Autonomous Vehicles - KPIT

Figure 2: 3-D view of a terrain recreated using Aerial LIDAR [5]
IV. Radar
The principal of Radar is similar to that of
LIDAR except that it uses other part of
electromagnetic spectrum i.e., Radio waves
and uses frequency change in the reflected
wave caused by Doppler effect (see Fig. 3). It
can be used to determine position of the
object. The radar can be used effectively for
long range characteristics – ranges at which
other electromagnetic wavelengths are
strongly attenuated. For example, it can be
used in adaptive cruise control to detect
obstacles up to 200 m in front of the car. The
disadvantage with Radar is that scattering
effect of radio waves highly depends on the
size, shape and material of the target. Smaller
objects reflect the original wave in similar
frequency results in inability to identify position
of the object. Similarly, objects made up of
radar absorbing material and magnetic
substances, sometimes, hinder the efficiency
of radar in finding position of the object. The
ability of radar to sense the range, altitude,
direction or speed of objects helps the
unmanned vehicle to visualise the real scene
and drive safely. Radars are available in
market at different ranges around $30 USD to
$300 USD depending upon the accuracy and
additional features [13].
V. Ultrasonic sensor
Unmanned vehicles using ultrasonic sensors
navigate similar to Bats by using ultrasound
with frequency greater than that of human
hearing range. The principal is similar to
Radar but can be used to provide proximity for
low speed events i.e., the sensors are blind if
cars move fast. This kind of sensors can be
used for APS, low-speed ACC and automatic
door opener (opens the door when sensor
detects a person coming towards it). Although
ultrasonic-sensor technology is more mature
and less expensive than radar, car
manufacturers are reluctant to have too many
ultrasound sensor apertures visible on the
car's exterior. At present, Ultrasonic sensors
are used in conventional cars for assisting
reverse parking and the whole system cost is
around $70 USD [9].
Figure 3: Doppler Effect – The frequency of radio wave
increases when object approaches towards receiver
and increases when moves away [6]
VI. Infrared Sensor
Most of the objects near room temperature
emit thermal radiation which corresponds to
electromagnetic radiation of longer
wavelength. These radiations are not visible to
normal human eye and hence this sensor in
autonomous vehicles helps to avoid
distraction of neighboring drivers with visible
light. Unlike radar, LIDAR and ultrasonic, long
wavelength infrared called as Far Infra-Red
(FIR) sensor doesn't radiate or generate any
energy for detection purpose. Instead, it
detects infrared radiation from an object. But,
Near Infra-Red (NIR) sensors require infrared
headlights over the car to illuminate the road
ahead. The detection is possible even in the
night time and hence used in unmanned
vehicles to provide night vision (see Fig. 4) for
smart driving. Infrared camera for automobile
costs around $150 USD [11]. Thermal
cameras use infrared sensors.
24 TechTalk@KPIT, Volume 6, Issue 4, 2013