LiDAR Remote Sensing: Principle, Application,Free Resources and Software

Airborne LiDAR sensors can either capture specific points from a laser pulse, known as discrete return measurements, or record the complete signal as it returns, called full-waveform, at fixed intervals like 1 ns (which covers about 15 cm). Full-waveform LiDAR is mostly used in forestry, while discrete return LiDAR has broader applications across various fields. This article primarily discusses discrete return LiDAR and its uses. In this chapter, we'll cover several key topics about LiDAR, including its basic components, how it works, its accuracy, systems, and available resources.

Basic Components of LiDAR

Ground-based LiDAR systems typically use lasers with wavelengths between 500–600 nm, while airborne LiDAR systems use lasers with longer wavelengths, ranging from 1000–1600 nm. A standard airborne LiDAR setup includes a laser scanner, a unit for measuring distance (ranging unit), and systems for control, monitoring, and recording. It also includes a Differential Global Positioning System (DGPS) and an Inertial Measurement Unit (IMU), often integrated into a single system known as a position and orientation system. This system provides precise location (longitude, latitude, and altitude) and orientation (roll, pitch, and heading) data.

 The patterns in which the laser scans the area can vary, including zigzag, parallel, or elliptical paths. The combination of DGPS and IMU data, along with calibration data and mounting parameters, allows the system to accurately process the collected laser points. These points are then assigned coordinates (x, y, z) in a geographic coordinate system using the World Geodetic System of 1984 (WGS84) datum.

How LiDAR Remote Sensing Works? Explain in a Simple Way

A LiDAR system emits rapid laser pulses towards a target object or surface.

The laser pulses reflect off the target and return to the LiDAR sensor.

The sensor precisely measures the time it takes for each pulse to travel to the target and back.

Using the speed of light and the travel time, the distance to the target is calculated.

Combined with the position and orientation data from GPS and IMU sensors, the precise 3D coordinates of the laser reflections are determined.

This results in a dense 3D point cloud representing the scanned surface or object.

Physical Principle of LiDAR

LiDAR systems use two types of lasers: pulsed and continuous wave. Pulsed LiDAR systems work by sending out a short light pulse and then measuring the time it takes for this pulse to travel to the target and back to the receiver. This measurement of round-trip time helps determine the distance to the target. An example is shown in a diagram where the amplitudes of both the transmitted light signal (AT) and the received light signal (AR) are displayed. The basic equation used in this system involves the speed of light (c) and the distance to the target (R), allowing the system to calculate the distance based on how long it takes for the light to return.