A Clarification on Waveform in LiDAR

Provided by guest blogger, Qassim Abdullah, PhD, PLS, CP, subject matter expert, Arlington

From “Mapping Matters, Your Questions Answered” in Photogrammetric Engineering & Remote Science (PE&RS), ASPRS’s monthly publication

Q: Can you clarify waveform or signal echo digitizing? How is this data provided and how would you analyze it? Is the echo signal return intensity? Phase?

A: LiDAR, since its introduction to the geospatial community in the last two decades, focused mainly on recording the discrete return of the signal or the laser pulse. Such recording of the signal return is eventually presented to the user as a point cloud, after some processing. The point cloud can then be used in a variety of applications, such as extracting a digital terrain model (DTM).

The signal return, however, represented by the returned flux of photons, is not a discrete event by nature but a continuous phenomenon that lasts some time until the preset range gate shuts off the recording of the signal and prepares the system for the next pulse.

Recent LiDAR systems are equipped with a digitizer that samples and records the returned signal at a given time interval (usually around 2 nanoseconds), resulting in an accurate representation of the waveform. Advanced signal processing techniques then applied to the waveform extract a wealth of information surrounding the environment where the signal is reflected from.

The waveform digitization is useful in analyzing forested areas to reveal detailed composition of the forest down to the forest floor. The waveform can also be used to extract discrete events that can be used to densify the original point cloud of the discrete LiDAR collection mode, resulting in an enhanced-quality DTM.

Read my full answer on the ASPRS website.

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