Down the Road Lidar Technology and Conformance Testingworkgroups.oiml.org/tcsc/tc-07/tc-07-sc-04/july-16-18-2013-workshop... · Speed Measurement Lidar Technology and Conformance
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Speed Measurement Lidar Technology and Conformance Testing Mike Rieger Director of Technical Support 1
Speed Measurement Lidar Technology and Conformance Testing
Mike Rieger Director of Technical Support
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Presenter
Presentation Notes
Laser Technology, Inc. Speed Measurement Lidar Technology Presenter: Mike Rieger – Director of Technical Support
Centennial Colorado
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Presenter
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Laser Technology, Inc. is located in Centennial Colorado, USA. Centennial is located on the southeast side of the Denver metro area.
Corporate Headquarters
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In June 2012 Laser Technology moved into a new building only ½ mile from its last location. The new facility increased the size of all departments including engineering and manufacturing. All aspects of the business (engineering, manufacturing, service, sales, marketing, and administration) are housed at our corporate headquarters here in Centennial.
Brief History of Laser Technology, Inc.
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A brief history of Laser Technology, Inc. provides an understanding of the products and technology we are involved in.
1985 International Measurement and Control
Dredge Guidance Hydrographic Mapping
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In 1985, the company’s name was International Measurement and Control. IMC had developed and was selling hydrographic survey systems based on a ranging laser. The Hydro I (on the right) was used for underwater mapping operations. The Dredge Guidance System was able to provide range-range 2D and 3D solutions.
1988 US Navy Project
30,000 ft. to a prism on an aircraft
(Airborne Turret Infrared Measurement System)
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The ranging laser technology led to a project with the Navy. ATIMS was a Navy project in which the laser was placed in a swivel turret under an F4 phantom aircraft. Other electronics including missile guidance systems were included in the pod. The ATIMS provided range information during counter-measure testing against missile guidance systems.
The ATIMS was modified to measure vehicle speed and demonstrated to the California Highway Patrol. The demonstrations showed that there was a market for laser speed measurement technology.
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The ranging laser applications led to the addition of speed measurement to the technology. A prototype of the ATIMS was demonstrated to the California Highway Patrol in 1988. Based on interest from CHP, LTI searched for funding to develop the speed measurement laser.
1990 LTI 20-20
The company was incorporated and the name changed to Laser Technology, Inc. (LTI)
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During 1989 – 1990, the company incorporated and changed its name. The first speed measurement laser, the LTI 20-20, was released.
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LTI 20-20 Speed Measurement Laser
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This 1989 Popular Mechanics article includes a prediction of a possible laser jamming device shown in the lower right graphic.
1992 Surveying Products And Worldwide Distribution
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In 1992, LTI released the Criterion survey laser (a hand-held total station), and branched into the surveying and mapping market. International dealers for the 3 product lines (Hydrographic, Speed Measurement, and Survey Mapping) were established.
1993 NASA The NASA laser project was used for closing speed monitoring when docking with the space station or for satellite recovery missions. The instrument measures velocity in feet per second.
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In 1993, LTI entered into an agreement with NASA to build custom lasers to be used as standard equipment on each space shuttle mission. The lasers were used to measure closing velocity of objects such as the space station during docking maneuvers.
US Patent 5,359,404
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In 1994, the US patent office granted Laser Technology, Inc. a patent for a Laser Based Speed Measuring Device.
US Patent 5,359,404
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This is an overview of the technology from the patent abstract.
Laser Technology Patents
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5,521,696 5,528,518 5,539,513
0776458
5,652,651 690003
2,203,278 10-0278806
5,574,552 5,703,678 5,880,821 6,057,910
6,226,077 6,445,444 5,612.779 5,617,199
45799 5,715,045 714599 2,254,897
5,696,705 5,938,717 5,780,999
718038 2,263,918
5,790,244 729572 5,889,583
6,043,868
729740 2,263,853
5,926,260 5,806,020
729605
6,057,777
6,377, 186
5,781,147
6,064,330
5,859,693 735001
2,303,843
5,949,529
6,282,803
6,055,490
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LTI is a leader in pulsed laser technology and has been awarded over 80 patents.
1994 Ship Docking Systems
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In 1994, LTI developed a laser and radar based ship docking system and distributed it through a sister company named Laser Communications.
1994 Speed Measurement with Digital Image
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The Laser DigiCam system was LTI’s first speed measurement system which captured and stored digital photographic evidence. The Laser DigiCam captured a single greyscale image and stored it to a removable PCMCIA hard drive.
1994 Bushnell Partnership
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In 1994, LTI established a partnership with Bushnell to design consumer range finders. The partnership has been very successful and continues today. LTI and Bushnell work continually on new designs and improvements to Bushnell’s consumer range finder technology.
LTI 20-20 Court Acceptance The ‘landmark’ case on Laser speeding tickets in New Jersey: Judge Reginald Stanton wrote: “I am satisfied from the evidence presented in the proceedings which led to the issuance of my Opinion of June 13, 1996 and from the evidence presented during the recent hearings before me that the general concept of using lasers to calculate the speed of motor vehicles is generally accepted within the relevant scientific community and is valid.”
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During 1996 to 1998, the validity of the LTI 20-20’s lidar technology was challenged in a New Jersey court. The court accepted the scientific principles and reliability of lidar speed measurement after additional field testing was performed.
1995 - 2000 Impulse series UltraLyte Series Micro Digi-Cam System
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A redesign of the technology between 1995 to 2000 resulted in the second generation of LTI lasers; surveying, speed measurement, and speed measurement with digital color image capture.
ASIC
Industrial
Bushnell (digital)
Survey
2001 Digital Signal Processing
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In 2001, LTI added digital signal processing to its surveying products, industrial products, and the Bushnell consumer laser range finders (LRF) products.
TruSpeed 2007 TruCAM 2009
The 3rd generation of Speed Measurement
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Another redesign, starting around 2006, resulted in the third generation of speed measurement products. The TruCAM contains integrated color image and video capture.
The Digital Generation (4th)
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TruSpeed S 2011
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Presentation Notes
In 2011, LTI released its first speed measurement device using digital signal processing. DSP has been used for years in the surveying and Bushnell products. DSP allows for improved target acquisition with smaller optics.
Principles of Operation
1. Laser Pulse Generation
2. Timing Analysis and Processing
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Speed Measurement Lidar Principles of Operation. Overview of the main technology sections: laser pulse generator, timing analysis, and processing.
Laser Pulse Generation • Laser light (laser diode) is the working component of a LiDAR* system. • Speed of light is a constant: 299,792,458 m /s. • The time it takes the infrared laser light to travel to an object and return is
measured. The time of flight is proportional to the range to the target.
Laser light is the working component of a speed measurement laser. Light travels at a constant velocity allowing the device to measure the time it takes laser light to leave the instrument and return. Laser light is created using a laser diode. The laser diode has a p-n junction formed by two doped gallium arsenide layers. The light produced is infrared laser energy with a wavelength of 905 nanometers. The working component is the laser, the device is called a lidar Light Detection And Ranging.
Laser Pulse Generation With the use of optics, the diverse energy produced by the laser diode is focused into a tight, narrow beam.
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The laser energy produced by the laser diode is diverse. The diverse energy is focused into a narrow beam by the optical system. In other words, it is the design of the optical system which creates the beam size and shape. The beam size and shape will not change unless the optical system is changed.
Target Discrimination
90 m
0.4 m
150 m
RADAR
LASER BEAM WIDTH COMPARISON
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In LTI speed measurement lasers, the beam shape ranges from 2 milliradians to 3.5 milliradians in size. The shape in some units is square, while others are rectangular. The shape is formed by the p-n junctions on the laser diode. Some diodes have use 2 layers, some 3 layers, and newer diodes are ‘micro’ stripe which means that the layers are so close that they almost cannot be seen, giving the appearance of a single stripe (junction).
Focused laser energy –> Laser Class 1
The laser energy is below the level at which it is believed eye damage will occur.
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International Standard: EN 60825-1 laser class 1 US: ANSI Z136.1 and manufacturer's requirements: CDRH 21 CFR Parts 1040.10 and 1040.11 (regulated by the FDA)
Conformance testing - Laser Pulse Generation Laser Safety Classification Class 1 required (is Class 1m acceptable?) One of the main features of a speed measurement laser in comparison to radar is its beam size and target discrimination capability. Too wide of a beam can reduce the instrument’s ability to pick out a single target at a long range. To assure this does not occur, standards such as the IACP’s MPS have a beam width requirement of less-than or equal-to 5 milliradians.
Principles of Operation
1. Laser Pulse Generation
2. Timing Analysis and Processing
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Timing Analysis and Processing The analysis and processing of the laser’s pulse time-of-flight determines the accuracy (quality) of the speed measurement laser design.
Timing analysis and Processing
The lidar device measures the time it takes the laser pulse to travel to and return from an object. Distance to the object is proportional to the time-of-flight of a laser pulse divided by two.
d = cAIR ∗ tRT ÷ 2
Distance = velocity * time
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The speed measurement lidar uses the well known formula for time, distance, and rate. Rate (of speed) equals distance divided by time: r = d / t
Timing analysis and Processing
One event (distance) per laser pulse
A counter is started when the laser light is transmitted, and the counter is stopped when a portion of the signal is detected.
By definition, a lidar device is a precise time measurement device which performs complex mathematical calculations.
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By definition, a LiDAR device is a precise time measurement device which performs complex mathematical calculations. In most systems, one pulse equals one measruement.
By sending out multiple pulses ( 2 or more ) we can calculate speed.
Δd = quantitative change in distance (distance change from pulse 1 and pulse 2) Δt = quantitative change in time (elapsed time from pulse 1 and pulse 2)
Distance traveled / Elapsed Time
Pulse 1
Pulse 2
Timing analysis and Processing
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By definition, the velocity of the target is the change of distance divided by the elapsed time.
In theory, it is possible to make a speed measurement using only two laser
pulses.
In practice, this would be prone to errors, such as a shift of the aiming point
between the two pulses during the measurement.
( often referred to as ‘sweep’ error )
To eliminate the possibility of such errors, most LiDAR devices uses multiple
pulses ( 40 to 100 ) to calculate the targets speed. The actual speed calculation is
not the simple distance divided by time formula; the target speed is instead
derived from the entire data set using statistical analysis.
Timing analysis and Processing
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Presentation Notes
In theory, it is possible to make a speed measurement using only two pulses, however; due to limited data, this simple method would be prone to errors. Thus, most Lidar devices use multiple pulses for each measurement. This allows the device to apply statistical analysis to the data returned.
Timing analysis and Processing
1469
1479
1489
1499
1509
1519
distance in feet
pulse time
Given perfect distance measurement and a constant vehicle velocity, all distance measurements would fall on a single straight line. The slope of the line represents vehicle speed and direction.
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This is a graphical view of a multiple pulse measurement. In this case, the distances (measurements) are decreasing over time representing a approaching vehicle. The slope of the line represents the vehicle’s velocity.
Timing analysis and Processing
Using a multiple pulse measurement provides information on the steadiness of the beam on the vehicle during the measurement and is used to assure accuracy in the speed calculation. In other words, the system can detect ‘sweep’ error, or unintentional errors due to operator hand shake.
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Using a multiple pulse measurement, the device can detect and reject too much operator hand-shake, or movement of the beam on the target during the measurement. The device can detect ‘sweep’ error, where the operator moves the beam on the vehicle during the measurement. And the device can detect excessive acceleration/deceleration. Most Lidar devices have sophisticated software to detect and ‘trap’ out excessive movement of the beam during the measurement to prevent an erroneous speed measurement from being produced.
Conformance Testing Timing analysis and Processing
1. Verify Accuracy of Internal Time Base ( a precise time measurement device must operate from an accurate internal clock )
2. Accurate Range Measurement ( ability of instrument to accurately measure time and perform a calculation)
3. Accurate Speed Calculation ( ability of instrument to accurately calculate speed under perfect conditions) 4. Measurement Analysis ( software is able to detect and reject ‘sweep’ and other unfavorable measurement conditions which could effect speed accuracy )
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Conformance testing of the timing analysis and processing parts of the speed measurement laser The quality of the optical system will determine the instrument’s ability to acquire a moving target without reflectors at a long range. The accuracy of the time-of-flight measurement(s) will produce accurate range measurements and accurate speed calculations. Test the internal time base. Test baseline range accuracy. Accuracy of the speed calculation. Speed calculations are based on relative accuracy, not absolute accuracy. In other words, the quality of the design under perfect conditions Lidar Target Simulator. The quality and sophistication of the measurement analysis software. Can the device detect operator hand-shake and other measurement conditions which can reduce or skew the accuracy of the speed calculation.
Speed Accuracy can be Confirmed through:
• Field testing
• Laboratory Simulations • Low and high temperature limits • Low source voltage • Electromagnetic interference • Simulated sweep error
Conformance Testing Timing analysis and Processing
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Presenter
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Field Testing: A quality test program will contain field testing to verify speed accuracy under many real world conditions. Field testing is important and should be done, however its details will not be discussed in this presentation. Laboratory Speed Simulations: The ability to simulate the laser light pulses, and time-of-flight delays is a critical step in evaluating the design of a speed measurement laser. Laboratory simulations provide the opportunity to test speed accuracy under the following conditions: Low and high temperature limits Low battery or low supply voltage conditions. Electromagnetic interference ( police radar, CB radio transmission, etc. ) Simulated operator ‘sweep’ error. These items can be done in field testing, but would be much harder to test and quantify the accuracy of the results.
LiDAR Target Simulator (LTS)
March 2000
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This is the cover of the NIST developed Lidar Target Simulator. The document was published in 2000 and many LTS’s were built and used.
Lidar Target Simulator (LTS)
“The ideal computer is an AT compatible with a 486 chip running at 66 MHz. Hardware floating-point support is required. Useful data have been taken using a 20 MHz 386 PC.”
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Overview diagram of the LTS system.
Lidar Target Simulator (LTS)
Key Points:
• PC loads delay into DDG via GPIB between pulses
• Max pulse rate = 390 Hz
• Lidar unit must operate using a fixed pulse rate
• Pulse rate is part of simulation calculation
• Optical interface converts laser pulses into electrical signals
• Designed to use off the shelf parts to maintain independence from manufacturers
• Includes a sweep test
(simulates sweeping towards the lidar, 1.52 m (5 ft.) along a smooth
sheet-metal area in 0.178 s )
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Highlights of the LTS.
Lidar Speed Measurement Simulator The LTS hit obsolescence in the early 2000’s when replacement parts were difficult to find. In 2004, the IACP contracted with Laser Technology, Inc. to design a replacement LTS. The LSMS was designed and 3 systems delivered to IACP. Since then many systems have been sold worldwide.
Key Points:
• Built for purpose system
• All timing and delays loaded internally
• Original Specification = 1 KHz max pulse rate
• Has since been increased to 13 KHz
• Based on lidar units which operate using a fixed PRR
• Optical interface handles high pulse rates
• Includes a sweep test
(simulates sweeping towards the lidar, 1.52 m (5 ft.) along a
Smooth sheet-metal area in 0.178 s ) 41
Presenter
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Due to obsolescence, LTI was contracted to build a replacement Lidar speed simulator. The Laser Speed Measurement Simulator (LSMS) was developed and 3 units provided to the IACP.
Pulse Repetition Rate For many years the Lidar pulse rate was a fixed frequency. Thus this is the reason that the Lidar speed simulators, old and new, are based on fixed pulse rates. However appearance of Lidar jammers on the market have given manufacturers incentive to move away from fixed pulse repetition rates.
Image from: www.blinder.net 42
Presenter
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Laser jammers have provided incentive for manufacturers to move away from fixed pulse repetition rates.
Laser Jammers Fixed pulse rates are more easily detected than random pulse rates (or pseudo random), as fixed frequencies do not naturally occur. A random pulse rate is hard to detect from normal background noise. In many cases, the jamming device will not activate.
Image from: www.blinder.net 43
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Laser jammers can more easily detect fixed pulse rates than random or pseudo random pulse rates.
Laser jammer avoidance and improvements in Lidar technology will change the way speed measurement Lidar devices transmit laser pulses.
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Changes to the way Lidar devices transmit pulses is inevitable. The changes are due somewhat to laser jammers, and somewhat to improvements in the technology.
14 pulses @ 4 KHz
LTI TruSpeed S
2.8 KHz average rate
Class 1 eye safety provides the limits. Burst rates greater than 55 KHz may be considered a single pulse increasing the laser classification, thus it is expected that the burst rates will be limited to 55KHz or less.
Digital Signal Processing
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For Laser Technology, Inc., an improvement in the technology is digital signal processing. With DSP, laser pulses can be transmitted at a high rate, increasing system performance and accuracy.
The future of speed measurement Lidar technology is here today. Performance standards and conformance testing must take into consideration new technologies such as: • Digital signal processing and high pulse repetition rates. • Laser jammer avoidance techniques. • On board data storage. • Integrated cameras. • Ability to transfer data wirelessly, in real time. • GPS
Conclusion
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In conclusion, the future of speed measurement laser technology is changing and diverse. Performance standards must take into consideration the new technologies on the horizon.
