Estimation of the Angle of Incidence based on Echo Pulse Width in Airborne LiDAR

Abstract

As Airborne and UAV LiDAR have become widely used techniques to map large quantities of terrestrial and bathymetric landscapes, the extraction of more data from the returned signal is an important topic of research. Improvement in LiDAR sensors enable detailed detection of the returned laser pulse, which opens up the opportunity to extract more information from the recorded full signal waveform than ever before. Compared to infrared lasers, green LiDAR typically exhibits a significantly shorter wavelength, which in turn requires a wider footprint on the ground, as eye safety becomes a non-neglectable concern. Together with the typically shorter pulse duration, the bigger footprint is more susceptible towards a nonzero angle of incidence, as the change in reflecting area increases drastically with high angle of incidence. This can be seen in the change of the return signal waveform, which decreases in amplitude and widens in length, as the angle of incidence increases. Based on these effects we can estimate a point-based angle of incidence using the width of the waveform, as there exists a proportionality between the width of the signal and the angle. This opens the possibility to derive surface normal information purely from analysing the reflected echo waveform without considering neighbourhood information. Therefore an improvement is made as more pointwise information can be extracted and furthermore computational resources can be conserved.