Lect Sum

• Microwaves


  Smaller radio waves that are part of the radio wave spectrum

  
• Microwaves


  • Capable of seeing through the atmosphere under nearly all weather conditions
  • Can penetrate through snow, clouds, smoke, haze, etc.
  • What appears "rough" in the visible could be "smooth" in the microwave
• Remote sensing systems


  Can be active or passive
• Radar


  • RAdio Detection And Ranging
  • An active microwave sensor that supplies its own energy
• Radar transmits radio waves or microwaves that reflect from any object in its path

  
• Radar applications


  • Measuring distance, altitude, direction and speed of moving & fixed objects
  • Weather forecasting
  • Early warning detection
  • Missile guidance
  • Tracking of birds & insects, and self-driving vehicles

  
• Soil response to radar


  • The presence of water in soil can be detected, but the water must be at the top of the soil (a few centimeters)
  • Soil moisture usually limits the ability of radar waves to penetrate the surface
  • Signal penetration of several meters has been observed for extremely dry soil
• Vegetation response to radar


  • Shorter wavelengths are best for sensing crop canopies or the top layer of a forest canopy
  • Longer wavelengths are best for sensing tree trunks, limb & soil
  • If plant canopy is dense, there will be stronger backscatter
• Passive microwave sensors


  • Detect microwave radiation naturally (i.e. low energy levels) from the Earth
  • Clouds are poor emitters of microwave radiation, but not sea ice
  • Advantage: view surface day or night, regardless of clouds
  • Disadvantage: low energy levels require a larger coverage area for radiation collection
• Microwave radiometer


  • A passive sensor that measures microwave energy being emitted at extremely low levels (sub-millimeter-to-centimeter wavelengths)
  • Used primarily for spacecraft measuring terrestrial & atmospheric radiation, and water vapor
• Types of active microwave sensors


  • Non-Imaging Radar: Scatterometer, Altimeter, Doppler Radar
  • Imaging Radar: Side-Looking Airborne Radar (SLAR), Synthetic Aperture Radar (SAR), Advanced Synthetic Aperture Radar (ASAR)

  
• Scatterometer


  • A microwave radar sensor that measures the amount of energy being reflected from Earth's surface
  • Can see through cloud cover
  • Has nearly the same imaging details as passive microwave imagery

  
• Altimeter


  • A sensor that sends a radar pulse towards Earth and measures the time it takes to return to it
  • Used to measure the altitude of Earth's surface features
  • Can determine the height of sea ice surfaces, which can be used to calculate total sea ice thickness
• Doppler radar


  A specialized radar that uses the Doppler effect to acquire velocity data from objects at a given distance

  
• Side-Looking Airborne Radar (SLAR)


  • Images acquired by an antenna aimed from the side of an aircraft
  • Sends one pulse at a time and measures what it gets back
  • Since it's an active sensor, SLAR can be used during the night or day

  
• Synthetic Aperture Radar (SAR)


  • An advanced version of SLAR that sends multiple pulses at one time, resulting in higher resolution
  • Can produce 2D or 3D images in day or nighttime settings
  • Provides complimentary information to optical systems

  
• Advanced Synthetic Aperture Radar (ASAR)


  • An upgraded version of SAR that can see through all weather, day or night
  • Observational capabilities are enhanced (e.g. observing different light polarities), as are the range of measurements
  • Many maritime applications, including data on high ocean swells

  
• The first of three space shuttle imaging radar (SIR) missions that imaged Earth using radar pulses was SIR-A in 1981
• The second space shuttle imaging radar mission was SIR-B in 1984, which was the first spaceborne SAR with a tiltable antenna
• The third space shuttle imaging radar mission was SIR-C in 1994, which found the remnants of ancient riverbeds in the Sahara desert that were buried beneath sand
• LIDAR


  • Stands for light-detection and ranging
  • Data can be collected from the ground, air or space, with air data being the most common
  • Green or near-infrared is used, as it is highly reflective off vegetation
  • Scans the Earth from side-to-side, so that it covers more ground

  
• LIDAR applications


  • Agriculture
  • Archaeology
  • Forestry
  • Geology
  • Police
  • Robotics
  • Seismology
  • Self-Driving Vehicles
• The Geoscience Laser Altimeter System (GLAS) was the first LIDAR instrument used for global coverage of the Earth, measuring ice sheet topography, atmospheric properties, and cloud properties
• Microwaves


  Smaller radio waves that are part of the radio wave spectrum
• Microwaves


  • Capable of seeing through the atmosphere under nearly all weather conditions
  • Can penetrate through snow, clouds, smoke, haze, etc.
  • What appears "rough" in the visible could be "smooth" in the microwave
• Remote sensing systems


  Can be active or passive
• Radar


  RAdio Detection And Ranging
• Radar


  • Active microwave sensor that supplies its own energy
  • Transmits radio waves or microwaves that reflect from any object in its path

  
• Radar applications


  • Measuring distance, altitude, direction and speed of moving & fixed objects
  • Weather forecasting
  • Early warning detection
  • Missile guidance
  • Tracking of birds & insects
  • Self-driving vehicles

  
• Soil response to radar

  • Presence of water in soil can be detected, but water must be at the top of the soil (a few centimeters)
  • Soil moisture usually limits the ability of radar waves to penetrate the surface
  • Signal penetration of several meters has been observed for extremely dry soil
• Vegetation response to radar

  • Shorter wavelengths are best for sensing crop canopies or the top layer of a forest canopy
  • Longer wavelengths are best for sensing tree trunks, limb & soil
  • If plant canopy is dense, there will be stronger backscatter
• Passive microwave sensors


  Detect microwave radiation naturally (i.e. low energy levels) from the Earth
• Passive microwave sensors


  • Clouds are poor emitters of microwave radiation, but not sea ice
  • Advantage: view surface day or night, regardless of clouds
  • Disadvantage: low energy levels require a larger coverage area for radiation collection
• Microwave radiometer


  A passive sensor that measures microwave energy being emitted at extremely low levels (sub-millimeter-to-centimeter wavelengths)
• Types of active microwave sensors

  • Non-Imaging Radar (Scatterometer, Altimeter, Doppler Radar)
  • Imaging Radar (Side-Looking Airborne Radar, Synthetic Aperture Radar, Advanced Synthetic Aperture Radar)

  
• Scatterometer


  A microwave radar sensor that measures the amount of energy being reflected from Earth's surface
• Altimeter


  A sensor that sends a radar pulse towards Earth and measures the time it takes to return to it, used to measure the altitude of Earth's surface features
• Doppler radar


  A specialized radar that uses the Doppler effect to acquire velocity data from objects at a given distance
• Side-Looking Airborne Radar (SLAR)


  Images acquired by an antenna aimed from the side of an aircraft, sends one pulse at a time and measures what it gets back
• Synthetic Aperture Radar (SAR)


  An advanced version of SLAR that sends multiple pulses at one time, resulting in higher resolution, can produce 2D or 3D images in day or nighttime settings