study notes pt 3

• Across-track thermal scanning mechanism


  Learn about the across-track thermal scanning mechanism

  2. Learn about the thermal radiation principles

  3. Learn how to interpret thermal scanner imagery

  4. Analyse the geometric characteristics of across-track scanner imagery

  5. Learn about temperature mapping with thermal scanner data

  6. Learn about FLIR systems and thermal scanners

  7. Learn about radiant temperature, kinetic temperature, real body and black body radiations

  8. Learn about the geometric distortions found in thermal imagery

  9. Learn about thermal remote sensing, Planck Radiation Law, diurnal-heating effects, thermal properties of water, various thermal sensors

  10. Discuss heat capacity mapping mission and other weather satellites
• The approach of study or learning will be section by section or sub-topic by sub-topic until we will complete all mode of study.
• Microwave sensing


  Encompasses both active and passive forms of remote sensing
• Microwave portion of the spectrum


  • Covers the range from approximately 1cm to 1m in wavelength
  • Longer wavelength microwave radiation can penetrate through cloud cover, haze, dust, and all but the heaviest rainfall as the longer wavelengths are not susceptible to atmospheric scattering which affects shorter optical wavelengths
  • This property allows detection of microwave energy under almost all weather and environmental conditions so that data can be collected at any time

  
• Passive microwave sensing


  Similar in concept to thermal remote sensing, all objects emit microwave energy of some magnitude, but the amounts are generally very small. A passive microwave sensor detects the naturally emitted microwave energy within its field of view. This emitted energy is related to the temperature and moisture properties of the emitting object or surface.

  
• Passive microwave sensors


  Typically radiometers or scanners and operate in much the same manner as systems discussed previously except that an antenna is used to detect and record the microwave energy
• Sources of microwave energy recorded by a passive sensor


  • Emitted by the atmosphere
  • Reflected from the surface
  • Emitted from the surface
  • Transmitted from the subsurface
• Passive microwave remote sensing


  • Characterized by low spatial resolution as the fields of view must be large to detect enough energy to record a signal

  
• Applications of passive microwave remote sensing


  • Meteorology
  • Hydrology
  • Oceanography
• Active microwave sensors


  Provide their own source of microwave radiation to illuminate the target
• Categories of active microwave sensors


  • Imaging
  • Non-imaging
• RADAR


  The most common form of imaging active microwave sensors, an acronym for RAdio Detection And Ranging, which essentially characterizes the function and operation of a radar sensor
• Radar sensor operation


  Transmits a microwave (radio) signal towards the target and detects the backscattered portion of the signal, the strength of the backscattered signal is measured to discriminate between different targets and the time delay between the transmitted and reflected signals determines the distance (or range) to the target
• Non-imaging microwave sensors


  • Altimeters
  • Scatterometers
• Radar altimeters


  Transmit short microwave pulses and measure the round trip time delay to targets to determine their distance from the sensor, generally look straight down at nadir below the platform and thus measure height or elevation

  
• Radar scatterometers


  Make precise quantitative measurements of the amount of energy backscattered from targets, the amount of energy backscattered is dependent on the surface properties (roughness) and the angle at which the microwave energy strikes the target

  
• Radar and optical data can be complementary to one another as they offer different perspectives of the Earth's surface providing different information content

  
• History of imaging radar


  First demonstration of the transmission of radio microwaves and reflection from various objects achieved by Hertz in 1886

  2. First rudimentary radar developed for ship detection shortly after the turn of the century

  3. Experimental ground-based pulsed radars developed for detecting objects at a distance in the 1920s and 1930s

  4. First imaging radars used during World War II had rotating sweep displays which were used for detection and positioning of aircrafts and ships

  5. Side-looking airborne radar (SLAR) developed for military terrain reconnaissance and surveillance after World War II

  6. Advances in SLAR and development of higher resolution synthetic aperture radar (SAR) in the 1950s for military purposes

  7. Radars declassified and began to be used for civilian mapping applications in the 1960s

  8. Canada's involvement in radar remote sensing started in the mid-1970s, SURSAT project from 1977 to 1979 led to participation in the SEASAT radar satellite

  9. Convair-580 airborne radar program, Radar Data Development Program (RDDP) in the 1980s and 1990s

  10. Launch of ESA's ERS-1 in 1991, Japan's J-ERS in 1992, ERS-2 in 1995, and Canada's RADARSAT in 1995
• Radar


  A ranging or distance measuring device consisting of a transmitter, a receiver, an antenna, and an electronics system to process and record the data
• Radar operation


  Transmitter generates successive short bursts (or pulses) of microwave at regular intervals

  2. Antenna focuses the radar beam to illuminate the surface obliquely at a right angle to the motion of the platform

  3. Antenna receives a portion of the transmitted energy reflected (or backscattered) from various objects within the illuminated beam

  4. By measuring the time delay between the transmission of a pulse and the reception of the backscattered "echo" from different targets, their distance from the radar and thus their location can be determined

  5. As the sensor platform moves forward, recording and processing of the backscattered signals builds up a two-dimensional image of the surface
• Microwave wavelength bands


  • Ka, K, and Ku bands
  • X-band
  • C-band
  • S-band
  • L-band
  • P-band
• Radar images of the same agricultural fields acquired using different radar bands can show significant differences due to the different ways in which the radar energy interacts with the fields and crops depending on the radar wavelength
• Radar polarization


  Refers to the orientation of the electric field, most radars are designed to transmit microwave radiation either horizontally polarized (H) or vertically polarized (V), and the antenna receives either the horizontally or vertically polarized backscattered energy

  
• Radar polarization combinations


  • HH - horizontal transmit and horizontal receive
  • VV - vertical transmit and vertical receive
  • HV - horizontal transmit and vertical receive
  • VH - vertical transmit and horizontal receive
• due to the different ways in which the radar energy interacts with the fields and crops depending on the radar wavelength
• Polarization


  The orientation of the electric field (recall the definition of electromagnetic radiation from Chapter 1)
• Polarization combinations


  • HH - horizontal transmit and horizontal receive
  • VV - vertical transmit and vertical receive
  • HV - horizontal transmit and vertical receive
  • VH - vertical transmit and horizontal receive
• Like-polarized


  Transmit and receive polarizations are the same
• Cross-polarized


  Transmit and receive polarizations are opposite of one another
• Both wavelength and polarization affect how a radar "sees" the surface

  
• Radar imagery collected using different polarization and wavelength combinations may provide different and complementary information about the targets on the surface

  
• Nadir


  Directly beneath the platform
• Range


  Across-track dimension perpendicular to the flight direction
• Azimuth


  Along-track dimension parallel to the flight direction
• Near range


  Portion of the image swath closest to the nadir track of the radar platform

  
• Far range


  Portion of the swath farthest from the nadir
• Incidence angle


  Angle between the radar beam and ground surface
• Look angle


  Angle at which the radar "looks" at the surface

  
• Slant range distance


  Radial line of sight distance between the radar and each target on the surface
• Ground range distance


  True horizontal distance along the ground corresponding to each point measured in slant range