LiDAR & Satellite Incorporated Application(2)
Principle of LiDAR (Light Detection and Ranging)
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
The functionality of the core device of LiDAR including its mechanical structure is in fact same as the one of SAR (Synthetic Aperture Radar) installed in shuttles and satellites, thus regularly emit human-made photons. Their time interval of emitted photons can be nano-second or pico-second depending on which material creates laser. However, the wave-particle duality of photon should always be kept into mind because explaining a lot of relevant phenomena relies on it (see Figure 1 and 2).
Signal collection and Fourier Transformation
So-called signal is a term in electronic engineering, which is substantially generated by each scattered-back photon which is emitted by the induced or polarized atom, molecule and ion locating at ground due to electron being transitioned between two different energy level.
Owing to wave-particle duality of photon, that leads to that massive time-based frequency phases are produced in a time domain. Non-device is capable of handling them; therefore, the best way of dealing with them is that these signals are expressed by frequency domain spectrum through Fourier Transformation by means of computer. Very clear, the source intensity thus the magnitude of received signals can be indirectly depicted by certain interval of frequency domain. This frequency domain is designed by need, which can be expressed by wave length or wavenumber. The classified wave length or wavenumber is called as channel or band in remote sensing.
Although it is difficult for us to know how signal intensity changes, the useful or best way is that only signal intensity changes appearing one channel (for example NIR channel used in this research) are considered, hence we do not need to consider other source intensity appearing in other channels. Accordingly, the situation becomes quite simple (see figure 3 and 4).
LiDAR Return Cloud Point Classification
As mentioned before, the objects on ground can be identified by signals.
American Society for Photogrammetry and Remote Sensing (ASPRS) have built several standard (called ASPRS standard). According to LAS SPECIFICATION VERSION 1.4 – R13, some often-used standard for LiDAR point classes are listed in Figure 5.
The full list can be downloaded from
or here
In this research, for the sake of simplicity the results in most cases are depicted by the standard number defined in this specification.
