LiDAR measures distance by sending out laser pulses and timing how long it takes for the light to return after hitting an object.
Understanding LiDAR Distance Measurement
Essentially, LiDAR is a ranging device, which measures the distance to a target. The fundamental principle behind LiDAR's distance measurement is known as the Time-of-Flight (ToF) method. This involves calculating the time a laser pulse takes to travel from the sensor to an object and back.
The Time-of-Flight Principle
The core process involves these steps:
- Sending the Pulse: A LiDAR unit emits a short, rapid pulse of laser light towards a target object.
- Reflection: The laser pulse hits the object's surface and is reflected back towards the LiDAR sensor.
- Detecting the Return: The LiDAR sensor's receiver detects the scattered light pulse returning.
- Timing: The system precisely measures the time elapsed between when the pulse was sent out and when the reflected pulse was detected.
Based on the reference provided: "The distance is measured by sending a short laser pulse and recording the time lapse between outgoing light pulse and the detection of the reflected (back-scattered) light pulse." This 'time lapse' is the crucial measurement.
Calculating the Distance
Since the speed of light in the air is a known constant, the distance to the object can be calculated using a simple formula:
Distance = (Speed of Light * Time of Flight) / 2
- The speed of light is approximately 299,792,458 meters per second.
- The Time of Flight is the measured time lapse for the round trip.
- We divide by 2 because the measured time is for the light to travel to the object and back to the sensor.
Factors Influencing Measurement
While the principle is straightforward, several factors can affect the accuracy of LiDAR distance measurement:
- Target reflectivity: The type of surface the laser hits (e.g., dark asphalt vs. reflective paint) influences how much light is reflected back.
- Atmospheric conditions: Fog, rain, or dust can scatter or absorb the laser light.
- Pulse characteristics: The duration and power of the laser pulse play a role.
- Sensor sensitivity: The ability of the sensor to detect faint return signals is critical.
LiDAR systems often send out thousands or even millions of pulses per second in different directions to build a detailed 3D map of the environment, with each pulse providing a specific distance measurement.
