection and Ranging)
  transmitter(s) operating at either radio or
  microwave frequencies to emit electromagnetic
  radiation and a directional antenna(s) or
  receiver(s) to measure the arrival time of
  reflected or backscattered pulses of radiation
  from the measured object(s)

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Types of active remote sensing contd

• The distance to the object can then be determined
  since we know electromagnetic radiation travels
  at the speed of light

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Types of active remote sensing contd

• Scatterometer high frequency microwave radar
  designed specifically to measure the
  backscattered radiation
• Can be used to derive maps of surface wind speed
  and direction over ocean surfaces

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Types of active remote sensing contd

• Lidar (Light Detection and Ranging) uses a
  laser (light amplification by stimulated emission
  of radiation) to transmit a light pulse and a
  receiver with very sensitive detectors to measure
  the backscattered or reflected light
• Uses the same principle as radar for the ranging
  aspect of the measurement

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Types of active remote sensing contd

• Used to determine atmospheric profiles of
  aerosols, clouds, and other constituents in the
  atmosphere

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Types of active remote sensing contd

• Laser Altimiter uses a Lidar to measure the
  height of the instrument platform above the
  surface
• By independently knowing this height of the
  platform with respect to the mean Earths
  surface, the topography of the underlying surface
  can then be determined

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References

• http//www.nasa.gov
• http//www.udtinstruments.com/products/radiometric
  /radiometers.shtml
• http//en.wikipedia.org/wiki/ImageSpektrometr.jpg
  
• http//en.wikipedia.org/wiki/ImageScattometer_pri
  nciple.GIF

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References contd

• http//en.wikipedia.org/wiki/LIDAR
• http//glas.gsfc.nasa.gov/gifs/icesat_construction
  1.jpg