Fig. 2

a–d Types of laser returns. Depending on sensor capabilities, one or more signals can be recorded by the scanner. Phase-shift scanners only record a single signal (a), whereas four types can be found for time-of-flight terrestrial (T)-LiDAR. For the (a), (b), and (c) return types, only peaks (defined by specific thresholds) are taken into account. Full waveform T-LiDAR scanners (d) are able to record the entire waveform of the returning signal