LiDAR (light detection and ranging) is a sensing technology that’s similar to radar but uses light instead of radio waves. It applies the principles of reflected light and accurate timing to measure the distance of an object. LiDAR technology permits superior depth sensing due to its high levels of depth and angular resolution. In addition, it’s able to operate in all light conditions due to the active approach that uses an infrared light transmitter along with a receiver.
From an article in Electric Design by Edel Cashman.
However, LiDAR is more sophisticated than just a distance measure. It can also be used in 3D mapping and imaging, making it very appealing in an engineering context as well as a very useful practical technology.
Light and Time-of-Flight
There are different approaches to LiDAR, but the simplest to comprehend is the single-shot direct time-of-flight (dToF) system (Fig. 1). Here, a light source (usually a laser) emits a pulse of light and a timer is activated. When the pulse of light hits an object, it’s reflected back to a sensor that’s usually co-located with the laser and the timer is stopped. Knowing the time (t) between the pulse being sent and the echo being received, it’s a simple matter to calculate the distance (D) to the target object using the speed of light constant (c).
In an alternative method, known as indirect ToF (iToF) LiDAR, a continuous sine wave of light is transmitted. iToF determines the time-of-flight (t) from the difference in phase between the transmitted and reflected waveforms.
Of the two approaches, iToF is more common. It’s generally the better method for shorter-range applications and works better where the ambient light levels are well-controlled. Conversely, dToF can be used in long- and short-range applications. Also, it offers faster operation and can measure more than a single echo, giving it the ability to detect multiple objects.
For a LiDAR system to work effectively, the return signal must be detectable within the ambient light that the system is required to work within. Clearly, this is easier indoors where light can be controlled, but many of the most exciting applications for LiDAR are outdoors, so a solution is necessary.
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