My Car and How It Sees the World
In the world of science fiction, self-driving cars are practically standard vehicles. In ‘real life’ we are catching up fast with authors’ imaginations. Whenever this automotive future begins, vehicle-environment sensing will play a major role in achieving this next step because in order to independently steer through traffic, the vehicle must always be able to keep an eye on its surroundings.
A Bat in the Car?
Locating objects and navigating by ultrasound has been seen before in nature, by bats, that emit ultrasonic waves and can recog-nise prey and obstacles by means of a reflected echo. Artificially generated sound waves have a comparatively short range; therefore, they can only be used at close range.
The first models with this assistance system came onto the market in the early 1980s. Ultrasonic technology is now not only used at the rear of the car but with blind spot sensors or to measure the distance to the vehicle ahead at low speeds as well.
A Car with Eyes
Camera systems probably come closest to imitating human perception. Software interprets the data to identify edges that might mean other vehicles or lane markings as well as traffic signs or traffic lights as well. This information helps to prevent accidents and contributes to orientation because the camera also recognises details that are not recorded on the digital maps of common navigation systems.
There are two main problems with camera-based systems - the lack of three-dimensionality and the limited viewing angle. A single camera reduces the three-dimensional world to two dimensions. In an environment like street traffic, where there is a lot of movement, this can lead to a misinterpretation of data. Field of view and 3D perception can be overcome by using several cam-eras simultaneously, possibly with different focal lengths.
RaDAR or LiDAR?
RaDAR and LiDAR do not just happen to have similar “names.” They are both used in detection and ranging. Like ultrasonic detec-tion, they are based on the analysis of reflected waves - except that in one case the waves are RAdio waves and in the other case LIght waves.
Radar: frequency-modulated continuous wave radars, in which the frequency of the electromagnetic wave is constantly modulated in the form of a ramp, are commonly used in environment recognition. Using the doppler effect, the distance and speed of an object can be determined from the propagation time of the wave and the frequency difference of the reflected wave. Radar does not provide any information about the size or shape of an object.
LiDAR: LiDAR measurements emit several thousand nanosecond laser pulses per second. The distance to the obstacle can be de-termined by the difference in transit time between the outgoing signal and the incoming reflection, the so-called time of flight (ToF).
Sensor arrays are used to monitor larger areas. The Fraunhofer Institute for Microelectronic Circuits and Systems (IMS) has re-cently even developed a chip that allows LiDAR measurements without moving elements (see box). Using the measurement points, a computer calculates a detailed three-dimensional image of the surroundings.
The LiDAR method, therefore, works considerably faster than the radar method and provides a greater amount of more precise data. Light attenuation by fog or humidity limits LiDAR to shorter ranges. For longer distances car manufacturers rely on long-range radars in the 77GHz frequency range.
Strength in Numbers
While a human being can intuitively draw on his wealth of experience and intuitively react to situations, a computer must con-stantly make new decisions. To do this, it needs as much data as possible. Each sensor system can contribute to this decision with its specific advantages and disadvantages.
Transmitter and Receiver from a Single Source
LiDAR systems need to be reliable, small, and cost effective at the same time. For manufacturers of laser-based measuring devices and optoelectronic components, this is a great challenge.
LASER COMPONENTS manufactures all components for powerful and future-oriented LiDAR solutions in its ISO-certified production facilities. Pulsed laser diodes with ultra-short pulses provide better resolution for distance measurement. In combination with highly-sensitive avalanche photodiodes (APDs), even the smallest signals can be detected.
In addition, there is a cooperation with the Fraunhofer Institute for Microelectronic Circuits and Systems (IMS) for 1-dimensional and 2-dimensional CMOS-SPAD arrays. The researchers from Duisburg can contribute new sensor technologies that promise par-ticularly precise measurements.
Laser Components Canada, Inc.
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|Company:||LASER COMPONENTS (UK) Ltd.|
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