# An Overview of Autonomous Vehicles Sensors and Their Vulnerability to Weather Conditions
## 4 Synopsis of Automotive Sensor Strengths  
Several strengths of different types of automotive sensors are shown in Figure 20. A variety of sensors are needed for reliability in which sensors must be placed in order to cover different ranges and speeds for high-speed driving, weather conditions, collision avoidance, and stationary safety. LiDAR sensors are vulnerable to precipitation conditions such as snow, hail, sleet, and rain, as shown in Figure 20. However, as a short wavelength technology, LiDAR can identify small objects and provide a precise 3D monochromatic picture of an item, which RADAR may lack. The perception of objects is predicted to be severely affected by inclement weather and a decrease in detection range. As a result of the diminished contrast in intensity, there is an increase in misclassifications and even incorrect detection systems [52]. If the raindrop is very close to the laser emitter, there is a considerable possibility of erroneous detection. Since the laser beam meets a particle and causes a flash of light similar to a small surface, there will be a return of peak that is similar to that of a road item [37]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Atmospheric** & **Altitude** & **Space Weather** & \\
**Layer** & **(km)** & **Effect Level** & **Applicable AV Sensors** \\ \hline \hline \multirow{2}{*}{Troposphere} & 0–14.5 & Low–Medium & RADAR, LiDAR, ultrasonic sensors, \\  & & & GNSS, and camera \\ Stratosphere & 14.5–50 & Medium & GNSS \\ Mesosphere & 50–85 & Medium–High & GNSS \\ Thermosphere & 85–600 & High & GNSS \\ Ionosphere & 48–965 & High & GNSS \\ Exosphere & 600–10,000 & High & GNSS \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Earth’s atmosphere layers. RADAR sensors can operate in varied weather conditions due to a wide spectrum wavelength and absence of mechanical moving parts, as opposed to passive visual sensors due to their lack of scope for climate range. A radio wave receiver and transmitter of the same wavelength can be used to generate radio noise, causing the device to count the speed of a moving object as zero. Then, when it comes to RADAR versus LiDAR autonomous automobile systems, both technologies are deceptive and have the same level of security [53]. Rain is the most important source of radar signal attenuation [54]. Since droplet sizes are equivalent to radar wavelengths, the rain backscatter effect was discovered to have a considerable impact on performance. The attenuation effect weakens the signal, whereas the backscatter effect adds interference at the receiver [55]. These indications are equally useful in the presence of snow or mist. When it comes to hall, millimeter-wave radar signals lose part of their power as they move through the weather [56; 57]. The mathematical models for snow and mist attenuation and backscatter are the same as those for wet conditions [58]. Cameras offer reliable information about the environment and can operate in a variety of weather conditions [59]. During self-parking, a visual navigation system can identify nearby obstructions and locate the vehicle, provided that a complete and accurate full view of the surroundings is taking place in a limited space. In order to accomplish this, a combination of stereo vision techniques can be used [60]. With the use of real-time depth map extraction, a precise dense map may be built up in the sequence of depth map extraction, obstacle extraction, and fusion across multiple camera frames to achieve an accurate estimation [60]. Ultrasonic or sonar sensors are used for near-obstacle detection and as a parking aid system. Due to their limited coverage range (less than 2 m) and poor angular sensing resolution, they do not obtain consistent information about the location and the velocity of vehicles on the road [61]. Moreover, ultrasonic sensors suffer disruptions in noisy environments such as roads, streets, and highways. When trying to enlarge the coverage range, the ping/pulse from the emitter can be produced loudly, which is harmful to citizens and the environment.