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Laser Distance and Speed Detection
Daniel KaputaEE 494 Dr. Cartwright
Feb 14th, 2001
Overview
?Motivation?History?Theory?Applications?Future
Motivation
?Many applications?Hope to implement laser
ranging into my robot?Easy concepts and very
versatile ?There are many different
applications to laser ranging
History of Laser Ranging
? 1840’s, First remote sensing used with pigeons
? 1969, the first lunar laser ranging done by using reflectors placed on the moon by Apollo 11
Theory?There are 3 types of laser distance measurements
1)Pulsed 2)Continuous wave3)Interferometer Method
?Laser ranging is called LIDAR which stands for Light Detection and Ranging
Pulsed Laser Ranging
?Short duration and high power? 1)Transmit pulse? 2)Detect reflection? 3)Measure time difference? 4)Compute distance from speed of light? Demo of Pulsed Laser
Pulsed Laser System
Non-cooperative Targets
Cooperative Targets
? Typical retro-reflective device used in satellites and on the moon
How to Compute the Distance
2R = C*TrR = distanceC = speed of lightTr = total travel time
30 cm over kilometers precision
Continuous Wave
? 1)Light travels in straight lines? 2)Laser light is coherent? 3)We know the speed of light
?Frequency modulated laser ranging
We know that:
Therefore we can compute the exact distance that the light has traveled
Beam-modulation Telemetry
How to Compute the Distance
?Frequency = (1/time) = (C/wavelength)? 100KHz = wavelength of 3x10^12 meters
Tr = roundtrip time
? r = phase
How to Compute the Distance
2R = C*TrR = distanceC = speed of lightTr = total travel time
1 cm over kilometers precision
Factors affecting accuracy1. Frequency of the tone or modulation.2. Accuracy of the phase-measurement loop. This depends on
signal strength, noise, and so on.3. Stability of the modulation oscillator.4. Number of cycles (or measurements) that can be averaged
together for a range. measurement.5. Turbulence in the air through which the. measurement is
made.6. Variations in the index of refraction of the air.
Taken from http://cord.org/cm/leot/Module6/module6.htm
Triangulation
? Triangulation is a method of determining distance by using angles and trigonometry.
? There are many different types of triangulation.
Applications of LIDAR
?There are countless applications for this new emerging technology.
?Anything previously measured by hand can be measured by lasers with much more accuracy.
?Examples.
Satellite Systems (SLR)
? Determine position of Earth’s satellites
? Topography? Oceanography? Gravity Waves? Plate Tectonics
Sensing of Surface Elevations
Rangefinders
? Uses pulses of infrared light
? Based on time difference from transmission to reception
? Bushnell's Page
Many Uses for Rangefinders
Golf
Hunting
Architecture
Ranging Video
Speed Traps
? pulsed light is used and 2 or 3 readings are taken to determining the velocity of the moving object
3D Body Scanning
GPS(Global Positioning System)
? GPS uses several satellites and the concept of triangulation.
? For this example there are 3 satellites that are used to pinpoint the location of the transmitting vehicle on earth
Step 1
? The vehicle determines how far away the first satellite is from it. Either pulsed or CW techniques can be used.
Step 2
? The vehicle determines how far away a second satellite is from it.
Step 3? The vehicle determines how far away a third satellite is
from it. Then it can combine all of the information and determine where on Earth it is located.
The Future of LIDAR
? In the future laser ranging will become more precise and cheaper, and many new applications will be implemented
LITE Lidar-in-space-technology-experiment
Used to measure clouds, atmospheric conditions, asteroids, and topography
Improved Accuracy
Bibliography? Slide 2,26,27,28,29 Trimble How GPS Works Step 1? Slide 3 EyeWire? Slide 4 Remote Sensing Tutorial Overview? Slide 8,9,12,13 Module 6: Laser Distance Measurement? Slide 20,21,33 http://ilrs.gsfc.nasa.gov/slrover.pdf? Slide 16 Better Optical Triangulation through Spacetime Analysis? Slide 17 Technology? Slide 18 Laser vs. LED vs. Superluminescent LED? Slide 22,23 Bushnell Sports Optics Worldwide? Slide 24 Laser? Slide 25 http://www.tc2.com/RD/RDBody.htm