What is long-range LiDAR scanning? Measurement range, accuracy, and use cases explained in 7 minutes

In recent years, LiDAR (pronounced "Lidar"), a 3D measurement technology, has attracted attention as a method that uses laser light to measure the surrounding environment and acquire three-dimensional point cloud data. Among these, long-range LiDAR scanning is characterized by its ability to measure distant objects, and its use is advancing in a variety of fields such as wide-area topographic surveying and environmental perception for autonomous vehicles. This article explains the overview and mechanism of long-range LiDAR scanning, how far it can measure, how accurate it is, and concrete use cases so that you can understand them in about seven minutes. Finally, we also touch on new developments enabled by combining this technology with high-precision positioning devices that support it.

Table of Contents

• What is long-range LiDAR scanning

• Measurement distance of long-range LiDAR scanning

• Accuracy of long-range LiDAR scanning

• Use cases of long-range LiDAR scanning

• Summary

What is long-range LiDAR scanning?

LiDAR stands for "Light Detection and Ranging" and is a technology that calculates the distance to a target by emitting laser light toward the target and measuring the flight time (Time of Flight) until the light reflects and returns. By recording the many obtained distance measurements as a collection of points (a point cloud), it can capture the three-dimensional shape of the surrounding environment with high accuracy. Unlike conventional cameras or photogrammetry, LiDAR emits its own light and directly measures distance, so it can operate at night and acquire actual-size shapes of objects regardless of their color or pattern.

Long-range LiDAR scanning, as the name suggests, refers to LiDAR measurement capable of measuring at long distances. General laser scanners can measure from tens to hundreds of meters (tens to hundreds of ft) ahead, but long-range-capable devices can detect objects separated by more than several hundred meters (more than several hundred ft). This is achieved by adopting the time-of-flight (ToF) measurement method and combining high-power laser pulses with high-sensitivity sensors. Triangulation-based proximity sensors (such as industrial displacement sensors and smartphone face-recognition sensors) can be highly accurate but are limited to measurement ranges of around a few meters (around a few ft); LiDAR’s time-of-flight measurement, however, allows it to achieve both wide measurement range and high accuracy.

The growing attention on long-range LiDAR scans, where laser beams reach distant targets, stems from improvements in safety and efficiency. For example, surveying vast areas that used to be done manually and time-consumingly can, with long-range-capable laser scanners, be performed from a remote position in one go, enabling data acquisition from afar and significantly reducing work time. Also, on fast-moving platforms such as autonomous vehicles, it is necessary to detect distant obstacles as early as possible, so LiDAR capable of long-range detection is indispensable. In this way, long-range LiDAR scans that can accurately capture distant objects without contact are becoming increasingly valuable across a variety of sites.

Measurement range for long-range LiDAR scans

How far long-range LiDAR scans can actually measure depends on the performance of the equipment used and the surrounding conditions. Typical ground-based 3D laser scanners can measure an area with a radius of several hundred meters (several hundred ft) at once, and especially high-performance models can sometimes acquire point clouds of targets up to 800 m (2624.7 ft) to 1000 m (3280.8 ft) away. Vehicle-mounted LiDAR for autonomous driving includes long-range types that can detect pedestrians and vehicles about 200 m (656.2 ft) to 300 m (984.3 ft) ahead while driving, and some advanced sensors have been reported to detect low-reflectivity dark objects at about 250 m (820.2 ft) and bright objects up to 500 m (1640.4 ft) ahead. Airborne LiDAR for surveying the ground from the air (drone-mounted LiDAR or aerial laser surveying) can also scan terrain and structures from several hundred meters (several hundred ft) above and obtain useful data.

However, the measurement distance of LiDAR is greatly affected by the nature of the target and environmental conditions. Laser light only returns to the sensor after striking the target, but if the target is a black object or a material that easily absorbs light, the returned light becomes very weak and the measurable range shortens. Conversely, brightly colored objects or highly reflective materials such as metals are easier to detect from relatively long distances. Also, when rain, fog, or dust is present in the air, the laser beam scatters and attenuates, so in bad weather the measurable range can be shorter than expected. Under strong sunlight during the day, increased ambient light noise can reduce the sensor’s sensitivity and somewhat limit the maximum range. Therefore, even long-range LiDARs advertised in catalogs as "maximum 800 m (2624.7 ft)" may only be able to stably measure to somewhat shorter distances in real-world field environments, so caution is necessary.

Key technical elements for extending LiDAR range are the laser wavelength and output. Many commercially available LiDAR systems use infrared lasers in the 905 nm band; although this wavelength is invisible to the human eye, at high power it can be harmful to the retina, so safety standards limit laser intensity. By contrast, lasers in the 1550 nm band are absorbed by the cornea, making them less likely to reach the retina, which allows relatively higher-energy pulses to be emitted under the same safety standards and thus enables light to reach longer distances. For this reason, in recent years long-range LiDAR systems using 1550 nm lasers have emerged that achieve detection ranges in the 500 m (1640.4 ft)-class. However, because longer wavelengths tend to increase the cost of sensors and optics, they are chosen according to application. In any case, selecting a LiDAR system that matches the required measurement range and taking into account site illumination and weather conditions will maximize the capability of long-range LiDAR scanning.

Because LiDAR is an optical measurement method, it can only measure within the range that the laser light reaches (within the line of sight). Areas that fall in the shadow of buildings or in terrain occlusions cannot be captured in a single scan; therefore, to record a large area comprehensively, you must either relocate the equipment to multiple positions to fill those blind spots or combine the survey with mobile measurements using drones or vehicles.

Accuracy of long-range LiDAR scans

Next, let's look at accuracy for long-range LiDAR scans. Although "accuracy" is a single term, there are two aspects: "distance measurement error (spatial accuracy)" and "how much detail can be captured (resolution and point density)." First, regarding distance measurement error, catalog specifications for high-performance laser scanners commonly state range-direction errors on the order of ± several millimeters. For example, some high-end terrestrial LiDAR units publish very small values such as "distance error ±1 mm (±0.04 in)." However, such values only indicate the instrument's performance under ideal conditions. In actual outdoor measurements, slight increases in error are unavoidable due to various factors such as the aforementioned weather and temperature, the material of the target object, and even glare from the ground. In typical field situations, it is realistic to expect that even good-quality LiDAR scans will fall within an error range of several millimeters to several centimeters. Even so, as a non-contact method capable of measuring from long distances, it can be said to offer extremely high accuracy. Also, because a very large number of points can be acquired, even if each point has a slight error, these errors are statistically averaged, which helps improve the accuracy of the overall shape. For example, just as fitting a plane to many points smooths out random errors and can yield millimeter-scale dimensions, point cloud data can also be expected to gain accuracy from the sheer quantity of points.

It is also necessary to pay attention to resolution and point density, another component of accuracy. In LiDAR scanning, many points are acquired by scanning the laser emission direction at very fine intervals, but the fineness of detail that can be reproduced is determined by that interval (angular resolution) and the size of the laser spot. Even if point clouds with millimeter-scale intervals (a few tenths of an inch) are obtained for nearby objects, with the same equipment targets several hundred meters (several hundred ft) away will have much larger spacing between points because the distance amplifies the angular step of the laser emission. Also, because the laser beam itself slightly diverges during propagation, the spot diameter becomes larger at long range, and small gaps and fine details tend to be aggregated into single points and become difficult to capture. As a result, the farther the target, the lower the fidelity (resolution) of fine shapes and the lower the density of the point cloud that can be obtained. Therefore, extremely thin targets such as power lines or cracks located, for example, 100 m (328.1 ft) away can be difficult to detect with long-range LiDAR. The important point is to plan measurements taking into account that accuracy (errors) worsens somewhat and resolution decreases at long range. Measures such as combining detailed scans from short range as needed or increasing the number of scanner positions to compensate for resolution should be considered.

In addition, securing the absolute accuracy of long-range LiDAR scans (accuracy with respect to the positioning coordinate system) requires careful alignment. When measuring single instances with fixed-installation LiDAR, the acquired point cloud data are recorded in relative coordinates referenced to the device installation location. When integrating data scanned from multiple locations, or when measuring over long distances while continuously traveling in mobile mapping (LiDAR mounted on moving platforms), aligning (localizing) the individual point clouds is important. By georeferencing (linking to geodetic coordinates) using latitude/longitude information obtained from GPS and GNSS (Global Navigation Satellite System) and known control points as appropriate, the accuracy of large-scale point cloud data can be improved. In particular, with vehicle-mounted or drone-mounted LiDAR, small errors in the sensor’s self-position estimation can accumulate so that positional offsets of several centimeters or more (several in or more) occur toward the end of long-distance movements. For that reason, practices such as applying high-precision position corrections at key points or driving in looped paths to cancel out errors are commonly implemented.

Applications of Long-Range LiDAR Scanning

Long-range LiDAR scanning is being utilized in various fields to take advantage of its benefits. Here, we introduce several representative use cases.

Civil surveying and topographic investigation: Ground-based long-range laser scanners are suitable for surveying extensive terrain and structures in a short time. For example, by installing laser scanners along road or tunnel routes, it is possible to measure the terrain and structures around roads extending over several kilometers (several thousand ft) all at once. In practice, mobile mapping systems with LiDAR mounted on vehicles can safely collect highway pavement profiles and roadside assets while driving, and these data are being used to support road design and infrastructure maintenance management. Conventional as-built surveys, which previously required enormous time and manpower when performed manually, can be greatly streamlined and made more efficient by utilizing long-range LiDAR scanning.

Measurement of buildings and structures: Long-range LiDAR scanning is also highly effective for surveying large-scale structures such as high-rise buildings, bridges, and plant facilities. Building façades, chimneys, and transmission towers can be difficult to measure up close, but by scanning with lasers from a distance you can capture the entire structure’s 3D shape while remaining in a safe location. This yields the data needed for creating building elevation drawings, inspecting structural integrity, and monitoring displacement. In particular, the ability to perform precise measurements remotely—without erecting scaffolding or using aerial work platforms—offers significant benefits for both safety and cost reduction.

Autonomous driving and traffic: As mentioned at the outset, LiDAR plays an important role as a sensor for autonomous vehicles (robot cars). By equipping a vehicle with long-range LiDAR sensors, it can detect vehicles, pedestrians, and obstacles ahead early, enabling smoother lane changes and deceleration. For example, when driving on the highway at 100 km/h, detecting an object 100 m (328.1 ft) ahead gives approximately 3.6 seconds of lead time, while a detection range of 200 m (656.2 ft) provides twice that time to respond. This expands the safety margin and directly reduces risk in emergencies. Because LiDAR can stably capture distance and shape even at night and in rain, it is used alongside cameras and millimeter-wave radar as the "eyes" of autonomous driving to provide 360-degree monitoring around the vehicle.

Drone surveying and aerial mapping: By equipping a drone (UAV) with a compact LiDAR unit, wide-area 3D laser surveying can be conducted from the air. Situations that previously required heavy machinery and manpower—such as surveying terrain on steep slopes that people cannot enter or assessing conditions at large-scale landslide sites—can be handled using drone LiDAR to acquire detailed topographic data from above in a short time. In forest tree measurement, emitting lasers from above allows the point cloud to reach not only the canopy but also the forest floor, capturing ground surface undulations that are not visible in aerial photographs, thereby contributing to forest resource surveys and the discovery of buried ruins. Long-range LiDAR scanning from the air is expected to have broad applications beyond surveying, including agriculture (understanding land drainage conditions, etc.) and environmental monitoring (observing coastline and river erosion, etc.).

Disaster prevention and maintenance: The use of long-range LiDAR is advancing in the disaster management field as well, such as deformation monitoring of river levees and hillsides and monitoring of landslide sites. Even without people entering hazardous locations, distant laser scanning can capture signs of collapse and rapidly assess damage after disasters. In power line patrol inspections, lasers are also used from the ground to measure the height of power lines and surrounding trees, helping to determine necessary tree trimming and conservation measures. By comparing fixed-point observation data from long-range LiDAR scans over time, it is possible to detect minute changes and degradation trends in infrastructure, which aids preventive maintenance and planned maintenance.

Summary

Long-range LiDAR scanning is a groundbreaking method that, using laser measurement technology, can capture distant objects with high accuracy and safety. In terms of measurement distance, with appropriate equipment selection and environmental conditions it is possible to measure targets up to several hundred meters (several hundred ft) away, enabling the rapid acquisition of wide-area data that would have been difficult to obtain manually. In terms of accuracy, compared with conventional optical ranging methods there is less degradation of accuracy with distance, and by analyzing the obtained point cloud data you can utilize information on the order of millimeters to several centimeters (mm to cm, mm to in / cm to in). However, as distance increases there are challenges such as decreased data resolution and accumulation of sensor positional errors, so it is important to combine multiple methods and apply corrections as necessary.

To address these challenges, peripheral technologies that provide accurate positional coordinates to LiDAR point clouds have advanced in recent years. One such technology is position correction using high-precision GNSS (Global Navigation Satellite System). For example, by using the LRTK, a GNSS high-precision positioning device that can be attached to an iPhone, it is possible to associate centimeter-level position information (cm level accuracy (half-inch accuracy)) with collected point cloud data in real time. By leveraging solutions like LRTK (an iPhone-mounted GNSS high-precision positioning device), high-precision geodetic coordinates can be assigned even to wide-area point clouds obtained by long-range LiDAR scanning, dramatically increasing the reliability of surveying results. These new measurement solutions are strongly supporting on-site digital transformation (DX). By combining long-range LiDAR scanning with the latest positioning technologies, we can safely and efficiently drive the digitization of worksites.