In this technique, the analogue echo signal is sampled at fine constant time intervals (black lines in Figure 7). The digital conversion of signal results in a digital data stream. The full wave measurement starts before the first detectable signal and lasts after the last detectable signal. The advantage of unlimited number of returns per pulse is that the canopy and sub-canopy details are revealed. The data can resolve surface roughness, slope and land cover within footprint. From full waveform the first significant return, first and last returns or multiple returns can be obtained in laboratory by data processing with more accuracy. The systems having this facility are RIEGL LMS-Q560, Litemapper and ALTM3100.
Figure 7: Capture of full waveform by sampling the analogue waveform at close intervals.