Why in News:

• The Consumer Electronic Show (CES), an influential tech event held annually has seen an increase in self-driving cars.

What is the technology behind Self Driving Cars

• At the heart of this technology are three sensors: camera, radar and LIDAR (Light Detection and Ranging), all of which help the vehicle accurately perceive its surroundings. 
• Cameras and radar sensors routinely provide ‘driver-assist’ features such as: ensuring that cars stay within lane markings, warning of approaching vehicles during lane changes and maintaining a safe distance to the vehicle in front. 
• A camera system operates much like a human eye — it can discern colours, shapes, recognise traffic signage, lane markings etc. Most cars have stereo cameras i.e., two cameras separated by a short distance. This enables it to perceive depth (like humans). However, a camera does have its limitations. It does not transmit any sensing signals and relies on ambient light that is reflected from objects. So, the absence of adequate ambient light (at night) limits its ability, as can other environmental conditions like fog and blinding sunlight. 
• A radar sensor transmits its own signals, which bounce off targets and reflect back to the radar. Thus, unlike a camera, a radar is not dependent on ambient light. Further, a radar transmits radio waves which can penetrate fog. The radar measures the time between the transmission of the signal and arrival of a reflected signal from a target to estimate the distance to the target. A moving target induces a frequency shift in the signal (‘Doppler shift’) which enables the radar to instantaneously and accurately measure target speed. Thus, radars can accurately measure the range and velocity of targets largely independent of environmental conditions such as fog, rain and bright sunlight. However, unlike a camera, a radar cannot discern colour nor recognise street signs. A radar also has poor ‘spatial resolution’.  
• A LIDAR scans the environment with a laser beam. In many respects, LIDAR combines the best features of both radar and camera. Like a radar, it generates its own transmit signal (thus does not depend on daylight), and can accurately determine distances by measuring the time difference between the transmitted and the reflected signal. The narrow laser beam that is used for sensing ensures that it has a spatial resolution that is similar to a camera. However, LIDAR does have its disadvantages — LIDAR signals cannot penetrate fog, discern colour or read traffic signs. The technology is also significantly costlier than radar or camera.

Latest developments 

• While radar companies are developing imaging radars that significantly improve the spatial resolution of radar, there is new technology being explored that can bring down the cost of LIDAR. 
• At the same time, the capabilities of camera-based vision perception continue to be enhanced with the application of Deep Learning. However, each sensor has its limitations based on physics and technology. 
• While only a camera can recognise traffic signs, it cannot match the performance of radar in adverse weather conditions. Likewise, a radar cannot match the spatial resolution of a camera or a LIDAR. 

 Reference:

1. https://www.thehindu.com/sci-tech/technology/sense-and-sensitivity-in-self-driving-cars/article38280953.ece