What is LiDAR?
LiDAR, an acronym for Light Detection and Ranging, is a popular remote sensing method that employs light in the form of a pulsed laser to detect and categorize objects. LiDAR sensors generate precise, 3-dimensional information about the shape of surrounding objects and their surface characteristics.The technology uses laser beams within the eye-safe range to create a 3D representation of the surveyed environment.
Typical LiDAR applications comprise surveying, geography, atmospheric physics, and archeology, but today it is used in many state-of-the-art applications as well as robotics, smart cities, and autonomous vehicles.
Key components of LiDAR
A LiDAR sensor that scans the surroundings and illustrates them in a virtual 3D format primarily consists of a laser source, shooting out laser pulses, a scanner, deflecting the light upon the scene, and a detector, collecting the reflected light. Other supporting elements are, for example, optical lenses.
How does the technology work?
A typical LiDAR sensor follows a simple principle, also known as the time of flight principle. It sends out pulsed light waves into the surrounding environment, and these pulses reflect or bounce off objects and return to the sensor’s detector. The time taken for each pulse to return can be used to calculate the distance it traveled.
The diagrams below succinctly explains the time of flight principle:
Repeat this process millions of times per second, and a precise, real-time 3D map of the environment is generated. This 3D map contains data that is easy to analyze and utilize, for example, for autonomous driving decisions.
What are the main types of LiDAR?
LiDAR sensors can be categorized into different types based on their platforms, underlying technologies, and modus operandi. The diagram below illustrates the main categories with respect to platforms.
On a high level, LiDAR systems can be divided into two types — Airborne LiDAR and Terrestrial LiDAR.
These were the first LiDAR systems, developed in the 1960s, predominantly for aeronautics and aerospace applications. Airborne LiDARs, as evident from the name, are usually installed on planes, helicopters, or sometimes even satellites to collect data. LiDAR sends out pulsed light waves towards the ground surface, which returns to the sensor after hitting the object. It gives an exact distance measurement and crucial information on the characteristics of the surface. Naturally, these LiDARs require very high-power emitters to cover such long distances, making them highly complicated and expensive technologies.
Airborne LiDARs can be further divided into two main categories: Topological LiDARs, used for monitoring and mapping topography of a region, and Bathymetric LiDARs, used for measuring the depth of water bodies. These are typically used for applications like topographic mapping of forests, scanning the ocean bed, and the atmosphere. Interestingly, even NASA’s Apollo 15 mission applied LiDAR for scanning and mapping the moon’s surface. Read about the complete evolution of the LiDAR technology here.
In comparison, terrestrial LiDARs operate from the ground level and can scan objects in several directions using mirrors instead of just scanning down. This allows them to scan and reach areas inaccessible to airborne LiDARs.
Terrestrial LiDARs can collect data points with high precision and density, which allows very accurate identification of objects. These dense point clouds are then utilized to identify vehicles, conduct highway and rail surveys, or create 3D city models, to name a few examples.
Terrestrial LiDAR systems again have two types — Static LiDAR and Mobile LiDAR.
Static LiDAR collects point clouds from a static location. They can scan in every direction, including upwards. The sensor can be transported to different locations after completing one scan, so the static system — although fixed during scans — is fully portable. Static LiDARs are generally used in mining, surveying, and archaeology applications.
Mobile LiDAR is leading the way for modern mapping and autonomous driving solutions and incorporates top of the line LiDAR technology to collect quality data points. The method can be employed to acquire millions of 3D design points per minute. The mobile laser can offer a data density of up to 150 points per square foot, making it the fastest way to acquire coordinates compared to all other LiDAR methods.
Types of mobile LiDAR sensors
Within the mobile LiDARs, there are yet two more types, namely mechanical or rotating LiDARs and solid-state LiDARs.
The rotating LiDARs rely on gears and motors to mechanically steer the laser diodes. Although this allows them to offer a 360-degree view of the surroundings, the moving mechanical components are prone to technical failures, more sensitive to vibrations, and expensive due to their intricate design, set-up, and manual construction. This makes them not very cost-effective, even when produced in large quantities.
In comparison, solid-state LiDAR systems are based on semiconductor technology and therefore do not have any freely moving mechanical parts. This makes the entire systems less complicated, more compact, and longer-lasting. They are also less expensive and can be mass-produced reliably. Therefore, the solid-state LiDAR systems act as a breakthrough for many applications, especially the next level of autonomous driving.
What differentiates LiDAR from other sensing technologies?
LiDARs phased out several other technologies and sensors that were not precise enough in their detection and data encapsulation. For many challenges, such as scanning between trees, LiDAR proves to be a valuable technology as it offers a fast, precise, and direct method of 3D mapping while producing accurate and easy-to-analyze data.
Also in mobility applications, where high precision and reliability is required, the LiDAR technology is gaining popularity, quickly.
These features make LiDAR stand out from most of the alternatives, e.g., photogrammetric techniques that faced difficulties in interpreting ground elevations. Modern LiDARs are also mostly independent of environmental factors and can work 24/7, giving them a significant edge on sensors like cameras, which are nearly useless in the dark or rain.
LiDAR is capable of providing high-resolution 3D vision by generating millions of data points in real-time. This creates a precise map of the ever-changing surroundings that allow the objects to be recognized and categorized. For instance, a car can easily be distinguished from a cyclist, which is not possible using just radars or ultra-sonic sensors.
LiDAR’s robust performance, an extended range of up to 200 meters, and distance accuracy of a few centimeters allows it to detect objects quickly. And thanks to the advent and adoption of solid-state technology, the cost of these high-resolution 3D sensors has also been considerably reduced, making them a perfect fit for a wide range of technologies.
LiDARs are the future:
Given the host of benefits, LiDAR technology is indispensable for many modern-day applications, such as autonomous navigation, HD mapping, and people counting. Offering remarkable performance advantages over other technologies, it is only a matter of time when they become the go-to sensors for most industries.