Light detection and range (LiDAR) is a powerful measurement technique that uses the light emitted by a sensor to measure the range of a target object. In simple terms, the sensor emits a pulse of light and then measures the time needed to receive the reflected pulse to estimate the range of the target object, given the constant of the speed of light. From an airplane or helicopter, LiDAR systems send light to the ground and measure the time it takes for the light to return to the sensor. This is how LiDAR measures distance.
Modern LiDAR sensors have multiple lasers or channels, from 8 to 128, that can produce up to 2.2 million dots per second. The LiDAR unit scans from side to side, and some have a full 360-degree horizontal field of view (FOV), creating a very dense point cloud that represents the surrounding area. Topographic LIDAR usually uses a near-infrared laser to map the land, while bathymetric LIDAR uses green light that penetrates the water to also measure the elevations of the seabed and riverbeds. The relative accuracy of LiDAR refers to the internal quality of LiDAR elevation data without using inspected ground control points. To ensure that LiDAR data is precisely georeferenced, direct georeferencing is required, using an accurate GNSS receiver and an inertial measurement unit (IMU) that measures the posture (orientation and positioning) of the LiDAR sensor.
For example, the accuracy requirements of LiDAR data for detailed design of infrastructure, such as a dam, may be higher compared to LiDAR data for agriculture. The American Society for Photogrammetry and Remote Sensing (ASPRS) provides recommendations for LiDAR point density for terrain mapping with LiDAR. This helps users understand what resolution they should expect from their LiDAR data. When it comes to understanding LiDAR resolution measurement, it is important to consider several factors such as accuracy requirements, point density, and GNSS receiver accuracy. By taking these factors into account, users can ensure they are getting accurate and reliable results from their LiDAR data.