Section 1 - General Information

1.1 Scope
This module is limited in scope to laser speed-measuring devices and systems used by law enforcement agencies to enforce vehicle speed regulations. It applies to devices that comply with FDA Class 1 eye safety regulations (§ 2.2.3).

1.2 Purpose
The purpose of this module is to specify minimum performance specifications and test procedures for lidar devices used by law enforcement agencies to enforce vehicle speed regulations.

1.3 Application
This document applies to laser speed-measuring devices and systems that transmit coherent infra-red light pulses, measure the time of flight for the pulses reflected from moving vehicles, then calculate and display or output the speed of the target vehicle, and may automatically record images of those vehicles which exceed a preset speed.

1.4 Definitions

1.4.1 Accuracy - the degree to which the lidar device measures and displays the speed of a vehicle.

1.4.2 Acquired Target - a vehicle that enters the beam of a lidar device, allowing for a measurement of its speed.

1.4.3 Ambient Interference - the conducted and/or radiated electromagnetic interference and/or mechanical motion interference at a specific test location and time that might be detrimental to proper lidar device performance.

1.4.4 Attended Operation - an operator is an integral part of the evidence acquisition process.

1.4.5 Automatic Lock - a control function of a lidar device that, when activated, causes the device to automatically retain the displayed speed of a target vehicle whenever the target speed exceeds some preset value, and to preserve that displayed speed until manually reset by the operator.

1.4.6 Certified Radar Unit - a radar unit selected from the IACP’s current Consumer Products List (CPL) that has been modified by its manufacturer to display speed in one-tenths units and certified by an IACP-approved testing laboratory to be accurate to within +0.2 km/h, -0.3 km/h (+0.1 mph, -0.2 mph) over a speed range of 32 km/h to 144 km/h (20 mph to 90 mph).

1.4.7 Closing Speed - the speed at which a target is moving toward the speed-measuring device, measured as the rate of change of the distance separating the device and the target.

1.4.8 Cosine Angle Effect - the discrepancy between the target vehicle's speed along its path and the closing speed measured by the device.

1.4.9 Display - a visual readout device.

1.4.10 Erroneous Reading - an incorrect target speed displayed by the lidar device that is not due to a target vehicle, or which is not within the required accuracy tolerance of a target vehicle's speed after accounting for the cosine angle effect.

1.4.11 Functional Beamwidth - the angular range over which a small, stationary retro reflective target can be detected against a background of sky or distant scenery.

1.4.12 Horizontal Beamwidth - the functional beamwidth measured in the horizontal plane, usually expressed in milliradians (mrad).

1.4.13 I/O Port - Input/Output interface for connecting external devices to the lidar unit.

1.4.14 Laser Speed-measuring Device - a lidar unit.

1.4.15 LCD - Liquid Crystal Display; a type of electronic display.

1.4.16 LED - Light Emitting Diode; a type of electronic display.

1.4.17 Lidar - (from LIght Detection And Ranging) the technology of measuring target range using reflected light. In today's engineering usage lidar includes many intricate devices, but this standard is concerned with the class of lidar devices that determine target range and speed from the time-of-flight of laser pulses.

1.4.18 Lidar Device (Unit) - down-the-road speed-measuring equipment which, determines target range and speed based on the time-of-flight of laser light pulses reflected off a target. Lidar device is synonymous with "laser speed-measuring device" and “lidar unit” for the purpose of this standard.

1.4.19 Lidar System - a lidar device that incorporates additional equipment that is used to gather, process and/or recorded images to be used as part of speed enforcement efforts.

1.4.20 Nominal Value - the numerical value of a performance characteristic of a device as specified by the manufacturer or as used for identification. For instance, vehicle batteries often have a nominal voltage of 12 V, although in normal driving the terminal voltage can be above 14 V.
1.4.21 Operational Test - a test involving realistic conditions of operation. For instance, a lidar unit receiving its power from a stationary patrol vehicle and used to measure the speed of another vehicle traveling at a known speed.

1.4.22 Range - the distance from the reference plane of the lidar unit to the point where the transmitted beam strikes the target, for which valid distance measurements can be acquired.

1.4.23 Recorded Images - images recorded on photographs, microphotographs, electronic images, videotape, or any other medium.

1.4.24 Remote Control - a means by which many functions of the lidar unit can be controlled through a computer or a separate control panel.

1.4.25 Remote Trigger - a means by which the lidar unit can be triggered remotely. It is envisioned (though not required) that a remote control would involve a two-way computer data link, while a remote trigger can be as simple as a pair of wires leading from a switch to the lidar unit.

1.4.26 RS-232 - an Electronics Industries Association (EIA) standard for serial digital communications. Historically, this standard was put into wide use before the details were well-defined, and it was often a challenge to interconnect two devices claiming to meet RS-232 specifications. In the 1980s, following the adoption of standard RS-232 by EIA, implementation became more consistent.

1.4.27 Serial Port - a module within a computer or a computerized instrument which permits communication over a cable. The individual bits of a data byte are sent or received one after the other, or "serially."

1.4.28 Target Discrimination - the ability of a speed-measuring device to differentiate between target vehicles.

1.4.29 Target Speed - the speed of the target vehicle along its path, with respect to the ground.

1.4.30 Target Speed Simulator - a laboratory device capable of receiving light pulses from a lidar unit and then sending return pulses with changing delays. The changing delays simulate a target vehicle moving at a specified speed and direction, and at a particular range.

1.4.31 Target Vehicle - the vehicle at which the lidar unit is aimed using the unit’s visual sighting device.

1.4.32 Unattended Operation - an operator is not an integral part of the evidence acquisition process.

1.4.33 UUT - unit under test.

1.4.34 Unit Under Test - a lidar device or lidar system whose performance is being tested, as distinguished from other equipment used to do the test.

1.4.35 Vertical Beamwidth - the functional beamwidth measured in the vertical plane, usually expressed in milliradians (mrad).

1.5 Units of Measure

This document is a specification for practical measuring devices of comparatively low precision. We have attempted to develop specifications that are practical, whether the UUT reads in kilometers per hour (km/h) and meters (m), or miles per hour (mph) and feet (ft). The speed accuracy requirement as stated below is +2 km/h, -3 km/h (+1 mph, -2 mph). Direct conversion from km/h to mph would give a tolerance band of +1.24 mph, -1.86 mph. Practical lidar devices read to integer precision only, so some decision must be made in order to give the tolerances in integers.

The same spirit of practicality is carried over into other measurements. For instance, to check a lidar device's distance measurement function, two somewhat arbitrary baselines are needed, as specified in §2.4.1. One baseline shall be in the range of 6 m (20 ft) to 30 m (100 ft), and the other shall be at least 90 m (300 ft). Again, the conversions are not exact.

In the simulator software, the settings for the primary system of units are those that are appropriate for the UUT. These determine the ranges and units of most inputs and outputs. Again, some liberty was taken in rounding the range limits. The presence of round-off discrepancies should not motivate sloppy measurement. When the actual baseline is set up, it should be measured by surveying methods to an accuracy of 1 cm or better. Also, if the measured baseline is, for instance, 90 m (295.28 ft), a traditional-units lidar device should be moved forward 0.28 ft from the fiduciary mark, so that it is presented with a less ambiguous measurement task.