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RADAR and LIDAR
An Introduction


Prof. David Bernstein
James Madison University

Computer Science Department
bernstdh@jmu.edu

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Motivation
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  • Our Need:
    • A way to detect "distant" objects, determine their range (i.e., distance away), and determine their velocity
  • Other Technologies with "Similar/Related" Objectives:
    • Determine "our" static latitude and longitude
    • Determine "our" dynamic location
    • Determine "our" heading and acceleration
Determining Range
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  • Recall:
    • When an electromagnetic wave contacts an object it will be absorbed, scattered, or reflected
    • Electromagnetic waves travel at (essentially) the speed of light
  • Using this Information:
    • Transmit an electromagnetic wave, receive the reflection, and use the transit time to determine the distance
Determining Velocity
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  • Recall:
    • The Doppler Effect - When the source of a wave is moving towards (away from) and observer, the observed frequency of the wave increases (decreases)
  • Using this Information:
    • Transmit an electromagnetic wave, receive the reflection, and use the difference in frequency to determine the relative velocity
RADAR
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  • The Acronym:
    • RAdio Detection And Ranging
  • The Waves:
    • Radio waves
  • The History:
    • Used for detection as early as 1904
    • Used for range determination in the 1930s
RADAR (cont.)
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  • Transmitter:
    • The signal can be generated in a variety of different ways depending on the application
  • Receiver:
    • Is typically at the same location as the transmitter
  • Antenna:
    • The same antenna is sometimes used for both the transmitter and the receiver, so must switch between the two
    • Can be omnidirectional or not (e.g., parabolic)
    • Can move (e.g., rotate) or not
RADAR (cont.)
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  • Advantages:
    • Little attenuation in the atmosphere (even with bad weather) so works at long ranges
  • Disadvantages:
    • The reflected signal is weak (the power declines with the 4th power of the range) and must be amplified or processed
    • The amount of reflection depends on the wavelength (i.e., wavelengths that are much longer than the target may not be detected)
LIDAR
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  • Acronyms:
    • LIght raDAR
    • LIght Detection and Ranging
    • Laser Imaging, Detection and Ranging
  • The Waves:
    • Can use ultraviolet, visible, or near infrared (varying to suit the target)
    • Eye-safety is an issue (e.g., 1550nm lasers are eye-safe even at high power)
  • The History:
    • COherent Light Detecting and Ranging used lasers for range finding in the 1960s
LIDAR (cont.)
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  • Type of Reflection:
    • Diffuse (i.e., scattered at multiple angles) as opposed to specular (i.e., all of the light reflected at one angle) in one
    • Often referred to as backscatter
    • The specific kind of scattering depends on the wavelength (so is application dependent)
  • Photosensors:
    • Charge-Coupled Devices (CCDs)
    • CMOS Image Sensors
  • Illumination Methods:
    • Scanning - a single point is illuminated at a time (and a mirror, often MEMS, is used to direct the light)
    • Flash - the entire field of view is illuminated with a single pulse
SONAR
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  • The Acronym:
    • SOund Navigation And Randing
  • The Basics:
    • Uses sound waves (which are mechanical waves)
    • Most frequently used underwater
There's Always More to Learn
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