Radar VS Lidar 2

• Radar

- As with cameras, many vehicles today are already equipped with one or more radar sensors. This sensor type is most commonly used in driver assistance systems such as "adaptive cruise control" or "autonomous emergency braking".

- Radars are active sensors, as they emit an electromagnetic wave, which is reflected from objects with certain properties (e.g. metal).

- Based on the run-time of the signal, radar sensors can estimate the distance very accurately.

- Also, based on a physical principle called the "Doppler effect", radars can measure the speed of moving objects by evaluating the frequency shift in the return signal, which is proportional to the velocity of the object.

 

• advantages of Radar

- The  ability to work reliably in almost all weather conditions.

 

• disadvantages of Radar

It has a very low spatial resolution, which is why they are not suitable to measure the dimension of objects very accurately. Also, objects with little or no metal content (e.g. pedestrians) do not produce a strong return signal and are hard to separate from background noise.

 

• two frequency bands of Radar

Automotive radar sensors typically work in one of two frequency bands.

- 24GHz radar sensors : are used for short-range applications and have a wider opening angle.

- 77GHz sensors : are used for long-range sensing in a narrow cone.

 

• LiDAR

- LiDAR also belongs to the group of active sensors.

- The basic principle is based on emitting beams of laser light and measuring the time it takes the light to bounce back from objects and return to the sensor.

 

• advantages of LiDAR

The most prominent LiDAR types currently used in autonomous vehicle are top-mounted devices on the roof of the vehicle, spinning rapidly in a 360 degree arc and generating thousands of measurements per second. Such rotating LiDAR sensors create very accurate 3D point maps of the surrounding environments and as a result can detect vehicles, pedestrians, cyclists, and other obstacles. This sensor type is also called scanning LiDAR, because it needs to move its parts to progressively raster ("scan") the field of view.

 

• Flash LiDAR

- It's a non-scanning sensor. The term “Flash” refers to the idea that the field of view is entirely illuminated by the laser source, like a camera with a flash light, while an array of photodetectors simultaneously receives the reflected laser pulses.

- Flash LiDAR sensors do not have any moving parts, which is why they are resistant to vibrations and have a significantly smaller package size than scanning LiDAR sensors.

 

• disadvantages of Flash LiDAR

The limited range and the comparatively narrow field of view compared to the roof-mounted LiDAR types.

 

• scanning and non-scanning LiDARs in autonomous vehicles

In autonomous vehicles, both scanning and non-scanning LiDARs are used to observe different areas around the vehicle.

- The roof-mounted scanning LiDAR : generates a 360-degree view up until a range of approx.

- 80-100m while the non-scanning LiDAR sensors (usually mounted at the four corners) : observe the direct vicinity of the vehicle in areas where the top-mounted sensor is blind.