Lidar has a wide range of applications; one use is in traffic enforcement and in particular speed limit enforcement, has been gradually replacing radar since 2000.[1] Current devices are designed to automate the entire process of speed detection, vehicle identification, driver identification and evidentiary documentation.[2]
Police officer operating a hand-held lidar speed detection device
History
Jeremy Dunn (Laser Technology Inc.) developed a police lidar device in 1989,[3] and in 2004 10% of U.S. sales of traffic enforcement devices were lidar rising to 30% in 2006,[1] given the advantages of lidar it appears likely that the majority of current sales are lidar, although sophisticated radar units are still being sold.[4]
Current units combine five operations; speed detection; operator viewing, even under adverse conditions; imaging synchronised with speed detection; acquisition of court ready evidence; downloading of evidence to an external device. They can operate in automatic mode either attended or unattended.[5]
Advantages of lidar over radar
Radar has wide signal beam divergence,[3] so that an individual vehicle cannot be targeted, requiring significant operator skill, training and certification in order to visually estimate speed so as to locate an offender in a traffic stream, and offenders may use the defence that some other vehicle was offending. Radar will register the speed of any object in its field, for example a tree swaying or an airplane passing overhead.[1]
Lidar has a narrow beam, and easily targets an individual vehicle, thereby eliminating the need for visual estimation,[3][1] and some models can record an image of the license plate at the same instant as recording the speed violation. Speed estimation takes less than half a second, which, together with the narrow, targeted beam, results in offending vehicles having little warning even when using an evasion device. Lidar can measure the distance between vehicles to detect 'too close' (tailgating) infringements. The speed of a vehicle occluded by (hidden behind) another vehicle cannot be measured.
Lidar specifications
The US Department of Transportation National Highway Traffic Safety Administration (NHTSA) has issued specifications for lidar devices,[6] a conforming products list,[7] and guidelines regarding implementation of traffic enforcement.[8]
A typical NHTSA approved[7] device weighs less than 2 kilograms, is battery powered, has speed detection accuracy +2km/h and -3km/h, distance accuracy +- 0.3 metres at 90 metres, and minimum long-range measurement capability of 300 metres. Devices must be capable of meeting these accuracy standards while exposed to ambient temperatures between -30°C and 60°C, relative humidity of 90% at 37°C and normal urban road ambient electromagnetic radiation. The range of speeds required to be accurately detected is 16km/h to 320km/h. In some jurisdictions speeding violations are required to be documented by the device with a recorded image showing license plate, location, speed, date, time and operator identification, some units identify the driver by image and record the direction of travel.[2] The light emitted is required to be in the infrared range, meet eye safety standards, and have pulse repetition less than one kHz with beam divergence less than 5 milliradians.
Registration plates
Vehicle registration plates are an important part of traffic enforcement and in most jurisdictions the government holds a monopoly on their manufacture, although this may be contracted out. Normally it is illegal for private citizens to modify, make and affix their own plates, as this is equivalent to forging an official document. California plates are required to be 6in tall and 12in wide, a usual standard, and have a reflective surface that is particularly sensitive to infrared light,[9] which enables it to be imaged at night, enables Automatic License Plate Recognition, allows LIDAR devices to receive a strong reflective signal return, and have tamper-resistant markings.
Some jurisdictions do not require a front license plate on automobiles and many do not require them on certain vehicles such as motorcycles. Police generally prefer to detect from the front while observing oncoming traffic, which also enables the offender to be waved over and avoid the risks of high speeds required to catch up to the vehicle.
Evasion
A number of jurisdictions prohibit any methods to thwart speed limit enforcement, and lidar manufacturers endeavour to stay ahead of detection avoidance measures.
Current lidar devices have a horizontal beam width of one meter at 300 meters, compared to the registration plate width of 30cm, ensuring that little of the signal is scattered to following vehicles. Detecting the LIDAR signal in advance is difficult as the tight beam, short signal duration and targeting of individual vehicles minimizes scatter of the LIDAR signal to following or adjacent vehicles. Modifying the vehicle to deflect, absorb or jumble the signal is difficult, as it is typically the registration plate that is targeted. Modifying the registration plate is easily detected and may not be legal. Returning a false separate signal will be detected by current police lidar models and may not be legal, depending on the jurisdiction.
Principle
A typical NHTSA approved[7] lidar device emits 30 ns pulses of laser light with wavelength 905 nm and 50 milliwatts of power with 3 milliradian beam divergence. The power is sufficiently low to ensure no ocular damage occurs. At 905nm wavelengths, IEC 60825-1 Edition 2.0 allows a maximum energy per pulse of 0.5uJ.
Light travels approximately 30cm per ns so each pulse has a length of about nine metres. At a target distance of 300 metres the light pulses take 2,000 ns to complete the round trip. The time interval between pulses is no less than one million ns, providing time to make a distance estimation from each pulse. Up to several hundred pulse readings are taken over a period less than half a second and used to estimate the change in distance over time, thereby estimating vehicle speed. Returning light is filtered to exclude light not in the wavelength range 899nm to 909nm. An internal proprietary algorithm rejects inaccurate readings; detection avoidance methods usually attempt to overload the filter and persuade the error rejection algorithm to incorrectly reject a reading.
Operation
An expert operator will use the viewing capability to select a likely offender prior to speed detection, this has the advantage that minimum signal is scattered to warn following vehicles equipped with lidar signal detection devices, this is not so important on sparsely trafficked roads and a lower capability lidar device may be used. Once a likely offender is detected and the registration plate targeted the operator triggers speed detection which includes acquisition of evidence, an audible tone indicates a good return signal. To produce an accurate reading the operator must focus the pulse on a single point for the duration of the read. At long range this is accomplished through the use of a stationary tripod to steady the aim. For speed detection any part of the vehicle may be targeted, although the registration plate is highly preferred.
Limitations
Normal weather conditions have negligible impact on device performance but may impede operator ability to target a vehicle. This includes occasions when the sun is directly behind the target vehicle, nighttime, or when the device is used within a stationary vehicle with a soiled windshield, in which case the signal might be scattered. Heavy weather may reduce the range of the device and in particular heavy fog will render it unusable.
When used within a moving vehicle, the device measures the relative speed of the police and target vehicle.
Sweeping the device while taking a reading so that (particularly at long range where angular separation between targets is slight) returning pulses from more than one target creates a false reading. Sweeping along the side of a vehicle may also cause false readings.
A false reading is produced when the pulse reflects off for example a wing mirror, hits a stationary reflective object and then returns to reflect off the mirror a second time.
Use in court
United States
In 2008, the D.C. Superior Court upheld the admissibility of lidar evidence in its jurisdiction. In addition to expert testimony, the court noted that it factored scientific publications into its decision:
The Court conducted an extensive four-day Frye [Daubert] hearing... [in which it] considered such issues as the basic science of laser technology, the technical methodology of, and theoretical challenges to, the reliability of radar guns... including the possibility of other “pulses” in the vicinity of use, difficulties in target identification, possible errors caused by vehicle license plates, windshield glass, shape, and color, and potential malfunction of the device. The Court also took judicial notice of at least six scientific publications on the subject in various journals of interest, together with two police-related studies in Florida, one New Jersey [study], and one independent study in Florida on this and similar radar devices, all of which met the standards set forth by [the] National Highway Safety Administration...
The court also noted that not a single court had conducted full-blown hearings on the issue that found LiDAR unreliable, while more than a dozen jurisdictions had decided that lidar is reliable.[10]
Detectors and jammers
Passport x50 Radar/Laser detector
A lidar detector or laser detector is a passive device designed to detect infrared emissions, especially those of law enforcement agencies' lidar speed detection devices, and warn motorists that their speed is being measured.
A limitation of lidar is that it cannot be used while a police car is in motion, because it requires the operator to actively target each vehicle, whereas traditional radar can be operated while the police officer is driving. Other restrictions include a precipitation-free environment, as the laser can produce erratic readings from airborne moisture or smoke.[11] Popularity of lidar speed detection is on the rise, though, as costs decline, ease of operation approaches radar and existing radar equipment reaches its end-of-service life and is rotated out of service.
Lidar detectors are generally less effective than radar detectors as the emissions they monitor are briefer, more concentrated and less easily scattered than radar. A motorist may therefore not have sufficient time to respond to the burst transmission of a lidar device, or the narrow beam might be focused on a specific part of a vehicle where the sensor cannot detect it.
A laser jammer or lidar jammer is an electronic device used by drivers to prevent users of a LIDAR (or laser) gun from obtaining speed readings of their vehicle. Laser jammers are not to be confused with radar jammers.
To jam LIDAR, laser jammers first must detect the emitted light, normally infrared light on the 904nm wavelength.[12] After detecting the lidar gun's light, the jammer will send out light on the same wavelength at a higher intensity, effectively confusing the gun into returning no speed reading. Newer laser jammer models can detect the pulse rate (the rate at which the gun takes distance measurements, upon which it bases the speed measurement) of the laser gun, and then emulate that pulse rate, further increasing the difficulty of getting an accurate reading from the laser gun.
Laser jammers for civilian use have evolved in recent years. The first laser jammer ever produced was by K40 Electronics in April 1994, known as the K40 Laser Defuser. Next came the Lidatek LE-10 Laser Echo by Lidatek LLC, then the Blinder M06 HP by blinder.dk, then the Blinder M10 Twin, then the LE-20 to LE-30. Blinder remade the M10 Twin into the smarter M20 X-treme series. Laser diode based jammers came out in 2006, known as the Anti-Laser, Laser Pro Park, and Privacy-Plate is using the newest technology that only jams and does not safeguard privacy by blocking IR cameras from performing Image Recognition on a vehicle's license plate. Most cameras take 1 photo with normal light and 1 with IR light meaning the camera can take an image without interference .
Radar is a radiolocation system that uses radio waves to determine the distance (ranging), angle (azimuth), and radial velocity of objects relative to the site. It is used to detect and track aircraft, ships, spacecraft, guided missiles, and motor vehicles, and map weather formations, and terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the objects. Radio waves from the transmitter reflect off the objects and return to the receiver, giving information about the objects' locations and speeds.
Lidar is an acronym of "light detection and ranging" or "laser imaging, detection, and ranging". It is a method for determining ranges by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It is sometimes called 3-D laser scanning, a special combination of 3-D scanning and laser scanning. LIDAR has terrestrial, airborne, and mobile applications.
A Doppler radar is a specialized radar that uses the Doppler effect to produce velocity data about objects at a distance. It does this by bouncing a microwave signal off a desired target and analyzing how the object's motion has altered the frequency of the returned signal. This variation gives direct and highly accurate measurements of the radial component of a target's velocity relative to the radar. The term apply to radar systems in many domains like aviation, police radar detectors, navigation, meteorology, etc.
A traffic enforcement camera is a camera which may be mounted beside or over a road or installed in an enforcement vehicle to detect motoring offenses, including speeding, vehicles going through a red traffic light, vehicles going through a toll booth without paying, unauthorized use of a bus lane, or for recording vehicles inside a congestion charge area. It may be linked to an automated ticketing system.
Semi-automatic command to line of sight (SACLOS) is a method of missile command guidance. In SACLOS, the operator must continually point a sighting device at the target while the missile is in flight. Electronics in the sighting device and/or the missile then guide it to the target.
Time of flight (ToF) is the measurement of the time taken by an object, particle or wave to travel a distance through a medium. This information can then be used to measure velocity or path length, or as a way to learn about the particle or medium's properties. The traveling object may be detected directly or indirectly.
A radar speed gun, also known as a radar gun, speed gun, or speed trap gun, is a device used to measure the speed of moving objects. It is commonly used by police to check the speed of moving vehicles while conducting traffic enforcement, and in professional sports to measure speeds such as those of baseball pitches, tennis serves, and cricket bowls.
The pulse repetition frequency (PRF) is the number of pulses of a repeating signal in a specific time unit. The term is used within a number of technical disciplines, notably radar.
A radar detector is an electronic device used by motorists to detect if their speed is being monitored by police or law enforcement using a radar gun. Most radar detectors are used so the driver can reduce the car's speed before being ticketed for speeding. In general sense, only emitting technologies, like doppler RADAR, or LIDAR can be detected. Visual speed estimating techniques, like ANPR or VASCAR can not be detected in daytime, but technically vulnerable to detection at night, when IR spotlight is used. There are no reports that piezo sensors can be detected. LIDAR devices require an optical-band sensor, although many modern detectors include LIDAR sensors. Most of today's radar detectors detect signals across a variety of wavelength bands: usually X, K, and Ka. In Europe the Ku band is common as well. The past success of radar detectors was based on the fact that radio-wave beams can not be narrow-enough, so the detector usually senses stray and scattered radiation, giving the driver time to slow down. Based on a focused laser-beam, LIDAR technology does not suffer this shortcoming; however it requires precise aiming. Modern police radars incorporate formidable computing power, producing a minimum number of ultra-short pulses, reusing wide beams for multi-target measurement, which renders most detectors useless. But, mobile Internet allows GPS navigation devices to map police radar locations in real-time. These devices are also often called "radar detectors", while not necessary carrying an RF sensor.
A pulse-Doppler radar is a radar system that determines the range to a target using pulse-timing techniques, and uses the Doppler effect of the returned signal to determine the target object's velocity. It combines the features of pulse radars and continuous-wave radars, which were formerly separate due to the complexity of the electronics.
A laser rangefinder, also known as a laser telemeter, is a rangefinder that uses a laser beam to determine the distance to an object. The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in a narrow beam towards the object and measuring the time taken by the pulse to be reflected off the target and returned to the sender. Due to the high speed of light, this technique is not appropriate for high precision sub-millimeter measurements, where triangulation and other techniques are often used.
Radar jamming and deception is a form of electronic countermeasures that intentionally sends out radio frequency signals to interfere with the operation of radar by saturating its receiver with noise or false information. Concepts that blanket the radar with signals so its display cannot be read are normally known as jamming, while systems that produce confusing or contradictory signals are known as deception, but it is also common for all such systems to be referred to as jamming.
VASCAR is a type of device for calculating the speed of a moving vehicle. The first VASCAR device was created in 1966 by Arthur Marshall. It is used by police officers to enforce speed limits, and may be preferred where radar or lidar is illegal, such as some jurisdictions in Pennsylvania, or to prevent detection by those with radar detectors.
An atomic line filter (ALF) is a more effective optical band-pass filter used in the physical sciences for filtering electromagnetic radiation with precision, accuracy, and minimal signal strength loss. Atomic line filters work via the absorption or resonance lines of atomic vapors and so may also be designated an atomic resonance filter (ARF).
Electro-optical MASINT is a subdiscipline of Measurement and Signature Intelligence, (MASINT) and refers to intelligence gathering activities which bring together disparate elements that do not fit within the definitions of Signals Intelligence (SIGINT), Imagery Intelligence (IMINT), or Human Intelligence (HUMINT).
Speed limits are enforced on most public roadways by authorities, with the purpose to improve driver compliance with speed limits. Methods used include roadside speed traps set up and operated by the police and automated roadside 'speed camera' systems, which may incorporate the use of an automatic number plate recognition system. Traditionally, police officers used stopwatches to measure the time taken for a vehicle to cover a known distance. More recently, radar guns and automated in-vehicle systems have come into use.
LEDDAR is a proprietary technology owned by LeddarTech. It uses the time of flight of light signals and signal processing algorithms to detect, locate, and measure objects in its field of view.
Counter-IED equipment are created primarily for military and law enforcement. They are used for standoff detection of explosives and explosive precursor components and defeating the Improvised Explosive Devices (IEDs) devices themselves as part of a broader counter-terrorism, counter-insurgency, or law enforcement effort.
Atmospheric lidar is a class of instruments that uses laser light to study atmospheric properties from the ground up to the top of the atmosphere. Such instruments have been used to study, among other, atmospheric gases, aerosols, clouds, and temperature.
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