Lidar and Radar: History and Applications
From self-driving cars to weather prediction, lidar and radar have transformed how we perceive and interact with the world. Radar, which dates back to World War II, has been instrumental in aviation, military defense, and weather monitoring. Lidar, developed in the 1960s following the invention of the laser, was initially used for atmospheric research and military applications before evolving into a powerful tool for 3D geospatial applications broadly. Today, lidar has been widely adopted for myriad purposes including topographic surveys, AEC (architecture, engineer, and construction), forestry, robotics, archaeology, and autonomous vehicles. While both technologies help detect and measure objects remotely, their underlying principles and use cases vary significantly.
Understanding the Electromagnetic Spectrum
At the core of their differences is the electromagnetic spectrum. Electromagnetic radiation is composed of photons, massless quantum particles that carry energy and momentum. All electromagnetic radiation travels at the speed of light (~300,000 km/s in a vacuum but frequency and wavelength vary. Wavelength is the distance between corresponding points of two consecutive waves (a). Frequency is the number of waves that pass a point in a period of time (b).
Keeping in mind that all electromagnetic waves travel the same speed (the speed of light), the figure above leads us to understand that frequency and wavelength are very closely related to each other.
λ = wavelength (measured in meters, typically)
f = frequency (measured in hertz, Hz)
Therefore, wavelength and frequency are inversely related.
What we really want to know, though, is how the wavelength and frequency of radio waves (RAdio Detection And Ranging) and light waves (LIght Detection And Ranging) changes the behavior of these technologies. The basic principle is that shorter wavelengths provide better resolution.
When light interacts with an object, it can either be absorbed, reflected, refracted, or diffracted. Diffraction is the bending of light around the corners of an obstacle or aperture. The amount of diffraction that occurs is directly proportional to the wavelength of the light. Therefore, shorter wavelengths will diffract less and can more accurately pinpoint the location of an object, leading to a higher resolution image.
However, the trade-off is that short wavelengths interact more with their environment, meaning they are more likely to be scattered, absorbed, or reflected by small particles and molecules in the atmosphere. This is the same concept that explains why the sky is blue. Shorter blue light (wavelength ~450 nm) is scattered more by air molecules (Rayleigh scattering) than longer red light (~700 nm), causing blue light to be redirected in all directions, making the sky appear blue. Similarly, this scattering effect limits the range of short-wavelength sensors, as they struggle to penetrate through haze, fog, and dust compared to longer-wavelength systems like radar.
Radar operates in the radio wave range, typically between millimeter and meter wavelengths, allowing it to detect objects over long distances and through obstacles like fog, clouds, and rain. Lidar, on the other hand, uses much shorter wavelengths in the near-infrared and visible light spectrum, typically around 900–1,550 nanometers. Because lidar operates at such a short wavelength, it interacts more precisely with surfaces, allowing it to capture fine details that radio waves would miss.
Lidar and Radar: Strengths and Limitations
The difference in wavelength plays a critical role in how each technology interacts with its environment. Lidar’s short wavelengths allow it to detect small objects and fine textures with extreme accuracy, making it capable of producing high-resolution 3D maps of terrain, buildings, and even vegetation. However, because lidar operates a shorter wavelengths, it is more susceptible to interference from atmospheric conditions such as fog, rain, and dust, which can scatter the laser pulses and reduce accuracy. Radar, with its longer wavelengths, is much less affected by atmospheric interference and can penetrate through obstacles like clouds and precipitation. The tradeoff is that longer wavelengths result in lower resolution, as they do not reflect as precisely off small details, leading to coarser object detection compared to lidar.
Applications of Lidar and Radar
Because of these strengths and limitations, lidar and radar are often used for different applications or together for complementary purposes. Lidar excels in applications that require precise, high-resolution mapping and object recognition, such as autonomous vehicle navigation, surveying, engineering, forestry management, and infrastructure inspection. Its ability to capture intricate details makes it indispensable in city planning, archaeological site mapping, and environmental studies like coastal erosion monitoring. Radar, on the other hand, is preferred for applications that require long-range detection and operation in challenging conditions, such as aviation, meteorology, maritime navigation, and military defense. It is commonly used for air traffic control, weather forecasting, and even automotive safety systems, where its ability to detect objects through fog and rain provides critical reliability. By understanding these differences, industries can select the right technology—or a combination of both—to optimize performance for their specific needs.
Interested in this topic? Take it to the next level and read our article, What’s the difference between Laser Radar and LIDAR technology?
