## 5 LiDAR 3D Point-Cloud Acquisition Techniques
### Solid-State LiDAR Camera
#### 5.2.2 3D Flash LiDAR Camera  
The flash LiDAR camera uses integrated sensor arrays that have time sensitivity multiple detectors and therefore maps time onto intensity. This form of focal plane array imaging uses a high-resolution CMOS sensor for 2D digital imaging at high resolution and precision. In this approach, an emitted single light pulse fills the scene, and the camera lens focuses some part of the reflected signal onto the digital imager through a modulator. The range is estimated from the pulsed ToF of the received signal. The measuring range varies from one meter to several kilometers [51]. The scan rate is 30 or more frames per second. Since the camera beams are not affected by the sunlight, they can be used for indoor or outdoor measurements. Optical ToF and GMAPD techniques are used in flash LiDAR measurement. Along with the distance (\(r\)) of the object point, the intensity (I) of the reflected beam is also measured and recorded (Figure 8).  
The flash LiDAR camera does not contain any moving parts for measuring. Therefore, it has a solid structure that will not be affected by vibrations. The imaging sensor is very small in size and can be integrated with IMU systems. Flash cameras are used in UAVs due to their low weight. Accuracy and point density is decreased when the measuring distance is increased. Since intense light is emitted from the laser source in flash cameras, the negative effect of this beam on human health must be eliminated. Three-dimensional flash LiDAR cameras with different features have been produced by commercial companies so far (Table 7).  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Brand/Model** & **LW** **(nm)** & **Pixel Array** & \begin{tabular}{c} **FoV** \\ **(H\({}^{\circ}\times V^{\circ}\))** \\ \end{tabular} & \begin{tabular}{c} **Range** \\ **Principle** \\ \end{tabular} & \begin{tabular}{c} **Max.** \\ **Range** \\ \end{tabular} & \begin{tabular}{c} **Frame** \\ **Rate** \\ \end{tabular} & \begin{tabular}{c} **Range** \\ **Accuracy** \\ \end{tabular} & **PC** \\ \hline Terabee/3 Dcam & IR & 80 \(\times\) 60 & 74 \(\times\) 57 & \begin{tabular}{c} Phase-shift \\ (indoor) \\ \end{tabular} & 4 m & 30 fps & \begin{tabular}{c} 1\%of \\ distance \\ \end{tabular} & 4 W \\ LUCID/Helios2+ & 850 nm & 640 \(\times\) 480 & 69 \(\times\) 51 & \begin{tabular}{c} Phase-shift \\ (indoor) \\ \end{tabular} & 8.3 m & 103 fps & 12 W \\ Panasonic/HC4W & 940 nm & 640 \(\times\) 480 & 90 \(\times\) 70 & \
\begin{tabular}{c} Pulsed \\ (outdoor) \\ \end{tabular} & 4 m & 30 fps & Na & 5.4 W \\ Odos Imaging/Swift-E & 850 nm & 640 \(\times\) 480 & 43 \(\times\) 33 &
\begin{tabular}{c} Pulsed \\ (outdoor) \\ \end{tabular} & 6 m & 44 fps & 1 cm & 30 W \\ \hline \hline \end{tabular}
\end{table}
Table 6: Properties of solid-state ToF cameras. (LW: Laser wavelength, PC: Power consumption).  
Flash LiDAR cameras are used for many purposes such as navigation, object tracking, 3D modeling, mapping, robot navigation, autonomous vehicles, and more. They are used to detect obstacles around the vehicle, especially in driverless vehicles.