LiDAR Technology

LiDAR Technology and its Impact on Demining

Purpose:LiDAR Technology and its impact on Demining
Last Updated: June 2024

Abstract:

     Over the past couple of decades, Light Detection and Ranging (LiDAR) technology has become common in many areas. Military applications are no exception, where LiDAR is used to detect explosive objects and mines on the earth’s surface. This article discusses the use of LiDAR in searching for mines and unexploded ordnance and how it complements modern technology.

The sections covered will be Introduction to LiDAR, Current Demining, and its Technology, and How LiDAR can help with demining. The conclusion will summarize the benefits of using LiDAR for demining by comparing it to its counterparts.

Section 1. Introduction to LiDAR

The first step is to get acquainted with the basic principles of LiDAR. The term LiDAR is short for light detection and ranging. LiDAR is a geospatial technology based on the emission and transmission of a focused light wave and measuring the time it takes to reflect from an obstacle. Light is reflected back to the sensor when a LiDAR laser beam hits an object like a tree or building. By timing the exact return of each laser pulse, the LiDAR system can calculate the distance to each reflected point. These calculations are based on the time-of-flight (ToF) method, according to which the speed of light is considered constant.

Figure 1. Conditional demonstration of LiDAR operation.

Each collected point forms a “point cloud” – a three-dimensional display of the scanned area in dots.

The main differences between LiDAR models are the scanning angle, maximum range, return count, and accuracy. Most modern LiDARs can operate in several scanning modes. For example, the XT32 can adjust the rotation speed, scanning angle, and the number of returns, affecting the density of the point cloud and the penetration ability of lasers under trees, grass, etc.

The combination of LiDAR technology and an inertial navigation system (INS) manufactures a system by which each point can be geo-referenced with centimeter precision and accuracy [1]. An example of a device that takes advantage of these is the Inertial Labs RESEPI Payload [2]. RESEPI Payload is a small package fully customizable to suit any use case. Users can select a configuration with a camera, LiDAR model, and GNSS receiver. The most common use is on drones and other types of sUAS (small, unmanned aircraft systems).

After LiDAR payloads collect data, sending the raw data through post-processing is necessary before obtaining the point cloud. For this, companies like Inertial Labs have developed special software – PCMasterPro [3]. The software does not require preliminary preparation; all operations are performed semi-automatically. Everything is designed for easy use within the full hardware and software package.

Section 2. Current Demining and its Technology

LiDAR technology systems installed on unmanned aerial vehicles (UAV) can be used to survey areas to determine the presence of mines and other explosive objects. The figure below shows an undetonated mine. Searching for these unexploded shells, mines, and other explosive objects is a long and dangerous process.

Figure 2. Example of unexploded landmine.

Landmines pose a severe threat to civilians in conflict-affected regions. “According to the Monitor report, 4,710 people were injured or killed by landmines and explosive remnants of war (ERW) across 49 states and two other areas in 2022” [4].

There are many other methods used to clear landmines. Some of which can be briefly reviewed below.

  • Geolocation radars. The operating principle of georadar devices is based on the emission of radio waves reflected from mines, stones, pipes, and other objects in the soil. Unlike metal detectors, ground penetrating radars can detect non-metallic shells of mines. The wavelengths of the emitters may vary; short waves provide better image quality but cannot penetrate deep into the soil. This performance trade-off depends on the properties of the soil and other environmental factors, as well as the properties of the mines [5,6].
  • Infrared and hyperspectral methods: It is like radar except that the former uses radio waves while these measure infrared radiation from the soil. The soil absorbs the sun’s rays and heats up, causing the infrared radiation it emits to change. Mines are better insulators than soil. As a result, topsoil tends to warm up faster during the day and cool down faster at night. Hyperspectral measurements can recognize multiple frequency bands. The technology is not limited to visible light; the frequency range can reach long-wave infrared radiation. The weakness of this technology is the data processing algorithms. The algorithms are underdeveloped and have difficulty coping with the extreme dependence of performance on environmental conditions, mainly because many surface effects are most substantial immediately after the mines are laid and soon disappear due to weather conditions [5,6].

It is important to note that georadar, infrared, and hyperspectral equipment can be used from a safe distance, including on aerial platforms.

  • Use of sniffer dogs and metal detectors: Dogs are very effective, but their performance is affected by weather and vegetation, and they can become entangled in a densely mined area. Sappers use metal detectors to find mines because almost all mines contain enough metal to be detected. However, no single detector finds all mines, as effectiveness depends on soil, mine type, and depth. [6,7].
  • UAV, photogrammetry: Drones are equipped with cameras to survey areas (mapping) and monitor soil changes. The information obtained allows us to identify patterns in the placement of mines and predict new places where they can be installed. The method is helpful for quickly surveying and estimating the situation, which can be useful for planning access routes to minefields. Drones can be equipped with magnetometers and other sensors, including those from the methods described above [5,6].

As can be observed, many methods are used for demining. Next is the application of LiDAR, specifically in the next section, “How can LiDAR help with demining?”

Section 3. How can LiDAR help in demining?

Lidar is the fastest way to survey a mined area, eliminating the need to involve demining teams. You only need to search for mines with lidar using a drone, lidar, and a base station. After recording the data, there is no need to revisit the survey place to obtain additional data since the point cloud model is reasonably sufficient, mainly when using a photogrammetric solution. As a result, the time the user spends on-site is significantly reduced. In addition, the speed of retrieval and accuracy of this data helps reduce the cost of money that would otherwise be spent on manual searching.

Unlike some methods in the previous section, using LIDAR technology with a drone will allow an area to be scanned, as shown in Figure 3. Typically, the recommended drone speed for a LiDAR mission is five m/s. For the XT-32, the recommended flight altitude is 50m while achieving optimal accuracy and coverage (100x28m). Thus, scanning an area of 0.5 km^2 will require only 20 minutes.

Thanks to multiple returns, mine detection will also be available in vegetation or under trees. If it is too dense, the detail will not be enough to determine the geometry of objects [7]. However, other scanners like the XT32-M2X can offer a much higher point density cloud and triple returns to compensate for canopy cover.

Unlike photogrammetry, LiDAR can scan at night since the emitter generates rays in the infrared range and, therefore, does not require illumination visible to the human eye. In addition, LiDAR data provides a three-dimensional picture of the area. The ability to map an area in detail and with satellite coordinates can reveal irregularities, like craters, indicating buried mines. In addition, LIDAR can detect both metallic and non-metallic objects.

It is also essential that remote scanning is used to detect landmines safely.

Figure 3. Inertial Labs RESEPI Payload installed on a drone.

Inertial Labs’ geo-referencing software outputs “las” files in WGS84 with the Universal Transverse Mercator (UTM) projection [8]. The PCMasterPro software allows users to convert between datums using a coordinate axis translation.

Thanks to integrating a 24 MP camera with a resolution of 350 DPI, the user can also export a colored cloud after processing. In this case, photographs taken by the camera are superimposed on each point in the point cloud, resulting in a colored point cloud, as shown in Figure 4.

Figure 4. Point cloud obtained using RESEPI XT-32.

Because of this point cloud, neural networks can be trained to search for three-dimensional figures, and terrain color analysis can detect objects that are different in color from the ground or surrounding grass. These methods may require third-party software to perform. Intensity filtering removes soil and vegetation, leaving only the objects of interest, as seen in Figure 5.       

                                           

Figure 5. Shows point cloud filtering by intensity.

LiDAR has its disadvantages, like all the methods mentioned above. Since LiDAR radiation does not penetrate underground, its use is limited to ground-based objects only. As with photogrammetry, using a drone imposes restrictions on weather conditions. For example, when the drone may lose control, searching for mines is impossible in rain or high winds. When scanning at night, the user cannot obtain a colored point cloud. There is also heavy difficulty identifying objects in the cloud whose size is equal to a couple of cm, such as at the LiDAR noise level.

To start using RESEPI PAYLOAD, the user will need a drone, flight license, RESEPI payload, base station, and a PCMasterPro software license for data processing [9].

Conclusion

Despite the many methods for searching for mines and other explosive objects, each has advantages and disadvantages. Ground penetrating radar, infrared, and hyperspectral techniques are sensitive to soil properties, environment, and weather conditions. Photogrammetry is limited to two-dimensional images, which do not provide information about the volume of objects and don’t work at night without additional lighting. Manual methods using metal detectors are slow and dangerous as they do not give 100% detection of mines. Finally, dogs are effective, but their performance is affected by weather and vegetation, and they can become entangled in a densely mined area.

Although land-based explosives and weather conditions limit LiDAR payloads such as RESEPI Payload from Inertial Labs, they allow the user to obtain highly accurate geo-referenced colorized point clouds with camera integration. They can also operate at any time of day. Another benefit is utilizing the camera images for photogrammetry if needed. Thanks to third-party software, the user can use the collected information to automate searching for mines in point clouds.

Taking advantage of all these capabilities of LiDAR unlocks the full potential of demining, making it safe and effective.

References:

[1] Wikipedia Contributors. “Inertial Navigation System.” Wikipedia, Wikimedia Foundation, 21 May 2019, en.wikipedia.org/wiki/Inertial_navigation_system.

[2] “RESEPI – LiDAR Payload & SLAM Solutions.” RESEPI, lidarpayload.com. Accessed 3 June 2024.

[3] Inertial Labs. “RESEPI Quick-Start Guide – Setting up Your LiDAR Survey System and PCMaster – Inertial Labs.” YouTube, 4 Aug. 2022, youtu.be/AygQTBVNrKw. Accessed 3 June 2024.

[4] “Landmine Monitor 2023 [EN/AR] – World | ReliefWeb.” Reliefweb.int, 14 Nov. 2023, reliefweb.int/report/world/landmine-monitor-2023-enar.

[5] Wikipedia Contributors. “Demining.” Wikipedia, Wikimedia Foundation, 9 Jan. 2020, en.wikipedia.org/wiki/Demining.

[6] Gibson, Jacqueline MacDonald, and J. R. Lockwood. “Alternatives for Landmine Detection.” Www.rand.org, 1 Jan. 2003, www.rand.org/pubs/monograph_reports/MR1608.html.

[7] “Multiple return LiDAR” Iitk.ac.in, 2024, home.iitk.ac.in/~blohani/LiDAR_Tutorial/Multiple%20return%20LiDAR.htm. Accessed 3 June 2024.

[8] “LAS File Format.” Wikipedia, 22 Dec. 2023, en.wikipedia.org/wiki/LAS_file_format.

[9] “Buy Reach RS2+ | Buy Multi-Band RTK GNSS Receiver.” Emlid Store US, store.emlid.com/products/reach-rs2-plus?variant=47253689467185. Accessed 3 June 2024.

Latest White Papers

Website maintenance has been scheduled for Sunday, April 2 from 7 am to 9 pm EDT.
The resource may be unavailable at this time. Please accept our apologies for any inconvenience.