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