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Metrology

What’s the Difference Between Laser Radar and LIDAR Technology?

These close cousins in the metrology field have distinct specialties

Published: Thursday, June 4, 2020 - 12:03

Confusion between the two terms “RADAR” and “LIDAR” is understandable. Their names are nearly synonymous, and the terms are often used interchangeably. The acronyms are RADAR, which stands for RAdio Detection And Ranging; and LIDAR, which stands for LIght Detection And Ranging. The major difference between the two is the wavelength of the signal and the divergence of the signal beam.

LIDAR is typically a collimated light beam with minimal divergence over long distances from the transmitter; RADAR is a cone-shaped signal fanning out from the source. Both calculate distance by comparing the time it takes for the outgoing wave or pulse to return to the source. LIDAR uses light wave frequencies that have a shorter wavelength, which enhances the capability of collecting data with high precision. RADAR uses longer microwave frequencies, which have lower resolution but the ability to collect signals with reduced impact from environmental obstructions. RADAR and LIDAR signals both travel at the speed of light.

LIDAR is used as a generic term for most light-based metrology technologies. Typical devices use laser beams, structured light mesh, even pulsed white light, based on the system’s design and application. All are used in radar-like fashion to measure the position of target points. They typically measure in three dimensions by monitoring a vertical angle, a horizontal angle, and the distance—or range—from the intersection of the vertical and horizontal axes. Similar to RADAR, some LIDAR systems measure in only two dimensions by monitoring a single angle and the range.

Knowing the similarities between RADAR and LIDAR, let’s now take a look at LIDAR vs. laser radar. By definition, LIDAR and laser radar refer to the same principle methodologies of measuring an object’s position. In the recent past, the term “laser radar” was adopted to define measurement systems designed to collect data with extremely high precision. This is done by using a narrowly focused light source of a specific wavelength or a combination of wavelengths. The low divergent beam is capable of focusing on small details with high return resolution.

For comparative purposes, let’s take a closer look at two laser-based scanning units.

Laser radar


Figure 1: Nikon MV351

Figure 1 shows a MV351, a “laser radar” system manufactured by Nikon Metrology, in which the laser beam is steered by rotating around horizontal and vertical axes. This unit sends a distinct, focused laser pulse to an object and reads the return signal as described above. Unlike laser tracking and other surveying instruments, it does not need to use a retroreflector. Its signal is the reflected light from the actual objects surface. It is engineered to provide precise, industrial measurements with tolerances of thousandths or even tenths of thousandths of an inch. The units have an effective range of measurement up to 150 ft in radius, although in practical use, the range is usually shorter.

Rather than taking large sweeps of an object, the laser radar system shown in figure 2, takes smaller scans of area where high accuracy and detail is the priority. Because of this, speed of data collection is sacrificed for resolution in comparison to LIDAR systems.


Figure 2: Nikon operating parameters

LIDAR


Figure 3: FARO FocusS

The photo in figure 3 is a FARO FocusS Plus laser scanner, a phase-based, long-range laser scanner or LIDAR system. This is a typical 3D-scanning unit used for large-scale data collecting at high speed. The laser emitter is fixed horizontally within the left half of the case and is pointed at the center of a rotating angled mirror that pulses a continuous series of laser beams into a plane perpendicular to the common axis of the laser and mirror. The entire case rotates on the base, as shown in figure 4, to provide measurements within a 360-degree horizontal arc. The resulting pattern of laser data produces what is referred to as a point cloud, a series of data points with x,y,z information that creates a digital 3D environment of any object or landscape which is scanned. The LIDAR system is capable of collecting large amounts of data in a very short amount of time.


Figure 4: FARO operating parameters

These two devices illustrate a key difference between LIDAR and laser radar: A LIDAR system is usually constantly in motion while gathering measurements. LIDAR continuously sweeps a laser beam over a large area to gather millions of points while the head is moving at a rapid speed. Laser radar, like the Nikon unit, is more of a point, stabilize, and measure device. It can be used to scan an area, but the points are carefully chosen, and acquired more slowly and accurately.

The cardinal distinction in these two systems is mostly acknowledged through applications. The term “LIDAR” is used frequently in surveying and mapping. Attach a laser-scanning LIDAR system to an aircraft or automobile, combine it with GPS or another orientation system, and you can map out large swathes of terrain or roadside. Other LIDAR examples are drone-mounted scanners or autonomous-vehicle guidance systems. The required accuracy for this kind of work can range from one-tenth of an inch to a foot; ranges can be thousands of feet, provided there is line-of-sight to the target. Portable “long-range” 3D laser scanners that measure rooms, buildings, aircraft, ships, or similarly sized objects to accuracies of 0.030–0.120 in. are also in the LIDAR category. This is the kind of LIDAR technology that is often used in construction or engineering.

Laser radar systems have found their value in measuring finely detailed objects. Their tightly focused beam is capable of collecting precise data points with high levels of resolution on a specific detail of an object. By minimizing the contact area, these systems will reduce the chance of corners and edges adversely affecting the return signal, resulting in precise dimensional data. Reaching targets that are difficult to access with handheld scanning devices has proven to be the most useful application of these systems. With accuracies in the realm of portable coordinate measuring machine (PCMM) devices, laser radar data are perfect for reverse engineering, inspection, and part-to-CAD comparison. Small details such as hole locations and diameters are easier to obtain with the more precise, focused beam of laser radar units. These systems have found a niche in the aerospace and automotive industry, where precision data ae easily obtained with minimal intrusion.

First published by East Coast Metrology.

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About The Authors

John Smits’s picture

John Smits

John Smits is the vice president of the AEC/3D Laser Scanning Division at East Coast Metrology.

Gary Confalone’s picture

Gary Confalone

Gary Confalone is the president and CEO of ECM Global Measurement Solutions. He has worked in the metrology industry for the past 20-plus years, including stints at Sikorsky Aircraft, SpatialMetrix Corp., and Laser Projection Technologies. In 2001 Confalone started East Coast Metrology, an engineering and service provider for the 3D metrology industry. He has been an active member of the Coordinate Metrology Society’s certification committee, which was formed to help qualify technical personnel in the various disciplines of 3D metrology.

Tom Kinnare’s picture

Tom Kinnare

Tom Kinnare is the director of engineering at East Coast Metrology.