However, the velocity of ultrasonic wave travel in air is
affected by environmental parameters such as temperature,
humidity and appearance of ambient noise. Nevertheless, US
sensors have limitations due to their wide beam-width and
sensitivity to the mirror-like surfaces [6]. Because of having
the properties of a mirror, only reflecting objects that are
almost normal to the sensor acoustic axis may be accurately
detected [7]. Alternatively, infrared sensors can be used in
obstacle detection because of their high resolution, low cost
and faster response times compared to ultrasonic sensors [8].
However, these sensors have non-linear characteristics and they depend on the reflectance properties of the object
surfaces. Therefore, knowledge of the surface properties
must be known beforehand. In other words, the nature in
which a surface reflects and absorbs infrared energy is
needed to interpret the sensor output as distance measure [9].
The distance estimation could be obtained by using Phong
Illumination model